Κυριακή 1 Απριλίου 2018

No association between circulating concentrations of vitamin D and risk of lung cancer: An analysis in 20 prospective studies in the Lung Cancer Cohort Consortium (LC3)

Abstract
Background
There is observational evidence suggesting that high vitamin D concentrations may protect against lung cancer. To investigate this hypothesis in detail, we measured circulating vitamin D concentrations in pre-diagnostic blood from 20 cohorts participating in the Lung Cancer Cohort Consortium (LC3).
Patients and methods
The study included 5,313 lung cancer cases and 5,313 controls selected from. Blood samples for the cases were collected, on average, 5 years prior to lung cancer diagnosis. Controls were individually matched to the cases by cohort, sex, age, race/ethnicity, date of blood collection, and smoking status in 5 categories. Liquid chromatography coupled with tandem mass spectrometry was used to separately analyze 25-hydroxyvitamin D2 (25(OH)D2) and 25-hydroxyvitamin D3 (25(OH)D3) and their concentrations were combined to give an overall measure of 25(OH)D. We used conditional logistic regression to calculate odds ratios (OR) and 95% confidence intervals (CI) for 25(OH)D as both a continuous and categorical variable.
Results
Overall, no apparent association between 25(OH)D and risk of lung cancer was observed (multivariable adjusted OR for a doubling in concentration: 0.98, 95% confidence interval: 0.91, 1.06). Similarly, we found no clear evidence of interaction by cohort, sex, age, smoking status, or histology.
Conclusion
This study did not support an association between vitamin D concentrations and lung cancer risk.

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No association between circulating concentrations of vitamin D and risk of lung cancer: An analysis in 20 prospective studies in the Lung Cancer Cohort Consortium (LC3)

Abstract
Background
There is observational evidence suggesting that high vitamin D concentrations may protect against lung cancer. To investigate this hypothesis in detail, we measured circulating vitamin D concentrations in pre-diagnostic blood from 20 cohorts participating in the Lung Cancer Cohort Consortium (LC3).
Patients and methods
The study included 5,313 lung cancer cases and 5,313 controls selected from. Blood samples for the cases were collected, on average, 5 years prior to lung cancer diagnosis. Controls were individually matched to the cases by cohort, sex, age, race/ethnicity, date of blood collection, and smoking status in 5 categories. Liquid chromatography coupled with tandem mass spectrometry was used to separately analyze 25-hydroxyvitamin D2 (25(OH)D2) and 25-hydroxyvitamin D3 (25(OH)D3) and their concentrations were combined to give an overall measure of 25(OH)D. We used conditional logistic regression to calculate odds ratios (OR) and 95% confidence intervals (CI) for 25(OH)D as both a continuous and categorical variable.
Results
Overall, no apparent association between 25(OH)D and risk of lung cancer was observed (multivariable adjusted OR for a doubling in concentration: 0.98, 95% confidence interval: 0.91, 1.06). Similarly, we found no clear evidence of interaction by cohort, sex, age, smoking status, or histology.
Conclusion
This study did not support an association between vitamin D concentrations and lung cancer risk.

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By the Numbers: Novel Drugs Approved by the FDA, 2011-2017 [News in Brief]

In 2017, the FDA approved 12 novel cancer drugs. The agency also approved two chimeric antigen receptor T-cell therapies for blood cancers.



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The Pancreatic Cancer Microbiome Promotes Oncogenesis by Induction of Innate and Adaptive Immune Suppression [Research Briefs]

We found that the cancerous pancreas harbors a markedly more abundant microbiome compared with normal pancreas in both mice and humans, and select bacteria are differentially increased in the tumorous pancreas compared with gut. Ablation of the microbiome protects against preinvasive and invasive pancreatic ductal adenocarcinoma (PDA), whereas transfer of bacteria from PDA-bearing hosts, but not controls, reverses tumor protection. Bacterial ablation was associated with immunogenic reprogramming of the PDA tumor microenvironment, including a reduction in myeloid-derived suppressor cells and an increase in M1 macrophage differentiation, promoting TH1 differentiation of CD4+ T cells and CD8+ T-cell activation. Bacterial ablation also enabled efficacy for checkpoint-targeted immunotherapy by upregulating PD-1 expression. Mechanistically, the PDA microbiome generated a tolerogenic immune program by differentially activating select Toll-like receptors in monocytic cells. These data suggest that endogenous microbiota promote the crippling immune-suppression characteristic of PDA and that the microbiome has potential as a therapeutic target in the modulation of disease progression.

Significance: We found that a distinct and abundant microbiome drives suppressive monocytic cellular differentiation in pancreatic cancer via selective Toll-like receptor ligation leading to T-cell anergy. Targeting the microbiome protects against oncogenesis, reverses intratumoral immune tolerance, and enables efficacy for checkpoint-based immunotherapy. These data have implications for understanding immune suppression in pancreatic cancer and its reversal in the clinic. Cancer Discov; 8(4); 403–16. ©2018 AACR.

See related commentary by Riquelme et al., p. 386.

This article is highlighted in the In This Issue feature, p. 371



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Immunotherapy for Pancreatic Cancer: More Than Just a Gut Feeling [In the Spotlight]

Summary: Development of pancreatic cancer in spontaneous murine models is associated with enrichment of specific strains of gut and intratumoral bacteria that induce a tolerogenic immunosuppressive microenvironment favoring cancer progression and resistance to immunotherapies. Ablation of the microbiome with antibiotics reshapes the tumor microenvironment, inducing T-cell activation, improving immune surveillance, and increasing sensitivity to immunotherapy in established tumors. Cancer Discov; 8(4); 386–8. ©2018 AACR.

See related article by Pushalkar et al., p. 403.



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BRD4 Profiling Identifies Critical Chronic Lymphocytic Leukemia Oncogenic Circuits and Reveals Sensitivity to PLX51107, a Novel Structurally Distinct BET Inhibitor [Research Articles]

Bromodomain and extra-terminal (BET) family proteins are key regulators of gene expression in cancer. Herein, we utilize BRD4 profiling to identify critical pathways involved in pathogenesis of chronic lymphocytic leukemia (CLL). BRD4 is overexpressed in CLL and is enriched proximal to genes upregulated or de novo expressed in CLL with known functions in disease pathogenesis and progression. These genes, including key members of the B-cell receptor (BCR) signaling pathway, provide a rationale for this therapeutic approach to identify new targets in alternative types of cancer. Additionally, we describe PLX51107, a structurally distinct BET inhibitor with novel in vitro and in vivo pharmacologic properties that emulates or exceeds the efficacy of BCR signaling agents in preclinical models of CLL. Herein, the discovery of the involvement of BRD4 in the core CLL transcriptional program provides a compelling rationale for clinical investigation of PLX51107 as epigenetic therapy in CLL and application of BRD4 profiling in other cancers.

Significance: To date, functional studies of BRD4 in CLL are lacking. Through integrated genomic, functional, and pharmacologic analyses, we uncover the existence of BRD4-regulated core CLL transcriptional programs and present preclinical proof-of-concept studies validating BET inhibition as an epigenetic approach to target BCR signaling in CLL. Cancer Discov; 8(4); 458–77. ©2018 AACR.

This article is highlighted in the In This Issue feature, p. 371



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Medulloblastoma Circulating Tumor Cells Form Leptomeningeal Metastases [Metastasis]

NCAM+CD45+ medulloblastoma cells were shown to be medulloblastoma circulating tumor cells (CTC).



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Natural Killer Cells Recruit Dendritic Cells to Promote Antitumor Immunity [Immunology]

Natural killer (NK) cells recruit conventional type 1 dendritic cells (cDC1) to the tumor microenvironment.



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Plasma DNA and Metastatic Castration-Resistant Prostate Cancer: The Odyssey to a Clinical Biomarker Test [In the Spotlight]

Summary: Comprehensive plasma DNA analysis identifies clinically actionable genomic aberrations. Cancers harboring disruption of TP53 or BRCA2 or ATM detected in plasma have significantly worse outcomes on novel AR targeting. Cancer Discov; 8(4); 392–4. ©2018 AACR.

See related article by Annala et al., p. 444.



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Combined BRAF, EGFR, and MEK Inhibition in Patients with BRAFV600E-Mutant Colorectal Cancer [Research Articles]

Although BRAF inhibitor monotherapy yields response rates >50% in BRAFV600-mutant melanoma, only approximately 5% of patients with BRAFV600E colorectal cancer respond. Preclinical studies suggest that the lack of efficacy in BRAFV600E colorectal cancer is due to adaptive feedback reactivation of MAPK signaling, often mediated by EGFR. This clinical trial evaluated BRAF and EGFR inhibition with dabrafenib (D) + panitumumab (P) ± MEK inhibition with trametinib (T) to achieve greater MAPK suppression and improved efficacy in 142 patients with BRAFV600E colorectal cancer. Confirmed response rates for D+P, D+T+P, and T+P were 10%, 21%, and 0%, respectively. Pharmacodynamic analysis of paired pretreatment and on-treatment biopsies found that efficacy of D+T+P correlated with increased MAPK suppression. Serial cell-free DNA analysis revealed additional correlates of response and emergence of KRAS and NRAS mutations on disease progression. Thus, targeting adaptive feedback pathways in BRAFV600E colorectal cancer can improve efficacy, but MAPK reactivation remains an important primary and acquired resistance mechanism.

Significance: This trial demonstrates that combined BRAF + EGFR + MEK inhibition is tolerable, with promising activity in patients with BRAFV600E colorectal cancer. Our findings highlight the MAPK pathway as a critical target in BRAFV600E colorectal cancer and the need to optimize strategies inhibiting this pathway to overcome both primary and acquired resistance. Cancer Discov; 8(4); 428–43. ©2018 AACR.

See related commentary by Janku, p. 389.

See related article by Hazar-Rethinam et al., p. 417.

This article is highlighted in the In This Issue feature, p. 371



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Pembrolizumab for primary malignant melanoma of the central nervous system



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Forkhead Box F2 Suppresses Gastric Cancer through a Novel FOXF2-IRF2BPL-{beta}-Catenin Signaling Axis

DNA methylation has been identified as a hallmark of gastric cancer (GC). Identifying genes that are repressed by DNA promoter methylation is essential in providing insights into the molecular pathogenesis of gastric cancer. Using genome-wide methylation studies, we identified that transcription factor forkhead box F2 (FOXF2) was preferentially methylated in gastric cancer. We then investigated the functional significance and clinical implication of FOXF2 in gastric cancer. FOXF2 was silenced in gastric cancer cell lines and cancer tissues by promoter methylation, which was negatively associated with mRNA expression. Ectopic expression of FOXF2 inhibited proliferation, colony formation, G1–S cell-cycle transition, induced apoptosis of gastric cancer cell lines, and suppressed growth of xenograft tumors in nude mice; knockdown of FOXF2 elicited opposing effects. FOXF2 inhibited Wnt signaling by inducing β-catenin protein ubiquitination and degradation independently of GSK-3β. FOXF2 directly bound the promoter of E3 ligase interferon regulatory factor 2-binding protein-like (IRF2BPL) and induced its transcriptional expression. IRF2BPL in turn interacted with β-catenin, increasing its ubiquitination and degradation. Multivariate Cox regression analysis identified FOXF2 hypermethylation as an independent prognostic factor of poor survival in early-stage gastric cancer patients. In conclusion, FOXF2 is a critical tumor suppressor in gastric carcinogenesis whose methylation status serves as an independent prognostic factor for gastric cancer patients.Significance: FOXF2-mediated upregulation of the E3 ligase IRF2BPL drives ubiquitylation and degradation of β-catenin in gastric cancer, blunting Wnt signaling and suppressing carcinogenesis. Cancer Res; 78(7); 1643–56. ©2018 AACR.

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In Silico Evaluation of Pharmacokinetic Optimization for Antimitogram-Based Clinical Trials

Antimitograms are prototype in vitro tests for evaluating chemotherapeutic efficacy using patient-derived primary cancer cells. These tests might help optimize treatment from a pharmacodynamic standpoint by guiding treatment selection. However, they are technically challenging and require refinements and trials to demonstrate benefit to be widely used. In this study, we performed simulations aimed at exploring how to validate antimitograms and how to complement them by pharmacokinetic optimization. A generic model of advanced cancer, including pharmacokinetic–pharmacodynamic monitoring, was used to link dosing schedules with progression-free survival (PFS), as built from previously validated modules. This model was used to explore different possible situations in terms of pharmacokinetic variability, pharmacodynamic variability, and antimitogram performance. The model recapitulated tumor dynamics and standalone therapeutic drug monitoring efficacy consistent with published clinical results. Simulations showed that combining pharmacokinetic and pharmacodynamic optimization should increase PFS in a synergistic fashion. Simulated data were then used to compute required clinical trial sizes, which were 30% to 90% smaller when pharmacokinetic optimization was added to pharmacodynamic optimization. This improvement was observed even when pharmacokinetic optimization alone exhibited only modest benefit. Overall, our work illustrates the synergy derived from combining antimitograms with therapeutic drug monitoring, permitting a disproportionate reduction of the trial size required to prove a benefit on PFS. Accordingly, we suggest that strategies with benefits too small for standalone clinical trials could be validated in combination in a similar manner.Significance: This work offers a method to reduce the number of patients needed for a clinical trial to prove the hypothesized benefit of a drug to progression-free survival, possibly easing opportunities to evaluate combinations. Cancer Res; 78(7); 1873–82. ©2018 AACR.

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Pyruvate Dehydrogenase PDH-E1{beta} Controls Tumor Progression by Altering the Metabolic Status of Cancer Cells

Downregulation of pyruvate dehydrogenase (PDH) is critical for the aberrant preferential activation of glycolysis in cancer cells under normoxic conditions. Phosphorylation-dependent inhibition of PDH is a relevant event in this process, but it is not durable as it relies on PDH kinases that are activated ordinarily under hypoxic conditions. Thus, it remains unclear how PDH is durably downregulated in cancer cells that are not hypoxic. Building on evidence that PDH activity depends on the stability of a multi-protein PDH complex, we found that the PDH-E1β subunit of the PDH complex is downregulated to inhibit PDH activity under conditions of prolonged hypoxia. After restoration of normoxic conditions, reduced expression of PDH-E1β was sustained such that glycolysis remained highly activated. Notably, PDH-E1β silencing in cancer cells produced a metabolic state strongly resembling the Warburg effect, but inhibited tumor growth. Conversely, enforced exogenous expression of PDH-E1β durably increased PDH activity and promoted the malignant growth of breast cancer cells in vivo. Taken together, our results establish the specific mechanism through which PDH acts as an oncogenic factor by tuning glycolytic metabolism in cancer cells.Significance: This seminal study offers a mechanistic explanation for why glycolysis is aberrantly activated in normoxic cancer cells, offering insights into this long-standing hallmark of cancer termed the Warburg effect. Cancer Res; 78(7); 1592–603. ©2018 AACR.

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Fc-Mediated Anomalous Biodistribution of Therapeutic Antibodies in Immunodeficient Mouse Models

A critical benchmark in the development of antibody-based therapeutics is demonstration of efficacy in preclinical mouse models of human disease, many of which rely on immunodeficient mice. However, relatively little is known about how the biology of various immunodeficient strains impacts the in vivo fate of these drugs. Here we used immunoPET radiotracers prepared from humanized, chimeric, and murine mAbs against four therapeutic oncologic targets to interrogate their biodistribution in four different strains of immunodeficient mice bearing lung, prostate, and ovarian cancer xenografts. The immunodeficiency status of the mouse host as well as both the biological origin and glycosylation of the antibody contributed significantly to the anomalous biodistribution of therapeutic monoclonal antibodies in an Fc receptor-dependent manner. These findings may have important implications for the preclinical evaluation of Fc-containing therapeutics and highlight a clear need for biodistribution studies in the early stages of antibody drug development.Significance: Fc/FcγR-mediated immunobiology of the experimental host is a key determinant to preclinical in vivo tumor targeting and efficacy of therapeutic antibodies. Cancer Res; 78(7); 1820–32. ©2018 AACR.

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Polyol Pathway Links Glucose Metabolism to the Aggressiveness of Cancer Cells

Cancer cells alter their metabolism to support their malignant properties. In this study, we report that the glucose-transforming polyol pathway (PP) gene aldo-keto-reductase-1-member-B1 (AKR1B1) strongly correlates with epithelial-to-mesenchymal transition (EMT). This association was confirmed in samples from lung cancer patients and from an EMT-driven colon cancer mouse model with p53 deletion. In vitro, mesenchymal-like cancer cells showed increased AKR1B1 levels, and AKR1B1 knockdown was sufficient to revert EMT. An equivalent level of EMT suppression was measured by targeting the downstream enzyme sorbitol-dehydrogenase (SORD), further pointing at the involvement of the PP. Comparative RNA sequencing confirmed a profound alteration of EMT in PP-deficient cells, revealing a strong repression of TGFβ signature genes. Excess glucose was found to promote EMT through autocrine TGFβ stimulation, while PP-deficient cells were refractory to glucose-induced EMT. These data show that PP represents a molecular link between glucose metabolism, cancer differentiation, and aggressiveness, and may serve as a novel therapeutic target.Significance: A glucose-transforming pathway in TGFβ-driven epithelial-to-mesenchymal transition provides novel mechanistic insights into the metabolic control of cancer differentiation. Cancer Res; 78(7); 1604–18. ©2018 AACR.

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Keratin 19 Expression in Hepatocellular Carcinoma Is Regulated by Fibroblast-Derived HGF via a MET-ERK1/2-AP1 and SP1 Axis

Keratin (KRT) 19 is a poor prognostic marker for hepatocellular carcinoma (HCC); however, regulatory mechanisms underlying its expression remain unclear. We have previously reported the presence of fibrous tumor stroma in KRT19-positive HCC, suggesting that cross-talk between cancer-associated fibroblasts (CAF) and tumor epithelial cells could regulate KRT19 expression. This was investigated in this study using an in vitro model of paracrine interaction between HCC cell lines (HepG2, SNU423) and hepatic stellate cells (HSC), a major source of hepatic myofibroblasts. HSCs upregulated transcription and translation of KRT19 in HCC cells via paracrine interactions. Mechanistically, hepatocyte growth factor (HGF) from HSCs activated c-MET and the MEK–ERK1/2 pathway, which upregulated KRT19 expression in HCC cells. Furthermore, AP1 (JUN/FOSL1) and SP1, downstream transcriptional activators of ERK1/2, activated KRT19 expression in HCC cells. In clinical specimens of human HCC (n = 339), HGF and KRT19 protein expression correlated with CAF levels. In addition, HGF or MET protein expression was associated with FOSL1 and KRT19 expression and was found to be a poor prognostic factor. Analysis of data from The Cancer Genome Atlas also revealed KRT19 expression was closely associated with CAF and MET-mediated signaling activities. These results provide insights into the molecular background of KRT19-positive HCC that display an aggressive phenotype.Significance: These findings reveal KRT19 expression in hepatocellular carcinoma is regulated by cross-talk between cancer-associated fibroblasts and HCC cells, illuminating new therapeutic targets for this aggressive disease. Cancer Res; 78(7); 1619–31. ©2018 AACR.

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TRIM59 Promotes Gliomagenesis by Inhibiting TC45 Dephosphorylation of STAT3

Aberrant EGFR signaling is a common driver of glioblastoma (GBM) pathogenesis; however, the downstream effectors that sustain this oncogenic pathway remain unclarified. Here we demonstrate that tripartite motif-containing protein 59 (TRIM59) acts as a new downstream effector of EGFR signaling by regulating STAT3 activation in GBM. EGFR signaling led to TRIM59 upregulation through SOX9 and enhanced the interaction between TRIM59 and nuclear STAT3, which prevents STAT3 dephosphorylation by the nuclear form of T-cell protein tyrosine phosphatase (TC45), thereby maintaining transcriptional activation and promoting tumorigenesis. Silencing TRIM59 suppresses cell proliferation, migration, and orthotopic xenograft brain tumor formation of GBM cells and glioma stem cells. Evaluation of GBM patient samples revealed an association between EGFR activation, TRIM59 expression, STAT3 phosphorylation, and poor prognoses. Our study identifies TRIM59 as a new regulator of oncogenic EGFR/STAT3 signaling and as a potential therapeutic target for GBM patients with EGFR activation.Significance: These findings identify a novel component of the EGFR/STAT3 signaling axis in the regulation of glioma tumorigenesis. Cancer Res; 78(7); 1792–804. ©2018 AACR.

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MBD2 Ablation Impairs Lymphopoiesis and Impedes Progression and Maintenance of T-ALL

Aberrant DNA methylation patterns in leukemia might be exploited for therapeutic targeting. In this study, we employed a genetically deficient mouse model to explore the role of the methylated DNA binding protein MBD2 in normal and malignant hematopoiesis. MBD2 ablation led to diminished lymphocytes. Functional defects of the lymphoid compartment were also observed after in vivo reconstitution of MBD2-deficient hematopoietic stem cells (HSC). In an established model of Notch1-driven T-cell acute lymphoblastic leukemia (T-ALL), MBD2 ablation impeded malignant progression and maintenance by attenuating the Wnt signaling pathway. In clinical specimens of human T-ALL, Wnt signaling pathway signatures were significantly enhanced and positively correlated with the expression and function of MBD2. Furthermore, a number of typical Wnt signaling inhibitory genes were abnormally hypermethylated in primary human T-ALL. Abnormal activation of Wnt signaling in T-ALL was switched off by MBD2 deletion, partially by reactivating epigenetically silenced Wnt signaling inhibitors. Taken together, our results define essential roles for MBD2 in lymphopoiesis and T-ALL and suggest MBD2 as a candidate therapeutic target in T-ALL.Significance: This study highlights a methylated DNA binding protein as a candidate therapeutic target to improve the treatment of T-cell acute lymphoblastic leukemias, as a new starting point for developing epigenetic therapy in this and other lymphoid malignancies. Cancer Res; 78(7); 1632–42. ©2018 AACR.

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Selective mTORC2 Inhibitor Therapeutically Blocks Breast Cancer Cell Growth and Survival

Small-molecule inhibitors of the mTORC2 kinase (torkinibs) have shown efficacy in early clinical trials. However, the torkinibs under study also inhibit the other mTOR-containing complex mTORC1. While mTORC1/mTORC2 combined inhibition may be beneficial in cancer cells, recent reports describe compensatory cell survival upon mTORC1 inhibition due to loss of negative feedback on PI3K, increased autophagy, and increased macropinocytosis. Genetic models suggest that selective mTORC2 inhibition would be effective in breast cancers, but the lack of selective small-molecule inhibitors of mTORC2 have precluded testing of this hypothesis to date. Here we report the engineering of a nanoparticle-based RNAi therapeutic that can effectively silence the mTORC2 obligate cofactor Rictor. Nanoparticle-based Rictor ablation in HER2-amplified breast tumors was achieved following intratumoral and intravenous delivery, decreasing Akt phosphorylation and increasing tumor cell killing. Selective mTORC2 inhibition in vivo, combined with the HER2 inhibitor lapatinib, decreased the growth of HER2-amplified breast cancers to a greater extent than either agent alone, suggesting that mTORC2 promotes lapatinib resistance, but is overcome by mTORC2 inhibition. Importantly, selective mTORC2 inhibition was effective in a triple-negative breast cancer (TNBC) model, decreasing Akt phosphorylation and tumor growth, consistent with our findings that RICTOR mRNA correlates with worse outcome in patients with basal-like TNBC. Together, our results offer preclinical validation of a novel RNAi delivery platform for therapeutic gene ablation in breast cancer, and they show that mTORC2-selective targeting is feasible and efficacious in this disease setting.Significance: This study describes a nanomedicine to effectively inhibit the growth regulatory kinase mTORC2 in a preclinical model of breast cancer, targeting an important pathogenic enzyme in that setting that has been undruggable to date. Cancer Res; 78(7); 1845–58. ©2018 AACR.

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Forkhead Box F2 Suppresses Gastric Cancer through a Novel FOXF2-IRF2BPL-{beta}-Catenin Signaling Axis

DNA methylation has been identified as a hallmark of gastric cancer (GC). Identifying genes that are repressed by DNA promoter methylation is essential in providing insights into the molecular pathogenesis of gastric cancer. Using genome-wide methylation studies, we identified that transcription factor forkhead box F2 (FOXF2) was preferentially methylated in gastric cancer. We then investigated the functional significance and clinical implication of FOXF2 in gastric cancer. FOXF2 was silenced in gastric cancer cell lines and cancer tissues by promoter methylation, which was negatively associated with mRNA expression. Ectopic expression of FOXF2 inhibited proliferation, colony formation, G1–S cell-cycle transition, induced apoptosis of gastric cancer cell lines, and suppressed growth of xenograft tumors in nude mice; knockdown of FOXF2 elicited opposing effects. FOXF2 inhibited Wnt signaling by inducing β-catenin protein ubiquitination and degradation independently of GSK-3β. FOXF2 directly bound the promoter of E3 ligase interferon regulatory factor 2-binding protein-like (IRF2BPL) and induced its transcriptional expression. IRF2BPL in turn interacted with β-catenin, increasing its ubiquitination and degradation. Multivariate Cox regression analysis identified FOXF2 hypermethylation as an independent prognostic factor of poor survival in early-stage gastric cancer patients. In conclusion, FOXF2 is a critical tumor suppressor in gastric carcinogenesis whose methylation status serves as an independent prognostic factor for gastric cancer patients.Significance: FOXF2-mediated upregulation of the E3 ligase IRF2BPL drives ubiquitylation and degradation of β-catenin in gastric cancer, blunting Wnt signaling and suppressing carcinogenesis. Cancer Res; 78(7); 1643–56. ©2018 AACR.

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Highlights from Recent Cancer Literature



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Myeloma Cells Are Activated in Bone Marrow Microenvironment by the CD180/MD-1 Complex, Which Senses Lipopolysaccharide

Multiple myeloma (MM) cells acquire dormancy and drug resistance via interaction with bone marrow stroma cells (BMSC) in a hypoxic microenvironment. Elucidating the mechanisms underlying the regrowth of dormant clones may contribute to further improvement of the prognosis of MM patients. In this study, we find that the CD180/MD-1 complex, a noncanonical lipopolysaccharide (LPS) receptor, is expressed on MM cells but not on normal counterparts, and its abundance is markedly upregulated under adherent and hypoxic conditions. Bacterial LPS and anti-CD180 antibody, but not other Toll-like receptor ligands, enhanced the growth of MM cells via activation of MAP kinases ERK and JNK in positive correlation with expression levels of CD180. Administration of LPS significantly increased the number of CD180/CD138 double-positive cells in a murine xenograft model when MM cells were inoculated with direct attachment to BMSC. Knockdown of CD180 canceled the LPS response in vitro and in vivo. Promoter analyses identified IKZF1 (Ikaros) as a pivotal transcriptional activator of the CD180 gene. Both cell adhesion and hypoxia activated transcription of the CD180 gene by increasing Ikaros expression and its binding to the promoter region. Pharmacological targeting of Ikaros by the immunomodulatory drug lenalidomide ameliorated the response of MM cells to LPS in a CD180-dependent manner in vitro and in vivo. Thus, the CD180/MD-1 pathway may represent a novel mechanism of growth regulation of MM cells in a BM milieu and may be a therapeutic target of preventing the regrowth of dormant MM cells.Significance: This study describes a novel mechanism by which myeloma cells are regulated in the bone marrow, where drug resistance and dormancy can evolve after treatment, with potential therapeutic implications for treating this often untreatable blood cancer. Cancer Res; 78(7); 1766–78. ©2018 AACR.

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Integrative Genomic Analysis Predicts Causative Cis-Regulatory Mechanisms of the Breast Cancer-Associated Genetic Variant rs4415084

Previous genome-wide association studies (GWAS) have identified several common genetic variants that may significantly modulate cancer susceptibility. However, the precise molecular mechanisms behind these associations remain largely unknown; it is often not clear whether discovered variants are themselves functional or merely genetically linked to other functional variants. Here, we provide an integrated method for identifying functional regulatory variants associated with cancer and their target genes by combining analyses of expression quantitative trait loci, a modified version of allele-specific expression that systematically utilizes haplotype information, transcription factor (TF)–binding preference, and epigenetic information. Application of our method to a breast cancer susceptibility region in 5p12 demonstrates that the risk allele rs4415084-T correlates with higher expression levels of the protein-coding gene mitochondrial ribosomal protein S30 (MRPS30) and lncRNA RP11-53O19.1. We propose an intergenic SNP rs4321755, in linkage disequilibrium (LD) with the GWAS SNP rs4415084 (r2 = 0.988), to be the predicted functional SNP. The risk allele rs4321755-T, in phase with the GWAS rs4415084-T, created a GATA3-binding motif within an enhancer, resulting in differential GATA3 binding and chromatin accessibility, thereby promoting transcription of MRPS30 and RP11-53O19.1. MRPS30 encodes a member of the mitochondrial ribosomal proteins, implicating the role of risk SNP in modulating mitochondrial activities in breast cancer. Our computational framework provides an effective means to integrate GWAS results with high-throughput genomic and epigenomic data and can be extended to facilitate rapid functional characterization of other genetic variants modulating cancer susceptibility.Significance: Unification of GWAS results with information from high-throughput genomic and epigenomic profiles provides a direct link between common genetic variants and measurable molecular perturbations. Cancer Res; 78(7); 1579–91. ©2018 AACR.

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In Silico Evaluation of Pharmacokinetic Optimization for Antimitogram-Based Clinical Trials

Antimitograms are prototype in vitro tests for evaluating chemotherapeutic efficacy using patient-derived primary cancer cells. These tests might help optimize treatment from a pharmacodynamic standpoint by guiding treatment selection. However, they are technically challenging and require refinements and trials to demonstrate benefit to be widely used. In this study, we performed simulations aimed at exploring how to validate antimitograms and how to complement them by pharmacokinetic optimization. A generic model of advanced cancer, including pharmacokinetic–pharmacodynamic monitoring, was used to link dosing schedules with progression-free survival (PFS), as built from previously validated modules. This model was used to explore different possible situations in terms of pharmacokinetic variability, pharmacodynamic variability, and antimitogram performance. The model recapitulated tumor dynamics and standalone therapeutic drug monitoring efficacy consistent with published clinical results. Simulations showed that combining pharmacokinetic and pharmacodynamic optimization should increase PFS in a synergistic fashion. Simulated data were then used to compute required clinical trial sizes, which were 30% to 90% smaller when pharmacokinetic optimization was added to pharmacodynamic optimization. This improvement was observed even when pharmacokinetic optimization alone exhibited only modest benefit. Overall, our work illustrates the synergy derived from combining antimitograms with therapeutic drug monitoring, permitting a disproportionate reduction of the trial size required to prove a benefit on PFS. Accordingly, we suggest that strategies with benefits too small for standalone clinical trials could be validated in combination in a similar manner.Significance: This work offers a method to reduce the number of patients needed for a clinical trial to prove the hypothesized benefit of a drug to progression-free survival, possibly easing opportunities to evaluate combinations. Cancer Res; 78(7); 1873–82. ©2018 AACR.

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Pyruvate Dehydrogenase PDH-E1{beta} Controls Tumor Progression by Altering the Metabolic Status of Cancer Cells

Downregulation of pyruvate dehydrogenase (PDH) is critical for the aberrant preferential activation of glycolysis in cancer cells under normoxic conditions. Phosphorylation-dependent inhibition of PDH is a relevant event in this process, but it is not durable as it relies on PDH kinases that are activated ordinarily under hypoxic conditions. Thus, it remains unclear how PDH is durably downregulated in cancer cells that are not hypoxic. Building on evidence that PDH activity depends on the stability of a multi-protein PDH complex, we found that the PDH-E1β subunit of the PDH complex is downregulated to inhibit PDH activity under conditions of prolonged hypoxia. After restoration of normoxic conditions, reduced expression of PDH-E1β was sustained such that glycolysis remained highly activated. Notably, PDH-E1β silencing in cancer cells produced a metabolic state strongly resembling the Warburg effect, but inhibited tumor growth. Conversely, enforced exogenous expression of PDH-E1β durably increased PDH activity and promoted the malignant growth of breast cancer cells in vivo. Taken together, our results establish the specific mechanism through which PDH acts as an oncogenic factor by tuning glycolytic metabolism in cancer cells.Significance: This seminal study offers a mechanistic explanation for why glycolysis is aberrantly activated in normoxic cancer cells, offering insights into this long-standing hallmark of cancer termed the Warburg effect. Cancer Res; 78(7); 1592–603. ©2018 AACR.

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Fc-Mediated Anomalous Biodistribution of Therapeutic Antibodies in Immunodeficient Mouse Models

A critical benchmark in the development of antibody-based therapeutics is demonstration of efficacy in preclinical mouse models of human disease, many of which rely on immunodeficient mice. However, relatively little is known about how the biology of various immunodeficient strains impacts the in vivo fate of these drugs. Here we used immunoPET radiotracers prepared from humanized, chimeric, and murine mAbs against four therapeutic oncologic targets to interrogate their biodistribution in four different strains of immunodeficient mice bearing lung, prostate, and ovarian cancer xenografts. The immunodeficiency status of the mouse host as well as both the biological origin and glycosylation of the antibody contributed significantly to the anomalous biodistribution of therapeutic monoclonal antibodies in an Fc receptor-dependent manner. These findings may have important implications for the preclinical evaluation of Fc-containing therapeutics and highlight a clear need for biodistribution studies in the early stages of antibody drug development.Significance: Fc/FcγR-mediated immunobiology of the experimental host is a key determinant to preclinical in vivo tumor targeting and efficacy of therapeutic antibodies. Cancer Res; 78(7); 1820–32. ©2018 AACR.

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Antiestrogen Therapy Increases Plasticity and Cancer Stemness of Prolactin-Induced ER{alpha}+ Mammary Carcinomas

Although antiestrogen therapies are successful in many patients with estrogen receptor alpha-positive (ERα+) breast cancer, 25% to 40% fail to respond. Although multiple mechanisms underlie evasion of these treatments, including tumor heterogeneity and drug-resistant cancer stem cells (CSC), further investigations have been limited by the paucity of preclinical ERα+ tumor models. Here, we examined a mouse model of prolactin-induced aggressive ERα+ breast cancer, which mimics the epidemiologic link between prolactin exposure and increased risk for metastatic ERα+ tumors. Like a subset of ERα+ patient cancers, the prolactin-induced adenocarcinomas contained two major tumor subpopulations that expressed markers of normal luminal and basal epithelial cells. CSC activity was distributed equally across these two tumor subpopulations. Treatment with the selective estrogen receptor downregulator (SERD), ICI 182,780 (ICI), did not slow tumor growth, but induced adaptive responses in CSC activity, increased markers of plasticity including target gene reporters of Wnt/Notch signaling and epithelial–mesenchymal transition, and increased double-positive (K8/K5) cells. In primary tumorsphere cultures, ICI stimulated CSC self-renewal and was able to overcome the dependence of self-renewal upon Wnt or Notch signaling individually, but not together. Our findings demonstrate that treatment of aggressive mixed lineage ERα+ breast cancers with a SERD does not inhibit growth, but rather evokes tumor cell plasticity and regenerative CSC activity, predicting likely negative impacts on patient tumors with these characteristics.Significance: This study suggests that treatment of a subset of ERα+ breast cancers with antiestrogen therapies may not only fail to slow growth but also promote aggressive behavior by evoking tumor cell plasticity and regenerative CSC activity. Cancer Res; 78(7); 1672–84. ©2018 AACR.

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Metformin-Induced Reduction of CD39 and CD73 Blocks Myeloid-Derived Suppressor Cell Activity in Patients with Ovarian Cancer

Metformin is a broadly prescribed drug for type 2 diabetes that exerts antitumor activity, yet the mechanisms underlying this activity remain unclear. We show here that metformin treatment blocks the suppressive function of myeloid-derived suppressor cells (MDSC) in patients with ovarian cancer by downregulating the expression and ectoenzymatic activity of CD39 and CD73 on monocytic and polymononuclear MDSC subsets. Metformin triggered activation of AMP-activated protein kinase α and subsequently suppressed hypoxia-inducible factor α, which was critical for induction of CD39/CD73 expression in MDSC. Furthermore, metformin treatment correlated with longer overall survival in diabetic patients with ovarian cancer, which was accompanied by a metformin-induced reduction in the frequency of circulating CD39+CD73+ MDSC and a concomitant increase in the antitumor activities of circulating CD8+ T cells. Our results highlight a direct effect of metformin on MDSC and suggest that metformin may yield clinical benefit through improvement of antitumor T-cell immunity by dampening CD39/CD73-dependent MDSC immunosuppression in ovarian cancer patients.Significance: The antitumor activity of an antidiabetes drug is attributable to reduced immunosuppressive activity of myeloid-derived tumor suppressor cells. Cancer Res; 78(7); 1779–91. ©2018 AACR.

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TRIM59 Promotes Gliomagenesis by Inhibiting TC45 Dephosphorylation of STAT3

Aberrant EGFR signaling is a common driver of glioblastoma (GBM) pathogenesis; however, the downstream effectors that sustain this oncogenic pathway remain unclarified. Here we demonstrate that tripartite motif-containing protein 59 (TRIM59) acts as a new downstream effector of EGFR signaling by regulating STAT3 activation in GBM. EGFR signaling led to TRIM59 upregulation through SOX9 and enhanced the interaction between TRIM59 and nuclear STAT3, which prevents STAT3 dephosphorylation by the nuclear form of T-cell protein tyrosine phosphatase (TC45), thereby maintaining transcriptional activation and promoting tumorigenesis. Silencing TRIM59 suppresses cell proliferation, migration, and orthotopic xenograft brain tumor formation of GBM cells and glioma stem cells. Evaluation of GBM patient samples revealed an association between EGFR activation, TRIM59 expression, STAT3 phosphorylation, and poor prognoses. Our study identifies TRIM59 as a new regulator of oncogenic EGFR/STAT3 signaling and as a potential therapeutic target for GBM patients with EGFR activation.Significance: These findings identify a novel component of the EGFR/STAT3 signaling axis in the regulation of glioma tumorigenesis. Cancer Res; 78(7); 1792–804. ©2018 AACR.

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MBD2 Ablation Impairs Lymphopoiesis and Impedes Progression and Maintenance of T-ALL

Aberrant DNA methylation patterns in leukemia might be exploited for therapeutic targeting. In this study, we employed a genetically deficient mouse model to explore the role of the methylated DNA binding protein MBD2 in normal and malignant hematopoiesis. MBD2 ablation led to diminished lymphocytes. Functional defects of the lymphoid compartment were also observed after in vivo reconstitution of MBD2-deficient hematopoietic stem cells (HSC). In an established model of Notch1-driven T-cell acute lymphoblastic leukemia (T-ALL), MBD2 ablation impeded malignant progression and maintenance by attenuating the Wnt signaling pathway. In clinical specimens of human T-ALL, Wnt signaling pathway signatures were significantly enhanced and positively correlated with the expression and function of MBD2. Furthermore, a number of typical Wnt signaling inhibitory genes were abnormally hypermethylated in primary human T-ALL. Abnormal activation of Wnt signaling in T-ALL was switched off by MBD2 deletion, partially by reactivating epigenetically silenced Wnt signaling inhibitors. Taken together, our results define essential roles for MBD2 in lymphopoiesis and T-ALL and suggest MBD2 as a candidate therapeutic target in T-ALL.Significance: This study highlights a methylated DNA binding protein as a candidate therapeutic target to improve the treatment of T-cell acute lymphoblastic leukemias, as a new starting point for developing epigenetic therapy in this and other lymphoid malignancies. Cancer Res; 78(7); 1632–42. ©2018 AACR.

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Selective mTORC2 Inhibitor Therapeutically Blocks Breast Cancer Cell Growth and Survival

Small-molecule inhibitors of the mTORC2 kinase (torkinibs) have shown efficacy in early clinical trials. However, the torkinibs under study also inhibit the other mTOR-containing complex mTORC1. While mTORC1/mTORC2 combined inhibition may be beneficial in cancer cells, recent reports describe compensatory cell survival upon mTORC1 inhibition due to loss of negative feedback on PI3K, increased autophagy, and increased macropinocytosis. Genetic models suggest that selective mTORC2 inhibition would be effective in breast cancers, but the lack of selective small-molecule inhibitors of mTORC2 have precluded testing of this hypothesis to date. Here we report the engineering of a nanoparticle-based RNAi therapeutic that can effectively silence the mTORC2 obligate cofactor Rictor. Nanoparticle-based Rictor ablation in HER2-amplified breast tumors was achieved following intratumoral and intravenous delivery, decreasing Akt phosphorylation and increasing tumor cell killing. Selective mTORC2 inhibition in vivo, combined with the HER2 inhibitor lapatinib, decreased the growth of HER2-amplified breast cancers to a greater extent than either agent alone, suggesting that mTORC2 promotes lapatinib resistance, but is overcome by mTORC2 inhibition. Importantly, selective mTORC2 inhibition was effective in a triple-negative breast cancer (TNBC) model, decreasing Akt phosphorylation and tumor growth, consistent with our findings that RICTOR mRNA correlates with worse outcome in patients with basal-like TNBC. Together, our results offer preclinical validation of a novel RNAi delivery platform for therapeutic gene ablation in breast cancer, and they show that mTORC2-selective targeting is feasible and efficacious in this disease setting.Significance: This study describes a nanomedicine to effectively inhibit the growth regulatory kinase mTORC2 in a preclinical model of breast cancer, targeting an important pathogenic enzyme in that setting that has been undruggable to date. Cancer Res; 78(7); 1845–58. ©2018 AACR.

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PHD3 Controls Lung Cancer Metastasis and Resistance to EGFR Inhibitors through TGF{alpha}

Lung cancer is the leading cause of cancer-related death worldwide, in large part due to its high propensity to metastasize and to develop therapy resistance. Adaptive responses to hypoxia and epithelial–mesenchymal transition (EMT) are linked to tumor metastasis and drug resistance, but little is known about how oxygen sensing and EMT intersect to control these hallmarks of cancer. Here, we show that the oxygen sensor PHD3 links hypoxic signaling and EMT regulation in the lung tumor microenvironment. PHD3 was repressed by signals that induce EMT and acted as a negative regulator of EMT, metastasis, and therapeutic resistance. PHD3 depletion in tumors, which can be caused by the EMT inducer TGFβ or by promoter methylation, enhanced EMT and spontaneous metastasis via HIF-dependent upregulation of the EGFR ligand TGFα. In turn, TGFα stimulated EGFR, which potentiated SMAD signaling, reinforcing EMT and metastasis. In clinical specimens of lung cancer, reduced PHD3 expression was linked to poor prognosis and to therapeutic resistance against EGFR inhibitors such as erlotinib. Reexpression of PHD3 in lung cancer cells suppressed EMT and metastasis and restored sensitivity to erlotinib. Taken together, our results establish a key function for PHD3 in metastasis and drug resistance and suggest opportunities to improve patient treatment by interfering with the feedforward signaling mechanisms activated by PHD3 silencing.Significance: This study links the oxygen sensor PHD3 to metastasis and drug resistance in cancer, with implications for therapeutic improvement by targeting this system. Cancer Res; 78(7); 1805–19. ©2018 AACR.

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Highlights from Recent Cancer Literature



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Tumor-Stroma IL1{beta}-IRAK4 Feedforward Circuitry Drives Tumor Fibrosis, Chemoresistance, and Poor Prognosis in Pancreatic Cancer

Targeting the desmoplastic stroma of pancreatic ductal adenocarcinoma (PDAC) holds promise to augment the effect of chemotherapy, but success in the clinic has thus far been limited. Preclinical mouse models suggest that near-depletion of cancer-associated fibroblasts (CAF) carries a risk of accelerating PDAC progression, underscoring the need to concurrently target key signaling mechanisms that drive the malignant attributes of both CAF and PDAC cells. We previously reported that inhibition of IL1 receptor–associated kinase 4 (IRAK4) suppresses NFκB activity and promotes response to chemotherapy in PDAC cells. In this study, we report that CAF in PDAC tumors robustly express activated IRAK4 and NFκB. IRAK4 expression in CAF promoted NFκB activity, drove tumor fibrosis, and supported PDAC cell proliferation, survival, and chemoresistance. Cytokine array analysis of CAF and microarray analysis of PDAC cells identified IL1β as a key cytokine that activated IRAK4 in CAF. Targeting IRAK4 or IL1β rendered PDAC tumors less fibrotic and more sensitive to gemcitabine. In clinical specimens of human PDAC, high stromal IL1β expression associated strongly with poor overall survival. Together, our studies establish a tumor–stroma IL1β-IRAK4 feedforward signal that can be therapeutically disrupted to increase chemotherapeutic efficacy in PDAC.Significance: Targeting the IL1β-IRAK4 signaling pathway potentiates the effect of chemotherapy in pancreatic cancer. Cancer Res; 78(7); 1700–12. ©2018 AACR.

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miR-508 Defines the Stem-like/Mesenchymal Subtype in Colorectal Cancer

Colorectal cancer includes an invasive stem-like/mesenchymal subtype, but its genetic drivers, functional, and clinical relevance are uncharacterized. Here we report the definition of an altered miRNA signature defining this subtype that includes a major genomic loss of miR-508. Mechanistic investigations showed that this miRNA affected the expression of cadherin CDH1 and the transcription factors ZEB1, SALL4, and BMI1. Loss of miR-508 in colorectal cancer was associated with upregulation of the novel hypoxia-induced long noncoding RNA AK000053. Ectopic expression of miR-508 in colorectal cancer cells blunted epithelial-to-mesenchymal transition (EMT), stemness, migration, and invasive capacity in vitro and in vivo. In clinical colorectal cancer specimens, expression of miR-508 negatively correlated with stemness and EMT-associated gene expression and positively correlated with patient survival. Overall, our results showed that miR-508 is a key functional determinant of the stem-like/mesenchymal colorectal cancer subtype and a candidate therapeutic target for its treatment.Significance: These results define a key functional determinant of a stem-like/mesenchymal subtype of colorectal cancers and a candidate therapeutic target for its treatment. Cancer Res; 78(7); 1751–65. ©2018 AACR.

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Antiestrogen Therapy Increases Plasticity and Cancer Stemness of Prolactin-Induced ER{alpha}+ Mammary Carcinomas

Although antiestrogen therapies are successful in many patients with estrogen receptor alpha-positive (ERα+) breast cancer, 25% to 40% fail to respond. Although multiple mechanisms underlie evasion of these treatments, including tumor heterogeneity and drug-resistant cancer stem cells (CSC), further investigations have been limited by the paucity of preclinical ERα+ tumor models. Here, we examined a mouse model of prolactin-induced aggressive ERα+ breast cancer, which mimics the epidemiologic link between prolactin exposure and increased risk for metastatic ERα+ tumors. Like a subset of ERα+ patient cancers, the prolactin-induced adenocarcinomas contained two major tumor subpopulations that expressed markers of normal luminal and basal epithelial cells. CSC activity was distributed equally across these two tumor subpopulations. Treatment with the selective estrogen receptor downregulator (SERD), ICI 182,780 (ICI), did not slow tumor growth, but induced adaptive responses in CSC activity, increased markers of plasticity including target gene reporters of Wnt/Notch signaling and epithelial–mesenchymal transition, and increased double-positive (K8/K5) cells. In primary tumorsphere cultures, ICI stimulated CSC self-renewal and was able to overcome the dependence of self-renewal upon Wnt or Notch signaling individually, but not together. Our findings demonstrate that treatment of aggressive mixed lineage ERα+ breast cancers with a SERD does not inhibit growth, but rather evokes tumor cell plasticity and regenerative CSC activity, predicting likely negative impacts on patient tumors with these characteristics.Significance: This study suggests that treatment of a subset of ERα+ breast cancers with antiestrogen therapies may not only fail to slow growth but also promote aggressive behavior by evoking tumor cell plasticity and regenerative CSC activity. Cancer Res; 78(7); 1672–84. ©2018 AACR.

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Metformin-Induced Reduction of CD39 and CD73 Blocks Myeloid-Derived Suppressor Cell Activity in Patients with Ovarian Cancer

Metformin is a broadly prescribed drug for type 2 diabetes that exerts antitumor activity, yet the mechanisms underlying this activity remain unclear. We show here that metformin treatment blocks the suppressive function of myeloid-derived suppressor cells (MDSC) in patients with ovarian cancer by downregulating the expression and ectoenzymatic activity of CD39 and CD73 on monocytic and polymononuclear MDSC subsets. Metformin triggered activation of AMP-activated protein kinase α and subsequently suppressed hypoxia-inducible factor α, which was critical for induction of CD39/CD73 expression in MDSC. Furthermore, metformin treatment correlated with longer overall survival in diabetic patients with ovarian cancer, which was accompanied by a metformin-induced reduction in the frequency of circulating CD39+CD73+ MDSC and a concomitant increase in the antitumor activities of circulating CD8+ T cells. Our results highlight a direct effect of metformin on MDSC and suggest that metformin may yield clinical benefit through improvement of antitumor T-cell immunity by dampening CD39/CD73-dependent MDSC immunosuppression in ovarian cancer patients.Significance: The antitumor activity of an antidiabetes drug is attributable to reduced immunosuppressive activity of myeloid-derived tumor suppressor cells. Cancer Res; 78(7); 1779–91. ©2018 AACR.

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Downregulation of Membrane Trafficking Proteins and Lactate Conditioning Determine Loss of Dendritic Cell Function in Lung Cancer

Restoring antigen presentation for efficient and durable activation of tumor-specific CD8+ T-cell responses is pivotal to immunotherapy, yet the mechanisms that cause subversion of dendritic cell (DC) functions are not entirely understood, limiting the development of targeted approaches. In this study, we show that bona fide DCs resident in lung tumor tissues or DCs exposed to factors derived from whole lung tumors become refractory to endosomal and cytosolic sensor stimulation and fail to secrete IL12 and IFNI. Tumor-conditioned DC exhibited downregulation of the SNARE VAMP3, a regulator of endosomes trafficking critical for cross-presentation of tumor antigens and DC-mediated tumor rejection. Dissection of cell-extrinsic suppressive pathways identified lactic acid in the tumor microenvironment as sufficient to inhibit type-I IFN downstream of TLR3 and STING. DC conditioning by lactate also impacted adaptive function, accelerating antigen degradation and impairing cross-presentation. Importantly, DCs conditioned by lactate failed to prime antitumor responses in vivo. These findings provide a new mechanistic viewpoint to the concept of DC suppression and hold potential for future therapeutic approaches.Significance: These findings provide insight into the cell-intrinsic and cell-extrinsic mechanisms that cause loss of presentation of tumor-specific antigens in lung cancer tissues. Cancer Res; 78(7); 1685–99. ©2018 AACR.

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PHD3 Controls Lung Cancer Metastasis and Resistance to EGFR Inhibitors through TGF{alpha}

Lung cancer is the leading cause of cancer-related death worldwide, in large part due to its high propensity to metastasize and to develop therapy resistance. Adaptive responses to hypoxia and epithelial–mesenchymal transition (EMT) are linked to tumor metastasis and drug resistance, but little is known about how oxygen sensing and EMT intersect to control these hallmarks of cancer. Here, we show that the oxygen sensor PHD3 links hypoxic signaling and EMT regulation in the lung tumor microenvironment. PHD3 was repressed by signals that induce EMT and acted as a negative regulator of EMT, metastasis, and therapeutic resistance. PHD3 depletion in tumors, which can be caused by the EMT inducer TGFβ or by promoter methylation, enhanced EMT and spontaneous metastasis via HIF-dependent upregulation of the EGFR ligand TGFα. In turn, TGFα stimulated EGFR, which potentiated SMAD signaling, reinforcing EMT and metastasis. In clinical specimens of lung cancer, reduced PHD3 expression was linked to poor prognosis and to therapeutic resistance against EGFR inhibitors such as erlotinib. Reexpression of PHD3 in lung cancer cells suppressed EMT and metastasis and restored sensitivity to erlotinib. Taken together, our results establish a key function for PHD3 in metastasis and drug resistance and suggest opportunities to improve patient treatment by interfering with the feedforward signaling mechanisms activated by PHD3 silencing.Significance: This study links the oxygen sensor PHD3 to metastasis and drug resistance in cancer, with implications for therapeutic improvement by targeting this system. Cancer Res; 78(7); 1805–19. ©2018 AACR.

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Tumor-Stroma IL1{beta}-IRAK4 Feedforward Circuitry Drives Tumor Fibrosis, Chemoresistance, and Poor Prognosis in Pancreatic Cancer

Targeting the desmoplastic stroma of pancreatic ductal adenocarcinoma (PDAC) holds promise to augment the effect of chemotherapy, but success in the clinic has thus far been limited. Preclinical mouse models suggest that near-depletion of cancer-associated fibroblasts (CAF) carries a risk of accelerating PDAC progression, underscoring the need to concurrently target key signaling mechanisms that drive the malignant attributes of both CAF and PDAC cells. We previously reported that inhibition of IL1 receptor–associated kinase 4 (IRAK4) suppresses NFκB activity and promotes response to chemotherapy in PDAC cells. In this study, we report that CAF in PDAC tumors robustly express activated IRAK4 and NFκB. IRAK4 expression in CAF promoted NFκB activity, drove tumor fibrosis, and supported PDAC cell proliferation, survival, and chemoresistance. Cytokine array analysis of CAF and microarray analysis of PDAC cells identified IL1β as a key cytokine that activated IRAK4 in CAF. Targeting IRAK4 or IL1β rendered PDAC tumors less fibrotic and more sensitive to gemcitabine. In clinical specimens of human PDAC, high stromal IL1β expression associated strongly with poor overall survival. Together, our studies establish a tumor–stroma IL1β-IRAK4 feedforward signal that can be therapeutically disrupted to increase chemotherapeutic efficacy in PDAC.Significance: Targeting the IL1β-IRAK4 signaling pathway potentiates the effect of chemotherapy in pancreatic cancer. Cancer Res; 78(7); 1700–12. ©2018 AACR.

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SETD1A Interacts with Cyclin K to Promote Leukemia Cell Survival [Leukemia]

SETD1A enhances leukemic cell growth and survival independent of its methyltransferase activity.



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A Next-Generation Chimeric Antigen Receptor Induces JAK-STAT Signaling [Immunotherapy]

CAR-T cells designed to activate JAK–STAT signaling show enhanced persistence and antitumor activity.



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Noted [News in Brief]

A collection of recently published news items.



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NIH Offers Funding for Genome-Editing Projects [News in Brief]

The NIH is launching a new funding program for genome-editing technologies. The agency will award $190 million for projects including new delivery methods for genome editors, new editing technologies, and preclinical models to test their safety.



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Convergent Therapeutic Strategies to Overcome the Heterogeneity of Acquired Resistance in BRAFV600E Colorectal Cancer [Research Briefs]

Clonal heterogeneity associated with acquired resistance presents a critical therapeutic challenge. Whole-exome sequencing of paired tumor biopsies and targeted sequencing of cell-free DNA (cfDNA) from patients with BRAFV600E colorectal cancer receiving BRAF inhibitor combinations identified 14 distinct alterations in MAPK pathway components driving acquired resistance, with as many as eight alterations in a single patient. We developed a pooled clone system to study clonal outgrowth during acquired resistance, in vitro and in vivo. In vitro, the dynamics of individual resistant clones could be monitored in real time in cfDNA isolated from culture media during therapy. Outgrowth of multiple resistant clones was observed during therapy with BRAF, EGFR, and MEK inhibitor combinations. However, ERK inhibition, particularly in combination with BRAF and EGFR inhibition, markedly abrogated clonal outgrowth in vitro and in vivo. Thus, convergent, up-front therapy may suppress outgrowth of heterogeneous clones harboring clinically observed resistance alterations, which may improve clinical outcome.

Significance: We observed heterogeneous, recurrent alterations in the MAPK pathway as key drivers of acquired resistance in BRAFV600E colorectal cancer, with multiple concurrent resistance alterations detectable in individual patients. Using a novel pooled clone system, we identify convergent up-front therapeutic strategies capable of intercepting multiple resistance mechanisms as potential approaches to suppress emergence of acquired resistance. Cancer Discov; 8(4); 417–27. ©2018 AACR.

See related commentary by Janku, p. 389.

See related article by Corcoran et al., p. 428.

This article is highlighted in the In This Issue feature, p. 371



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Drug Combo Bests Sunitinib in RCC [News in Brief]

The phase III IMmotion151 trial found that the combination of atezolizumab and bevacizumab boosts progression-free survival compared with sunitinib in patients with advanced or metastatic renal cell carcinoma. The increase was 2.8 months in all patients and 3.5 months in patients with PD-L1–positive tumors.



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The Oncolytic Adenovirus DNX-2401 Has Antitumor Activity in Glioblastoma [Clinical Trials]

In a phase I trial, DNX-2401 is safe and achieves durable responses in patients with recurrent glioma.



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BMI Can Underestimate Breast Cancer Risk [News in Brief]

New findings suggest that postmenopausal women with high levels of body fat are at increased risk of ER-positive breast cancer, even if their body mass index is within the normal range. If confirmed, these results would put many more women at elevated risk for breast cancer than was previously thought, with implications for the way that healthy-weight women should be counseled to reduce their health risks.



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Advances on the BRAF Front in Colorectal Cancer [In the Spotlight]

Summary: Colorectal cancer with BRAFV600E mutation can be effectively treated with combination approaches involving inhibition of BRAF, MEK, and EGFR proteins. However, activation of the MAPK pathway, often due to emergence of previously undetected molecular alterations, ultimately leads to adaptive therapeutic resistance. Novel combination strategies combining inhibition of BRAF, ERK, and EGFR can be used to prevent MAPK pathway–driven resistance and warrant further investigation. Cancer Discov; 8(4); 389–91. ©2018 AACR.

See related article by Corcoran et al., p. 428.

See related article by Hazar-Rethinam et al., p. 417.



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Axitinib plus Pembrolizumab Is Effective in Renal Cell Carcinoma [Clinical Trials]

Axitinib plus pembrolizumab has a 73% response rate in previously untreated advanced renal cell carcinoma.



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MEF2C Phosphorylation Is Required for Chemotherapy Resistance in Acute Myeloid Leukemia [Research Articles]

In acute myeloid leukemia (AML), chemotherapy resistance remains prevalent and poorly understood. Using functional proteomics of patient AML specimens, we identified MEF2C S222 phosphorylation as a specific marker of primary chemoresistance. We found that Mef2cS222A/S222A knock-in mutant mice engineered to block MEF2C phosphorylation exhibited normal hematopoiesis, but were resistant to leukemogenesis induced by MLL–AF9. MEF2C phosphorylation was required for leukemia stem cell maintenance and induced by MARK kinases in cells. Treatment with the selective MARK/SIK inhibitor MRT199665 caused apoptosis and conferred chemosensitivity in MEF2C-activated human AML cell lines and primary patient specimens, but not those lacking MEF2C phosphorylation. These findings identify kinase-dependent dysregulation of transcription factor control as a determinant of therapy response in AML, with immediate potential for improved diagnosis and therapy for this disease.

Significance: Functional proteomics identifies phosphorylation of MEF2C in the majority of primary chemotherapy-resistant AML. Kinase-dependent dysregulation of this transcription factor confers susceptibility to MARK/SIK kinase inhibition in preclinical models, substantiating its clinical investigation for improved diagnosis and therapy of AML. Cancer Discov; 8(4); 478–97. ©2018 AACR.

This article is highlighted in the In This Issue feature, p. 371



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The PI3K{alpha} Inhibitor Alpelisib Has Activity in PIK3CA-altered Tumors [Clinical Trials]

The PI3Kα inhibitor alpelisib achieved a 58.2% disease control rate in PIK3CA-altered solid tumors.



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AR Inhibition Achieves Responses in AR+ Triple-Negative Breast Cancer [Clinical Trials]

The AR inhibitor enzalutamide achieved responses in patients with advanced TNBC in a phase II trial.



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SLFN11 Blocks DNA Replication Independently of ATR Activity [DNA Repair]

SLFN11 inhibits replication in response to DNA damage or cell cycle checkpoint inhibition.



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MEK Binding to KSR Promotes Allosteric Activation of BRAF [Structural Biology]

KSR–MEK complexes allosterically activate BRAF, which then phosphorylates a second MEK molecule.



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TGF{beta} Promotes Immune Evasion to Limit the Efficacy of Anti-PD-1/PD-L1 [Immunotherapy]

The TGFβ-activated stroma induces T-cell exclusion to suppress antitumor immunity.



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Tissue-Specific Immunoregulation: A Call for Better Understanding of the "Immunostat" in the Context of Cancer [Prospective]

Checkpoint inhibitor therapy has been a breakthrough in cancer research, but only some patients with cancer derive substantial benefit. Although mechanisms underlying sensitivity and resistance to checkpoint inhibitors are being elucidated, the importance of organ-specific regulation of immunity is currently underappreciated. Here, we call for a greater understanding of tissue-specific immunoregulation, namely, "tissue-specific immunostats," to make advances in treatments for cancer. A better understanding of how individual organs at baseline regulate the immune system could enable an improved precision medicine approach to cancer immunotherapy. Cancer Discov; 8(4); 395–402. ©2018 AACR.



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MYCN Amplification Promotes Enhancer Invasion in Neuroblastoma [Neuroblastoma]

Excess MYCN binds noncanonical enhancers as well as promoters to drive tumor-specific gene expression.



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Characterizing the Potency and Impact of Carbon Ion Therapy in a Primary Mouse Model of Soft Tissue Sarcoma

Carbon ion therapy (CIT) offers several potential advantages for treating cancers compared with X-ray and proton radiotherapy, including increased biological efficacy and more conformal dosimetry. However, CIT potency has not been characterized in primary tumor animal models. Here, we calculate the relative biological effectiveness (RBE) of carbon ions compared with X-rays in an autochthonous mouse model of soft tissue sarcoma. We used Cre/loxP technology to generate primary sarcomas in KrasLSL-G12D/+; p53fl/fl mice. Primary tumors were irradiated with a single fraction of carbon ions (10 Gy), X-rays (20 Gy, 25 Gy, or 30 Gy), or observed as controls. The RBE was calculated by determining the dose of X-rays that resulted in similar time to posttreatment tumor volume quintupling and exponential growth rate as 10 Gy carbon ions. The median tumor volume quintupling time and exponential growth rate of sarcomas treated with 10 Gy carbon ions and 30 Gy X-rays were similar: 27.3 and 28.1 days and 0.060 and 0.059 mm3/day, respectively. Tumors treated with lower doses of X-rays had faster regrowth. Thus, the RBE of carbon ions in this primary tumor model is 3. When isoeffective treatments of carbon ions and X-rays were compared, we observed significant differences in tumor growth kinetics, proliferative indices, and immune infiltrates. We found that carbon ions were three times as potent as X-rays in this aggressive tumor model and identified unanticipated differences in radiation response that may have clinical implications. Mol Cancer Ther; 17(4); 858–68. ©2018 AACR.



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Adaptive Resistance to Chemotherapy, A Multi-FAK-torial Linkage

Oncogenes provide tumor cells with a growth and survival advantage. Directed therapies targeted to oncogenic mutations (such as BRAF V600E) are part of effective late-stage melanoma treatment. However, tumors with BRAF V600E mutations, in approximately 10% of colorectal cancer, are generally treatment-insensitive. Research has identified various "feedback" mechanisms that result in BRAF signal pathway reactivation in response to BRAF inhibition. Herein, we highlight key findings from Chen and colleagues (this issue) showing that integrin-associated focal adhesion kinase (FAK) activation selectively occurs in BRAF V600E-mutant colorectal cancer cells in response to pharmacological BRAF inhibition. FAK activation results in elevated β-catenin protein levels, β-catenin nuclear localization, and increased gene transcription. Small-molecule inhibitors of β-catenin or FAK synergize with vemurafenib BRAF inhibitor to prevent BRAF V600E colorectal cancer cell proliferation in vitro and xenograft tumor growth in mice. This study complements findings linking FAK to β-catenin in intestinal tumorigenesis, resistance to radiotherapy, and cancer stem cell survival. Thus, FAK activation may occur as a frequent tumor cell "adaptive resistance" mechanism. Although FAK (PTK2) is not mutated in most cancers, targeting FAK activity in combinational approaches may limit tumor cell escape mechanisms and enhance durable responses to treatment. Mol Cancer Ther; 17(4); 719–23. ©2018 AACR.



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A Spatio-Temporal Model of Macrophage-Mediated Drug Resistance in Glioma Immunotherapy

The emergence of drug resistance is often an inevitable obstacle that limits the long-term effectiveness of clinical cancer chemotherapeutics. Although various forms of cancer cell-intrinsic mechanisms of drug resistance have been experimentally revealed, the role and the underlying mechanism of tumor microenvironment in driving the development of acquired drug resistance remain elusive, which significantly impedes effective clinical cancer treatment. Recent experimental studies have revealed a macrophage-mediated drug resistance mechanism in which the tumor microenvironment undergoes adaptation in response to macrophage-targeted colony-stimulating factor-1 receptor (CSF1R) inhibition therapy in gliomas. In this study, we developed a spatio-temporal model to quantitatively describe the interplay between glioma cells and CSF1R inhibitor–targeted macrophages through CSF1 and IGF1 pathways. Our model was used to investigate the evolutionary kinetics of the tumor regrowth and the associated dynamic adaptation of the tumor microenvironment in response to the CSF1R inhibitor treatment. The simulation result obtained using this model was in agreement with the experimental data. The sensitivity analysis revealed the key parameters involved in the model, and their potential impacts on the model behavior were examined. Moreover, we demonstrated that the drug resistance is dose-dependent. In addition, we quantitatively evaluated the effects of combined CSFR inhibition and IGF1 receptor (IGF1R) inhibition with the goal of designing more effective therapies for gliomas. Our study provides quantitative and mechanistic insights into the microenvironmental adaptation mechanisms that operate during macrophage-targeted immunotherapy and has implications for drug dose optimization and the design of more effective combination therapies. Mol Cancer Ther; 17(4); 814–24. ©2018 AACR.



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Engaging Anaphase Catastrophe Mechanisms to Eradicate Aneuploid Cancers

Cancer cells often have supernumerary centrosomes that promote genomic instability, a pathognomonic feature of cancer. During mitosis, cancer cells with supernumerary centrosomes undergo bipolar cell division by clustering centrosomes into two poles. When supernumerary centrosome clustering is antagonized, cancer cells are forced to undergo multipolar division leading to death of daughter cells. This proapoptotic pathway, called anaphase catastrophe, preferentially eliminates aneuploid cancer cells and malignant tumors in engineered mouse models. Anaphase catastrophe occurs through the loss or inhibition of the centrosomal protein CP110, a direct cyclin-dependent kinase 1 (CDK1) and CDK2 target. Intriguingly, CP110 is repressed by the KRAS oncoprotein. This sensitizes KRAS-driven lung cancers (an unmet medical need) to respond to CDK2 inhibitors. Anaphase catastrophe-inducing agents like CDK1 and CDK2 antagonists are lethal to cancer cells with supernumerary centrosomes, but can relatively spare normal cells with two centrosomes. This mechanism is proposed to provide a therapeutic window in the cancer clinic following treatment with a CDK1 or CDK2 inhibitor. Taken together, anaphase catastrophe is a clinically tractable mechanism that promotes death of neoplastic tumors with aneuploidy, a hallmark of cancer. Mol Cancer Ther; 17(4); 724–31. ©2018 AACR.



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Characterization of ABBV-221, a Tumor-Selective EGFR-Targeting Antibody Drug Conjugate

Depatuxizumab mafodotin (depatux-m, ABT-414) is a tumor-selective antibody drug conjugate (ADC) comprised of the anti-EGFR antibody ABT-806 and the monomethyl auristatin F (MMAF) warhead. Depatux-m has demonstrated promising clinical activity in glioblastoma multiforme (GBM) patients and is currently being evaluated in clinical trials in first-line and recurrent GBM disease settings. Depatux-m responses have been restricted to patients with amplified EGFR, highlighting the need for therapies with activity against tumors with nonamplified EGFR overexpression. In addition, depatux-m dosing has been limited by corneal side effects common to MMAF conjugates. We hypothesized that a monomethyl auristatin E (MMAE) ADC utilizing an EGFR-targeting antibody with increased affinity may have broader utility against tumors with more modest EGFR overexpression while mitigating the risk of corneal side effects. We describe here preclinical characterization of ABBV-221, an EGFR-targeting ADC comprised of an affinity-matured ABT-806 conjugated to MMAE. ABBV-221 binds to a similar EGFR epitope as depatux-m and retains tumor selectivity with increased binding to EGFR-positive tumor cells and greater in vitro potency. ABBV-221 displays increased tumor uptake and antitumor activity against wild-type EGFR-positive xenografts with a greatly reduced incidence of corneal side effects relative to depatux-m. ABBV-221 has similar activity as depatux-m against an EGFR-amplified GBM patient derived xenograft (PDX) model and is highly effective alone and in combination with standard-of-care temozolomide in an EGFRvIII-positive GBM xenograft model. Based on these results, ABBV-221 has advanced to a phase I clinical trial in patients with advanced solid tumors associated with elevated levels of EGFR. Mol Cancer Ther; 17(4); 795–805. ©2018 AACR.



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JAK2 Inhibitor SAR302503 Abrogates PD-L1 Expression and Targets Therapy-Resistant Non-small Cell Lung Cancers

Lung cancer is the leading cause of cancer-related deaths worldwide. Approximately 85% of all lung cancers are non–small cell histology [non–small cell lung cancer (NSCLC)]. Modern treatment strategies for NSCLC target driver oncogenes and immune checkpoints. However, less than 15% of patients survive beyond 5 years. Here, we investigated the effects of SAR302503 (SAR), a selective JAK2 inhibitor, on NSCLC cell lines and tumors. We show that SAR is cytotoxic to NSCLC cells, which exhibit resistance to genotoxic therapies, such as ionizing radiation, cisplatin, and etoposide. We demonstrate that constitutive IFN-stimulated gene expression, including an IFN-related DNA damage resistance signature, predicts for sensitivity to SAR. Importantly, tumor cell–intrinsic expression of PD-L1 is IFN-inducible and abrogated by SAR. Taken together, these findings suggest potential dual roles for JAK2 inhibitors, both as a novel monotherapy in NSCLCs resistant to genotoxic therapies, and in tandem with immune checkpoint inhibition. Mol Cancer Ther; 17(4); 732–9. ©2018 AACR.



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MCT4 Expression Is a Potential Therapeutic Target in Colorectal Cancer with Peritoneal Carcinomatosis

Monocarboxylate transporters (MCT) are transmembrane proteins that control the lactate metabolism and are associated with poor prognosis in solid tumors, including colorectal cancer. Here, we aimed to investigate the biological and clinical role of MCTs in colorectal cancer and to assess the potential of therapeutic application. A total of 16 human colorectal cancer cell lines, 11 patient-derived cells from malignant ascites [patient-derived cells (PDC)], and 39 matched pairs of primary colorectal cancer and normal colorectal tissues were used to assess the role of MCT in vitro and in vivo. siRNA methodology was used to determine the effect of MCT inhibition and molecular mechanism of hypoxia- and angiogenesis-related factors in addition to MCT4. The effect of MCT inhibition was confirmed in mouse xenograft models. MCT4 expression in surgical tissue was evaluated by IHC and used for survival analysis. Expression of MCTs was demonstrated in colorectal cancer cell lines. siRNA-mediated MCT silencing caused significant decline of cell proliferation both in vitro and in vivo. An additive effect of MCT inhibition was induced by combined treatment with chemotherapy or radiotherapy. In particular, the expression of MCT4 was markedly increased in PDCs, and MCT4 inhibition significantly decreased PDC proliferation. Hypoxia-inducible factor 1-α (HIF1α) was also highly expressed in PDCs, whereas HIF1α knockdown reduced MCT4 expression and of other angiogenesis-related mediators. The patients with high MCT4 expression by IHC showed shorter relapse-free survival compared with low expression. These findings suggest that MCT4 may represent a new therapeutic target for colorectal cancer with peritoneal carcinomatosis and serve as a prognostic indicator. Mol Cancer Ther; 17(4); 838–48. ©2018 AACR.



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Pharmacological and Structural Characterizations of Naquotinib, a Novel Third-Generation EGFR Tyrosine Kinase Inhibitor, in EGFR-Mutated Non-Small Cell Lung Cancer

Multiple epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (EGFR-TKI) have been developed to effectively inhibit EGFR-derived signals in non–small cell lung cancer (NSCLC). In this study, we assessed the efficacy of EGFR-TKIs, including a novel third-generation inhibitor naquotinib (ASP8273), in clinically relevant EGFR mutations, including L858R, exon 19 deletion, L858R+T790M, exon 19 deletion+T790M with or without a C797S mutation, and several exon 20 insertion mutations. Using structural analyses, we also elucidated the mechanism of activation and sensitivity/resistance to EGFR-TKIs in EGFR exon 20 insertion mutations. The efficacy of naquotinib in cells with L858R, exon 19 deletion and exon 19 deletion+T790M was comparable with that of osimertinib. Interestingly, naquotinib was more potent than osimertinib for L858R+T790M. Additionally, naquotinib and osimertinib had comparable efficacy and a wide therapeutic window for cells with EGFR exon 20 insertions. Structural modeling partly elucidated the mechanism of activation and sensitivity/resistance to EGFR-TKIs in two EGFR exon 20 insertion mutants, A767_V769dupASV and Y764_V765insHH. In summary, we have characterized the efficacy of EGFR-TKIs for NSCLC using in vitro and structural analyses and suggested the mechanism of activation and resistance to EGFR-TKIs of EGFR exon 20 insertion mutations. Our findings should guide the selection of appropriate EGFR-TKIs for the treatment of NSCLC with EGFR mutations and help clarify the biology of EGFR exon 20 insertion mutations. Mol Cancer Ther; 17(4); 740–50. ©2018 AACR.



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Highlights of This Issue



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Preclinical Evaluation of SCC244 (Glumetinib), a Novel, Potent, and Highly Selective Inhibitor of c-Met in MET-dependent Cancer Models

Because the receptor tyrosine kinase c-Met plays a critical role in tumor growth, metastasis, tumor angiogenesis, and drug resistance, the c-Met axis represents an attractive therapeutic target. Herein, we report the first preclinical characterization of SCC244, a novel, potent, and highly selective inhibitor of c-Met kinase. SCC244 showed subnanomolar potency against c-Met kinase activity and high selectivity versus 312 other tested protein kinases, making it one of the most selective c-Met inhibitors described to date. Moreover, this inhibitor profoundly and specifically inhibits c-Met signal transduction and thereby suppresses the c-Met–dependent neoplastic phenotype of tumor and endothelial cells. In xenografts of human tumor cell lines or non–small cell lung cancer and hepatocellular carcinoma patient-derived tumor tissue driven by MET aberration, SCC244 administration exhibits robust antitumor activity at the well-tolerated doses. In addition, the in vivo antitumor activity of SCC244 involves the inhibition of c-Met downstream signaling via a mechanism of combined antiproliferation and antiangiogenic effects. The results of the current study provide a strong foundation for the clinical investigation of SCC244 in patients with tumors harboring c-Met pathway alterations. Mol Cancer Ther; 17(4); 751–62. ©2017 AACR.



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Wnt/{beta}-Catenin Pathway Activation Mediates Adaptive Resistance to BRAF Inhibition in Colorectal Cancer

One of the most encouraging developments in oncology has been the success of BRAF inhibitors in BRAF-mutant melanoma. However, in contrast to its striking efficacy in BRAF-mutant melanomas, BRAF inhibitor monotherapy is ineffective in BRAF-mutant colorectal cancer. Although many studies on BRAF inhibitor resistance in colorectal cancer have focused on mechanisms underlying the reactivation of the EGFR/RAS/RAF/MEK/ERK pathway, the current study focuses on identifying novel adaptive signaling mechanisms, a fresh angle on colorectal cancer resistance to BRAF inhibition. We found that treatment with BRAF inhibitors (both current and next-generation BRAF inhibitors) upregulated the Wnt/β-catenin pathway in BRAFV600E-mutant colorectal cancer cell lines through activating the cytoplasmic tyrosine kinase focal adhesion kinase (FAK). The results showed that FAK activation upon BRAF inhibitor treatment did not require EGFR or ERK1/2 activation, implying that BRAF inhibitor treatment-induced hyperactivation of Wnt signaling is "pathway reactivation"-independent. BRAF inhibition–induced Wnt pathway activation was further validated in preclinical models of BRAFV600E-mutant colorectal cancer, including cell line xenograft model and a patient-derived xenograft model. Combined inhibition of BRAF/Wnt pathways or BRAF/FAK pathways exerted strong synergistic antitumor effects in cell culture model and mouse xenograft model. Overall, the current study has identified activation of the Wnt/β-catenin pathway as a novel fundamental cause of colon cancer resistance to BRAF inhibition. Our results suggest that although complete vertical pathway blockade is pivotal for effective and durable control of BRAF-mutant colorectal cancer, cotargeting parallel adaptive signaling—the Wnt/β-catenin pathway—is also essential. Mol Cancer Ther; 17(4); 806–13. ©2017 AACR.



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SKLB-23bb, A HDAC6-Selective Inhibitor, Exhibits Superior and Broad-Spectrum Antitumor Activity via Additionally Targeting Microtubules

Our previous study reported that SKLB-23bb, an orally bioavailable HDAC6-selective inhibitor, exhibited superior antitumor efficiency both in vitro and in vivo in comparison with ACY1215, a HDAC6-selective inhibitor recently in phase II clinical trial. This study focused on the mechanism related to the activity of SKLB-23bb. We discovered that despite having HDAC6-selective inhibition equal to ACY1215, SKLB-23bb showed cytotoxic effects against a panel of solid and hematologic tumor cell lines at the low submicromolar level. Interestingly, in contrast to the reported HDAC6-selective inhibitors, SKLB-23bb was more efficient against solid tumor cells. Utilizing HDAC6 stably knockout cell lines constructed by CRISPR–Cas9 gene editing, we illustrated that SKLB-23bb could remain cytotoxic independent of HDAC6 status. Investigation of the mechanism confirmed that SKLB-23bb exerted its cytotoxic activity by additionally targeting microtubules. SKLB-23bb could bind to the colchicine site in β-tubulin and act as a microtubule polymerization inhibitor. Consistent with its microtubule-disrupting ability, SKLB-23bb also blocked tumor cell cycle at G2–M phase and triggered cellular apoptosis. In solid tumor xenografts, oral administration of SKLB-23bb efficiently inhibited tumor growth. These results suggested that SKLB-23bb was an orally bioavailable HDAC6 and microtubule dual targeting agent. The microtubule targeting profile enhanced the antitumor activity and expanded the antitumor spectrum of SKLB-23bb, thus breaking through the limitation of HDAC6 inhibitors. Mol Cancer Ther; 17(4); 763–75. ©2018 AACR.



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Essential Role of Polo-like Kinase 1 (Plk1) Oncogene in Tumor Growth and Metastasis of Tamoxifen-Resistant Breast Cancer

The most common therapy for estrogen receptor–positive breast cancer is antihormone therapy, such as tamoxifen. However, acquisition of resistance to tamoxifen in one third of patients presents a serious clinical problem. Polo-like kinase 1 (Plk1) is a key oncogenic regulator of completion of G2–M phase of the cell cycle. We assessed Plk1 expression in five chemoresistant cancer cell types and found that Plk1 and its downstream phosphatase Cdc25c were selectively overexpressed in tamoxifen-resistant MCF-7 (TAMR-MCF-7) breast cancer cells. Real-time monitoring of cell proliferation also showed that TAMR-MCF-7 cells were more sensitive to inhibition of cell proliferation by the ATP-competitive Plk1 inhibitor BI2536 than were the parent MCF-7 cells. Moreover, BI2536 suppressed expression of epithelial–mesenchymal transition marker proteins and 3D spheroid formation in TAMR-MCF-7 cells. Using TAMR-MCF-7 cell–implanted xenograft and spleen–liver metastasis models, we showed that BI2536 inhibited tumor growth and metastasis in vivo. Our results suggest that Plk1 could be a novel target for the treatment of tamoxifen-resistant breast cancer. Mol Cancer Ther; 17(4); 825–37. ©2018 AACR.



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Relative Target Affinities of T-Cell-Dependent Bispecific Antibodies Determine Biodistribution in a Solid Tumor Mouse Model

Anti-HER2/CD3, a T-cell–dependent bispecific antibody (TDB) construct, induces T-cell–mediated cell death in cancer cells expressing HER2 by cross-linking tumor HER2 with CD3 on cytotoxic T cells, thereby creating a functional cytolytic synapse. TDB design is a very challenging process that requires consideration of multiple parameters. Although therapeutic antibody design strategy is commonly driven by striving for the highest attainable antigen-binding affinity, little is known about how the affinity of each TDB arm can affect the targeting ability of the other arm and the consequent distribution and efficacy. To our knowledge, no distribution studies have been published using preclinical models wherein the T-cell–targeting arm of the TDB is actively bound to T cells. We used a combined approach involving radiochemistry, invasive biodistribution, and noninvasive single-photon emission tomographic (SPECT) imaging to measure TDB distribution and catabolism in transgenic mice with human CD3 expression on T cells. Using CD3 affinity variants, we assessed the impact of CD3 affinity on short-term pharmacokinetics, tissue distribution, and cellular uptake. Our experimental approach determined the relative effects of (i) CD3 targeting to normal tissues, (ii) HER2 targeting to HER2-expressing tumors, and (iii) relative HER2/CD3 affinity, all as critical drivers for TDB distribution. We observed a strong correlation between CD3 affinity and distribution to T-cell–rich tissues, with higher CD3 affinity reducing systemic exposure and shifting TDB distribution away from tumor to T-cell–containing tissues. These observations have important implications for clinical translation of bispecific antibodies for cancer immunotherapy. Mol Cancer Ther; 17(4); 776–85. ©2018 AACR.



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PIM Kinases Are a Potential Prognostic Biomarker and Therapeutic Target in Neuroblastoma

The majority of high-risk neuroblastoma patients are refractory to, or relapse on, current treatment regimens, resulting in 5-year survival rates of less than 50%. This emphasizes the urgent need to identify novel therapeutic targets. Here, we report that high PIM kinase expression is correlated with poor overall survival. Treatment of neuroblastoma cell lines with the pan-PIM inhibitors AZD1208 or PIM-447 suppressed proliferation through inhibition of mTOR signaling. In a panel of neuroblastoma cell lines, we observed a marked binary response to PIM inhibition, suggesting that specific genetic lesions control responses to PIM inhibition. Using a genome-wide CRISPR-Cas9 genetic screen, we identified NF1 loss as the major resistance mechanism to PIM kinase inhibitors. Treatment with AZD1208 impaired the growth of NF1 wild-type xenografts, while NF1 knockout cells were insensitive. Thus, our data indicate that PIM inhibition may be a novel targeted therapy in NF1 wild-type neuroblastoma. Mol Cancer Ther; 17(4); 849–57. ©2018 AACR.



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MI130004, a Novel Antibody-Drug Conjugate Combining Trastuzumab with a Molecule of Marine Origin, Shows Outstanding In Vivo Activity against HER2-Expressing Tumors

In the search for novel payloads to design new antibody–drug conjugates (ADC), marine compounds represent an interesting opportunity given their unique chemical features. PM050489 is a marine compound that binds β-tubulin at a new site and disrupts the microtubule network, hence leading to mitotic aberrations and cell death. PM050489 has been conjugated to trastuzumab via Cys residues through a noncleavable linker, and the resulting ADC, named MI130004, has been studied. Analysis of MI130004 delivered data consistent with the presence of two molecules of PM050489 per antibody molecule, likely bound to both sides of the intermolecular disulfide bond connecting the antibody light and heavy chains. The antitumor activity of MI130004 was analyzed in vitro and in vivo in different cell lines of diverse tumor origin (breast, ovary, and gastric cancer) expressing different levels of HER2. MI130004 showed very high in vitro potency and good selectivity for tumor cells that overexpressed HER2. At the cellular level, MI130004 impaired tubulin polymerization, causing disorganization and disintegration of the microtubule network, which ultimately led to mitotic failure, mirroring the effect of its payload. Treatment with MI130004 in mice carrying histologically diverse tumors expressing HER2 induced a long-lasting antitumor effect with statistically significant inhibition of tumor growth coupled with increases in median survival time compared with vehicle or trastuzumab. These results strongly suggest that MI130004 is endowed with remarkable anticancer activity and confirm the extraordinary potential of marine compounds for the design of new ADCs. Mol Cancer Ther; 17(4); 786–94. ©2018 AACR.



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Impact of Chemical-Induced Mutational Load Increase on Immune Checkpoint Therapy in Poorly Responsive Murine Tumors

A recurring historic finding in cancer drug development is encouraging antitumor effects observed in tumor-bearing mice that fail to translate into the clinic. An intriguing exception to this pattern is immune checkpoint therapy, as the sustained tumor regressions observed in subsets of cancer patients are rare in mice. Reasoning that this may be due in part to relatively low mutational loads of mouse tumors, we mutagenized transplantable mouse tumor cell lines EMT-6/P, B16F1, RENCA, CT26, and MC38 in vitro with methylnitro-nitrosoguanidine (MNNG) or ethylmethane sulfonate (EMS) and tested their responsiveness to PD-L1 blockade. Exome sequencing confirmed an increase in somatic mutations by mutagen treatment, an effect mimicked in EMT-6 variants chronically exposed in vivo to cisplatin or cyclophosphamide. Certain mutagenized variants of B16F1, EMT-6/P, CT26, and MC38 (but not RENCA) were more immunogenic than their parents, yet anti-PD-L1 sensitization developed only in some EMT-6/P and B16F1 variants. Treatment response patterns corresponded with changes in immune cell infiltration and especially increases in CD8+ T cells. Chronically cisplatin-exposed EMT-6 variants were also more responsive to anti-PD-L1 therapy. Although tumor PD-L1 expression was upregulated in in vivo chemotherapy-exposed variants, PD-L1 expression levels were not consistently associated with anti-PD-L1 treatment activity across mutagenized or chemotherapy-exposed variants. In summary, mutagenized and more immunogenic mouse tumors were not universally sensitized to PD-L1 blockade. Chemically mutagenized variants may be useful to evaluate the impact of immunologically "hot" or "cold" tumors with a high mutational load, to which certain chemotherapy agents may contribute, on immunotherapy outcomes. Mol Cancer Ther; 17(4); 869–82. ©2018 AACR.



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JAK2 Inhibitor SAR302503 Abrogates PD-L1 Expression and Targets Therapy-Resistant Non-small Cell Lung Cancers

Lung cancer is the leading cause of cancer-related deaths worldwide. Approximately 85% of all lung cancers are non–small cell histology [non–small cell lung cancer (NSCLC)]. Modern treatment strategies for NSCLC target driver oncogenes and immune checkpoints. However, less than 15% of patients survive beyond 5 years. Here, we investigated the effects of SAR302503 (SAR), a selective JAK2 inhibitor, on NSCLC cell lines and tumors. We show that SAR is cytotoxic to NSCLC cells, which exhibit resistance to genotoxic therapies, such as ionizing radiation, cisplatin, and etoposide. We demonstrate that constitutive IFN-stimulated gene expression, including an IFN-related DNA damage resistance signature, predicts for sensitivity to SAR. Importantly, tumor cell–intrinsic expression of PD-L1 is IFN-inducible and abrogated by SAR. Taken together, these findings suggest potential dual roles for JAK2 inhibitors, both as a novel monotherapy in NSCLCs resistant to genotoxic therapies, and in tandem with immune checkpoint inhibition. Mol Cancer Ther; 17(4); 732–9. ©2018 AACR.



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SKLB-23bb, A HDAC6-Selective Inhibitor, Exhibits Superior and Broad-Spectrum Antitumor Activity via Additionally Targeting Microtubules

Our previous study reported that SKLB-23bb, an orally bioavailable HDAC6-selective inhibitor, exhibited superior antitumor efficiency both in vitro and in vivo in comparison with ACY1215, a HDAC6-selective inhibitor recently in phase II clinical trial. This study focused on the mechanism related to the activity of SKLB-23bb. We discovered that despite having HDAC6-selective inhibition equal to ACY1215, SKLB-23bb showed cytotoxic effects against a panel of solid and hematologic tumor cell lines at the low submicromolar level. Interestingly, in contrast to the reported HDAC6-selective inhibitors, SKLB-23bb was more efficient against solid tumor cells. Utilizing HDAC6 stably knockout cell lines constructed by CRISPR–Cas9 gene editing, we illustrated that SKLB-23bb could remain cytotoxic independent of HDAC6 status. Investigation of the mechanism confirmed that SKLB-23bb exerted its cytotoxic activity by additionally targeting microtubules. SKLB-23bb could bind to the colchicine site in β-tubulin and act as a microtubule polymerization inhibitor. Consistent with its microtubule-disrupting ability, SKLB-23bb also blocked tumor cell cycle at G2–M phase and triggered cellular apoptosis. In solid tumor xenografts, oral administration of SKLB-23bb efficiently inhibited tumor growth. These results suggested that SKLB-23bb was an orally bioavailable HDAC6 and microtubule dual targeting agent. The microtubule targeting profile enhanced the antitumor activity and expanded the antitumor spectrum of SKLB-23bb, thus breaking through the limitation of HDAC6 inhibitors. Mol Cancer Ther; 17(4); 763–75. ©2018 AACR.



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Characterizing the Potency and Impact of Carbon Ion Therapy in a Primary Mouse Model of Soft Tissue Sarcoma

Carbon ion therapy (CIT) offers several potential advantages for treating cancers compared with X-ray and proton radiotherapy, including increased biological efficacy and more conformal dosimetry. However, CIT potency has not been characterized in primary tumor animal models. Here, we calculate the relative biological effectiveness (RBE) of carbon ions compared with X-rays in an autochthonous mouse model of soft tissue sarcoma. We used Cre/loxP technology to generate primary sarcomas in KrasLSL-G12D/+; p53fl/fl mice. Primary tumors were irradiated with a single fraction of carbon ions (10 Gy), X-rays (20 Gy, 25 Gy, or 30 Gy), or observed as controls. The RBE was calculated by determining the dose of X-rays that resulted in similar time to posttreatment tumor volume quintupling and exponential growth rate as 10 Gy carbon ions. The median tumor volume quintupling time and exponential growth rate of sarcomas treated with 10 Gy carbon ions and 30 Gy X-rays were similar: 27.3 and 28.1 days and 0.060 and 0.059 mm3/day, respectively. Tumors treated with lower doses of X-rays had faster regrowth. Thus, the RBE of carbon ions in this primary tumor model is 3. When isoeffective treatments of carbon ions and X-rays were compared, we observed significant differences in tumor growth kinetics, proliferative indices, and immune infiltrates. We found that carbon ions were three times as potent as X-rays in this aggressive tumor model and identified unanticipated differences in radiation response that may have clinical implications. Mol Cancer Ther; 17(4); 858–68. ©2018 AACR.



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