Stress-Related Signaling and Lethal Prostate Cancer

Purpose: Recent data suggest that neuroendocrine signaling may influence progression in some cancers. We aimed to determine whether genes within the five major stress-related signaling pathways are differentially expressed in tumor tissue when comparing prostate cancer patients with lethal and nonlethal disease.

Experimental Design: We measured mRNA expression of 51 selected genes involved in predetermined stress-related signaling pathways (adrenergic, glucocorticoid, dopaminergic, serotoninergic, and muscarinic systems) in tumor tissue and normal prostate tissue collected from prostate cancer patients in the Physicians' Health Study (n = 150; n = 82 with normal) and the Health Professionals Follow-Up Study (n = 254; n = 120 with normal). We assessed differences in pathway expression in relation to prostate cancer lethality as the primary outcome and to biomarkers as secondary outcomes.

Results: Differential mRNA expression of genes within the adrenergic (P = 0.001), glucocorticoid (P < 0.0001), serotoninergic (P = 0.0019), and muscarinic (P = 0.0045) pathways in tumor tissue was associated with the risk of lethality. The adrenergic pathway was also statistically significant (P = 0.001) when comparing against differential expression of genes not involved in the pathways. In adjacent normal prostate tissue, none of the pathways was clearly differentially expressed between lethal and nonlethal prostate cancer. The glucocorticoid and adrenergic pathways were associated with cell proliferation, while the glucocorticoid pathway was additionally associated with angiogenesis and perineural invasion.

Conclusions: Our study suggests that stress-related signaling pathways, particularly the adrenergic and glucocorticoid, may be dysregulated in the tumors of men whose prostate cancer proves to be lethal, and motivates further investigation of these pathways in functional studies. Clin Cancer Res; 22(3); 765–72. ©2015 AACR.

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How HIPAA Regulation Changes Affect Research

In 2013, the U.S. Department of Health and Human Services modified the Health Insurance Portability and Accountability Act Privacy Rule to "strengthen privacy and security protections" while "improving workability and effectiveness to increase flexibility for and decrease burden on regulated entities." In this article, we attempt to translate these generalized goals into the real-world implications of these changes. Under the new rules, researchers can obtain participants' permission to use their protected health information for more research activities with a single, upfront authorization (thereby reducing paperwork for participants, researchers, and institutional review boards) while providing potential participants with more information upon which to base their decisions about participation. The combined authorizations can be used in clinical trials and their optional substudies and in stand-alone biospecimen-banking research that includes authorization to permit future research use. We also suggest best practices for taking advantage of the flexibility offered by the new rules while maintaining strong privacy protections for human subjects. Clin Cancer Res; 22(3); 533–9. ©2016 AACR.

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Local HPV Vaccinia Boost Enhances T-cell Responses

Purpose: Two viral oncoproteins, E6 and E7, are expressed in all human papillomavirus (HPV)–infected cells, from initial infection in the genital tract to metastatic cervical cancer. Intramuscular vaccination of women with high-grade cervical intraepithelial neoplasia (CIN2/3) twice with a naked DNA vaccine, pNGVL4a-sig/E7(detox)/HSP70, and a single boost with HPVE6/E7 recombinant vaccinia vaccine (TA-HPV) elicited systemic HPV-specific CD8 T-cell responses that could traffic to the lesion and was associated with regression in some patients (NCT00788164).

Experimental Design: Here, we examine whether alteration of this vaccination regimen by administration of TA-HPV vaccination in the cervicovaginal tract, rather than intramuscular (IM) delivery, can more effectively recruit antigen-specific T cells in an orthotopic syngeneic mouse model of HPV16⁺ cervical cancer (TC-1 luc).

Results: We found that pNGVL4a-sig/E7(detox)/HSP70 vaccination followed by cervicovaginal vaccination with TA-HPV increased accumulation of total and E7-specific CD8⁺ T cells in the cervicovaginal tract and better controlled E7-expressing cervicovaginal TC-1 luc tumor than IM administration of TA-HPV. Furthermore, the E7-specific CD8⁺ T cells in the cervicovaginal tract generated through the cervicovaginal route of vaccination expressed the α4β7 integrin and CCR9, which are necessary for the homing of the E7-specific CD8⁺ T cells to the cervicovaginal tract. Finally, we show that cervicovaginal vaccination with TA-HPV can induce potent local HPV-16 E7 antigen-specific CD8⁺ T-cell immune responses regardless of whether an HPV DNA vaccine priming vaccination was administered IM or within the cervicovaginal tract.

Conclusions: Our results support future clinical translation using cervicovaginal TA-HPV vaccination. Clin Cancer Res; 22(3); 657–69. ©2015 AACR.

See related commentary by Nizard et al., p. 530

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Mitochondrial Control of Tumor Progression

Small-molecule inhibitors of the phosphoinositide 3-kinase (PI3K), Akt, and mTOR pathway currently in the clinic produce a paradoxical reactivation of the pathway they are intended to suppress. Furthermore, fresh experimental evidence with PI3K antagonists in melanoma, glioblastoma, and prostate cancer shows that mitochondrial metabolism drives an elaborate process of tumor adaptation culminating with drug resistance and metastatic competency. This is centered on reprogramming of mitochondrial functions to promote improved cell survival and to fuel the machinery of cell motility and invasion. Key players in these responses are molecular chaperones of the Hsp90 family compartmentalized in mitochondria, which suppress apoptosis via phosphorylation of the pore component, Cyclophilin D, and enable the subcellular repositioning of active mitochondria to membrane protrusions implicated in cell motility. An inhibitor of mitochondrial Hsp90s in preclinical development (gamitrinib) prevents adaptive mitochondrial reprogramming and shows potent antitumor activity in vitro and in vivo. Other therapeutic strategies to target mitochondria for cancer therapy include small-molecule inhibitors of mutant isocitrate dehydrogenase (IDH) IDH1 (AG-120) and IDH2 (AG-221), which opened new therapeutic prospects for patients with high-risk acute myelogenous leukemia (AML). A second approach of mitochondrial therapeutics focuses on agents that elevate toxic ROS levels from a leaky electron transport chain; nevertheless, the clinical experience with these compounds, including a quinone derivative, ARQ 501, and a copper chelator, elesclomol (STA-4783) is limited. In light of this evidence, we discuss how best to target a resurgence of mitochondrial bioenergetics for cancer therapy. Clin Cancer Res; 22(3); 540–5. ©2015 AACR.

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PD-L1 Expression and TILs in HNSCC

Purpose: Programmed death-ligand 1 (PD-L1; also known as CD274 or B7-H1) expression represents a mechanism of immune escape for cancer. Our purpose was to characterize tumor PD-L1 expression and associated T-cell infiltration in primary laryngeal squamous cell carcinomas (SCC).

Experimental Design: A well-annotated cohort of 260 operable primary laryngeal SCCs [formalin-fixed paraffin-embedded (FFPE) specimens] was morphologically characterized for stromal tumor-infiltrating lymphocytes (TIL), on hematoxylin/eosin-stained whole sections and for PD-L1 mRNA expression by qRT-PCR in FFPE specimens. For PD-L1 protein expression, automated quantitative protein analysis (AQUA) was applied on tissue microarrays consisting of two cores from these tumors. In addition, PD-L1 mRNA expression in fresh-frozen tumors and normal adjacent tissue specimens was assessed in a second independent cohort of 89 patients with primary laryngeal SCC.

Results: PD-L1 mRNA levels were upregulated in tumors compared with surrounding normal tissue (P = 0.009). TILs density correlated with tumor PD-L1 AQUA levels (P = 0.021). Both high TILs density and high PD-L1 AQUA levels were significantly associated with superior disease-free survival (DFS; TILs: P = 0.009 and PD-L1: P = 0.044) and overall survival (OS; TILs: P = 0.015 and PD-L1: P = 0.059) of the patients and retained significance in multivariate analysis.

Conclusions: Increased TILs density and PD-L1 levels are associated with better outcome in laryngeal squamous cell cancer. Assessment of TILs and PD-L1 expression could be useful to predict response to immune checkpoint inhibitors. Clin Cancer Res; 22(3); 704–13. ©2015 AACR.

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ALK in Pediatric Cancer

In this era of more rational therapies, substantial efforts are being made to identify optimal targets. The discovery of translocations involving the anaplastic lymphoma kinase (ALK) receptor tyrosine kinase in a subset of non–small cell lung cancers has become a paradigm for precision medicine. Notably, ALK was initially discovered as the fusion gene in anaplastic large cell non-Hodgkin lymphoma, a disease predominantly of childhood. The discovery of activating kinase domain mutations of the full-length ALK receptor as the major cause of hereditary neuroblastoma, and that somatically acquired mutations and amplification events often drive the malignant process in a subset of sporadic tumors, has established ALK as a tractable molecular target across histologically diverse tumors in which ALK is a critical mediator of oncogenesis. We are now uncovering the reexpression of this developmentally regulated protein in a broader subset of pediatric cancers, providing therapeutic targeting opportunities for diseases with shared molecular etiology. This review focuses on the role of ALK in pediatric malignancies, alongside the prospects and challenges associated with the development of effective ALK-inhibition strategies. Clin Cancer Res; 22(3); 546–52. ©2015 AACR.

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p53-KLF4-CEBPA Axis in AML

Purpose: In acute myeloid leukemia (AML), the transcription factors CEBPA and KLF4 as well as the universal tumor suppressor p53 are frequently deregulated. Here, we investigated the extent of dysregulation, the molecular interactions, and the mechanisms involved.

Experimental Design: One hundred ten AML patient samples were analyzed for protein levels of CEBPA, KLF4, p53, and p53 modulators. Regulation of CEBPA gene expression by KLF4 and p53 or by chemical p53 activators was characterized in AML cell lines.

Results: We found that CEBPA gene transcription can be directly activated by p53 and KLF4, suggesting a p53–KLF4–CEBPA axis. In AML patient cells, we observed a prominent loss of p53 function and concomitant reduction of KLF4 and CEBPA protein levels. Assessment of cellular p53 modulator proteins indicated that p53 inactivation in leukemic cells correlated with elevated levels of the nuclear export protein XPO1/CRM1 and increase of the p53 inhibitors MDM2 and CUL9/PARC in the cytoplasm. Finally, restoring p53 function following treatment with cytotoxic chemotherapy compounds and p53 restoring non-genotoxic agents induced CEBPA gene expression, myeloid differentiation, and cell-cycle arrest in AML cells.

Conclusions: The p53–KLF4–CEBPA axis is deregulated in AML but can be functionally restored by conventional chemotherapy and novel p53 activating treatments. Clin Cancer Res; 22(3); 746–56. ©2015 AACR.

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Toxicity Attribution in Phase I Trials

Purpose: Phase I studies rely on investigators to accurately attribute adverse events as related or unrelated to study drug. This information is ultimately used to help establish a safe dose. Attribution in the phase I setting has not been widely studied and assessing the accuracy of attribution is complicated by the lack of a gold standard. We examined dose–toxicity relationships as a function of attribution and toxicity category to evaluate for evidence of toxicity misattribution.

Experimental Design: Individual patient records from 38 phase I studies activated between 2000 and 2010 were used. Dose was defined as a percentage of maximum dose administered on each study. Relationships between dose and patient-level toxicity were explored graphically and with logistic regression. All P values were two-sided.

Results: 11,909 toxicities from 1,156 patients were analyzed. Unrelated toxicity was not associated with dose (P = 0.0920 for grade ≥3, P = 0.4194 for grade ≥1), whereas related toxicity increased with dose (P < 0.0001, both grade ≥3 and ≥1). Similar results were observed across toxicity categories. In the five-tier system, toxicities attributed as "possibly," "probably," or "definitely" related were associated with dose (all P < 0.0001), whereas toxicities attributed as "unlikely" or "unrelated" were not (all P > 0.1).

Conclusions: Reassuringly, we did not observe an association between unrelated toxicity rate and dose, an association that could only have been explained by physician misattribution. Our findings also confirmed our expectation that related toxicity rate increases with dose. Our analysis supports simplifying attribution to a two-tier system by collapsing "possibly," "probably," and "definitely" related. Clin Cancer Res; 22(3); 553–9. ©2015 AACR.

See related commentary by Sharma and Ratain, p. 527

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Selected Articles from This Issue

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Prosigna ROR Score Predicts Chemosensitivity

Purpose: Most hormone receptor (HR)⁺/HER2^– breast cancer patients respond unfavorably to neoadjuvant chemotherapy (NAC); however, genomic tests may identify those patients who are likely to benefit. Using the Prosigna assay, we first evaluated the technical performance of core needle biopsy (CNB) tissues. We then determined whether Prosigna risk of relapse (ROR) score and intrinsic subtype predicted response to NAC in HR⁺/HER2^– patients using CNB samples.

Experimental Design: Using the NanoString's nCounter Dx analysis system and a development tissue sample set, we established tissue requirements and assay output variance. We then evaluated the concordance in subtype and correlation in ROR between CNBs and corresponding surgical resection specimens (SRS) in a second independent sample set. Finally, we analyzed 180 independent CNB samples from HR⁺/HER2^– patients who were treated with NAC and correlated ROR and intrinsic subtype with pathologic response.

Results: Intra- and interbiopsy variabilities were 2.2 and 6.8 ROR units, respectively. Subtype concordance within multiple CNBs was high for the 4- and 3-subtype classifications (k = 0.885 and 0.889, respectively). Correlation in Prosigna ROR score observed between paired CNBs and SRS was high (r ≥ 0.90), and subtype concordance was also high for the 4- and 3-subtype classifications (kappa = 0.81 and 0.91, respectively). Prosigna results obtained from the HR⁺/HER2^– patient samples showed that both ROR (P = 0.047) and intrinsic subtype (OR LumA vs. non-LumA = 0.341, P = 0.037) were significant predictors of response to NAC.

Conclusions: Prosigna ROR and intrinsic subtype are readily obtained from CNB samples in normal practice and reliably predict response to NAC in HR⁺/HER2^– patients. Clin Cancer Res; 22(3); 560–6. ©2015 AACR.

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Therapeutic Wnt Pathway Inhibition in Colorectal Cancer

Purpose: Oncogenic mutations in the KRAS/PI3K/AKT pathway are one of the most frequent alterations in cancer. Although PI3K or AKT inhibitors show promising results in clinical trials, drug resistance frequently emerges. We previously revealed Wnt/β-catenin signaling hyperactivation as responsible for such resistance in colorectal cancer. Here we investigate Wnt-mediated resistance in patients treated with PI3K or AKT inhibitors in clinical trials and evaluate the efficacy of a new Wnt/tankyrase inhibitor, NVP-TNKS656, to overcome such resistance.

Experimental Design: Colorectal cancer patient-derived sphere cultures and mouse tumor xenografts were treated with NVP-TNKS656, in combination with PI3K or AKT inhibitors.We analyzed progression-free survival of patients treated with different PI3K/AKT/mTOR inhibitors in correlation with Wnt/β-catenin pathway activation, oncogenic mutations, clinicopathological traits, and gene expression patterns in 40 colorectal cancer baseline tumors.

Results: Combination with NVP-TNKS656 promoted apoptosis in PI3K or AKT inhibitor-resistant cells with high nuclear β-catenin content. High FOXO3A activity conferred sensitivity to NVP-TNKS656 treatment. Thirteen of 40 patients presented high nuclear β-catenin content and progressed earlier upon PI3K/AKT/mTOR inhibition. Nuclear β-catenin levels predicted drug response, whereas clinicopathologic traits, gene expression profiles, or frequent mutations (KRAS, TP53, or PIK3CA) did not.

Conclusions: High nuclear β-catenin content independently predicts resistance to PI3K and AKT inhibitors. Combined treatment with a Wnt/tankyrase inhibitor reduces nuclear β-catenin, reverts such resistance, and represses tumor growth. FOXO3A content and activity predicts response to Wnt/β-catenin inhibition and together with β-catenin may be predictive biomarkers of drug response providing a rationale to stratify colorectal cancer patients to be treated with PI3K/AKT/mTOR and Wnt/β-catenin inhibitors. Clin Cancer Res; 22(3); 644–56. ©2015 AACR.

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Prognostic Value of BRAF Mutation Detection in Circulation

Purpose: Tumor-derived circulating cell–free DNA (cfDNA) is a potential alternative source from which to derive tumor mutation status. cfDNA data from four clinical studies of the BRAF inhibitor (BRAFi) dabrafenib or the MEK inhibitor (MEKi) trametinib were analyzed to determine the association between BRAF mutation status in cfDNA and tumor tissue, and the association of BRAF cfDNA mutation status with baseline factors and clinical outcome.

Experimental Design: Patients with BRAF V600 mutation–positive melanoma were enrolled in each study after central confirmation of BRAF status in tumor using a PCR-based assay. BRAF mutation status in cfDNA from patient plasma collected at baseline, 732 of 836 (88%) enrolled patients in total, was determined.

Results: BRAF mutations were detectable in cfDNA in 76% and 81% of patients with BRAF V600E/V600K–positive tumors, respectively. Patients negative for BRAF mutations in cfDNA had longer progression-free survival (PFS) and overall survival in each of the four studies, compared with patients with detectable cfDNA BRAF mutations. The presence of BRAF-mutant cfDNA was an independent prognostic factor for PFS after multivariate adjustment for baseline factors in three of four studies. Patients negative for BRAF mutation–positive cfDNA in plasma had higher response rates to dabrafenib and trametinib.

Conclusions: BRAF mutations in cfDNA are detectable in >75% of late-stage melanoma patients with BRAF mutation–positive tumors. The lack of circulating, BRAF mutation–positive cfDNA is clinically significant for metastatic melanoma patients, and may be a prognostic marker for better disease outcome. Clin Cancer Res; 22(3); 567–74. ©2015 AACR.

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Prostate Cancer Stem Cell Therapy

Purpose: Clinical evidence suggests increased cancer stem cells (CSCs) in a tumor mass may contribute to the failure of conventional therapies because CSCs seem to be more resistant than differentiated tumor cells. Thus, unveiling the mechanism regulating CSCs and candidate target molecules will provide new strategy to cure the patients.

Experimental design: The stem-like cell properties were determined by a prostasphere assay and dye exclusion assay. To find critical stem cell marker and reveal regulation mechanism, basic biochemical and molecular biologic methods, such as quantitative real-time PCR, Western blot, reporter gene assay, and chromatin immunoprecipitation assay, were used. In addition, to determine the effect of combination therapy targeting both CSCs and its progeny, in vitro MTT assay and in vivo xenograft model was used.

Results: We demonstrate immortalized normal human prostate epithelial cells, appeared nontumorigenic in vivo, become tumorigenic, and acquire stem cell phenotype after knocking down a tumor suppressor gene. Also, those stem-like cells increase chemoresistance to conventional anticancer reagent. Mechanistically, we unveil that Wnt signaling is a key pathway regulating well-known stem cell marker CD44 by directly interacting to the promoter. Thus, by targeting CSCs using Wnt inhibitors synergistically enhances the efficacy of conventional drugs. Furthermore, the in vivo mouse model bearing xenografts showed a robust inhibition of tumor growth after combination therapy.

Conclusions: Overall, this study provides strong evidence of CSC in castration-resistant prostate cancer. This new combination therapy strategy targeting CSC could significantly enhance therapeutic efficacy of current chemotherapy regimen only targeting non-CSC cells. Clin Cancer Res; 22(3); 670–9. ©2015 AACR.

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Response Assessment of Recurrent Glioblastoma Patients

Purpose: The RANO criteria have not been assessed using outcome data from prospective trials. We examined the radiologic data of patients with recurrent glioblastoma from the randomized phase II trial (AVF3708g) to determine the effect of including T2/FLAIR evaluation as per RANO criteria on measurements of objective response rates (ORRs) and progression-free survival (PFS) compared with assessment based on contrast enhancement (Macdonald criteria).

Experimental Design: The ORRs and median PFS were determined using the RANO criteria and compared with those obtained using the Macdonald criteria. Landmark analyses were performed at 2, 4, and 6 months, and Cox proportional hazard models were used to determine the associations between OR and progression with subsequent survival.

Results: The ORRs were 0.331 [95% confidence interval (CI), 0.260–0.409] and 0.393 (95% CI, 0.317–0.472) by RANO and Macdonald criteria, respectively (P < 0.0001). The median PFS was 4.6 months (95% CI, 4.1–5.5) using RANO criteria, compared with 6.4 months (95% CI, 5.5–7.1) as determined by Macdonald criteria (P = 0.01). At 2-, 4-, and 6-month landmarks, both OR status and PFS determined by either RANO or Macdonald criteria were predictive of overall survival [OS; hazard ratios for 4-month landmark (OR HR = 1.93, P = 0.0012; PFS HR, 4.23, P < 0.0001)].

Conclusions: The inclusion of T2/FLAIR assessment resulted in statistically significant differences in median PFS and ORRs compared with assessment of solely enhancing tumor (Macdonald criteria), although OR and PFS determined by both RANO and Macdonald criteria correlated with OS. Clin Cancer Res; 22(3); 575–81. ©2015 AACR.

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STAT3{beta} Dictates the Opposing Function of STAT3 in ESCC

Purpose: STAT3 is known to have both oncogenic and tumor suppressive effects, but the regulation of these opposing effects is elusive. We hypothesized that STAT3β, one of the two STAT3 isoforms, is the key determinant in this context.

Experimental Design: The prognostic significance of STAT3β and phospho-STAT3α^Y705 (pSTAT3α^Y705) was evaluated in 286 cases of patients with esophageal squamous cell carcinoma (ESCC). STAT3β-induced changes in the chemosensitivity to cisplatin and 5-fluorouracil were assessed both in vitro and in vivo. STAT3β-induced changes in the frequency of cancer stem cells were evaluated using Hoechst and CD44 staining. How STAT3β regulates STAT3α was determined using immunoprecipitation, confocal microscopy, DNA-binding, and chromatin immunoprecipitation-PCR.

Results: STAT3β expression is an independent protective prognostic marker in patients with ESCC, which strongly correlated with longer overall survival (P = 0.0009) and recurrence-free survival (P = 0.0001). STAT3β significantly decreased the cancer stem cell population, and sensitized ESCC cells to cisplatin and 5-fluorouracil in tumor xenografts. Mechanistically, STAT3β markedly attenuated the transcription activity of STAT3α via inducing STAT3α:STAT3β heterodimers. However, the heterodimer formation decreased the binding between STAT3α and PTPN9 (better known as PTP-MEG2), a protein tyrosine phosphatase, thereby promoting the phosphorylation of STAT3α^Y705 and enhancing its nuclear translocation and DNA binding. Correlating with this, high STAT3β expression converts the prognostic value of pSTAT3α^Y705 from unfavorable to favorable in patients with ESCC.

Conclusions: STAT3β suppresses chemoresistance and cancer stemness by blocking the transcriptional activity of STAT3α. The paradoxical increase in pSTAT3α^Y705 induced by STAT3β carries important implications as to how the biologic and prognostic significance of STAT3 in cancers should be interpreted. Clin Cancer Res; 22(3); 691–703. ©2015 AACR.

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MLK4 Mutations in Colon Cancer Enhance Tumor Growth

MLK4 is a member of the mixed-lineage family of kinases that regulate the JNK, p38, and ERK kinase signaling pathways. MLK4 mutations have been identified in various human cancers, including frequently in colorectal cancer, where their function and pathobiological importance have been uncertain. In this study, we assessed the functional consequences of MLK4 mutations in colon tumorigenesis. Biochemical data indicated that a majority of MLK4 mutations are loss-of-function (LOF) mutations that can exert dominant-negative effects. In seeking to understand the abrogated activity of these mutants, we elucidated a new MLK4 catalytic domain structure. To determine whether MLK4 is required to maintain tumorigenic phenotypes, we reconstituted its signaling axis in colon cancer cells harboring MLK4-inactivating mutations. We found that restoring MLK4 activity reduced cell viability, proliferation, and colony formation in vitro and delayed tumor growth in vivo. Mechanistic investigations established that restoring the function of MLK4 selectively induced the JNK pathway and its downstream targets, cJUN, ATF3, and the cyclin-dependent kinase inhibitors CDKN1A and CDKN2B. Our work indicates that MLK4 is a novel tumor-suppressing kinase harboring frequent LOF mutations that lead to diminished signaling in the JNK pathway and enhanced proliferation in colon cancer. Cancer Res; 76(3); 724–35. ©2015 AACR.

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Fat, Calories, and Cancer

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Oncogenic KRAS Modulates EZH2 Expression in NSCLC

EZH2 overexpression promotes cancer by increasing histone methylation to silence tumor suppressor genes, but how EZH2 levels become elevated in cancer is not understood. In this study, we investigated the mechanisms by which EZH2 expression is regulated in non–small cell lung carcinoma cells by oncogenic KRAS. In cells harboring KRASG12C and KRASG12D mutations, EZH2 expression was modulated by MEK–ERK and PI3K/AKT signaling, respectively. Accordingly, MEK–ERK depletion decreased EZH2 expression in cells harboring the KRASG12C mutation, whereas PI3K/AKT depletion decreased EZH2 expression, EZH2 phosphorylation, and STAT3 activity in KRASG12D-mutant cell lines. Combined inhibition of EZH2 and MEK–ERK or PI3K/AKT increased the sensitivity of cells with specific KRAS mutations to MEK–ERK and PI3K/AKT–targeted therapies. Our work defines EZH2 as a downstream effector of KRAS signaling and offers a rationale for combining EZH2 inhibitory strategies with MEK–ERK- or PI3K/AKT–targeted therapies to treat lung cancer patients, as stratified into distinct treatment groups based on specific KRAS mutations. Cancer Res; 76(3); 675–85. ©2015 AACR.

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Observations on Radiation-Induced Lymphoid Tumors of Mice

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Highlights from Recent Cancer Literature

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Macrophage-Directed Cancer Immunotherapy

Successful immunotherapy of cancer is becoming a reality aided by the realization that macrophages play an important role in the growth or regression of tumors. Specifically, M2/repair-type macrophages predominate in human cancers and produce growth-promoting molecules that actively stimulate tumor growth in much the same way they help wounds heal. However, modulating M2/repair-type macrophages to M1/kill-type can slow or stop cancer growth. The effects involve direct activity of M1 kill-type as well as the ability of M1-type macrophages to stimulate Th1-type cytotoxic T cells and other effector cells. Macrophage responses can also predict cancer susceptibility; individuals with a high M1/kill to M2/repair ratio are less prone. That macrophages/innate immunity can be modulated to play a central role in directly or indirectly combating cancer is a breakthrough that seems likely to finally make successful immunotherapy of cancer a reality. Cancer Res; 76(3); 513–6. ©2016 AACR.

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Hydroxamic Acid and Benzoic Acid-Based STAT3 Inhibitors

STAT3 offers an attractive target for cancer therapy, but small-molecule inhibitors with appealing pharmacologic properties have been elusive. Here, we report hydroxamic acid–based and benzoic acid–based inhibitors (SH5-07 and SH4-54, respectively) with robust bioactivity. Both inhibitors blocked STAT3 DNA-binding activity in vitro and in human glioma, breast, and prostate cancer cells and in v-Src–transformed murine fibroblasts. STAT3-dependent gene transcription was blocked along with Bcl-2, Bcl-xL, Mcl-1, cyclin D1, c-Myc, and survivin expression. Nuclear magnetic resonance analysis of STAT3-inhibitor complexes defined interactions with the SH2 and DNA-binding domains of STAT3. Ectopic expression of the SH2 domain in cells was sufficient to counter the STAT3-inhibitory effects of SH4-54. Neither compound appreciably affected STAT1 or STAT5 DNA-binding activities, STAT3-independent gene transcription, or activation of a panel of oncogenic kinases in malignant cells. Each compound decreased the proliferation and viability of glioma, breast, and prostate cancer cells and v-Src–transformed murine fibroblasts harboring constitutively active STAT3. Further, in mouse xenograft models of glioma and breast cancer, administration of SH5-07 or SH4-54 effectively inhibited tumor growth. Our results offer preclinical proof of concept for SH5-07 and SH4-54 as candidates for further development as cancer therapeutics. Cancer Res; 76(3); 652–63. ©2015 AACR.

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Antiangiogenesis Restores Bone Marrow Vascular Niche

Antiangiogenesis–based cancer therapies, specifically those targeting the VEGF-A/VEGFR2 pathway, have been approved for subsets of solid tumors. However, these therapies result in an increase in hematologic adverse events. We surmised that both the bone marrow vasculature and VEGF receptor–positive hematopoietic cells could be impacted by VEGF pathway–targeted therapies. We used a mouse model of spontaneous breast cancer to decipher the mechanism by which VEGF pathway inhibition alters hematopoiesis. Tumor-bearing animals, while exhibiting increased angiogenesis at the primary tumor site, showed signs of shrinkage in the sinusoidal bone marrow vasculature accompanied by an increase in the hematopoietic stem cell–containing Lin-cKit+Sca1+ (LKS) progenitor population. Therapeutic intervention by targeting VEGF-A, VEGFR2, and VEGFR3 inhibited tumor growth, consistent with observed alterations in the primary tumor vascular bed. These treatments also displayed systemic effects, including reversal of the tumor-induced shrinkage of sinusoidal vessels and altered population balance of hematopoietic stem cells in the bone marrow, manifested by the restoration of sinusoidal vessel morphology and hematopoietic homeostasis. These data indicate that tumor cells exert an aberrant systemic effect on the bone marrow microenvironment and VEGF-A/VEGFR targeting restores bone marrow function. Cancer Res; 76(3); 517–24. ©2015 AACR.

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DR5 Targeting Triggers Gastrointestinal Toxicity

The combination of TRAIL death receptor agonists and radiochemotherapy to treat advanced cancers continues to be investigated in clinical trials. We previously showed that normal cells with a functional DNA damage response (DDR) upregulate the expression of death-inducing receptor DR5/TRAILR2/TNFRSF10B in a p53-dependent manner that sensitizes them to treatment with DR5 agonists. However, it is unclear if targeting DR5 selectively sensitizes cancer cells to agonist treatment following exposure to DNA-damaging chemotherapy, and to what extent normal tissues are targeted. Here, we show that the combined administration of the DR5 agonistic monoclonal antibody (mAb) and chemotherapy to wild-type mice triggered synergistic gastrointestinal toxicities (GIT) that were associated with the death of Lgr5+ crypt base columnar stem cells in a p53- and DR5-dependent manner. Furthermore, we confirmed that normal human epithelial cells treated with the human DR5-agonistic mAb and chemotherapeutic agents were also greatly sensitized to cell death. Interestingly, our data also indicated that genetic or pharmacologic targeting of Chk2 may counteract GIT without negatively affecting the antitumor responses of combined DR5 agonist/chemotherapy treatment, further linking the DDR to TRAIL death receptor signaling in normal cells. In conclusion, the combination of DR5-targeting agonistic mAbs with DNA damaging chemotherapy may pose a risk of developing toxicity-induced conditions, and the effects of mAb-based strategies on the dose-limiting toxicity of chemotherapy must be considered when establishing new combination therapies. Cancer Res; 76(3); 700–12. ©2015 AACR.

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