Caveolae-mediated endocytosis as a novel mechanism of resistance to trastuzumab emtansine (T-DM1)

Trastuzumab emtansine (T-DM1) is an antibody-drug conjugate (ADC) that has demonstrated clinical benefit for patients with HER2+ metastatic breast cancer, however its clinical activity is limited by inherent or acquired drug resistance. The molecular mechanisms that drive clinical resistance to T-DM1, especially in HER2+ tumors, are not well understood. We used HER2+ cell lines to develop models of T-DM1 resistance utilizing a cyclical dosing schema in which cells received T-DM1 in an "on-off" routine until a T-DM1 resistant population was generated. T-DM1 resistant N87 cells (N87-TM) were cross-resistant to a panel of trastuzumab-ADCs (T-ADCs) with non-cleavable-linked auristatins. N87-TM cells do not have a decrease in HER2 protein levels or an increase in drug transporter protein (e.g. MDR1) expression compared to parental N87 cells. Intriguingly, T-ADCs utilizing auristatin payloads attached via an enzymatically cleavable linker overcome T-DM1 resistance in N87-TM cells. Importantly, N87-TM cells implanted into athymic mice formed T-DM1 refractory tumors which remain sensitive to T-ADCs with cleavable-linked auristatin payloads. Comparative proteomic profiling suggested enrichment in proteins that mediate caveolae formation and endocytosis in the N87-TM cells. Indeed, N87-TM cells internalize T-ADCs into intracellular caveolin-1 (CAV1) positive puncta and alter their trafficking to the lysosome compared to N87 cells. T-DM1 colocalization into intracellular CAV1 positive puncta correlated with reduced response to T-DM1 in a panel of HER2+ cell lines. Together, these data suggest caveolae-mediated endocytosis of T-DM1 may serve as a novel predictive biomarker for patient response to T-DM1.

http://ift.tt/2yDWTpZ