Aberrant intracellular metabolism of T‐DM1 confers T‐DM1 resistance in human epidermal growth factor receptor 2‐positive gastric cancer cells

Abstract

Trastuzumab emtansine (T‐DM1), an antibody–drug conjugate (ADC) consisting of human epidermal growth factor receptor 2 (HER2)‐targeted mAb trastuzumab linked to antimicrotubule agent mertansine (DM1), has been approved for the treatment of HER2‐positive metastatic breast cancer. Acquired resistance has been a major obstacle to T‐DM1 treatment, and mechanisms remain incompletely understood. In the present study, we established a T‐DM1‐resistant N87‐KR cell line from HER2‐positive N87 gastric cancer cells to investigate mechanisms of acquired resistance and develop strategies for overcoming it. Although the kinetics of binding, internalization, and externalization of T‐DM1 were the same in N87‐KR cells and N87 cells, N87‐KR was strongly resistant to T‐DM1, but remained sensitive to both trastuzumab and DM1. T‐DM1 failed to inhibit microtubule polymerization in N87‐KR cells. Consistently, lysine‐MCC‐DM1, the active T‐DM1 metabolite that inhibits microtubule polymerization, accumulated much less in N87‐KR cells than in N87 cells. Furthermore, lysosome acidification, achieved by vacuolar H+‐ATPase (V‐ATPase), was much diminished in N87‐KR cells. Notably, treatment of sensitive N87 cells with the V‐ATPase selective inhibitor bafilomycin A1 induced T‐DM1 resistance, suggesting that aberrant V‐ATPase activity decreases T‐DM1 metabolism, leading to T‐DM1 resistance in N87‐KR cells. Interestingly, HER2‐targeted ADCs containing a protease‐cleavable linker, such as hertuzumab‐vc‐monomethyl auristatin E, were capable of efficiently overcoming this resistance. Our results show for the first time that a decrease in T‐DM1 metabolites induced by aberrant V‐ATPase activity contributes to T‐DM1 resistance, which could be overcome by HER2‐targeted ADCs containing different linkers, including a protease‐cleavable linker. Accordingly, we propose that V‐ATPase activity in lysosomes is a novel biomarker for predicting T‐DM1 resistance.

STAT3 activation confers trastuzumab‐emtansine (T‐DM1) resistance in HER2‐positive breast cancer

“…11 Unlike mechanisms underlying resistance to trastuzumab, pertuzumab or lapatinib, which are generally well understood, however, the mechanisms responsible for T-DM1 resistance are poorly characterized. Among the known mechanisms of T-DM1 resistance are hindrance of trastuzumab binding to HER2 caused by mucin 4 (MUC4) expression, 12 defects in intracellular metabolism of T-DM1 owing to impaired lysosomal proteolytic activity, 13,14 and efflux of DM1 as a result of the expression of multidrug resistance (MDR) transporters. 15,16 Clearly, additional effort is required to understand and overcome T-DM1 resistance.…”

Systematic identification of regulators of antibody-drug conjugate toxicity using CRISPR-Cas9 screens

“…Indeed, payload release from VC-linked ADCs occurs within tens of minutes after ADC internalization, suggesting that resistance to noncleavable ADCs due to impaired lysosomal delivery may be circumvented by ADCs bearing cleavable VC linkers. These results may help explain why ADCs with cleavable linkers are efficacious in a broader range of target cancers 12,16 and remain toxic to cell lines resistant to noncleavable linker ADCs [46][47][48][49] . Importantly, these genes regulating late endosomal trafficking and processing of ADCs may serve as potential predictive biomarkers for resistance against noncleavable linker ADCs.…”

Current therapeutic landscape for advanced gastroesophageal cancers

“…In the future, high intratumor heregulin level could be used for predicting anti-HER2 therapy resistance and for improving patient selection in clinical studies. In the same way, aberrant V-ATPase activity in lysosomes could also be a potential biomarker for predicting T-DM1 resistance (127). Concerning immunotherapy, tumor PD-L1 expression reveals its limitations for predicting immune checkpoint inhibitor efficacy.…”