Abstract 1830: Antibody-drug conjugates with modified linker-payloads overcome resistance to a trastuzumab-maytansinoid conjugate in multiple cultured tumor cell models

Antibody-drug conjugates (ADCs) enable targeted delivery of therapeutics to cancer cells and offer potential for more selective therapy. Several ADCs are demonstrating promising clinical efficacy, however due to the complexity of human cancer, tumors become refractory to most drug treatments. We hypothesized that cultured tumor cells chronically treated with an ADC would acquire mechanisms of resistance unique to ADC-based therapy. As a model system, we used a trastuzumab-maytansinoid ADC (TM) similar to T-DM1 to treat cultured tumor cell lines at high doses followed by recovery. We previously reported the generation of two breast cancer cell lines with acquired resistance to TM. These parental lines, MDA-MB-361 and JIMT1, express moderate levels of Her2. We now report the induction of resistance to TM-ADC in a high Her2 expressing gastric carcinoma cell line, N87. Chronic exposure of N87 cells to TM-ADC on a 3 day on/ 4 day off cycle results in ∼240 fold resistance. Two parallel flasks of N87 cells were treated with TM, and identical levels of resistance, cross-resistance, and sensitivity to other agents are observed, suggesting common selective pressure upon drug exposure in a single tumor cell type. Interestingly, both the N87 and 361 cell models developed similar patterns of cross-resistance (up to >1000X) to ADCs of trastuzumab containing non-cleavable linkers and microtubule inhibitors. In contrast, ADCs with proteolytic cleavable linkers which also release tubulin inhibitors completely overcome resistance. Moreover, the TM-resistant cell lines retain sensitivity to ADCs delivering payloads with non-tubulin mechanisms of action, including DNA inhibitor calicheamicin. Minimal or no resistance (1 - 6X) was observed to free drugs, including maytansine or other standard-of-care tubulin or DNA targeted chemotherapeutics. In 361-TM cells, ABCC1 (MRP1) is induced and may partially mediate resistance to TM-ADC and other non-cleavable ADCs. In contrast, N87-TM cells do not express ABCC1 (MRP1) or ABCB1 (MDR1), as demonstrated by immunoblot and flow cytometry, nor are these cells cross-resistant to free drugs which are substrates of such transporter proteins. Proteomic profiling of N87-TM cells is underway to fully characterize the protein changes in TM-ADC-resistant cells. These data suggest that chronic cycling treatment of TM-ADC at high doses can induce resistance in different tumor cell models. In 2 of 3 cell lines tested, high level resistance was observed, including nearly identical patterns of cross-resistance to other non-cleavable linked trastuzumab ADCs, yet sensitivity to cleavable linked ADCs. The same selection pressure may be inducing different mechanisms of drug resistance, dependent upon the cell background. These data suggest that ADC resistant cancers may be treated with conjugates targeting the same antigen but with modified linker payloads. Citation Format: Xingzhi Tan, Bingwen Lu, Guixian Jin, Fang Wang, Jeremy Myers, Sylvia Musto, My-Hanh Lam, William Hu, Kiran Khandke, Kim Arndt, Hans-Peter Gerber, Frank Loganzo. Antibody-drug conjugates with modified linker-payloads overcome resistance to a trastuzumab-maytansinoid conjugate in multiple cultured tumor cell models. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1830. doi:10.1158/1538-7445.AM2014-1830