Mechanisms of Acquired Resistance to Trastuzumab Emtansine in Breast Cancer Cells

Abstract

The receptor tyrosine kinase HER2 is overexpressed in approximately 20% of breast cancer, and its amplification is associated with reduced survival. Trastuzumab emtansine (Kadcyla, T-DM1), an antibody-drug conjugate that is comprised of trastuzumab covalently linked to the antimitotic agent DM1 through a stable linker, was designed to selectively deliver DM1 to HER2-overexpressing tumor cells. T-DM1 is approved for the treatment of patients with HER2-positive metastatic breast cancer following progression on trastuzumab and a taxane. Despite the improvement in clinical outcome, many patients who initially respond to T-DM1 treatment eventually develop progressive disease. The mechanisms that contribute to T-DM1 resistance are not fully understood. To this end, we developed T-DM1-resistant models to examine the mechanisms of acquired T-DM1 resistance. We demonstrate that decreased HER2 and upregulation of MDR1 contribute to T-DM1 resistance in KPL-4 T-DM1-resistant cells. In contrast, both loss of SLC46A3 and PTEN deficiency play a role in conferring resistance in BT-474M1 T-DM1-resistant cells. Our data suggest that these two cell lines acquire resistance through distinct mechanisms. Furthermore, we show that the KPL-4 T-DM1 resistance can be overcome by treatment with an inhibitor of MDR1, whereas a PI3K inhibitor can rescue PTEN loss-induced resistance in T-DM1-resistant BT-474M1 cells. Our results provide a rationale for developing therapeutic strategies to enhance T-DM1 clinical efficacy by combining T-DM1 and other inhibitors that target signaling transduction or resistance pathways..

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

“…Moreover, a major mechanism of acquired resistance to ADCs shown in in vitro models is altered ADC trafficking and lysosomal function 47,53,54 , a signature that is also identified in our 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.…”

“…Many of the hits identified in our study are required for ADC toxicity; therefore loss-of-function of these genes may be potential resistance mechanisms for ADCs used in the clinic. For example, decreased expression of SLC46A3, a lysosomal transporter we identified as critical for cytotoxicity of the anti-CD22 noncleavable ADC, has been shown to be a mechanism of innate and acquired resistance to other noncleavable ADCs targeting a wide range of antigenic targets in patient-derived xenografts and primary multiple myeloma bone marrow samples 22,47,52 .…”

The Second Generation Antibody-Drug Conjugate SYD985 Overcomes Resistances to T-DM1

“…Using HER2-positive breast cancer cell lines chronically treated with T-DM1, multiple mechanisms of resistance have been identified (for reviews, see [5,13]). Notably, despite the variety of mechanisms described, downmodulation of HER2 has been repeatedly identified by different groups [15,25,27].…”

“…Using established breast cancer cell lines, several groups have identified mechanisms of resistance to T-DM1. These include downregulation of HER2 [7][8][9], activation of alternative RTKs or intracellular signaling pathways downstream of HER2 [7], upregulation of Bcl-2/X L [8], defective intracellular routing [9] defective lysosomal function [10][11][12] and upregulation of multidrug resistance transporters [13][14][15].…”