Therapeutic Strategies to Overcome Payload Resistance of Trastuzumab Deruxtecan in <scp>HER2</scp> ‐Positive Cancers

Antibody-drug conjugates (ADCs) are emerging as a promising class of targeted cancer therapy. Trastuzumab deruxtecan (T-DXd), a human epidermal growth factor receptor 2 (HER2)-directed ADC, has demonstrated clinical efficacy in HER2-positive gastric and breast cancers, as well as in HER2-mutant non-small cell lung cancer. However, the development of acquired resistance limits their long-term efficacy. To elucidate the resistance mechanism, we established T-DXd-resistant cell lines derived from HER2-amplified gastric xenografts (N87 acquired resistance [AR]) and leptomeningeal carcinomatosis (Calu-3 AR) lung cancer cells. N87 AR cells exhibited cross-resistance to T-DXd, payload DXd, and topoisomerase I inhibitor SN-38 despite preserved HER2 expression and intact drug internalization. As payload resistance-related molecules, ATP-binding cassette (ABC) transporter ABCG2 and ABCB1 were markedly upregulated in N87 AR and Calu-3 cells, respectively. Inhibition of ABCG2 and ABCB1 in N87 AR and Calu-3 cells, respectively, through siRNA-mediated knockdown restored T-DXd sensitivity in both models. As a strategy to overcome resistance, pharmacological inhibitors of ABCG2 and ABCB1 restored the T-DXd sensitivity of N87 AR and Calu-3 cells, respectively. Moreover, BB-1701, a novel HER2-ADC containing eribulin as a payload, to which N87 AR cells are sensitive, exhibited antitumor effects in N87 AR cells in vitro and in vivo. These findings indicate that ABC transporter-mediated drug efflux is an important mechanism underlying T-DXd resistance in HER2-positive gastric and lung cancer models. Furthermore, our study suggests that both targeting drug efflux pathways and utilizing alternative payloads may be effective strategies for overcoming T-DXd resistance in HER2-positive gastric and lung cancers.