Abstract 1691: Site-specific dual-payload antibody conjugation enhances antitumor efficacy

Abstract We have developed a site-specific conjugation platform enabling controlled dual-payload delivery on antibodies. The antibody is enzymatically trimmed and modified to allow sequential bioorthogonal attachment of two payloads. This approach permits precise control of payload type and DAR number, enabling combinations that improve in vivo tumor suppression at lower payload doses. Here we present dual-payload HER2 ADCs as a proof-of-concept. A trastuzumab-based ADC carrying DM1 (DAR 2) and seco-DUBA (DAR 2) demonstrated potent inhibition of JIMT-1 xenograft tumors, a model known to be resistant to T-DM1. Additionally, a dual-payload MMAE/exatecan ADC (DAR 2+2) achieved antitumor activity comparable to T-DXd (DAR 8), despite using substantially lower total payload. These results show the versatility and therapeutic potential of our dual-payload site-specific conjugation strategy. The platform provides a method to overcoming drug resistance and expanding therapeutic windows for next-generation ADCs. Citation Format: Wei-Ting Sun, Shih-Hsien Chuang, Shih-Chong Tsai, Cheng-Chou Yu. Site-specific dual-payload antibody conjugation enhances antitumor efficacy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 1 (Regular Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(7 Suppl):Abstract nr 1691.