Abstract 1804: An innovative dual-payload ADC combining topoisomerase 1 inhibitor and a tubulin inhibitor efficiently overcomes drug resistance

Antibody Drug Conjugates (ADC) have achieved great success as anti-cancer therapies, with 15 ADC drugs approved in global market. Despite the initial response to ADC treatment, drug resistance and tumor relapse inevitably happen due to the high heterogeneity in advanced tumors. The mechanism of resistance can be due to downregulation of drug targets, upregulation of multi-drug resistance mechanisms, such as ABCB1/ABCG2 and others. Overcoming these resistance mechanisms are a big challenge to next-generation ADC development for cancer therapy. To address these challenges, MediLink has developed an innovative dual-payload ADC with two payloads of different MOAs: a topoisomerase 1 inhibitor and a tubulin inhibitor. Two conjugation methods were developed: (1) Tubulin inhibitor payload-linkers were conjugated at specific lysine sites of antibody while Topo1i payload-linker were conjugated with free cysteine thiols via TMALIN® Technology, resulting in a dual-payload ADC with DAR of 2 and 8 for each payload-linker, respectively. (2) Reduced antibody conjugates with pre-mixed or step wisely added Topo1i payload linker and Tubulin payload linker in different proportions to obtain any desired ratio of the two different payloads. ADC characterization showed good stability, homogeneity and precise DAR values for the conjugation of both payload-linkers to Trastuzumab. In vitro, the dual-payload Her2 ADC demonstrated strong cytotoxicity against tumor cells with different levels of Her2 expression, especially in cells overexpressing ABCB1 and ABCG2, and Enhertu-resistant tumor cells. In vivo, the dual-payload ADC exhibited superior efficacy in Enhertu-resistance CDX model and Her2 low CDX models. In summary, we developed dual-payload ADCs with intention for resolving topo1 inhibitor induced tumor resistance issues. The dual-payload Her2 ADC demonstrated potent in vitro and in vivo anti-tumor activities, showing the potential to overcome the multidrug resistant mechanism and Enhertu resistance. Citation Format: Ailin Shan, Chun Deng, Peng Zou, Shuai Song, Jiaqiang Cai, Tongtong Xue. An innovative dual-payload ADC combining topoisomerase 1 inhibitor and a tubulin inhibitor efficiently overcomes drug resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1804.