Abstract 2870: Enhancing Topo1i ADC efficacy: development of homogeneous dual-payload ADCs combining Topo1i with microtubule inhibitors or PARP inhibitors

There is a critical need to safely enhance the potency of antibody-drug conjugates (ADCs) for targeting low-expression and heterogeneous tumors, as well as to overcome drug resistance and relapse. Cancer cells often develop resistance to single-agent therapies, making it essential to explore combination approaches. One promising strategy presented in this work is combining two payloads with different mechanisms of action (MOA) into a single ADC, creating dual-payload ADCs. Clinical data have shown that if resistance develops to a topoisomerase I inhibitor (Topo1i) ADC, it will also result in resistance to a Topo1i ADC administered sequentially, regardless of the target antigen. This implies that anti-tumor activity of Topo1 ADCs is limited by formation of resistance towards the payload (cross-payload resistance). In contrast, switching to a payload with different MOAs, such as transitioning from Topo1i to microtubule inhibitor or vice versa, can help to restore the effectiveness of ADCs. The combination study of sacituzumab govitecan and enfortumab vedotin has clinically validated the concept of concomitant administration of a Topo1i payload with a microtubule inhibitor (MTi) payload to increase response rates without significantly increasing toxicity. Dual-payload ADCs that combine Topo1i and MTi agents are specifically designed to maximize their anti-tumor activity by overcoming resistance and broadening the therapeutic potential. Another promising dual-payload strategy involves combining PARP inhibitors (PARPi) with Topo1i, as PARP plays a critical role in repairing DNA damage induced by Topo1i. Such a Topo1i/PARPi dual-payload ADC has the potential to improve anti-tumor activity while avoiding toxicities commonly associated with conventional PARPi chemotherapy, due to the lack of targeted delivery. By leveraging Sutro’s cell-free expression platform and its precise dual conjugation technology, we fine-tuned the drug-to-antibody ratio (DAR) and dual payload ratios to achieve optimal synergy between the two MOAs. The homogeneous, dual-payload ADCs demonstrate desirable physicochemical properties, enabled by the careful selection of conjugation sites and a best-in-class hydrophilic β-glucuronide linker. These design features also resulted in favorable pharmacokinetics and stability of dual-payload ADCs. Using this approach, we identified superior anti-tumor activities against low-antigen and Topo1 ADC-resistant tumor models treated with dual-payload ADCs compared to mono-payload ADCs. Furthermore, the dual payload approach streamlines preclinical, clinical development and the manufacturing process compared to the parallel development of two mono-payload ADCs. Citation Format: Gang Yin, Daniel Calarese, Alice Yam, Werner Rubas, Krishna Bajjuri, Xiaofan Li, Helena Kiefei, Miao Wen, Guifen Xu, Abigail Yu, Hans-Peter Gerber. Enhancing Topo1i ADC efficacy: development of homogeneous dual-payload ADCs combining Topo1i with microtubule inhibitors or PARP inhibitors [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 2870.