Abstract 7334: Targeting Nectin-4 with a first-in-class triple MMAE/dual TOP1i payload ADC showing synergistic and durable activity across all target expression levels and favorable tolerability

Abstract The Araris’ site-specific and one-step linker conjugation technology aims at generating stable, safe and highly potent ADCs without the need for antibody engineering prior to payload conjugation. We here present a novel Nectin-4 targeting triple-warhead ADC using a combination of MMAE and two different topoisomerase-1 inhibitors (TOP1i, DAR2+2+2) designed to treat a broad range of Nectin-4 expressing solid tumors. With this novel ADC we aim to 1) effectively kill heterogenous and resistant tumors by delivering multiple cytotoxic payloads to the same tumor cell, 2) control and limit bystander activity to avoid excessive toxicities and 3) maximize payload delivery through stable linker-payload coupling resulting antibody-like ADC pharmacokinetic exposure profiles. The triple-warhead ADC was shown to be highly homogenous and pure with a DAR of 6, as desired. The ADC showed high stability under stressed conditions with no signs of aggregation, which we attribute to the hydrophilic nature of the peptide-linker-payload design. On target-positive cancer cell lines, the ADC showed high and target-specific cytotoxic activity. It further showed excellent stability in mouse, cyno and human sera with no linker-payload deconjugation or linker cleavage, and the DAR remaining unchanged. Most importantly, the ADC was extremely stable in circulation showing an exposure profile like the unmodified parent antibody in rodents. Notably, the tolerability in rats showed an HNSTD of more than 20 mg/kg in a dose-range-finder study (vs. Enfortumab vedotin (EV): 5mg/kg). No significant skin or hematological toxicities were observed, implying that the triple warhead did not result in toxicities exceeding the mono-payload toxicity profiles in rats. Strikingly, in a receptor high-expressing breast cancer SUM-190PT xenograft model, the triple warhead ADC administered as a single dose at 0.5 mg/kg on day 0 led to long-lasting and complete tumor regression (more than 100d), indicating synergistic activity of the different payloads. Interestingly, the combination using the respective MMAE (DAR2) and TOPi (DAR2+2) ADCs, each dosed at 0.5 mg/kg, showed no response whatsoever and neither did Enfortumab vedotin (EV) at this dose, the current Nectin-4 targeting standard of care in mUC. Further, in a low Nectin-4-expressing TNBC PDX model, the high anti-tumor activity was confirmed leading to high and complete anti-tumor responses at 2.5 mg/kg compared to EV and Sacituzumab govitecan, the FDA-approved ADC for TNBC. In conclusion, the first-in-class Nectin-4 targeting triple-payload ADC leads to very high anti-tumor efficacy in CDX and PDX models and is well tolerable in rats. We show for the first time, that combination of multiple payloads in one ADC can lead to synergistic effects in mouse models while still being well tolerable. Citation Format: Isabella Attinger-Toller, Philipp Probst, Romain Bertrand, Rachael Fay, Lia Kallenberger, Patrick Maurhofer, Ramona Stark, Emma Renard, Roger Santimaria, Dragan Grabulovski, Bernd Schlereth, Philipp R. Spycher. Targeting Nectin-4 with a first-in-class triple MMAE/dual TOP1i payload ADC showing synergistic and durable activity across all target expression levels and favorable tolerability [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 7334.