Abstract LB219: Inducing significant and efficient tumor growth inhibition vs trastuzumab deruxtecan with low drug-load topoisomerase 1 inhibitor ADC using novel peptide linkers for payload conjugation

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. Here, we generated an anti-HER2 ADC using a Topoisomerase 1 (Topo1) inhibitor as payload with highly favorable biophysical properties and superior anti-tumor efficacy compared to Trastuzumab deruxtecan in head-to-head in vitro and in vivo studies. Based on trastuzumab as the targeting antibody and a Topoisimerase 1 inhibitor as payload, we generated highly homogeneous and pure ADCs with a drug-to antibody-ratio (DAR) of 2. In in-vitro assays on target positive cell-lines, the Araris Topo 1 ADC demonstrated potent cell-cytotoxicity in the low nM-range similar to the approved Trastuzumab deruxtecan which has a DAR of 8. Moreover, the ADC showed excellent stability in mouse, cynomolgus and human sera exemplified by the absence of payload deconjugation or linker cleavage while Trastuzumab deruxtecan showed significant payload loss during the 14d incubation period. Interestingly, despite the improved stability, the kinetics for payload release was highly efficient in human Cathepsin B or human liver-lysosome (HLL) enzyme cleavage assays. Most importantly, the ADC was extremely stable in circulation as shown in pharmacokinetic studies in rodents, demonstrating an exposure profile similar to the unmodified trastuzumab parent antibody. In efficacy studies using an established NCI-N87 colon cancer model (therapeutic setting), a single injection of the Araris Topo 1 ADC at DAR2 at a dose of 52ug/kg (adjusted payload dose) induced superior anti-tumor activity compared to Trastuzumab deruxtecan at DAR of 8, injected at the same payload dose. Complete tumor regression of all tumors (7/7) was obtained at 104ug/kg payload dose and lasted throughout the whole study duration (total 80 days) and was very well tolerated. The data show that Araris Topo 1 ADCs assembled using novel peptide linkers, even at a DAR of as low as 2 have a very efficient anti-tumor activity suggesting optimal drug exposure, targeting and release of the payload. In summary, we show that the Araris Topo1 linker-payloads result in highly potent ADCs with very favorable biophysical properties and extremely efficient payload release as well as an antibody-like exposure profile making them ideal linker-payloads for solid tumor targeting. We anticipate the low-drug load to be favorable in avoiding excessive toxicities in non-targeted tissues. Finally, the Araris bioconjugation technology allows for the generation of tailor-made ADC candidates with improved therapeutic indices. Citation Format: Isabella Attinger-Toller, Rachael Fay, Romain Bertrand, Philipp Probst, Ramona Stark, Roger Santimaria, Dragan Grabulovski, Bernd Schlereth, Philipp Rene Spycher. Inducing significant and efficient tumor growth inhibition vs trastuzumab deruxtecan with low drug-load topoisomerase 1 inhibitor ADC using novel peptide linkers for payload conjugation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB219.