Abstract 2623: Enabling 5T4 for targeted cancer therapy: TUB-030, a novel ADC built with ethynylphosphonamidate conjugation chemistry, shows long-lasting anti-tumor activity via Topoisomerase-I inhibition with an optimized therapeutic index

Abstract TUB-030 is a novel Antibody-Drug Conjugate (ADC) targeting the oncofetal 5T4 antigen, a glycoprotein, that is functionally involved in regulation of the Wnt signalling pathway and promoting cellular motility and adhesion. Immunohistochemical analysis identified 5T4 overexpressed in many types of cancers, including bladder, lung, breast, stomach, esophagus, head and neck, colon, and ovarian. Analysis in fresh frozen healthy human tissue with the therapeutic mAb candidate of TUB-030 revealed limited cross reactivity. Ethynylphosphonamidate conjugation chemistry was used to build TUB-030 with a homogenous DAR (drug-antibody-ratio) of 8 and the Topoisomerase I inhibitor Exatecan as payload, which is connected to a humanized, Fc-silenced IgG1 antibody targeting 5T4 using a cleavable linker system. Overall, TUB-030 contrasts previous ADC designs targeting 5T4, implementing several layers of differentiation in terms of antibody, payload and conjugation technology. In vitro, TUB-030 is characterized by sub-nanomolar affinity to 5T4, efficient target-mediated internalization and strong cytotoxicity towards cancer cells from different tumor indications with a broad range of 5T4 expression levels. Differently to previous 5T4-targeting ADCs, TUB-030 has efficient bystander activity against co-cultured target-negative cells, which facilitates targeting of tumors with heterogenous 5T4 expression. Pharmacokinetic analysis showed that TUB-030 is highly stable - and does not lose or transfer its linker-payload to serum proteins during blood circulation and antibody-like clearance profile contrasting maleimide-conjugated ADCs and enabling most efficient and continued delivery of Exatecan to the tumor site. Single-dose treatment with TUB-030 results in long-lasting tumor regression with high complete remission rates across a variety of both cell-line derived xenograft (CDX) and patient-derived xenograft (PDX) cancer models of multiple tumor indications in vivo, including models with low target expression. Preliminary repeat-dose toxicological assessment of TUB-030 in a pharmacologically relevant non-human primate species demonstrated that TUB-030 is well tolerated. The preclinical results underline that TUB-030 with novel ADC technology has the potential to enable 5T4 as a therapeutic target and provide treatment options in numerous solid cancer indications with high unmet medical need supporting further development towards the clinic. Citation Format: Saskia Schmitt, Isabelle Mai, Paul Machui, Sarah Herterich, Danila Hauswald, Philipp Ochtrop, Philipp Cyprys, Izabela Kozlowska, Annabel Kitowski, Marcus Gerlach, Olivier Marcq, Pamela A. Trail, Dominik Schumacher, Marc-André Kasper, Günter Fingerle-Rowson, Björn Hock, Jonas Helma-Smets, Annette M. Vogl. Enabling 5T4 for targeted cancer therapy: TUB-030, a novel ADC built with ethynylphosphonamidate conjugation chemistry, shows long-lasting anti-tumor activity via Topoisomerase-I inhibition with an optimized therapeutic index abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2623.