Abstract 2622: TUB-040, a novel Napi2b-targeting ADC built with ethynylphosphonamidate conjugation chemistry, demonstrates high and long-lasting anti-tumor efficacy via Topoisomerase-I inhibition and excellent tolerability predictive of a wide therapeutic window in humans

Abstract TUB-040 is a novel Antibody-Drug Conjugate (ADC) targeting Napi2b, a highly overexpressed target in ovarian cancer and lung adenocarcinoma. Napi2b is a member of the solute-carrier transporter family with eight transmembrane domains and an antibody-accessible extracellular loop, that regulates sodium-dependent phosphate homeostasis. Ethynylphosphonamidate conjugation chemistry was used to build TUB-040 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 Napi2b using a cleavable linker system. In vitro, TUB-040 is characterized by sub-nanomolar affinity and specific binding to Napi2b, efficient target-mediated internalization and high cytotoxicity towards Napi2b-expressing ovarian and lung cancer cell lines as well as bystander activity against co-cultured target-negative cells. TUB-040 induces DNA damage and apoptosis in a dose-dependent fashion as well as markers of immunogenic cell death. In addition, no unspecific uptake and cytotoxicity in healthy, target-negative human cells could be detected, reducing the risk of target-independent toxicities. Pharmacokinetic analysis showed that - in contrast to maleimide-conjugated ADCs - TUB-040 is highly stable - and does not lose or transfer its linker-payload to serum proteins during blood circulation, thus enabling most efficient and continued delivery of Exatecan to the tumor. Across a variety of cell line derived xenograft (CDX) and patient derived xenograft (PDX) models of ovarian and non-small cell lung cancer, including models with low target expression, single dose administration of TUB-040 results in long-lasting tumor growth inhibition with high complete remission rates in vivo. The minimally effective dose (MED) leading to complete remission is 1 mg/kg. Preliminary repeat-dose toxicological assessment of TUB-040 in the pharmacologically relevant species cynomolgus monkey demonstrated that TUB-040 is well tolerated with no signs of lung toxicity and thrombocytopenia. Allometric scaling and PK/PD modelling predicts a human serum half-life greater 10 days and a therapeutic index in humans up to 55. Based on these results, TUB-040, designed with differentiating technology for optimal efficacy and tolerability, is ready for testing in clinical trials. 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. TUB-040, a novel Napi2b-targeting ADC built with ethynylphosphonamidate conjugation chemistry, demonstrates high and long-lasting anti-tumor efficacy via Topoisomerase-I inhibition and excellent tolerability predictive of a wide therapeutic window in humans 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 2622.