Abstract CT291: A phase 1/2, first-in-human study of DS-3939a in patients with advanced solid tumors: A new DXd ADC targeting TA-MUC1

Abstract Background: Mucin 1 (MUC1), a single-transmembrane glycoprotein, is expressed on the apical membrane of the epithelial surface. In normal tissues, it is highly glycosylated and protects the underlying epithelia. In cancer cells, however, MUC1 is hypoglycosylated due to changes in the expression patterns of some sialyltransferases, and exposes new epitopes on MUC1 in tumors, referred to as tumor-associated MUC1 (TA-MUC1). TA-MUC1 loses cell polarity and is redistributed over the cell surface and within the cytoplasm. Overexpression of TA-MUC1 in several malignancies is associated with poor prognosis and development of metastasis, thus making it an attractive therapeutic target. DS-3939a is a novel antibody-drug conjugate in development for the treatment of malignant tumors composed of a humanized anti-TA-MUC1 antibody, a peptide-based cleavable linker, and a potent topoisomerase I inhibitor (deruxtecan [DXd]). This study will assess the safety, tolerability, and efficacy of DS-3939a in patients with advanced solid tumors. Trial design: This phase 1/2, first-in-human, open-label, multicenter, 2-part, dose-escalation, and dose-expansion study (NCT05875168) is active and plans to enroll a maximum of 430 adult patients. Part 1 (dose-escalation) is accruing patients with locally advanced, metastatic, or unresectable urothelial, non-small cell lung, breast, ovarian, biliary tract, or pancreatic cancers, and Part 2 (dose-expansion) will enroll patients with various advanced solid tumors. In Parts 1 and 2, DS-3939a will be administered intravenously on Day 1 of a 21-day cycle. The primary endpoints in Parts 1 and 2 include safety and tolerability of DS3939a as assessed by the number of patients with dose-limiting toxicities (Part 1 only), treatment-emergent adverse events, and other safety parameters. Part 2 will also evaluate efficacy by objective tumor response rate per RECIST version 1.1 as a primary endpoint. Secondary endpoints include the disease control rate, duration of response, time to response, progression-free survival, overall survival, TA-MUC1 expression (detected by immunohistochemistry), the pharmacokinetic profile of DS-3939a, and the number of patients with anti-drug antibodies against DS-3939a. Citation Format: Noboru Yamamoto, Toshihiko Doi, Manish R. Patel, Ignacio Garrido-Laguna, Sutun Wu, Satoshi Nishioka, Keiko Nakajima, Benedito A. Carneiro. A phase 1/2, first-in-human study of DS-3939a in patients with advanced solid tumors: A new DXd ADC targeting TA-MUC1 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT291.