NAV-001, a high-efficacy antibody-drug conjugate targeting mesothelin with improved delivery of potent payload by counteracting MUC16/CA125 effects

Abstract Subsets of tumor-produced proteins, referred to as Humoral Immuno-Oncology (HIO) factors, can bind to IgG1 antibodies and suppress their immune-effector activities. Antibody-drug conjugates (ADCs) targeting tumor cell surface antigens can internalize and kill target cells upon liberation of their cytotoxic payload. Binding of the antibody component of an ADC by a HIO factor may potentially hamper the efficacy of a bound ADC. To assess any suppression of ADC’s activity by HIO factors, we evaluated the efficacy of a HIO-refractory ADC, NAV-001, and a HIO-bound ADC, SS1, both targeting mesothelin. The HIO factor MUC16/CA125 protein, which binds to SS1 ADC, was shown to have a negative effect on its internalization and tumor cell killing. The MUC16/CA125 refractory NAV-001 ADC was shown to have robust killing of tumor cells regardless of MUC16/CA125 expression in vitro (EC50 ~20 pM) as well as in vivo at single, sub-mg/kg dosing. Moreover, NAV-001-PNU, which contains the PNU-159682 topoisomerase II inhibitor as a payload, demonstrated good stability in vitro and in vivo as well as robust bystander activity against tumor and stromal cells not expressing the target antigen mesothelin, while maintaining a tolerable safety profile in vivo. Single-dose NAV-001-PNU demonstrated robust tumor regression of a number of patient-derived xenograft models from different tumor types regardless of MUC16/CA125 expression. These findings suggest that identification of HIO-refractory antibodies to be used in ADC format may improve therapeutic efficacy as observed for NAV-001 and warrants NAV-001-PNU’s advancement to human clinical trials as a monotherapy to treat mesothelin-positive cancers. Citation Format: Luigi Grasso, J. Bradford Kline, Nicholas C. Nicolaides. NAV-001, a high-efficacy antibody-drug conjugate targeting mesothelin with improved delivery of potent payload by counteracting MUC16/CA125 effects [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1876.