Abstract 4151: Anti-CEACAM5 immune stimulant TLR7/8 agonist antibody drug conjugate is a potent myeloid cell activator for the treatment of CEACAM5-expressing tumors

Abstract Toll Like Receptor 7 and 8 (TLR7/8) agonists are a promising approach to treat tumors by harnessing the innate immune system to trigger anti-tumor innate and adaptive immunity. One of the main obstacles to the use of this class of low molecular weight molecules in cancer treatment is the toxicity associated with systemic immune activation after intravenous administration. We developed a novel immune stimulant ADC by conjugating the anti-CEACAM5 (carcinoembryonic antigen related cell adhesion molecule 5) tusamitamab antibody with a resiquimod (R848) TLR7/8 agonist payload. This tumor-targeted compound administered systemically and locally active, is expected to eradicate CEACAM5-positive (+) tumors by recruiting and activating immune cells in tumor microenvironment to promote anti-tumor immune response. Tusamitamab R848 ADC, evaluated in vitro, binds to CEACAM5+ tumor cells via its Fab moiety, and to myeloid cells via its Fc part at nanomolar (nM) concentrations. TLR7/8 pathway activation was evaluated on myeloid THP1 reporter cells. The conjugate elicits a potent and FcyR-dependent activity at low nM concentration. In co-culture of human blood cells and human CEACAM5+ gastric cancer cells, it was shown to induce phagocytosis activity, associated with increased activation/maturation of both monocytes and dendritic cells. Tusamitamab R848 ADC evaluated in vivo in CEACAM5+ pancreatic human tumor model, HPAFII, leads to robust antitumor activity with complete regressions (CR) after single administration at 5 mg/kg. In a pharmacodynamic study using lung tumor patient-derived xenograft mouse model, this ADC triggers murine cytokine inductions, innate immune cell enrollment at tumor site, and tumor necrosis in a dose-dependent manner. Based on preclinical in vitro and in vivo data, the tusamitamab R848 ADC is an innovative ADC approach with the potential to eradicate CEACAM5+ tumors in patients. Citation Format: Stephanie Decary, Lydia Blot, Charlotte Lahoute, Sandrine Benoist, Anne Caron, Francesca Graziano, Marc Trombe, Loreley Calvet, Alexandra Ferrier, Marc Frederic, Sukhvinder Sidhu, Marie-Priscille Brun, Marielle Chiron. Anti-CEACAM5 immune stimulant TLR7/8 agonist antibody drug conjugate is a potent myeloid cell activator for the treatment of CEACAM5-expressing tumors. [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 4151.