Introduction: Immune-stimulating antibody conjugates (ISACs) direct a TLR7/8 agonist into tumors through engagement of cell surface antigens to activate tumor-associated myeloid cells and initiate a broad innate and adaptive anti-tumor immune response. We are developing the ISAC BDC-2034 to target the tumor antigen, CEA (CEACAM5), which is expressed in many solid tumors. BDC-2034 comprises our proprietary antibody, CEA1, covalently conjugated to a potent TLR7/8 agonist via a non-cleavable linker. The strong pro-phagocytic capacity and slow internalization rate of CEA1 makes it an ideal antibody for the ISAC approach.

Methods: The ability of BDC-2034 to induce the secretion of pro-inflammatory cytokines was evaluated in vitro using co-cultures of tumor cells and primary immune cells (including monocytes and dendritic cells). Anti-tumor efficacy was demonstrated in vivo with xenograft and syngeneic mouse tumor models. In parallel studies, the mechanism of BDC-2034 action was assessed by quantifying intratumoral immune infiltration, cytokine levels, and transcript profile.

Results: In co-cultures of CEA-expressing tumor cells and immune cells, BDC-2034 induced the secretion of cytokines and chemokines that are essential for a broad anti-tumor immune response, including IL-12p70, CXCL10, and TNFα. These effects were accompanied by myeloid cell activation as demonstrated by elevation in costimulatory surface markers such as CD40. In vivo, BDC-2034 inhibited tumor growth in multiple xenograft and syngeneic mouse tumor models having CEA expression comparable to human cancers. Consistent with the proposed mechanism of action, BDC-2034 induced intratumoral immune cell infiltration, inflammatory cytokine secretion, and myeloid re-programming in a dose-dependent and CEA-dependent fashion. The constellation of BDC-2034 effects translated to durable therapeutic activity.

Conclusions: These preclinical findings demonstrate the potential of BDC-2034 to generate anti-tumor activity in CEA-expressing cancers through direct innate immune activation and the induction of adaptive anti-tumor immunity.

Citation Format: Lisa K. Blum, Cecelia I. Pearson, Laughing Bear Torrez Dulgeroff, Rishali Gadkari, Angela Luo, Andrew Luo, Jennifer E. Melrose, Jess L. Nolin, Hai Li, Arthur Lee, Matthew N. Zhou, Puneet Anand, Ganapathy Sarma, Karla A. Henning, Steven J. Chapin, Shelley E. Ackerman, Romas Kudirka, Yuyi Shen, Bruce Hug, Edith A. Perez, Marcin Kowanetz, Michael N. Alonso, Brian S. Safina, David Dornan, William G. Mallet. The CEA-targeted ISAC, BDC-2034, shows preclinical efficacy associated with innate immune activation, phagocytosis, and myeloid reprogramming [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2911.