OMTX705, a Novel FAP-Targeting ADC Demonstrates Activity in Chemotherapy and Pembrolizumab-Resistant Solid Tumor Models

Purpose: The tumor microenvironment plays a key role in cancer development and progression and is involved in resistance to chemo- and immunotherapy. Cancer-associated fibroblast expressing fibroblast-activating protein alpha (FAP alpha) is one of the predominant stroma cell types and is involved in resistance to immunotherapy. Experimental Design: We generated OMTX705, a novel antibody-drug conjugate from a humanized anti-FAP antibody linked to a new cytolysin. Here, we studied its antineoplastic activity in vitro and in preclinical mouse models alone and in combination with chemotherapy as well as immunotherapy in PD-1-resistant tumors. Results: In Avatar models, OMTX705 showed a 100% tumor growth inhibition and prolonged tumor regressions as single agent and in combination with chemotherapy. Treatment rechallenge following treatment discontinuation induced additional tumor regression, suggesting lack of treatment resistance. In a mouse model with a humanized immune system resistant to PD-1 inhibition, OMTX705 increased tumor infiltration by CD8(+) T cells, induced complete regressions, and delayed tumor recurrence. Conclusions: These data suggest that FAP targeting with OMTX705 represents a novel and potent strategy for cancer treatment, including tumors resistant to immunotherapy, and support its clinical development.