Development and in Vivo Testing of Antibodies Targeting Cancer-Associated Fibroblasts

An expanding body of work suggests that the tumor stroma plays an integral role in the initiation and development of epithelial cancers. Within the stroma, cancer-associated fibroblasts (CAFs) are involved in several functions that form key aspects of tumor progression, including immune suppression, metabolism, and invasion and metastasis. Despite the demonstrated importance of CAFs within the tumor microenvironment, targeting CAFs in a therapeutic context remains a challenge. The work presented here details the development of a suite of antibodies targeting multiple epitopes of fibroblast activation protein-alpha (FAP), a membrane-bound protease selectively overexpressed on CAFs in numerous epithelial cancers. Using yeast surface display with a synthetic antibody library, more than 50 unique antibodies recognizing FAP were identified, with close to 30 of these proteins recognizing both the human and murine forms of the antigen. In vitro characterizations using yeast-produced scFv-Fc forms of the binding candidates enabled the efficient identification of clones recognizing distinct epitopes of FAP. After affinity maturation, these candidates were converted to full-length IgGs and found to retain their favorable binding properties. These antibodies exhibited good biophysical characteristics and reasonable pharmacokinetic properties in mice, making them suitable for therapeutic studies. A combination immunotherapy involving one of the anti-FAP antibodies has resulted in potent control of tumor growth in a syngeneic mouse model of colon carcinoma. These results suggest that targeting FAP with an immunotherapeutic approach may serve as a general strategy for the treatment of solid tumors.