Abstract 2138: Targeting cancer-associated fibroblasts using antibodies recognizing fibroblast activation protein-alpha.

Abstract

Abstract 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 integral 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 isolation and characterization of antibody fragments targeting multiple epitopes of fibroblast activation protein-alpha (FAP), a membrane-bound protease selectively overexpressed on CAFs in numerous epithelial cancers. The combination of a minimalist antibody fragment library and yeast surface display allowed for the isolation of more than 50 unique antibodies recognizing the human or murine forms of FAP, with close to 30 exhibiting cross-reactivity. To narrow the pool of cross-reactive antibodies to a biologically relevant subset, the fragments were converted to an antibody-like format that could be secreted from yeast. Without purification, the soluble proteins were first used to investigate the abilities of individual fragments to recognize FAP transiently expressed on the surface of HEK293 cells. Proteins for which binding to FAP could be confirmed were then used in combination with antibody fragments displayed on the surface of yeast in order to determine which sets of fragments bind distinct epitopes of FAP. Flow cytometry-based assays revealed that the isolated fragments recognize two or more distinct epitopes of the antigen. A handful of fragments is currently being subjected to affinity maturation and conversion to IgGs, and work to further investigate the in vitro and in vivo characteristics of the proteins is ongoing. These proteins may allow for the ablation of cancer-associated fibroblasts or interference with the proteolytic activity of FAP in the tumor microenvironment, providing biological insights into the roles of CAFs and therapeutic approaches to cancer treatment. Furthermore, the general antibody isolation and characterization approaches used in this work are accessible to many single-investigator laboratories and should be applicable to the targeting of numerous cancer antigens. Citation Format: James A. Van Deventer, Karl D. Wittrup. Targeting cancer-associated fibroblasts using antibodies recognizing fibroblast activation protein-alpha. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2138. doi:10.1158/1538-7445.AM2013-2138