69O - A small molecule human PD-1/PD-L1 inhibitor promotes T cell immune activation and reduces tumor growth in a preclinical model

Abstract

Background: In recent years, antibody-based therapies targeting the Programmed cell Death-1/Programmed Death-Ligand 1 (PD-1/PD-L1) immune checkpoint axis have gained tremendous success in cancer immunotherapy. We embarked on an effort to identify and develop small molecules capable of targeting this immune checkpoint, with an aim to provide new therapeutic options with improved anticancer immune responses, increased tumor penetration, shorter half-life to better managing immune related adverse events, and lower cost of goods. Methods: We developed a number of small molecule inhibitors based on the crystal structure of human PD-1/PD-L1 complex. Active compounds were first identified by an ELISA assay measuring inhibition of the PD-1/PD-L1 interaction, followed by functional cell-based reporter and mixed lymphocyte reaction (MLR) assays. Since these inhibitors specifically block human PD-1/PD-L1 interaction, we co-implanted A375 human melanoma cells along with human peripheral blood mononuclear cells (PBMCs) into immunodeficient NOD/SCID mice to test their efficacy in vivo. Results: We have obtained potent human PD-1/PD-L1 inhibitors with marked activities in both the cell-based reporter and MLR assays. Moreover, lead compound CCX4503 reduced tumor growth in vivo to a similar extent as the positive control anti-human PD-L1 antibody. Anti-tumor activity was completely dependent on the presence of human PBMCs. The tumor microenvironment analysis indicated that the anti-tumor activity of CCX4503 was accompanied by a significantly higher CD8+ T-Cell/CD4+ T-cell ratio. An X-ray structure of CCX4503 co-crystallized with PD-L1 provided information about the structural basis by which the compound disrupts the PD-1/PD-L1 immune checkpoint interaction. Conclusions: We have identified and advanced unique small molecule inhibitors of human PD-1/PD-L1 by rational design. Molecules resulting from these efforts, such as CCX4503, exhibited marked inhibition of the PD-1/PD-L1 interaction and signaling in vitro, and also clear anti-tumor effects in an animal model system in vivo. Legal entity responsible for the study: ChemoCentryx, Inc., Mountain View, CA. Funding: ChemoCentryx, Inc., Mountain View, CA. Disclosure: M. Vilalta Colomer, S. Li, V. Malathong, C. Lange, D. McMurtrie, J. Yang, H. Roth, J. McMahon, J.J. Campbell, L.S. Ertl, R. Ong, Y. Wang, N. Zhao, S. Yau, T. Dang, P. Zhang, T.J. Schall, R. Singh: Full-time employee of ChemoCentryx. S. Punna: Stock holder: ChemoCentryx.