D peptide inhibitors of SIRPα anti phagocytic signaling

PROJECT SUMMARY The cell surface CD protein is a marker of self and signals through its receptor signal regulatory protein SIRP expressed by macrophages to transmit an anti phagocytic donandapos t eat me signal CD is expressed by virtually all cell types is overexpressed by cancer cells as a mechanism to avoid immune surveillance and phagocytosis and is a negative prognostic factor for survival Blocking this interaction is of therapeutic interest because it results in increased cancer cell phagocytosis innate immunity as well as priming of a cytotoxic antitumor T cell response adaptive immunity However due to ubiquitous CD expression anti CD immunotherapies must overcome a large antigen sink reduced bioavailability and are limited by on target off tumor toxicity such as thrombocytopenia and anemia In contrast the receptor SIRP is mainly expressed on myeloid cells such that inhibitors targeting SIRP will have reduced toxicity and increased bioavailability SIRP is a transmembrane protein composed of a conserved cytoplasmic tail region and three N terminal extracellular immunoglobulin superfamily IgSF domains one V set and two C set IgSF domains The related family members SIRP and SIRP share homologous IgSF domains but have distinct cytoplasmic domains and signaling properties The region of SIRP that interacts with CD is contained within the soluble amino acid N terminal IgSF V set domain making synthesis of this target very feasible Using a drug discovery platform that employs enantiomeric screening mirror image phage display coupled with protein design we have successfully developed protease stable D peptide entry inhibitors of HIV RSV and Ebola viruses These inhibitors bind pockets that are similarly involved in functionally critical protein protein interactions traditionally deemed undruggable by small molecule approaches Our anti HIV D peptide entry inhibitor is in advanced preclinical trials and was trimerized to simultaneously bind all three pockets on HIVandapos s trimeric envelope protein resulting in extremely high pM potency In this year grant application we propose to discover D peptides that specifically bind only to SIRP and inhibit its interaction with CD and then characterize their binding profile on SIRP and SIRP D peptides typically display extended in vivo half lives and low immunogenicity and their small size gives them the potential for enhanced tumor penetration Also the chemical synthesis of these D peptides will result in a much more cost effective cancer immunotherapeutic compared to biologics Success here will warrant subsequent structural characterization affinity maturation testing in cell culture and animal models and IND enabling toxicology studies on our D peptide inhibitors of SIRP to aid in the treatment of cancer PROJECT NARRATIVE CD interaction with signal regulatory protein SIRP constitutes an immune checkpoint regulating the phagocytic behavior of innate immune cells such as macrophages We propose to discover D peptides that specifically bind to SIRP and inhibit its interaction with CD These inhibitors will enhance immune responses to tumors and be broadly applicable in cancer therapy