Abstract 1611: A novel anti-human CD47 antibody prodrug as cancer therapeutics to lower on-target side effects

Abstract

Abstract CD47 is highly expressed in many types of cancers, including human acute myeloid leukemia (AML), non-Hodgkin's lymphoma (NHL), and solid tumors such as small-cell lung cancer (SCLC). Binding of CD47 to its receptor, SIRPα, on macrophages leads to inhibition of macrophage activation and phagocytosis. CD47 overexpression is one of the mechanisms cancer cells employ to evade immune surveillance and correlates with poor prognosis in cancers. Several strategies have been used to block CD47 binding to SIRPα, including anti-CD47 blocking antibodies and SIRPα-Fc fusion proteins. However, since CD47 is also expressed on normal cells, a major concern is that anti-CD47 antibodies could also cause on-target side effects, such as red blood cell hemagglutination and anemia. We have identified a panel of high affinity anti-human CD47 blocking antibodies. The lead antibodies bound to human CD47 with sub-nanomolar affinities and displayed a range of activities in blocking CD47:SIRPα interaction. These antibodies showed robust activities in stimulating macrophage-mediated phagocytosis of cancer cells. To minimize the on-target side effects of anti-CD47 antibodies, we have taken an antibody prodrug approach in which the antibody is inactive for normal cells while it becomes functional in the tumor microenvironment enriched with proteases. By screening a phage peptide library, we identified peptides that specifically block the anti-CD47 antibody binding activity. These peptides were fused to the humanized anti-CD47 antibody via a linker containing protease substrate sequences to derive the anti-CD47 antibody prodrug. We demonstrated that the anti-CD47 antibody prodrug lacked CD47 binding activity and was unable to block CD47:SIRPα interaction. Upon cleavage of the anti-CD47 antibody prodrug with proteases, the antibody regained full activities in both CD47 binding and blocking CD47:SIRPα interaction. Importantly, we showed that the anti-CD47 antibody prodrug had minimal hemagglutination and RBC binding activities. These data suggest that the novel anti-CD47 antibody prodrug is a promising candidate for the next generation anti-CD47 therapeutics with improved safety profile. Citation Format: Richard Zhang, Hunter Drobenaire, Huey Li, Veronica Pizzarella, Haishan Lin. A novel anti-human CD47 antibody prodrug as cancer therapeutics to lower on-target side effects [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1611.