Abstract 2894: QL401, a dual PD-L1/CD47 blocker effective against both solid and hematological malignancies with improved blood safety

Abstract

Abstract Upregulation of CD47, a “Do Not Eat Me” signal, is observed in nearly all solid and hematological malignancies. Engagement of CD47 on tumor cells with SIRPα on macrophages inhibits phagocytosis of tumor cells. Anti-CD47 antibodies block the CD47 - SIRPα engagement and reactivate phagocytosis of tumor cells by macrophages. Yet the ubiquitous expression of CD47 on normal cells, including red blood cells, presents a therapeutic challenge. Systemic targeting of CD47, by either anti-CD47 monoclonal antibodies or SIRPα-Fc fusion proteins, yielded only moderate clinical benefit due to severe adverse side effects, mainly anemia. QL401 is PD-L1 x CD47 bispecific antibody engineered to reduce binding to red blood cells while retaining potent phagocytic activation of macrophages in vitro and delayed tumor growth in vivo. QL401 comprises three functional components: a PD-L1 binding Fab arm, a CD47 binding scFv arm, and a human IgG4 backbone. The PD-L1 binding arm provides both tumor targeting and blocking of PD-1 for reactivating T cells. The CD47 arm blocks the binding of SIRPα, the “Do Not Eat Me” signal, while the IgG4 Fc retains Fc gamma receptor binding to provide a phagocytic “Eat Me” signal. Therefore, QL401 is multi-functional antibody that re-actives both the innate and adaptive immune response. In preclinical efficacy studies, QL401 potently blocked SIRPα to promote phagocytosis of tumor cells with sub-nanomolar potency. In vivo efficacy studies in mouse models of solid and hematological tumors showed QL401 to be comparable or superior to PD-L1 or CD47 monoclonal antibodies alone and in combination. In vitro safety evaluation of Q401 showed significantly reduced binding and phagocytosis of red blood cells, in contrast to CD47 monoclonal antibodies. In addition, Q401 did not induce hemagglutination. In non-human primates, QL401 was well tolerated up to 100 mg/kg without reduction of red blood cells below normal range. A phase 1 dose escalation and expansion study is expected to start Q1 2022 to evaluate the safety, tolerability, and early efficacy of QL401. Citation Format: Irene Tang, Lauren Schwimmer, Shenda Gu, Wei Wei Prior, Hieu V. Tran, Allan Chan, Anna McClain, Shihao Chen, Chuanzeng Cao, Chunyan Sun, Meimei Si, Guijiang Wang. QL401, a dual PD-L1/CD47 blocker effective against both solid and hematological malignancies with improved blood safety [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2894.