RT Journal Article SR Electronic T1 Selection and Characterization of FD164, a High-Affinity Signal Regulatory Protein α Variant with Balanced Safety and Effectiveness, from a Targeted Epitope Mammalian Cell-Displayed Antibody Library JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 193 OP 202 DO 10.1124/molpharm.120.000202 VO 100 IS 3 A1 Zhihong Wang A1 Naijing Hu A1 Xinying Li A1 Haitao Wang A1 Caiping Ren A1 Chunxia Qiao A1 Guojiang Chen A1 Jing Wang A1 Liuzhong Zhou A1 Jiaguo Wu A1 Dingmu Zhang A1 Jiannan Feng A1 Beifen Shen A1 Hui Peng A1 Longlong Luo YR 2021 UL http://molpharm.aspetjournals.org/content/100/3/193.abstract AB Phagocytic resistance plays a key role in tumor-mediated immune escape, so phagocytosis immune checkpoints are a potential target for cancer immunotherapy. CD47 is one of the important phagocytosis immune checkpoints; thus, blocking the interaction between CD47 and signal regulatory protein α (SIRPα) may provide new options for cancer treatment. Using computer-aided targeted epitope mammalian cell-displayed antibody library, we screened and obtained an engineered SIRPα variant fragment crystallizable fusion protein, FD164, with higher CD47-binding activity than wild-type SIRPα. Compared with wild-type SIRPα, FD164 has approximately 3-fold higher affinity for binding to CD47, which further enhanced its phagocytic effect in vitro and tumor suppressor activity in vivo. FD164 maintains the similar antitumor activity of the clinical research drug Hu5F9 in the mouse xenograft model. Furthermore, FD164 combined with rituximab can significantly improve the effect of single-agent therapy. On the other hand, compared with Hu5F9, FD164 does not cause hemagglutination, and its ability to bind to red blood cells or white blood cells is weaker at the same concentration. Finally, it was confirmed by computer structure prediction and alanine scanning experiments that the N45, E47, 52TEVYVK58, K60, 115EVTELTRE122, and E124 residues of CD47 are important for SIRPα or FD164 recognition. Briefly, we obtained a high-affinity SIRPα variant FD164 with balanced safety and effectiveness.SIGNIFICANCE STATEMENT Up to now, few clinically marketed drugs targeting CD47 have been determined to be effective and safe. FD164, a potential signal regulatory protein α variant fragment crystallizable protein with balanced safety and effectiveness, could provide a reference for the development of antitumor drugs.