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Published on: January 17, 2015
Selection and Characterization of FD164, a High-Affinity Signal Regulatory Protein α Variant with Balanced Safety and
Zhihong Wang1, Naijing Hu1, Xinying Li1
1State Key Laboratory of Toxicology and Medical Countermeasures, Beijing Institute of Pharmacology and Toxicology, Beijing, China (Z.W., N.H., X.L., C.Q., G.C., J.W., L.Z., J.W., D.Z., J.F., B.S., L.L.); School of Basic Medicine and Clinical Pharmacy, China Pharmaceutical University, Nanjing, China (H.W., H.P.); Department of Operational Medicine, Tianjin Institute of Environmental & Operational Medicine, Tianjin, China (H.P.); Department of Hematology, Fourth Medical Center, Chinese PLA General Hospital, Beijing, China (H.W.); and Cancer Research Institute, School of Basic Medical Science, Central South University, Changsha, China (C.R.).
Abstract:
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.
Insights
A novel engineered protein, FD164, targets the CD47 immune checkpoint with higher affinity than wild-type SIRPα. This enhanced binding boosts anti-tumor activity and safety, offering a promising new cancer immunotherapy approach.
Area of Science:
- Immunology
- Oncology
- Biochemistry
Background:
- Phagocytic resistance is a key mechanism of tumor immune escape.
- CD47 acts as a crucial phagocytosis immune checkpoint, mediating tumor immune evasion.
- Blocking the CD47-SIRPα interaction is a potential strategy for cancer immunotherapy.
Purpose of the Study:
- To develop an engineered signal regulatory protein α (SIRPα) variant with enhanced CD47-binding activity.
- To evaluate the in vitro and in vivo efficacy and safety of the engineered SIRPα variant, FD164.
- To identify key residues on CD47 involved in SIRPα and FD164 recognition.
Main Methods:
- Computer-aided screening of a mammalian cell-displayed antibody library.
- Engineering of a SIRPα variant fragment crystallizable (Fc) fusion protein (FD164).
- Affinity measurements, in vitro phagocytosis assays, in vivo tumor suppressor activity studies, and computer structure prediction with alanine scanning.
Main Results:
- FD164 demonstrated approximately 3-fold higher affinity for CD47 binding compared to wild-type SIRPα.
- FD164 enhanced phagocytosis in vitro and exhibited significant tumor suppressor activity in vivo.
- FD164 showed comparable antitumor activity to the clinical drug Hu5F9 but without hemagglutination and with weaker binding to blood cells.
Conclusions:
- The engineered SIRPα variant FD164 exhibits high affinity for CD47, enhanced anti-tumor efficacy, and an improved safety profile.
- FD164, alone or in combination with rituximab, represents a promising candidate for cancer immunotherapy.
- Specific CD47 residues (N45, E47, TEVYVK58, K60, EVTELTRE122, E124) are critical for SIRPα/FD164 recognition.
