SIRPα-Fc fusion protein IMM01 exhibits dual anti-tumor activities by targeting CD47/SIRPα signal pathway via blocking the “don’t eat me” signal and activating the “eat me” signal

Abstract

A novel recombinant SIRPα-Fc fusion protein, IMM01, was constructed and produced using an in-house developed CHO-K1 cell expression system, and the anti-tumor mechanism of IMM01 targeting the CD47-SIRPα pathway was explored. The phagocytosis and in vitro anti-tumor activity of IMM01 were evaluated by antibody-dependent cellular phagocytosis (ADCP), antibody-dependent cell-mediated cytotoxicity (ADCC), and complement-dependent cytotoxicity (CDC) assays. In vivo mouse tumor model studies were used to explore therapeutic efficacy as well as the mechanism of action. An in vitro binding assay revealed that IMM01 has a strong binding affinity to CD47 with an EC50 of 0.4967 nM. IMM01 can induce strong ADCP and moderate ADCC, but not CDC. IMM01-induced strong phagocytosis against tumor cells was attributed to dual activities of blocking the "don’t eat me" signal and activating the "eat me" signal, and IMM01 exhibits strong and robust in vivo anti-tumor activities either as monotherapy on hematological malignancies, or in combination therapy with PD-L1 monoclonal antibody (mAb), PD-1 mAb, and HER-2 mAb on solid tumors. Finally, IMM01 demonstrated a favorable safety profile with no human RBC binding activity or hemagglutination induction. IMM01 inhibits the growth of tumor cells by the following three possible mechanisms: (1) directly activating macrophages to phagocytize tumor cells; (2) activated macrophages degrade phagocytized tumor cells and present tumor antigens to T cells through MHC molecules to activate T cells; (3) activated macrophages can convert "cold tumors" into "hot tumors" and increase the infiltration of immune cells through chemotaxis by secreting some cytokines and chemokines.

IMM0306, a fusion protein of CD20 mAb with the CD47 binding domain of SIRPα, exerts excellent cancer killing efficacy by activating both macrophages and NK cells via blockade of CD47-SIRPα interaction and FcɣR engagement by simultaneously binding to CD47 and CD20 of B cells

“…IMM0306 can be used as monotherapy or in combination with other targeted immune checkpoint inhibitors. Combining with our previous study [14], we believed that for therapeutic purposes by targeting the CD47/SIRPα signal pathway, two prerequisites must be met for full activation of macrophages, blocking of the CD47 "don't eat me" signal and activation of the Fc-receptor "eat me" signal. Either one of the two prerequisites Fig.…”

SIRPα: A key player in innate immunity

“…Additionally, mimics of SIRPα based on its structure have been generated as recombinant proteins targeting CD47. For example, IMM01 has shown dual activities by interfering with “don't eat me” signaling and activating ‘eat me’ signaling [101]. These approaches represent potential therapeutic strategies to modulate the CD47‐SIRPα axis.…”

HX009, a novel BsAb dual targeting PD1 x CD47, demonstrates potent anti-lymphoma activity in preclinical models

“…To date, targeting CD47 has been achieved with an investigational anti-CD47 mAb drug (e.g. magrolimab, also called Hu5F9-G4) 8 , and with a SIRPα fusion protein 21 , 22 , which blocks the CD47-SIRPα interaction. While both have demonstrated encouraging activity against a variety of hematological malignances, including lymphoma 8 , 10 , 19 , 20 , 23 , neither has been approved to date for any indication.…”