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CD47-signal regulatory protein-? (SIRP?) interactions form a barrier for antibody-mediated tumor cell destruction.

ABSTRACT: Monoclonal antibodies are among the most promising therapeutic agents for treating cancer. Therapeutic cancer antibodies bind to tumor cells, turning them into targets for immune-mediated destruction. We show here that this antibody-mediated killing of tumor cells is limited by a mechanism involving the interaction between tumor cell-expressed CD47 and the inhibitory receptor signal regulatory protein-? (SIRP?) on myeloid cells. Mice that lack the SIRP? cytoplasmic tail, and hence its inhibitory signaling, display increased antibody-mediated elimination of melanoma cells in vivo. Moreover, interference with CD47-SIRP? interactions by CD47 knockdown or by antagonistic antibodies against CD47 or SIRP? significantly enhances the in vitro killing of trastuzumab-opsonized Her2/Neu-positive breast cancer cells by phagocytes. Finally, the response to trastuzumab therapy in breast cancer patients appears correlated to cancer cell CD47 expression. These findings demonstrate that CD47-SIRP? interactions participate in a homeostatic mechanism that restricts antibody-mediated killing of tumor cells. This provides a rational basis for targeting CD47-SIRP? interactions, using for instance the antagonistic antibodies against human SIRP? described herein, to potentiate the clinical effects of cancer therapeutic antibodies.

SUBMITTER: Zhao XW

PROVIDER: S-EPMC3215076 | biostudies-literature | 2011 Nov

REPOSITORIES: biostudies-literature

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CD47-signal regulatory protein-α (SIRPα) interactions form a barrier for antibody-mediated tumor cell destruction.

Zhao Xi Wen XW van Beek Ellen M EM Schornagel Karin K Van der Maaden Hans H Van Houdt Michel M Otten Marielle A MA Finetti Pascal P Van Egmond Marjolein M Matozaki Takashi T Kraal Georg G Birnbaum Daniel D van Elsas Andrea A Kuijpers Taco W TW Bertucci Francois F van den Berg Timo K TK

Proceedings of the National Academy of Sciences of the United States of America 20111031 45

Monoclonal antibodies are among the most promising therapeutic agents for treating cancer. Therapeutic cancer antibodies bind to tumor cells, turning them into targets for immune-mediated destruction. We show here that this antibody-mediated killing of tumor cells is limited by a mechanism involving the interaction between tumor cell-expressed CD47 and the inhibitory receptor signal regulatory protein-α (SIRPα) on myeloid cells. Mice that lack the SIRPα cytoplasmic tail, and hence its inhibitory ...[more]

PMID: 22042861

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Project description:BACKGROUND:Signal Regulatory Protein ? (SIRP?) is a member of a closely related family of three cell surface receptors implicated in modulating immune/inflammatory responses. SIRP? is expressed on T lymphocytes where it appears to be involved in the integrin-independent adhesion of lymphocytes to antigen-presenting cells. Here we describe the first full length structure of the extracellular region of human SIRP?. RESULTS:We obtained crystals of SIRP? by making a complex of the protein with the Fab fragment of the anti-SIRP antibody, OX117, which also binds to SIRP? and SIRP?. We show that the epitope for FabOX117 is formed at the interface of the first and second domains of SIRP? and comprises residues which are conserved between all three SIRPs. The FabOX117 binding site is distinct from the region in domain 1 which interacts with CD47, the physiological ligand for both SIRP? and SIRP? but not SIRP?. Comparison of the three domain structures of SIRP? and SIRP? showed that these receptors can adopt different overall conformations due to the flexibility of the linker between the first two domains. SIRP? in complex with FabOX117 forms a dimer in the crystal. Binding to the Fab fixes the position of domain 1 relative to domains 2/3 exposing a surface which favours formation of a homotypic dimer. However, the interaction appears to be relatively weak since only monomers of SIRP? were observed in sedimentation velocity analytical ultracentrifugation of the protein alone. Studies of complex formation by equilibrium ultracentrifugation showed that only a 1:1 complex of SIRP?: FabOX117 was formed with a dissociation constant in the low micromolar range (Kd?=?1.2 +/- 0.3 ?M). CONCLUSION:The three-domain extracellular regions of SIRPs are structurally conserved but show conformational flexibility in the disposition of the amino terminal ligand-binding Ig domain relative to the two membrane proximal Ig domains. Binding of a cross-reactive anti-SIRP Fab fragment to SIRP? stabilises a conformation that favours SIRP dimer formation in the crystal structure, though this interaction does not appear sufficiently stable to be observed in solution.

Project description:BACKGROUND:Accumulating preclinical data indicate that targeting the SIRP?/CD47 axis alone or in combination with existing targeted therapies or immune checkpoint inhibitors enhances tumor rejection. Although several CD47-targeting agents are currently in phase I clinical trials and demonstrate activity in combination therapy, high and frequent dosing was required and safety signals (acute anemia, thrombocytopenia) were recorded frequently as adverse events. Based on the restricted expression pattern of SIRP? we hypothesized that antibodies targeting SIRP? might avoid some of the concerns noted for CD47-targeting agents. METHODS:SIRP?-targeting antibodies were generated and characterized for binding to human SIRP? alleles and blockade of the interaction with CD47. Functional activity was established in vitro using human macrophages or neutrophils co-cultured with human Burkitt's lymphoma cell lines. The effect of SIRP? versus CD47 targeting on human T-cell activation was studied using an allogeneic mixed lymphocyte reaction and a Staphylococcus enterotoxin B-induced T-cell proliferation assay. Potential safety concerns of the selected SIRP?-targeting antibody were addressed in vitro using a hemagglutination assay and a whole blood cytokine release assay, and in vivo in a single-dose toxicity study in cynomolgus monkeys. RESULTS:The humanized monoclonal IgG2 antibody ADU-1805 binds to all known human SIRP? alleles, showing minimal binding to SIRP?1, while cross-reacting with SIRP?, and potently blocking the interaction of SIRP? with CD47. Reduced Fc?R binding proved critical to retaining its function towards phagocyte activation. In vitro characterization demonstrated that ADU-1805 promotes macrophage phagocytosis, with similar potency to anti-CD47 antibodies, and enhances neutrophil trogocytosis. Unlike CD47-targeting agents, ADU-1805 does not interfere with T-cell activation and is not expected to require frequent and extensive dosing due to the restricted expression of SIRP? to cells of the myeloid lineage. ADU-1805 is cross-reactive to cynomolgus monkey SIRP? and upon single-dose intravenous administration in these non-human primates (NHPs) did not show any signs of anemia, thrombocytopenia or other toxicities. CONCLUSIONS:Blocking the SIRP?-CD47 interaction via SIRP?, while similarly efficacious in vitro, differentiates ADU-1805 from CD47-targeting agents with respect to safety and absence of inhibition of T-cell activation. The data presented herein support further advancement of ADU-1805 towards clinical development.

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CD47-signal regulatory protein-? (SIRP?) interactions form a barrier for antibody-mediated tumor cell destruction.

Publications

CD47-signal regulatory protein-α (SIRPα) interactions form a barrier for antibody-mediated tumor cell destruction.

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