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Effects of a humanized CD47 antibody and recombinant SIRPα proteins on triple negative breast carcinoma stem cells
Sukhbir Kaur1, Bianca Reginauld1, Sam Razjooyan1
1Laboratory of Pathology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD, United States.
Abstract:
Signal regulatory protein-α (SIRPα, SHPS-1, CD172a) expressed on myeloid cells transmits inhibitory signals when it engages its counter-receptor CD47 on an adjacent cell. Elevated CD47 expression on some cancer cells thereby serves as an innate immune checkpoint that limits phagocytic clearance of tumor cells by macrophages and antigen presentation to T cells. Antibodies and recombinant SIRPα constructs that block the CD47-SIRPα interaction on macrophages exhibit anti-tumor activities in mouse models and are in ongoing clinical trials for treating several human cancers. Based on prior evidence that engaging SIRPα can also alter CD47 signaling in some nonmalignant cells, we compared direct effects of recombinant SIRPα-Fc and a humanized CD47 antibody that inhibits CD47-SIRPα interaction (CC-90002) on CD47 signaling in cancer stem cells derived from the MDA-MB- 231 triple-negative breast carcinoma cell line. Treatment with SIRPα-Fc significantly increased the formation of mammospheres by breast cancer stem cells as compared to CC-90002 treatment or controls. Furthermore, SIRPα-Fc treatment upregulated mRNA and protein expression of ALDH1 and altered the expression of genes involved in epithelial/mesenchymal transition pathways that are associated with a poor prognosis and enhanced metastatic activity. This indicates that SIRPα-Fc has CD47-mediated agonist activities in breast cancer stem cells affecting proliferation and metastasis pathways that differ from those of CC-90002. This SIRPα-induced CD47 signaling in breast carcinoma cells may limit the efficacy of SIRPα decoy therapeutics intended to stimulate innate antitumor immune responses.
Insights
Signal regulatory protein-α (SIRPα) binding to CD47 on breast cancer stem cells acts as an agonist, promoting proliferation and metastasis. This finding suggests SIRPα decoy therapies may be less effective than anticipated.
Area of Science:
- Immunology
- Oncology
- Cell Biology
Background:
- Signal regulatory protein-α (SIRPα) on myeloid cells inhibits phagocytosis via CD47 interaction.
- Elevated CD47 on cancer cells acts as an immune checkpoint, hindering tumor cell clearance.
- SIRPα blockade therapies show anti-tumor potential but direct SIRPα effects on cancer cells are less understood.
Purpose of the Study:
- To investigate the direct effects of recombinant SIRPα-Fc and a CD47-blocking antibody (CC-90002) on CD47 signaling in triple-negative breast cancer stem cells.
- To compare the distinct signaling pathways activated by SIRPα-Fc versus CD47 blockade in cancer stem cells.
Main Methods:
- Utilized MDA-MB-231 triple-negative breast carcinoma cell line-derived cancer stem cells.
- Treated cells with recombinant SIRPα-Fc, CC-90002, and control conditions.
- Assessed mammosphere formation, ALDH1 expression (mRNA and protein), and epithelial/mesenchymal transition (EMT) gene expression.
Main Results:
- SIRPα-Fc treatment significantly increased mammosphere formation compared to CC-90002 or controls.
- SIRPα-Fc upregulated ALDH1 mRNA and protein expression.
- SIRPα-Fc altered gene expression related to EMT pathways, associated with poor prognosis and metastasis.
Conclusions:
- Recombinant SIRPα-Fc exhibits CD47-mediated agonist activity in breast cancer stem cells, distinct from CD47-blocking antibodies.
- SIRPα-Fc promotes proliferation and metastasis-associated pathways, potentially limiting the efficacy of SIRPα decoy therapeutics.
- Understanding SIRPα's dual role is crucial for developing effective cancer immunotherapies.
