A function-blocking CD47 antibody suppresses stem cell and EGF signaling in triple-negative breast cancer.

Sukhbir Kaur,Satya P Singh,Daoud M Meerzaman,Abdel G Elkahloun,Nidhi Manu,Weiwei Wu,Timothy Song,Poonam Mannan,David D Roberts,Susan H Garfield,Qing-Rong Chen

doi:10.18632/oncotarget.7100

Abstract

CD47 is a signaling receptor for thrombospondin-1 and the counter-receptor for signal-regulatory protein-α (SIRPα). By inducing inhibitory SIRPα signaling, elevated CD47 expression by some cancers prevents macrophage phagocytosis. The anti-human CD47 antibody B6H12 inhibits tumor growth in several xenograft models, presumably by preventing SIRPα engagement. However, CD47 signaling in nontransformed and some malignant cells regulates self-renewal, suggesting that CD47 antibodies may therapeutically target cancer stem cells (CSCs). Treatment of MDA-MB-231 breast CSCs with B6H12 decreased proliferation and asymmetric cell division. Similar effects were observed in T47D CSCs but not in MCF7 breast carcinoma or MCF10A breast epithelial cells. Gene expression analysis in breast CSCs treated with B6H12 showed decreased expression of epidermal growth factor receptor (EGFR) and the stem cell transcription factor KLF4. EGFR and KLF4 mRNAs are known targets of microRNA-7, and B6H12 treatment correspondingly enhanced microRNA-7 expression in breast CSCs. B6H12 treatment also acutely inhibited EGF-induced EGFR tyrosine phosphorylation. Expression of B6H12-responsive genes correlated with CD47 mRNA expression in human breast cancers, suggesting that the CD47 signaling pathways identified in breast CSCs are functional in vivo. These data reveal a novel SIRPα-independent mechanism by which therapeutic CD47 antibodies could control tumor growth by autonomously forcing differentiation of CSC.

Highlights

Breast progenitor cells play an active role in the cyclic changes that take place during pregnancy and ovulation in women [1, 2]
Gene expression analysis by q-PCR of CD44 and CD24 mRNA in suspension and attached cells indicated that the suspension cells have 257-fold up-regulation of CD44 as compared to attached cells, and re-plating the suspension cells in stem cell medium further increased CD44 gene expression (Figure 1E)
High CD47 expression limits the stem cell character of non-transformed cells, the high expression of CD47 on cancer stem cells appeared paradoxical, suggesting that the CD47 expressed on CSC may lack the signaling activity to control stem cell self-renewal, either due to alterations in the CD47 or inactivation of pathways that mediate its signaling in CSC

Summary

Introduction

Breast progenitor cells play an active role in the cyclic changes that take place during pregnancy and ovulation in women [1, 2]. A minor subset of tumor cells has the capacity to initiate a new tumor upon transplantation into a healthy host. These tumor initiating cells have stem cell-like properties and are known as cancer stem cells (CSCs). In contrast to CSCs, the bulk tumor cells have limited proliferative capacity and cannot form new tumors. As few as 100 CD133+-expressing brain and breast cancer cells were sufficient to establish www.impactjournals.com/oncotarget a new cancer in non-obese diabetic, severe combined immunodeficient (NOD-SCID) mice. Engrafted CD133- cells did not form tumors [4, 5]. Most existing therapies to treat solid tumors do not efficiently target cancer stem cells

Methods

Results

Conclusion