Even though, molecular profiling of breast cancer has allowed for the development of new therapeutic drugs, cytotoxic chemotherapy remains a primary mode of therapy for many breast cancer patients including those diagnosed with triple negative breast cancer. Pre-clinical and clinical studies demonstrate that increased expression of CD47 is associated with poor prognosis in several types of cancer, including breast tumors. Our published evidence shows that blockade of CD47 enhances radiation-induced growth delay of tumors while remarkably protecting soft tissues from death associated to ionizing radiation. We now show that CD47 blockade significantly sensitizes breast tumors to anthracycline chemotherapy while protecting cardiac tissue from the off target effects of this drug. 4T1B breast cancer cells were implanted in the mammary fat-pad of Balb/C mice and treated with saline, doxorubicin, CD47 morpholino (CD47M), or CD47M with doxorubicin. Tumors of mice treated with saline tripled in size. Doxorubicin treatment caused a reduction in tumor volume and weight, but combining CD47 blockade and doxorubicin further reduced tumor volume by over 60%. The reduction of tumor growth was associated with an increased in PINK1 and Parkin gene expression, indicating activation of mitochondrial turnover by mitophagy. Further studies using the Seahorse XF-24 analyzer indicated that blockade of CD47 reduced glycolytic and mitochondrial metabolism measured as the extracellular acidification rate and oxygen consumption rate in 4T1B cells and human MDA-MB-231 cells. The regulation of glycolytic mechanism is associated with a reduction in glucose uptake and reduction in Glut-1 expression in breast tumors. Metastatic spread of tumors to lungs was observed in saline treated animals. Immunohistological analysis indicated that these lesions express CD47. Moreover, we observed positive immunoreactivity to CD47 in clinical samples of metastatic breast carcinoma indicating that CD47 signaling may play an important role in tumor spread and its targeting could lead to reduction of metastatic burden. One of the most common side effects of doxorubicin chemotherapy is cardiac toxicity. Blockade of CD47 in tumor bearing mice protected cardiac tissue indicated by reduction in fibrosis and cell death. This was associated by an increase in autophagy gene expression as demonstrated by the observed increase in ATG5 and ATG7. Therefore blockade CD47 enhances doxorubicin reduction of breast tumor growth in a syngeneic tumor model indicating that CD47 potentiates anthracycline-mediated breast tumor therapy while protecting normal tissue from death associated with cytotoxic therapy.
Citation Format: David R. Soto-Pantoja, John M. Sipes, Arunima Ghosh, Maria J. Merino, David D. Roberts. Therapeutic targeting of CD47 regulates cell bioenergetics and autophagy to reduce breast tumor growth and protect against anthracycline-mediated cardiac toxicity. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2434. doi:10.1158/1538-7445.AM2014-2434