Hypoxia-inducible factor-1α and vascular endothelial growth factor expression in circulating tumor cells of breast cancer patients

INTRODUCTION: The detection of peripheral blood circulating tumor cells (CTCs) and bone marrow disseminated tumor cells (DTCs) in breast cancer patients is associated with a high incidence of disease relapse and disease-related death. Since hypoxia-inducible factor-1α (HIF-1α) and vascular endothelial growth factor (VEGF) play an important role in angiogenesis and tumor progression, the purpose of the current study was to investigate their expression in CTCs. METHODS: The expression of cytokeratins (CK), VEGF, vascular endothelial growth factor receptor-2 (VEGF2), HIF-1α and phosphorylated-focal adhesion kinase (pFAK) in CTCs from 34 patients with metastatic breast cancer who had detectable CK-19 mRNA-positive CTCs was assessed using double staining experiments and confocal laser scanning microscopy. Peripheral blood mononuclear cells (PBMCs) were stained with a monoclonal A45-B/B3 pancytokeratin antibody in combination with either VEGF or VEGFR2 or HIF-1α or pFAK antibodies, respectively. RESULTS: pFAK expression in circulating tumor cells was detected in 92% of patients whereas expression of VEGF, VEGF2 and HIF-1α was observed in 62%, 47% and 76% of patients, respectively. VEGF, VEGF2, HIF-1α and pFAK were expressed in 73%, 71%, 56% and 81%, respectively, of all the detected CTCs. Vascular endothelial growth mRNA was also detected by quantitative real-time RT-PCR in immunomagnetically-separated CTCs. Double and triple staining experiments in cytospins of immunomagnetically-isolated CTCs showed that VEGF co-expressed with HIF-1α and VEGF2. CONCLUSIONS: The expression of pFAK, HIF-1α, VEGF and VEGF2 in CTCs of patients with metastatic breast cancer could explain the metastatic potential of these cells and may provide a therapeutic target for their elimination.