Expression of VEGF, CXCR4, CD133, AND HIF-1 alpha in osteosarcoma

Abstract

Osteosarcoma is the most common primary malignant bone tumor seen in orthopaedic practice. Despite intensive treatments of chemotherapy and surgical excision, the current five-year survival rate is only 60% to 78%. We investigated the correlation of vascular endothelial growth factor (VEGF) expression with osteosarcoma growth and metastasis and explored a therapeutic strategy by blocking VEGF. Recent studies suggest that a subpopulation of cancer stem cells (CSCs) plays a role in cancer survival and metastasis. We hypothesized that CD133+ osteosarcoma stem cells are present within the osteosarcoma cell lines and they will be less responsive to VEGF blockage treatment than other tumor cells. Using polymerase chain reaction and immunocytochemistry techniques, we studied the expression of VEGF, CXCR4, and cancer stem cell marker CD133 at transcriptional and post-translational levels among different VEGF-expressing osteosarcoma cells. We examined the tumor cell growth patterns and compared the subpopulation ratio of CD133+ cells after VEGF blockage with VEGF inhibitor SU4312. We also investigated the effects of hypoxia on the proliferation and apoptosis in 1547 osteosarcoma cell line. We chose 1547 cells because of their rapid growth compared to the other osteosarcoma cell lines we used. Hypoxia-inducible factor-1 (HIF-1) activates a series of genes including VEGF which contribute to tumor aggressiveness. Thus we examined the relationship between the expression of HIF-α1 or VEGF and osteosarcoma metabolism. Results showed a decline in cell proliferation and an increase in apoptosis under hypoxia. There were more significant fluctuations after inhibition of HIF-1a and/or VEGF which suggested that HIF-1a and VEGF were involved in the promotion of proliferation and anti-apoptosis of 1547 cells under hypoxia or normoxia.