Purpose: Glucocorticoids such as prednisone, hydrocortisone, and dexamethasone are known to provide some clinical benefit for patients with hormone-refractory prostate cancer. However, the underlying mechanisms by which glucocorticoids affect hormone-refractory prostate cancer progression are not well established as yet. Our previous study has shown that glucocorticoids inhibit tumor angiogenesis possibly by down-regulation of vascular endothelial growth factor (VEGF) and interleukin 8. Here, we hypothesized that the therapeutic effect of dexamethasone on hormone-refractory prostate cancer can be partly attributed to a direct inhibition of lymphangiogenesis through the glucocorticoid receptor by down-regulating a major lymphangiogenic factor, VEGF-C.
Experimental design: The effects of dexamethasone on the expression of VEGF-C and its receptor, VEGF receptor-3 (VEGFR-3), were examined using an androgen-independent human prostate cancer cell line, DU145, which expresses glucocorticoid receptor. The effects of dexamethasone on tumor-associated lymphangiogenesis in DU145 xenografts were determined by analyzing VEGF-C gene expression, lymphatic vessel density, and relative lymphatic vessel area.
Results: Dexamethasone significantly down-regulated VEGF-C gene expression and protein production by 48% (P = 0.003) and 44% (P = 0.002), respectively, under normoxic condition. Similarly, hydrocortisone down-regulated VEGF-C gene expression. The effects of dexamethasone were completely reversed by the glucocorticoid receptor antagonist RU486. Even under hypoxia-like conditions, dexamethasone inhibited VEGF-C gene expression. In DU145 xenografts, dexamethasone significantly down-regulated VEGF-C gene expression and decreased lymphangiogenesis. Dexamethasone did not affect VEGFR-3 gene expression in vitro and in vivo.
Conclusion: Glucocorticoids suppressed tumor-associated lymphangiogenesis by down-regulating VEGF-C through glucocorticoid receptor in androgen-independent prostate cancer cells in vivo.