Tamoxifen inhibits endothelial cell proliferation and attenuates VEGF-mediated angiogenesis and migration in vivo

Introduction: Angiogenesis is fundamental to tumour growth and vascular endothelial growth factor (VEGF) is one of the most potent proangiogenic cytokines known. We have previously demonstrated that tamoxifen reduces serum VEGF in certain cancer patients. We hypothesized that tamoxifen may attenuate the angiogenetic response to VEGF. Methods: Human dermal microvessel endothelial primary cell cultures (HMEC) were incubated with tamoxifen (1.25–5.0 μg) or vehicle. Cell proliferation was quantified using 5-bromo-2′-deoxyuridine (BrdU) labelling endothelial cell proliferation assay. The effect of oral tamoxifen (20 mg/day) on VEGF-mediated angiogenesis in vivo was assessed using a Matrigel angiogenesis assay in the Sprague–Dawley rat. Results: Tamoxifen (5.0 μg/ml) significantly reduced HMEC proliferation over 24 h when compared with cells treated with vehicle alone. Oral administration of tamoxifen in the rat (20 mg/day) significantly reduced endothelial cell proliferation and migration in response to VEGF. Conclusion: Tamoxifen (5.0 μg/ml) reduces proliferation of a VEGF-dependent endothelial cell line in vitro. In vivo, orally administered tamoxifen reduces VEGF-mediated angiogenesis in the rat. These findings indicate that tamoxifen may directly inhibit the effect of VEGF on the endothelial cell, in addition to its previously described effect of reducing serum VEGF levels. This data supports a role for tamoxifen in modulation of the VEGF-dependent angiogenic response to surgical trauma, particularly as an adjuvant therapy for VEGF-dependent tumours.