Anti-angiogenic and apoptotic actions of the natural flavonoid quercetin in a cellular model of Kaposi´s sarcoma.

Abstract

Quercetin (QUE) is a flavonoid that belongs to the family of phytoestrogen and exhibits anticancer properties in multiple types of solid tumor; nevertheless, its effect on virally oncogenic transformed cells is less studied. The viral G Protein-Coupled Receptor (vGPCR) is one of the molecules from the lytic phase of herpesvirus-8 able to induce cellular modifications through a paracrine oncogenic signaling cascade in Kaposi?s sarcoma. We preliminary showed that QUE exerts antiproliferative effects on endothelial cells that stably express vGPCR. In this work, we further explore the mechanism of QUE-induced cell death in vGPCR cells. First, the IC50 of QUE was calculated by crystal violet technique after the treatment of SVEC and vGPCR cells with different concentrations of QUE (1-100 µM) or vehicle (0.1% DMSO) for 48 h. We found that SVEC cells (IC50= 14.09 µM) were more susceptible to QUE treatment than vGPCR cells (IC50= 30.078 µM). Herein, 30 µM of QUE was selected to further characterize the cell death of vGPCR cells. Cell cycle analysis revealed that QUE increase sub G0 phase and reduce S phase of vGPCR treated with QUE for 24 h presuming an apoptotic event. Annexin V/PI stain and caspase-3 activity confirmed that apoptosis takes place in vGPCR cells after QUE treatment. The vGPCR activates and controls the HIF-1α transcription factor promoting the expression of pro-angiogenic molecules such as VEGF. Consistently, qRT-PCR studies indicated that QUE downregulates the expression of HIF-1α and VEGF mRNA in a concentration dependent manner. In conclusion, our findings from this study suggest that QUE promotes its anticancer effects triggering both, anti-angiogenic and pro-apoptotic, program to induce the cell death of the vGPCR cells.