Abstract 162: Everolimus Prevents Vascular Smooth Muscle Cell Proliferation by Repressing Cell Cycle-Dependent Telomerase Activation

Abstract

INTRODUCTION: Everolimus is a potent antiproliferative agent that prevents growth factor-stimulated proliferation of vascular smooth muscle cells and is frequently used as platform for drug-eluting coronary stents to prevent restenosis after coronary artery angioplasty. We have previously demonstrated that telomerase plays a crucial role in vascular smooth muscle cell proliferation. However, whether telomerase is involved in the anti-proliferative activity of everolimus and the putative molecular mechanisms underlying this activity remain elusive. In this study, we assessed the hypothesis that telomerase is a key downstream target for the anti-proliferative activity of everolimus. METHODS AND RESULTS: We demonstrate that everolimus treatment resulted in a dose-dependent inhibition of mitogen-induced telomerase activity in human coronary artery VSMCs (hcVSMCs). Moreover mitogen-induced telomerase reverse transcriptase (TERT) promoter activity and protein expression were dose-dependently repressed by everolimus treatment. Everolimus inhibited mitogen-induced cell proliferation as a result of a G1 →S phase arrest of the cell cycle. In addition, everolimus repressed protein expression of cell cycle-regulated genes (MCM 7, PCNA and Cyclin A) without altering phosphorylation of the retinoblastoma (Rb) protein, being the key gatekeeper of cell cycle transition. In addition, the effects of everolimus were not related to telomere shorting and cellular senescence, supporting the concept of a noncanonical telomere length-independent mechanism. Finally, we demonstrated in transient transfection studies that TERT overexpression abolished the anti-proliferative effect of everolimus in hcVSMC, pointing to a key role of telomerase as a target for the anti-proliferative effects of everolimus. CONCLUSIONS: These results indicate that telomerase constitutes a key target for the anti-proliferative activity of everolimus and identify a novel mechanism for the inhibition of hcVSMC proliferation.