P169 VEGF INHIBITION-INDUCED PARP OVERACTIVATION LEADS TO ENDOTHELIAL DYSFUNCTION AND INFLAMMATION: ROLE OF SIRTUIN 1 SIGNALLING

Hypertension is a common unwanted effect of VEGF inhibitors (VEGFi), which are used as anti-angiogenic drugs in cancer treatment. Clinical observations indicate that the magnitude of blood pressure elevation is lower in patients with cancer who are treated with combination VEGFi and olaparib (poly-ADP ribose polymerase[PARP] inhibitor[PARPi]), versus monotherapy. However, putative vascular mechanisms are still unknown. PARP plays a major role in the activation of TRPM2, a redox-sensitive Ca2+ channel associated with hypertension-induced vascular dysfunction, and sirtuin deacetylases activity, especially sirtuin 1 (SIRT1), which is involved in vascular homeostasis/diseases. Here we sought to determine whether VEGFi-induce oxidative stress and PARP activation lead to vascular dysfunction through disruption of SIRT1 signalling. Human aortic endothelial cells (HAEC) and mouse mesenteric arteries were studied. Cells were exposed to axitinib (VEGFi;1 μM) alone or in combination with olaparib (PARPi;1 μM) in the presence or absence of a SIRT1 activator (SRT1720;2 μM). Axitinib increased PARP activity in a ROS-dependent manner (au:[Veh] 0.31 vs. [Axi] 0.55; [Tiron+Axi] 0.38] whereas SIRT1 activity was reduced by VEGF inhibition (33760 vs. 23367), which was prevented by olaparib. Expression of acetyl-p53 (au: 0.17 vs. 0.35) was increased. SIRT1 activation decreased levels of MCP-1 and IL-6 and reduced mRNA expression of VCAM-1 and ICAM-1 in HAEC exposed to axitinib, which was accompanied by a reduction in monocyte adhesion to HAEC, as observed for olaparib. U46619- and ET-1-induced vasoconstriction were increased by axitinib (U4:101.2[Ct] vs. 141.4[Axi]-ET-1:122.6[Ct] vs. 152.5[Axi]), an effect not observed with axitinib plus olaparib. Pre-incubation with SRT1720 exacerbated the anti-contractile effects of olaparib. Axitinib impaired ACh-induced vasodilation (%70.5 vs. 34.8), which was blocked by olaparib and SRT1720. Phosphorylation of eNOS (Thr495) was increased in HAEC (au: 0.18 vs. 0.37) and restored by SRT1720. In conclusion, our findings show that VEGFi-induced PARP overactivation leads to endothelial dysfunction and inflammatory responses via disruption of SIRT1 signalling. We define a putative vasoprotective effect of olaparib that may ameliorate vascular injury induced by VEGFi during cancer treatment.