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

Abstract

Objective: 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 (PARP inhibitor [PARPi]), versus monotherapy. However putative vascular mechanisms are unknown. PARP plays major role in the activation of TRPM2, a redox-sensitive Ca2+ channel, which is associated with hypertension-induced vascular dysfunction. PARP also regulates sirtuin deacetylases activity, especially sirtuin 1 (SIRT1), which is involved in vascular homeostasis and diseases. Here our aim is to investigate whether VEGFi, via PARP activation, leads to vascular dysfunction through disruption of SIRT1 signalling. Design and method: Human aortic endothelial cells (HAEC) and mouse mesenteric arteries were studied. Cells were exposed to axitinib (VEGFi; 1uM) alone or in combination with olaparib (PARPi; 1uM) in the presence or absence of a SIRT1 activator (SRT1720; 2uM). Wire myograph was used to assess vascular function. Results: Axitinib increased PARP activity in a ROS-dependent manner in HAEC (au: [Veh]0.31 vs. [Axi]0.55; [Tiron+Axi] 0.38] whereas SIRT1 activity was reduced by VEGF inhibition (au: [Veh]33760 vs. [Axi]23367), which was prevented by olaparib. This was followed by an increase in expression of acetyl-p53. Activation of SIRT1 decreased levels of MCP-1 and IL-6 and VCAM-1 and ICAM-1 mRNA levels in HAEC exposed to axitinib, which, similarly to olaparib, was accompanied by a reduction in monocytes adhesion to HAEC. U46619- and ET-1-induced vasoconstriction were increased by axitinib, an effect not observed with axitinib plus Olaparib. Pre-incubation with SRT1720 exacerbated the anti-contractile effects of olaparib. Axitinib impaired ACh-induced vasodilation (% relaxation: 70.5 [Ct] vs. 34.8 [Axi]), which was blocked by olaparib and SRT1720. Phosphorylation of the inhibitory site of eNOS was also increased in HAEC (au: [Veh] 0.18 vs. [Axi] 0.37) and restored by SRT1720. Conclusions: Our data indicate that VEGF inhibition-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 in cancer treatment.