O6-methylguanine-DNA methyltransferase inhibition leads to cellular senescence and vascular smooth muscle dysfunction

Inhibiting O6-methylguanine-DNA methyltransferase (MGMT) is crucial for overcoming chemoresistance to alkylating agents, though its use is limited by myelosuppression. Beyond bone marrow, other adverse effects were not studied. Given chemotherapy-induced senescence in healthy tissues, e.g., cardiovascular damage, we investigated the impact of the MGMT inhibitor O6-benzylguanine (BG) on aortic vascular smooth muscle cells (VSMCs) and aorta. Starting on day 3 of BG incubation, VSMCs exhibited altered morphology, reduced growth, increased SAβGal activity and elevated senescence markers p27 or γH2A.X. BG activated senescence-related pathways, including Erk1/2, p38α, Akt and mTORC1; induced BCl2, MnSOD and CDK1; and decreased αSMA and skp2 levels. These changes suggest BG-induced γH2A.X, p38 and Akt activation, resulting in G2/M cell cycle arrest via pCDK1. Functionally, BG impaired the vascular reactivity of aortic rings to phenylephrine, isoprenaline and sodium nitrite. In rats, systemic BG administration similarly reduced the response to sodium nitrite but left phenylephrine and isoprenaline responses unchanged. Our findings highlight BG's potential adverse effects on vascular smooth muscle, marked by senescence activation and reduced vascular reactivity. These results emphasise the need for caution in the clinical use of MGMT inhibitors. Furthermore, we present the model of senescence in primary VSMCs characterised by the expression of several senescence markers and G2/M checkpoint arrest.