Trametinib Decreased Intracerebral Hemorrhages and Endothelial-to-Mesenchymal Transition in KRAS G12V -Induced Brain Arteriovenous Malformations in Mice

BACKGROUND: Brain arteriovenous malformations (bAVMs) are a major risk factor for intracerebral hemorrhages in young patients. Recent clinical studies have reported that the majority of human bAVMs harbor somatic KRAS mutations. In our previous study, we confirmed the causal role of endothelial KRAS G12V mutation in bAVM development in mice through hyperactivation of the MEK/ERK (extracellular signal–regulated kinase) pathway. However, the treatment efficacy of targeting MEK/ERK signaling in bAVMs, regarding clinical and biological outcomes, remains unclear. METHODS: In this study, we used the Food and Drug Administration–approved MEK inhibitor, trametinib, to treat mice with bAVMs induced by brain endothelial cell (EC)–specific KRAS G12V overexpression (KRAS G12V/bEC [mice injected with adeno-associated viral-BR1-KRAS G12V ] mice). We treated KRAS G12V/bEC mice with either vehicle or trametinib and evaluated outcomes on mortality and the alteration of bAVMs, and the hemorrhages. We also determined the effect of trametinib on the endothelial-to-mesenchymal transition, which has recently been explored in human bAVMs and implicated in bAVM pathology, in bAVMs of KRAS G12V/bEC mice and cultured mouse ECs transfected with KRAS G12V (EC G12V [EC transfected with the hKRAS G12V gene]). RESULTS: We observed that trametinib significantly improved survivability, potentially through improved vessel integrity and reduction in the severity of bAVM ruptures. Our longitudinal observation of mice bAVMs using noninvasive magnetic resonance imaging revealed that trametinib decreased the total hemorrhagic volume at 8 weeks of treatment when administered at 1 mg/kg compared with the vehicle group, which was confirmed by histological analyses. In addition, trametinib altered endothelial-to-mesenchymal transition by reducing the expression levels of mesenchymal markers (N-Cad [N-cadherin], Slug, CD44) and increasing an EC marker (VE-Cad [vascular endothelial cadherin]) in bAVMs of KRAS G12V/bEC mice. Trametinib also decreased proliferation (Ki-67) and angiogenic (CD34 and pVEGFR2) markers in KRAS G12V/bEC mice’s bAVMs. We also confirmed that trametinib normalized the endothelial-to-mesenchymal transition-associated marker expression and functions in EC G12V . CONCLUSIONS: Our data demonstrate that trametinib improves bAVM pathology by reducing hemorrhagic risk and normalizing endothelial-to-mesenchymal transition. These findings suggest that trametinib is a promising agent to treat patients with bAVM.