Abstract Body: Neurovascular disorders- including stroke, brain aneurysm, and vascular malformations- strike an estimated seven million Americans annually and can lead to vascular pathologies, neurological disability, and death. Brain arteriovenous malformation (bAVM) is a neurovascular disease characterized by abnormally enlarged arteriovenous connections that shunt high-pressure, low-resistance blood flow directly from artery to vein, bypassing the normal capillary network. Research suggests that 95% of bAVMs are sporadic with vast genetic heterogeneity, and current treatments are invasive and not applicable to all patients. There are currently no Food and Drug Administration-approved bAVM treatments, highlighting a critical need for mechanistic-based pharmacological therapies. In our endothelial Rbpj-deficient (mutant) mouse model of bAVM, we determined molecular and cellular abnormalities to brain vessels, including increased arteriovenous connections diameter (shunts vs capillaries), abnormal endothelial cell (EC) shape, increased vessel permeability, and altered gene expression in mutant mice compared to controls, contributing to impaired vascular remodeling. Most notably, transcript expression data from RNA-seq and quantitative PCR showed increased Adrenomedullin (AM) expression, sustained over time, in Rbpj-deficient brain ECs compared to controls. Our ChIP-sequencing data identified AM as a direct binding target of transcription factor Rbpj, a downstream effector of canonical Notch signaling. Our data, with recent studies that showed increased AM expression in human bAVM tissue, suggest AM as a potential therapeutic target during bAVM pathogenesis. Utilizing small molecule compound NSC16311 that prevents AM from binding its receptor, our work is testing whether in vivo administration of NSC16311 (four experimental cohorts, n = 12) during early bAVM pathogenesis effectively inhibits AM signaling and prevents bAVM features by evaluating expression levels of downstream effectors in AM signaling and assessing arteriovenous diameter, EC shape (length/width), vascular permeability (10kDa fluorescent dextran injection), and survivability in endothelial Rbpj-deficient mice. This study will determine whether the abnormalities observed in Rbpj-deficient brain ECs function, at least in part, through AM signaling and will test the therapeutic potential of inhibiting the AM signaling pathway to prevent EC abnormalities and bAVM formation.