Abstract 41: Synthesis And Pharmacological Validation Of Novel Neuroprotective Purinergic Receptor P2X4 Antagonists For The Treatment Of Ischemic Stroke

Background and Purpose: Identification of a novel treatment for ischemic stroke is urgently needed. We previously showed that genetic deletion as well as short term pharmacological inhibition of P2X4R, a purinergic receptor for adenosine triphosphate ATP, provides acute neuroprotection and thus can be potential drug targets to treat ischemic stroke. Here we synthesized and pharmacologically validated those experimental drugs for the treatment of ischemic stroke. Methods: We first performed the P2X4 receptor structure activity (SAR) relationship based on known heterocyclic antagonist P2X4 antagonists including NP-1815-PX Following extensive modification of the reported synthetic route, we synthesized several analogues that maintained or enhanced antagonist affinity. We used [Ca 2+ ] i influx assay in P2X4R overexpressing human HEK cells to identify potent and specific P2X4R antagonist. Two most potent leads (MRS4719 and 4596 given subcutaneously for 3 days post stroke) were then tested for their neuroprotective activity using middle cerebral artery occlusion (MCAo) model of ischemic stroke (60 min MCAo followed by 3 days of reperfusion) using both sexes of young and aged mice. MRS4719 was also tested in human primary monocyte derived macrophage obtained from the blood of de-identified aged healthy subjects (55±10 years). Results: Analogues MRS 4719 and MRS4596 were most potent at human (h) P2X4R (IC 50 0.503 and 1.38 μM, respectively), and were highly selective versus hP2X1R, hP2X2/3R, hP2X3R). Both MRS 4719 and MRS 4596 showed neuroprotective effects after 3 days of ischemic stroke in a dose dependent manner in young mice (8-12 weeks old). Optimal dose of MRS4719 (1.5 mg/kg/day) also significantly reduced infarct volume (59.6±5.3 vs. 27.47±10.23 mm 3 ; p<0.05) in middle-aged mice (11-12 months). MRS 4719 showed learning and memory enhancing activity when measured after 4 weeks of stroke. MRS 4719 inhibited ATP-induced [Ca 2+ ] i influx in primary human monocyte-derived macrophages, consistent with its blocking effect at endogenously expressed P2X4R. Conclusions: This study indicates MRS4719 is a potent P2X4R antagonist and has translational potential for the treating of ischemic stroke across the age.