Clinical development of the GluN2B-selective NMDA receptor inhibitor NP10679 for the treatment of neurologic deficit after subarachnoid hemorrhage

Aneurysmal subarachnoid hemorrhage (SAH) may be associated with cerebral vasospasm, which can lead to delayed cerebral ischemia, infarction, and worsened functional outcomes. The delayed nature of cerebral ischemia secondary to SAH-related vasculopathy presents a window of opportunity for the evaluation of well tolerated neuroprotective agents administered soon after ictus. Secondary ischemic injury in SAH is associated with increased extracellular glutamate, which can overactivate N-methyl-d-aspartate receptors (NMDARs), thereby triggering NMDAR-mediated cellular damage. In this study, we evaluated the effect of the pH-sensitive GluN2B-selective NMDAR inhibitor NP10679 on neurologic impairment after SAH. This compound demonstrates a selective increase in potency at the acidic extracellular pH levels that occur in the setting of ischemia. We found that NP10679 produced durable improvement of behavioral deficits in a well characterized murine model of SAH, and these effects were greater than those produced by nimodipine alone, the current standard of care. In addition, we observed an unexpected reduction in SAH-induced luminal narrowing of the middle cerebral artery. Neither nimodipine nor NP10679 alters each other's pharmacokinetic profile, suggesting no obvious drug-drug interactions. Based on allometric scaling of both toxicological and efficacy data, the therapeutic margin in humans should be at least 2. These results further demonstrate the utility of pH-dependent neuroprotective agents and GluN2B-selective NMDAR inhibitors as potential therapeutic strategies for the treatment of aneurysmal SAH. SIGNIFICANCE STATEMENT: This report describes the properties and utility of the GluN2B-selective pH-sensitive N-methyl-d-aspartate receptor inhibitor, NP10679, in a well characterized rodent model of subarachnoid hemorrhage. We show that the administration of NP10679 improves long-term neurological function following subarachnoid hemorrhage and that in rats, there are no drug-drug interactions between NP10679 and nimodipine, the standard of care for this indication.