Endovascular thrombectomy (EVT) for acute ischemic stroke is beneficial in patients with acute ischemic stroke caused by large vessel occlusion. Five landmark clinical trials showed that EVT increases the substantial reperfusion rate by approximately 70%-80% and significantly decreased the risk of disability or death at 90 days compared to the control group [1-5]. However, EVT cannot prevent impairments in the ability to live independently in approximately half of patients with acute ischemic stroke [6]. Irreversible ischemic brain injury that has already occurred prior to reperfusion therapy plays a major role in contributing to disability in such cases. Moreover, the ischemic injury may continue even after reperfusion therapy because of incomplete reperfusion or reperfusion injury [7-9].

Nelonemdaz (Neu2000), a novel synthetic derivative of aspirin and sulfasalazine, selectively inhibits the 2B subunit of the glutamate N-methyl-D-aspartate (NMDA) receptor (NR2B) and is a potent scavenger of reactive oxygen species that plays a major role in reperfusion injury after thrombectomy [10,11]. Therefore, nelonemdaz may prevent neuronal injury after EVT by blocking NMDA-receptor-mediated neurotoxicity and free radical injury [12-14].

A previous phase II clinical trial with nelonemdaz revealed its favorable potential to improve clinical outcomes after EVT for acute ischemic stroke with large vessel occlusion without causing serious side effects [15]. The Rescue On reperfusion Damage in cerebral Infarction by Nelonemdaz (RODIN) trial aims to prove the efficacy and safety of nelonemdaz after EVT in acute ischemic stroke with intracranial large vessel occlusion by preventing ischemic and reperfusion injury.

Early clinical trials for neuroprotective molecules targeting either NMDA receptor-mediated excitotoxicity or oxidative stress have failed to identify beneficial effects in patients with acute ischemic stroke despite promising results in animal experiments [20]. Delayed delivery of neuroprotective drugs in clinical trials in comparison with preclinical studies might have caused these failures. Extensive evidence implies that excess activation of NMDA receptors underlies rapidly evolving fulminant neuronal cell necrosis over hours after an ischemic attack, which is accompanied by delayed neuronal and glial cell death occurring over hours and days through excess oxidative stress and apoptosis after reperfusion. The latter is unveiled by the administration of NMDA receptor antagonists, suggesting that blocking a single pathogenic pathway may be insufficient to achieve clinical benefit in ischemic-reperfusion injury. Since 2015, EVT has been approved for patients with acute ischemic stroke and large vessel occlusion, and a large portion of patients with the large vessel occlusion are reportedly reperfused by the treatment [6,21]. Patients who have similar conditions as the ischemia/reperfusion model can be enrolled, and neuroprotection treatment should be revisited [22]. It is conceivable to reason that a multi-target neuroprotection strategy appeals for a maximal prevention of ischemic-reperfusion injury. In this context, nelonemdaz was designed as a dual neuroprotectant that targets both the NMDA receptor and free radicals, the two major drivers of post-stroke neuronal death (Figure 2A) [7-9].

Previously tested NMDA antagonists have been nonselective and potentially too potent, leading to problematic side effects (e.g., psychosis) in humans, possibly accompanied by enhancement in delayed neuronal apoptosis [23,24]. Early clinical trials using NMDA receptor blockers reported higher mortality rates in the treatment group than in the placebo group [25,26], and reported psychological adverse effects among the treated patients [25]. Glutamate receptors purportedly have been proposed to have both pro-survival and pro-death signaling [27]. More specifically, the 2A subunit of the NMDA receptor (NR2A) may have both signaling pathways whereas NR2B may favor a pro-death signaling pathway [8]. Thus, a selective blocking NR2B would be theoretically more effective and safer for the treatment of acute cerebral infarction. The glutamate NR2B-postsynaptic density-95-neuronal nitric oxide synthase (GluN2B-PSD-95-nNOS) complex is one of the downstream death signaling pathways from NR2B, and nerinetide (NA1, Tat-NR2B9c) interferes with the PSD-95 so that the interaction between PSD-95 and NR2B is perturbed. In such a scenario, the glutamate toxicity can be ameliorated [8]. However, unfortunately, the phase III clinical trial, Safety and Efficacy of Nerinetide (NA-1) in Subjects Undergoing Endovascular Thrombectomy for Stroke (ESCAPE-NA1), has failed to show the efficacy of the drug. Again, a new clinical trial, Efficacy and Safety of Nerinetide in Participants With Acute Ischemic Stroke Undergoing Endovascular Thrombectomy Excluding Thrombolysis (ESCAPE-NEXT), is currently ongoing with a revised protocol, considering a drug interaction with alteplase [28].

Nelonemdaz attenuates NMDA-induced currents as a reversible, noncompetitive, and activity-dependent NMDA receptorgating modifier that was revealed to be more specific to NR2B but not to NR2A [11]. The unblocking rate of nelonemdaz from the nelonemdaz-NMDA receptor complex is approximately eight times faster than that of memantine, a moderate NMDA receptor antagonist approved for the treatment of Alzheimer’s disease. These characteristics indicate its additional safety in comparison to high affinity NMDA receptor antagonists that produce neurotoxicity and psychotic symptoms. Neurotoxicity produced by dizocilpine (MK-801), a nonselective NMDA receptor antagonist, is not observed in rodents exposed to supratherapeutic doses of nelonemdaz [10]. In two phase I clinical trials encompassing a total of 165 healthy subjects conducted in the USA and China, administration of nelonemdaz up to 6,000 mg was well tolerated. It was also devoid of any psychological symptoms associated with previous NMDA receptor antagonist drug candidates [12]. A recently published phase II clinical trial for nelonemdaz, Safety and Optimal Neuroprotection of neu2000 in Ischemic Stroke With Endovascular reCanalizion (SONIC), also revealed no serious adverse effects including psychological symptoms [15].

After attenuating glutamate toxicity, nelonemdaz scavenges free radicals in both downstream of NMDA receptor-related excitotoxicity and reperfusion injury (Figure 2B). This is the reason for administering a high dose of nelonemdaz in the beginning, followed by nine successive moderate doses of the drug for both targets. Nelonemdaz effectively controlled free radical production and neuronal death than therapeutic and investigational antioxidants including edaravone, NXY-059, and Trolox in cultured cortical cells exposed to prooxidants such as Fe2+ and buthionine sulfoximine, a glutathione-depleting agent [10]. Nelonemdaz directly and potently removes free radicals as a spin-trapping molecule and displays scavenging activity against hydroxyl radicals, superoxide, nitric oxide, and peroxynitrite [12,13]. The administration of nelonemdaz prevents the production of slowly evolving free radicals in brain regions that undergo neurodegeneration following transient focal cerebral and forebrain ischemia [14,29].

The study design of the RODIN trial, which was based on the results of the phase II SONIC trial, is similar to but slightly different from the ESCAPE-NA1 and ESCAPE-NEXT trials of nerinetide (Table 3) [28,30]. The participant characteristics were almost identical, since both trials included patients with acute ischemic stroke caused by intracranial large vessel occlusion and underwent EVT. The inclusion of neurological deficits and ASPECTS volume may indicate slightly greater disease severity in the RODIN trial than in the ESCAPE-NEXT trial. Moreover, while the ESCAPE-NEXT will involve the administration of a single intravenous infusion of nerinetide, nelonemdaz will be infused intravenously 10 times over 5 days (5,250 mg total) to prevent delayed reperfusion injury in the RODIN trial.

In summary, nelonemdaz targets (1) selective NR2B, the activation of which causes Na⁺ and Ca⁺⁺ influx into neuronal cells and then induces downstream death-signaling pathways, and (2) free radicals, which are released from the downstream pathways of glutamate receptors and subsequent reperfusion injury. In the RODIN phase III trial, the first high dose will be infused for the former target, and then the second to tenth moderate doses will be infused for the latter target. Therefore, the results of this study will show that nelonemdaz treatment improves the functional outcome of acute ischemic stroke patients undergoing reperfusion therapy by the preventing neuronal injury during acute ischemic conditions and prolonged free radical mediated neuronal injury after reperfusion.