ESCAPE-NA1 Trial Brings Hope of Neuroprotective Drugs for Acute Ischemic Stroke: Highlights of the Phase 3 Clinical Trial on Nerinetide

Stroke is a leading disease for morbidity and the second leading cause of mortality following ischemic heart disease. The health burden for stroke ranks the fourth of all diseases as measured in disability-adjusted life years [1]. Worldwide annual new stroke incidence is approximately 16 million with the increasing trend of an epidemic due to the aging population [2]. Despite significant progress in the management of stroke with the introduction of thrombolytic and endovascular thrombectomy therapies in recent years, a large number of patients are still left without any effective treatment due to delayed time windows and contraindications. Furthermore, these therapeutic interventions can only be used in a small fraction of stroke patients in centralized hospitals. For these reasons, neuroprotective therapy is urgently needed. However, even though thousands of neuroprotective drugs have been tested preclinically and clinically, there is no effective neuroprotective drug available for stroke [3]. The failure in neuroprotective drug development for stroke is frustrating and the hopeless situation has forced scientists shift attention from early neuroprotection to delayed mechanisms of stroke-related co-morbidities, regeneration, and plasticity [2].

A recent phase III clinical trial (ESCAPE-NA1) on the novel drug candidate nerinetide in acute ischemic stroke (AIS) certainly brings a new hope for neuroprotection [4]. Nerinetide is a neuroprotective eicosapeptide that suppresses the interaction of NMDAR/post-synaptic density protein 95 (PSD-95) to prevent the neurotoxic signaling of nNOS in AIS. It has proven effective in animal models, in particular in a primate model, to protect nerve tissue and function against ischemia/reperfusion injury [5]. A randomized, double-blind, placebo-controlled phase 2 trial in patients with iatrogenic stroke after endovascular aneurysm repair (ENACT) showed that this drug is safe and efficacious in reducing the infarct volume in the brain [6]. The ESCAPE-NA1 study was initiated based on the positive results of preclinical and clinical studies.

The study recruited 1105 acute ischemic stroke patients with large vessel occlusion within a 12-h treatment window between the first of March 2017 and the 12th of August, 2019 from 48 acute stroke care hospitals in 8 countries. The inclusion criteria include adults of 18 years or older suffering from disabling ischemic stroke with an Alberta Stroke Program Early CT Score (ASPECTS) > 4, moderate-to-good collateral circulation as diagnosed by multiphase CT angiography, and prior treatment with or without thrombolytic and/or declared endovascular thrombectomy at the time of randomization. All participants were randomized (1:1) to receive a single IV dose of nerinetide at 2.6 mg/kg, or saline placebo in a blind manner to all patients, the trialing personnel, and investigators. Patients were further stratified by IV alteplase treatment and declared endovascular device choice. The primary outcome was a favorable functional outcome at 90 days after stroke as assessed by a modified Rank Scale (mRS) score of 0–2. A number of secondary outcomes have also been investigated.

The result showed that there was no significant difference in the primary outcome of mRS score 0–2 at 90 days after stroke between the nerinetide group (337/549) and the placebo group (329/556) (adjusted risk ratio 1.04, 95% CI 0.96–1.14; P = 0.35). There was also no difference in the secondary outcomes. However, the trial found that there was a treatment effect of nerinetide in patients without the usual care of thrombolytic therapy with alteplase. In the stratum of patients without alteplase, 49.8% (113/227) receiving placebo achieved an mRS score 0–2, whereas 59.3% (130/219) receiving nerinetide achieved an mRS score 0–2 (adjusted RR 1.18, 95% CI 1.01–1.38). In addition, the trial also found a 7.5% risk reduction in mortality in the nerinetide subgroup of patients without using alteplase at 90 days, resulting in nearly 50% reduction in hazard of death (adjusted HR 0.56, 95% CI 0.35–0.95). Furthermore, the imaging data showed a reduction in infarction volume in the nerinetide subgroup with no alteplase treatment whereas no difference in infarction volume was found between subgroups of patients treated with alteplase. These findings suggest that there is a possible drug interaction between nerinetide and alteplase that suppresses the therapeutic effect of nerinetide.

While the overall result of this phase III trial is disappointing and fails to generate a new effective drug for AIS, it brings hope that developing a neuroprotective drug for acute ischemic stroke is possible. The trial also teaches a number of lessons on neuroprotective drug clinical trials. First, this trial is innovative in its design and the first large-scale trial to include patients undergoing both thrombolytic and thrombectomy therapies. This kind of design is clearly advantageous and necessary as both therapies have proven effective and become routine protocols for AIS in the stroke centers of any large hospitals [7]. Second, the time window of 12 h chosen for the intervention is also well thought out with strong rationales, based on the therapeutic windows of alteplase at 4.5 h and endovascular stent removal or suction of thrombosis within 12 h after onset. This design is also based on the preclinical primate trial where the same dose of drug was administered 3 h after stroke [5]. This time window is feasible as it falls within the duration of the onset-to-randomization time from 109 to 541 min. Theoretically, a neuroprotective drug should be used as soon as possible. One of the reasons for the failure of clinical trials on neuroprotective drugs is longer intervention time windows, which may generate a large variation. The third important improvement in the design is to use ASPECTS > 4 as an inclusion criterion to select patients with moderate-to-good collateral circulation as determined by multiphase CT angiography. Inclusion of this criterion is reasonable because only those patients with a relatively large area of penumbra can benefit from a neuroprotective drug. Patients with an infarction without any penumbra are unlikely to benefit from neuroprotective drugs as the infarct core has already undergone necrosis.

The most important information we have learnt from this trial is the creative design of the stratification and randomization of AIS patients with or without the alteplase therapy, which generated “unexpected” data useful for future studies. The positive results were obtained from an exploratory analysis indicating that patients not using alteplase can benefit from the study drug nerinetide. This result is very exciting, suggesting that NMDAR excitotoxic signaling is a valid target for the neuroprotective drugs to treat AIS in patients. Nerinetide is designed as a fusion peptide of the 11 amino-acid (aa) HIV Tat peptide with 9 aa from the C-terminus of the NR2B subunit of the N-methyl-D-aspartate receptor (NMDAR) [8], which is critical for the physiological regulation of synaptic plasticity by glutamate-activated Ca²⁺ entry through this ionotropic receptor (Fig. 1). In the pathological ischemic condition, released glutamate activates NMDARs. Consequently, the C-terminus of its subunit NR2B interacts with PSD-95 which activates neuronal nitric oxide synthase (nNOS). The overproduction NO by nNOS leads to the death of neurons (Fig. 1A). This pathological NMDAR-regulated NO signaling via PSD-95 is uncoupled from its regulated Ca²⁺ entry so that nerinetide can block NO signaling by competitive inhibition of the NMDAR-PSD-95 interaction without perturbing the Ca²⁺ signaling [8]. Indeed, this trial demonstrated a potential efficacy of nerinetide (NA1) in patients without using alteplase (Fig. 1B).

Fig. 1.

Schematic showing the interaction between alteplase and nerinetide. A A stroke elicits acute neurotoxicity mediated by the NMDAR/PSD-95/nNOS/NO signaling pathway. B The neuroprotective mechanism of nerinetide (NA1). C The potential drug-drug interaction between alteplase and nerinetide that negates its therapeutic benefit.

Unfortunately, the overall data failed to generate a positive result due to the unexpected action of alteplase on the drug peptide. Alteplase activates plasmin, which degrades the thrombotic clot to promote reperfusion. The pharmacokinetic profile of nerinetide showed that the drug exposure in patients with alteplase is much less (about 30%) than that without alteplase [4], indicating that nerinetide is also a target of plasmin for degradation, leading to inefficacy in AIS patients with alteplase (Fig. 1C).

Can we improve future trials based on the lessons learnt? At least two critical factors should be considered based on the known pharmacology of nerinetide in future trials. First, it is possible to titrate the dose in the presence of alteplase so that the drug exposure matches that in the absence of alteplase. The selected high dose of nerinetide should be tested for tolerability and safety in patients using alteplase. Potential side-effects are less likely as tPA-activated degradation can prevent any overdose. This approach should be applied to the development process of all peptide/protein drug candidates that are likely to be co-administered with alteplase. Second, in my opinion, a single dose of nerinetide may not be an optimal choice, despite preclinical trials showing its effectiveness [5, 9]. Based on the pharmacokinetics profile, it is clear that this peptide drug has a very short half-life. It is estimated that t_max is approximately 10 min and t_1/2 is < 10 min after IV injection. And the drug disappears completely from the blood in 60–120 min [4]. The excitotoxicity after stroke usually lasts from hours to days post-AIS. We envisage that multiple doses within the first 24 h would have more benefit in neuroprotection than a single dose. Future drug development of targeting the NMDAR-PSD-95 pathway should consider long half-life small molecules or novel technology to prevent degradation of the peptide drug.

The result of the trial encourages the current development of other neuroprotective drugs. We know that thrombolytic therapy and endovascular thrombectomy already occupy a major position in the management of AIS without much room for improvement. However, there is much work to be done in both neuroprotection and rehabilitation to achieve maximal functional recovery after AIS. Excitotoxicity, oxidative stress, apoptosis, and autophagy are excellent targets for the development of neuroprotective drugs. The ESCAPE-NA1 trial certainly negates the hopeless perception in the field of neuroprotective drug development. Investigations on inflammation, secondary degeneration, stem cell therapy, and exercise in the rehabilitation stage are also critical to achieve optimal functional recovery and prevent the detrimental secondary consequences of AIS.

Conflict of Interests

The author declares no conflict of interest.