Rapastinel

What is Rapastinel?#

Rapastinel (GLYX-13, BV-102) is a synthetic amidated tetrapeptide with the sequence Thr-Pro-Pro-Thr-NH2 and a molecular weight of 413.47 Da (C18H31N5O6, CAS 117928-94-6). It was developed by Naurex, Inc. (later acquired by Allergan in 2016) as a novel rapid-acting antidepressant targeting the NMDA receptor.

Rapastinel received FDA Fast Track designation in 2014 and Breakthrough Therapy designation in 2016 for adjunctive treatment of major depressive disorder (MDD), based on promising phase 2 data showing rapid onset of antidepressant effects. However, all three pivotal phase 3 trials failed in March 2019, and clinical development was discontinued.

Mechanism of Action#

Rapastinel acts as a functional partial agonist at the glycine binding site of the NMDA (N-methyl-D-aspartate) receptor, a subtype of ionotropic glutamate receptor critical for synaptic plasticity, learning, and memory.

NMDA Receptor Modulation#

The NMDA receptor requires binding of both glutamate and a co-agonist (glycine or D-serine) for activation. Rapastinel binds to a novel site on the NMDA receptor complex and enhances glutamate-mediated NMDA receptor activity at therapeutically relevant concentrations. Importantly, rapastinel does not block the ion channel (as ketamine does) but rather modulates the receptor's response to endogenous glutamate signaling.

Synaptic Plasticity Enhancement#

By enhancing NMDA receptor function, rapastinel promotes long-term potentiation (LTP) at excitatory synapses, a cellular mechanism underlying learning and memory. This enhanced synaptic plasticity in prefrontal cortex and hippocampal circuits is hypothesized to underlie the antidepressant effects, which are convergent with (but mechanistically distinct from) those of NMDA antagonists like ketamine.

Advantages Over Ketamine#

Unlike ketamine and other NMDA antagonists, rapastinel does not produce psychotomimetic symptoms, dissociation, cognitive impairment, or abuse potential. This favorable side effect profile was a major driver of clinical interest, as it suggested the possibility of a rapid-acting antidepressant without the safety and regulatory challenges associated with ketamine.

Research Overview#

Rapastinel's clinical development spanned from early 2000s preclinical work through phase 3 failure in 2019. The compound demonstrated promising efficacy signals in phase 2 but failed to replicate these results in the pivotal trials needed for FDA approval.

Phase 2 Success#

Preskorn et al. (2015) reported the key phase 2 proof-of-concept trial in which a single IV dose of GLYX-13 (5 or 10 mg/kg) reduced Hamilton Depression Rating Scale scores within 2 hours in patients with treatment-resistant MDD. The antidepressant effects lasted approximately 7 days following a single dose, without dissociative or psychotomimetic side effects.

Phase 3 Failure#

In March 2019, Allergan announced that three phase 3 studies failed to differentiate rapastinel from placebo on the primary endpoint. The reasons for the failure have not been fully elucidated but may include higher-than-expected placebo response rates, challenges in dose selection for the phase 3 population, and the inherent difficulty of developing IV-administered medications for outpatient depression treatment.

Important Considerations#

• Clinical development has been discontinued following phase 3 failure
• Administration requires intravenous infusion, limiting practical utility
• The phase 3 failure does not invalidate the NMDA modulation hypothesis for depression but raises questions about rapastinel's specific therapeutic utility
• Rapastinel remains a valuable research tool for studying NMDA receptor pharmacology and rapid-acting antidepressant mechanisms

Key Research Findings#

Randomized Proof of Concept Trial of GLYX-13, an N-Methyl-D-Aspartate Receptor Glycine Site Partial Agonist, in Major Depressive Disorder Nonresponsive to a Previous Antidepressant Agent, published in Journal of Psychiatric Practice (Preskorn S et al., 2015; PMID: 25782764):

Phase 2 proof-of-concept trial demonstrating that a single IV dose of GLYX-13 (5 or 10 mg/kg) produced rapid-onset antidepressant effects within 2 hours, lasting up to 7 days, without psychotomimetic side effects.

• GLYX-13 at 5 and 10 mg/kg reduced HDRS-17 scores at days 1-7 vs placebo
• Onset of antidepressant effect within 2 hours of single IV dose
• Inverted U-shaped dose-response curve (1 and 30 mg/kg not significant)

The Development of Rapastinel (Formerly GLYX-13); A Rapid Acting and Long Lasting Antidepressant, published in Current Neuropharmacology (Moskal JR et al., 2017; PMID: 26997507):

Review of rapastinel's development history, mechanism of action, and preclinical and clinical evidence supporting its potential as a rapid-acting antidepressant.

• NMDA receptor glycine site partial agonism enhances synaptic plasticity
• Antidepressant effects converge with ketamine pathway without side effects
• Promotes LTP and metaplasticity in prefrontal cortex and hippocampus

Related Reading#

• Rapastinel research studies and evidence
• Rapastinel dosing protocols
• Rapastinel side effects profile
• Semax research guide
• Selank research guide