Zalsupindole (DLX-001)

Mechanism of action

Low-potency, low-efficacy partial agonist at the serotonin 5-HT2A receptor (HTR2A), a Gq-coupled class-A GPCR, with moderate-efficacy partial agonism at 5-HT2C and antagonism (no measurable agonism) at 5-HT2B. The compound is selective for the 5-HT2 receptor family over 5-HT1A, dopamine receptors, adrenergic receptors and the kappa-opioid receptor. The therapeutic hypothesis is efficacy-threshold separation rather than target separation: zalsupindole activates 5-HT2A with sufficient intrinsic activity to engage the downstream plasticity machinery (protein synthesis, neuritogenesis, spinogenesis; mTOR-pathway participation is suggested by rapamycin-inhibition studies) but with too little intrinsic activity to produce the perceptual signalling of a hallucinogen. Support for a genuinely 5-HT2A-mediated mechanism is that ketanserin, a 5-HT2A antagonist, abolishes the psychoplastogenic effect. In rats the drug is orally bioavailable, brain-penetrant, and produces cortical neuritogenesis in vitro and increased prefrontal dendritic spine density in vivo comparable to or greater than ketamine, psilocybin and N,N-dimethyltryptamine, with rapid and sustained antidepressant-like responses in the forced swim test and VMAT2-deficient models after a single dose — all without the head-twitch response, without hyperlocomotion at therapeutic doses and without a glutamate surge. The absence of 5-HT2B agonism is the stated basis for the lack of cardiovascular safety signals, a known liability of 5-HT2B agonists. In humans the pharmacodynamic footprint is dose- and time-dependent change in resting-state qEEG power spectra (delta and theta) associated with synaptic potentiation, with measurable cerebrospinal-fluid concentrations confirming CNS penetration.

Formulations

Zalsupindole (DLX-001) for Major depressive disorder

Phase 1ActiveMajor depressive disorder indication →

Zalsupindole (DLX-001), an oral non-hallucinogenic neuroplastogen, for major depressive disorder — Delix Therapeutics' lead program and the only indication in which the compound has been dosed in patients. Development to date is two completed studies, NEITHER OF WHICH IS REGISTERED ON ANY PUBLIC TRIAL REGISTRY (see the record comment; ClinicalTrials.gov, EU CTIS and ISRCTN all return zero for the compound and for the sponsor). Phase 1 (initiated 2023-05-09 at the Center for Human Drug Research, Leiden, Netherlands) enrolled 106 healthy volunteers across three parts — placebo-controlled single ascending dose, open-label food effect, and placebo-controlled 7-day multiple ascending dose — covering 2 mg to 360 mg orally; full results were presented at ACNP 2024 on 2024-12-12 showing no serious adverse events, no psychotomimetic, hallucinatory or dissociative effects at any dose, dose- and time-dependent resting-state qEEG change consistent with synaptic potentiation, and measurable cerebrospinal-fluid drug concentrations confirming CNS penetration. Phase 1b (first patient dosed 2024-12-04) was a dose-blinded, single-centre, multiple-dose study in 18 adults with recurrent MDD, randomised to once-daily dosing for 7 days (Cohort A, n=9) or intermittent dosing on Days 1 and 4 (Cohort B, n=9), with in-clinic assessment through Day 8 and follow-up through Day 36; primary endpoints were pharmacodynamic (qEEG, polysomnography) and safety/PK, with MADRS as a preliminary efficacy measure. All 18 participants completed treatment. Topline was announced 2025-10-28: well tolerated with no serious adverse events, the most common treatment-related events transient nausea and headache, no psychotomimetic or dissociative effects and no acute or persistent cognitive impairment on digital cognitive testing, plasma concentrations consistent with target exposures, increased absolute slow-wave delta and theta qEEG power in both cohorts, and approximately 50% MADRS reduction by Day 8 sustained through Day 36 in BOTH the daily and the intermittent cohort. That efficacy signal is uncontrolled (n=18, no placebo arm) and hypothesis-generating. The same release disclosed that the FDA has cleared the IND for a Phase 2 program: multi-site, randomised, double-blind, placebo-controlled, three arms (placebo, once-daily, twice-weekly), with at-home patient self-administration permitted — the first FDA-cleared at-home design for a psychedelic-derived antidepressant and the core of the commercial thesis. As of 2026-07-24 Delix has not announced a Phase 2 start, first patient dosed, or a topline date, and no Phase 2 registration exists, so the program is recorded at phase_1. No discontinuations, dose-arm drops, clinical holds or safety signals have been disclosed; Delix is private, so there is no SEC filing against which to check that.