ASP-4345 — Safety, Research, Risks & Legal Status

Not medical advice. ASP-4345 is discussed here for informational and harm-reduction purposes only. We do not endorse use, and any dosing context is informational, not a protocol.

Also known as	ASP4345; CAS 1632257-75-0
Category	Research Chemical
Developer	Astellas Pharma
CAS Number	1632257-75-0
Mechanism class	Dopamine D1 receptor positive allosteric modulator (PAM)
Highest clinical phase	Phase 2a (discontinued; primary endpoint not met)
Primary indication studied	Cognitive impairment associated with schizophrenia (adjunctive to stable antipsychotics)
Pharmacokinetics (oral)	Tmax 1.0-3.0 hours; elimination half-life 9.1-26.8 hours; once-daily dosing evaluated
US legal status	Unapproved investigational drug in the United States. ASP-4345 was studied under an Astellas Pharma IND but never received FDA approval. Development was discontinued after Phase 2 failure (circa 2021). It carries no ATC code and is not available as a supplement or approved pharmaceutical. Any circulating material would be classified as an unapproved drug or research chemical not intended for human use.

What is ASP-4345?

ASP-4345 is a small-molecule dopamine D1 receptor positive allosteric modulator (PAM) developed by Astellas Pharma as an adjunctive treatment for cognitive impairment in schizophrenia. Unlike direct D1 agonists or partial agonists, it binds an allosteric site on the D1 receptor and potentiates the effect of endogenous dopamine rather than activating the receptor independently. The program reached Phase 2a clinical trials but was discontinued after failing its primary efficacy endpoint.

How it works

ASP-4345 selectively binds an allosteric site on the dopamine D1 receptor, enhancing dopamine-mediated signaling at that receptor without directly activating it. This positive allosteric modulation (PAM) mechanism is mechanistically distinct from D1 partial agonism: a PAM requires endogenous dopamine to be present and amplifies its effect, theoretically producing a ceiling tied to physiological dopamine release and potentially reducing off-target dopaminergic adverse effects seen with full or partial agonists. The therapeutic rationale was that prefrontal cortex D1 signaling is critical for working memory and executive function, and that augmenting this pathway might address the cognitive deficits of schizophrenia unaddressed by antipsychotics. Phase 1 electrophysiological work confirmed CNS engagement via auditory steady-state response (ASSR) and mismatch negativity (MMN) biomarkers, providing mechanistic proof-of-concept that the compound reached relevant neural circuits.

Background & history

ASP-4345 was developed by Astellas Pharma and entered human trials in the mid-to-late 2010s targeting the longstanding unmet need of cognitive impairment associated with schizophrenia (CIAS). A Phase 1 randomized study assessed safety, tolerability, and pharmacodynamic effects across four dose levels (3-150 mg) in patients with schizophrenia maintained on stable antipsychotics. That study reported favorable tolerability and modest-to-moderate cognitive and electrophysiological signals, supporting Phase 2 advancement. The Phase 2a study (NCT03557931), a 12-week double-blind placebo-controlled trial in approximately 210 participants comparing 50 mg and 150 mg doses, failed to demonstrate improvement on the MATRICS Consensus Cognitive Battery (MCCB) composite score -- the field's standard primary endpoint for CIAS trials. Development was discontinued; as of March 2021, no active development was reported. The compound joins a long list of D1-pathway agents that showed preclinical and Phase 1 promise but did not replicate in Phase 2 CIAS trials.

What the research says

Human data are limited to two completed trials. The Phase 1 study (n=36, four dose levels, patients on stable antipsychotics) reported that 80.6% of ASP-4345-treated participants experienced treatment-emergent adverse events versus 75% on placebo -- a difference consistent with noise at this sample size and severity distribution. Cognitive signals included moderate-to-large psychomotor function improvements across doses and modest visual attention gains; working memory enhancement was limited. Electrophysiology biomarkers (ASSR, MMN) showed modest-to-moderate improvements; P3a was unchanged. The Phase 2a trial (NCT03557931), the definitive efficacy test, did not meet its primary endpoint (MCCB composite change from baseline). No secondary cognitive endpoints demonstrating meaningful separation from placebo have been publicly reported. The negative Phase 2 outcome is the most informative data point: under rigorous controlled conditions with an adequate sample and validated endpoint, the compound did not demonstrate cognitive benefit in this population. No data exist in healthy populations, other psychiatric diagnoses, or non-schizophrenia cognitive disorders.

Reported effects

Positive allosteric modulation of dopamine D1 receptors -- potentiates endogenous dopamine signaling rather than directly activating the receptor
Modest-to-moderate psychomotor and visual attention improvements observed in Phase 1 (small n, no placebo-controlled working memory benefit)
Electrophysiological markers of cortical engagement (ASSR, MMN) modestly improved in Phase 1; P3a unaffected
No significant cognitive benefit demonstrated in Phase 2a placebo-controlled trial in schizophrenia (primary endpoint not met)
Did not induce extrapyramidal symptoms, movement disorders, mood alterations, or suicidality signals in clinical trials
Most common adverse events in trials were headache and somnolence, both mild and not substantially exceeding placebo rates

Dosing & administration (informational)

Published Phase 1 literature evaluated oral doses of 3, 10, 50, and 150 mg once daily. The Phase 2a trial used 50 mg and 150 mg once-daily arms. Reported pharmacokinetics: time to peak plasma concentration 1.0-3.0 hours post-dose; elimination half-life 9.1-26.8 hours, consistent with once-daily dosing. These parameters are reported here strictly as literature context. This is not a dosing protocol or recommendation. The compound has no approved indication, no established therapeutic dose, and no safety profile validated for unsupervised use. Consult a licensed clinician before considering any investigational compound.

This is general research/context information, not medical advice or a recommended protocol.

Safety & side effects

No serious adverse events or safety signals identified in Phase 1 or Phase 2a at doses up to 150 mg
Most common treatment-emergent adverse events were headache and somnolence, classified as mild
No extrapyramidal symptoms, tardive dyskinesia, or other movement disorders reported
No suicidality or mood destabilization signals observed
No clinically meaningful cardiovascular, hepatic, or metabolic signals reported in available summaries
Phase 2 sample size (~210) was powered for efficacy, not comprehensive rare-event safety surveillance; long-term safety is unknown given program discontinuation
No human data exist outside of schizophrenia patients on stable antipsychotics -- safety in other populations is entirely unknown

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Who should avoid it

Use outside a formal clinical trial or medical supervision -- no approved indication exists
Use as a substitute for antipsychotic therapy in schizophrenia -- it was studied only as adjunctive therapy in stabilized patients
Assumptions of cognitive benefit based on Phase 1 signals -- the Phase 2a controlled trial did not replicate efficacy
Combining with dopaminergic agents, stimulants, or other D1-pathway compounds without medical oversight -- interaction profile unknown
Use in pregnancy, pediatric populations, or elderly -- no data exist in these groups
Sourcing from unregulated chemical suppliers for human self-administration -- no pharmaceutical quality controls apply

How it is commonly combined

No evidence base exists for combining ASP-4345 with other compounds. The clinical trials studied it exclusively as adjunctive therapy in patients already on stable antipsychotics. Any stacking rationale (e.g., with other nootropics or dopaminergic agents) would be entirely speculative and unsupported by data.

Legal & regulatory. Unapproved investigational drug in the United States. ASP-4345 was studied under an Astellas Pharma IND but never received FDA approval. Development was discontinued after Phase 2 failure (circa 2021). It carries no ATC code and is not available as a supplement or approved pharmaceutical. Any circulating material would be classified as an unapproved drug or research chemical not intended for human use.

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Frequently asked questions

What makes ASP-4345 a PAM rather than a D1 agonist or partial agonist?

A positive allosteric modulator binds a site on the receptor distinct from the endogenous ligand binding site and enhances the receptor's response to dopamine when dopamine is present. It does not activate the receptor on its own. A partial agonist, by contrast, binds the orthosteric (dopamine) site and produces submaximal receptor activation independent of endogenous dopamine. The distinction matters clinically: a PAM's effect is theoretically ceiling-limited by endogenous dopamine release, which may reduce risks of excessive dopaminergic stimulation.

Did ASP-4345 show any benefit in clinical trials?

Phase 1 data in a small sample (n=36) suggested moderate-to-large psychomotor improvements and modest electrophysiological changes suggesting CNS engagement. However, the Phase 2a placebo-controlled trial (NCT03557931, approximately 210 participants, 12 weeks) failed its primary endpoint -- the MATRICS Consensus Cognitive Battery composite score. The Phase 2 outcome is the more informative result; Phase 1 signals did not replicate under rigorous controlled conditions.

Why was the program discontinued?

Astellas discontinued development following the Phase 2a efficacy failure. The compound did not demonstrate statistically significant cognitive benefit versus placebo on the MCCB composite, the primary endpoint. This is consistent with a broader pattern in CIAS drug development where Phase 1 cognitive signals have frequently failed to replicate in Phase 2 placebo-controlled trials.

What dose was studied and what were the pharmacokinetics?

Phase 1 studied 3, 10, 50, and 150 mg oral doses; Phase 2a used 50 mg and 150 mg once-daily arms. Time to peak plasma concentration was 1.0-3.0 hours and the elimination half-life was 9.1-26.8 hours, supporting once-daily oral dosing. These are literature-reported parameters from the discontinued program and are not a dosing recommendation. Any clinical use would require consultation with a licensed clinician.

Is ASP-4345 available or legal to obtain?

ASP-4345 was never approved by the FDA and has no approved indication anywhere. It is an unapproved investigational drug. Chemical suppliers may list it under its CAS number as a research compound, but such material is not manufactured to pharmaceutical standards and is not approved for human consumption. Acquiring or using it outside a formal clinical trial context raises both legal and safety concerns.

Are there safer, evidence-based alternatives for cognitive support?

Depending on the underlying condition, a clinician can advise on approved cognitive-enhancing or antipsychotic adjunct strategies that have demonstrated efficacy and acceptable safety profiles in controlled trials. No over-the-counter supplement or research chemical has an evidence base comparable to approved treatments, and self-treating cognitive symptoms of a psychiatric disorder with investigational compounds carries meaningful risk.

References & further reading

PubMed: ASP-4345 dopamine D1 positive allosteric modulator schizophrenia Phase 1 safety tolerability pharmacodynamic electrophysiology
PubMed: dopamine D1 receptor positive allosteric modulator cognitive impairment schizophrenia clinical trial
ClinicalTrials.gov: NCT03557931 -- ASP4345 cognitive impairment schizophrenia add-on Phase 2a efficacy
ClinicalTrials.gov: NCT03678688 -- ASP4345 Phase 1b pharmacodynamic schizophrenia
PubMed: MATRICS Consensus Cognitive Battery MCCB schizophrenia cognitive impairment clinical trials outcome measures