ASP-4345

ASP-4345 is a benzimidazole-based compound designed to selectively bind and enhance the activity of the dopamine type 1 (D1) receptor rather than to activate it directly ^[2]. Cognitive impairment is a central and persistent problem in schizophrenia that current antipsychotics do not address, and dopamine D1 signaling in the prefrontal cortex is closely tied to working memory and attention, which made D1 an attractive target ^[2]. Earlier attempts to use direct D1 agonists for this purpose were limited by off-target safety concerns, so Astellas pursued an allosteric modulator intended to work together with the brain's own dopamine ^[1][2].

In a Phase 1 multiple-ascending-dose study in patients with schizophrenia or schizoaffective disorder who were already on stable antipsychotic treatment, ASP-4345 was generally well tolerated; the most common side effects were headache and somnolence, and no changes in mood or suicidal thinking were observed ^[1]. The study also recorded early signs of benefit, including trends toward improved psychomotor function and visual attention and favorable changes in electrophysiological markers of auditory information processing, though the authors stressed that these needed confirmation in larger trials ^[1]. Companion pharmacokinetic studies found that the drug was suitable for once-daily dosing and, importantly, measured it in cerebrospinal fluid, confirming that it reaches the brain ^[2].

Despite the encouraging early data, ASP-4345 advanced to a Phase 2 trial for cognitive impairment in schizophrenia that did not show it to be effective, and development was subsequently discontinued, with no further progress reported after around 2021 ^[1][2]. It is not an approved medicine and is not available as a supplement; it stands as an example of a mechanistically rational D1 modulator that did not ultimately demonstrate clinical benefit ^[1].

ASP-4345 is investigational and only reached Phase 1, so the safety read is early and limited. In those studies it was generally well tolerated, with headache among the most common effects and some somnolence reported; it was only ever given in supervised clinical settings, and there is no long-term safety data. Just as important, the cognitive signals seen were trend-level rather than clear wins, so larger trials would be needed to confirm any real benefit. It is not approved and not available as a consumer product, which makes any use outside a trial purely experimental.

ASP-4345 is a dopamine D1 receptor modulator developed by Astellas Pharma as an oral adjunctive therapy for the cognitive impairment associated with schizophrenia. The candidate advanced through early clinical development in the late 2010s; a Phase 1 multiple ascending-dose study (NCT02720263) enrolled 36 patients with schizophrenia or schizoaffective disorder across doses of 3 to 150 mg, using Cogstate cognitive testing and electrophysiological biomarkers to gauge pharmacodynamic effect. Astellas then ran a Phase 2 study (NCT03557931) evaluating it as add-on treatment for cognition in patients on stable antipsychotics. It has never reached approval and remains an investigational compound, familiar mainly from its trial record and the nootropic community's interest in D1-targeted cognition drugs.