Chemistry:ALTO-203

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ALTO-203 is a histamine H3 receptor inverse agonist which is under development for the treatment of major depressive disorder with anhedonia.[1][2][3][4][5] It was also under development for other psychiatric disorders and neurodegenerative disorders, but development for these indications was discontinued.[1] The drug is taken orally.[1] It has been found to increase dopamine release in the nucleus accumbens and produce antianhedonic-like effects in rodents, effects which another histamine H3 receptor inverse agonist, pitolisant, did not produce.[5] ALTO-203 is under development by Alto Neuroscience.[1][2] As of July 2025, it is in phase 2 clinical trials for major depressive disorder.[1][2] In a phase 1 trial, ALTO-203 was reported to increase subjective positive mood to a similar degree as modafinil.[6] On the other hand, the drug failed to meet its primary endpoint, a measure of mood and alertness, compared to placebo in a phase 2 trial.[7][8]

See also

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 "ALTO 203". 7 July 2025. https://adisinsight.springer.com/drugs/800071570. 
  2. ↑ 2.0 2.1 2.2 "Synapse". https://synapse.patsnap.com/drug/072749d803854a678a8c91e05ec99177. 
  3. ↑ "Validation of assessments for reward processing, positive emotion, and anhedonia for use in a phase 2 study of a novel histamine H3 inverse agonist, ALTO-203, in major depression". Neuropsychopharmacology 49: 505–506. December 2024. 
  4. ↑ "Prospective replication of an EEG biomarker for predicting changes in attention in ALTO-203, an H3 inverse agonist". Neuropsychopharmacology 51 (Suppl 1). January 2026. 
  5. ↑ 5.0 5.1 "ALTO-203, a Novel Histamine H3 Inverse Agonist, Increase Sucrose Preference in Dopamine-depleted Rats". Society of Biological Psychiatry's 2025 Meeting. 2025. https://altoneuroscience.com/wp-content/uploads/2025/04/SOBP2025_ALTO203_Sucrose_Preference_final.pdf. 
  6. ↑ "Effects of ALTO-203 on positive emotion and reward processing: methods and supporting data for an ongoing phase 2 proof-of-concept study". European College of Neuropsychopharmacology (ECNP) 2024. 2024. https://altoneuroscience.com/wp-content/uploads/2024/10/ECNP_2024_P2300_Cooper_A4.pdf. 
  7. ↑ "Alto misses primary efficacy endpoint in phase 2 depression trial". 26 June 2025. https://www.fiercebiotech.com/biotech/alto-misses-primary-efficacy-endpoint-phase-2-depression-trial-sings-cheerful-tune-anyway. 
  8. ↑ "ALTO-203 Fails to Meet Primary Efficacy Endpoint in Phase 2 Major Depressive Disorder Trial". 5 June 2026. https://www.psychiatrictimes.com/view/alto-203-fails-to-primary-efficacy-endpoint-in-phase-2-major-depressive-disorder-trial. 



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