Preclinical (cell/animal)Neuroprotection & CognitionNot a peptide — synthetic research compound

Dihexa

Synthetic angiotensin IV analog (N-acylated peptidomimetic) – not a natural peptide · PNB-0408 · CAS no. 1401708-83-5

Dihexa (development code PNB-0408) is a small, synthetic molecule – an N-acylated peptidomimetic derived from the hormone fragment angiotensin IV. It is not a naturally occurring peptide but was designed in the laboratory of Joseph Harding at Washington State University as a metabolically stabilized, brain-penetrant compound. The central hypothesis was that Dihexa amplifies the hepatocyte growth factor/c-Met system (HGF/c-Met) and thereby promotes the formation of new synapses – with an allegedly cognition-enhancing effect. In animal and cell models, spectacular effects were reported. Several of the key biochemical works on this mechanistic hypothesis were, however, officially retracted in 2025 due to falsified or fabricated data. Clinical trials in humans with Dihexa itself do not exist.

Machine-assisted translation. The German original is the authoritative version.

At a glance

Substance class: Small synthetic molecule; N-acylated peptidomimetic derived from angiotensin IV (not a natural peptide)
Development status: Purely preclinical – no clinical trials with Dihexa itself
Origin: Joseph Harding laboratory, Washington State University; commercialized via M3 Biotechnology → Athira Pharma
Postulated mechanism: Amplification of the HGF/c-Met system → synaptogenesis (hypothesis, the evidence for which has partly been retracted)
CAS number: 1401708-83-5
Evidence warning: Several key biochemical publications retracted in 2025 due to falsified/fabricated data
Successor prodrug: Fosgonimeton (ATH-1017) – missed the Phase 2/3 trial LIFT-AD in Alzheimer's in 2024

Origin & development

Dihexa arose from the basic research of Joseph W. Harding and colleagues at Washington State University, who investigated the renin-angiotensin system in the brain and in particular the fragment angiotensin IV as a possible point of intervention for memory and learning ability. The goal was a metabolically stable, small molecule that overcomes the short half-life of natural angiotensin IV peptides and crosses the blood-brain barrier.

For commercialization, the company M3 Biotechnology was founded in 2011, which was renamed Athira Pharma in 2019. Athira, however, concluded that Dihexa itself has unfavorable drug-like properties, and instead further developed a successor: Fosgonimeton (ATH-1017), a prodrug.

The scientific basis of the program came under criticism from 2021 onward: an investigation by Washington State University found that image data were manipulated in the dissertation and several publications of the later Athira CEO Leen Kawas. In 2021, four works received "Expressions of Concern"; in 2025, formal retractions followed.

Postulated mechanism of action

The mechanistic hypothesis for Dihexa rests on the renin-angiotensin system in the brain. Angiotensin IV, a short cleavage product of angiotensin, was linked to learning and memory processes. Dihexa was designed as a stabilized analog intended to make these effects usable.

The claimed molecular point of attack is the system of hepatocyte growth factor (HGF) and its receptor c-Met. According to the hypothesis, Dihexa binds to HGF and amplifies its signaling effect, which is said to stimulate the formation of new synaptic connections (synaptogenesis). Importantly, however: precisely the original biochemical works that established this HGF/c-Met mechanism were retracted in 2025. The mechanistic basis is therefore considered unsecured.

Derived from angiotensin IV; conceived as a brain-penetrant, metabolically stable molecule
Claimed point of attack: HGF/c-Met system → synaptogenesis
The reported extreme neurotrophic potency comes from the criticized/retracted works
The causal link HGF/c-Met → cognitive effect is shaken by the retractions

Evidence base and the 2025 retractions

The publicly circulated efficacy promises for Dihexa rest almost exclusively on animal and cell experiments – and a substantial part of this foundational work has now been formally retracted. Following an investigation by Washington State University that found falsified and/or fabricated data, the Journal of Pharmacology and Experimental Therapeutics retracted several key publications in 2025 (previously flagged in 2021 with "Expressions of Concern").

Affected are, among others, works from the years 2011, 2012, and 2014 that established the HGF/c-Met mechanism and the synaptogenic effects; the retraction notices cite manipulated figures. In parallel, in January 2025 Athira Pharma paid over USD 4 million to settle allegations under the False Claims Act – the issue was that manipulated image data had been used in NIH grant applications.

No clinical trials in humans with Dihexa itself – all efficacy claims are preclinical
2025 formal retraction of central HGF/c-Met publications (2011, 2012, 2014) due to falsified/fabricated data
WSU investigation: manipulated figures
January 2025: Athira settlement of more than USD 4 million (False Claims Act, NIH funding)
The derived prodrug Fosgonimeton (ATH-1017) missed its endpoints in the Phase 2/3 trial LIFT-AD in Alzheimer's in 2024

Safety and legal status

For Dihexa there are no controlled safety data in humans whatsoever – neither on tolerability nor on side effects or long-term effects. Statements about safety are therefore fundamentally unsupported. As an unapproved research chemical, Dihexa is recognized as a medicinal product nowhere; material offered commercially is subject to no pharmaceutical quality control, so that identity, purity, and content are unclear.

This article serves solely to provide information about the substance class, mechanistic hypotheses, evidence, and regulatory status. It deliberately contains no usage or dosing instructions.

No human safety data; all risk statements are speculative
Not approved as a medicinal product – status: research chemical
As a research chemical without quality control: purity/identity not assured
An amplification of the c-Met signaling pathway is not without concern oncologically

Regulatory status

General

Not approved

Dihexa is not approved as a medicinal product in any country. It is considered a purely preclinical, investigational research substance; clinical trials in humans with Dihexa itself do not exist.

Germany (AMG)

Not an approved medicinal product

An unapproved agent with a pharmacological purpose falls under the German Medicines Act. Placing on the market and importing unapproved medicinal products for use in humans are in principle impermissible.

Sport (WADA)

Prohibited (at all times)

As a pharmacologically active, unapproved substance, Dihexa falls under the general prohibition of non-approved substances (category S0); in addition, its postulated growth-factor/synaptogenesis mechanism touches on the logic of category S2 (growth factors).

Safety & context

There are no controlled safety or tolerability data in humans.
All reported effects come from animal/cell models – partly from publications retracted in 2025.
The central mechanistic hypothesis (HGF/c-Met) was shaken by retractions due to data falsification.
As an unapproved research chemical without quality control, the identity, purity, and content of the traded material are unsecured.
The derived prodrug Fosgonimeton failed at its efficacy endpoints in 2024 despite clinical testing – evidence that the preclinical promises were not clinically confirmed.
Long-term and cancer risks are completely unassessed; an amplification of the c-Met signaling pathway is not without concern oncologically.

Frequently asked questions

Is Dihexa a peptide?: No, not in the strict sense. Dihexa is a small synthetic molecule – an N-acylated peptidomimetic derived from the hormone fragment angiotensin IV. It does not occur in nature and is treated here precisely because it is not a natural peptide.
What do the 2025 retractions mean for the efficacy evidence?: They weigh heavily. Several of the key biochemical works that established the HGF/c-Met mechanism and the cognition-enhancing effect were retracted in 2025 due to falsified or fabricated data. The mechanistic basis is therefore considered unsecured – and there are no human studies on Dihexa itself.
Is Fosgonimeton the same as Dihexa?: No. Fosgonimeton (ATH-1017) is an independent successor compound from Athira Pharma that was conceived as a prodrug. Athira had discarded Dihexa itself due to unfavorable drug-like properties. Fosgonimeton was tested clinically but missed its endpoints in the Phase 2/3 trial LIFT-AD in Alzheimer's in 2024.

Sources

This profile is for information and education only. It does not replace medical advice and deliberately contains no dosing, reconstitution, usage or sourcing information.

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