Dihexa and the HGF/c-Met Synaptogenesis Pathway: Mechanism, Evidence, and Limitations

Hepatocyte growth factor (HGF) is a pleiotropic growth factor originally identified for its role in liver regeneration, but now recognized as a critical signaling molecule in the central nervous system. Its receptor, c-Met (also known as MET), is a receptor tyrosine kinase expressed on neurons, glial cells, and neural progenitors throughout the brain.

In neural tissue, HGF/c-Met signaling promotes synaptogenesis (the formation of new synaptic connections), neurite outgrowth, and neuronal survival. A 2021 comprehensive review by Desole et al. (PMID 34179015) detailed the multifaceted roles of HGF/MET in brain development, synaptic plasticity, and neuroprotection, establishing this pathway as a legitimate therapeutic target for cognitive disorders.

HGF/MET signaling declines with aging, and this decline correlates with cognitive impairment. Wei et al. (2022) demonstrated reduced HGF/MET expression in Alzheimer's disease mouse models (PMID 35903536), providing a rationale for therapeutic approaches that restore or enhance this signaling axis.

Downstream of c-Met activation, several well-characterized cascades are engaged: the PI3K/Akt pathway (promoting cell survival and synaptic plasticity), the Ras/MAPK pathway (driving gene expression changes necessary for long-term memory formation), and the STAT3 pathway (involved in neuroprotection and anti-inflammatory responses). These cascades collectively support the molecular processes underlying learning and memory.

Dihexa (N-hexanoic-Tyr-Ile-(6) aminohexanoic amide) was developed from research into the brain renin-angiotensin system, specifically the angiotensin IV/AT4 receptor (IRAP) pathway and its connection to hepatocyte growth factor signaling. Wright and Harding (2019) reviewed this lineage in detail (PMID 30664507), tracing how investigations into angiotensin IV's cognitive effects led to the discovery that the AT4 receptor (insulin-regulated aminopeptidase, IRAP) modulates HGF/c-Met signaling, and ultimately to the design of Dihexa as a more potent and stable HGF potentiator.

Critically, Dihexa does not directly activate c-Met. Instead, it acts as an allosteric potentiator — it binds to the HGF/c-Met complex in a way that increases the affinity of endogenous HGF for its receptor. This means Dihexa amplifies existing signaling rather than generating artificial receptor activation, a distinction with important pharmacological implications. Allosteric potentiators generally carry lower risk of receptor desensitization and tachyphylaxis compared to direct agonists.

McCoy et al. (2013) reported that Dihexa was active in synaptogenesis assays at picomolar concentrations (PMID 23055539), making it orders of magnitude more potent than HGF itself in these assays. However, it is essential to note that this paper now carries an Expression of Concern (see Evidence Limitations section below).

The therapeutic approach of modulating HGF/MET signaling has been independently validated by the development of fosgonimeton, a small-molecule positive modulator of HGF/MET currently in clinical trials for Alzheimer's disease and dementia with Lewy bodies. Johnston et al. (2023) described fosgonimeton's mechanism and early clinical results (PMID 36538176), demonstrating that the HGF/MET axis is considered a viable drug target by the broader pharmaceutical research community.

The preclinical evidence for Dihexa-driven synaptogenesis comes from a small number of studies, with mixed provenance regarding research integrity.

McCoy et al. (2013) (PMID 23055539) reported that Dihexa improved spatial learning in aged rats when administered at low doses, and promoted new synapse formation in hippocampal neuron cultures at picomolar concentrations via the HGF/c-Met pathway. This was the foundational study establishing Dihexa's mechanism and efficacy. However, this paper has received an Expression of Concern (detailed in the next section).

Sun et al. (2021) (PMID 34827486) provided an independent replication from a Chinese research group using APP/PS1 transgenic Alzheimer's disease model mice. This study confirmed that Dihexa improved cognitive function and promoted synaptic protein expression via PI3K/AKT pathway activation. Importantly, this replication comes from a laboratory entirely independent of the original Washington State University group, strengthening the evidence that Dihexa's cognitive effects are reproducible.

Supporting the broader biological plausibility, independent studies on HGF/MET signaling in synaptogenesis provide a mechanistic framework. Xie et al. (2016) demonstrated that HGF/MET promotes synapse formation through beta-catenin signaling (PMID 27595133), while Eagleson et al. (2016) showed that MET uses distinct downstream signaling pathways for dendritic growth versus synaptogenesis (PMID 26818605), providing molecular detail for how c-Met activation specifically drives new synapse formation.

This section is included because Peptide Encyclopedia is a health-related (YMYL) resource, and transparency about evidence quality is essential for informed decision-making.

The foundational evidence base for Dihexa has significant research integrity concerns that must be clearly stated:

Expression of Concern — McCoy et al. (2013): The landmark paper establishing Dihexa's mechanism and efficacy received an Expression of Concern in 2021 (PMID 34551989). Expressions of Concern are issued by journal editors when questions about the reliability of published work are raised but not yet fully resolved. The specific concerns have not been publicly detailed in full, but the notice signals that the editorial board has identified issues warranting caution.

Retraction — Benoist et al. (2014): A follow-up study from the same research group was retracted in April 2025 (PMID 40312093). Retractions indicate that the journal editors no longer stand behind the published findings. This removes one of the few studies that had supported and extended the original Dihexa claims.

Concentration of evidence in a single lab: The majority of published research on Dihexa originates from a single laboratory at Washington State University. When a compound's evidence base is dominated by one research group, independent replication becomes especially important for establishing reliability.

Limited independent replication: The Sun et al. (2021) study provides the only fully independent replication of Dihexa's cognitive effects. While this is an encouraging data point, a single independent study is insufficient to consider the compound's efficacy firmly established.

No human data: No human pharmacokinetic, pharmacodynamic, or safety studies have been published for Dihexa. All efficacy and safety claims are based entirely on rodent models and in vitro assays.

Despite the evidence limitations, the HGF/c-Met pathway itself remains a scientifically credible therapeutic target for cognitive disorders. The key question is whether Dihexa specifically — as opposed to other HGF/MET modulators — will prove to be a viable drug candidate.

Supporting the pathway's relevance, Xia et al. (2021) demonstrated that conditional knockout of MET in mouse forebrain neurons produces age-dependent cognitive deficits (PMID 33524570), confirming that MET signaling is necessary for maintaining cognitive function throughout the lifespan. This genetic evidence strengthens the rationale for pharmacological approaches that enhance MET signaling.

c-Met and cancer risk: A significant safety concern for any compound that potentiates c-Met signaling is the receptor's well-documented role in cancer. MET is overexpressed or constitutively activated in multiple human cancers, including lung, liver, gastric, and renal cell carcinomas. Any therapeutic strategy targeting this pathway would need to demonstrate that it does not promote tumor growth or metastasis — a challenge that has not been addressed for Dihexa in any published study.

No formal toxicology: No GLP-compliant toxicology or dose-finding studies have been published for Dihexa. Without these data, the therapeutic window (the range between effective and toxic doses) is entirely unknown.

What would be needed for clinical translation: For Dihexa to credibly advance toward human trials, the following steps would be required: (1) additional independent replications of cognitive efficacy in validated animal models; (2) formal pharmacokinetic studies characterizing absorption, distribution, metabolism, and excretion; (3) GLP-compliant safety and toxicology studies including carcinogenicity assessment given c-Met's oncogenic potential; and (4) an IND-enabling Phase 1 safety/tolerability trial in healthy volunteers. None of these steps have been initiated as of 2026.