Adamax (Dihexa) Research: HGF/c-Met Potentiation and Cognitive Biology

Adamax (Dihexa, PNB-0408) is a synthetic peptidomimetic derived from the angiotensin IV analogue Norleucine1-angiotensin IV (Nle1-AngIV) through systematic structural optimisation for blood-brain barrier penetration, oral bioavailability, and metabolic stability. Developed by Joseph Harding and colleagues at Washington State University, Dihexa targets the HGF (hepatocyte growth factor)/c-Met receptor tyrosine kinase signalling axis as a potentiator of neuroplasticity and synaptogenesis.

Pharmacological Mechanism

HGF/c-Met Potentiation: The primary pharmacological mechanism of Dihexa is potentiation of HGF-mediated c-Met receptor tyrosine kinase activation. HGF is a pleiotropic growth factor acting through c-Met (MET, hepatocyte growth factor receptor) — a receptor tyrosine kinase expressed in neurons, hepatocytes, epithelial cells, and many other cell types. c-Met activation drives: synaptogenesis (dendritic spine formation), axonal guidance, neuronal survival (PI3K/Akt anti-apoptotic signalling), and hepatocyte proliferation/migration.

McCoy et al. (Journal of Pharmacology and Experimental Therapeutics, 2010) published that Dihexa and related angiotensin IV analogues potentiate HGF-stimulated c-Met signalling at picomolar concentrations — an extraordinary potency suggesting high-affinity binding to a site that allosterically enhances HGF/c-Met interaction. The published potency (approximately 10^7-fold greater than HGF itself in some assay formats) has generated both interest and methodological scrutiny, making careful experimental design essential for rigorous Dihexa research.

IRAP/AT4 Receptor: The original AT4 receptor hypothesis proposes that Dihexa and angiotensin IV analogues inhibit IRAP (insulin-regulated aminopeptidase, also known as leucine-cystinyl aminopeptidase LNPEP), protecting endogenous neuropeptides from degradation. IRAP is a zinc-dependent aminopeptidase localised in GLUT4 storage vesicles in neurons. Its inhibition would extend the half-life of oxytocin, vasopressin, and other IRAP substrates, potentially contributing to cognitive enhancement through neuropeptide system amplification. Whether IRAP inhibition or HGF/c-Met potentiation is the primary mechanism remains an active research question that can be directly addressed using selective pharmacological tools.

Research Design Considerations

Concentration-response characterisation: Given the extraordinary potency claims, rigorous concentration-response research is essential. Prepare Dihexa in DMSO at 10mM stock, then perform 10-fold serial dilutions in culture medium across a range from 1fM to 10µM (10 log units). Use low-binding plasticware (polypropylene tubes and plates) to minimise adsorption at sub-nanomolar concentrations. Include vehicle controls at matched DMSO concentration (less than 0.1% final) at every concentration point.

Pathway confirmation controls: c-Met-selective inhibitor crizotinib (100nM) or c-Met-selective antibody (MetMAb, 10µg/mL) as pre-treatment before Dihexa plus sub-threshold HGF should abolish potentiation if the mechanism is c-Met-dependent. IRAP inhibitor HFI-419 (1µM) in parallel experiments can be used to dissect the IRAP contribution.

HGF-potentiation assay design: Use HGF at its EC20 concentration (producing 20% of maximal c-Met phosphorylation, sub-saturating) to create a window for potentiation detection. Add Dihexa (1fM-10nM) to HGF-EC20 and measure: c-Met phosphorylation at pTyr1234/1235 (activation loop, Western blot or PathScan ELISA); downstream Akt phosphorylation (Ser473); ERK1/2 phosphorylation (Thr202/Tyr204); and cell scatter (if using MDCK cells, a classical c-Met activation endpoint).

Synaptogenesis Research

The neuroplasticity dimension of Dihexa research uses primary rat hippocampal neurons (embryonic day 18, culture to DIV7) plated at low density (30,000 cells/cm2) on poly-D-lysine/laminin-coated coverslips. Treat with Dihexa (1pM-10nM) in Neurobasal-B27 for 72 hours beginning at DIV7 (the active synaptogenesis period). Fix and stain for: synapsin-1 (pre-synaptic marker), PSD-95 (post-synaptic density marker), MAP2 (dendritic marker), and drebrin (dendritic spine marker). Automated image analysis of synaptic puncta density (synapsin-1 puncta per µm of MAP2-positive dendrite) quantifies synaptogenic activity.

Key Published Research

• McCoy AT, et al. "Evaluation of metabolically stabilized angiotensin IV analogs as procognitive/antidementia agents." Journal of Pharmacology and Experimental Therapeutics, 2010. PMID: 20826566
• Wright JW, Harding JW. "The brain hepatocyte growth factor/c-Met receptor system: a new target for the treatment of Alzheimer's disease." Journal of Alzheimer's Disease, 2015. PMID: 25471195
• Benoist CC, et al. "Facilitation of hippocampal synaptogenesis and spatial memory by C-terminal truncated Nle1-angiotensin IV." Journal of Pharmacology and Experimental Therapeutics, 2011. PMID: 21183612

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For laboratory and analytical research purposes only. Not for human or veterinary use.