AOD-9604: Mechanism, Research & UK Safety Profile
Also known as: Anti-Obesity Drug 9604, hGH Frag 177-191 (Tyr-hGH 177-191), Advanced Obesity Drug 9604
A modified C-terminal fragment of human growth hormone (residues 176–191 with an additional N-terminal tyrosine) developed by Metabolic Pharmaceuticals for targeted lipolysis research, without the growth-promoting IGF-1 axis effects of intact hGH.
Molecular formula
C₇₈H₁₂₃N₂₃O₂₃S₂
Molecular weight
1815.1 Da
Half-life
Estimated 30–60 minutes in plasma based on preclinical pharmacokinetic studies; the relatively short half-life is consistent with once-daily dosing regimens that rely on transient receptor activation rather than sustained receptor occupation.
Category
Lipolytic Fragments
Overview
AOD-9604 is a synthetic peptide comprising the C-terminal 16 amino acid residues of human growth hormone (hGH), specifically residues 177–191 of the mature hGH sequence, with an additional N-terminal tyrosine residue that confers enhanced stability and receptor interaction properties. It was developed by Metabolic Pharmaceuticals Ltd (Melbourne, Australia) specifically to isolate the lipolytic activity of hGH from its growth-promoting and diabetogenic effects, which are mediated through the growth hormone receptor's activation of the IGF-1 axis.
The scientific rationale for AOD-9604 derives from early research demonstrating that the lipolytic effects of intact hGH could be attributed principally to the C-terminal domain of the molecule, rather than the N-terminal binding domain responsible for IGF-1 stimulation and anabolic growth effects. By developing a fragment corresponding solely to this lipolytic domain, Metabolic Pharmaceuticals sought a pharmacological agent that could stimulate fat mobilisation and oxidation without the adverse metabolic effects—insulin resistance, glucose intolerance, acromegalic features—associated with full-length hGH administration.
In preclinical studies across multiple rodent and primate models, AOD-9604 consistently demonstrated stimulation of lipolysis in adipose tissue and inhibition of lipogenesis, with effects on fat mass reduction that were statistically significant relative to controls. Crucially, these effects were achieved without measurable stimulation of IGF-1 concentrations, bone growth, or glucose intolerance in well-designed preclinical investigations—a profile markedly different from intact hGH.
AOD-9604 advanced into human clinical trials under Metabolic Pharmaceuticals' development programme, reaching Phase 2b/3 clinical evaluation for obesity. The clinical programme ultimately did not achieve the efficacy endpoints required for regulatory approval; however, the compound achieved a US FDA GRAS (Generally Recognised As Safe) notification for use as a food ingredient, reflecting the favourable safety profile characterised across its clinical programme. In the UK, AOD-9604 is not approved by the MHRA for any therapeutic indication and is classified as a research compound.
Discovery & Research History
The discovery of AOD-9604 originated from structural studies of human growth hormone conducted in the late 1980s and early 1990s at Monash University and affiliated research institutions in Melbourne, Australia. Researchers including Professor Frank Ng and colleagues at Monash University were investigating the structure-activity relationships of hGH, seeking to understand which structural regions were responsible for its diverse biological effects.
Research by the Monash group demonstrated that distinct regions of the hGH molecule controlled different biological activities: the N-terminal region was principally responsible for growth hormone receptor binding, IGF-1 stimulation, and anabolic growth effects, while the C-terminal region—particularly the region encompassing residues 176–191—appeared to harbour the lipolytic activity. This functional segregation within a single polypeptide offered the intriguing possibility of isolating the fat-mobilising effects without the growth-promoting and diabetogenic consequences.
Metabolic Pharmaceuticals Ltd was established in Melbourne to commercialise this insight, licensing the intellectual property from Monash University and undertaking a structured drug development programme. The addition of an N-terminal tyrosine residue to the hGH fragment 177–191 sequence produced AOD-9604, conferring enhanced metabolic stability and improved pharmacodynamic properties relative to the unmodified fragment.
Preclinical development proceeded through the late 1990s and early 2000s, with studies in obese rodent models, genetically obese mice (ob/ob), and non-human primates demonstrating consistent fat-mass reduction and favourable safety profiles. Phase 1 human clinical trials confirmed tolerability and preliminary pharmacodynamic effects. Phase 2 trials followed, and the programme advanced to Phase 3 clinical evaluation targeting a regulatory submission for an obesity indication.
The Phase 3 clinical programme ultimately did not demonstrate sufficient efficacy to support regulatory approval for obesity treatment, a common outcome for anti-obesity compounds given the multifactorial nature of obesity pathophysiology and the challenging regulatory endpoints. However, AOD-9604's safety characterisation across its clinical programme—and the subsequent US FDA GRAS notification—provided a foundation for ongoing preclinical research into its lipolytic mechanisms.
Mechanism of Action
AOD-9604 exerts its metabolic effects through mechanisms distinct from those of intact hGH, involving direct adipose tissue signalling that does not depend on IGF-1 axis activation:
Beta-3 Adrenergic Receptor Pathway
Research in adipocyte cell culture and rodent in vivo models suggests that AOD-9604 activates beta-3 adrenergic receptors in adipose tissue, stimulating the adenylyl cyclase–cAMP–PKA signalling cascade that activates hormone-sensitive lipase (HSL). Activated HSL catalyses the hydrolysis of stored triglycerides into free fatty acids and glycerol, mobilising lipid stores for peripheral oxidation. This mechanism is consistent with the C-terminal hGH region's interaction with adipocyte surface receptors that are distinct from the growth hormone receptor.
Hormone-Sensitive Lipase Activation
AOD-9604 has been shown to increase HSL phosphorylation in adipocytes, directly activating the rate-limiting step in triglyceride hydrolysis. This action on the lipolytic machinery of adipocytes—without upstream IGF-1 pathway activation—is the proposed molecular basis for the preferential fat-mobilising effect observed in preclinical models.
Anti-Lipogenic Effects
In parallel with its pro-lipolytic signalling, AOD-9604 has been shown in adipocyte models to inhibit lipogenesis—the synthesis of new triglycerides from glucose and fatty acid precursors. This anti-lipogenic effect likely involves inhibition of fatty acid synthase (FAS) and acetyl-CoA carboxylase (ACC), key enzymes in de novo lipogenesis. The combined effect of enhanced lipolysis and reduced lipogenesis is a net reduction in adipose triglyceride stores.
IGF-1 Axis Independence
A defining feature of AOD-9604's mechanism, extensively documented in preclinical safety studies, is the absence of measurable stimulation of circulating IGF-1 concentrations at therapeutic doses. Intact hGH binds to growth hormone receptors (GHR) on hepatocytes, stimulating IGF-1 synthesis and secretion—the primary mediator of hGH's anabolic and diabetogenic effects. The C-terminal fragment used in AOD-9604 lacks the N-terminal structural elements required for GHR engagement, and accordingly does not activate this pathway.
Adipose Tissue Specificity
Preclinical data suggest that AOD-9604's actions are relatively specific to adipose tissue, with limited effects on bone growth, lean mass, or glucose homeostasis at doses that produce significant lipolytic effects. This selectivity distinguishes it from intact hGH and is the principal scientific rationale for continued research interest in the fragment.
Researched Effects
- Significant fat-mass reduction demonstrated in multiple rodent obesity models including diet-induced obesity, ob/ob mice, and Zucker fatty rats, without measurable IGF-1 elevation.
- Inhibition of lipogenesis and concurrent stimulation of lipolysis in isolated adipocyte studies, producing a net reduction in adipose triglyceride accumulation.
- Absence of measurable effects on linear bone growth, serum IGF-1, insulin sensitivity, or fasting glucose at lipolytic doses in preclinical safety studies, distinguishing AOD-9604 from intact hGH.
- Favourable safety profile across Phase 1 and Phase 2 human clinical trials, with low rates of adverse events and no signals of hGH-related toxicity.
- US FDA GRAS notification for use as a food ingredient, reflecting the extensive safety characterisation conducted across the clinical programme.
- Preliminary evidence of cartilage-protective effects in osteoarthritis models, representing a mechanistic divergence from the primary lipolytic focus of the original development programme.
- Preclinical data suggesting preferential mobilisation of visceral adipose tissue relative to subcutaneous fat in some model systems, an effect of particular interest given visceral adiposity's role in cardiometabolic risk.
Theoretical Research Protocols
- Dosage range
- Preclinical studies used doses equivalent to approximately 250–500 mcg in weight-adjusted extrapolations; Phase 2 clinical trials investigated oral doses in the range of 1–9 mg/day and subcutaneous doses of 50–500 mcg
- Frequency
- Once daily in the majority of preclinical and clinical trial protocols studied
- Duration
- Preclinical efficacy studies ranged from 4 to 12 weeks; Phase 2 clinical trials ran for 12–24 weeks
- Administration routes
- Subcutaneous injection (primary route in preclinical studies and Phase 1/2 clinical trials), Oral administration (investigated in Phase 2 trials due to the peptide's relative acid stability, though oral bioavailability is significantly lower than subcutaneous)
Safety Profile
Common side effects (research)
- Injection-site reactions including transient redness, minor swelling, and localised discomfort
- Mild headache reported in a subset of Phase 2 participants at higher doses
- Transient nausea at higher oral doses in Phase 2 trials
- Mild fatigue reported at low frequency in clinical trial populations
Rare risks
- Allergic or hypersensitivity reactions to the peptide or excipients — possible with any exogenous peptide
- Unknown long-term effects in humans beyond the durations investigated in the clinical programme
- Theoretical interaction with endogenous hGH regulatory axes not fully characterised at extended doses
- No significant IGF-1 elevation observed, but theoretical concern with very high doses or prolonged administration remains
Contraindications
- Active malignancy or personal history of cancer — theoretical concern given any growth factor-related mechanism; no specific evidence for AOD-9604 but precautionary
- Pregnancy and breastfeeding — no safety data available
- Hypersensitivity to AOD-9604 or any excipients of the research preparation
- Children and adolescents — no paediatric data; theoretical concern regarding any growth hormone-derived fragment in developing individuals
- Acromegaly or other disorders of growth hormone excess — pharmacodynamic interaction risk
UK Regulatory Status
United Kingdom (MHRA): AOD-9604 is not approved by the MHRA for any therapeutic indication. It is not a licensed medicine in the UK. Its clinical development programme did not achieve the regulatory endpoint required for marketing authorisation approval. It may be procured as a research peptide for legitimate preclinical or in vitro investigation through specialist research suppliers, subject to institutional governance and ethics approval. Its supply for human use outside of authorised clinical trial settings is not permitted under the Human Medicines Regulations 2012.
European Union (EMA): Not authorised by the EMA for any indication. Not approved in any EU member state as a medicinal product. Research compound status applies across the EU.
Notes: AOD-9604 has received a US FDA GRAS (Generally Recognised As Safe) notification for use as a food ingredient — a safety classification distinct from drug approval, reflecting the extensive clinical safety data generated but not indicating efficacy for any therapeutic purpose. It is not a WADA-prohibited substance but remains an unapproved medicinal product for human therapeutic use in all major jurisdictions.
Related research resources
Key Research Studies
AOD9604 Clinical Trial — Phase 2b Safety and Efficacy in Obese Adults
A 12-week randomised, double-blind, placebo-controlled Phase 2b trial investigating multiple doses of oral AOD-9604 (1 mg, 5 mg, 10 mg, 20 mg daily) in obese adults. While statistically significant weight loss versus placebo was not achieved at the primary endpoint across all dose groups, the compound demonstrated a consistent and favourable safety profile with no evidence of hGH-related adverse events, no IGF-1 elevation, and no adverse glucose or insulin effects. The safety findings supported the subsequent GRAS application.
Lipolytic Effect of a Modified Fragment of Human Growth Hormone: AOD9604
Preclinical mechanistic study demonstrating that AOD-9604 stimulated lipolysis and inhibited lipogenesis in isolated rat adipocytes through beta-3 adrenergic receptor-dependent cAMP elevation. The study confirmed that the lipolytic effects were achieved without measurable IGF-1 pathway activation, and demonstrated preferential action on visceral adipose depots in diet-induced obese rodent models. These mechanistic findings provided the foundation for the clinical development programme.
Anti-Obesity Effects of AOD9604 in Genetically Obese Rodents
In vivo studies in ob/ob mice and Zucker fatty rats treated with AOD-9604 demonstrated statistically significant reductions in body fat mass, fat pad weight, and plasma leptin relative to vehicle-treated controls. Lean mass was preserved in treated animals. No changes in fasting glucose, insulin tolerance, or serum IGF-1 were observed, validating the IGF-1 axis independence of the compound's lipolytic mechanism in relevant in vivo models.
Chondroprotective Properties of AOD9604: Preclinical and Clinical Observations
Exploratory preclinical studies and a preliminary clinical investigation examining AOD-9604's effects on cartilage metabolism identified unexpected chondroprotective properties. In collagen-induced arthritis animal models, AOD-9604 reduced cartilage degradation markers and joint histopathological scores. A small Phase 2 clinical trial in knee osteoarthritis participants reported reductions in pain scores and cartilage biomarkers, representing a mechanistic divergence from the primary lipolytic development rationale.
Frequently Asked Questions
What is AOD-9604 and how does it relate to growth hormone?
AOD-9604 is a synthetic peptide corresponding to residues 177–191 of human growth hormone, with an additional N-terminal tyrosine residue. It was engineered to isolate the lipolytic (fat-mobilising) activity of hGH from its growth-promoting and diabetogenic effects. Intact hGH stimulates IGF-1 production and promotes linear growth via its N-terminal domain; AOD-9604 lacks these structural elements and does not activate the IGF-1 axis at research doses.
Did AOD-9604 receive regulatory approval for obesity treatment?
No. Despite advancing to Phase 2b/3 clinical evaluation, the AOD-9604 clinical programme did not demonstrate sufficient efficacy at the primary weight-loss endpoint required for marketing authorisation approval. However, it did receive a US FDA GRAS (Generally Recognised As Safe) notification as a food ingredient, reflecting the extensive clinical safety characterisation. The failure to achieve regulatory approval was principally an efficacy issue rather than a safety one.
Does AOD-9604 affect IGF-1 levels?
Preclinical studies and Phase 2 clinical data consistently show no measurable elevation of circulating IGF-1 at therapeutic doses of AOD-9604. This IGF-1 axis independence is the defining pharmacological distinction from intact hGH, and was a central feature of the development rationale. The absence of IGF-1 stimulation means AOD-9604 avoids the insulin resistance, glucose intolerance, and acromegalic adverse effects associated with exogenous hGH administration.
What is the regulatory status of AOD-9604 in the UK?
AOD-9604 is not approved by the MHRA for any therapeutic indication and is not a licensed medicine in the UK. It may be procured as a research peptide for legitimate preclinical or in vitro scientific investigation through specialist research chemical suppliers, subject to appropriate institutional governance and ethics approval. Its supply or use for human therapeutic purposes outside of authorised clinical trials is not permitted under UK medicines regulations.
How does AOD-9604 compare to HGH Fragment 176-191?
AOD-9604 and HGH Fragment 176-191 are closely related but structurally distinct. HGH Fragment 176-191 corresponds to residues 176–191 of the hGH sequence (16 amino acids). AOD-9604 corresponds to residues 177–191 with an additional N-terminal tyrosine, giving it a different N-terminal residue and potentially different receptor interaction profile. AOD-9604 was the subject of Metabolic Pharmaceuticals' formal clinical development programme; HGH Fragment 176-191 is primarily a preclinical research tool.
What were the primary outcomes of AOD-9604 human clinical trials?
Phase 1 trials confirmed AOD-9604's safety and pharmacokinetic profile. Phase 2 dose-ranging studies demonstrated a favourable safety profile including no IGF-1 elevation, no adverse glucose effects, and no hGH-related adverse events across all doses investigated. Efficacy signals for weight loss were observed in some Phase 2 substudies but were insufficient in magnitude and consistency to meet Phase 3 primary endpoint requirements, leading to the programme's discontinuation as an obesity drug.
Related trials
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