AOD-9604

What is AOD-9604?#

AOD-9604 (Anti-Obesity Drug 9604) is a synthetic peptide corresponding to residues 176-191 of the C-terminal region of human growth hormone (hGH) with a tyrosine residue substituted at the N-terminus in place of the native phenylalanine. This 16-amino acid peptide was designed to isolate the lipolytic (fat-burning) activity of growth hormone from its growth-promoting, diabetogenic, and anabolic effects. The full amino acid sequence is Tyr-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe, with an intramolecular disulfide bond between the two cysteine residues (Cys7 and Cys14).

AOD-9604 was developed by Metabolic Pharmaceuticals Ltd. (later Calzada Ltd.) in Australia during the 1990s, building on earlier research that identified the C-terminal domain of hGH as the region responsible for the hormone's lipolytic activity. The molecular formula is C78H123N23O23S2 with a molecular weight of 1815.12 Da and CAS number 221231-10-3.

The peptide underwent an extensive clinical development program, completing six human clinical trials involving over 900 participants. However, AOD-9604 failed to demonstrate statistically significant weight loss in its largest Phase IIb trial, and pharmaceutical development was terminated in 2007. Despite this clinical failure for the obesity indication, the peptide has attracted renewed interest for potential applications in cartilage repair and osteoarthritis.

AOD-9604 is not approved for human therapeutic use by any regulatory agency worldwide.

Mechanism of Action#

Lipolytic Activity#

AOD-9604's primary pharmacological effect is the stimulation of lipolysis (breakdown of stored fat). The proposed mechanism involves:

1. Beta-3 adrenergic receptor upregulation: Chronic treatment with AOD-9604 increases the expression of beta-3 adrenergic receptors (beta-3 AR) on adipocytes. While AOD-9604 does not act directly through the beta-3 AR, the increased receptor expression may enhance lipolytic sensitivity to endogenous catecholamines. Studies in beta-3 AR knockout mice showed that the weight loss effects of AOD-9604 were abolished, confirming the importance of this pathway (PMID: 11713213).

2. Fat oxidation enhancement: AOD-9604 increases the rate of fat oxidation (the metabolic burning of fatty acids for energy). This was demonstrated in obese mice, where chronic AOD-9604 treatment significantly increased in vivo fat oxidation rates (PMID: 11673763).

3. Lipogenesis inhibition: AOD-9604 may also inhibit de novo lipogenesis (the formation of new fat), contributing to net fat loss.

Separation from hGH Effects#

A critical feature of AOD-9604's design is the separation of lipolytic activity from other hGH effects:

This selectivity is possible because the C-terminal domain of hGH (from which AOD-9604 is derived) contains the lipolytic region of the molecule, which operates through a mechanism distinct from the growth hormone receptor (GHR). The N-terminal and central domains of hGH are responsible for GHR binding, IGF-1 stimulation, and growth promotion.

Cartilage Repair Potential#

More recently, AOD-9604 has been investigated for cartilage and joint repair. The proposed mechanisms include stimulation of proteoglycan and collagen synthesis in chondrocytes, though this area of research is still in early stages.

Clinical Development History#

Preclinical Studies#

Heffernan et al. published two landmark studies in 2001:

1. PMID: 11673763: Demonstrated that chronic treatment of obese (ob/ob) mice with AOD-9604 increased fat oxidation and reduced body weight without affecting insulin secretion or glucose homeostasis, establishing the metabolic selectivity of the fragment.

2. PMID: 11713213: Showed that AOD-9604's lipolytic effects in obese mice were mediated through beta-3 adrenergic receptor pathways. In beta-3 AR knockout mice, AOD-9604 failed to produce weight loss, confirming the receptor dependence of the mechanism.

Clinical Trials#

AOD-9604 underwent six human clinical trials:

Phase I studies: Established safety and tolerability in healthy volunteers. AOD-9604 was administered orally and demonstrated no significant adverse effects. No changes in serum IGF-1 levels were observed, confirming the absence of growth-promoting activity.

Phase IIa studies: Early efficacy trials showed trends toward weight loss in obese subjects. In a 12-week study, subjects receiving oral AOD-9604 (1 mg/day) lost an average of 2.6 kg compared to 0.8 kg in the placebo group.

Phase IIb trial: The pivotal 24-week trial enrolled 536 obese subjects. Despite trends toward weight loss, the study failed to achieve its primary endpoint of statistically significant weight reduction compared to placebo. This failure led to the termination of the obesity development program in 2007.

Post-Clinical Development#

Following the failure of the obesity program, AOD-9604 was reclassified as a GRAS (Generally Recognized as Safe) ingredient in the United States for use as a food supplement. The company explored alternative indications including:

• Osteoarthritis: Intra-articular injection for cartilage repair
• Metabolic health: As a nutraceutical ingredient for metabolic support

Research Beyond Obesity#

Cartilage and Joint Health#

AOD-9604 has been investigated for potential cartilage repair properties, with research exploring:

• Stimulation of chondrocyte metabolism
• Enhancement of proteoglycan synthesis
• Potential for intra-articular administration in osteoarthritis
• Combination with hyaluronic acid for joint treatment

This research direction represents the primary area of ongoing investigation for AOD-9604, though the evidence base is still limited.

Metabolic Health#

Despite failing as a weight loss drug, AOD-9604's metabolic effects remain of research interest:

• Fat oxidation enhancement without IGF-1 stimulation
• Potential role in metabolic syndrome management
• Safety profile supporting metabolic applications
• Novel mechanism distinct from other anti-obesity approaches

Safety Profile#

The most notable aspect of AOD-9604's clinical history is its extensive safety database. Key safety findings from clinical trials include:

• No effect on IGF-1: Serum IGF-1 levels unchanged during treatment
• No hyperglycemia: Unlike hGH, AOD-9604 does not impair glucose metabolism
• No growth effects: No cell proliferation or growth-promoting activity detected
• Well tolerated: Adverse event rates similar to placebo across clinical trials
• No hormonal disruption: No significant effects on thyroid, adrenal, or gonadal function

Evidence Gaps and Limitations#

• AOD-9604 failed its primary weight loss endpoint in the largest clinical trial
• Cartilage repair evidence is primarily preclinical
• The mechanism of action for cartilage effects is not well characterized
• Long-term safety data beyond 24 weeks is limited
• Optimal dosing for cartilage applications has not been established
• Products available from research chemical suppliers lack pharmaceutical standardization
• Whether oral bioavailability is sufficient for systemic effects remains debated
• The relationship between AOD-9604 and full-length hGH in cartilage repair is unclear

Key Research Findings#

Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone, published in Hormone Research (Ng FM et al., 2000; PMID: 11146367):

• The study demonstrated demonstrated that oral AOD-9604 at 500 mcg/kg/day reduced body weight gain by over of 50% in obese Zucker rats over 19 days, with increased lipolytic activity and no adverse effect on insulin sensitivity.

Related Reading#

• AOD-9604 research studies and evidence
• AOD-9604 dosing protocols
• AOD-9604 side effects profile
• Adipotide research guide
• CJC-1295 DAC research guide