AOD-9604: Lipolytic Growth Hormone Fragment Research

AOD-9604 (anti-obesity drug 9604) is a 16-amino-acid synthetic peptide corresponding to residues 177-191 of human growth hormone with a tyrosine residue at the N-terminus (Tyr-hGH 177-191), and a disulphide-bridged cyclic conformation. It was specifically developed to isolate the lipolytic activity of GH's C-terminal domain while eliminating anabolic, diabetogenic, and mitogenic effects associated with full-length GH.

Development Rationale

Full-length GH has well-characterised lipolytic effects via stimulation of hormone-sensitive lipase (HSL) in adipocytes, promoting hydrolysis of stored triglycerides. However, GH also has anabolic effects on muscle and bone (via IGF-1), promotes insulin resistance, and stimulates cell proliferation through IGF-1R-mediated pathways — effects that are undesirable in an obesity treatment agent. The hypothesis behind AOD-9604 was that the lipolytic activity resides in a specific region of the GH molecule separable from its growth-promoting activity.

Research at Monash University identified the C-terminal region (residues 177-191) as the lipid metabolism regulatory domain of GH. AOD-9604 was synthesised to test whether this fragment could stimulate lipolysis in isolation, and subsequent work demonstrated it retains potent lipolytic activity without activating the GH receptor for anabolic or glycaemic signalling.

Mechanism: Lipolysis Without IGF-1 Stimulation

AOD-9604 does not bind or activate the classical GH receptor (GHR) at the binding sites that trigger JAK2-STAT5 signalling and subsequent IGF-1 production. Instead, it appears to directly activate β-3 adrenergic receptors on adipocytes and may interact with a distinct binding site on fat cells that triggers cAMP-mediated HSL activation. Importantly, AOD-9604 does not increase IGF-1 levels, does not produce insulin resistance, and does not stimulate bone or muscle growth — confirming the intended separation of activities.

Clinical Trial Programme

Metabolic Pharmaceuticals (Australia) conducted an extensive clinical programme in obesity:

• Phase I: Established safety and pharmacokinetic profile. Single IV and oral doses in healthy volunteers showed no adverse metabolic effects, no IGF-1 stimulation, and a half-life of approximately 30-40 minutes.
• Phase II (METRO trials): Multiple randomised controlled trials in obese subjects demonstrated statistically significant weight loss vs placebo with oral AOD-9604 (400-1600 µg/day) over 12 weeks. Body composition analysis confirmed preferential loss of adipose tissue.
• Phase III: A larger Phase III study did not achieve primary endpoint of statistically significant weight loss vs placebo in the intent-to-treat population — a result attributed to higher than expected placebo response and dose selection challenges. The compound's development as an obesity drug was not progressed to regulatory submission.

FDA GRAS Determination

In 2014, the FDA granted AOD-9604 Generally Recognized As Safe (GRAS) status as a food ingredient, reflecting its established safety profile across the clinical programme. This is a notable regulatory milestone for a synthetic peptide and confirms the extensive human safety data generated during its development.

Cartilage and Bone Research

Subsequent to the obesity programme, research has investigated AOD-9604 in osteoarthritis and cartilage repair models. Preclinical data from Monash University demonstrated that AOD-9604 stimulates chondrocyte proliferation, proteoglycan synthesis, and cartilage matrix repair independent of its lipolytic effects. Phase II trials in knee osteoarthritis (Syngen study) showed improvements in pain and function scores, opening a new research direction for this compound.