Potent melanocortin MC3 and MC4 receptor antagonist (IC50 values are 0.23 and 0.06 nM respectively) and MC5 partial agonist (EC50 = 0.12 nM). Upregulates expression of genes promoting lipogenesis and triglyceride storage (SCD1, LPL, ACCα and FAS), increases triglyceride synthesis and promotes insulin resistance. Increases food intake, body weight and fat mass when administered centrally in vivo. MW (observed): 1074.25.