SKNY-1, a THCV Analog, Produces Weight Loss, Lipid Normalization and Attenuation of Reward-Associated Behaviors in an mc4r(G894C) Zebrafish Model of Obesity

Obesity resulting from melanocortin-4 receptor (MC4R) dysfunction is characterized by combined metabolic dysregulation and maladaptive reward-related behaviors that limit the durability of existing therapies. The endocannabinoid system is a central regulator of appetite, lipid metabolism, and reward processing; however, first-generation cannabinoid receptor 1 (CB1) antagonists were limited by adverse neuropsychiatric effects. SKNY-1 is an orally active tetrahydrocannabivarin (THCV) analog designed to engage pathway-biased CB1 signaling, modulate cannabinoid receptor 2 (CB2), and selectively inhibit monoamine oxidase B (MAO-B), with the objective of addressing both metabolic and behavioral components of obesity while minimizing central nervous system liability through biased CB1 signaling, CB2 modulation, and potential complementary MAO-B inhibition. Here, we integrated in vitro pharmacological profiling of SKNY-1 with in vivo evaluation in an adult mc4r(G894C) zebrafish model exhibiting obesity-associated metabolic and reward-related phenotypes. In vitro, SKNY-1 displayed low-potency modulation of CB1 cyclic AMP signaling (EC50 ~30 µM) but more potent antagonism of the CB1 β-arrestin pathway (IC50 ~6 µM), consistent with differential CB1 pathway modulation. SKNY-1 acted as a CB2 partial agonist (EC50 ~0.1 µM), with antagonist activity emerging at higher concentrations, and selectively inhibited MAO-B at low affinity with no activity against MAO-A. In vivo, mc4r(G894C) zebrafish mutants exhibited dyslipidemia, hepatic triglyceride accumulation, altered appetite-regulatory gene expression, increased metabolic rate, and enhanced compulsive high-calorie feeding and nicotine-seeking behaviors. Oral administration of SKNY-1 for six days produced dose-dependent effects. Both doses normalized total cholesterol and low-density lipoprotein levels and reduced hepatic triglycerides toward wild-type values without affecting circulating triglycerides. The higher dose (200 ng per fish per day) induced significant body weight reduction while preserving body density and attenuated reward-associated feeding and nicotine-seeking behaviors. The lower dose (20 ng per fish per day) more effectively normalized the leptin a-to-ghrelin expression ratio. Collectively, these findings demonstrate that SKNY-1 engages integrated endocannabinoid and potential dopaminergic mechanisms to improve metabolic parameters and attenuate maladaptive reward-related behaviors in an MC4R-deficient vertebrate model, supporting its further translational investigation for obesity complicated by compulsive eating and substance-seeking behaviors.