UCLA

Ghrelin O-acyl Transferase (GOAT) is a recently discovered member of the membrane bound O-acyl transferase (MBOAT) family of enzymes. GOAT is uniquely able to catalyze the transfer of an n-octanoyl group to its substrate, the peptide hormone ghrelin. Acylated ghrelin is insulinostatic and can promote feeding behavior in higher mammals. Pharmacological inhibition of GOAT has emerged as an attractive means to modulate the ghrelin signaling pathway. GOAT is the only humanenzyme known to promote octanoylation. Ghrelin is the only substrate of GOAT, and ghrelin is the only known octanoylated hormone. Further, ghrelin and GOAT are produced principally in the digestive tract. Unlike ligands of the ghrelin receptor, a GOAT inhibitor would not need to penetrate the blood brain barrier.

Herein, we detail our efforts to develop potent, in vivo active small molecule GOAT inhibitors by a peptidomimetic approach. Towards this goal we outline experimental procedures for assaying GOAT activity in vitro, and address unique challenges overcome during this work. Our medicinal chemistry has been driven by hypotheses concerning the catalytic mechanism and binding mode of GOAT and its co-substrates ghrelin and octanoyl-CoA. We unify our understanding of structure-activity relationships for a new class of GOAT inhibitors, and examine the progression of inhibitor structure which has led to these conclusions. Multiple synthetic routes appropriate for small and large scale syntheses of GOAT inhibitors are presented.

Top performing inhibitors exhibit high nanomolar potency in vitro, and suppress circulating acyl-ghrelin in-vivo for up to three hours in a mouse. We have extensively characterized the in vivo and in vitro pharmacokinetic properties of these materials. These inhibitors lay a strong foundation for further medicinal chemistry refinement, and provide a powerful new means of interrogating ghrelin biology and assessing the therapeutic potential of GOAT inhibition.