Discovery and characterization of GSK256073, a non-flushing hydroxy-carboxylic acid receptor 2 (HCA2) agonist.

Niacin has been used for many years in the treatment of dyslipidemia due to its ability to decrease serum levels of triglycerides and low-density lipoprotein cholesterol and to increase levels of high density lipoprotein cholesterol. However, niacin causes severe flushing resulting in poor patient compliance. The discovery of hydroxy-carboxylic acid receptor 2 (HCA2) as a high affinity receptor for niacin has opened avenues to investigate the mechanism of action of niacin, and to potentially discover agonists which maintain the antilipolytic effects of niacin accessed by a decrease in circulating non-esterified fatty acids (NEFA) and thereby perhaps the lipid/lipoprotein effects, but avoid the flushing effects. Here we describe the strategy we implemented to identify such compounds. This approach resulted in the discovery of GSK256073, a highly potent HCA2 agonist, which produced similar NEFA lowering effects to niacin in preclinical models (rat and guinea pig). A guinea pig model was used to predict flushing, via an increase in ear temperature, and GSK256073 was found to have a minimal effect in this model. These preclinical models appeared to be predictive of human response, since in a first-time-in-human study, GSK256073 displayed long lasting NEFA and triglyceride lowering effects in healthy male subjects, which were not associated with flushing. GSK256073 can be used as a pharmacological tool to better understand the role of HCA2 in lipid metabolism.