Targeting platelet G-protein coupled receptors (GPCRs): looking beyond conventional GPCR antagonism

Platelets are key mediators of thrombosis. Drugs that interfere with platelet activation substantially improve survival in arterial thrombotic disease. One attractive family of drug targets which has already been exploited in the development of antiplatelet agents are G-protein coupled receptors (GPCRs). Yet limitations of present antiplatelet agents, including incomplete efficacy, bleeding and drug resistance, have spurred the development of new drugs directed at alternative platelet GPCRs. Compounds that target platelet receptors including P2Y(12), protease-activated receptor-1 (PAR1), the thromboxane A(2) receptor (TP receptor), the prostaglandin receptor (EP3 receptor), and the serotonin receptor (5-HT(2A) receptor) have been identified and are in various phases of clinical development and use. Yet, improving the clinical profile of reagents targeting platelet GPCRs may not be only a matter of blocking alternative GPCRs. A more detailed understanding of GPCR function is leading to the development of pharmacophores with novel mechanisms of drug action. Identifying compounds that work by alternative mechanisms may be equally or more valuable than developing reagents targeting different GPCRs. Pharmacological concepts such as GPCR oligomerization, allosterism, and targeting GPCR-G protein interactions may ultimately provide opportunities to more effectively control platelet activation in the clinical setting. In this review, we will discuss the utility and limitations of GPCR-targeted antiplatelet therapies in clinical use and development. We will also consider emerging concepts in GPCR pharmacology that have the potential to foster the development of GPCR-targeted reagents with novel mechanisms of action and improved clinical profiles.