Targeting G protein-coupled receptor signalling by blocking G proteins

Identifying ligands of G protein-coupled receptors (GPCRs) that elicit biased downstream signalling is an established strategy for separating the desired and unwanted effects of these receptors. Campbell and Smrcka describe how inhibiting the downstream G proteins themselves could also be used to bias GPCR signalling, as well as block pathways shared by multiple GPCRs involved in complex diseases, and discuss how the currently available G protein ligands could be optimized to generate therapeutic leads. G protein-coupled receptors (GPCRs) are the largest class of drug targets, largely owing to their druggability, diversity and physiological efficacy. Many drugs selectively target specific subtypes of GPCRs, but high specificity for individual GPCRs may not be desirable in complex multifactorial disease states in which multiple receptors may be involved. One approach is to target G protein subunits rather than the GPCRs directly. This approach has the potential to achieve broad efficacy by blocking pathways shared by multiple GPCRs. Additionally, because many GPCRs couple to multiple G protein signalling pathways, blocking specific G protein subunits can 'bias' GPCR signals by inhibiting only a subset of these signals. Molecules that target G protein α or βγ-subunits have been developed and show strong efficacy in multiple preclinical disease models and biased inhibition of G protein signalling. In this Review, we discuss the development and characterization of G protein α and βγ-subunit ligands and the preclinical evidence that this exciting new approach has potential for therapeutic efficacy in a number of indications, such as pain, thrombosis, asthma and heart failure.