G protein-coupled receptors (GPCRs) elicit an ability to activate multiple downstream signalling pathways. It is becoming evident that for many GPCRs, agonists are able to activate several of these pathways, each to differing extents; a phenomenon termed pathway bias, or biased agonism.

Here, work is presented quantifying biased agonism for the: adenosine A1 and A2A receptors, as well as the calcitonin-like receptor (CLR). For the adenosine receptors, novel selective, and non-selective, agonists are identified and characterised. Further, the extent of biased agonism is determined for A1R agonists with respect to their abilities to positively and negatively regulate cAMP production, mobilise intracellular Ca2+ and activate ERK1/2. The activity of triazoloquinazoline compounds against the A2AR is validated, identifying 3 to be selective. Further investigations into the ability of triazoloquinazolines to mediate cAMP production and ERK1/2 activation uncovers each tested agonist to be biased towards activating ERK1/2, at the A2AR. A characterisation of the effects of receptor activity modifying proteins (RAMPs) upon signalling from the CLR is presented: quantifying the extent of biased agonism, with respect to the ability of RAMP-CLR heterodimers to: mediate cAMP production and inhibition, as well as mobilise intracellular Ca2+, uncovering this to be a Gαq/11-mediated process. Further, through applying a saturation mutagenesis approach to the CLR, a potential interaction is identified between intracellular loop 1 (ICL1) and helix 8, which is broken upon receptor activation, further identifying ICL1 to be a region of the CLR responsible for influencing G protein specificity.

Ultimately, these findings relating to both adenosine and CLR-based receptors uncovers further evidence of biased agonism at GPCRs, which may have potential implications upon improving the efficacy and safety profiles of novel pharmaceutics targeting these clinically relevant GPCRs.