Challenge: Because they are involved in so many physiological processes, G protein coupled receptors (GPCRs) are engaged by roughly 40% of marketed drugs and remain a prime target for the development of new therapeutics. To test the activity of drug candidates, understanding their action on their target in living animals is essential. However, this goal represents a significant challenge due to the complexity of GPCR signaling in normal physiology and disease states.

Solution: To tackle this challenge, the team has combined its expertise in GPCR signaling and in vivo imaging to generate new genetically engineered single and /or double knock-in mice. They have developed 9 single knock-in mouse lines expressing vYFP-tagged GPCRs (GPR88, mGluR5, MOR1, CXCR7, NTSR1) or mTq2-tagged effectors (Gαq, Gαi2, Gγ2 and βarrestin2) and 3 double knock-in mouse lines (mMOR1-vYFP/βarrestin2-mTq2, mMOR1-vYFP/Gαi2-mTq2, mMOR1-vYFP/Gγ2-mTq2). These animal models enable the direct monitoring of drug action on specific GPCR signaling pathways through newly developed microscopy imaging techniques that rely on fluorescent and bioluminescent resonance energy transfer (F/BRET) between sensors.

Achievements/Impact: These new tools (FRET biosensors) and promising models (knock-in mice) enable physiological and directly detectable expression of the targeted receptor and/or effector protein. Receptors and signaling pathways evaluated were selected for their potential therapeutic value as targets for cancer as well as neurologic disease. These new mouse lines permit the visualization of the effects of candidate drugs on their target GPCRs at the cellular and molecular level. This enables preclinical screening and selection of compounds with an appropriate signaling bias to mediate efficacy without concomitant toxicity.