Rational design of opioid analgesics for treatment of chronic pain
Opioids are the most efficacious analgesics known, and elective in the treatment of acute severe pain. In contrast, their use in the management of chronic pain syndromes remains limited, requiring a compromise between preserving analgesic efficacy and controlling side effects such as respiratory depression, somnolence, nausea, constipation as well as abuse, dependence and analgesic tolerance. Tolerance involves a self-perpetrating cycle of insufficient analgesia and increasing incidence of side effects as a result of dose escalation.
Mechanisms that contribute to tolerance take place at different organizational levels within the nervous system, including molecular, cellular and neuronal circuit adaptations. The focus of the project is on the adaptations that occur at the two first levels, namely opioid receptor regulation by endocytic/post-endocytic trafficking and the associated cellular changes (morphology and texture) that result from cytoskeletal rearrangements supporting receptor trafficking. By combining a number of new target-based approaches that we have developed to capture more of the relevant signals that control trafficking, together with a broader examination of cellular phenotypes using high content miscroscopy, it should be possible to identify clusters of opioid receptor ligands with the common ability to activate specific protein kinases and promote distinctive modalities of beta-arrestin1/2 recruitment that correlate with distinct trafficking phenotypes and tolerance profiles. To validate this notion we will pursue three aims:
SPECIFIC AIMS
a) Use resonance energy transfer-based assays to quantify i) ligand-specific patterns of kinase activation, ii) beta-arrestin1/2 recruitment to MORs/DORs and iii) their redistribution from the membrane to the endosomal compartment;
b) Monitor beta-arrestin1/2 mobilization and endocytic redistribution of receptor proteins with a high content microscopy platform
c) Correlate outcomes in a) and b) with high content-based readouts of cytoskeletal rearrangements and changes in cell morphology/texture analyses.
Integrating data obtained with phenotypic screens and target-based screening techniques will allow definition of a regulatory footprint for different ligands. Correlation of the latter with well described profiles of ligand potential for generating tolerance should establish the bases for simple drug stratification algorithms that are predictive of pharmacodynamic tolerance to the analgesic actions of opioid receptor ligands much earlier in the drug development pipeline.
