In-vitro pharmacological characterization of novel peptide and non-peptide ligands for the mu-opioid receptor

The mu-opioid belongs to the family of G protein-coupled receptors; they possess a seven transmembrane α-helical structure, and the mu receptor is a crucial target for opioid analgesic drugs. These drugs are potent analgesics, but they are also responsible for some undesired side effects, such as constipation, respiratory depression, tolerance, and physical dependence. An innovative approach to increasing the therapeutic index of such medicaments is the so-called “biased agonism.” Biased agonists are molecules that can trigger a subset of all possible biological outputs of a given receptor compared to unbiased endogenous agonists. This thesis aims to characterize Fentanyl, Furanylfentanyl, FBD1, FBD3, Endomorphin-2, C11, C13, and Dermorphin, molecules of peptide and non-peptide, biased and unbiased mu-opioid receptor agonists pharmacologically. We attempted to highlight the G protein vs. β-arrestin2 coupling preferences in the condition of native vs. overexpressed GRK2, a protein crucial for β-arrestin2 function. We employed bioluminescence resonance energy transfer approaches for receptor-transducer interaction and a bioluminescence method to inhibit cAMP accumulation. Regarding standards, our data are largely in line with those from the literature for G protein and β-arrestin2 coupling. Finally, the overexpression of GRK2 can significantly increase the coupling of the receptor to β-arrestin2 and mitigate the bias toward G protein without dramatically affecting the effects on G protein signalling (cAMP).