Discovery and exploration of disubstituted [1,2,5]oxadiazolo- [3,4-b]pyrazines as novel C-C chemokine receptor type 5 signaling inhibitors targeting the intracellular allosteric binding pocket

The C-C chemokine receptor type 5 is a G protein-coupled receptor expressed on various immune cells, playing a crucial role in inflammation and chemotaxis. Beyond its physiological functions, C-C chemokine receptor type 5 is implicated in numerous diseases, including cardiovascular, central nervous system, immune system, and infectious diseases, as well as in the progression of cancer. The therapeutic potential of C-C chemokine receptor type 5 inhibition has been demonstrated by antagonists targeting the extracellular domain, notably maraviroc, a Food and Drug Administration-approved Human Immunodeficiency Virus entry inhibitor. However, challenges such as suboptimal pharmacokinetics and efficacy necessitate new antagonists with unique modes of action. Recent advancements in G protein-coupled receptor structural characterization have identified a novel intracellular allosteric binding site in chemokine receptors. This study introduces a series of disubstituted [1,2,5]oxadiazolo-[3,4-b]pyrazines targeting the intracellular allosteric binding pocket of C-C chemokine receptor type 5. Among these, compound 3ad emerged as a promising C-C chemokine receptor type 5-selective allosteric antagonist with an half-maximal inhibitory concentration of 1.09 μM and an almost 30-fold selectivity over C-C chemokine receptor type 2. Molecular dynamics simulations and a competition assay with a Gα_q11 mimetic were used to confirm the intracellular binding mode of these compounds. This novel class of C-C chemokine receptor type 5-selective intracellular antagonists offers a foundation for developing molecular tools and therapeutic agents, potentially overcoming the limitations of current extracellular C-C chemokine receptor type 5 antagonists.