Phenotype-Led\nIdentification of IL-10 Upregulators\nin Human CD4<sup>+</sup> T‑cells and Elucidation of Their Pharmacology\nas Highly Selective CDK8/CDK19 Inhibitors

Therapeutics\npromoting the endogenous production of IL-10 have\nthe potential to restore homeostasis in inflammatory disorders such\nas inflammatory bowel disease (IBD). Here we describe the identification\nof a series of IL-10 upregulators based on a pyrimidyl-piperidine\nscaffold through a high throughput phenotypic CD4<sup>+</sup> T-cell\nmultiplex assay. <i>In vitro</i> optimization of the initial\nhit yielded a lead with good potency and an <i>in vitro</i> clearance profile, compound 3–7, which additionally demonstrated\nefficacy in a murine endotoxin challenge PK–PD mechanistic\nmodel. Target deconvolution efforts identified compound 3–7\nas a highly selective CDK8/19 inhibitor, and crystallographic studies\nunveiled its binding mode to the CDK8/Cyclin-C complex, characterized\nby an unusual water-mediated hydrogen bond to the kinase hinge region.