CDK4 and rheumatoid arthritis: Cell cycle regulation is another potential target for RA since a characteristic of RA is overgrowth of synovial fibroblasts, which has led researchers to explore targeting the CDKs and CDK4/6 inhibitors have been shown to suppress synovial hyperplasia in animal models [11], while the results of a phase 1b/2a trial aimed at establishing safety and maximal tolerated dose of Seliciclib, an orally available CDK inhibitor in patients with active rheumatoid arthritis, has been reported [12].