(R)-Roscovitine (Seliciclib) is an orally bioavailable and selective CDKs inhibitor with IC50s of 0.2 μM, 0.65 μM, and 0.7 μM for CDK5, Cdc2, and CDK2, respectively.IC50 & Target:IC50: 0.2 μM (CDK5), 0.65 μM (Cdc2), 0.7 μM (CDK2)In Vitro:(R)-Roscovitine (Seliciclib) displays high efficiency and high selectivity towards some cyclin-dependent kinases. The kinase specificity of Seliciclib is investigated with 25 highly purified kinases (including protein kinase A, G and C isoforms, myosin light-chain kinase, casein kinase 2, IR tyrosine kinase, c-src, v-abl). Most kinases are not significantly inhibited by (R)-Roscovitine. Cdc2, Cdk2, and Cdk5 only are substantially inhibited (IC50 values of 0.65, 0.7, and 0.2 μM, respectively). Cdk4k and Cdk6 are very poorly inhibited by (R)-Roscovitine (IC50>100 μM). Extracellular regulated kinases erk1 and erk2 are inhibited with an IC50 of 34 μM and 14 μM, respectively. (R)-Roscovitine inhibits the proliferation of mammalian cell lines with an average IC50 of 16 μM. (R)-Roscovitine (Seliciclib) decreases the level of CDK5 and p35 with upregulation of E-cadherin, but downregulation of Vimentin and Collagen IV. Moreover, (R)-Roscovitine inhibits the ability of high glucose cultured NRK52E cells to migrate and invade[2].In Vivo:Compare with normal controls, (R)-Roscovitine (Seliciclib) downregulates phosphorylated ERK1/2 and PPARγ with concomitant increase in E-cadherin, but decrease in Vimentin and Collagen IV. Correspondingly, (R)-Roscovitine decreases renal tubulointerstitial fibrosis of diabetic rats. (R)-Roscovitine is effective in decreasing tubulointerstitial fibrosis via the ERK1/2/PPARγ pathway in diabetic rats[2]. (R)-Roscovitine (Seliciclib) (16.5 mg/kg) significantly reduces the rate of tumor growth and increases survival of treated mice. Strikingly, (R)-Roscovitine treatment leads to complete tumor disappearance in one mouse (25%); moreover, no tumor regrowth in this mouse is found 5 months after completion of the treatment. Mouse weights do not differ significantly between mice treated with (R)-Roscovitine and control mice, and behavioral differences between the two groups are also negligible. These results suggest that (R)-Roscovitine can be used effectively as a selective tumor growth inhibitor in HPV+ head and neck cancer.