The G1 restriction point is crucial for controlling the cell cycle and it is controlled through the Rb path (CDK4/6-cyclin D1-Rb-p16/ink4a). This path is essential due to its inactivation in most human tumors. Transition with the restriction point requires phosphorylation of retinoblastoma protein (Rb) by CDK4/6, that are highly validated cancer drug targets. We present the identification and portrayal of the potent CDK4/6 inhibitor, LY2835219. LY2835219 inhibits CDK4 and CDK6 with low nanomolar potency, inhibits Rb phosphorylation producing a G1 arrest and inhibition of proliferation, and it is activity is particular for Rb-proficient cells. In vivo target inhibition research has shown LY2835219 is really a potent inhibitor of Rb phosphorylation, induces an entire cell cycle arrest and suppresses expression of countless Rb-E2F-controlled proteins 24 hrs following a single dose. Dental administration of LY2835219 inhibits tumor development in human tumor xenografts representing different histologies in tumor-bearing rodents. LY2835219 works well and well tolerated when administered as much as 56 days in immunodeficient rodents without significant lack of bodyweight or tumor outgrowth. In calu-6 xenografts, LY2835219 in conjunction with gemcitabine enhanced in vivo antitumor activity with no G1 cell cycle arrest, but was connected having a decrease in ribonucleotide reductase expression. These results suggest LY2835219 can be utilized alone or in conjunction with standard-of-care cytotoxic therapy. In conclusion, we’ve identified a powerful, orally active small-molecule inhibitor of CDK4/6 that’s active in xenograft tumors. LY2835219 is presently in clinical development.