A pharmacological approach to inhibition of cyclin-dependent kinases 4 and 6 (Cdk4/6) using highly selective small molecule inhibitors has the potential to provide novel cancer therapies for clinical use. Achieving high levels of selectivity for Cdk4/6, versus other ATP- dependent kinases, presents a significant challenge. The pyrido [2, 3-d] pyrimidin-7-one template provides an effective platform for the inhibition of a broad cross-section of ...