Purvalanol A is a purine derivative anticancer compound that inhibits cyclin-dependent kinases (CDKs). Purvalanol A induces cell cycle arrest and apoptosis in breast cancer cells and is clinically used to increase efficacy of co-administered chemotherapeutics by inhibiting breast cancer resistance protein (ABCG2) transport. In adipose-derived stem cells, purvalanol A inhibits CDK1/Cdc2 and CDK2/cyclin E, altering differentiation potential. Purvalanol A also inhibits JAK2/STAT activation and RNA polymerase II activity in gastric adenocarcinoma cells. Additionally, this compound decreases human T-cell leukemia virus type 1 (HTLV-1) proliferation.