NVP-2 is an ATP-competitive, highly potent and selective cyclin-dependent kinase CDK9 inhibitor (human Cdk9/CycT1 IC50 = 0.3 nM with 6 μM ATP; DYRK1B IC50 = 350 nM; CDK7 IC50 >10 ?M; 0-63% inhibition of 366 other kinases at 1 μM, including CDK2/3/4/5/8). NVP-2 inhibits RNA Pol II-mediated transcription by blocking Cdk9-dependent RNA Pol II CTD phosphorylation (250 nM for 1-24 hrs; MOLT4 cells), displaying higher apoptosis-inducing and antiproliferation efficacy than the CDK2/7/9 inhibitor SNS-032 (BMS-387032) in leukemia cultures (MOLT4 IC50 = 9 nM/NVP-2 vs. 173 nM/SNS-032).