In vitro activity: SNS-032 has low sensitivity to CDK1 and CDK4 with IC50 of 480 nM and 925 nM, respectively. SNS-032 effectively kills chronic lymphocytic leukemia cells in vitro regardless of prognostic indicators and treatment history. Compared with flavopiridol and roscovitine, SNS-032 is more potent, both in inhibition of RNA synthesis and at induction of apoptosis. SNS-032 activity is readily reversible; removal of SNS-032 reactivates RNA polymerase II, which led to resynthesis of Mcl-1 and cell survival. SNS-032 inhibits three dimensional capillary network formations of endothelial cells. SNS-032 completely prevents U87MG cell–mediated capillary formation of HUVECs. In addition, SNS-032 significantly prevents the production of VEGF in both cell lines, SNS-032 prevents in vitro angiogenesis, and this action is attributable to blocking of VEGF. Preclinical studies have shown that SNS-032 induces cell cycle arrest and apoptosis across multiple cell lines. SNS-032 blocks the cell cycle via inhibition of CDKs 2 and 7, and transcription via inhibition of CDKs 7 and 9. SNS-032 activity is unaffected by human serum. SNS-032 induces a dose-dependent increase in annexin V staining and caspase-3 activation. At the molecular level, SNS-032 induces a marked dephosphorylation of serine 2 and 5 of RNA polymerase (RNA Pol) II and inhibits the expression of CDK2 and CDK9 and dephosphorylated CDK7.

Kinase Assay: SNS-032 is a selective inhibitor of CDK2, CDK7, and CDK9 with IC50s of 38 nM, 62 nM and 4 nM, respectively.

Cell Assay: CLL cells treated with SNS-032 for 6 or 24 hrs showed a decrease in the phosphorylation of Ser2 and Ser5 of the CTD of RNA Pol II, which appeared to be both time- and concentration- dependent, and remarkably consistent among samples. For the phosphorylation of Ser2, the inhibition of SNS-032 was greater than that for the phosphorylation of Ser5, this was consistent with the fact that IC50 for the inhibition of CDK9 was lower compared with that for the inhibition of CDK7 (4 nM vs 62 nM). After 6 hrs of SNS-032 exposure, protein levels of CDK7 and CDK9 were stable, but declined at 24 hrs.