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SNS-032 (BMS-387032) is a potent and selective inhibitor of cyclin-dependent kinases (CDKs) 2, 7, and 9 [1], with IC50 values of 38 nM, 62 nM and 4 nM, respectively [2].

CDKs mean a family of serine/threonine kinases regulating cell cycle process. Some CDKs are related to transcription control and are often perturbed in cancer cells [3].

Decrease in the phosphorylation at Ser5 and Ser2 in the C-terminal domain (CTD) of RNA Pol II can indicate the inhibition to CDK9 and CDK7 [1]. Chronic lymphocytic leukemia (CLL) cells treated with SNS-032 for 6 or 24 hours showed a decrease in the phosphorylation of Ser2 and Ser5 of the CTD of RNA Pol II, this 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 hours of SNS-032 exposure, protein levels of CDK7 and CDK9 were stable, but declined at 24 hours [4].

In patients with chronic lymphocytic leukemia (CLL), infusion of SNS-032 in a total dose of 75 mg/m2 resulted in a decrease in the phosphorylation at Ser5 and Ser2 in the C-terminal domain of RNA Pol II. This indicated the inhibition to Cdk9 and Cdk7 by SNS-032. This inhibition was first seen 2 hours after the beginning of the infusion with SNS-032, was pronounced after 6 hours and returned to baseline after 24 hours [1].

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