SEL120-34A hydrochloride (SEL-120-34A; SEL12034A) is a novel, potent and selective ATP-competitive inhibitor of CDK8 (Cyclin-dependent kinase 8) with anticancer activity. It regulates transcription by associating with the Mediator complex. SEL120-34A inhibits the kinase activities of CDK8/CycC and CDK19/CycC complexes with IC50s of 4.4 nM and 10.4 nM, respectively, with a Kd of 3 nM for CDK8. X-ray crystallography has shown SEL120-34A to be a type I inhibitor forming halogen bonds with the protein's hinge region and hydrophobic complementarities within its front pocket. SEL120-34A inhibits phosphorylation of STAT1 S727 and STAT5 S726 in cancer cells in vitro. Consistently, regulation of STATs- and NUP98-HOXA9- dependent transcription has been observed as a dominant mechanism of action in vivo. Treatment with the compound resulted in a differential efficacy on AML cells with elevated STAT5 S726 levels and stem cell characteristics. In contrast, resistant cells were negative for activated STAT5 and revealed lineage commitment. In vivo efficacy in xenotransplanted AML models correlated with significant repression of STAT5 S726. Favorable pharmacokinetics, confirmed safety and in vivo efficacy provide a rationale for the further clinical development of SEL120-34A as a personalized therapeutic approach in AML.

References: Oncotarget. 2017 May 16;8(20):33779-33795.

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