In vitro activity: THZ1 uses a unique mechanism, combining ATP-site and allosteric covalent binding, as a means of attaining potency and selectivity for CDK7. THZ1 irreversibly inhibits RNAPII CTD phosphorylation by covalently targeting a unique cysteine located outside the kinase domain of CDK7. THZ1, but not THZ1-R, completely inhibits the phosphorylation of the established intracellular CDK7 substrate RNAPII CTD at Ser 5 and Ser 7, with concurrent loss of Ser 2 phosphorylation at 250 nM in Jurkat cells. THZ1 exhibits strong antiproliferative effects across a broad range of cancer cell lines from various cancer types. In Jurkat cells, low-dose THZ1 has a profound effect on a small subset of genes, including the key regulator RUNX1, thus contributing to subsequent loss of the greater gene expression program and cell death. THZ1 causes defects in Pol II(polymerase II) phosphorylation, co-transcriptional capping, promoter proximal pausing, and productive elongation.

Kinase Assay: THZ1 is a novel selective and potent covalent CDK7 inhibitor with IC50(binding affinity) of 3.2 nM.

Cell Assay: Cells (Jurkat, Loucy, KOPTK1 and DND-41 cell lines) are treated with THZ1, THZ1-R or dimethylsulphoxide (DMSO) for 0-6 h to assess the effect of time on the THZ1-mediated inhibition of RNAPII CTD phosphorylation. For subsequent experiments cells are treated with compounds for 4 h as determined by the time-course experiment described earlier, unless otherwise noted. For inhibitor washout experiments, cells are treated with THZ1, THZ1-R or DMSO for 4 h. Medium containing inhibitors is subsequently removed to effectively 'washout' the compound and the cells are allowed to grow in the absence of inhibitor. For each experiment, lysates are probed for RNAPII CTD phosphorylation and other specified proteins.

Nature. 2014 Jul 31;511(7511):616-20; Mol Cell. 2015 Aug 20;59(4):576-87.