Abstract 697: Synthesis and biological evaluation of 2,4,5-substituted pyrimidines as highly selective CDK9 inhibitors for cancer treatment.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC Cyclin-dependent kinases (CDKs) are a family of Ser/Thr kinases involved in cell cycle and transcriptional regulation. Most of the CDK inhibitors reported to date have multiple targets and it is unclear whether specific inhibition of one of the CDKs or combined inhibition of several CDKs results in optimal anti-proliferative activities, and in what context. CDK9 is a key regulator of RNA Polymerase II function in the initiation and elongation phases of RNA synthesis, inhibition of which selectively targets pro-survival signalling and reinstates apoptosis in cancer cells. We hypothesise that the selective inhibition of CDK9 is sufficient to induce cancer-specific apoptosis because multiple cancer-related pathways are inhibited at the same time. We will report the design, synthesis and biological evaluation of highly selective CDK9 inhibitors. Compounds have been designed based on new CDK-ligand complex crystal structure data, computational modelling and previous established SARs. Detailed SAR information was obtained by functional kinase assays and a 48-hour MTT assay against HCT-116 (colonic) and MCF-7 (breast) cancer cell lines. All the compounds were first tested against CDK2, CDK9 and two cancer cell lines, and several selective compounds were further tested against CDK1 and CDK7. Compounds with greater than 100-fold selectivity for CDK9 were identified. One of the most selective compounds was subjected to more extensive kinase screening and an evaluation of its cellular mode of action. This compound showed potent anti-proliferative activity in diverse human tumour cell lines with sub-micromolar GI50 values. A good therapeutic window was indicated by the selectivity for tumour over normal human cell lines. Phosphorylation of Ser-2 of RNAP II and expression of Mcl-1 and Mdm-2 proteins were reduced, indicating cellular CDK9 inhibition. The mechanism will be discussed in detail. In conclusion, highly selective CDK9 inhibitors were identified which showed potent CDK9 inhibition in both kinase and cell-based assays. Our study provides a rationale for further development of CDK9 inhibitors for the treatment of cancer and suggests that highly selective CDK9 inhibitors may have the potential to be anti-cancer agents. Citation Format: Hao Shao, David Foley, Abdullahi Y. Abbas, Alison J. Hole, Shiliang Huang, Shenhua Shi, Sonja Baumli, Tracey D. Bradshaw, Martin Noble, Jane A. Endicott, Chris Pepper, Shudong Wang, Peter M. Fischer. Synthesis and biological evaluation of 2,4,5-substituted pyrimidines as highly selective CDK9 inhibitors for cancer treatment. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 697. doi:10.1158/1538-7445.AM2013-697