In a routine screening of our small-molecule compound collection we recently identified 4-arylazo-3,5-diamino-1H-pyrazoles as a novel group of ATP antagonists with moderate potency against CDK2-cyclin E. A preliminary SAR study based on 35 analogues suggests ways in which the pharmacophore could be further optimized, for example, via substitutions in the 4-aryl ring. Enzyme kinetics studies with the lead compound and X-ray crystallography of an inhibitor-CDK2 complex demonstrated that its mode of inhibition is competitive. Functional kinase assays confirmed the selectivity toward CDKs, with a preference for CDK9-cyclin T1. The most potent inhibitor, 4-[(3,5-diamino-1H-pyrazol-4-yl)diazenyl]phenol 31b (CAN508), reduced the frequency of S-phase cells of the cancer cell line HT-29 in antiproliferation assays. Further observed cellular effects included decreased phosphorylation of the retinoblastoma protein and the C-terminal domain of RNA polymerase II, inhibition of mRNA synthesis, and induction of the tumor suppressor protein p53, all of which are consistent with inhibition of CDK9.

中文翻译：

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4-芳基偶氮-3,5-二氨基-1H-吡唑CDK抑制剂：SAR研究，与CDK2结合的晶体结构，选择性和细胞效应。

在常规筛选小分子化合物的过程中，我们最近鉴定出4-芳基偶氮-3,5-二氨基-1H-吡唑类为新的ATP拮抗剂，对CDK2-cyclin E具有中等效力。基于35的SAR初步研究类似物提出了可以例如通过在4-芳基环中的取代来进一步优化药效团的方式。用先导化合物进行的酶动力学研究和抑制剂-CDK2复合物的X射线晶体学表明，其抑制方式具有竞争性。功能性激酶测定证实了对CDK的选择性，优选CDK9-cyclin T1。最有效的抑制剂4-[（（3,5-二氨基-1H-吡唑-4-基）重氮基]苯酚] 31b（CAN508）在抗增殖试验中降低了癌细胞系HT-29的S期细胞的频率。