SMARCA4 Phosphorilation inhibition

Cyclin-Dependent Kinase 9 (CDK9) as part of the PTEFb complex promotes transcriptional elongation and high-level gene expression. We now report that, paradoxically, CDK9 is also essential for maintaining gene silencing at heterochromatic loci. Through a live cell screen, we discovered that CDK9 inhibition reactivates epigenetically silenced genes in cancer, leading to restored tumor suppressor gene expression and cell differentiation, along with activation of endogenous retrovirus (ERV) genes. CDK9 inhibition maintains gene silencing directly through phosphorylation of the SWI/SNF protein SMARCA4 and indirectly through HP1α activation. Based on gene activation, we developed the highly selective and 2 potent CDK9 inhibitor MC180295 (IC50 =5.1nM) that has broad anti-cancer activity in-vitro and is effective in in-vivo cancer models. Additionally, CDK9 inhibition synergizes with the immune checkpoint inhibitor α-PD-1 in vivo, making it an excellent target for epigenetic therapy of cancer.

细胞周期蛋白依赖性激酶9（Cyclin-Dependent Kinase 9，CDK9）作为PTEFb复合物的组成部分，可促进转录延伸与高水平基因表达。我们在此报告，矛盾的是，CDK9对于维持异染色质位点的基因沉默同样至关重要。通过活细胞筛选实验，我们发现抑制CDK9可重新激活癌症中表观遗传沉默的基因，进而恢复抑癌基因表达并诱导细胞分化，同时激活内源性逆转录病毒（Endogenous Retrovirus，ERV）基因。CDK9抑制可通过直接磷酸化SWI/SNF蛋白SMARCA4，以及间接通过异染色质蛋白1α（Heterochromatin Protein 1 α，HP1α）激活来维持基因沉默。基于基因激活相关研究，我们开发了高选择性且强效的CDK9抑制剂MC180295（半数抑制浓度（Half Maximal Inhibitory Concentration，IC50）=5.1nM），其在体外具有广谱抗癌活性，且在体内癌症模型中疗效显著。此外，CDK9抑制在体内可与免疫检查点抑制剂α-PD-1产生协同作用，使其成为癌症表观遗传治疗的优质靶点。