Cyclin dependent kinase 9 inhibition as a potential treatment for hepatocellular carcinoma.

Abstract

425 Background: Composite cyclin dependent kinase (CDK) inhibition has shown potential as a treatment for hepatocellular carcinoma (HCC) in preclinical studies. We tested whether the specific inhibition of CDK9 was effective against HCC. Methods: The effects of two specific CDK9 inhibitors, BAY1143572 and AZD4573, on cell viability and apoptosis in HCC cell lines were examined. We tested the in vivo efficacy of CDK9 inhibition in mouse xenograft models of HuH7 human HCC cells and in an orthotopic model of BNL mouse HCC cells. Overexpression and knockdown of CDK9 were performed to confirm the efficacy of CDK9 inhibition. Results: Both BAY1143572 and AZD4573 exhibited potent antiproliferative activities in HCC cell lines including HuH7, HLE, and HepG2, regardless of the levels of c-myc expression while inhibiting the downstream signals of CDK9, such as the phosphorylation of RNA polymerase II. These 2 CDK9 inhibitors induced apoptosis in HCC cells and reduced the expression of antiapoptotic proteins such as myeloid cell leukemia-1, survivin, BimEL, and the X-linked inhibitor of apoptosis protein. Reduction of CDK9 expression through siRNA knockdown also reduced the phosphorylation of RNA polymerase II and the colony formations of HuH7 and HLE cells. In the xenograft studies, mice receiving either CDK9 inhibitor exhibited a significantly lower tumor growth rate than did the mice receiving vehicles. In the orthotopic model, the HCC growth in mice receiving BAY1143572 also tended to be slower than that in the control group. Overexpression of CDK9 in HuH7 cells reduced the efficacy of both CDK9 inhibitors. Conclusions: We demonstrated the in vitro and in vivo activity of CDK9 inhibition on multiple HCC cell lines. Our data support further clinical development of CDK9 inhibitors as a treatment for HCC.