Abstract 2831: Composite cyclin dependent kinase inhibition shows potent activity against hepatocellular carcinoma

Abstract

Abstract Background: Almost a decade after its approval, sorafenib remains the only approved therapy for advanced hepatocellular carcinoma (HCC). Novel treatment is warranted for advanced HCC. Previous preclinical studies reported that inhibition of various cyclin dependent kinases (CDKs), whether cell cycle dependent or independent, showed activity against HCC. Dinaciclib is a potent inhibitor of CDK1, 2, 5, and 9 and has an acceptable safety profile in humans. We thus examined the efficacy of dinaciclib in HCC using preclinical models. Methods: In a panel of HCC cell lines with high Rb expression (HuH7, PLC5, HepG2, SK-Hep1, SNU387, SNU449, SNU426 and SNU475) and low Rb expression (Hep3B and HLE), dinaciclib was examined for its effect on cell viability. The impacts of dinaciclib on cell cycle distribution, apoptosis induction, and the expressions of phospho- (p-) Rb (the target of CDK1 and 2), p-ATM (the target of CDK5), c-myc, and p-RNA polymerase II (the target of CDK9) were explored in selected cell lines including HuH7 and PLC5. The in vivo efficacy of dinaciclib on HCC was tested in mouse xenografts of HuH7 cells implanted subcutaneously. Knockdown of various CDKs using RNA interference was conducted to explore the mechanisms of dinaciclib. Results: Dinaciclib showed potent anti-proliferative activities in all the tested HCC cell lines. The IC50s to dinaciclib by the MTT assay did not significantly differ between cell lines with high Rb expression (8.5 to 20.1 nM) and cell lines with low Rb expression (9.4 to 15.6 nM). After 48 hours of dinaciclib treatment, HuH7 and PLC5 cells showed G2/M arrest in a dose-dependent manner. Apoptosis assays including sub-G1 fraction analysis, DNA fragmentation detection, and cleaved PARP-1 confirmed the occurrence of apoptosis in HuH7 and PLC5 cells treated with dinaciclib. Dinaciclib at the concentration near the IC50 inhibited the phosphorylation of Rb, RNA polymerase II, and ATM in HuH7 and PLC5 cells; it also inhibited the expressions of multiple anti-apoptotic proteins including Mcl-1, XIAP, and survivin. In xenograft studies with HuH7 cells, mice receiving dinaciclib had a significantly slower tumor growth rate compared with mice receiving vehicles. The TUNEL assay showed that tumors treated with dinaciclib exhibited higher apoptosis activity. Mice tolerated the dinaciclib treatment well without significant body weight change. Knockdown of CDK 1, 2, 5, and 9 using RNA interference showed that CDK1 and CDK9 may contribute the most to the efficacy of dinaciclib. Conclusions: Composite knockdown of CDK 1, 2, 5, and 9 with dinaciclib showed potent activity against HCC. (This study was supported by Ministry of Science and Technology, Taiwan [MOST-103-2314-B-002-181-MY2, MOST-103-2314-B-002-090, MOST-103-2314-B-002-092]). Citation Format: Yi-Hsin Liang, Yu-Yun Shao, Yong-Shi Li, Hang Lin, Han-Yu Wang, Ann-Lii Cheng, Chih-Hung Hsu. Composite cyclin dependent kinase inhibition shows potent activity against hepatocellular carcinoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2831.