Dinaciclib improves treatment response in chemoresistant hepatoblastoma.

Chemoresistant hepatoblastoma (HB) is associated with poor outcomes. Cyclin-dependent kinases (CDKs) are potential therapeutic targets because of their critical role in cell growth and chemoresistance. To evaluate the efficacy of CDK inhibition, HB cell lines were treated with dinaciclib and evaluated with cytotoxic, cell-death reversal, and immunoblotting assays. A HB patient-derived xenograft (PDX) model was treated with placebo, vincristine + irinotecan (VI), dinaciclib, or VI + dinaciclib to evaluate tumor growth and response to therapy. We found that dinaciclib had a marked effect on HB cell viability, induced PARP cleavage, and decreased CDK9 protein expression in vitro. Overexpression of CDK9 increased resistance to dinaciclib. Dinaciclib induced cytotoxicity through a mitochondrial-mediated apoptotic pathway with reversal of cell death observed with co-treatment of cells with an apoptosis inhibitor, Z-VAD. In our PDX model, treatment with VI + dinaciclib resulted in decreased tumor volume, viability and HB cell proliferation. Given these findings, combination treatment with VI and dinaciclib should be investigated further as a treatment for chemoresistant HB.