The novel cyclin-dependent kinase inhibitor dinaciclib (SCH727965) promotes apoptosis and abrogates microenvironmental cytokine protection in chronic lymphocytic leukemia cells.

The cyclin dependent kinase (CDK) inhibitor flavopiridol has demonstrated promising clinical results in relapsed CLL patients leading to efforts to develop improved CDK inhibitors. Dinaciclib (SCH727965) is a pan-CDK inhibitor, derived from a detailed screen in ovarian xenograft mouse models for therapeutic index, whose toxicity in solid tumor phase I studies appears favorable. Dinaciclib in CLL cells demonstrates concentration dependent apoptosis that is superior to flavopiridol following a clinically relevant 2-hour exposure. Dinaciclib potently down-regulates expression of Mcl-1 in CLL cells and antagonizes protection mediated by multiple soluble proteins important in the microenvironment of CLL including TNF-α IL-4, BAFF, and CD40-ligand. In contrast, contact with stromal cells or fibronectin abrogates the cytotoxicity of dinaciclib that is antagonized by a pan inhibitor and p110 alpha isoform specific inhibitor of the phosphatidylinositol 3-kinase pathway suggesting potential for combination strategies. These data justify clinical development of dinaciclib in CLL.