Drug combination therapies are commonly used for the treatment of
cancers to increase therapeutic efficacy, reduce toxicity, and decrease the incidence of drug resistance. Although
drug combination therapies were originally devised primarily by empirical methods, the increased understanding of drug mechanisms and the pathways they modulate provides a unique opportunity to design combinations that are based on mechanistic rationale. We have identified
protein kinase CK2 as a promising therapeutic target for combination
therapy, because CK2 regulates not just one but many oncogenic pathways and processes that play important roles in drug resistance, including DNA repair,
epidermal growth factor receptor signaling, PI3K/AKT/mTOR signaling, Hsp90 machinery activity,
hypoxia, and
interleukin-6 expression. In this article, we show that
CX-4945, a clinical stage selective small molecule inhibitor of CK2, blocks the DNA repair response induced by
gemcitabine and
cisplatin and synergizes with these agents in models of
ovarian cancer. Mechanistic studies show that the enhanced activity is a result of inactivation of XRCC1 and MDC1, two mediator/adaptor
proteins that are essential for DNA repair and that require phosphorylation by CK2 for their function. These data position CK2 as a valid pharmacologic target for intelligent
drug combinations and support the evaluation of
CX-4945 in combination with
gemcitabine and
platinum-based chemotherapeutics in the clinical setting.