Increased activity of both CDK1 and CDK2 is necessary for the combinatorial activity of WEE1 inhibition and cytarabine.

Inhibition of WEE1 is emerging as a promising chemosensitization strategy in many cancers including acute leukemia. Our lab and others have demonstrated that a small-molecule inhibitor of WEE1, AZD1775, sensitizes acute leukemia cells to cytarabine; however, a mechanism of combinatorial activity has remained elusive. Thus, we sought to determine the relative contribution of WEE1 targets CDK1 and CDK2 to the combinatorial activity of AZD1775 and cytarabine. To accomplish this, we expressed "WEE1 resistant" CDK1 (CDK1-AF) and CDK2 (CDK2-AF) constructs in a T-ALL cell line. Expression of CDK1/2-AF together, but neither alone, enhanced the anti-proliferative effects, DNA damage and apoptosis induced by cytarabine. Furthermore, pharmacologic inhibition of CDK1 alone or CDK1 and CDK2 together reduced the combinatorial activity of AZD1775 and cytarabine. Thus, increased activity of both CDK1 and CDK2 in response to WEE1 inhibition is necessary for the combinatorial activity of AZD1775 and cytarabine. This suggests the role of WEE1 in cells with accumulated DNA damage extends beyond regulation of CDK1 and the G2/M checkpoint and highlights the importance of WEE1 in mediating progression through the cell cycle.