Inhibition of Chk1 with Prexasertib Enhances the Anticancer Activity of Ciclopirox in Non-Small Cell Lung Cancer Cells

Lung cancer is a leading cause of cancer-related deaths worldwide. Non-small cell lung cancer (NSCLC) is the most prevalent lung cancer subtype. Ciclopirox olamine (CPX), an off-patent fungicide, has been identified as a new anticancer agent. Prexasertib (PRE), a Chk1 inhibitor, is in phase 1/2 clinical trials in various tumors. The anticancer effect of the combination of CPX with PRE on NSCLC cells is unknown. Here, we show that CPX is synergistic with PRE in inhibiting cell proliferation and inducing apoptosis of NSCLC (A549 and A427) cells. Combined treatment with CPX and PRE significantly increased the cell population in the G1/G0 and sub-G1 phases, compared to the single treatment with CPX or PRE. Concurrently, the combined treatment downregulated the protein levels of cyclins (A, B1), cyclin-dependent kinases 4, 6, 2 (CDK4, CDK6, CDK2), cell division cycle 25 B, C (Cdc25B, Cdc25C), and upregulated the protein levels of the CDK inhibitors p21 and p27, leading to decreased phosphorylation of Rb. In addition, the combined treatment increased DNA damage, evidenced by increased expression of γH2AX. In line with this, the combined treatment induced more apoptosis than either single treatment. This was associated with increased expression of DR4, DR5, Fas, and FADD and decreased expression of survivin, resulting in activation of caspase 8 and caspase 3 as well as cleavage of poly (ADP ribose) polymerase (PARP). Taken together, the results suggest that inhibition of Chk1 with PRE can enhance the anticancer activity of CPX at least partly by decreasing cell proliferation and increasing apoptosis in NSCLC cells.