Small Molecule Therapeutics Preclinical Evaluation of the WEE 1 Inhibitor MK-1775 as Single-Agent Anticancer Therapy

Inhibitionof theDNAdamage checkpoint kinaseWEE1potentiates genotoxic chemotherapies byabrogating cell-cycle arrest and proper DNA repair. However, WEE1 is also essential for unperturbed cell division in the absence of extrinsic insult. Here, we investigate the anticancer potential of a WEE1 inhibitor, independent of chemotherapy, and explore a possible cellular context underlying sensitivity toWEE1 inhibition.We show that MK-1775, a potent and selectiveATP-competitive inhibitor ofWEE1, is cytotoxic across a broad panel of tumor cell lines and induces DNA double-strand breaks. MK-1775–induced DNA damage occurs without added chemotherapy or radiation in S-phase cells and relies on active DNA replication. At tolerated doses, MK-1775 treatment leads to xenograft tumor growth inhibition or regression. To begin addressing potential response markers for MK-1775 monotherapy, we focused on PKMYT1, a kinase functionally related to WEE1. Knockdown of PKMYT1 lowers the EC50 of MK-1775 by five-fold but has no effect on the cell-based response to other cytotoxic drugs. In addition, knockdown of PKMYT1 increases markers of DNA damage, gH2AX and pCHK1, induced by MK-1775. In a post hoc analysis of 305 cell lines treated with MK-1775, we found that expression of PKMYT1 was below average in 73% of the 33 most sensitive cell lines. Our findings provide rationale for WEE1 inhibition as a potent anticancer therapy independent of a genotoxic partner and suggest that lowPKMYT1 expression could serve as an enrichment biomarker forMK-1775 sensitivity.MolCancer Ther; 12(8); 1442–52. 2013 AACR.