ABSTRACT
Inhibition of the DNA damage checkpoint kinase WEE1 potentiates genotoxic chemotherapies by abrogating 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 to WEE1 inhibition. We show that MK-1775, a potent and selective ATP-competitive inhibitor of WEE1, 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 EC(50) 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, γH2AX and pCHK1(S345), 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 low PKMYT1 expression could serve as an enrichment biomarker for MK-1775 sensitivity.
Subject(s)
Antineoplastic Agents/pharmacology , Cell Cycle Proteins/antagonists & inhibitors , Nuclear Proteins/antagonists & inhibitors , Protein Kinase Inhibitors/pharmacology , Protein-Tyrosine Kinases/antagonists & inhibitors , Pyrazoles/pharmacology , Pyrimidines/pharmacology , Animals , Antineoplastic Agents/administration & dosage , Antineoplastic Agents/chemistry , Cell Cycle/drug effects , Cell Line, Tumor , Cell Proliferation/drug effects , DNA Damage/drug effects , Disease Models, Animal , Drug Evaluation, Preclinical , Drug Resistance, Neoplasm/genetics , Female , Gene Knockdown Techniques , Humans , Membrane Proteins/genetics , Membrane Proteins/metabolism , Mice , Neoplasms/drug therapy , Neoplasms/genetics , Neoplasms/metabolism , Neoplasms/pathology , Protein Kinase Inhibitors/administration & dosage , Protein Kinase Inhibitors/chemistry , Protein Serine-Threonine Kinases/genetics , Protein Serine-Threonine Kinases/metabolism , Protein-Tyrosine Kinases/genetics , Protein-Tyrosine Kinases/metabolism , Pyrazoles/administration & dosage , Pyrimidines/administration & dosage , Pyrimidinones , Tumor Burden/drug effects , Xenograft Model Antitumor AssaysABSTRACT
Inhibition of the protein kinase WEE1 synergizes with chemotherapy in preclinical models and WEE1 inhibitors are being explored as potential cancer therapies. Here, we investigate the mechanism that underlies this synergy. We show that WEE1 inhibition forces S-phase-arrested cells directly into mitosis without completing DNA synthesis, resulting in highly abnormal mitoses characterized by dispersed chromosomes and disorganized bipolar spindles, ultimately resulting in mitotic exit with gross micronuclei formation and apoptosis. This mechanism of cell death is shared by CHK1 inhibitors, and combined WEE1 and CHK1 inhibition forces mitotic entry from S-phase in the absence of chemotherapy. We show that p53/p21 inactivation combined with high expression of mitotic cyclins and EZH2 predispose to mitotic entry during S-phase with cells reliant on WEE1 to prevent premature cyclin-dependent kinase (CDK)1 activation. These features are characteristic of aggressive breast, and other, cancers for which WEE1 inhibitor combinations represent a promising targeted therapy.
