MK-1775, a Novel Wee1 Kinase Inhibitor, Radiosensitizes p53-Defective Human Tumor Cells

Abstract

Purpose Radiotherapy is commonly used to treat a variety of solid tumors. However, improvements in the therapeutic ratio for several disease sites are sorely needed leading us to assess molecularly targeted therapeutics as radiosensitizers. The aim of this study was to assess the wee1 kinase inhibitor, MK-1775, for its ability to radiosensitize human tumor cells. Experimental Design Human tumor cells derived from lung, breast and prostate cancers were tested for radiosensitization by MK-1775 using clonogenic survival assays. Both p53 wild-type and p53-defective lines were included. The ability of MK-1775 to abrogate the radiation-induced G2 block, thereby allowing cells harboring DNA lesions to prematurely progress into mitosis, was determined using flow cytometry and detection of γ-H2AX foci. The in vivo efficacy of the combination of MK-1775 and radiation was assessed by tumor growth delay experiments using a human lung cancer cell line growing as a xenograft tumor in nude mice. Results Clonogenic survival analyses indicated that nanomolar concentrations of MK-1775 radiosensitized p53-defective human lung, breast, and prostate cancer cells but not similar lines with wild-type p53. Consistent with its ability to radiosensitize, MK-1775 abrogated the radiation-induced G2 block in p53-defective cells but not in p53 wild-type lines. MK-1775 also significantly enhanced the anti-tumor efficacy of radiation in vivo as shown in tumor growth delay studies, again for p53-defective tumors. Conclusions These results indicate that p53-defective human tumor cells are significantly radiosensitized by the potent and selective wee1 kinase inhibitor, MK-1775, in both the in vitro and in vivo settings. Taken together, our findings strongly support the clinical evaluation of MK-1775 in combination with radiation.

Cytokinetic effects of Wee1 disruption in pancreatic cancer

“…Since the G2 phase of the cell cycle provides a pause during which post-replication errors and breaks are corrected, its premature termination by Wee1 inhibition might promote the mitotic death of cells failing to complete repair. 12,25,35 This could be particularly relevant to pancreatic cancers, given their high degree of genomic instability. However, there was no significant single agent activity in our PDX models, which is consistent with the low response rate of MK-1775 (AZD1775) in human clinical trials.…”

“…11 Preclinical studies have shown that Wee1 inhibition can sensitize cells to mitotic catastrophe following exposure to DNA damaging agents, and several studies are ongoing to test this possibility this in the clinic. 7,[12][13][14][15] Wee1 has an additional role as a Cdk2 kinase, which is relevant to the development of cancer treatment strategies that incorporate Wee1 inhibitors. 16,17 The activation of Cdk2 promotes origin firing during S-phase, and regulates the overall timing of DNA replication.…”

“…Here the anticipated effect of Wee1 inhibition would be to abrogate the G2 checkpoint, resulting in cells entering mitosis with unresolved radiation-induced chromosomal damage, and thereby undergoing death through mitotic catastrophe. 12,23,24 Pancreatic cancers are characterized by their poor response to both chemotherapy and radiotherapy. Preclinical studies suggest that MK-1775 might be combined effectively with either of these treatment modalities, and improve the outcome for pancreatic cancer patients.…”

A haploid genetic screen identifies the G1/S regulatory machinery as a determinant of Wee1 inhibitor sensitivity

“…Inhibition of Wee1 potentiates DNA-damaging chemotherapeutics and radiotherapy and has cytotoxic effects as a single agent (19)(20)(21)(22). The consensus view is that Wee1 inhibition facilitates tumor cell killing through G 2 /M checkpoint inactivation, which would catalyze mitotic catastrophe (23)(24)(25).…”

Science in Focus: Combining Radiotherapy with Inhibitors of the DNA Damage Response

“…More recently, inhibition of Wee1, another kinase that promotes G2/M checkpoint activation in response to radiation, has emerged as a potential therapeutic strategy [17]. As with ATM inhibitors, a number of studies have indicated that the effects of ATR or Wee1 inhibitors are more pronounced in p53 defective contexts [18,19].…”