MK-8776, a novel chk1 kinase inhibitor, radiosensitizes p53-defective human tumor cells.

Kathleen A Bridges,Xingxing Chen,Crosby Rock,Huifeng Liu,Thomas A Buchholz,Heath D Skinner,Raymond E Meyn,Stuart D Shumway

doi:10.18632/oncotarget.12311

Abstract

Radiotherapy is commonly used to treat a variety of solid tumors but improvements in the therapeutic ratio are sorely needed. The aim of this study was to assess the Chk1 kinase inhibitor, MK-8776, for its ability to radiosensitize human tumor cells. Cells derived from NSCLC and HNSCC cancers were tested for radiosensitization by MK-8776. The ability of MK-8776 to abrogate the radiation-induced G2 block was determined using flow cytometry. Effects on repair of radiation-induced DNA double strand breaks (DSBs) were determined on the basis of rad51, γ-H2AX and 53BP1 foci. Clonogenic survival analyses indicated that MK-8776 radiosensitized p53-defective tumor cells but not lines with wild-type p53. Abrogation of the G2 block was evident in both p53-defective cells and p53 wild-type lines indicating no correlation with radiosensitization. However, only p53-defective cells entered mitosis harboring unrepaired DSBs. MK-8776 appeared to inhibit repair of radiation-induced DSBs at early times after irradiation. A comparison of MK-8776 to the wee1 inhibitor, MK-1775, suggested both similarities and differences in their activities. In conclusion, MK-8776 radiosensitizes tumor cells by mechanisms that include abrogation of the G2 block and inhibition of DSB repair. Our findings support the clinical evaluation of MK-8776 in combination with radiation.

Highlights

The combination of molecular targeted agents with radiation for the treatment of human cancer continues to be an area of active investigation [1,2,3]
We found that this concentration of MK-8776 and treatment schedule did not result in any appreciable cytotoxicity with drug alone thereby allowing maximum sensitivity for assessing radiosensitization
We focused our tests of MK-8776 on cell lines derived from types of human tumors, i.e. NSCLC and head and neck squamous cell carcinomas (HNSCC), where radiotherapy typically plays a key role in the management of patients with these tumors

Summary

Introduction

The combination of molecular targeted agents with radiation for the treatment of human cancer continues to be an area of active investigation [1,2,3]. Radiation and many cancer chemotherapy drugs kill tumor cells by inducing DNA damage. Such damage triggers a network of multiprotein complexes that initially sense the DNA lesions and subsequently signal their repair and this process has been referred to as the DNA damage response (DDR) [5]. The DNA lesions induced by radiation include single strand breaks (SSBs) and double strand breaks (DSBs) and these breaks activate ataxia telangiectasia mutated (ATM) and ATM and Rad related (ATR) [6]. ATM and ATR activate the checkpoint kinases Chk and Chk which block cell cycle progression at multiple steps in G1, S and G2 phases to allow time for repair of the DNA damage prior to entry into mitosis [7]. The G2 block which is mediated by Chk becomes critical for controlling cell survival following irradiation

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