Inhibition of ATM Increases the Radiosensitivity of Uveal Melanoma Cells to Photons and Protons

Rumana N Hussain,Jakub Khzouz,Helen Kalirai,Sarah E Coupland,Jason L Parsons

doi:10.3390/cancers12061388

Rumana N Hussain, Jakub Khzouz + Show 3 more

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https://doi.org/10.3390/cancers12061388

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Abstract

Treatment of uveal melanoma (UM) is generally successful, with local primary tumour control being at 90–95%. Localized radiotherapy in the form of plaque brachytherapy or proton beam radiotherapy is the most common treatment modality in the UK. However, the basic mechanisms of radiation response, DNA repair and tissue reactions in UM have not been well documented previously. We have investigated the comparative radiosensitivity of four UM cell lines in response to exogenous radiation sources (both X-rays and protons), and correlated this with DNA repair protein expression and repair efficiency. We observed a broad range of radiosensitivity of different UM cell lines to X-rays and protons, with increased radioresistance correlating with elevated protein expression of ataxia telangiectasia mutated (ATM), a protein kinase involved in the signaling and repair of DNA double strand breaks. The use of an ATM inhibitor in UM cell lines enhanced radiosensitivity following both X-ray and proton irradiation, particularly in cells that contained high levels of ATM protein which are otherwise comparatively radioresistant. In proton-irradiated compared with non-irradiated primary enucleated UM patient samples, there was no significant difference in ATM protein expression. Our study therefore suggests that ATM is a potential target for increasing the radiosensitivity of more resistant UM subgroups.

Highlights

Uveal melanoma (UM) is the most common primary intraocular malignancy, it is a rare condition with an annual incidence of 5–8 cases per million [1]
There are limited data available analyzing the radiosensitivity of uveal melanoma (UM) cell lines to both protons and photons, and the relationship to DNA repair protein expression
We first analysed the levels of key proteins involved in DNA base damage and single strand break repair (poly(ADP-ribose) polymerase-1, PARP-1; X-ray repair cross-complementing protein 1, XRCC1, polynucleotide kinase phosphatase, PNKP and AP endonuclease 1, APE1) and DNA double strand breaks (DSBs) repair (Ku86, DNA-Pk, ataxia telangiectasia mutated (ATM), ATR, 53BP1 and RAD51) in extracts from four UM cell lines derived from primary (Mel270 and 92.1)

Summary

Introduction

Uveal melanoma (UM) is the most common primary intraocular malignancy, it is a rare condition with an annual incidence of 5–8 cases per million [1]. Cancers 2020, 12, 1388 spectrum of radiosensitivity to X-ray radiation, with no apparent difference as to whether the cells were derived from the primary or metastatic tumor [6,7]. This was supported by a more recent study performed in a range of UM cell lines (SP6.5, Mel270, μ2, TP17, 92.1 and MKT-BR), which again demonstrated broad radiosensitivity to X-ray radiation, which was neither influenced by cell cycle synchronization (asynchronous or confluent cells in G0 /G1) nor by hypoxic conditions (1% oxygen) preand post-irradiation [8]. This study, demonstrated the increased effectiveness of high linear energy transfer (LET) carbon ions, compared to low-LET X-rays, in significantly reducing cell survival

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