• Open Access

Methotrexate induces oxidative DNA damage and is selectively lethal to tumour cells with defects in the DNA mismatch repair gene MSH2

Authors

  • Sarah A. Martin,

    1. Cancer Research UK Gene Function and Regulation Group, The Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, London, UK
    2. The Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, London, UK
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  • Afshan McCarthy,

    1. The Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, London, UK
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  • Louise J. Barber,

    1. Cancer Research UK Gene Function and Regulation Group, The Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, London, UK
    2. The Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, London, UK
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  • Darren J. Burgess,

    1. Cancer Research UK Gene Function and Regulation Group, The Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, London, UK
    2. The Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, London, UK
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  • Suzanne Parry,

    1. The Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, London, UK
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  • Christopher J. Lord,

    Corresponding author
    1. The Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, London, UK
    • Tel: +44 (0)20 7153 5333; Fax: +44 (0)20 7153 5340

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  • Alan Ashworth

    Corresponding author
    1. Cancer Research UK Gene Function and Regulation Group, The Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, London, UK
    2. The Breakthrough Breast Cancer Research Centre, The Institute of Cancer Research, London, UK
    • Tel: +44 (0)20 7153 5333; Fax: +44 (0)20 7153 5340

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Abstract

Mutations in the MSH2 gene predispose to a number of tumourigenic conditions, including hereditary non-polyposis colon cancer (HNPCC). MSH2 encodes a protein in the mismatch repair (MMR) pathway which is involved in the removal of mispairs originating during replication or from damaged DNA. To identify new therapeutic strategies for the treatment of cancer arising from MMR deficiency, we screened a small molecule library encompassing previously utilized drugs and drug-like molecules to identify agents selectively lethal to cells lacking functional MSH2. This approach identified the drug methotrexate as being highly selective for cells with MSH2 deficiency. Methotrexate treatment caused the accumulation of potentially lethal 8-hydroxy-2'-deoxyguanosine (8-OHdG) oxidative DNA lesions in both MSH2 deficient and proficient cells. In MSH2 proficient cells, these lesions were rapidly cleared, while in MSH2 deficient cells 8-OHdG lesions persisted, potentially explaining the selectivity of methotrexate. Short interfering (si)RNA mediated silencing of the target of methotrexate, dihydrofolate reductase (DHFR), was also selective for MSH2 deficiency and also caused an accumulation of 8-OHdG. This suggested that the ability of methotrexate to modulate folate synthesis via inhibition of DHFR, may explain MSH2 selectivity. Consistent with this hypothesis, addition of folic acid to culture media substantially rescued the lethal phenotype caused by methotrexate. While methotrexate has been used for many years as a cancer therapy, our observations suggest that this drug may have particular utility for the treatment of a subset of patients with tumours characterized by MSH2 mutations.

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