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

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.

Mapping genetic alterations causing chemoresistance in cancer: identifying the roads by tracking the drivers

“…273 Defects in the mismatch system has been related to inferior response to 5-fluorouracil in cancer of the large bowel, 272 but more lately to an inferior response to cisplatin in germ-cell tumours (testicular seminomas and non-seminomas) as well. 274 In contrast, there is experimental evidence indicating enhanced response to methotrexate-induced oxidative damage in MSH2-deficient endometrial and colon cancer-derived cells, 275 but reduced response to thiopurines in leukemia cells. 276 O 6 -METHYL-GUANINE-DNA-METHYLTRANSFERASE In addition to the mechanisms described above, MGMT has a role in therapy sensitivity.…”

Parallel High-Throughput RNA Interference Screens Identify PINK1 as a Potential Therapeutic Target for the Treatment of DNA Mismatch Repair–Deficient Cancers

“…We have previously shown that synthetic lethality with MMR genes can be achieved by causing oxidative DNA damage in an MMR-deficient background (10,16). More specifically, MSH2 deficiency is synthetically lethal with genetic changes that result in an accumulation of 8-oxoG lesions in nuclear DNA (one of the more common oxidized DNA bases that are caused by oxidative damage), whereas MLH1 deficiency is synthetically lethal with genetic changes that cause mitochondrial DNA 8-oxoG accumulation (10).…”

Therapeutic Targeting of the DNA Mismatch Repair Pathway

“…We have applied this approach to MMR-deficient cancers by identifying a synthetic lethal interaction between MSH2 deficiency and treatment with the chemotherapeutic agent methotrexate (45 (45). Similarly, MSH2-deficient cells are sensitive to psoralen, an agent that induces DNA interstrand crosslinks, but MLH1-deficient cells tend to be more resistant (46,47).…”