Evidence for Nucleotide Excision Repair as a Modifying Factor ofO6-Methylguanine-DNA Methyltransferase-Mediated Innate Chloroethylnitrosourea Resistance in Human Tumor Cell Lines

  1. Zhong-Ping Chen1,
  2. Areti Malapetsa1,
  3. Angela McQuillan,
  4. Daniela Marcantonio1,
  5. Vanessa Bello1,
  6. Gérard Mohr1,
  7. Joanna Remack2,
  8. Thomas P. Brent2 and
  9. Lawrence C. Panasci1
  1. 1Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital, 3755 Côte Ste. Catherine, Montreal, Quebec, Canada H3T 1E2 (Z.P.C., A.M., A.Mc., D.M., V.B., G.M., L.C.P.), and 2Department of Molecular Pharmacology, St. Jude Children’s Research Hospital, Memphis, Tennessee 38105-2794 (J.R., T.P.B.)

    Abstract

    We examined the O6-methylguanine-DNA methyltransferase (MGMT) protein as well as MGMT activity levels and the excision repair cross-complementing rodent repair deficiency gene,ERCC2 (XPD), protein levels in 14 human tumor cell lines not selected for chloroethylnitrosourea (CENU) resistance. These results were compared with 1,3-bis-(2-chloroethyl)-1-nitrosourea (BCNU) cytotoxicity and UV light sensitivity. MGMT protein correlated significantly with MGMT activity (r = 0.9497, p = 0.0001). There was no significant linear correlation between BCNU cytotoxicity and MGMT content as determined by both Western analysis (r = 0.139, p = 0.6348) and activity assay (r = 0.131, p = 0.6515). However, MGMT-rich cell lines were found to be more resistant than MGMT-poor cell lines to BCNU (t = 2.2375,p = 0.0225) but not to UV (t = 1.1734, p = 0.1317). Furthermore, the most BCNU-sensitive cell lines were all MGMT-poor. UV sensitivity was significantly correlated to BCNU cytotoxicity (r = 0.858, p = 0.0001). Significant correlations were found between ERCC2 protein levels and BCNU cytotoxicity (r = 0.786, p = 0.0009) or UV sensitivity (r = 0.874, p = 0.0001). Our results confirm that MGMT plays an important role in CENU resistance, but not in UV resistance. The correlation of UV sensitivity with BCNU cytotoxicity suggests that nucleotide excision repair is an important modifying factor of MGMT-mediated innate CENU resistance in human tumor cell lines, especially in highly resistant cell lines.ERCC2 may be implicated in this process.

    Footnotes

    • Send reprint requests to: Dr. Lawrence C. Panasci, Lady Davis Institute for Medical Research, Sir Mortimer B. Davis Jewish General Hospital, 3755 Côte Ste. Catherine, Montreal, Quebec, H3T 1E2 Canada.

    • This work was supported by the National Institute of Neurological Disorders and Stroke Grant NS22230, National Institutes of Health Grants 8457 and CA14799, American Lebanese Syrian Associated Charities, and a private donation from Helen and Nicki Lang.

    • Abbreviations:
      CENU
      chloroethylnitrosourea
      BCNU
      1,3-bis-(2-chloroethyl)-1-nitrosourea
      CHO
      Chinese hamster ovary
      ERCC
      excision repair cross-complementing
      GST
      glutathioneS-transferase
      MGMT
      O6-methylguanine-DNA methyltransferase
      Mer+
      O6-methylguanine-DNA methyltransferase-rich
      Mer−
      O6-methylguanine-DNA methyltransferase-poor
      NER
      nucleotide excision repair
      TFIIH
      transcription factor IIH
      XPD
      xeroderma pigmentosum complementation group D
      FBS
      fetal bovine serum
      SRB
      sulforhodamine B
      CAK
      cyclin-dependent kinase-activating kinase
      • Received May 16, 1997.
      • Accepted July 15, 1997.
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    1. Molecular Pharmacology November 1, 1997 vol. 52 no. 5 815-820
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