A single cycle of treatment with temozolomide, alone or combined with O6-benzylguanine, induces strong chemoresistance in melanoma cell clones in vitro: role of O6-methylguanine-DNA methyltransferase and the mismatch repair system

  • Authors:
    • Ester Alvino
    • Daniele Castiglia
    • Simona Caporali
    • Rita Pepponi
    • Patrizia Caporaso
    • Pedro Miguel Lacal
    • Giancarlo Marra
    • Franziska Fischer
    • Giovanna Zambruno
    • Enzo Bonmassar
    • Joseph Jiricny
    • Stefania D'Atri
  • View Affiliations

  • Published online on: October 1, 2006     https://doi.org/10.3892/ijo.29.4.785
  • Pages: 785-797
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Abstract

Clinically achievable concentrations of temozolomide (TMZ) produce cytotoxic effects only in mismatch repair (MMR)-proficient cells endowed with low O6-methylguanine-DNA methyltransferase (MGMT) activity. Aim of the present study was to investigate the molecular mechanisms underlying acquired resistance of melanoma cells to TMZ and the effect of O6-benzylguanine (BG), a specific MGMT inhibitor, on the development of a TMZ-resistant phenotype. Three MMR-proficient melanoma cell clones with low or no MGMT activity were treated daily for 5 days with 50 µmol/l TMZ, alone or in combination with 5 µmol/l BG. Parental clones and sublines established after one or four cycles of treatment were analyzed for sensitivity to TMZ or TMZ+BG and for other parameters. The sublines established after one cycle of TMZ or TMZ+BG exhibited a marked increase in MGMT activity and resistance to TMZ alone. BG only partially reversed acquired resistance to the drug. In some cases, alterations in the MMR system accounted for MGMT-independent resistance to TMZ. Up-regulation of MGMT activity was associated with either demethylation of the MGMT promoter or hypermethylation of the body of the gene, and partially reversed by 5-aza-2'-deoxycytidine. The sublines established after four cycles of TMZ or TMZ+BG did not show a further increase in resistance to TMZ alone. However, two out of three sublines established after TMZ+BG treatment exhibited increased resistance to TMZ+BG. In conclusion, our data demonstrate that a single cycle of TMZ is sufficient to induce high levels of drug resistance in melanoma clones, principally, but not exclusively, via up-regulation of MGMT expression. Exposure to TMZ+BG favors the development of MGMT-independent mechanisms of TMZ resistance.

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October 2006
Volume 29 Issue 4

Print ISSN: 1019-6439
Online ISSN:1791-2423

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APA
Alvino, E., Castiglia, D., Caporali, S., Pepponi, R., Caporaso, P., Lacal, P.M. ... D'Atri, S. (2006). A single cycle of treatment with temozolomide, alone or combined with O6-benzylguanine, induces strong chemoresistance in melanoma cell clones in vitro: role of O6-methylguanine-DNA methyltransferase and the mismatch repair system. International Journal of Oncology, 29, 785-797. https://doi.org/10.3892/ijo.29.4.785
MLA
Alvino, E., Castiglia, D., Caporali, S., Pepponi, R., Caporaso, P., Lacal, P. M., Marra, G., Fischer, F., Zambruno, G., Bonmassar, E., Jiricny, J., D'Atri, S."A single cycle of treatment with temozolomide, alone or combined with O6-benzylguanine, induces strong chemoresistance in melanoma cell clones in vitro: role of O6-methylguanine-DNA methyltransferase and the mismatch repair system". International Journal of Oncology 29.4 (2006): 785-797.
Chicago
Alvino, E., Castiglia, D., Caporali, S., Pepponi, R., Caporaso, P., Lacal, P. M., Marra, G., Fischer, F., Zambruno, G., Bonmassar, E., Jiricny, J., D'Atri, S."A single cycle of treatment with temozolomide, alone or combined with O6-benzylguanine, induces strong chemoresistance in melanoma cell clones in vitro: role of O6-methylguanine-DNA methyltransferase and the mismatch repair system". International Journal of Oncology 29, no. 4 (2006): 785-797. https://doi.org/10.3892/ijo.29.4.785