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 micromol/l TMZ, alone or in combination with 5 micromol/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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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 |
Journal | International journal of oncology
(Int J Oncol)
Vol. 29
Issue 4
Pg. 785-97
(Oct 2006)
ISSN: 1019-6439 [Print] Greece |
PMID | 16964376
(Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
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Chemical References |
- Antineoplastic Agents
- Enzyme Inhibitors
- O(6)-benzylguanine
- Guanine
- Dacarbazine
- O(6)-Methylguanine-DNA Methyltransferase
- Temozolomide
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Topics |
- Antineoplastic Agents
(pharmacology)
- Base Pair Mismatch
(physiology)
- DNA Methylation
- DNA Repair
- Dacarbazine
(analogs & derivatives, pharmacology)
- Drug Resistance, Neoplasm
(genetics)
- Enzyme Inhibitors
(pharmacology)
- Guanine
(analogs & derivatives, pharmacology)
- Humans
- Melanoma
(enzymology, genetics)
- O(6)-Methylguanine-DNA Methyltransferase
(antagonists & inhibitors, genetics, physiology)
- Promoter Regions, Genetic
- Temozolomide
- Tumor Cells, Cultured
- Up-Regulation
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