Abstract
The DNA repair protein O6-methylguanine-DNA methyltransferase (MGMT) is important in cellular resistance to certain alkylating antitumor agents such as the methylating drug temozolomide (TMZ). To provide a more rational basis for clinical combinations with another commonly used drug, cisplatin, we assessed the modulation of MGMT protein and mRNA levels in the human leukemic cell line Jurkat after treatment with these agents. Cisplatin decreased MGMT activity in a time- and dose-dependent manner, with maximal suppression (50%) observed 24 h after treatment with 25 μM cisplatin. This was probably the result of decreased transcription of the MGMT gene, because there was an earlier nadir of MGMT mRNA levels after cisplatin treatment and neither cisplatin nor DNA reacted with cisplatin in vitro was able to inhibit MGMT activity in an in vitro assay. TMZ alone depleted MGMT activity in a time- and dose-dependent manner with almost complete loss of activity occurring immediately after treatment with 500 μM TMZ. Combinations of cisplatin (12.5 μM) and TMZ (250 μM) caused substantial and prolonged MGMT depletion with recovery to only 30% of pretreatment levels by 48 h. These results suggest that the clinical efficacy of TMZ and cisplatin may be improved by appropriate schedules of combinations of these agents.
Footnotes
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Send reprint requests to: Dr. Stefania D'Atri, Laboratory of Pharmacology, Istituto Dermopatico Dell'Immacolata (IDI-IRCCS), Via dei Monti di Creta 104, 00167 Rome, Italy. E-mail: s.datri{at}idi.it
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↵1 This study was supported by a grant from the Italian Ministry of Health. Work at the Paterson Institute was supported by the Cancer Research Campaign.
- Abbreviations:
- O6-G
- O6-guanine
- BCNU
- 1,3-bis(2-chloroethyl)-1-nitrosourea
- CM
- complete medium
- DTIC
- 5-(3,3-dimethyl-1-triazeno)imidazole-4-carboxamide
- GAPDH
- glyceraldehyde-3-phosphate dehydrogenase
- MTIC
- 5-(3-methyl-1-triazeno)imidazole-4-carboxamide
- MGMT
- O6-methylguanine-DNA methyltransferase
- rhMGMT
- recombinant humanO6-methylguanine-DNA methyltransferase
- MMR
- mismatch repair
- O6-BeG
- O6-benzylguanine
- O6-MeG
- O6-methylguanine
- TE
- Tris-HCl/EDTA
- PTT
- paired Student's t test
- TMZ
- temozolomide [8-carbamoyl-3-methyl-imidazo[5,1-d]-1,2,3,5-tetrazin-4(3H)-one]
- Received January 18, 2000.
- Accepted May 2, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
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