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  • 1
    ISSN: 1573-7373
    Keywords: brain tumors ; O 6-methylguanine ; ACNU ; augmentation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary O 6-Methylguanine is a substrate of the DNA repair enzymeO 6-methylguanine-DNA methyltransferase, which is involved in the repair mechanism of DNA damage induced by chloroethylnitrosoureas such as 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-chloroethyl)-3-nitrosourea hydrochloride (ACNU). We tested the enhancement effect ofO 6-methylguanine pretreatment on ACNU cytotoxicity in ACNU-resistant brain tumors. Exposure toO 6-methylguanine at various times ranging from 2 to 48 hours increased the cytotoxic effects of ACNU on C6-1 cells, and this effect was highest at higher concentrations 500 and 1,000 μM. Colorimetric cytotoxicity assay revealed at least a two-fold increase in ACNU cytotoxicity relative to controls withoutO 6-methylguanine. Intraarterial ACNU after treatment withO 6-methylguanine (two intravenous bolus injections of 80 and 40 mg/kg) significantly (P 〈 0.05 or P 〈 0.01) reduced the proliferation activity of transplanted C6-1 tumors for 96 hours after injection, whereas intravenous ACNU together withO 6-methylguanine significantly (P 〈 0.05) reduced C6-1 activity for only 48 hours. Thus, pretreatment withO 6-methylguanine prolonged the suppression effect of ACNU. The C6-1 tumors treated only with intravenous or intraarterial ACNU showed transient inhibition and rapid regrowth for 24 hours after treatment. These results indicate thatO 6-methylguanine increases ACNU cytotoxicity in anin vitro andin vivo brain tumor model.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-7373
    Keywords: brain tumors ; intracarotid administration ; ACNU ; BUdR labeling index
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Chloroethy1nitrosourea (CENU) chemotherapy has yielded limited benefit on survival of malignant brain tumors. Intracarotid administration of CENU is expected to have the advantage of increasing drug concentration reaching tumors. To understand basic knowledge of intracarotid chemotherapy, we monitor changes of proliferating rate after intracarotid injection of 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2chloroethyl)-3-nitrosourea hydrochloride (ACNU), using a bromodeoxyuridine (BUdR) labeling index (LI) in transplanted brain tumors of three cell strains. C6-2 tumor cells were in vitro sensitive to ACNU, and C6-2/ACNU and C6-1 cells were resistant. The drug sensitivity to ACNU was as follows: 11.9 μtM in the C6-2 cells, 46.0 μM in the C6-2/ACNU cells, and 49.7 μM in the C6-1 cells at SD10, which gives 10% survival of clonogenic cells. The intracarotid ACNU at a dose of 30 mg/kg abruptly decreased the LI to 11% (mean) from 36% in C6-2 transplanted tumors. The LI remained low between 12 and 48 hours after, and then increased to the pretreatment level by 96 hours. In contrast, the LI of C6-1 tumors transiently fell to 15% from 42% at 12 hours after the injection, and subsequently increased to 36% at 24 hours and 37% at 48 hours. These results indicate that intracarotid ACNU administration shortly suppresses proliferating activity of tumors and that combined and alternating chemotherapy are mandatory for enhancing effectiveness of brain tumor chemotherapy.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-7373
    Keywords: glioma ; cell line ; establishment ; cloroethylnitrosourea ; chemosensitivity ; O6-methylguanine-DNA methyltransferase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We have characterized two human glioblastoma cell lines, which were designated as YH cells and AM cells. The two cell lines maintained morphological appearance observed in the primary culture and immunohis-tochemically expressed glial fibrillary acidic protein (GFAP) and S-100 protein. Population doubling time for YH cells and AM cells indicated 30 hours and 25 hours, respectively, in an exponential phase of culture. Inoculation of AM cells into athymic nude mice formed large tumors at a high incidence. As with chemo-sensitivity to chloroethylnitrosourea, O6-methylguanine-DNA methyltransferase (MGMT) activity was measured inin vitro cultured cells as well as tumor specimens obtained at surgery. YH cells showed a high MGMT activity of 1196 fmol/mg and drug resistance to 1-(4-amino-2-methyl-5-pyrimidinyl)methyl-3-(2-cloroethyl)-3-nitrosourea hydrochloride (ACNU) using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. YH tumor specimens indicated an MGMT activity of 301 fmol/mg, which reflected poor effectiveness of ACNU chemotherapy in the clinical evaluation. AM cells had an extremely low MGMT activity of 16 fmol/mg and were vulnerable to ACNU. Original tumor specimens of AM cells however expressed a high value of 628 fmol/mg. Considering that ACNU chemotherapy was not effective in the both patients, an MGMT activity of original tumors related with responsiveness to ACNU. Discrepancy in an MGMT activity between thein vitro cell lines and the respective tumor specimens comes from selection of ACNU-sensitive cells or alteration in biological characteristics during long term culture. These results suggest that cell lines derived human brain tumors are useful targets for understanding the chemosensitivity of human malignant gliomas and for establishing a pertinent chemosensitivity test.
    Type of Medium: Electronic Resource
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