|Budget Amount *help
¥5,500,000 (Direct Cost : ¥5,500,000)
Fiscal Year 1994 : ¥1,300,000 (Direct Cost : ¥1,300,000)
Fiscal Year 1993 : ¥4,200,000 (Direct Cost : ¥4,200,000)
A major problem of chemotherapy for malignant brain tumors is existence of tumor cells refractory to chemotherapeutic agents. Chloroetylnitrosouresa (CENUs) have widely been used singly or in combination. These agents from O_6-alkylguanines on DNA,which are repaired by the enzyme O_6-methylguanine-DNA methyltransferase (MGMT) . The first aim of the present research project was to study the distribution and quantification of MGMT activities and MGMT mRNA in brain tumors. The second was to facilitate a strategy aiming at overcoming MGMT-related resistance through inactivation of MGMT by exogenous deplators.
Brain tumor cells showing high MGMT activities had a large number of MGMT mRNA using a probe pKW100 and RT-PCR method, whereas those showing low MGMT activities had less MGMT mRNA.Amplification of MGMT mRMA is closely related with MGMT activities. Measurements of MGMT mRNA will be therefore a useful index of application of CENU chemotherapy. This indicates great advantage in the evalua
tion of MGMT activity of brain tumors.resected samples of which are too limited.
We tested effect of O_6-methylguanine, O_6-benzylguanine, O_6- (p-methylbenzyl) guanine, O_6- (p-chlorobenzy) guanine, O_6- (p-methoxybenzyl) guanine, O_6-methylhypoxantine, and O_6-benzylhypoxanthine on the sensitivity of ten tumor cell lines to ACNU.The sensitivity of MGMT-proficient tumor cells was greatly enhanced by pretreatment O_6-benzylguanine, O_6- (p-methylbenzl) guanine, and O_6- (p-chlorobenzyl) guanine, but not by O_6-methylguanine or O_6-methylhypoxanthine. O_6- (p-Methoxybenzyl) guanine moderately sensitized two cell lines to ACNU cytotoxicity. Biological effects O_6-alkylguanine derivatives suggest that the exocyclic 2-amino and O_6-benzyl groups in O_6-benzylguanine skeleton are both essential for the inhibition of MGMT activity.
The results of the present study offer molecular biological basis for selective chemotherapy of CENU in relation to DNA repair enzyme MGMT,and promise to potentiate therapeutic effects and to increase long survivors in malignant brain tumors. Less