Treatment of subcutaneous and intracranial brain tumor xenografts with O6-benzylguanine and 1,3-bis(2-chloroethyl)-1-nitrosourea.
O6-Alkylguanine-DNA alkyltransferase (AT) is a cellular protein that protects cells from the cytotoxic effects of nitrosoureas by repairing alkyl lesions at the O6 position of guanine. We have studied the ability of O6-benzylguanine to deplete AT activity in brain tumor xenografts and thereby increase the sensitivity of these tumors to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). In toxicity studies, pretreatment of athymic mice with O6-benzylguanine increased the toxicity of BCNU significantly. After i.p. injection of O6-benzylguanine into athymic mice carrying subcutaneous (s.c.) D341MED, a human medulloblastoma xenograft with a high AT activity, the AT activity of the tumors became undetectable within 1 h and remained depleted until 36 h. In s.c. xenografts to D341MED, treatment with O6-benzylguanine followed 1 h later by BCNU produced a significantly greater growth delay (14.8 days) than was seen with BCNU alone (2.3 days). A lower pretreatment dose of O6-benzylguanine produced a significantly smaller therapeutic effect. Delaying the administration of BCNU until 36 h after O6-benzylguanine resulted in a growth delay (1.2 days) that was not significantly different from that produced by the control or BCNU alone. In athymic mice with intracranial (i.c.) xenografts of D341MED, pretreatment with O6-benzylguanine followed 1 h later by BCNU produced a significantly increased survival as compared with that of the control, BCNU alone, O6-benzylguanine alone, and O6-benzylguanine followed 36 h later by BCNU. In experiments with s.c. xenografts of D245MG, a human glioma xenograft with undetectable AT activity, pretreatment with O6-benzylguanine 1 h prior to BCNU produced a significantly greater effect than was seen with BCNU treatment alone. The combination regimen, however, was not as effective as an equitoxic dose of BCNU alone. These studies suggest that O6-benzylguanine may be a useful adjuvant to nitrosourea therapy in human malignancies that exhibit a range of AT activities and that dose and timing are important variables in achieving therapeutic success. These data also indicate that therapeutic potentiation of BCNU by O6-benzylguanine can be achieved in i.c. tumors. As a result, this approach may be useful in the treatment of neoplasms of the central nervous system.
Felker
G M
GM
Duke University School of Medicine, Durham, NC 27710.
Friedman
H S
HS
Dolan
M E
ME
Moschel
R C
RC
Schold
C
C
D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D001932:Brain Neoplasms / Q000188:drug therapy*; D002330:Carmustine / Q000008:administration & dosage; D004357:Drug Synergism; D006147:Guanine / Q000008:administration & dosage / Q000031:analogs & derivatives; D006801:Humans; D008527:Medulloblastoma / Q000188:drug therapy*; D008780:Methyltransferases / Q000037:antagonists & inhibitors; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009368:Neoplasm Transplantation; D019853:O(6)-Methylguanine-DNA Methyltransferase; D013997:Time Factors
C064976:O(6)-benzylguanine; D006147:Guanine; D008780:Methyltransferases; D019853:O(6)-Methylguanine-DNA Methyltransferase; D002330:Carmustine