Ae. Pegg et al., Inactivation of human O-6-alkylguanine-DNA alkyltransferase by modified oligodeoxyribonucleotides containing O-6-benzylguanine, J PHARM EXP, 296(3), 2001, pp. 958-965
Citations number
39
Categorie Soggetti
Pharmacology & Toxicology
Journal title
JOURNAL OF PHARMACOLOGY AND EXPERIMENTAL THERAPEUTICS
Inactivation of the DNA repair protein O-6-alkylguanine-DNA alkyltransferas
e (AGT) enhances tumor cell killing by therapeutic alkylating agents. O-6-B
enzylguanine (b(6)G) can inactivate AGT and is currently in clinical trials
to enhance therapy. Short oligodeoxyribonucleotides containing b(6)G are m
uch more effective inactivators, but their use for therapeutic purposes is
likely to be compromised by metabolic instability. We have therefore examin
ed the ability to inactivate AGT of an 11-mer oligodeoxyribonucleotide cont
aining b(6)G (11-mpBG) when modified with terminal methylphosphonate linkag
es to protect it from nucleases. This modification did not reduce the abili
ty to serve as a substrate/inactivator for AGT, and 11-mpBG had an ED50 val
ue of 1.3 nM, more than 300-fold lower than that for b(6)G. A similar oligo
deoxyribonucleotide containing O-6-methyl-guanine (m(6)G) was also found to
be a good substrate (ED50 value of 10 nM), but the benzylated form was rep
aired more rapidly and preferentially. When added to HT29 cell cultures, 5
muM 11-mpBG was able to cause a prolonged inactivation of cellular AGT for
at least 72 h and to greatly sensitize the cells to killing by 1,3-bis(2-ch
loroethyl)-1-nitrosourea (BCNU). The 11-mpMG was ineffective at up to 20 mu
M, suggesting that the benzyl group allows better uptake into the cell. How
ever, even with 11-mpBG, the 1000-fold decrease in potency toward AGT in HT
29 cells compared to that toward the protein in vitro suggests that uptake
may be a limiting factor. These results suggest that oligodeoxyribonucleoti
des such as 11-mpBG may prove to be useful drugs for potentiation of alkyla
ting agent chemotherapy if uptake can be improved.