Resistance-modifying agents. 8. Inhibition of O(6)-alkylguanine-DNA alkyltransferase by O(6)-alkenyl-, O(6)-cycloalkenyl-, and O(6)-(2-oxoalkyl)guanines and potentiation of temozolomide cytotoxicity in vitro by O(6)-(1-cyclopentenylmethyl)guanine.
A series of O(6)-allyl- and O(6)-(2-oxoalkyl)guanines were synthesized and evaluated, in comparison with the corresponding O(6)-alkylguanines, as potential inhibitors of the DNA-repair protein O(6)-alkylguanine-DNA alkyltransferase (AGT). Simple O(6)-alkyl- and O(6)-cycloalkylguanines were weak AGT inactivators compared with O(6)-allylguanine (IC(50) = 8.5 +/- 0.6 microM) with IC(50) values ranging from 100 to 1000 microM. The introduction of substituents at C-2 of the allyl group of O(6)-allylguanine reduced activity compared with the parent compound, while analogous compounds in the O(6)-(2-oxoalkyl)guanine series exhibited very poor activity (150-1000 microM). O(6)-Cycloalkenylguanines proved to be excellent AGT inactivators, with 1-cyclobutenylmethylguanine (IC(50) = 0.55 +/- 0.02 microM) and 1-cyclopentenylmethylguanine (IC(50) = 0.39 +/- 0.04 microM) exhibiting potency approaching that of the benchmark AGT inhibitor O(6)-benzylguanine (IC(50) = 0.18 +/- 0.02 microM). 1-Cyclopentenylmethylguanine also inactivated AGT in intact HT29 human colorectal carcinoma cells (IC(50) = 0.20 +/- 0.07 microM) and potentiated the cytotoxicity of the monomethylating antitumor agent Temozolomide by approximately 3- and 10-fold, respectively, in the HT29 and Colo205 tumor cell lines. The observation that four mutant AGT enzymes resistant to O(6)-benzylguanine also proved strongly cross-resistant to 1-cyclopentenylmethylguanine indicates that the O(6)-substituent of each compound makes similar binding interactions within the active site of AGT.
Griffin
R J
RJ
Department of Chemistry, Bedson Building, The University, Newcastle upon Tyne NE1 7RU, UK. r.j.griffin@ncl.ac.uk
Arris
C E
CE
Bleasdale
C
C
Boyle
F T
FT
Calvert
A H
AH
Curtin
N J
NJ
Dalby
C
C
Kanugula
S
S
Lembicz
N K
NK
Newell
D R
DR
Pegg
A E
AE
Golding
B T
BT
D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D002457:Cell Extracts; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D006147:Guanine / Q000031:analogs & derivatives / Q000138:chemical synthesis* / Q000737:chemistry / Q000494:pharmacology; D006801:Humans; D009154:Mutation; D019853:O(6)-Methylguanine-DNA Methyltransferase / Q000037:antagonists & inhibitors* / Q000235:genetics; D013329:Structure-Activity Relationship; D000077204:Temozolomide; D014407:Tumor Cells, Cultured
D018906:Antineoplastic Agents, Alkylating; D002457:Cell Extracts; D004791:Enzyme Inhibitors; C416347:O(6)-(1-cyclopentenylmethyl)guanine; D006147:Guanine; D003606:Dacarbazine; D019853:O(6)-Methylguanine-DNA Methyltransferase; D000077204:Temozolomide