Inactivation of O⁶-Alkylguanine-DNA Alkyltransferase. 1. Novel O⁶-(Hetarylmethyl)guanines Having Basic Rings in the Side Chain

Abstract

A number of novel guanine derivatives containing heterocyclic moieties at the O6-position have been synthesized using a purine quaternary salt which reacts with alkoxides under mild conditions. Initially O6-substituents were investigated in which the benzene ring of the known agent, O6-benzylguanine, was replaced by unsubstituted heterocyclic rings. The ability of these agents to inactivate the DNA repair protein O6-alkylguanine-DNA alkyltransferase (ATase), both as pure recombinant protein and in the human lymphoblastoid cell line Raji, has been compared with that of O6-benzylguanine. The present paper focuses on O6-substituents with basic rings, and under standard conditions several of them proved more effective than benzyl for inactivation of both recombinant and Raji ATase. Among the pyridine derivatives, the 2-picolyl compound 7 is not very active in contrast to the 3- and 4-picolyl compounds, and this influenced our choice of isomers of other basic ring systems for study. Since halogen substitution in the thiophene ring considerably increased the activity (17 versus 6), similar modifications in the pyridine series were examined. The more polar O6-substituents in this study are on the whole compatible with the stereochemical requirements of the ATase protein, and their pharmacological properties may be valuable in subsequent in vivo investigations, particularly the thenyl (6), 5-thiazolylmethyl (12), 5-bromothenyl (17), and 2-chloro-4-picolyl (21) derivatives.

Labeling of fusion proteins with synthetic fluorophores in live cells

“…In these experiments, CHO cells transiently expressing tsVSVG-AGT were incubated for 20 h at 34°C and subsequently labeled with fluorescein. To quench residual AGT fusion protein not labeled with fluorescein, cells were incubated for 15 min with the AGT inhibitor O 6 -(4-bromothenyl)-guanine (29). The temperature of the medium then was shifted to 40°C, which should lead to misfolding of newly synthesized tsVSVG-AGT and its retention in the endoplasmic reticulum.…”

O6-(4-bromothenyl)guanine reverses temozolomide resistance in human breast tumour MCF-7 cells and xenografts

“…These have been hampered by the similar toxicities of the two agents, and no useful increase in therapeutic index has been demonstrated (Micetich et al, 1992;Lee et al, 1993;Smith et al, 1996;Hammond et al, 2004). Because of this, interest has turned to inactivation of MGMT using inherently nontoxic pseudosubstrates for the protein, such as O 6 -benzylguanine (O 6 -BeG; reviewed in Pegg et al, 1995;Dolan and Pegg, 1997) and O 6 -(4-bromothenyl)guanine (PaTrin-2, Lomeguatrib;McElhinney et al, 1998;Middleton et al, 2002;Middleton and Margison, 2003).…”

Inhibition of O6-Methylguanine-DNA Methyltransferase by Glucose-Conjugated Inhibitors: Comparison with Nonconjugated Inhibitors and Effect on Fotemustine and Temozolomide-Induced Cell Death

“…The fluorinated compounds 2-amino-6-(2-fluoropyridine-4-yl-methoxy)-9H-purine (3) and 2-amino-6-(2-fluoro-pyridine-4-yl-methoxy)-9-(octyl-␤-D-glucosyl)-purine (8) were synthesized according to Schirrmacher et al (2002a,b). 2-Amino-6-(benzyloxy)-9H-purine (McElhinney et al, 1998) (1), 2-amino-6-(4-bromothiophen-2-ylmethoxy)-9H-purine (Reinhard et al, 2001a) (4), 2-amino-6-(3-iodo-benzyloxy)-9H-purine (Vaidyanathan et al, 2000) (2), and -bromo-octyltetra-O-benzoyl-␣-D-glucopyranoside (Gallo-Rodriguez et al, 1998) were obtained via published analogous procedures. 2-Amino-6-(5-iodothiophen-2-yl-methoxy)-9H-purine (5) was synthesized from (5-iodothiophen-2-yl)-methanol (D'Auria et al, 1987) and 2-amino-N,N,N-trimethyl-9H-purine-6-yl-ammonium chloride (McElhinney et al, 1998;Schirrmacher et al, 2002b).…”

“…Even more important, however, would be to inactivate MGMT in tumors to sensitize the tumor to an antineoplastic agent. Various highly efficient MGMT inhibitory compounds have been developed that are promising tools for tumor sensitization (Dolan et al, 1990;Pegg et al, 1995;Margison et al, 1996;Friedman et al, 1998;McElhinney et al, 1998McElhinney et al, , 2003. However, despite encouraging in vitro studies and lack of systemic side effects in patients (Friedman et al, 1998), a recent phase II trial did not reveal significant increase in the therapeutic efficacy of N, -N-nitrosourea in the treatment of malignant glioblastomas (Quinn et al, 2002).…”