Received for publication January 11, 2006.
Revised March 18, 2006.
Accepted for publication March 20, 2006.

N-methylpurine DNA glycosylase and 8-oxoguanine DNA glycosylase metabolize the antiviral nucleoside 2-bromo-5,6-dichloro-1-(-D-ribofuranosyl)benzimidazole

Abstract

The rapid in vivo degradation of the potent HCMV inhibitor BDCRB compared to a structural L-analog, maribavir, has been attributed to selective glycosidic bond cleavage. An enzyme responsible for this selective BDCRB degradation, however, has not been identified. Here, we report the identification of two enzymes, 8-oxoguanine DNA glycosylase (OGG1) and N-methylpurine DNA glycosylase (MPG), that catalyze N-glycosidic bond cleavage of BDCRB and its 2-chloro homolog, TCRB, but not maribavir. To our knowledge, this is the first demonstration that free nucleosides are substrates of OGG1 and MPG. To understand how these enzymes might process BDCRB, docking and molecular dynamics simulations were performed with the native hOGG1 crystal coordinates. These studies showed that OGG1 was not able to bind a negative control, guanosine, yet BDCRB and maribavir were stabilized through interactions with various binding site residues, including Phe³¹⁹, His²⁷⁰, Ser³²⁰, and Asn¹⁴⁹. Only BDCRB, however, achieved orientations whereby its anomeric carbon, C1', could undergo nucleophilic attack by the putative catalytic residue, Lys²⁴⁹. Thus, in silico observations were in perfect agreement with experimental observations. These findings implicate DNA glycosylases in drug metabolism.

Key words: antivirals, enzyme kinetics, gastrointestinal pharmacology, microarrays