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Inactivation of O6-alkylguanine-DNA alkyltransferase by 8-substituted O6-benzylguanine analogs in mice

R B Ewesuedo1, L R Wilson, H S Friedman

  • 1Department of Pediatrics, University of Chicago, IL 60637, USA.

Cancer Chemotherapy and Pharmacology
|February 28, 2001
PubMed
Abstract

Insights

New O6-benzylguanine (BG) analogs show promise in modulating O6-alkylguanine-DNA alkyltransferase (AGT) activity. These 8-substituted analogs offer unique inactivation profiles, potentially improving therapeutic strategies against AGT-dependent conditions.

Area of Science:

  • Biochemistry and Molecular Biology
  • Pharmacology and Drug Discovery
  • Cancer Research

Background:

  • O6-alkylguanine-DNA alkyltransferase (AGT) is a DNA repair protein involved in cellular resistance to certain DNA-damaging agents.
  • O6-benzylguanine (BG) is an AGT inhibitor that has undergone clinical trials, but its rapid metabolism to 8-oxoguanine (8-oxoBG) affects its efficacy.
  • Developing BG analogs with altered pharmacological properties could lead to improved AGT modulation and therapeutic outcomes.

Purpose of the Study:

  • To evaluate the effectiveness of various 8-substituted O6-benzylguanine (BG) analogs in modulating O6-alkylguanine-DNA alkyltransferase (AGT) activity in vivo.
  • To compare the AGT inactivation capabilities of 8-oxoBG, 8-azaBG, 8-bromoBG, and 8-tfmBG with that of BG.
  • To investigate the tissue distribution and AGT inactivation profiles of these BG analogs in mouse tissues and tumors.

Main Methods:

  • Athymic nude mice bearing lung or brain tumor xenografts were administered various 8-substituted BG analogs via intraperitoneal or intracerebral injection.
  • AGT activity was quantified in harvested tissues (brain, liver, kidney) and tumors using a biochemical assay with radiolabeled DNA.
  • Drug concentrations (BG and 8-oxoBG) were determined using High-Performance Liquid Chromatography (HPLC) with fluorescence detection.

Main Results:

  • All tested 8-substituted BG analogs exhibited variable AGT inactivation capabilities, with some showing comparable or superior activity to BG, particularly in kidney and brain.
  • BG demonstrated more effective AGT inactivation in brain and brain tumor xenografts compared to 8-oxoBG, attributed to higher overall drug concentrations (BG + metabolite).
  • Area Under the Curve (AUC) values for BG were significantly higher than for 8-oxoBG in brain, kidney, and liver tissues, indicating better tissue bioavailability.

Conclusions:

  • 8-substituted BG analogs possess distinct in vivo AGT inactivation profiles that differ from the parent compound, BG.
  • The AGT inhibitory efficacy of BG and its metabolite 8-oxoBG is closely linked to their respective tissue distribution and disposition.
  • These findings suggest that 8-substituted BG analogs may offer unique therapeutic advantages for targeting AGT in various tissues and tumors.

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