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O6-3-[125I]iodobenzyl-2'-deoxyguanosine ([125I]IBdG): synthesis and evaluation of its usefulness as an agent for quantification of alkylguanine-DNA alkyltransferase (AGT).

Publication ,  Journal Article
Shankar, S; Zalutsky, MR; Vaidyanathan, G
Published in: Bioorg Med Chem
June 2, 2005

The development of O(6)-(3-[(125)I]iodobenzyl)-2'-deoxyguanosine ([(125)I]IBdG), the glycosylated analogue of the O(6)-3-iodobenzylguanine (IBG), as an agent for the in vivo mapping of the DNA repair protein alkylguanine-DNA alkyltransferase (AGT) is described. Synthesis of its tin precursor, O(6)-3-trimethylstannylbenzyl-2'-deoxyguanosine (TBdG) was achieved in four steps from deoxyguanosine. Radioiodination of TBdG in a single step gave [(125)I]IBdG in 70-85% isolated radiochemical yield. [(125)I]IBdG bound specifically to pure AGT with an IC(50) of 7.1 microM. From paired-label assays, [(125)I]IBdG showed a 2- to 3-fold higher cellular uptake than [(131)I]IBG in DAOY medulloblastoma, TE-671 rhabdomyosarcoma, SK-Mel-28 melanoma, and HT-29 colon carcinoma human cell lines. Uptake of both labeled compounds in these cell lines decreased with increasing concentrations of unlabeled O(6)-benzylguanine (BG) when BG was present in the medium during incubation with the labeled compounds. Compared to BG, unlabeled IBdG diminished the uptake of [(125)I]IBdG and [(131)I]IBG in DAOY cells more efficiently (IC(50)<1 microM vs >10 microM for BG). There was no significant change in cell-bound activity of [(125)I]IBdG and [(131)I]IBG when BG was removed from the incubation medium before incubating cells with the tracers, suggesting that only a very small portion of radioactivity taken up by the cells is AGT bound. This was corroborated by gel-electrophoresis performed on extracts from cells treated with varying amounts of BG and then incubated with [(125)I]IBdG in the presence of BG. No radiolabeled AGT band was discernable by phosphor-imaging, signifying low cellular AGT binding of the radiotracer. In contrast, when cell extracts were prepared from BG pre-treated cells and aliquots were incubated with [(125)I]IBdG subsequently, the intensity of radiolabeled AGT band decreased linearly as a function of BG concentration. This suggests that the low level of [(125)I]IBdG that binds to AGT does so in a concentration dependent manner. These data suggest that IBdG is transported across the cell membrane to a higher degree than IBG. However, to be a practical tracer for quantifying cellular AGT, considerable localization of such derivatives need to occur within the cell nucleus where AGT is present predominantly.

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Published In

Bioorg Med Chem

DOI

ISSN

0968-0896

Publication Date

June 2, 2005

Volume

13

Issue

12

Start / End Page

3889 / 3898

Location

England

Related Subject Headings

  • Radiopharmaceuticals
  • O(6)-Methylguanine-DNA Methyltransferase
  • Medicinal & Biomolecular Chemistry
  • Iodine Radioisotopes
  • Humans
  • Drug Resistance, Neoplasm
  • Dose-Response Relationship, Drug
  • Deoxyguanosine
  • Cell Line, Tumor
  • 3405 Organic chemistry
 

Citation

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Shankar, S., Zalutsky, M. R., & Vaidyanathan, G. (2005). O6-3-[125I]iodobenzyl-2'-deoxyguanosine ([125I]IBdG): synthesis and evaluation of its usefulness as an agent for quantification of alkylguanine-DNA alkyltransferase (AGT). Bioorg Med Chem, 13(12), 3889–3898. https://doi.org/10.1016/j.bmc.2005.04.014
Shankar, Sriram, Michael R. Zalutsky, and Ganesan Vaidyanathan. “O6-3-[125I]iodobenzyl-2'-deoxyguanosine ([125I]IBdG): synthesis and evaluation of its usefulness as an agent for quantification of alkylguanine-DNA alkyltransferase (AGT).Bioorg Med Chem 13, no. 12 (June 2, 2005): 3889–98. https://doi.org/10.1016/j.bmc.2005.04.014.
Shankar, Sriram, et al. “O6-3-[125I]iodobenzyl-2'-deoxyguanosine ([125I]IBdG): synthesis and evaluation of its usefulness as an agent for quantification of alkylguanine-DNA alkyltransferase (AGT).Bioorg Med Chem, vol. 13, no. 12, June 2005, pp. 3889–98. Pubmed, doi:10.1016/j.bmc.2005.04.014.
Journal cover image

Published In

Bioorg Med Chem

DOI

ISSN

0968-0896

Publication Date

June 2, 2005

Volume

13

Issue

12

Start / End Page

3889 / 3898

Location

England

Related Subject Headings

  • Radiopharmaceuticals
  • O(6)-Methylguanine-DNA Methyltransferase
  • Medicinal & Biomolecular Chemistry
  • Iodine Radioisotopes
  • Humans
  • Drug Resistance, Neoplasm
  • Dose-Response Relationship, Drug
  • Deoxyguanosine
  • Cell Line, Tumor
  • 3405 Organic chemistry