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O (4)-benzylfolic acid inactivates O (6)-alkylguanine-DNA alkyltransferase in brain tumor cell lines.

Publication ,  Journal Article
Johnson, SP; Kamen, BA; Bigner, DD; Friedman, HS
Published in: Cancer Chemother Pharmacol
November 2007

PURPOSE: The DNA repair protein, O (6)-alkylguanine-DNA alkyltransferase (AGT), is a primary source of tumor resistance to agents such as temozolomide and chloroethylnitrosoureas that form DNA lesions at the O (6)-position of guanines. To increase the efficacy of these drugs, pseudosubstrate inactivators of AGT such as O (6)-benzylguanine have been developed. A novel inactivator of AGT, O (4)-benzylfolic acid (O(4)-BFA), has been reported which is more potent and water soluble than O (6)-benzylguanine. Previous studies have suggested that uptake of O(4)-BFA is mediated by the folate receptor (FR), and, thus, its use may be limited to cells expressing FR. METHODS: We measured AGT activity in cell extracts from a panel of brain tumor cells exposed to O(4)-BFA. Inactivation of AGT by O(4)-BFA was measured in cells grown without folic acid as well as in cells grown in folic acid-containing media. Competitive binding studies were performed using purified FR to determine its affinity for O(4)-BFA. RESULTS: The observed IC(50) for O(4)-BFA in brain tumor cell lines ranged from 0.2 to 1.3 microM for cells grown in media containing 2.3 microM folic acid. At this concentration, folic acid would saturate the FR and the FR would be unable to take up O(4)-BFA. When cells were grown in folic acid free media, there was at most a 50% decrease in the observed IC(50)s, indicating that the FR was not essential for O(4)-BFA uptake. Competitive binding studies using purified FR confirmed that the IC(50) for O(4)-BFA is approximately 180 times greater than folic acid, i.e., it has a very weak affinity for FR. CONCLUSION: These results indicate that O(4)-BFA has potentially broad use as an inactivator of AGT as its use is not limited to tumors expressing high levels of FR.

Duke Scholars

Published In

Cancer Chemother Pharmacol

DOI

ISSN

0344-5704

Publication Date

November 2007

Volume

60

Issue

6

Start / End Page

883 / 889

Location

Germany

Related Subject Headings

  • Temozolomide
  • Receptors, Cell Surface
  • Oncology & Carcinogenesis
  • O(6)-Methylguanine-DNA Methyltransferase
  • Inhibitory Concentration 50
  • Humans
  • Folic Acid
  • Folate Receptors, GPI-Anchored
  • Drug Screening Assays, Antitumor
  • Drug Resistance, Neoplasm
 

Citation

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MLA
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Johnson, S. P., Kamen, B. A., Bigner, D. D., & Friedman, H. S. (2007). O (4)-benzylfolic acid inactivates O (6)-alkylguanine-DNA alkyltransferase in brain tumor cell lines. Cancer Chemother Pharmacol, 60(6), 883–889. https://doi.org/10.1007/s00280-007-0435-6
Johnson, Stewart P., Barton A. Kamen, Darell D. Bigner, and Henry S. Friedman. “O (4)-benzylfolic acid inactivates O (6)-alkylguanine-DNA alkyltransferase in brain tumor cell lines.Cancer Chemother Pharmacol 60, no. 6 (November 2007): 883–89. https://doi.org/10.1007/s00280-007-0435-6.
Johnson SP, Kamen BA, Bigner DD, Friedman HS. O (4)-benzylfolic acid inactivates O (6)-alkylguanine-DNA alkyltransferase in brain tumor cell lines. Cancer Chemother Pharmacol. 2007 Nov;60(6):883–9.
Johnson, Stewart P., et al. “O (4)-benzylfolic acid inactivates O (6)-alkylguanine-DNA alkyltransferase in brain tumor cell lines.Cancer Chemother Pharmacol, vol. 60, no. 6, Nov. 2007, pp. 883–89. Pubmed, doi:10.1007/s00280-007-0435-6.
Johnson SP, Kamen BA, Bigner DD, Friedman HS. O (4)-benzylfolic acid inactivates O (6)-alkylguanine-DNA alkyltransferase in brain tumor cell lines. Cancer Chemother Pharmacol. 2007 Nov;60(6):883–889.
Journal cover image

Published In

Cancer Chemother Pharmacol

DOI

ISSN

0344-5704

Publication Date

November 2007

Volume

60

Issue

6

Start / End Page

883 / 889

Location

Germany

Related Subject Headings

  • Temozolomide
  • Receptors, Cell Surface
  • Oncology & Carcinogenesis
  • O(6)-Methylguanine-DNA Methyltransferase
  • Inhibitory Concentration 50
  • Humans
  • Folic Acid
  • Folate Receptors, GPI-Anchored
  • Drug Screening Assays, Antitumor
  • Drug Resistance, Neoplasm