Abstract
The c-Myc oncoprotein is overexpressed in many tumors and is essential for maintaining the proliferation of transformed cells. To function as a transcription factor, c-Myc must dimerize with Max via the basic helix-loop-helix leucine zipper protein (bHLH-ZIP) domains in each protein. The small molecule 7-nitro-N-(2-phenylphenyl)-2,1,3-benzoxadiazol-4-amine (10074-G5) binds to and distorts the bHLH-ZIP domain of c-Myc, thereby inhibiting c-Myc/Max heterodimer formation and inhibiting its transcriptional activity. We report in vitro cytotoxicity and in vivo efficacy, pharmacodynamics, pharmacokinetics, and metabolism of 10074-G5 in human xenograft-bearing mice. In vitro, 10074-G5 inhibited the growth of Daudi Burkitt's lymphoma cells and disrupted c-Myc/Max dimerization. 10074-G5 had no effect on the growth of Daudi xenografts in C.B-17 SCID mice that were treated with 20 mg/kg 10074-G5 intravenously for 5 consecutive days. Inhibition of c-Myc/Max dimerization in Daudi xenografts was not seen 2 or 24 h after treatment. Concentrations of 10074-G5 in various matrices were determined by high-performance liquid chromatography-UV, and metabolites of 10074-G5 were identified by liquid chromatography/tandem mass spectrometry. The plasma half-life of 10074-G5 in mice treated with 20 mg/kg i.v. was 37 min, and peak plasma concentration was 58 μM, which was 10-fold higher than peak tumor concentration. The lack of antitumor activity probably was caused by the rapid metabolism of 10074-G5 to inactive metabolites, resulting in tumor concentrations of 10074-G5 insufficient to inhibit c-Myc/Max dimerization. Our identification of 10074-G5 metabolites in mice will help design new, more metabolically stable small-molecule inhibitors of c-Myc.
Footnotes
This work was supported by the National Institutes of Health National Cancer Institute [Grants P30-CA47904, CA078039, CA140624]. J.H.B. is the recipient of a Hillman Fellows for Innovative Cancer Research Award. M.J.E. is the recipient of an American Society of Clinical Oncology Cancer Foundation Translational Research Professorship.
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
doi:10.1124/jpet.110.170555.
↵ The online version of this article (available at http://jpet.aspetjournals.org) contains supplemental material.
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ABBREVIATIONS:
- bHLH-ZIP
- basic helix-loop-helix leucine zipper protein
- PBS
- phosphate-buffered saline
- HPLC
- high-performance liquid chromatography
- LC-MS/MS
- liquid chromatography/tandem mass spectrometry
- MTT
- methylthiazolyldiphenyl-tetrazolium bromide
- 10074-G5
- 7-nitro-N-(2-phenylphenyl)-2,1,3-benzoxadiazol-4-amine
- 10058-F4
- [Z-E]-5-[4-ethylbenzylidene]-2-thioxo-1,3-thiazolidin-4-one
- AUC
- area under the concentration
- Cmax
- maximum peak concentration
- DAD
- diode array detector
- DMSO
- dimethyl sulfoxide.
- Received May 25, 2010.
- Accepted August 24, 2010.
- Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics
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