In vitro cytotoxicity and in vivo efficacy, pharmacokinetics, and metabolism of 10074-G5, a novel small-molecule inhibitor of c-Myc/Max dimerization

• Published in: The Journal of pharmacology and experimental therapeutics 2010-12, Vol.335 (3), p.715-727
• Main Authors: Clausen, Dana M, Guo, Jianxia, Parise, Robert A, Beumer, Jan H, Egorin, Merrill J, Lazo, John S, Prochownik, Edward V, Eiseman, Julie L
• Format: Article
• Language: English
• Subjects: Animal Structures - metabolism; Animals; Basic Helix-Loop-Helix Leucine Zipper Transcription Factors - antagonists & inhibitors; Basic Helix-Loop-Helix Leucine Zipper Transcription Factors - metabolism; Blood Proteins - metabolism; Cell Line, Tumor; Cell Survival - drug effects; Doxorubicin - therapeutic use; Feces - chemistry; Female; Glucuronates - metabolism; Glucuronidase - metabolism; HL-60 Cells; Humans; Inhibitory Concentration 50; Liver - metabolism; Mice; Mice, SCID; Neoplasms - metabolism; Neoplasms - pathology; Oxadiazoles - metabolism; Oxadiazoles - pharmacokinetics; Oxadiazoles - pharmacology; Oxadiazoles - therapeutic use; Oxadiazoles - toxicity; Plasma - metabolism; Protein Binding - drug effects; Protein Multimerization - drug effects; Proto-Oncogene Proteins c-myc - antagonists & inhibitors; Proto-Oncogene Proteins c-myc - metabolism; Tandem Mass Spectrometry; Thiazoles - pharmacology; Treatment Outcome; Urine - chemistry; Xenograft Model Antitumor Assays
• ISSN: 0022-3565; 1521-0103
• DOI: 10.1124/jpet.110.170555

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.