Abstract
(Z)-5-[(1,2-Dihydro-2-oxo-3H-indol-3-ylidene)methyl]-2,4-dimethyl-1H-pyrrole-3-propanoic acid (TSU-68) is a new anticancer drug that inhibits angiogenic receptor tyrosine kinases, which play a crucial role in tumor-induced vascularization. TSU-68 undergoes hepatic oxidation and glucuronidation. Incubation of TSU-68 with human liver microsomes in the presence of NADPH resulted in the formation of three major metabolites: 5-, 6-, and 7-hydroxyindolinone derivatives. The 5-, 6-, and 7-hydroxylation followed simple Michaelis-Menten kinetics with Vmax/Km values (an indicator of intrinsic clearance) of 13, 25, and 6 μl/min/mg, respectively. Of the 10 cDNA-expressed human cytochrome P450 isoforms examined, only CYP1A1 and CYP1A2 exhibited appreciable TSU-68 hydroxylation activity. Inhibition studies with α-naphthoflavone (a selective CYP1A2 inhibitor) and anti-CYP1A2 antibody also indicated the almost exclusive role of CYP1A2 in microsomal TSU-68 hydroxylation. Treatment of human hepatocytes with 10 μM TSU-68 resulted in a 28- to 140-fold increase in CYP1A1/2-mediated ethoxyresorufin O-deethylase activity. The protein levels of CYP1A2 were increased in TSU-68-treated hepatocytes, and those of CYP1A1, which were undetectable in control hepatocytes, were also increased to detectable levels in the TSU-68-treated hepatocytes. Thus, TSU-68 was shown to induce CYP1A1/2 expression, which was responsible for its hydroxylation. The observation that TSU-68 treatment resulted in a 10- to 45-fold increase in 5-, 6-, and 7-hydroxylation directly demonstrated the autoinduced hydroxylation of TSU-68. In conclusion, TSU-68 has the potential to cause induction of its own CYP1A1/2-mediated oxidative metabolism in humans. This autoinductive effect provides a clear explanation for the clinically observed decrease in TSU-68 plasma concentrations during repeated administration of the drug.
Footnotes
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.107.019877.
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ABBREVIATIONS: TSU-68, SU6668, (Z)-5-[(1,2-dihydro-2-oxo-3H-indol-3-ylidene)methyl]-2,4-dimethyl-1H-pyrrole-3-propanoic acid; P450, cytochrome P450; UGT, UDP-glucuronosyltransferase; HPLC, high-performance liquid chromatography; DMSO, dimethyl sulfoxide; LC, liquid chromatography; MS/MS, tandem mass spectrometry; MRM, multiple reaction monitoring; EROD, ethoxyresorufin O-deethylation; SU5416, [3-(3,5-dimethyl-1H-pyrrol-2-ylmethylene)-1,3-dihydro-indol-2-one]; AhR, arylhydrocarbon-receptor.
- Received November 23, 2007.
- Accepted March 3, 2008.
- The American Society for Pharmacology and Experimental Therapeutics
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