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SYUIQ-5, a novel telomerase inhibitor, has demonstrated antitumor activity in nude mouse studies. The objective of the present study was to examine the metabolism and pharmacokinetics of SYUIQ-5 in rats. The plasma pharmacokinetics of SYUIQ-5 was nonlinear following i.p. administration at 15, 30 and 60 mg/kg. SYUIQ-5 metabolism in rat liver microsomes followed Michaelis-Menten kinetics, with Km and Vmax values of 12.3 microM and 2.01 nmol/min/mg protein, respectively. Ketoconazole significantly inhibited the metabolism of SYUIQ-5 in liver microsomes from rats pretreated with control vehicle or various inducers, whereas sulphaphenazole, ticlopidine, quinidine, and methylpyrazole had no inhibitory effects on SYUIQ-5 metabolism. Dexamethasone and beta-naphthoflavone (BNF), but not phenobarbital and ethanol, significantly induced SYUIQ-5 metabolism in rats. Alpha-naphthoflavone significantly inhibited SYUIQ-5 metabolism in liver microsomes from BNF-pretreated rats. Similar to other secondary amines, SYUIQ-5 underwent N-demethylation and O-oxygenation to at least two metabolites by rat liver microsomes. Pretreatment of rats with SYUIQ-5 at 0.1, 5 or 10 mg/kg for 5 days significantly induced the expression and activity of rat Cyp1A1/2, and induced Cyp3A1/2 expression at 10 mg/kg, but not Cyp2E1 and 2B1/2. These results indicate that that SYUIQ-5 exhibits dose-dependent pharmacokinetics in rats and it is mainly metabolized by Cyp3A1/2.

A sensitive assay for the determination of SYUIQ-5, a novel telomerase inhibitor and anti-tumor drug, in rat liver microsomes was developed by using high-performance liquid chromatography with ultraviolet detection. SYUIQ-5 was incubated in vitro with liver microsomes from rats pre-treated with control vehicle, beta-naphthofIavone, phenobarbital, 20% ethanol or dexamethasone. The analytes were extracted with diethyl ether and separated a C(18) 5-microm analytical column. Elution was conducted with 30 mM dipotassium hydrogen phosphate (pH 8.0)-methanol-triethylamine (30:70:0.05, v/v/v) at a flow-rate of 1.0 ml/min and the detection of UV absorbance was conducted at 278 nm. Intra-day and inter-day precision and accuracy of the method were within 10%. The mean analytical recoveries of SYUIQ-5 ranged from 78.8 to 95.3%. The linearity of the calibration curve was in the range of 1.0-80.0 microM. The lower limit of quantification (LOQ) was 1.0 microM. Kinetic analysis showed that beta-naphthofIavone and dexamethasone significantly induced SYUIQ-5 metabolism, suggesting that cytochrome P450 1A and 3A are the major contributor to SYUIQ-5 metabolism in rat liver microsomes.