Carbendazim: Disposition, cellular permeability, metabolite identification, and pharmacokinetic comparison with its nanoparticle

The purpose of this study was to systematically evaluate the pharmacokinetic profiles of carbendazim, a novel anticancer drug. Carbendazim reached the highest concentrations in stomach and small intestine by 1 h after oral administration (500 mg/kg) to tumor-bearing nude mice. Four hours later, carbendazim in the large intestine reached maximum concentrations, probably because of pH-induced precipitation of the drug in the large intestine. The highest concentrations of carbendazim in well-perfused tissues, solid tumor, and blood ranged from 63 to 164 mug/g by 4 h. The percentage of carbendazim distributed to solid tumor by 4 h was higher than most well-perfused tissues. Carbendazim concentrations in blood were similar to, or somewhat lower than, those in tumor and other tissues. By 24 h post-dosing, carbendazim concentrations in tissues and blood declined to almost basal levels. The total percentage of administered carbendazim eliminated in urine was 25.7%, and in feces 16.6% within 24 h. Carbendazim exhibited fast permeation across Caco-2 and HT-29 carcinoma cell lines with corresponding permeability coefficients 7.74-8.06 x 10(-5) and 6.8-8.42 x 10(-5) (cm/s). The overall plasma protein binding of carbendazim (0.2-125 mug/mL) assessed by ultrafiltration ranged from 60 to 74%. Comparative pharmacokinetics was conducted in rats by high-pressure liquid chromatography to evaluate the relative bioavailability of carbendazim versus its nanoparticle formulation. Carbendazim and its nanoparticle reached T-max at 2.01 and 1.57 h, respectively. The relative bioavailability of nanoparticle carbendazim versus regular carbendazim was 166%. High-pressure liquid chromatography analysis of the rat serum obtained at 20 h after oral dosing revealed a carbendazim metabolite, which was identified by mass spectroscopy analysis as 2-aminobenzimidazole, a hydrolyzed product of carbendazim. Incubation of carbendazim with human and rat liver microsomes produced a metabolite identified by mass spectrometry as 5(6)- or 4(7)-hydroxyl carbendazim. The comprehensive pharmacokinetic information is important to the current clinical investigation of carbendazim. (C) 2002 Wiley-Liss, Inc.