| XK469 (NSC 697887), (+/-)-2-[4-(7-Chloro-2-quinoxaliny) oxy]phenoxy propionic acid, is an analog of the herbicide AssureRTM synthesized by DuPont Company. In a screening system, it was found that XK469 possesses broad activity against murine solid tumors and human xenografts, and because of this, it was selected for preclinical development with no known mechanism of action. Snapka et al. in collaboration with our laboratory elucidated its mechanism of anti-tumor activity as the first selective topoisomerase II beta poison. R(+)-XK469 has now been selected for clinical evaluation by the National Cancer Institute.; The project aimed to develop a chiral HPLC assay and to investigate the stereoselective pharmacokinetics and metabolism of XK469. A chiral HPLC that utilizes Chirobiotic T column for the measurement of enantiomers of XK469 in plasma and urine was developed.; Pharmacokinetics of R(+)-, S(-)- and (+/-)-XK469 in Fischer 344 rats were investigated, following their separate i.v. administrations, using the chiral HPLC method. In the rat, the plasma concentration-time profiles for both isomers follow a two-compartment pharmacokinetics. S(-)-XK469 was found to be predominantly converted to the R-isomer in circulation, as estimated by the fractional formation clearance of R(+)XK469 of 0.94. Urinary and fecal elimination in 72 hr as the intact drug were 7--10% and 8% of the administered dose, respectively, with less than 3% excreted into the bile. Oral bioavailability was estimated to be 90% by the non-crossover method following oral dosing, and this high absorption was supported by Caco-2 cell monolayer studies.; Two major urinary oxidative metabolites of XK469 were detected using liquid chromatography-mass spectrometry. The structures were initially assigned as N-oxides based on multi-state mass spectral data and later confirmed by chemical synthesis with XK469 using m-chloroperoxybenzoic acid, HPLC peak enhancement, and reduction experiment with titanium chloride, all generating consistent data to support the N-oxide structures. Proton NMR studies in comparison with reference compounds provided the final structural assignment with the slower eluting metabolite being identified as the 4N-oxide, while the faster eluting one is the 1N-oxide. Metabolism study suggests their formation may be mediated by cytochrome P450.; In Chapter 5, future directions to extend this dissertation work are presented. |
