Chiral high-performance liquid chromatographic analysis of the enantiomers of XK469, a new antitumor agent, in plasma and urine

Abstract

XK469 (NSC697887), (±)-2-[4-(7-Chloro-2-quinoxaliny)oxy]-phenoxy propionic acid, an analog of the herbicide Assure®, which possesses antitumor activity, especially against murine solid tumors and human xenografts, has recently been found to be the first topoisomerase IIβ poison. Both R(+) and S(−) isomers are cytotoxic, although the R-isomer is more potent. A chiral high-performance liquid chromatography (HPLC) assay that utilizes Chirobiotic T column for the measurement of enantiomers of XK469 in plasma has been developed with a limit of quantitation (LOQ) of 0.2 μg/ml using a 0.2 ml plasma sample. Chloroqinoxaline sulfonamide (CQS) was used as the internal standard and the assay has been validated in rat plasma. The within-run coefficient of variations (CVs) were 5.9, 5.0, and 3.1% for the S-isomer and 8.1, 4.2, 6.4% for R(+)-XK469 at 0.2, 1, and 2 μg/ml, respectively. The between-run CVs were 10.5, 5.3, and 1.9% for S(−)- and 10.9, 6.3, and 3.6% for R(+)-XK469. Using this chiral assay, a plasma concentration time data of R(+)-,S(−)-XK469 in a Fischer 344 rat receiving i.v. dosing of S(−)XK469 at 10 mg/kg was monitored. S(−)XK469 was found to be significantly converted to the R-enantiomer in circulation even when the S-enantiomer was administered. The predominant inversion from S(−)- to R(+)-XK469 was also observed in the mouse and dog plasma. In the rat, the plasma concentration–time profiles for both isomers follow two compartmental pharmacokinetics with the t 1/2β for the R-enantiomer slightly longer and the clearance of the S-enantiomer higher than the R-enantiomer.