HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHIC ANALYSIS OF THE LACTONE AND CARBOXYLATE FORMS OF A TOPOISOMERASE-I INHIBITOR (THE ANTITUMOR DRUG GI147211) IN PLASMA

A sensitive reversed-phase high-performance liquid chromatographic met hod has been developed and validated for the quantitation of the lacto ne form (GI147211) of a topoisomerase I inhibitor and its carboxylate form (GI190421) from dog plasma. The method consists of two solid-phas e extraction methods. The first method, referred to as the lactone-onl y method, utilizes a diol Bond Elut cartridge to separate the two form s and measures the lactone directly. The second method, referred to as the total method, converts the carboxylate form to the lactone throug h acidification of the plasma sample. Total lactone is then extracted from the sample using a C-18 Bond Elut cartridge. The carboxylate is q uantitated indirectly from the difference of the total and lactone-onl y. The range of the standard curve for the lactone-only method is 0.09 6-38.5 nM (0.05-20 ng/ml) and for the total method is 0.193-19.3 nM (0 .1-10 ng/ml). This is the most sensitive method reported to date for a camptothecin analogue.