ISOLATION AND STRUCTURAL CONFIRMATION OF N-DESMETHYL TOPOTECAN, A METABOLITE OF TOPOTECAN

A sensitive high-performance liquid chromatography (HPLC) method for t he determination of topotecan and total levels of topotecan (lactone p lus its ring-opened hydroxycarboxylate form) was developed by the auth ors and used in several pharmacokinetics studies. During the analysis of plasma and urine samples collected in those studies, an additional peak eluting just after topotecan was observed. Approximately 100 ng o f this potential metabolite was isolated from human urine using a soli d-phase extraction procedure and purification by HPLC. Analysis of the isolated material by HPLC showed it to be approximately 95% pure. Mas s spectrometry data along with the HPLC retention data and fluorescenc e data (in comparison with synthetic reference standard) are consisten t with the metabolite's being N-desmethyl topotecan. The maximal conce ntrations of metabolite deteced in human plasma and urine were relativ ely low. When topotecan was given as a 30-min infusion at 1.0 mg/m(2) daily for 5 days every 3 weeks, the maximal plasma metabolite concentr ation (lactone plus the ring- opened hydroxycarboxylate form) was abou t 0.7% (n = 4) of the maximal total topotecan concentration. The avera ge amount of metabolite excreted in urine during the treatment was 1-4 % (n = 20) of the delivered dose.