title: An HPLC assay for the lipophilic camptothecin analog AR-67 carboxylate and lactone in human whole blood.
abstract: AR-67 (7-t-butyldimethylsilyl-10-hydroxycamptothecin, DB-67) is a camptothecin analog currently in early stage clinical trials. The lactone moiety of camptothecins hydrolyzes readily in blood to yield the pharmacologically inactive carboxylate form. However the lactone form of third-generation lipophilic congeners, such as AR-67, is more stable, possibly due to partitioning into red cell membranes. This prompted us to develop a reverse-phase HPLC method with fluorescence detection (excitation 380 nm/emission 560 nm), which could quantitate the concentration of AR-67 lactone and carboxylate in whole blood. Samples were prepared by red cell lysis, protein precipitation with methanol and centrifugation to remove denatured materials. Recovery was estimated to be >85%. Analytes were eluted isocratically with 0.15 m ammonium acetate buffer containing 10 mm TBAP (pH 6.5) and acetonitrile (65:35, v/v) on a Nova-Pak C(18) column (4 µm; 3.9 × 150 mm). The assay was linear in the ranges 0.5-300 and 2.5-300 ng/mL for carboxylate and lactone, respectively. Accuracy and precision were acceptable. AR-67 forms were stable in whole blood and in methanolic supernatants. This assay has been successfully applied to measure AR-67 concentrations in whole blood of patients enrolled in a phase I study.
authors.affiliation: Department of Pharmaceutical Sciences, College of Pharmacy, University of Kentucky, Lexington, KY 40536, USA.
authors.forename: Eleftheria
authors.initials: E
authors.lastname: Tsakalozou
authors.forename: Jamie
authors.initials: J
authors.lastname: Horn
authors.forename: Mark
authors.initials: M
authors.lastname: Leggas
mesh_terms: D002166:Camptothecin / Q000031:analogs & derivatives* / Q000097:blood / Q000737:chemistry / Q000493:pharmacokinetics; D002264:Carboxylic Acids / Q000097:blood / Q000737:chemistry / Q000493:pharmacokinetics; D002851:Chromatography, High Pressure Liquid / Q000379:methods*; D004355:Drug Stability; D006801:Humans; D007783:Lactones / Q000097:blood / Q000737:chemistry / Q000493:pharmacokinetics; D016014:Linear Models; D017646:Organosilicon Compounds / Q000097:blood* / Q000737:chemistry / Q000493:pharmacokinetics; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
chemical_list: D002264:Carboxylic Acids; D007783:Lactones; D017646:Organosilicon Compounds; C415575:7-tert-butyldimethylsilyl-10-hydroxycamptothecin; D002166:Camptothecin