Determination of total and lactone form of a new camptothecin derivative gimatecan (ST1481) and its metabolite ST1698 in human plasma by high-performance liquid chromatography with fluorimetric detection

A new sensitive high-performance liquid chromatographic (HPLC) method for the determination of gimatecan (ST1481), a new camptothecin derivative, and its metabolite (ST1698) in plasma sample has been developed. The method consisted of on-line column solid phase extraction of analytes from human plasma, chromatographic separation by isocratic elution, then fluorimetric detection. The limits of quantitation were 0.25 ng/mL for both the analytes. The recovery of the extraction procedure was in the range of 62.8–71.1% for all the compounds. Good linearity (R2 > 0.999) was observed within the calibration ranges studied: 0.25–25 ng/mL for both ST1481 and ST1698. Precision was in the range 1.2–4.3%, and accuracy was always lower than 4.7%. Surprisingly, after administration of ST1481 to humans, plasma concentrations found were higher than expected, while metabolite plasma concentrations were negligible. For this reason, a second calibration curve range was validated to quantify ST1481 in human plasma, ranging from 5 to 200 ng/mL. A good accuracy and precision were obtained, confirming the usefulness of the procedure. By using neutral analytical condition the intact lactone form was estimated in plasma samples from a patient. The lactone form amounted to 80–100% of the total ST1481.