Development of a method to quantify total and free irinotecan and 7-ethyl-10-hydroxycamptothecin (SN-38) for pharmacokinetic and bio-distribution studies after administration of irinotecan liposomal formulation

In 2015, liposomal formulation of irinotecan (ONIVYDE) has been approved by FDA and widely applied in the treatment of pancreatic cancer. ONIVYDE is a novel liposome formulation, entrapping CPT-11 in the aqueous core of vesicles using a modified gradient loading method. Due to toxicity concerns, it is essential to explore a rapid and reliable method to effectively isolate and quantify the non-liposomal, namely, free CPT-11and total CPT-11 in plasma. This study focuses on separation of non-liposomal CPT-11, evaluation of the pharmacokinetics of free CPT-11 and total CPT-11 and bio-distribution after intravenous administration of CPT-11 liposome. Free CPT-11 in plasma was separated by solid-phase extraction (SPE). The amount of total CPT-11 and main metabolite 7-ethyl-10-hydroxycamptothecin (SN-38) in plasma was quantified by ultra-performance liquid chromatography–MS/MS. The calibration curves fitted well and lower limit of quantitation for SN-38, free CPT-11, total CPT-11 and CPT-11 in tissue and were 5 ng/ml, 10 ng/ml, 4.44 ng/ml and 25 ng/ml respectively. The recoveries, precision and accuracy of the method appear satisfactory. Using this method, the pharmacokinetics and bio-distribution of CPT-11 liposome formulation after an intravenous dose of 2.5 mg/kg were then investigated.