Abstract 5464: Determination of total and encapsulated drug pharmacokinetics for CPX-351, a nanoscale liposomal fixed molar ratio of cytarabine-daunorubicin (Cyt:Daun)

Abstract

Abstract Background: CPX-351 is a liposomal formulation that delivers elevated concentrations of Cyt and Daun after administration in vivo and maintains the two drugs at a 5:1 molar ratio shown to be synergistic in preclinical studies. Pharmacokinetic analysis of CPX-351 in advanced leukemia patients demonstrated prolonged plasma exposure of the drugs with quantifiable concentrations of both agents being observed as long as 7 days after the final CPX-351 dose. Here we developed a method to separate liposome-bound from unencapsulated drugs, thereby allowing the pharmacokinetics of encapsulated agents to be determined in comparison to total plasma drug concentrations. Methods: CPX-351 was administered to female Sprague-Dawley rats via IV bolus injection. Plasma samples were harvested at five timepoints from 1 – 24 hours. Unencapsulated drug analysis was conducted by addition of internal standards (gemcitabine (Cyt) and doxorubicin (Daun)) to the plasma, followed by a 5-fold dilution in buffer and ultrafiltration using Microcon YM-30. Unencapsulated drug levels were determined by reversed-phase HPLC-MS (SIM, 244.2 m/z (Cyt) and 528.3 m/z (Daun)). Total analysis was conducted by protein precipitation and analysis was determined by reversed-phase HPLC-UV (Cyt) and reversed-phase HPLC-Fluorescence (Daun). Results: A separation method was developed to separate 0.22 – 4.33% unencapsulated Cyt and 0.13 – 2.50% unencapsulated Daun from liposome in plasma matrix. Encapsulated drug was calculated by subtracting the amount of unencapsulated analyte from the corresponding amount of total analyte. The total drug curves and the calculated encapsulated drug curves from 1 – 24 hours were superimposable for Cyt and Daun. A maximum of 1.9% unencapsulated Cyt and 0.4% unencapsulated Daun was measured in the plasma at any time point. Conclusions: Unencapsulated drug levels in rat plasma are insignificant compared to the total drug levels such that levels of total and encapsulated are within the spread of the data and therefore indistinguishable. These results suggest that CPX-351 remains in circulation in rats as intact liposomes at least 24 hours post administration. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 5464. doi:10.1158/1538-7445.AM2011-5464