Investigation on the thermal behaviour of doxorubicin sulphate nanocrystals in Doxil® liposomal formulation

Liposomes are nano-sized lipid bilayer vesicles of great interest in drug delivery. Doxil® is an example of a marketed liposomal formulation containing the anticancer drug doxorubicin. These liposomes, composed of soy phosphatidylcholine, cholesterol and PEGylated phosphoethanolamine have a stable loading of doxorubicin sulphate (DOX). When loaded, DOX originates fibrillar supramolecular structures as evidenced by X-rays scattering techniques and electron microscopy.AimsThe aim of this work is to characterize the thermal behaviour of DOX nanocrystals in the confined environment of the PEGylated liposomes.MethodsDoxil® and unloaded liposomes were analysed by differential scanning calorimetry (mDSC), high-resolution ultrasonic spectroscopy (HR-US) and scattering techniques as dynamic light scattering (DLS) and small angle x-rays scattering (SAXS).ResultsAll techniques confirmed the crystalline state of DOX inside PEGylated liposomes. Particularly, mDSC and HR-US resulted to be very sensitive to highlight the changes in the melting behaviour of the crystals when subjected to different heating programmes. DOX nanocrystals were found to be stable after heating up to 90? degrees C, but an irreversibile thermal behaviour was observed after a prolonged heating at elevated temperatures.Summary/ConclusionA detailed characterization of the thermal behaviour of PEGylated liposomes loaded with doxorubicin (Doxil®) was performed by combining different techniques. These techniques highlighted a dependence of the reversibility of DOX melting transition on thermal conditions. Overall, this study provides new insights for the characterization of the physical state of drugs in confined environments.