Characterization of Liposomal Release Temperature Using a Low Field Magnetic Resonance System

The use of liposomes as chemotherapeutic carriers has been the subject of many research studies, with emphasis on enhancing the therapeutic index by increasing effect on cancer cells and reducing side effects. An important parameter to characterize for thermosensitive liposomes, TSLs, is the release temperature, Tr, the temperature at which liposomes release most of their content. By loading liposomes with a contrast agent such as Mn2+, a benchtop NMR system can be used to determine Tr through incremental heating. In this work, the release temperature was extracted from relaxometry measurements of Mn2+-loaded TSLs. Tr values were then compared with transition temperature values, Tm, the temperature at which liposomes’ bilayer changes state, obtained by a standard technique. The difference of the average values between Tr and Tm was approximately 0.5 oC. The discrepancy is due to artifacts produced by the standard technique. Nonetheless, Tm can be used to predict Tr.