title: Encapsulation of doxorubicin into thermosensitive liposomes via complexation with the transition metal manganese.
abstract: In the present study, doxorubicin was encapsulated into two thermosensitive liposome formulations which were composed of DPPC/MSPC/DSPE-PEG(2000) (90/10/4 mole ratio) or DPPC/DSPE-PEG(2000) (95/5 mole ratio). Doxorubicin loading was achieved through the use of a pH gradient or a novel procedure that involved doxorubicin complexation with manganese. Regardless of the initial drug-to-lipid ratios (D:L), the final D:L reached a maximum of 0.05 (w/w) when doxorubicin was encapsulated via a pH gradient for both thermosensitive liposome formulations. In contrast, the final maximum D:L achieved through manganese complexation was 0.2 (w/w), and this loading method did not affect temperature-induced drug release, with 85% of drug released from MSPC-containing liposomes within 10 min at 42 degrees C but <5% released over 60 min at 37 degrees C. When the thermosensitive liposomes prepared via the two different loading methods were injected into mice, similar plasma elimination profiles were observed. Cryo-transmission electron microscopy analysis indicated the presence of doxorubicin fiber bundles in liposomes loaded via pH gradient, compared to a stippled and diffuse morphology in those loaded via manganese complexation. To investigate the effect of intraliposomal pH on drug precipitate morphology, the A23187 ionophore (mediates Mn(2+)/H(+) exchange) was added to liposomes loaded with doxorubicin-manganese complex, and the stippled and diffuse appearance could be converted to one exhibiting fiber bundles after acidification of the liposome core. This suggests that the formation of doxorubicin-manganese complex is favored when the intraliposomal pH is >6.5. During the conversion to the fiber bundle morphology, no doxorubicin release was observed when A23187 was added to liposomes exhibiting a 0.05 (w/w), whereas a significant release was noted when the initial D:L was 0.2 (w/w). Following acidification of the liposomal interior and establishment of an apparent new D:L equilibrium, the measured D:L ratio was 0.05 (w/w). In conclusion, the manganese complexation loading method increased the encapsulation efficiency of doxorubicin in thermosensitive liposomes with no major impact on temperature-triggered drug release or pharmacokinetics.
authors.affiliation: Department of Advanced Therapeutics, British Columbia Cancer Agency (Research Center), 675 West 10th Ave., Vancouver, BC, Canada V5Z 1L3. gchiu@bccrc.ca
authors.forename: Gigi N C
authors.initials: GN
authors.lastname: Chiu
authors.forename: Sheela A
authors.initials: SA
authors.lastname: Abraham
authors.forename: Ludger M
authors.initials: LM
authors.lastname: Ickenstein
authors.forename: Rebecca
authors.initials: R
authors.lastname: Ng
authors.forename: Göran
authors.initials: G
authors.lastname: Karlsson
authors.forename: Katarina
authors.initials: K
authors.lastname: Edwards
authors.forename: Ellen K
authors.initials: EK
authors.lastname: Wasan
authors.forename: Marcel B
authors.initials: MB
authors.lastname: Bally
mesh_terms: D000001:Calcimycin / Q000494:pharmacology; D020285:Cryoelectron Microscopy; D004317:Doxorubicin / Q000008:administration & dosage*; D004337:Drug Carriers; D006863:Hydrogen-Ion Concentration; D008081:Liposomes; D008345:Manganese / Q000008:administration & dosage*
chemical_list: D004337:Drug Carriers; D008081:Liposomes; D000001:Calcimycin; D008345:Manganese; D004317:Doxorubicin