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Novel Temperature-Sensitive Liposomes with Prolonged Circulation Time

¹ Department of Internal Medicine III, Klinikum Grosshadern Medical Center (KGMC), Ludwig-Maximilians-University, Munich, Germany; ² KKG Hyperthermia/GSF-National Research Center for Environment and Health, Munich, Germany; ³ Departments of Surgery and ⁴ Otorhinolaryngology and ⁵ Institute for Surgical Research, Klinikum Grosshadern, University of Munich, Germany; and ⁶ Max-Planck-Institute for Biophysical Chemistry, Goettingen, Germany

Hyperthermia increases the efficiency of various chemotherapeutic drugs and is administered as an adjunct to chemotherapy for the treatment of cancer patients. The temperature-dependent effect can be strongly increased by the use of temperature-sensitive liposomes in combination with regional hyperthermia, which specifically releases the entrapped drug in the heated tumor tissue. The novel lipid 1.2-dipalmitoyl-sn-glycero-3-phosphoglyceroglycerol (DPPGOG), which is closely related to the naturally occurring 1.2-dipalmitoyl-sn-glycero-3-phosphoglycerol, in combination with 1.2-dipalmitoyl-sn-glycero-3-phosphocholine and 1.2-distearoyl-sn-glycero-3-phosphocholine provides long-circulating temperature-sensitive liposomes with favorable properties under mildly hyperthermic conditions (41–42°C). DPPGOG facilitates temperature-triggered drug release from these liposomes (diameter, 175 nm) and leads to a substantially prolonged plasma half-life for the encapsulated drug with t_1/2 = 9.6 h in hamsters and t_1/2 = 5.0 h in rats. Quantitative fluorescence microscopy of amelanotic melanoma grown in the transparent dorsal skin fold chamber of hamsters demonstrated a favorable drug accumulation in heated tissue after i.v. application of these liposomes (42°C for 1 h). The mean area under the curve for tissue drug concentration was increased by more than sixfold by application of the new liposomes compared with nonliposomal drug delivery. In summary, we present a new DPPGOG-based liposomal formulation enabling long circulation time combined with fast and efficient drug release under mild hyperthermia. This adds positively to the results with lipid-grafted polyethylenglycol used thus far in temperaturesensitive liposomes and widens the possibilities for clinical applications.

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