Insights into composition/structure/function relationships of Doxil® gained from "high-sensitivity" differential scanning calorimetry.
Thermotropic behavior of Doxil® and its generic, Lipodox®, was characterized using "high-sensitivity" differential scanning calorimetry (DSC). This is the first report that two distinct endotherms were observed in Doxil and Lipodox upon heating. The first (Tm at 51±2°C) is broad and of low enthalpy, representing the membrane lipid phase transition, which occurs despite having high (38mole%) cholesterol. The second (Tm at ∼70°C) is narrow, representing melting of the intraliposomal doxorubicin-sulfate nanocrystals. The thermograms of Doxil and Lipodox are practically identical. The membrane phase transition is similar to that of drug-free nanoliposomes of the same size and lipid composition as Doxil, suggesting lack of significant drug-membrane interaction. The melting endotherm of the intraliposomal nanocrystals is 2.0-2.5-fold narrower than that of the crystals formed in a solution of 250mM ammonium sulfate and >60mg/ml doxorubicin. This suggests that nanovolume of liposomes improves doxorubicin-sulfate crystallinity. Moreover, both phase transitions are reversible in cycled DSC scanning (15-90-15°C). This indicates an unexpected "non-leaky" phospholipid phase transition and excellent physical and chemical stabilities of Doxil after short exposure to high temperature. Reducing mole% of cholesterol results in a "leaky" membrane phase transition of higher enthalpy. Namely, high mole% cholesterol is essential for the resistance to drug leakage during phase transition. Pegylated liposomal doxorubicin in which HSPC was replaced by DPPC shows the same non-leaky phase transition but at a lower temperature, indicating this type of phase transition is not unique to Doxil. The presence of DSPE-PEG2k increases the cooperativity of the phase transition. High-sensitivity DSC helps illuminate composition/structure/function relationships of Doxil, and is useful for the equivalence/similarity studies.
Laboratory of Membrane and Liposome Research, The Hebrew University-Hadassah Medical School, IMRIC, Jerusalem, Israel; School of Pharmacy, Shanghai Jiao Tong University, Shanghai, China.
Xiaohui
X
Wei
Laboratory of Membrane and Liposome Research, The Hebrew University-Hadassah Medical School, IMRIC, Jerusalem, Israel.
Rivka
R
Cohen
Laboratory of Membrane and Liposome Research, The Hebrew University-Hadassah Medical School, IMRIC, Jerusalem, Israel. Electronic address: chezyb@gmail.com.
Yechezkel
Y
Barenholz
D002152:Calorimetry, Differential Scanning; D004317:Doxorubicin / Q000031:analogs & derivatives* / Q000737:chemistry / Q000494:pharmacology; D011092:Polyethylene Glycols / Q000737:chemistry / Q000494:pharmacology; D013329:Structure-Activity Relationship
C506643:liposomal doxorubicin; D011092:Polyethylene Glycols; D004317:Doxorubicin
DSC; Doxorubicin; Liposomes; PLD; Thermodynamics