Optimization and characterization of a sphingomyelin/cholesterol liposome formulation of vinorelbine with promising antitumor activity |
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Authors: | Semple Sean C Leone Robert Wang Jinfang Leng Esther C Klimuk Sandra K Eisenhardt Merete L Yuan Zuan-Ning Edwards Katarina Maurer Norbert Hope Michael J Cullis Pieter R Ahkong Quet-Fah |
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Affiliation: | Inex Pharmaceuticals Corporation, 200-8900 Glenlyon Parkway, Glenlyon Business Park, Burnaby, British Columbia, Canada V5J 5J8. ssemple@inexpharm.com |
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Abstract: | Vinorelbine (VRL) is a particularly lipophilic member of the vinca alkaloids which, as a class of drugs, exhibit improved cytotoxicity and therapeutic activity through increased duration of exposure. Here, we describe and optimize a sphingomyelin/cholesterol (SM/Chol) liposome formulation of VRL to maximize in vivo drug retention, plasma circulation time, and therapeutic activity. VRL was efficiently encapsulated (>90%) into 100 nm liposomes using an ionophore-mediated loading method. VRL retention in SM/Chol liposomes after intravenous injection in mice was dependent on drug-to-lipid ratio (D/L), with higher D/L ratios exhibiting increased drug retention (0.3 > 0.2 > 0.1, wt/wt) and improved pharmacokinetics. Cryo-electron microscopic examination of a high D/L ratio formulation indicated that the intravesicular regions of these liposomes were electron dense compared with empty liposomes. The optimized, high D/L ratio SM/Chol VRL formulation showed promising activity against subcutaneous B16 melanoma tumors compared with VRL or SM/Chol formulations of vincristine or vinblastine. Finally, the stability of the formulation was excellent (<5% drug leakage, >99% intact VRL, no changes in liposome size after 1 year at 2-8 degrees C). The optimized drug retention properties of the SM/Chol formulation of VRL, combined with its promising antitumor activity and pharmaceutical stability, make this formulation an excellent candidate for future clinical development. |
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