Strategies for Optimizing Liposomal Doxorubicin

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Abstract
Liposome encapsulation of doxorubicin can dramatically alter its biological activity, resulting in decreased toxicity and equivalent or increased antitumor potency. Since the physical characteristics of the liposome carrier system (size, lipid composition, and lipid dose) can have profound effects on the pharmacologic properties of vesicles administered intravenously, it may be expected that the therapeutic activity of liposomal doxorubicin will be sensitive to these properties. To determine the influence of these variables on the toxicity and efficacy properties of liposomal doxorubicin, transmembrane pH gradient-dependent active encapsulation techniques have been utilized to generate liposomal doxorubicin preparations in which the vesicle size, lipid composition, and drug to lipid ratio can be independently varied. these studies indicate that the toxicity of liposomal doxorubicin is related to the stability of the preparation in the circulation. This property is dictated primarily by vesicle lipid composition, although the drug to lipid ratio can also exert an influence. In contrast, the antitumor activity of liposomal doxorubicin appears most sensitive to the size of the vesicle system. Specifically, antitumor drug potency increases as the vesicle size is decreased. these studies demonstrate that manipulating the physical characteristics of liposomal anticancer pharmaceuticals can lead to preparations with optimized therapeutic activity.