Liposomes for intracavitary and intratumoral drug delivery

The local application of liposomes into body cavities or directly into body tissues such as solid tumors has many potential therapeutic advantages. These advantages can exceed the well-known improvement in distribution and pharmacokinetics observed for encapsulated agents delivered intravenously (1). The pharmacokinetic behavior of a liposome encapsulated-therapeutic agent that has been injected locally is greatly altered in comparison to the intracavitary administration of the same agent as an unencapsulated free drug. For example, when free drugs are injected into a body cavity, they are generally cleared very rapidly fromthat cavity by direct absorption through membranes that line the cavity (2). This situation is very different in comparison with administration of the same drug encapsulated within a liposome. The liposome-encapsulated drug is prevented from passing through the lining of the cavity and must be cleared from the cavity by passage through the lymphatic system (3). This lymphatic clearance results in a prolonged retention of the therapeutic agent in the body cavity, increasing the possibility of achieving higher, more sustained drug levels in targeted tissue as the liposomes slowly degrade. By attaching ligands to the surface of liposomes administered intracavitarily, they can be targeted to specific cells or structures located within the cavity.