Organ-specific delivery of biofunctional agents is thought to enhance their activity and to reduce their side effects.
Liposomes have been used as
drug carriers in
cancer chemotherapy, since they accumulate passively in
tumor tissues due to an enhanced permeability and retention (EPR) effect. In addition, modification of
liposomes with specific
ligands enables active targeting. A small
peptide having a high affinity for a certain
antigen is suitable for modification of
liposomes, since it is biocompatible, biodegradable, and less antigenic compared with antibody and other modifiers.
Oligopeptide-modified
liposomes are prepared by using lipophilic derivatives of the
peptide, which are synthesized easily and incorporated readily into the liposomal bilayer. We describe two examples of the use of liposomal
oligopeptides: one for antimetastatic
therapy and the other for antineovascular
therapy.
Arg-Gly-Asp (RGD)-related
peptides are known to contribute various cellular functions such as adhesion and invasion and to inhibit
tumor metastasis. However,
peptide drugs are generally rapidly hydrolyzed and eliminated from the bloodstream. Liposomal RGD enables the half-lives and affinity to be improved, resulting in enhancement of antimetastatic activity. We then describe the usefulness of liposomal
Ala-Pro-Arg-Pro-Gly (APRPG) for
tumor treatment, which is specific for
tumor angiogenic vessels. APRPG is originally isolated by use of a phage-displayed
peptide library.
Adriamycin encapsulated in APRPG-modified
liposomes accumulated specifically in and damage
tumor neovessels, resulting in notable antitumor efficacy.