One of the biggest obstacles for efficient
drug delivery is specific cellular targeting.
Liposomes have long been used for
drug delivery, but do not possess targeting capabilities. This limitation may be circumvented by surface coating of colloidal delivery systems with
peptides,
proteins,
carbohydrates,
vitamins, or
antibodies that target
cell surface receptors or other biomolecules. Each of these coatings has significant drawbacks. One idealized system for
drug delivery combines stabilized "
protein module"
ligands with a colloidal delivery vehicle. Prior studies have shown that
peptide-amphiphiles, whereby both a
peptide "head group" and a
lipid-like "tail" are present in the same molecule, can be used to engineer
collagen-like triple-helical or alpha-helical miniproteins. The tails serve to stabilize the head group structural elements. These
peptide-amphiphiles can be designed to bind to specific
cell surface receptors with high affinity. Structural stabilization of the integrated targeting
ligand in the
peptide-amphiphile system equates to prolonged in vivo stability through resistance to proteolytic degradation.
Liposomes have been prepared incorporating a
melanoma targeting
peptide-amphiphile
ligand, and shown to be stable with retention of
peptide-amphiphile triple-helical structure. Encapsulated
fluorescent dyes are selectively delivered to cells. In this chapter we describe the methods and techniques employed in the preparation and characterization of
peptide-amphiphiles and
peptide-amphiphile-targeted large and small
unilamellar vesicles (LUVs and SUVs). Fluorescence microscopy is subsequently utilized to examine the targeting capabilities of
peptide-amphiphile LUVs, which should allow for improved
drug selectivity towards
melanoma vs normal cells based on differences in the relative abundance of the targeted
cell surface receptors.