Tumor-specific drug delivery mediated by the folate endocytosis pathway
Abstract
Folate-protein conjugates are previously shown to be taken up via receptor-mediated endocytosis. In this dissertation, it is further demonstrated that smaller molecules such as deferoxamine and large drug carriers such as liposome can also be delivered via the same route. It is found that folate-mediated targeting of liposomes requires a long polyethyleneglycol (PEG) spacer between the ligand and the lipid bilayer. Folate-PEG-liposomes have an affinity orders of magnitude higher than folic acid due to their capacity for multivalent interactions with the cell surface receptors. Folate conjugated macromolecules or liposomes are internalized into acidified compartments by the cell via receptor-mediated endocytosis. The compartmental pH following folate-mediated endocytosis is determined by both a spectrofluorimetric method using FITC-BSA as a pH-sensor, and by ratioing confocal images of cells dual-labeled with folate-DM-NERF-dextran, a pH indicator, and folate-Texas Red-dextran, a pH-insensitive reference. The majority of the compartments have pH values between 4.5 and 5.8. The low pH environment in these compartments may facilitate the cytoplasmic release of some liposome-encapsulated drugs such as doxorubicin. Folate-PEG-liposome-encapsulated cytatoxic drugs such as doxorubicin, cytosine arabinoside, and antisense oligonucleotides show greatly enhanced growth inhibitory effects against cultured tumor cells overexpressing the folate receptor. Folate conjugate of a metal chelator deferoxamine (DF) is synthesized as a candidate for an in vivo tumor imaging agent. The $\sp{67}{\rm Ga}$ complex of the folate-DF conjugate is rapidly taken up by cultured KB cells with a t$\sb{1/2}$ of $\sim$ 3 min. In addition, some aspects of folate-protein conjugation chemistry are examined. Also, a toxin-folate conjugate, folate-LysPE38, is evaluated for its tumor-inhibitory efficacy in nude mice carrying xenographic implants, and the conjugate was found to be partially active in tumor suppression. Furthermore, a novel pH-sensitive liposome formulation using octadecanol as a fusogenic component is also characterized.
Degree
Ph.D.
Advisors
Low, Purdue University.
Subject Area
Pharmaceuticals|Pharmacology|Pharmacology
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