Abstract:The oral delivery of drugs is regarded as the optimal means for achieving therapeutic effects owing to increased patient compliance. Unfortunately, the oral delivery route is beset with problems such as gastrointestinal (GI) destruction of labile molecules, low levels of macromolecular absorption, etc. To reduce the impact of digestive enzymes and to ensure the absorption of bioactive agents in an unaltered form, molecules may be incorporated into microparticulate carriers. Many approaches to achieve the oral absorption of a wide variety of drugs are currently under investigation. Among the different polymer-based drug delivery systems, polymeric micelles represent a promising delivery vehicle especially intended for poorly water-soluble pharmaceutical active ingredients in order to improve their oral bioavailability. Recent findings of a dextran-based polymeric micelle study for solubilization of a highly lipophilic drug, cyclosporin A (CsA), will be discussed.

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Folate conjugates (PNIPAM-NH-FA) of a copolymer of N-isopropylacrylamide (NIPAM) and amino-N'-ethylenedioxy-bis(ethylacrylamide) were prepared by an efficient synthesis leading to random grafting, via a short dioxyethylene spacer, of approximately 7 folic acid residues per macromolecule. The chemical composition of the copolymer was characterized by (1)H NMR and UV/vis spectroscopy. A fluorophore-labeled folate PNIPAM conjugate was tested by in vitro assays performed with cultured KB-31 cells overexpressing the folate receptor. The cellular uptake of the copolymer was found to be temperature dependent and was competitively decreased by free folic acid, indicating that the polymer uptake is mediated specifically by the folate receptor. Hydrophobically modified folate conjugates of NIPAM, amino-N'-ethylenedioxy-bis(ethylacrylamide) copolymers, bearing a small number of n-octadecyl groups were prepared following a modified synthetic procedure for use in future studies of FA-targeted liposomes.

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