New cyclodextrin bioconjugates for active tumour targeting

A new cyclodextrin-based carrier for active targeting of low soluble and degradable drugs has been synthesized and characterized. Beta-cyclodextrins were first reacted with excess hexamethylene diisocyanate and the resulting CD-(C6-NCO)5 derivative was reacted with 700 Da diamino-PEG to yield CD-(C6-PEG-NH2)5. About one out of five free amino groups of PEG were functionalised with folic acid (FA) as a tumour targeting moiety. The chemical structures of the intermediates as well as the final product, CD-(C6-PEG)5-FA, were characterized by 1H and 13C NMR, reverse phase and gel permeation chromatography, and UV-Vis spectroscopy. After modification, the haemolytic activity of beta-cyclodextrins decreased by about 70%. In the presence of the new carrier, the beta-estradiol solubility increased by more than 300 fold and the chlorambucil degradation rate decreased by 50-60%. CD-(C6-PEG)5-FA formed an inclusion complex with curcumin displaying an association constant of 954,732 M(-1). The new carrier increased the curcumin solubility by about 3200 fold as compared to native beta-cyclodextrins and reduced its degradation rate at pH 6.5 and 7.2 by 10 and 45 fold, respectively. FA receptor-overexpressing human nasopharyngeal tumour KB cell lines and non-folic acid receptor-expressing human breast cancer MCF7 cells were used to evaluate the targeting properties of the new drug delivery system. The in vitro studies demonstrate that the new carrier possesses potential selectivity for the folate receptor-overexpressing tumour cells as ED50 values of 52 microM, 58 microM and 21 microM were obtained with curcumin-loaded CD-(C6-PEG-NH2)5, curcumin in foetal serum medium and CD-(C6-PEG)5-FA, respectively.