Facile preparation of cyclodextrin-grafted chitosans and their conversion into nanoparticles for an anticancer drug delivery system

Chitosan (CS) is a natural polysaccharide, composed of β-d-glucosamine (<60%) and β-d-N-acetylglucosamine linking through a β-(1→4) linkage, obtained by chitin deacetylation.¹ CS is one of the most commercially important biocompatible polymers from an environmental or biomedical viewpoint.² Because of CS’s biocompatibility and the high reactivity of amino groups, considerable research efforts have been directed toward developing safe and efficient CS-based materials as biomaterials.^{1, 2, 3}

Cyclodextrin (CyD) is a host molecule that forms inclusion complexes with a variety of guests.⁴ It has thus been widely used as an excipient to improve the physicochemical and pharmaceutical properties of drug molecules. The grafting of CyD onto CS can result in an increase in the extent of complexation ability, sorption and controlled-release properties because of CyD’s inclusion properties.⁵ We previously reported interesting abilities of a β-CyD−grafted CS (β-CyD-g-CS) that formed supramolecular aggregates with insulin⁶ and cholesterol⁷. Although CyD-g-CS is scientifically fascinating and potentially applicable as a biomaterial, its synthesis is not easy because multiple steps and cumbersome isolations are necessary to prepare a CyD derivative bearing one reactive group such as carboxylic acid or aldehyde.^{5, 6, 7, 8} A facile method with shorter steps and an easier procedure would accelerate the further application and functionalization of CyD-g-CS. Besides, both CS^{9, 10, 11, 12} and CyD derivatives^{13, 14, 15} are known as candidate materials for anticancer drug delivery systems. Thereby, CyD-g-CSs, which are conjugates of both candidates, and their derivatives would provide improved anticancer drug delivery systems showing enhanced binding of a drug as well as improved therapeutic efficacy.

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