S-protected thiolated cyclodextrins as mucoadhesive oligomers for drug delivery

Aim: The purpose of this study was to develop a novel mucoadhesive thiolated and S-protected gamma cyclodextrin (gamma-CD) with an intact ring backbone to assure a prolonged residence time at specific target sites. Method: Thiolated gamma-CD was generated through bromine substitution of its hydroxyl groups followed by replacement to thiol groups using thiourea. In the second step, thiol groups were protected by disulfide bond formation with 2-mercaptonicotinic acid (2-MNA). Result: Thiolated gamma-CD displayed 1385 +/- 84 mu mol thiol groups per gram of oligomer and the amount of MNA determined in the S-protected oligomer was 1153 +/- 41 mu mol per gram of oligomer. In-vitro screening of mucoadhesive properties of thiolated and S-protected gamma-CD was done by two methods. Rheological investigation revealed the conjugates non-mucolytic with only a slight increase in viscosity of thiolated and S-protected gamma-CD as compared to unmodified gamma-CD, whereas mucoadhesive properties of the new thiolated and S-protected gamma-CD performed on freshly excised porcine intestinal mucosa showed 44.4- and 50.9-fold improvement in mucoadhesion, respectively. The new conjugates did not show any cytotoxicity to Caco-2 cells even at a concentration of 1% (m/v) for 24 h. In addition, in-vitro studies of a-amylase degradation of gamma-CD, gamma-CD-SH and gamma-CD-SS-MNA confirmed that all conjugates are biodegradable. Conclusion: These outcomes predict that these new conjugates of gamma-CD might provide a new favorable tool for drug delivery providing a prolonged residence time on mucosal surfaces. (C) 2018 Elsevier Inc. All rights reserved.