Liposomal Encapsulation of Camptothecin/Carboxymethyl-β-Cyclodextrin Complexes: Stability, Solubility and Cytotoxicity

The clinical utility of the anticancer drug camptothecin (CPT) is limited by its poor aqueous solubility and instability in the bloodstream, hindering bioavailability and efficacy. This study explores the complexation of CPT with carboxymethyl-beta-cyclodextrin (cmβCD) to overcome these limitations. Fluorescence spectroscopy and molecular modeling demonstrated 1:1 inclusion complexes, with stability constants governed by electrostatic interactions that were inversely correlated with pH. To validate this effect, a cationic amino-beta-cyclodextrin (amβCD) was used as a mechanistic control, revealing that Coulombic forces significantly modulate binding strength and stoichiometry. Crucially, cmβCD enhanced CPT solubility by up to 11-fold at 14 × 10−3 moldm−3, enabling a 385-fold increase in drug loading into liposomal carriers compared to the cyclodextrin-free system. Fluorescence-based release studies indicated high liposomal stability at physiological pH and partial CPT release under acidic conditions. Furthermore, CPT-loaded liposomes demonstrated cytotoxicity against cancer cell lines, particularly BT-474, with IC50 values generally comparable to or slightly higher than those of free CPT and the CPT:cmβCD complex, likely due to the distinct lysosomal cellular uptake pathway. This work highlights cmβCD complexation as a promising strategy to enhance CPT solubility and liposomal loading for improved drug delivery.