The host–guest inclusion complex of Anle 138b with Methyl-β-cyclodextrin: in vitro characterization and possible formulation development for anti-Parkinson application

Anle 138b has been studied as anti-Parkinson disease (PD) drug, whose mechanism consists of the inhibition of α-synuclein (α-syn) aggregation. Its aqueous solubility was found less than 1 μM at 25 °C and, hence, no liquid formulation has been investigated for the pharmaceutical market. In the present study, we considered the performance of some formulations based on the inclusion complex (ICX) of the α-syn aggregation inhibitor with methyl-β-cyclodextrin (Me-β-CD) for brain delivery by intranasal administration. Firstly, the Anle 138b/Me-β-CD ICX significantly enhanced the intrinsic Anle 138b solubility (i.e., almost 300 times higher than drug alone). Structural insights concerning the Anle 138b/Me-β-CDICX were derived from 1H NMR spectra which evidenced sets of signals due to the presence of conformers and tautomers. Furthermore, the ICX was also evaluated by FT-IR spectroscopy and X-Ray diffraction (XRD) showing that a reduction of the crystalline state occurs promoting an amorphous state confirmed by the presence of very broad bands in the relative XRD diffraction pattern. While UV–Vis spectroscopy gave a weak indication for ICX formation, strong evidence in this regard was gained by phase-solubility studies showing an AL-type profile indicative of ICX formation with 1:1 stoichiometry. Cytocompatibility assays conducted on Olfactory Ensheathing Cells demonstrated that the Anle 138b/Me-β-CD ICX formulation did not induce cytotoxic effects after 24 h of incubation at Me-β-CD concentrations up to 2.5 mM and Anle 138b concentrations up to 10 μM. Finally, the in vitro Thioflavin T assay evidenced that the Anle 138b/Me-β-CD ICX showed efficacy equal to, if not superior to, the free Anle 138b concerning the inhibition of α–syn aggregation. Definitely, it appears that solid dosage forms based on ICX could be promising for anti-PD application.