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.