Repositioning of the Anthelmintic Drugs Bithionol and Triclabendazole as Transthyretin Amyloidogenesis Inhibitors.

Transthyretin (TTR) is a causative protein of TTR amyloidosis (ATTR amyloidosis), a general term for diseases characterized by deposition of TTR amyloid fibrils in specific organs. ATTR amyloidosis can be ameliorated by stabilization of the TTR tetramer through the binding of small molecules. Here, we show that the clinical anthelmintic drugs bithionol (42) and triclabendazole (43) potently inhibit aggregation of the amyloidogenic variant V30M-TTR. A competitive binding assay using a fluorescence probe showed that the binding affinity of 42 with V30M-TTR was significantly higher than that of the first-in-class drug tafamidis (1), and the binding affinity of 43 was similar to that of 1. The crystallographic and thermodynamic analysis revealed that 42 efficiently occupied the halogen-binding grooves of TTR, resulting in the favorable binding entropy. Multifaceted in vitro studies of anthelmintic drugs have the potential to reposition these drugs as ATTR amyloidosis inhibitors.

Improving the Dissolution of Triclabendazole from Stable Crystalline Solid Dispersions Formulated for Oral Delivery.

Triclabendazole belongs to the class II/IV of the Biopharmaceuticals Classification System, and its low aqueous solubility represents a major drawback during the development of effective dosage forms. Therefore, the goal of this study was to elucidate whether polymeric solid dispersions would represent a suitable approach to overcome such disadvantage. Due to the lack of information on triclabendazole release, four different dissolution media were evaluated to analyze drug dissolution rate. The polymeric solid dispersions were characterized by X-ray diffraction and Fourier transform infrared spectroscopy. The selected final formulations were further stored for 24 months, and their physical stability was evaluated by means of X-ray diffraction and drug dissolution assays. Drug solubility studies indicated that poloxamer 407 (P407) solubilized a higher amount of drug than polyethylene glycol 6000. Drug-to-carrier ratio, nature of the selected carriers, and the type of dissolution media were important factors for increasing dissolution. By infrared spectroscopy, there were no specific interactions between the drug and polymers. The physicochemical characterization of the systems showed a detectable evidence of drug amorphization by increasing the carrier ratio. Micromeritic studies indicated that raw triclabendazole, physical mixtures, and reference formulation showed poor flow properties, in contrast to the triclabendazole:P407 solid dispersion sample. Both the crystalline properties and dissolution rate of selected samples were very similar after 24 months at room temperature. Thus, considering physical stability and dissolution studies, the development of the solid dispersion is a very suitable methodology to improve triclabendazole dissolution and, potentially, its biopharmaceutical performance.

Chitosan-based nanodelivery systems applied to the development of novel triclabendazole formulations.

Triclabendazole is a poorly-water soluble (0.24 µg/mL) compound classified into the Class II/IV of the Biopharmaceutical Classification System. It is the drug of choice to treat fascioliasis, a neglected parasitic disease worldwide disseminated. Triclabendazole is registered as veterinary medicine and it is only available for human treatment as 250 mg tablets. Thus, the aim of this work was to develop novel drug delivery systems based on nanotechnology approaches. The chitosan-based nanocapsules and nanoemulsions of triclabendazole were fully characterized regarding their particle size distribution, polydispersity index and zeta potential, in-vitro release and stability in biological media. Cytotoxicity evaluation and cellular uptake studies using CaCo-2 cell line were also investigated. The results indicated an average hydrodynamic size around ~160 nm were found for unloaded nanoemulsions which were slightly increased up to ~190 nm for loaded one. In contrast, the average hydrodynamic size of the nanocapsules increased from ~160 nm up to ~400 nm when loaded with triclabendazole. The stability studies upon 30 days storage at 4, 25 and 37°C showed that average size of nanoemulsions was not modified with varying amounts of loaded TCBZ while an opposite result was seen in case of loaded nanocapsules. In addition, a slight reduction of zeta potential values over time was observed in both triclabendazole nanosystems. Release of TCBZ from nanoformulations over 6 h in simulated gastric fluid was 9 to 16-fold higher than with untreated TCBZ dispersion. In phosphate buffer saline solution there was no drug release for neither nanocapsules nor nanoemulsions. Cell viabilities studies indicated that at certain concentrations, drug encapsulation can lower its cytotoxic effects when compared to untreated drug. Confocal laser scanning microscopy study has shown that nanocapsules strongly interacted with Caco-2 cells in vitro which could increase the passage time of triclabendazole after oral administration. The results of this study constitute the first step towards the development of nanoformulations intended for the oral delivery of anti-parasitic drugs of enhanced bioavailability.