Deciphering remyelinating mechanisms induced by clinically-used azole antifungals with exploitable repurposing properties : An in silico approach

Recent evidence demonstrated the ability of some antifungal azoles to induce (re)myelination in oligodendrocyte precursor cell (OPC). These compounds, already marketed for different pathologies, are interesting candidates for a repurposing strategy in neurodegenerative diseases, like multiple sclerosis (MS). Previous results showed that antifungal azoles inhibit enzymes involved in retinoic acid (RA) catabolism i.e. CYP26, therefore increasing cellular RA concentration. Our hypothesis was that this inhibition is the mechanism leading to the azoles myelinating effect. Since no crystal structure is yet available for any member of the CYP26 family, models of the 3D structures of all CYP26 isoenzymes were built via comparative modelling, using the X-ray structure of the RA-bound cyanobacterial CYP120A1 cytochrome as template. With molecular docking seven different azoles in clinical use and RA as a control were investigated for their propensity to inhibit CYP26. Accurate binding free energy values (affinity) were computed by refining the docking complexes, relaxing the ligand within the binding pocket and applying a constrained forcefield energy minimization. Dissociation constants (Ki) were estimated on the basis of their in silico affinity. All the in silico procedures were carried out with the MOE Suite 2016.08. The prioritized azoles were then tested in three different cell models, characterized by increasing complexity: i) OPC cultures, a maturation assay for myelin-producing cells; ii) OPC-dorsal root ganglion (DRG) neuron co-cultures, a myelination assay; iii) cerebral micromass cultures, a cell differentiation assay for CNS. Our results confirm that molecules interfering with the RA metabolic pathway indeed alter the myelination profile and support the proposed mechanism of action that azoles may increase myelin levels in OPCs, by inhibiting RA degradation. Itraconazole and fluconazole emerged as the most promising candidates for repurposing.