Objectives: To discover an ER ligand that induces differentiation of oligodendrocyte progenitor cells (OPCs) into mature oligodendrocytes, thereby leading to remyelination of demyelinated axons. A potent ER ligand would then be developed into a therapeutic for treating MS patients.
Methods: Based on molecular modeling, modifications to the core structure of E2 were designed with different C-6 alkoxyalkyl moieties and/or substitution of the C-18 methyl group. Structurally similar, but distinct, E2 analogs (NDC-1308, NDC-1022 and NDC-1352) were synthesized to greater than 99% purity and characterized for ER binding affinity in competitive assays using recombinant human ERs. ER dimerization was assessed using BRET assays, while ER activation was determined using luciferase reporter constructs, all in human cells. Differential gene expression of the E2 analogs was evaluated in human cell lines by microarray, followed by pathway analysis related to OPC differentiation and myelin synthesis. Gene expression patterns were integrated with the receptor biology to predict which E2 analogs would cause OPC differentiation in vitro. The E2 analogs were formulated using various cyclodextrins, with lead NDC-1308 further evaluated for efficacy in MS models.
Results: The E2 alterations caused pronounced changes in subtype selectivity for ER-α or ER-β, along with varying degrees of ER dimerization and ER activation. While several E2 analogs cause a dramatic up-regulation of genes (2 to 75-fold) in signaling pathways related to OPC differentiation and myelin production, NDC-1308 was the most potent of the E2 analogs and significantly more potent at differentiating OPCs than either estriol or E2. Following systemic dosing, NDC-1308 crosses the blood brain barrier in EAE-induced mice and is absorbed into CNS tissues. NDC-1308 administration (10 mg/Kg, daily) significantly reduced the level of apoptosis in the spinal cord of EAE mice. Studies employing different routes of administering NDC-1308, along with various dosing schedules, are currently being carried out in the cuprizone mouse model of demyelination to examine how NDC-1308 influences the remyelination process.
Conclusions: The findings presented here are consistent with NDC-1308 activating ERs in a unique way that upregulates genes necessary for inducing OPC differentiation. Further development of NDC-1308 as a therapeutic for remyelination in MS patients is ongoing, either alone or in combination with current immunomodulatory therapies.