Therapeutic Potential of Partial Retinoid Agonists against Vertebrate Rhodopsin Misfolding Disorders

Mutations in rod opsin are a leading cause of inherited retinal degenerative diseases such as retinitis pigmentosa (RP). Pharmacological compounds that stabilize rhodopsin (Rho) and mitigate cellular stress pathways hold promise for therapeutic intervention. Among these, retinoid analogs have shown efficacy in models of autosomal dominant RP (adRP) and age-related macular degeneration (AMD). In this study, we evaluated the pharmacological potential of two partial retinoid agonists, acyclic-retinal and 9-cis-9-demethyl-retinal, as well as newly synthesized retinol and amine derivatives of 9-cis-9-demethyl-retinal. A photoreceptor-derived 661W cell line stably expressing two RP-linked misfolding rod opsin mutants, P23H and T289P, was used to assess the compound activity. We investigated the effects on opsin folding, glycosylation, membrane localization, and pigment regeneration. Both acyclic-retinal and 9-cis-9-demethyl-retinal promoted mature glycosylation and enhanced cell surface trafficking of P23H and T289P rod opsins. Spectroscopic analysis confirmed that these compounds regenerated functional, photosensitive pigments and stabilized the receptor in the Meta-I conformation upon light exposure. Notably, 9-cis-9-demethyl-retinal exhibited higher binding affinity than 9-cis-retinal, without impairing visual signaling postphotoisomerization. Among the derivatives, the amine form of 9-cis-9-demethyl-retinal was most effective in promoting proper folding and localization of misfolded rod opsin, outperforming the corresponding retinol analog. These findings support the therapeutic potential of acyclic-retinal, 9-cis-9-demethyl-retinal, and its derivatives for rescuing misfolded rod opsin and delaying photoreceptor degeneration in RP.