Uncovering a Mutation-Independent Therapeutic Strategy against Inherited Retinal Diseases: Development of Class I HDAC/LSD1 Hybrid Inhibitors

Among genetic retinal disorders, retinitis pigmentosa (RP) is characterized by degeneration of rod photoreceptors caused by a large number of diverse mutations, most of which act through different pathways to which epigenetic targets also contribute. The eraser enzymes lysine demethylase 1 (LSD1) and histone deacetylase 1 (HDAC1) play major roles in the development of rod photoreceptors, and their inhibitors were shown to block inherited rod degeneration, preserving vision and contributing to a general anti-inflammatory profile at the retinal level. In this work, we proposed the development of polypharmacological agents targeting class I HDAC/LSD1 enzymes with the aim of treating the <i>rd10</i> mice model of RP. The new small library of compounds is typified by hybrid (±)-<b>3d,</b> which showed IC₅₀ values of 1702, 842, and 358 nM against HDAC1, HDAC2, and HDAC3, respectively, while inhibiting LSD1 with an IC₅₀ value of 1074 nM. When tested on hydrogen peroxide-stressed ARPE-19 and 661W retinal cells at a concentration of 10 μM, (±)-<b>3d</b> showed a promising antioxidant profile, increasing the cellular levels of acetylated and methylated histone H3, and was selected for further studies also in light of its calculated IH-L. In the <i>rd10</i> mice RP model, a single intravitreal injection of (±)-<b>3d</b>, at the same concentration used in cells, enhanced photoreceptor survival, downregulated retinal expression of the inflammatory genes GFAP, Ccl2, and Ccl12, and effectively preserved the retinal pigment epithelium barrier. Furthermore, (±)-<b>3d</b> promoted the acetylation and methylation of histone H3, thus confirming the engagement of both class I HDAC and LSD1.