Safety and neuroprotective efficacy of the VCP inhibitor ML240 in large-animal and human retinal explants: a preclinical ex vivo study

Background: Retinal degenerative diseases represent a complex global health problem due to their significant impact on patients' daily lives and their highly heterogeneous pathogenesis, which challenges therapeutic development. Despite this complexity, many diseases, such as retinitis pigmentosa (RP) and age-related macular degeneration (AMD), share common features, including disrupted proteostasis, oxidative stress, and inflammatory responses, eventually leading to photoreceptor (PR) degeneration and vision loss. The inhibition of valosin-containing protein (VCP) has emerged as a promising mutation-independent therapeutic strategy for RP. However, clinical translation requires rigorous validation in models that closely reflect human retinal physiology. Methods: Organotypic retinal explants from porcine, macaque, and human donors were placed in an in vitro culture setup and treated with ML240, a selective VCP inhibitor, delivered either as a free compound or encapsulated in mPEG5kDa-cholane. Photoreceptor survival was assessed via TUNEL assay, outer nuclear layer (ONL) row quantification, and immunostaining. Retinal inflammation was evaluated by microglial staining. A dose-response study was performed to determine safety margins across species, and additional retinal markers were used to assess the preservation of non-photoreceptor retinal cell populations. Results: Porcine retinal explants exhibited progressive photoreceptor degeneration under ex vivo conditions. Treatment with ML240, particularly when formulated with mPEG5kDa-cholane, significantly reduced photoreceptor cell death and microglial activation. Macaque and human explants exhibited minimal to no signs of degeneration. Treatment did not affect morphological or histological features of the explant, demonstrating the safety of ML240 in the primate retina. Conclusions: VCP inhibition via ML240 demonstrates an uncompromised safety profile in porcine, macaque, and human retinal explants. In addition, the neuroprotective activity of ML240 was evident in porcine tissue. Formulation with mPEG5kDa-cholane enhances the overall performance of the compound, supporting its use for future clinical application as a mutation-independent therapeutic approach for retinal degenerative diseases.