Inherited retinal diseases (IRDs) are the leading cause of vision loss in persons aged 15 - 45 years and represent a substantial societal disease burden, with an incidence of 1 in 2,000. Treatment options for IRDs have been limited, although novel gene and molecular therapeutics are now demonstrating significant potential in the treatment of IRDs. RNA therapeutics in particular hold unique promise in these diseases, due to their even cellular level distribution and precise effects on gene expression. However, achieving safe and efficient delivery of molecular drugs to the retina, and the retinal pigmented epithelium in particular, remains a significant obstacle to clinical application. Antisense oligomers (AO) are a well-established class of RNA therapeutic whose potential is yet to be fully realised due to this delivery challenge. Here, we report on an AO conjugate that reaches the deepest layers of the retina after intravitreal administration and localises to the nucleus of the target cell type to modulate gene expression. This class of therapeutic holds substantial promise in the treatment of IRDs.
We exploit peptide libraries derived from 82 microorganism genomes and 118 synthetic viral genes to identify cell penetrating peptides (CPP) to deliver AO cargos to cells in vitro and to tissues and organs in vivo. The CPPs were screened initially against mammalian cells using a cytosolic extraction method, followed by next generation sequencing and selection using a combination of algorithms known to produce a favourable toxicology and efficacy profile in the eye. The CPPs were then conjugated to an antisense morpholino oligomer, that was used as an exon skipping reporter. Standout performance in the latter assay, when administered via intravitreal injection, and a clean toxicology profile identified a lead peptide for our retinal disease program.
Notable CPPs in pre-clinical and clinical development include chemical stabilisation or poly-arginine that can limit efficacy or increase toxicity. Our discovery peptides are derived from nature, lack chemical modifications, and yield optimal amino acid sequences with enhanced efficacy and tolerability performance in vitro and in vivo. The lead CPP traffics the AO through the vitreous, into the neural retina and retinal pigment epithelium, resulting in enhanced target engagement and 6-fold lower cytotoxicity than the competitor CPP, with no evidence of retinal damage.