In the dominantly inherited genetic disorders where the underlying pathomechanism is dominant-negative protein interference, such as the keratin disorders, an attractive therapy strategy is to selectively inhibit expression of the mutant allele, allowing the normal allele to function correctly. We are currently exploring two types of therapeutic RNA molecules for their ability to selectively and potently inhibit mutant gene expression. These are short interfering RNA (siRNA) molecules and antisense oligonucleotides (ASOs).
In families with a rare recessive type of the skin blistering disorder epidermolysis bullosa simplex, we have previously shown that heterozygous carriers of a null mutation in the keratin K14 gene have perfectly normal skin. This provides proof-of-concept in humans for our therapy strategy of silencing the dominant-negative mutant allele and allowing the single normal allele to function.
The majority of keratin mutations are single point mutations leading to amino acid substitutions. Using medium-throughput assay systems, we systematically screen therapeutic RNA molecules against wild-type and mutant reporter gene constructs to identify those positions where the mutant allele is potently and selectively inhibited. These inhibitors are then taken through secondary screening using biochemical and functional assays to arrive at lead molecules for clinical development.
Currently, we are exploring non-invasive methods to deliver therapeutic RNA molecules into the epidermis and into the cornea, using a variety of model systems. Our therapeutic RNA programme is funded by an MRC Programme Grant in partnership with our industry collaborator Wave Life Sciences (Cambridge Massachusetts), the skin blistering disease charity DEBRA UK and NHS Research Scotland.
The major thrust of our work right now is the development of a delivery system for therapeutic RNA molecules, with the aim of progressing to clinical trials in 2018/19.
- Smith FJD et al., (2008) Development of therapeutic siRNAs for pachyonychia congenita. J Invest Dermatol 128:50-58 (PubMed ID: 17762855)
- Hickerson RP et al., (2008). Single nucleotide-specific siRNA targeting of mutant keratin 6a responsible for the dominant-negative skin disorder pachyonychia congenita. J Invest Dermatol 128:594-605 (PubMed ID: 17914454)
- Leachman SA et al., (2010) First-in-human Mutation-targeted siRNA Phase Ib Trial of an Inherited Skin Disorder. Molecular Therapy 8:442-446 (PubMed ID: 19935778)
- McLean WHI and Moore CBT (2011) Keratin disorders: from gene to therapy. Hum Mol Genet 20:R189-197 [Epub ahead of print Sep 10] (PubMed ID: 21890491)
- Atkinson SD, McGilligan VE, Liao H, Szeverenyi I, Smith FJD, Moore CBT, McLean WHI (2011) Development of allele-specific therapeutic siRNA for keratin 5 mutations in epidermolysis bullosa simplex. J Invest Dermatol 131:2079-2086 [Epub ahead of print Jun 30] (PubMed ID: 21716320)
- Liao H, Irvine AD, MacEwen CJ, Weed KH, Porter L, Corden LD, Gibson AB, Moore JE, Smith FJD, McLean WHI* and Moore CBT (2011) Development of allele-specific therapeutic siRNA in Meesmann epithelial corneal dystrophy. PLoS ONE 6:e28582 [Epub ahead of print 12th Dec 2011] doi:10.1371/journal.pone.0028582
- Leslie Pedrioli DM, Fu DJ, Gonzalez-Gonzalez E, Contag CH, Kaspar RL, Smith FJD, McLean WHI (2012) Generic and Personalized RNAi-Based Therapeutics for a Dominant-Negative Epidermal Fragility Disorder. J Invest Dermatol 132:1627-1635 [Epub ahead of print 8th Mar 2012] (PubMed ID: 22402445)