RNA interference (RNAi) has the potential to revolutionize treatment of dominant genetic disorders. Small inhibitory RNAs (siRNAs) are highly potent and selective, demonstrating remarkable single-nucleotide specificity. Clinical trials using siRNAs are currently underway for a number of indications including skin. Facilitated by Phase 1 funding, a small one patient phase 1b clinical trial was undertaken for pachyonychia congenita (PC). This ultrarare skin disorder is caused by mutations, including single nucleotide changes, in the genes encoding keratins 6, 16, and 17. The major complaint of PC patients is the debilitating painful callusing and blistering which occurs on or near the pressure points of the feet. These defined regions on the soles of the feet were targeted for local siRNA treatment by intralesional injection of siRNA (TD101) with encouraging results. Unfortunately, the pain associated with injections into lesions (oral pain medication and regional nerve blocks were required to allow treatment), prevents widespread use of this mode of administration. This observation has led to intense efforts to identify patient-friendly (i.e., little or no pain) delivery options. This clinical trial was the first human use of siRNA in skin and also the first siRNA to target a mutated gene. In Phase 2 of this proposal, we extend the progress of Phase 1 and the Phase 1b clinical trial. We have found that unmodified or stabilized siRNAs are not taken up readily by skin keratinocytes but that modified, so-called "self-delivery" (sd) siRNAs are. Additional optimization of the sd-siRNA will be undertaken in mouse and human skin models followed by synthesis of GMP material for mouse and rabbit toxicology studies and clinical trials in which the siRNA will be delivered by dissolvable microneedle arrays or a topical GeneCream" formulation, both developed and manufactured at TransDerm. GeneCream and microneedle arrays are both designed to effectively deliver sd-siRNA with little or no pain (microneedle protrusions are designed to only penetrate to the non-innervated epidermis). Although PC is a rare disease, the nature of the disorder makes it an ideal prototype skin disorder (defined mutations with expression in limited, defined areas) for first-in-man siRNA skin clinical trials, and we fully expect the lessons learned will be readily generalized to other skin disorders.
Despite the discovery of the underlying mutations responsible for many inherited skin diseases, few effective treatments have emerged. The discovery that siRNAs can be developed to target specific disease-related mutations portends the advent of a new treatment paradigm. We have identified a potent and selective siRNA that targets a single nucleotide mutation in the keratin 6a gene that is responsible for the rare skin disorder pachyonychia congenita and blocks its expression. This siRNA (known to the FDA as TD101) was successfully tested in a Phase 1b clinical trial. Despite signs of efficacy, the painful nature of the administration route (intradermal injection of large volumes) required that we develop a more patient-friendly delivery system. Phase 2 of this proposal allows preclinical studies enabling a second clinical trial using microneedles loaded with a self-delivery version of TD101 siRNA. The lessons learned in applying siRNA technology for treatment of PC should be readily generalizable to a host of other dominant skin disorders and likely to other disorders resulting from mutated or overexpressed disease-causing genes.
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