Recessive dystrophic epidermolysis bullosa (RDEB) is a genetic blistering disorder caused by mutations in the COL7A1 gene encoding for type VII collagen (C7) protein. We have demonstrated that QR-313, an antisense oligonucleotide (AON), is efficient in the skipping of exon 73 from COL7A1 in skin, enabling removal of mutations in exon 73 of COL7A1. One of the main hurdles in development of potential medicines based AONs is sufficient delivery to the target organ. It has been shown that systemic (iv) administration leads to high AON concentrations in the liver and kidneys, with hardly detectable delivery to the skin. Current aim was to assess delivery of QR-313 in DEB-like skin after topical application of QR-313 formulated in a hydrogel. Hydrogels are part of the daily care of RDEB patients, therefore a conventional hydrogel based on carbomer was developed for QR-313. 
The delivery of topically applied Cy5 QR-313 was assessed using ex vivo pig skin, human skin equivalents (HSEs) and in vivo in minipigs. All skin sections were processed for histology, stained with DAPI or haematoxylin and analysed using fluorescent microscopy for the Cy5 label. On ex vivo pig skin pieces a DEB-like wound was created by removing the epidermis, next Cy5 QR-313 (0.5-10mg/g gel) was applied on wounded and intact skin for 2 to 48hrs. Results showed a deeper diffusion front into the dermis over time and stronger fluorescent signal with increasing concentrations. Cy5 QR-313 was not able to penetrate the intact skin. These results were corroborated in HSEs. In vivo, wounds of 2x3 cm and 0.35 mm deep were created under anaesthesia on the backs of minipigs. Delivery to the dermis was observed using Cy5 QR-313 at a strength of 0.5 mg/g gel either single or 3 times, using a 48 hour dose interval. After 7 days the wounds were closed by a newly formed epidermis and the Cy5 signal was seen in the upper dermis and throughout all newly formed epidermal cell layers. Together this demonstrates AON delivery to wounded skin after local application in a carbomer hydrogel.

Local delivery of an antisense oligonucleotide for recessive dystrophic epidermolysis bullosa