Towards the development of a RNAi-based topical treatment for psoriasis: Proof-of-concept in a 3D psoriasis skin model.

RNA interference has emerged as a powerful tool for therapeutic gene silencing, as it offers the possibility to silence virtually any known pathology-causing gene. However, in vivo delivery of RNAi molecules is hampered by their unfavourable physicochemical characteristics and susceptibility to degradation by endogenous enzymes. To overcome these limitations, we recently developed an elastic liposomal formulation, called DDC642, as topical delivery system of therapeutic RNAi molecules for skin disorders. In this study, we validated the therapeutic efficacy of DDC642-encapsulated RNAi molecules in the treatment of psoriasis using 3 different in vitro models: a standardized keratinocyte monolayer culture, psoriasis-induced keratinocytes and a psoriasis-reconstructed skin model. Four genes (IL22RA1, KRT17, DEFB4 and TSLP), known to be upregulated in psoriatic lesions, and thereby key players in psoriasis pathogenesis were selected. Moreover, the possibility of using a combined siRNA therapy in the topical treatment of psoriasis was explored. Results indicate a successful gene silencing of each different target, both at mRNA and protein levels. Additionally, siRNA-DDC642 treatment resulted in a reduced expression of specific psoriasis markers, indicating their potential in future therapeutic approach. The examined siRNA combination (ie simultaneous knockdown of KRT17, DEFB4 and TSLP) showed an enhanced reduction in TSLP expression, whereas the decrease in K17 protein expression was impaired in psoriatic keratinocytes. Although the here examined siRNA combination could still be further improved, our study proved already in vitro the clinical potential of targeting multiple genes at once, each playing a different role in a complex disease such as psoriasis.