Efficacy of topically applied rapamycin-loaded redox-sensitive nanocarriers in a human skin/T cell co-culture model

Rapamycin, also known as Sirolimus, is a promising anti-proliferative drug, but its therapeutic use for the topical treatment of inflammatory, hyperproliferative skin disorders is limited by insufficient penetration rates due to its high molecular weight (MW of 914.172 g/mol) and high lipophilicity. We have shown that core multi-shell (CMS) nanocarriers sensitive to oxidative environment can improve drug delivery to the skin. In this study, we investigated the mTOR inhibitory activity of these oxidation-sensitive CMS (osCMS) nanocarrier formulations in an inflammatory ex vivo human skin model. In this model, features of inflamed skin were introduced by treating the ex vivo tissue with low-dose serine protease (SP) and lipopolysaccharide (LPS), while phorbol 12-myristate 13-acetate and ionomycin were used to stimulate IL-17A production in the co-cultured SeAx cells. Furthermore, we tried to elucidate the effects of rapamycin on single cell populations isolated from skin (keratinocytes, fibroblast) as well as on SeAx cells. Further, we measured possible effects of the rapamycin formulations on dendritic cell (DC) migration and activation. The inflammatory skin model enabled the assessment of biological readouts at both the tissue and T cell level. All investigated formulations successfully delivered rapamycin across the skin as revealed by reduced IL-17A levels. Nevertheless, only the osCMS formulations reached higher anti-inflammatory effects in the skin compared to the control formulations with a significant downregulation of mTOR activity. These results indicate that osCMS formulations could help to establish rapamycin, or even other drugs with similar physico-chemical properties, in topical anti-inflammatory therapy.