Quantitative MALDI mass spectrometry imaging for exploring cutaneous drug delivery of tofacitinib in human skin

In skin penetration studies, HPLC-MS/MS analysis on extracts of heat-separated epidermis and dermis provides an estimate of the amount of drug penetrated. In this study, MALDI-MSI enabled qualitative skin distribution analysis of endogenous molecules and the drug molecule, tofacitinib and quantitative analysis of the amount of tofacitinib in the epidermis. The delivery of tofacitinib to the skin was investigated in a Franz diffusion cell using three different formulations (two oil-in-water creams, C1 and C2 and an aqueous gel). Further, in vitro release testing (IVRT) was performed and resulted in the fastest release of tofacitinib from the aqueous gel and the lowest from C2. In the ex vivo skin penetration and permeation study, C1 showed the largest skin retention of tofacitinib, whereas, lower retention and higher permeation were observed for the gel and C2. The quantitative MALDI-MSI analysis showed that the content of tofacitinib in the epidermis for the C1 treated samples was comparable to HPLC-MS/MS analysis, whereas, the samples treated with C2 and the aqueous gel were below LOQ. The study demonstrates that MALDI-MSI can be used for the quantitative determination of drug penetration in epidermis, as well as, to provide valuable information on qualitative skin distribution of tofacitinib.