Characterizing Cutaneous Drug Delivery Using Open-Flow Microperfusion and Mass Spectrometry Imaging.

Traditionally, cutaneous drug delivery is studied by skin accumulation or skin permeation, while alternative techniques may enable the interactions between the drug and the skin to be studied in more detail. Time-resolved skin profiling for pharmacokinetic monitoring of two Janus Kinase (JAK) inhibitors, tofacitinib and LEO 37319A, was performed using dermal open-flow microperfusion (dOFM) for sampling of perfusate in an ex vivo and in vivo setup in pig skin. Additionally, matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI-MSI) was performed to investigate depth-resolved skin distributions at defined time points ex vivo in human skin. By dOFM, higher skin concentrations were observed for tofacitinib compared to LEO 37319A, which was supported by the lower molecular weight, higher solubility, lipophilicity, and degree of protein binding. Using MALDI-MSI, the two compounds were observed to show different skin distributions, which was interpreted to be caused by the difference in the ability of the two molecules to interact with the skin compartments. In conclusion, the techniques assessed time- and depth-resolved skin concentrations and were able to show differences in the pharmacokinetic profiles of two JAK inhibitors. Thus, evidence shows that the two techniques can be used as complementary methods to support decision making in drug development.

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.

MALDI mass spectrometry imaging as a complementary analytical method for improved skin distribution analysis of drug molecule and excipients.

In cutaneous drug delivery, it is widely accepted that the choice of excipients affects the delivery of a drug molecule to the skin. MALDI mass spectrometry imaging (MALDI-MSI) is an imaging technique which enables the simultaneous detection of multiple compounds. MALDI-MSI was applied to study the penetration of tofacitinib and excipients in porcine skin from two formulations with sodium lauryl sulphate (SLS) and dexpanthenol (DXP) using Franz diffusion cells. Further, the receptor media was collected for analysis of the permeated amounts of tofacitinib and excipients. The MALDI images showed DXP to be co-localized with tofacitinib in the epidermal and deep dermal region while SLS was distributed in the entire skin compartment. The permeation of tofacitinib for the two formulations was similar after 24 h, whereas, the percentage of permeated DXP was higher than for SLS. This study provided an overview of the skin penetration and permeation of drug molecule and excipients. MALDI-MSI showed differences in the DXP and SLS distribution. This indicates that the excipients interact with the skin through different mechanisms. Compound-specific imaging methods such as MALDI-MSI are potential tools to increase the understanding of the complex interplay between skin, excipients and the drug molecule for optimized cutaneous drug delivery.