LB1116 Label-free quantification of the pharmacokinetics of small molecule drugs in skin

Abstract

Despite the number of drugs and formulations designed for treating inflammatory skin conditions such as psoriasis and atopic dermatitis, the available tools for precisely studying their performance in situ have been limited. For this reason, there is a major need for techniques that can enable the direct visualization and quantification of small molecule Pharmacokinetics and Pharmacodynamics (PK/PD). We have developed a quantitative imaging toolkit that utilizes Stimulated Raman Scattering (SRS) microscopy and is capable of detecting and tracking specific molecular species without the need for extrinsic labels. This includes image processing algorithms based on deep Convoluted Neural Networks (CNNs) that can be used to identify cells, cell junctions, and cell types in skin, thereby enabling multifactorial analysis of PK at the cellular-level for the first time. In this study, we have used two anti-inflammatory drugs, ruxolitinib and betamethasone-17,21-dipropionate (BMDP-D), in two vehicles, transcutol and a gel formulation produced by LEO Pharma. We imaged four epidermal compartments in ex vivo nude mouse ear skin: stratum corneum (SC), sebaceous glands (SG), adipocytes (AD) and subcutaneous fat (SCF), and extracted drug uptake patterns through image processing. An analysis of the drug uptake showed that, at the SC layer, drug concentration increases when transcutol is used as a vehicle, while it decreases when the gel is used. This is because the gel creates pores in the cell junctions between keratinocytes and allows for an easier downward flux of the drugs to deeper layers. In addition, we have found a nearly 5-fold difference (p-value < 0.05) in the downward flux of ruxolitinib compared to BMDP-D, which could be related to their 2-fold difference in the logP. As clinical imaging devices based on SRS are also being developed, we believe that this approach will serve a role in the future in transforming the way we develop, evaluate, and formulate drugs for skin diseases.