Assessing the skin pharmacokinetics of topical drugs, and the bio(in)equivalence of topical drug products, using non-invasive techniques

定量测定局部应用药物在其作用部位的生物利用度（BA） 代表了一个未满足的监管需求。大多数皮肤病药物靶点是 发现于表皮和上层真皮（包括附属物如毛囊和皮脂腺）中 腺体），在主要皮肤屏障角质层（SC）之下。虽然一些替代方案 临床终点BA和生物等效性（BE）研究的方法已经确定，评价 其他替代方法是一个“正在进行的工作”。研究的核心假设是 提出的策略是光谱（特别是拉曼）成像能够提供 非侵入性、准确、灵敏和可重复的测定， 其中局部给药的药物在SC以下的作用部位变得可用（并且， 特别是有活力的表皮）。最初的目标是建立实验方法， 拉曼和质谱成像，以证明这一假设离体;随后，目标 是开发体内拉曼成像，并使用互补技术校准该方法。 该项目有以下具体目标：（a）构思明确的拉曼 可以实现皮肤中药物的光谱分析， 背景信号干扰;（B）发展一种稳健的方法来纠正药物信号衰减 作为皮肤中测量深度增加的函数;（c）证明连续的、真实的- 局部应用制剂后的时间拉曼成像可以测量药物的“输入动力学” （d）关联和验证对表皮的拉曼光谱评估， 药物输入与平行，高灵敏度质谱分析和成像;（e）开发 拉曼成像，以量化药物输入到活表皮中的动力学， 方法使用SC采样和反向离子电渗疗法，另一种非侵入性方法， （f）证明经改良的光谱工具可 局部应用药物的表皮BA，并正确区分 （g）应用时空数学模型， 机制过程的基础上观察到的结果，探索药物性质的影响， 这些机制，并估计和验证局部生物利用度的关键指标。总的来说， 因此，拟议的项目结合了不同的，但协同作用，方法来评估专题 BA/BE与新的光谱成像策略，以证明常规，简便， 体内皮肤中药物药代动力学的非侵入性测量是可实现的目标， 在监管科学和决策方面具有相当大的应用潜力。

The quantitative determination of the bioavailability (BA) of a topically applied drug at its site of action in the skin represents an unmet regulatory need. The majority of dermatological drug targets are found in the epidermis and upper dermis (including appendages such as hair follicles and sebaceous glands), beneath the principal skin barrier, the stratum corneum (SC). While some alternative methods to clinical endpoint BA and bioequivalence (BE) studies have been identified, the evaluation of other surrogate approaches is a ‘work-in-progress’. The central hypothesis of the research strategy proposed is that spectroscopic (in particular, Raman) imaging is able to provide a non-invasive, accurate, sensitive and reproducible determination of the rate and extent to which a topically administered drug becomes available at its site of action below the SC (and, specifically, the viable epidermis). The initial goal is to establish experimental methods, combining Raman and mass spectrometry imaging, to prove this hypothesis ex vivo; subsequently, the objective is to develop Raman imaging in vivo, and to calibrate the approach using complementary techniques. The project has the following specific aims: (a) to conceive strategies by which unambiguous Raman spectroscopic analysis of a drug in the skin can be achieved despite the potential for significant, background signal interference; (b) to evolve a robust approach to correct for drug signal attenuation as a function of increasing depth of measurement in the skin; (c) to demonstrate that continuous, real- time Raman imaging after topical application of a formulation can measure the drug’s “input kinetics” into the viable epidermis ex vivo; (d) to correlate and validate Raman spectroscopic assessment of drug input with parallel, high-sensitivity mass spectroscopic analysis and imaging; (e) to develop Raman imaging to quantify drug input kinetics into the viable epidermis in vivo and to calibrate the method using SC sampling and reverse iontophoresis, another non-invasive method, in combination with mathematical modelling; (f) to demonstrate that the refined spectroscopic tool can characterise the epidermal BA of a topically applied drug and distinguish correctly between formulations that are BE and those that are not; and (g) to apply spatio-temporal mathematical modelling to identify the mechanistic processes underlying the observed results, to explore the impact of drug properties on those mechanisms, and to estimate and validate key metrics of topical bioavailability. In summary, therefore, the proposed project combines different, but synergistic, approaches to assess topical BA/BE with novel spectroscopic imaging strategies to demonstrate that the routine, facile and noninvasive measurement of drug pharmacokinetics in the skin in vivo is an attainable objective with considerable potential for application in regulatory science and decision-making.