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

局部应用药物作用部位生物利用度(BA)的定量测定 代表着一种未得到满足的监管需求。大多数皮肤科药物的靶点是 见于表皮和真皮上部(包括毛囊和皮脂腺等附属物 在主要皮肤屏障下的角质层(SC)。虽然有一些替代方案 方法对临床终点BA和生物等效性(BE)研究进行了确定、评价 其他替代方法中的一种是“正在进行中的工作”。这项研究的中心假设 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、灵敏和可重复性的测定 局部给药的药物在SC下方的作用部位可用(和， 具体地说，就是有活力的表皮)。最初的目标是建立实验方法，结合 拉曼和质谱学成像，以在体外证明这一假说；随后，目标 是开发活体拉曼成像，并使用互补技术校准方法。 该项目有以下具体目标：(A)构思战略，明确拉曼 可以实现皮肤中药物的光谱分析，尽管可能显著地， 背景信号干扰；(B)发展一种稳健的方法来校正药物信号衰减 作为增加皮肤测量深度的函数；(C)证明连续的、真实的- 局部用药后的时间拉曼成像可以测量药物的“输入动力学” (D)关联和验证拉曼光谱评估 用平行的、高灵敏度的质谱分析和成像输入药物；(E)开发 拉曼成像定量药物进入活体表皮的动力学并校准 方法采用SC采样和另一种非侵入性方法-反向离子导入相结合的方法 通过数学建模；(F)证明改进的光谱工具可以表征 外用药物的表皮BA，并正确区分 以及(G)应用时空数学模型来确定 观察结果背后的机理过程，以探索药物性质对 这些机制，并估计和验证局部生物利用度的关键指标。总而言之， 因此，拟议的项目结合了不同的但协同的方法来评估专题 BA/BE使用新的光谱成像策略来演示常规、方便和 非侵入性测量药物在体内的药代动力学是一个可以达到的目标，通过 在监管科学和决策方面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.