Tu Dandan, Lemberger Nick-Sidney, Wallmeier Kristin, Riseman Jackson, Kuzma Benjamin A, Wei Yuxiao, Khoo Ting Chean, Rantou Elena, Ghosh Priyanka, Luke Markham C, Raney Sam G, Fallnich Carsten, Evans Conor L
Wellman Center for Photomedicine, Massachusetts General Hospital, Harvard Medical School, CNY149-3, 13th St, Charlestown, MA 02129, USA.
Institute of Applied Physics, University of Münster, 48149 Münster, Germany.
Pharmaceutics. 2025 Sep 13;17(9):1193. doi: 10.3390/pharmaceutics17091193.
The use of optical microscopic techniques has gained increasing attention in recent years for studying the bioavailability (BA) and bioequivalence (BE) of topical drugs. Stimulated Raman scattering (SRS), one type of optical imaging technique, probes chemical-specific information and has excellent spatiotemporal resolution. It uses intrinsic molecular vibrational signatures, and therefore, labeling samples or other treatments is unnecessary to track a molecule. Because of its unique advantages, studies have used SRS for BA evaluations and, more recently, for BE evaluations. In BE evaluation, low data variance within a treatment group is important to ensure sensitivity and specificity in comparing treatment groups. When measuring forward-direction SRS signals transmitted through skin, the signal intensity is susceptible to variance due to several factors, such as the microscope system's performance, the different optical features of topical drug products, and the heterogeneity of skin in transmitting light. This work closely investigated the effects of these factors on an SRS signal and developed solutions to reduce their effects on the data variance. Specifically, we constructed a method using a dual-modality detector built in-house, which simultaneously measured both the SRS signal and total light transmission synchronized in time and co-registered in space. We developed equations to normalize SRS signals using the transmission intensity, and the results demonstrated a clear improvement in the SRS signal via a reduction in the signal variance (up to a 9.46% CV value decrease) that is otherwise caused by various factors associated with the use of topical drugs and the composition of the skin. We carried out an exploratory BE study using tretinoin-containing topical products and observed improvements in BE assessment with the developed method (could achieve a reduction of 0.11 in the CI value). This work has led to a better understanding of the factors that affect SRS imaging and has provided an effective method to compensate for these factors in BE assessments. This is a critical initial effort for better practical implementation of SRS in cutaneous pharmacokinetics (cPKs) studies of topical drugs.
近年来，光学显微镜技术在研究局部用药物的生物利用度（BA）和生物等效性（BE）方面越来越受到关注。受激拉曼散射（SRS）作为一种光学成像技术，可探测化学特异性信息并具有出色的时空分辨率。它利用分子固有的振动特征，因此无需对样品进行标记或其他处理即可追踪分子。由于其独特的优势，已有研究将SRS用于BA评估，最近还用于BE评估。在BE评估中，治疗组内低数据方差对于确保比较治疗组时的敏感性和特异性很重要。在测量透过皮肤传输的正向SRS信号时，由于多种因素，如显微镜系统的性能、局部用药物产品的不同光学特性以及皮肤透光的异质性，信号强度容易出现方差。这项工作深入研究了这些因素对SRS信号的影响，并开发了减少其对数据方差影响的解决方案。具体而言，我们构建了一种使用内部构建的双模态探测器的方法，该探测器可同时测量SRS信号和在时间上同步且在空间上共配准的总光传输。我们开发了使用传输强度对SRS信号进行归一化的方程，结果表明，通过减少由与局部用药物使用和皮肤组成相关的各种因素引起的信号方差（CV值降低高达9.46%），SRS信号有了明显改善。我们使用含维甲酸的局部用产品进行了一项探索性BE研究，并观察到使用所开发方法在BE评估方面有改善（CI值可降低0.11）。这项工作使我们对影响SRS成像的因素有了更好的理解，并提供了一种在BE评估中补偿这些因素的有效方法。这是在局部用药物的皮肤药代动力学（cPKs）研究中更好地实际应用SRS的关键初步工作。
