Currently there is a lack of in vivo techniques to evaluate the spatial bio-distribution of dermal drugs over time without the need to take multiple serial biopsies. To address this gap, we investigated the use of multi-photon optical imaging methods to non-invasively track drug distribution on miniature pig (Species: Sus scrofa, Strain: Göttingen) skin in vivo. Minipig skin is the standard comparative research model to human skin, and is anatomically and functionally similar. We employed fluorescence lifetime imaging microscopy (FLIM) to visualize the spatial distribution and residency time of a topically applied experimental dermatological cream. This was made possible by the endogenous fluorescent optical properties of the experimental drug (fluorescence lifetime > 3000 ps). Two different drug formulations were applied on 2 minipigs for 7 consecutive days, with the control creams applied on the contralateral side, followed by 7 days of post-application monitoring using a multi-modal optical imaging system (MPTflex-CARS, JenLab, Germany). FLIM images were obtained from the treated regions 24 hr post-application from day 1 to day 14 that allowed visualization of cellular and sub-cellular features associated with different dermal layers non-invasively to a depth of 200 µm. Five punch biopsies per animal were obtained from the corresponding treated regions between days 8 and 14 for bioanalytical analysis and comparison with results obtained using FLIM. In conclusion, utilization of non-invasive optical biopsy methods for dermal drug evaluation can provide true longitudinal monitoring of drug spatial distribution, remove sampling limitations, and be more time-efficient compared to traditional methods.
Aneesh Alex, Eric J. Chaney, Jennifer M. Criley, Darold R. Spillman, Phaedra B. Hutchison, Joanne Li, Marina Marjanovic, Steve Frey, Steven Cook, Stephen A. Boppart, and Zane A. Arp, "Imaging bio-distribution of a topically applied dermatological cream on minipig skin using fluorescence lifetime imaging microscopy (Conference Presentation)," Proc. SPIE 10046, Visualizing and Quantifying Drug Distribution in Tissue, 100460E (Presented at SPIE BiOS: January 28, 2017; Published: 19 April 2017); https://doi.org/10.1117/12.2253112.5370230219001.
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