Real-time Non-invasive Transdermal Monitoring of Photosensitizer Level in vivo for Pharmacokinetic Studies and Optimization of Photodynamic Therapy Protocol

Abstract

Efficient application of any therapeutic agent requires the knowledge of the time evolution of drug concentration in tissues. Usually, the collection of such pharmacokinetic data relies on sequential invasive measurements and sacrifice of many animals. Our aim was to establish a non-invasive analytical assay that would allow for determination of the levels of fluorescent (pro)drugs in the tissues. We have applied a portable fiber optics-based spectrophotometric setup to determine pharmacokinetic profiles of two water-soluble chlorophyll derivatives via transdermal emission measurements in vivo, in a model system consisting of DBA/2 mice bearing subcutaneous Cloudman S91 melanoma tumor. Based on their emission spectra, recorded transdermally in real-time, the in vivo peak levels and retention times of intraperitoneally and intravenously administered photosensitizers were estimated. These data served then to optimize the photodynamic therapy protocol. The effects of the treatment show a strong correlation between the efficacy of the therapy and the pharmacokinetic profiles, confirming the validity of the method. This approach has several important advantages, including (i) a maximization of therapeutic effects by indicating the optimal timing for irradiation; (ii) a non-invasive determination of the photosensitizer level in the tumor to predict the therapy outcome; (iii) an estimation of the safety dark period to minimize the side effects related to phototoxicity; (iv) a possibility of performing a whole series of non-invasive pharmacokinetic experiments in the same organism; and (v) a significant cut in the costs of pharmacokinetic studies. The measurements on human tissue indicate that this non-invasive method can be also applied in humans.