Optimizing the Pharmacological and Optical Dosimetry for Photodynamic Therapy with Methylene Blue and Nanoliposomal Benzoporphyrin on Pancreatic Cancer Spheroids

Photodynamic therapy (PDT) is a cancer treatment that relies on the remote-controlled activation of photocatalytic dyes (photosensitizers) in cancer tissues. To effectively treat cancer, a variety of pharmacological and optical parameters require optimization, which are dependent on the photosensitizer type. As most photosensitizers are hydrophobic molecules, nanoliposomes are frequently used to increase the biocompatibility of these therapeutics. However, as nanoliposomes can influence the therapeutic performance of photosensitizers, the most suitable treatment parameters need to be elucidated. Here, we evaluate the efficacy of PDT on spheroid cultures of PANC-1 and MIA PaCa-2 pancreatic cancer cells. Two strategies to photosensitize the pancreatic microtumors were selected, based on either nanoliposomal benzoporphyrin derivative (BPD), or non-liposomal methylene blue (MB). Using a comprehensive image-based assay, our findings show that the PDT efficacy manifests in distinct manners for each photosensitizer. Moreover, the efficacy of each photosensitizer is differentially influenced by the photosensitizer dose, the light dose (radiant exposure or fluence in J/cm2), and the dose rate (fluence rate in mW/cm2). Taken together, our findings illustrate that the most suitable light dosimetry for PDT strongly depends on the selected photosensitization strategy. The PDT dose parameters should therefore always be carefully optimized for different models of cancer.

TOWARDS A FRAMEWORK FOR LIGHT-DOSIMETRY STUDIES: METHODOLOGICAL CONSIDERATIONS

For field research of non-visual effects of light, accurate measurement of personal light exposure is required. A consensus framework for light-dosimetry could improve non-visual field research and ensure comparability between studies. Here we present a review of methodologies used in non-visual light-dosimetry studies published to date, focussing on considerations regarding the measurement and preparation of personal light exposure data. Overall, a large variability in the studies’ methodologies is observed, highlighting the need for a consensus framework. We propose methodological considerations that should be included in such a framework and that can guide future studies. Furthermore, we highlight important points that should be addressed in future research to ensure compatibility between different dosimetry studies. Taken together, this review effort underlines the importance of a systematic approach to light-dosimetry in order to harness all the power of integrative lighting research in real-life.

Validation of a Monte Carlo Modelling Based Dosimetry of Extraoral Photobiomodulation

An in vivo validation study was performed to confirm the accuracy of extraoral photobiomodulation therapy (PBMT) dosimetry determined by modelling. The Monte Carlo technique was utilized to calculate the fluence rate and absorbed power of light delivered through multi-layered tissue. Optical properties used during Monte Carlo simulations were taken from the literature. Morphological data of four study volunteers were acquired using magnetic resonance imaging (MRI) scans. Light emitting diode (LED) coupled to a power meter were utilized to measure transmitted power through each volunteer’s cheek, in vivo. The transmitted power determined by Monte Carlo modelling was compared to the in vivo measurements to determine the accuracy of the simulations. Experimental and simulation results were in good agreement for all four subjects. The difference between the mean values of the measured transmission was within 12% from the respective transmission obtained using Monte Carlo simulations. The results of the study indicate that Monte Carlo modelling is a robust and reliable method for light dosimetry.

Real-time IR700 Fluorescence Imaging During Near-infrared Photoimmunotherapy Using a Clinically-approved Camera for Indocyanine Green

Background/Aim: Near-infrared photoimmuno-therapy (NIR-PIT) is a newly approved cancer phototherapy. We aim to confirm whether a clinically approved camera for indocyanine green (ICG) could monitor IR700 fluorescence in real time during exposure to therapeutic NIR light. Materials and Methods: An NIR camera, LIGHTVISION, designed to image ICG fluorescence, was used. A431-GFP/luc tumor-bearing mice were exposed to therapeutic NIR light and real-time fluorescence imaging (RT-FI) was obtained and measured with LIGHTVISION. Bioluminescence imaging (BLI) was performed to confirm cell death. Results: RT-FI during NIR-PIT revealed an initial rapid loss of fluorescence, followed by a plateau which occurred at a light dose of approximately 30 J/cm2. Correlation between BLI and IR700 fluorescence loss showed that loss of fluorescence was associated with increased cell death. Conclusion: The efficacy of NIR-PIT could be monitored non-invasively and in real-time using weak fluorescence at wavelengths much longer than the peak fluorescence of IR700. This technique can achieve precise light dosimetry that allows us to decide on the optimal exposure.

Photophysical Properties of Protoporphyrin IX, Pyropheophorbide-a, and Photofrin® in Different Conditions

Photodynamic therapy (PDT) is an innovative treatment of malignant or diseased tissues. The effectiveness of PDT depends on light dosimetry, oxygen availability, and properties of the photosensitizer (PS). Depending on the medium, photophysical properties of the PS can change leading to increase or decrease in fluorescence emission and formation of reactive oxygen species (ROS) especially singlet oxygen (1O2). In this study, the influence of solvent polarity, viscosity, concentration, temperature, and pH medium on the photophysical properties of protoporphyrin IX, pyropheophorbide-a, and Photofrin® were investigated by UV-visible absorption, fluorescence emission, singlet oxygen emission, and time-resolved fluorescence spectroscopies.

Optical Characterization of an Intra-Arterial Light and Drug Delivery System for Photodynamic Therapy of Atherosclerotic Plaque

Although the versatility of photodynamic therapy (PDT) is well established, the technical aspects of light delivery systems vary significantly depending on the targeted organ. This article describes the optical properties of a light and drug delivery system (catheter and light diffuser) suitable for intra-arterial PDT by using a planar imaging goniometer to measure the full radiance longitudinal and angular profiles at the surface of the diffuser at 652 nm. The results show that the system emits almost Lambertian and “top hat” profiles, an interesting feature to determine the light dosimetry in the many vascular applications of PDT.