Insights into photodynamic therapy dosimetry: simultaneous singlet oxygen luminescence and photosensitizer photobleaching measurements

Modulating Excited State Properties and Ligand Ejection Kinetics in Ruthenium Polypyridyl Complexes Designed to Mimic Photochemotherapeutics

Ruthenium(II) polypyridyl complexes have gained significant interest as photochemotherapeutics (PCTs) due to their synthetic viability, strong light absorption, well understood excited state properties, and high phototoxicity indexes. Herein, we report the synthesis, characterization, electrochemical, spectrochemical, and preliminary cytotoxicity analyses of three series of ruthenium(II) polypyridyl complexes designed to mimic PCTs. The three series have the general structure of [Ru(bpy)2(N-N)]2+ (Series 1), [Ru(bpy)(dmb)(N-N)]2+ (Series 2), and [Ru(dmb)2(N-N)]2+ (Series 3, where N-N is a bidentate polypyridyl ligand, bpy = 2,2'-bipyridine, and dmb = 6,6'-dimethyl-2,2'-bipyridine). In the three series, the N-N ligand was systematically modified to incorporate increased conjugation and/or electronegative heteroatoms to increase dπ-π* backbonding, red-shifting the lowest energy metal-to-ligand charge transfer (MLCT) absorptions from λmax = 454 to λmax = 580 nm, nearing the therapeutic window for PCTs (600-1100 nm). In addition, steric bulk was systematically introduced through the series, distorting the Ru(II) octahedra, making the dissociative 3dd* state thermally accessible at room and body temperatures. This resulted in a 4 orders of magnitude increase in photoinduced ligand ejection kinetics, and demonstrates the ability to modulate both the MLCT* and dd* manifolds in the complexes, which is critical in PCT drug design. Preliminary cell viability assays suggest that the increased steric bulk to lower the 3dd* states may interfere with the cytotoxicity mechanism, limiting photoinitiated toxicity of the complexes. This work demonstrates the importance of understanding both the MLCT* and dd* manifolds and how they impact the ability of a complex to act as a PCT agent.

Transport of Nanoparticles into Plants and Their Detection Methods

Nanoparticle transport into plants is an evolving field of research with diverse applications in agriculture and biotechnology. This article provides an overview of the challenges and prospects associated with the transport of nanoparticles in plants, focusing on delivery methods and the detection of nanoparticles within plant tissues. Passive and assisted delivery methods, including the use of roots and leaves as introduction sites, are discussed, along with their respective advantages and limitations. The barriers encountered in nanoparticle delivery to plants are highlighted, emphasizing the need for innovative approaches (e.g., the stem as a new recognition site) to optimize transport efficiency. In recent years, research efforts have intensified, leading to an evendeeper understanding of the intricate mechanisms governing the interaction of nanomaterials with plant tissues and cells. Investigations into the uptake pathways and translocation mechanisms within plants have revealed nuanced responses to different types of nanoparticles. Additionally, this article delves into the importance of detection methods for studying nanoparticle localization and quantification within plant tissues. Various techniques are presented as valuable tools for comprehensively understanding nanoparticle-plant interactions. The reliance on multiple detection methods for data validation is emphasized to enhance the reliability of the research findings. The future outlooks of this field are explored, including the potential use of alternative introduction sites, such as stems, and the continued development of nanoparticle formulations that improve adhesion and penetration. By addressing these challenges and fostering multidisciplinary research, the field of nanoparticle transport in plants is poised to make significant contributions to sustainable agriculture and environmental management.

Optimizing the administrated light dose during 5-ALA-mediated photodynamic therapy: Murine 4T1 breast cancer model

Photodynamic therapy (PDT) is already used to treat many cancers, including breast cancer, the most common cancer in women worldwide. The destruction basis of this method is on produced singlet oxygen which is extremely reactive and is a major agent of tumor cell killing. The measurement of singlet oxygen produced within PDT is essential in predicting treatment outcomes and their optimization. This study aims to determine the optimal total light dose administered during PDT by calculating the singlet oxygen to facilitate the prediction of the treatment outcome in mice bearing 4T1 cell breast cancer. Monitoring the changes in photosensitizer fluorescence signals during PDT due to photobleaching can be one of the methods of determination of singlet oxygen generation in the PDT process. This study determined the oxygen singlet as a photodynamic dose from the three-dimensional Monte Carlo method and the photobleaching empirical dose constant. The photobleaching dose constant was established non-invasively by monitoring the in vivo protoporphyrin IX (PpIX) fluorescence and photobleaching during PDT. The photobleaching dose constant (β) in J/cm2 was calculated using empirical fluorescence data. The in vivo photobleaching dose constant of aminolevulinic acid was found to be 11.6 J/cm2 and based on this value, the optimal treatment light dose was estimated at 120 J/cm2 in mice bearing 4T1 breast cancer. It is concluded that information can be obtained regarding optimal treatment parameters by monitoring the in vivo PpIX fluorescence and photobleaching during PDT.

High Sensitivity Singlet Oxygen Luminescence Sensor Using Computational Spectroscopy and Solid-State Detector

This paper presents a technique for high sensitivity measurement of singlet oxygen luminescence generated during photodynamic therapy (PDT) and ultraviolet (UV) irradiation on skin. The high measurement sensitivity is achieved by using a computational spectroscopy (CS) approach that provides improved photon detection efficiency compared to spectral filtering methodology. A solid-state InGaAs photodiode is used as the CS detector, which significantly reduces system cost and improves robustness compared to photomultiplier tubes. The spectral resolution enables high-accuracy determination and subtraction of photosensitizer fluorescence baseline without the need for time-gating. This allows for high sensitivity detection of singlet oxygen luminescence emission generated by continuous wave light sources, such as solar simulator sources and those commonly used in PDT clinics. The value of the technology is demonstrated during in vivo and ex vivo experiments that show the correlation of measured singlet oxygen with PDT treatment efficacy and the illumination intensity on the skin. These results demonstrate the potential use of the technology as a dosimeter to guide PDT treatment and as an analytical tool supporting the development of improved sunscreen products for skin cancer prevention.

Local monitoring of photosensitizer transient states provides feedback for enhanced efficiency and targeting selectivity in photodynamic therapy

Photodynamic therapy (PDT) fundamentally relies on local generation of PDT precursor states in added photosensitizers (PS), particularly triplet and photo-radical states. Monitoring these states in situ can provide important feedback but is difficult in practice. The states are strongly influenced by local oxygenation, pH and redox conditions, often varying significantly at PDT treatment sites. To overcome this problem, we followed local PDT precursor state populations of PS compounds, via their fluorescence intensity response to systematically varied excitation light modulation. Thereby, we could demonstrate local monitoring of PDT precursor states of methylene blue (MB) and IRdye700DX (IR700), and determined their transitions rates under different oxygenation, pH and redox conditions. By fiber-optics, using one fiber for both excitation and fluorescence detection, the triplet and photo-radical state kinetics of locally applied MB and IR700 could then be monitored in a tissue sample. Finally, potassium iodide and ascorbate were added as possible PDT adjuvants, enhancing intersystem crossing and photoreduction, respectively, and their effects on the PDT precursor states of MB and IR700 could be locally monitored. Taken together, the presented procedure overcomes current methodological limitations and can offer feedback, guiding both excitation and PDT adjuvant application, and thereby more efficient and targeted PDT treatments.

The use of nanomaterials in advancing photodynamic therapy (PDT) for deep-seated tumors and synergy with radiotherapy

Photodynamic therapy (PDT) has been under development for at least 40 years. Multiple studies have demonstrated significant anti-tumor efficacy with limited toxicity concerns. PDT was expected to become a major new therapeutic option in treating localized cancer. However, despite a shifting focus in oncology to aggressive local therapies, PDT has not to date gained widespread acceptance as a standard-of-care option. A major factor is the technical challenge of treating deep-seated and large tumors, due to the limited penetration and variability of the activating light in tissue. Poor tumor selectivity of PDT sensitizers has been problematic for many applications. Attempts to mitigate these limitations with the use of multiple interstitial fiberoptic catheters to deliver the light, new generations of photosensitizer with longer-wavelength activation, oxygen independence and better tumor specificity, as well as improved dosimetry and treatment planning are starting to show encouraging results. Nanomaterials used either as photosensitizers per se or to improve delivery of molecular photosensitizers is an emerging area of research. PDT can also benefit radiotherapy patients due to its complementary and potentially synergistic mechanisms-of-action, ability to treat radioresistant tumors and upregulation of anti-tumoral immune effects. Furthermore, recent advances may allow ionizing radiation energy, including high-energy X-rays, to replace external light sources, opening a novel therapeutic strategy (radioPDT), which is facilitated by novel nanomaterials. This may provide the best of both worlds by combining the precise targeting and treatment depth/volume capabilities of radiation therapy with the high therapeutic index and biological advantages of PDT, without increasing toxicities. Achieving this, however, will require novel agents, primarily developed with nanomaterials. This is under active investigation by many research groups using different approaches.

High quantum efficiency ruthenium coordination complex photosensitizer for improved radiation-activated Photodynamic Therapy

Traditional external light-based Photodynamic Therapy (PDT)'s application is limited to the surface and minimal thickness tumors because of the inefficiency of light in penetrating deep-seated tumors. To address this, the emerging field of radiation-activated PDT (radioPDT) uses X-rays to trigger photosensitizer-containing nanoparticles (NPs). A key consideration in radioPDT is the energy transfer efficiency from X-rays to the photosensitizer for ultimately generating the phototoxic reactive oxygen species (ROS). In this study, we developed a new variant of pegylated poly-lactic-co-glycolic (PEG-PLGA) encapsulated nanoscintillators (NSCs) along with a new, highly efficient ruthenium-based photosensitizer (Ru/radioPDT). Characterization of this NP via transmission electron microscopy, dynamic light scattering, UV-Vis spectroscopy, and inductively coupled plasma mass-spectroscopy showed an NP size of 120 nm, polydispersity index (PDI) of less than 0.25, high NSCs loading efficiency over 90% and in vitro accumulation within the cytosolic structure of endoplasmic reticulum and lysosome. The therapeutic efficacy of Ru/radioPDT was determined using PC3 cell viability and clonogenic assays. Ru/radioPDT exhibited minimal cell toxicity until activated by radiation to induce significant cancer cell kill over radiation alone. Compared to protoporphyrin IX-mediated radioPDT (PPIX/radioPDT), Ru/radioPDT showed higher capacity for singlet oxygen generation, maintaining a comparable cytotoxic effect on PC3 cells.

Photodynamic Therapy for Glioblastoma: Illuminating the Path toward Clinical Applicability

Glioblastoma (GBM) is the most common adult brain cancer. Despite extensive treatment protocols comprised of maximal surgical resection and adjuvant chemo-radiation, all glioblastomas recur and are eventually fatal. Emerging as a novel investigation for GBM treatment, photodynamic therapy (PDT) is a light-based modality that offers spatially and temporally specific delivery of anti-cancer therapy with limited systemic toxicity, making it an attractive option to target GBM cells remaining beyond the margins of surgical resection. Prior PDT approaches in GBM have been predominantly based on 5-aminolevulinic acid (5-ALA), a systemically administered drug that is metabolized only in cancer cells, prompting the release of reactive oxygen species (ROS), inducing tumor cell death via apoptosis. Hence, this review sets out to provide an overview of current PDT strategies, specifically addressing both the potential and shortcomings of 5-ALA as the most implemented photosensitizer. Subsequently, the challenges that impede the clinical translation of PDT are thoroughly analyzed, considering relevant gaps in the current PDT literature, such as variable uptake of 5-ALA by tumor cells, insufficient tissue penetrance of visible light, and poor oxygen recovery in 5-ALA-based PDT. Finally, novel investigations with the potential to improve the clinical applicability of PDT are highlighted, including longitudinal PDT delivery, photoimmunotherapy, nanoparticle-linked photosensitizers, and near-infrared radiation. The review concludes with commentary on clinical trials currently furthering the field of PDT for GBM. Ultimately, through addressing barriers to clinical translation of PDT and proposing solutions, this review provides a path for optimizing PDT as a paradigm-shifting treatment for GBM.

Photodynamic Priming Overcomes Per- and Polyfluoroalkyl Substance (PFAS)-Induced Platinum Resistance in Ovarian Cancer†

Per- and polyfluoroalkyl substances (PFAS) are widespread environmental contaminants linked to adverse outcomes, including for female reproductive biology and related cancers. We recently reported, for the first time, that PFAS induce platinum resistance in ovarian cancer, potentially through altered mitochondrial function. Platinum resistance is a major barrier in the management of ovarian cancer, necessitating complementary therapeutic approaches. Photodynamic therapy (PDT) is a light-based treatment modality that reverses platinum resistance and synergizes with platinum-based chemotherapy. The present study is the first to demonstrate the ability of photodynamic priming (PDP), a low-dose, sub-cytotoxic variant of PDT, to overcome PFAS-induced platinum resistance. Comparative studies of PDP efficacy using either benzoporphyrin derivative (BPD) or 5-aminolevulinic acid-induced protoporphyrin IX (PpIX) were conducted in two human ovarian cancer cell lines (NIH:OVCAR-3 and Caov-3). BPD and PpIX are clinically approved photosensitizers that preferentially localize to, or are partly synthesized in, mitochondria. PDP overcomes carboplatin resistance in PFAS-exposed ovarian cancer cells, demonstrating the feasibility of this approach to target the deleterious effects of environmental contaminants. Decreased survival fraction in PDP + carboplatin treated cells was accompanied by decreased mitochondrial membrane potential, suggesting that PDP modulates the mitochondrial membrane, reducing membrane potential and re-sensitizing ovarian cancer cells to carboplatin.

Enabling In Vivo Optical Imaging of an Osmium Photosensitizer by Micellar Formulation

Osmium (Os)-based photosensitizers (PSs) exhibit unique broad, red-shifted absorption, favoring PDT activity at greater tissue depths. We recently reported on a potent Os(II) PS, rac-[Os(phen)₂(IP-4T)](Cl)₂ (ML18J03) with submicromolar hypoxia activity. ML18J03 exhibits a low luminescence quantum yield of 9.8 × 10^-5 in PBS, which limits its capacity for in vivo luminescence imaging. We recently showed that formulating ML18J03 into 10.2 nm DSPE-mPEG₂₀₀₀ micelles (Mic-ML18J03) increases its luminescence quantum yield by two orders of magnitude. Here, we demonstrate that Mic-ML18J03 exhibits 47-fold improved accumulative luminescence signals in orthotopic AT-84 head and neck tumors. We show, for the first time, that micellar formulation provides up to 11.7-fold tumor selectivity for ML18J03. Furthermore, Mic-ML18J03 does not experience the concentration-dependent quenching observed with unformulated ML18J03 in PBS, and formulation reduces spectral shifting of the emission maxima during PDT (variance = 6.5 and 27.3, respectively). The Mic-ML18J03 formulation also increases the production of reactive molecular species 2-3-fold. These findings demonstrate that micellar formulation is a versatile and effective approach to enable in vivo luminescence imaging options for an otherwise quenched, yet promising, PS.

Analysis of the Results of Severe Intraepithelial Squamous Cell Lesions and Preinvasive Cervical Cancer Phototheranostics in Women of Reproductive Age

(1) Purpose: To investigate the efficacy and safety of using PDT in the treatment of severe intraepithelial squamous lesions of the cervix and preinvasive cervical cancer associated with HPV in women of reproductive age. (2) Methods: The examination and treatment of 45 patients aged 22-49 years with morphologically confirmed HPV-associated cervical intraepithelial neoplasia of a severe degree (17 patients) and preinvasive cervical cancer (28 patients) were performed. All patients underwent PDT of the cervix using a chlorin e6 photosensitizer; after which, the affected areas of the cervix were evaluated using video and spectral fluorescence diagnostics. PDT effectiveness was assessed on the basis of colposcopy data, a cytological examination of exo- and endocervix and PAP test scrapings or the liquid cytology method, and polymerase chain reaction for HPV carriage 4 weeks after PDT, as well as on the basis of histological and immunohistochemical studies of biopsy materials 5 weeks after PDT. The expression levels of the Ki-67 and p16 markers in the affected areas of the cervix were also assessed. (3) Results. All patients included in the study tolerated the intravenous administration of the photosensitizer well, with no side effects or allergic reactions observed. In 88.2% of patients with CIN III/HSIL and in 85.7% of women with preinvasive cervical cancer, the effect of the treatment was noted after the first PDT procedure, while complete regression of the dysplasia foci was observed in 15 women (88.2%) with CIN III/HSIL and in 25 patients (89.3%) with preinvasive cervical cancer. Partial regression to the form of LSIL/CIN I was noted in two cases (11.8%) in the CIN III/HSIL group and in three cases (10.7%) in the group of patients with preinvasive cervical cancer. After PDT, a statistically significant decrease in the expression of the Ki-67 and p16 levels relative to the initial values was noted. (4) Conclusions. The results obtained indicate the high efficiency of PDT with intravenous administration of the chlorin photosensitizer for the treatment of intraepithelial lesions of the cervix with a selective effect on pathologically altered tissue. The use of this approach makes it possible to preserve the normal anatomical and functional characteristics of the cervix, which is especially important for maintaining the fertility of patients.

Gallium Protoporphyrin Liquid Crystalline Lipid Nanoparticles: A Third-Generation Photosensitizer against Pseudomonas aeruginosa Biofilms

The looming antimicrobial resistance pandemic has encouraged the investigation of antimicrobial photodynamic therapy (aPDT) as a promising technology to combat recalcitrant bacterial infections caused by antibiotic resistant strains. Here, we report on the optimization and effective application of gallium protoporphyrin liquid crystalline lipid nanoparticles (GaPP-LCNP) as a photosensitizer for aPDT against the Gram-negative bacteria P. aeruginosa in both planktonic and biofilm modes of growth. LCNP significantly enhanced the performance of GaPP as photosensitizer by two-fold, which was correlated with higher antibacterial activity, reducing the viability of planktonic P. aeruginosa by 7 log₁₀ using 0.8 µM GaPP-LCNP and a light dose of 17 J.cm⁻². Importantly, GaPP-LCNP also reduced the viability of biofilms by 6 log₁₀ at relatively low light dose of 34.2 J.cm⁻² using only 3 µM GaPP-LCNP. The high antibiofilm activity of GaPP-LCNP at low GaPP-LCNP dose indicated the high efficiency and safety profile of GaPP-LCNP as a promising platform for photodynamic inactivation of recalcitrant infections.

Photodisinfection of material surfaces and bacterial skin infections by a detergent loaded with curcumin

The development of technologies and therapeutic strategies is needed to combat skin infections and pathogenic microorganisms present on material surfaces that are still responsible for serious public health problems. In this study, detergents loaded with curcumin were prepared by a simple approach and characterized by UV-vis spectroscopy and fluorescence spectroscopy. Their antibacterial photodynamic effects were evaluated against Staphylococcus aureus in planktonic medium and in vivo (skin infection model), and showed a reduction up to 8 logs and 2 logs, respectively. Additionally, the curcumin-detergents were applied on photodisinfection of material surfaces such as wood, rubber, and stainless steel resulting in an efficient photoinactivation up to 3 logs. These developed detergents loaded with curcumin can improve the decontamination of material surfaces and skin infections (in vivo) when illuminated.

Balancing the interplay between ligand ejection and therapeutic window light absorption in ruthenium polypyridyl complexes

Ruthenium polypyridyl complexes have gained significant interest as photochemotherapies (PCTs) where their excited-state properties play a critical role in the photo-cytotoxicity mechanism and efficacy. Herein we report a systematic electrochemical, spectrochemical, and photophysical analysis of a series of ruthenium(II) polypyridyl complexes of the type [Ru(bpy)₂(N-N)]²⁺ (where bpy = 2,2'-bipyridine; N-N is a bidentate polypyridyl ligand) designed to mimic PCTs. In this series, the N-N ligand was modified through increased conjugation and/or incorporation of electronegative heteroatoms to shift the metal-to-ligand charge-transfer (MLCT) absorptions near the therapeutic window for PCTs (600-1100 nm) while incorporating steric bulk to trigger photoinduced ligand dissociation. The lowest energy MLCT absorptions were red-shifted from λ_max = 454 nm to 564 nm, with emission energies decreasing from λ_max = 620 nm to 850 nm. Photoinduced ligand ejection and temperature-dependent emission studies revealed an important interplay between red-shifting MLCT absorptions and accessing the dissociative ³dd* states, with energy barriers between the ³MLCT* and ³dd* states ranging from 850 cm^-1 to 2580 cm^-1 for the complexes measured. This work demonstrates the importance of understanding both the MLCT manifold and ³dd* state energy levels in the future design of ligands and complexes for PCT.

Comparative analysis of Radachlorin accumulation, localization, and photobleaching in three cell lines by means of holographic and fluorescence microscopy

In this paper we compare the response of cells of established lines of different origin: HeLa, A549 and 3T3 to photodynamic treatment with Radachlorin photosensitizer. The analysis was performed on different aspects of the treatment procedure including photosensitizer accumulation, localization and photobleaching in cells and post-treatment dynamics of changes in cellular morphology at different treatment doses. It was shown that in the three cell lines Radachlorin accumulated in lysosomes to much greater extent than in mitochondria. The cells' response to treatment was analyzed by identification of their death pathways and evaluation of average phase shift dynamics using digital holographic microscopy. The analysis performed on the three cell lines allowed us to evaluate treatment doses specific for each pathway in each line. Among the three lines HeLa cells were found to be the most susceptible to treatment while 3T3 cells the most resistant. The comparison of these results with the data on Radachlorin accumulation, localization and photobleaching rates showed that the observed higher sensitivity of HeLa cells to photodynamic treatment correlated with higher photosensitizer uptake and more intensive photobleaching while lower sensitivity of 3T3 cells correlated with lower uptake and less intensive photobleaching.

J, M.D.P. DE. C, RAJENDRAM S. Photodynamic Therapy : An Overview and Insights into a Prospective Mainstream Anticancer Therapy

Photodynamic therapy (PDT) procedure has minimum invasiveness in contrast to conventional anticancer surgical procedures. Although clinically approved a few decades ago, it is not commonly used due to its poor efficacy, mainly due to poor light penetration into deeper tissues. PDT uses a photosensitizer (PS), which is photoactivated on illumination by light of appropriate wavelength and oxygen in the tissue, leading to a series of photochemical reactions producing reactive oxygen species (ROS) triggering various mechanisms resulting in lethal effects on tumor cells. This review looks into the fundamental aspects of PDT, such as photochemistry, photobiological effects, and the current clinical applications in the light of improving PDT to become a mainstream therapeutic procedure against a broad spectrum of cancers and malignant lesions. The side effects of PDT, both early and late-onset, are elaborated on in detail to highlight the available options to minimize side effects without compromising therapeutic efficacy. This paper summarizes the benefits, drawbacks, and limitations of photodynamic therapy along with the recent attempts to achieve improved therapeutic efficacy via monitoring various cellular and molecular processes through fluorescent imagery aided by suitable biomarkers, prospective nanotechnology-based targeted delivery methods, the use of scintillating nanoparticles to deliver light to remote locations and also combining PDT with conventional anticancer therapies have opened up new dimensions for PDT in treating cancers. This review inquires and critically analyses prospective avenues in which a breakthrough would finally enable PDT to be integrated into mainstream anticancer therapy.

Unsymmetrical, monocarboxyalkyl meso-arylporphyrins in the photokilling of breast cancer cells using permethyl-β-cyclodextrin as sequestrant and cell uptake modulator

In the search for photosensitizers with chemical handles to facilitate their integration into complex drug delivery nanosystems, new, unsymmetrically substituted, water insoluble meso-tetraphenylporphyrin and meso-tetra(m-hydroxyphenyl)porphyrin derivatives bearing one carboxyalkyl side chain were synthesized. Permethyl-β-cyclodextrin (pMβCD) was their ideal monomerizing host and highly efficient shuttle to transfer them into water. New assembly modes of the extremely stable (K_binding > 10¹² M^-2) 2:1 complexes were identified. The complexes are photostable and do not disassemble in FBS-containing cell culture media for 24 h. Incubation of breast cancer MCF-7 cells with the complexes results in intense intracellular fluorescence, strongly enhanced in the endoplasmic reticulum (ER), high photokilling efficiency (~90%) and low dark toxicity. pMβCD stands out as a very capable molecular isolator of mono-carboxyalkyl-arylporphyrins that increases uptake and modulates their localization in the cells. The most efficient porphyrins are envisaged as suitable photosensitizers that can be linked to biocompatible drug carriers for photo- and chemo-therapy applications.

Combined Fluorescence and Optoacoustic Imaging for Monitoring Treatments against CT26 Tumors with Photoactivatable Liposomes

The newly developed multimodal imaging system combining raster-scan optoacoustic (OA) microscopy and fluorescence (FL) wide-field imaging was used for characterizing the tumor vascular structure with 38/50 μm axial/transverse resolution and assessment of photosensitizer fluorescence kinetics during treatment with novel theranostic agents. A multifunctional photoactivatable multi-inhibitor liposomal (PMILs) nano platform was engineered here, containing a clinically approved photosensitizer, Benzoporphyrin derivative (BPD) in the bilayer, and topoisomerase I inhibitor, Irinotecan (IRI) in its inner core, for a synergetic therapeutic impact. The optimized PMIL was anionic, with the hydrodynamic diameter of 131.6 ± 2.1 nm and polydispersity index (PDI) of 0.05 ± 0.01, and the zeta potential between -14.9 ± 1.04 to -16.9 ± 0.92 mV. In the in vivo studies on BALB/c mice with CT26 tumors were performed to evaluate PMILs' therapeutic efficacy. PMILs demonstrated the best inhibitory effect of 97% on tumor growth compared to the treatment with BPD-PC containing liposomes (PALs), 81%, or IRI containing liposomes (L-[IRI]) alone, 50%. This confirms the release of IRI within the tumor cells upon PMILs triggering by NIR light, which is additionally illustrated by FL monitoring demonstrating enhancement of drug accumulation in tumor initiated by PDT in 24 h after the treatment. OA monitoring revealed the largest alterations of the tumor vascular structure in the PMILs treated mice as compared to BPD-PC or IRI treated mice. The results were further corroborated with histological data that also showed a 5-fold higher percentage of hemorrhages in PMIL treated mice compared to the control groups. Overall, these results suggest that multifunctional PMILs simultaneously delivering PDT and chemotherapy agents along with OA and FL multi-modal imaging offers an efficient and personalized image-guided platform to improve cancer treatment outcomes.

In Vitro Low-Fluence Photodynamic Therapy Parameter Screening Using 3D Tumor Spheroids Shows that Fractionated Light Treatments Enhance Phototoxicity

The evaluation of novel photosensitizers (PSs) for photodynamic therapy (PDT) is difficult due to the limitations of two-dimensional cell culture and multiple parameters (dose, light intensity, uptake time), which complicate progression to in vivo experiments and clinical translation. Three-dimensional (3D) cell culture models like multicellular cancer tumor spheroids (MCTS) show great similarities to in vivo avascular tumor conditions, improving the speed and accuracy of screening novel compounds with various treatment combinations. In this study, we utilize C8161 human melanoma spheroids to screen PDT treatment combinations using protoporphyrin IX (PpIX) and drug-loaded carbon dot (CD) conjugates PpIX-CD and PpIX@CD at ultralow fluence values (<10 J/cm²). Conjugates show equivalent light-induced damage to PpIX from 1 μg/mL with significantly less dark cytotoxicity up to 72 h after exposure, shown by LDH release and dsDNA content. Fractionated treatments, carried out by dividing light exposure with 24 h intervals, demonstrate an enhanced PDT effect compared to single exposure at equal concentrations. Light sheet fluorescence microscopy combined with live/dead staining demonstrates that spheroids sustain extensive damage after PDT, with PpIX and PpIX-CD showing improved uptake compared to PpIX@CD. We show that PDT parameter screening can be carried out using a low-cost and convenient combination of assays to improve the efficiency of evaluating novel compounds.

High optical-throughput spectroscopic singlet oxygen and photosensitizer luminescence dosimeter for monitoring of photodynamic therapy

We report a high light-throughput spectroscopic dosimeter system that is able to noninvasively measure luminescence signals of singlet oxygen (¹ O₂ ) produced during photodynamic therapy (PDT) using a CW (continuous wave) light source. The system is based on a compact, fiber-coupled, high collection efficiency spectrometer (>50% transmittance) designed to maximize optical throughput but with sufficient spectral resolution (~7 nm). This is adequate to detect ¹ O₂ phosphorescence in the presence of strong luminescence background in vivo. This system provides simultaneous acquisition of multiple spectral data points, allowing for more accurate determination of luminescence baseline via spectral fitting and thus the extraction of ¹ O₂ phosphorescence signal based solely on spectroscopic decomposition, without the need for time-gating. Simultaneous collection of photons at different wavelengths improves the quantum efficiency of the system when compared to sequential spectral measurements such as filter-wheel or tunable-filter based systems. A prototype system was tested during in vivo PDT tumor regression experiments using benzoporphyrin derivative (BPD) photosensitizer. It was found that the treatment efficacy (tumor growth inhibition rate) correlated more strongly with ¹ O₂ phosphorescence than with PS fluorescence. These results indicate that this high photon-collection efficiency spectrometer instrument may offer a viable option for real-time ¹ O₂ dosimetry during PDT treatment using CW light.

Quantitative intracellular oxygen availability before and after 5-aminolevulinic acid skin photodynamic therapy

BACKGROUND

During photodynamic therapy (PDT) oxygen is transformed into reactive oxygen species (ROS) to induce cellular apoptosis in (pre)malignant cells. Real time oxygen availability measurement is clinically available with the Cellular Oxygen Metabolism (COMET) monitor.

METHODS

Primary objective is to show that mitochondrial oxygen availability (mitoPO₂) measurement is possible during clinical ALA-PDT. The secondary aim was to determine the pain sensation, because it is the most commonly reported side effect of PDT. Before and after the two fraction PDT treatment, with a 2-hour dark period, mitoPO₂ was measured and reported pain was documented with a visual analog scale (VAS) 0-100.

RESULTS

Nine patients were included. Before the first PDT session the median signal quality was [IQR] 55.0% [34.2-68.0], which decreased after session one to 0% [0.0-10.0]. MitoPO₂ was 40.0 [17.7-53.8] mmHg and increased afterwards to 61.8 [38.2-64.8] mmHg. This likely the result of the delay time between the illumination stop and the mitoPO₂ measurements in a vasodilated, visibly red lesion. Before session two signal quality was 10.4% [0-20.15], 40% lower than at the start. In 5 patients the signal quality after session 2 was too low because of photobleaching and insufficient regeneration of PpIX, median 0% [0-10]. Subjects reported low median VAS scores, all below 3, directly after the mitoPO₂ measurements.

CONCLUSION

With COMET we were able to reliably measure mitochondrial oxygen concentrations during photodynamic therapy. Signal quality drastically decreases after a PDT session because of PpIX deterioration during the illumination phase.

Visible Light-Induced Antibacterial Activity of Pigments Extracted from Dregs of Green and Black Teas

Chlorophyll and its derivatives are potential natural sensitizers frequently applied in antimicrobial photodynamic therapy. Chlorophyll derivatives are formed naturally during tea processing, but they do not contribute to the color of tea infusions and thus are presumably left in the tea dregs. The present study aimed to investigate (i) the chlorophyll remnants in the pigments recovered from dregs of green and black teas and (ii) the antibacterial activity of pigments extracted from the tea dregs upon illumination using a light-emitting diode (LED) as the light source. Pigment analysis using high-performance liquid chromatography (HPLC) revealed the presence of main degradation products of chlorophylls, such as pheophytin and its epimers, pyropheophytin, and pheophorbides. In vitro assays demonstrated significant reductions in the number of viable bacteria in the presence of the pigments after 30 min of incubation with LED light irradiation. The descending order of bacterial susceptibility was Listeria monocytogenes > Staphylococcus aureus > Escherichia coli > Salmonella typhi. At an equivalent irradiation intensity, the blue and red LEDs could stimulate a comparable inactivation effect through photodynamic reactions. These findings demonstrated the valorization potential of tea dregs as a source of chlorophyll derivatives with visible light-induced antibacterial activity.

Cationic zinc (II) phthalocyanine nanoemulsions for photodynamic inactivation of resistant bacterial strains

BACKGROUND

The growing emergence of microbial resistance to antibiotics represents a worldwide challenge. Antimicrobial photodynamic inactivation (aPDI) has been introduced as an alternative technique, especially when combined with nanotechnology. Therefore, this study was designed to investigate the therapeutic merits of combined aPDI and nanoemulsion in infections caused by resistant bacterial strains.

METHODS

Cationic zinc (II) phthalocyanine nanoemulsions (ZnPc-NE) were prepared using isopropyl myristate (IPM) as oil phase, egg phosphatidylcholine (egg PC) as emulsifier, and N-cetyl-N,N,N-trimethyl ammonium bromide (CTAB). Nanoemulsions were characterized for particle size, polydispersity, zeta potential, viscosity, and skin deposition. The in-vitro aPDI was investigated on human resistant pathogens; gram-positive methicillin-resistant Staphylococcus aureus (MRSA) and gram-negative Multidrug-resistant strain of Escherichia coli (MDR E. coli), under different experimental conditions. In addition, in-vivo model of abrasion wound infected by MDR E. coli was induced in rats to investigate the therapeutic potential of the selected formulation.

RESULTS

It was evident that the selected ZnPc formulation (20 % IPM, 2 % egg PC and 0.5 % CTAB) displayed a particle size of 209.9 nm, zeta potential +73.1 mV, and 23.66 % deposition of ZnPc in skin layers. Furthermore, the selected formulation combined with light achieved almost 100 % eradication of the two bacterial strains, with superior bacterial load reduction and wound healing propertiesin-vivo, compared to either the nanoemulsion formulation or laser alone.

CONCLUSION

ZnPc nanoemulsion improved antimicrobial photodynamic therapy in inactivating resistant bacterial infections and provided a promising therapeutic means of treating serious infections, and hence could be applied in diseases caused by other bacterial strains.

Red and blue light in antitumor photodynamic therapy with chlorin-based photosensitizers: a comparative animal study assisted by optical imaging modalities

The goal of this study is a comparative analysis of the efficiency of the PDT protocols for CT26 tumor model treatment in Balb/c mice employing red and blue light with both topical and intravenous administration of chlorin-based photosensitizers (PSs). The considered protocols include the doses of 250 J/cm² delivered at 660 nm, 200 J/cm² delivered at 405 nm, and 250 J/cm² delivered at both wavelengths with equal energy density contribution. Dual-wavelength fluorescence imaging was employed to estimate both photobleaching efficiency, typical photobleaching rates and the procedure impact depth, while optical coherence tomography with angiography modality (OCT-A) was employed to monitor the tumor vasculature response for up to 7 days after the procedure with subsequent histology inspection. Red light or dual-wavelength PDT regimes with intravenous PS injection were demonstrated to provide the most pronounced tumor response among all the considered cases. On the contrary, blue light regimes were demonstrated to be most efficient among topical application and irradiation only regimes. Tumor size dynamics for different groups is in good agreement with the tumor response predictions based on OCT-A taken in 24h after exposure and the results of histology analysis performed in 7 days after the exposure.

The Use of Fluorescent Probes to Detect ROS in Photodynamic Therapy

Photodynamic therapy employs nontoxic dyes called photosensitizers (PS) that are excited by visible light of the correct wavelength to produce a variety of reactive oxygen species (ROS) by an interaction between the long-lived PS triplet states with ambient oxygen. The most important type of ROS in photodynamic therapy (PDT) is singlet oxygen, which is produced by a Type II energy transfer process. On the other hand, superoxide, hydrogen peroxide, and hydroxyl radicals can be produced by a Type I electron transfer process. This chapter describes a set of fluorescent probes that can be used to tease apart these different ROS produced when various PS are illuminated in solution. Singlet oxygen sensor green (SOSG) is used for singlet oxygen, 4-hydroxyphenyl-fluorescein (HPF) for hydroxyl radicals, Amplex Red for hydrogen peroxide, and nitroblue-tetrazolium or XTT for superoxide.

Photodynamic therapy for prostate cancer - A narrative review

This article is a review of approaches to treatment of low and high-grade prostate cancer including a discussion of active treatment vs. active surveillance for patients with low-grade prostate cancer. In particular, we will review PDT as an option for active treatment of low-grade prostate cancer considered in light of recent clinical trials. The mechanism and clinical methods of PDT application and the key points from clinical trials using PDT for prostate cancer with the photosensitizers m-tetrahydroxyphenyl chloride, protoporphyrin IX, motexafin lutetium, padoporfin, and padeliporfin between the years 2002 and 2017 are reviewed. Recently developed methodologies for photodynamic prostate cancer treatment that are in the experimental stage, photodynamic diagnosis, fluorescence guided resection, and PSMA-targeted PDT will also be discussed.

Blue Light Protection, Part I-Effects of blue light on the skin

BACKGROUND

Blue light is emitted visible light between the wavelengths of 400 to 500 nm. The main source of blue light is sunlight, but digital screens, light-emitting diodes (LEDs), and fluorescent lighting serve as additional sources. Concerns about the negative effects of blue light on the skin have rapidly increased over the past 15 years, and consequently, the urge to learn more about this topic is increasing as well.

AIMS

Part I of this article provides up-to-date information on the definition of blue light and the negative and positive effects of blue light on the skin.

METHODS

An Internet search was completed using the Google scholar database for relevant literature.

RESULTS

Blue light can be both harmful and beneficial to the skin, depending on intensity and wavelength. Short-term safety information is more readily available from clinical studies; however, the biological effects of repeated and/or longer-term exposure are not fully understood yet.

CONCLUSIONS

Low-energy and low exposure times to high-energy blue light can help prevent skin diseases, while studies have revealed that longer exposure to high-energy blue light can increase the amount of DNA damage, cell and tissue death, and injury, eye damage, skin barrier damage, and photoaging.

Photoproducts of the Photodynamic Therapy Agent Verteporfin Identified via Laser Interfaced Mass Spectrometry

Verteporfin, a free base benzoporphyrin derivative monoacid ring A, is a photosensitizing drug for photodynamic therapy (PDT) used in the treatment of the wet form of macular degeneration and activated by red light of 689 nm. Here, we present the first direct study of its photofragmentation channels in the gas phase, conducted using a laser interfaced mass spectrometer across a broad photoexcitation range from 250 to 790 nm. The photofragmentation channels are compared with the collision-induced dissociation (CID) products revealing similar dissociation pathways characterized by the loss of the carboxyl and ester groups. Complementary solution-phase photolysis experiments indicate that photobleaching occurs in verteporfin in acetonitrile; a notable conclusion, as photoinduced activity in Verteporfin was not thought to occur in homogenous solvent conditions. These results provide unique new information on the thermal break-down products and photoproducts of this light-triggered drug.

PEG-PLGA nanospheres loaded with nanoscintillators and photosensitizers for radiation-activated photodynamic therapy

Photodynamic Therapy (PDT) is an effective treatment modality for cancers, with Protoporphyrin IX (PPIX)-based PDT being the most widely used to treat cancers in patients. However, PDT is limited to superficial, thin (few mm in depth) lesions that can be accessed by visible wavelength light. Interstitial light-delivery strategies have been developed to treat deep-seated lesions (i.e. prostate cancer). The most promising of these are X-ray-induced scintillation nanoparticles, which have shown potential benefits for PDT of deep-seated tumors. Herein, the design and use of a new nanoscintillator-based radiation-activated PDT (radioPDT) system is investigated in the treatment of deep-seated tumors. Poly(ethylene glycol) methyl ether-block-poly(lactide-co-glycolide) (PEG-PLGA) nanospheres were loaded with a scintillator (LaF₃:Ce³⁺) and photosensitizer (PPIX) to effect radioPDT. UV-Vis spectroscopy and electron microscopy studies demonstrated efficient encapsulation of nanoscintillators and PPIX (>90% efficiency) into the PEG-PLGA nanospheres. The nanoparticles were uniform in size and approximately 100 nm in diameter. They were highly stable and functional for up to 24 h under physiological conditions and demonstrated slow release kinetics. In vitro and in vivo toxicity studies showed no appreciable drug toxicity to human skin fibroblast (GM38), prostate cancer cells (PC3), and to C57/BL mice. Cell uptake studies demonstrated accumulation of the nanoparticles in the cytoplasm of PC3 cells. When activated, fluorescent resonant energy transfer (FRET) was evident via fluorescent spectroscopy and singlet oxygen yield. Determination of stability revealed that the nanoparticles were stable for up to 4 weeks. The nanoparticle production was scaled-up with no change in properties. This nanoparticle represents a unique, optimally designed therapeutic and diagnostic agent (theranostic) agent for radioPDT with characteristics capable of potentially augmenting radiotherapy for deep-seated tumors and integrating into current cancer radiotherapy.

Safety and delivery efficiency of a photodynamic treatment of the lungs using indocyanine green and extracorporeal near infrared illumination

Photodynamic inactivation (PDI) is a promising alternative for combating infections caused by antimicrobial resistant bacteria. Pneumonias are among the most worrisome infections because of their high-mortality rate. Previous studies have demonstrated the feasibility of using PDI with extracorporeal light to treat pneumonia. In this study, we analyzed key parameters for the viability of this treatment, including the selectivity of the photodynamic response for pathogens over host cells. Our results showed that PDI can induce killing of Staphylococcus aureus (of up to 4.18 log for the strain Xen29 and 3.62 log for Xen36) under conditions where little or no toxicity for host cells is observed. We validated pulmonary delivery of the photosensitizer and light in mice, using photobleaching as an indicator, and demonstrated preservation of healthy tissues as evidence of the safety of the protocol. Overall, PDI displays low toxicity on host tissues, making it a promising tool for treatment of pneumonias caused by S. aureus and other important pathogens.

Photocontrolled activation of small molecule cancer therapeutics

Cancer remains one of the leading causes of death worldwide. Conventional treatment of the disease is comprised of chemotherapy, radiation and surgery among other treatment approaches. Chemotherapy is plagued by multiple side-effects caused due to non-specific drug action. Light-based therapies offer an alternative treatment approach that can be fine tuned to achieve the desired effect to treat the disease and address challenges posed by chemotherapeutic side-effects. Photodynamic therapy (PDT) is one of the light mediated treatment modalities that has been successfully applied to treat superficial malignancies with high-efficiency, although its dependence on normoxic conditions limits its efficiency to treat deep-seated tumors. On the other hand, light-sensitive drug-mimetics and drug-release platforms have been deemed efficient in preclinical settings to induce cancer cell death with minimal collateral damage. Drawing from about a decade's worth of examples, we highlight the application of photosensitive molecules as an alternative therapeutic option to PDT and describe their designs that influence the biology of the cancer cells, in turn affecting their viability with high spatio-temporal control.

Radiodynamic therapy using 15-MV radiation combined with 5-aminolevulinic acid and carbamide peroxide for prostate cancer in vivo

Photodynamic therapy has been clinically proven to be effective, but its effect is limited to relatively shallow tumors because of its use of visible light. Radiodynamic therapy (RDT) has therefore been investigated as a means to treat deep-seated tumors. In this study, the treatment effect of a novel form of RDT consisting of radiation combined with 5-aminolevulinic acid (5-ALA) and carbamide peroxide was investigated using a mouse model. Male nude mice were injected bilaterally and subcutaneously with human prostate cancer (PC-3) cells and randomized into 8 treatment groups, consisting of various combinations of 15-MV radiotherapy (RT), 5-ALA, and carbamide peroxide. The treatment effect of a single fraction of treatment was measured by calculating tumor growth delay, monitored using weekly MR scans. The ability of the drugs to be delivered to the tumors was qualitatively measured using ¹⁸ F-FDG PET/CT scans. RDT was shown to significantly delay the tumor growth for the mouse model and tumor cell line investigated in this work. Tumors treated with RDT showed a decrease in tumor growth of 24 ± 9% and 21 ± 8% at one and two weeks post-treatment, respectively. Peroxide and 5-ALA did not contribute significantly to tumor growth delay when administered alone or separately with RT. Blood perfusion was shown to be able to deliver agents to the tumors investigated in this work, although uptake of ¹⁸ F-FDG was shown to be non-uniform.

Pluronic F-127: An Efficient Delivery Vehicle for 3-(1'-hexyloxy)ethyl-3-devinylpyropheophorbide-a (HPPH or Photochlor)

To determine the impact of delivery vehicles in photosensitizing efficacy of HPPH, a hydrophobic photosensitizer was dissolved in various formulations: 1% Tween 80/5% dextrose, Pluronic P-123 and Pluronic F-127 in 0.5%, 1% and 2% phosphate buffer solutions (PBS). HPPH was also conjugated to Pluronic F-127, and the resulting conjugate (PL-20) was formulated in PBS. Among the different delivery vehicles, only Pluronic P-123 displayed significant vehicle cytotoxicity, whereas Pluronic F127 was nontoxic. Compared to PL-20, HPPH formulated in Tween80 and Pluronic F-127 showed higher cell-uptake, but lower long-term retention in Colon26 cell compared to PL-20. The higher retention of PL-20 was similarly observed during in vivo uptake with BALB/c mice baring Ct26 tumors. In contrast to the in vitro uptake experiments, PL-20 showed slightly higher uptake compared to HPPH formulated in Tween or Pluronic-F127. A significant difference in pharmacokinetic profile was also observed between the HPPH-Pluronic formulation and PL-20. Under similar in vivo treatment parameters (drug dose 0.47 µmol kg^-1 , light dose: 135 J cm^-2 at 24 h post-injection of PS), HPPH formulated either in Tween or Pluronic F-127 formulation showed similar in vivo PDT efficacy (20-30% tumor cure on day 60), whereas PL-20 showed 40% tumor cure (day 60).

Boto R, Ferreira D, R. Fernandes J, Almeida P, F. V. Ferreira L, Silva AM, V. Reis L. Red and Near-Infrared Absorbing DicyanomethyleneSquaraine Cyanine Dyes: PhotophysicochemicalProperties and Anti-Tumor Photosensitizing Effects

Photodynamic therapy is a medical modality developed for the treatment of several diseases of oncological and non-oncological etiology that requires the presence of a photosensitizer, light and molecular oxygen, which combined will trigger physicochemical reactions responsible for reactive oxygen species production. Given the scarcity of photosensitizers that exhibit desirable characteristics for its potential application in this therapeutic strategy, the main aims of this work were the study of the photophysical and photochemical properties and the photobiological activity of several dicyanomethylene squaraine cyanine dyes. Thus, herein, the study of their aggregation character, photobleaching and singlet oxygen production ability, and the further application of the previously synthesized dyes in Caco-2 and HepG2 cancer cell lines, to evaluate their phototherapeutic effects, are described. Dicyanomethylene squaraine dyes exhibited moderate light-stability and, despite the low singlet oxygen quantum yields, were a core of dyes that exhibited relevant in vitro photodynamic activity, as there was an evident increase in the toxicity of some of the tested dyes exclusive to radiation treatments.

Photodynamic therapy dosimetry using multiexcitation multiemission wavelength: toward real-time prediction of treatment outcome

Evaluating the optical properties of biological tissues is needed to achieve accurate dosimetry during photodynamic therapy (PDT). Currently, accurate assessment of the photosensitizer (PS) concentration by fluorescence measurements during PDT is typically hindered by the lack of information about tissue optical properties. In the present work, a hand-held fiber-optic probe instrument monitoring fluorescence and reflectance is used for assessing blood volume, reduced scattering coefficient, and PS concentration facilitating accurate dosimetry for PDT. System validation was carried out on tissue phantoms using nonlinear least squares support machine regression analysis. It showed a high correlation coefficient (>0.99) in the prediction of the PS concentration upon a large variety of phantom optical properties. In vivo measurements were conducted in a PDT chlorine e6 dose escalating trial involving 36 male Swiss mice with Ehrlich solid tumors in which fluences of 5, 15, and 40  J cm  -  2 were delivered at two fluence rates (100 and 40  mW cm  -  2). Remarkably, quantitative measurement of fluorophore concentration was achieved in the in vivo experiment. Diffuse reflectance spectroscopy (DRS) system was also used to independently measure the physiological properties of the target tissues for result comparisons. Then, blood volume and scattering coefficient measured by the fiber-optic probe system were compared with the corresponding result measured by DRS and showed agreement. Additionally, tumor hemoglobin oxygen saturation was measured using the DRS system. Overall, the system is capable of assessing the implicit photodynamic dose to predict the PDT outcome.

In vivo Tissue Evaluation Reveals Improvements in Explicit PDT Dosimetry

Progress is needed before explicit photodynamic therapy (PDT) dosimetry can treat peritoneal carcinomatosis and yet spare all healthy tissue. A report by Cengel et al. in this issue of Photochemistry & Photobiology on tissue evaluation in a canine model may bring that goal a step closer and may even be dogma-changing.

Multispectral singlet oxygen and photosensitizer luminescence dosimeter for continuous photodynamic therapy dose assessment during treatment

SIGNIFICANCE

Photodynamic therapy (PDT) involves complex light-drug-pathophysiology interactions that can be affected by multiple parameters and often leads to large variations in treatment outcome from patient to patient. Direct PDT dosimetry technologies have been sought to optimize the control variables (e.g., light dose, drug administration, tissue oxygenation, and patient conditioning) for best patient outcomes. In comparison, singlet oxygen (O21) dosimetry has been tested in various forms to provide an accurate and perhaps comprehensive prediction of the treatment efficacy.

AIM

We discuss an advanced version of this approach provided by a noninvasive, continuous wave dosimeter that can measure near-infrared spectrally resolved luminescence of both photosensitizer (PS) and O21 generated during PDT cancer treatment.

APPROACH

This dosimetry technology uses an amplified, high quantum efficiency InGaAs detector with spectroscopic decomposition during the light treatment to continuously extract the maximum signal of O21 phosphorescence while suppressing the strong PS luminescence background by spectrally fitting the data points across nine narrow band wavelengths. O21 and PS luminescence signals were measured in vivo in FaDu xenograft tumors grown in mice during PDT treatment using Verteporfin as the PS and a continuous laser treatment at 690 nm wavelength.

RESULTS

A cohort of 19 mice was used and observations indicate that the tumor growth rate inhibition showed a stronger correlation with O21 than with just the PS signal.

CONCLUSIONS

These results suggest that O21 measurement may be a more direct dosimeter of PDT damage, and it has potential value as a definitive diagnostic for PDT treatment, especially with spectral separation of the background luminescence and online estimation of the PS concentration.

Predictors and Limitations of the Penetration Depth of Photodynamic Effects in the Rodent Brain

Fluorescence-guided surgery (FGS) is routinely utilized in clinical centers around the world, whereas the combination of FGS and photodynamic therapy (PDT) has yet to reach clinical implementation and remains an active area of translational investigations. Two significant challenges to the clinical translation of PDT for brain cancer are as follows: (1) Limited light penetration depth in brain tissues and (2) Poor selectivity and delivery of the appropriate photosensitizers. To address these shortcomings, we developed nanoliposomal protoporphyrin IX (Nal-PpIX) and nanoliposomal benzoporphyrin derivative (Nal-BPD) and then evaluated their photodynamic effects as a function of depth in tissue and light fluence using rat brains. Although red light penetration depth (defined as the depth at which the incident optical energy drops to 1/e, ~37%) is typically a few millimeters in tissues, we demonstrated that the remaining optical energy could induce PDT effects up to 2 cm within brain tissues. Photobleaching and singlet oxygen yield studies between Nal-BPD and Nal-PpIX suggest that deep-tissue PDT (>1 cm) is more effective when using Nal-BPD. These findings indicate that Nal-BPD-PDT is more likely to generate cytotoxic effects deep within the brain and allow for the treatment of brain invading tumor cells centimeters away from the main, resectable tumor mass.

Spatial energy transfer with observation of bimolecular singlet oxygen emission using quantum dots as donors and zinc-phthalocyanine as acceptors

This study reports the influence of CdSe-ZnS core-shell quantum dots (QDs) for formation of singlet oxygen using zinc-phthalocyanine (ZnPc) dyes in colloidal solutions. Using a microluminescence surface scan technique it was possible to measure accurately the photon diffusion length, or photon mean free path, inside the medium. Analyses were performed for a range of QD concentrations. Photon diffusion length was assigned to the bimolecular singlet oxygen emission at 707 nm. Related singlet oxygen emission was predicted by observing quenching of the photon diffusion length measured at the specific oxygen emission as a function of QD concentration, being a nontrivial phenomenon related to the QD donors. Diffusion length measured at 707 nm increased with QD concentration; in the absence of QDs, as in pure ZnPc samples, the emission peak at 707 nm was not observed.

On a heavy path – determining cold plasma-derived short-lived species chemistry using isotopic labelling

Cold atmospheric plasmas (CAPs) are promising medical tools and are currently applied in dermatology and epithelial cancers. While understanding of the biomedical effects is already substantial, knowledge on the contribution of individual ROS and RNS and the mode of activation of biochemical pathways is insufficient. Especially the formation and transport of short-lived reactive species in liquids remain elusive, a situation shared with other approaches involving redox processes such as photodynamic therapy. Here, the contribution of plasma-generated reactive oxygen species (ROS) in plasma liquid chemistry was determined by labeling these via admixing heavy oxygen ¹⁸O₂ to the feed gas or by using heavy water H₂¹⁸O as a solvent for the bait molecule. The inclusion of heavy or light oxygen atoms by the labeled ROS into the different cysteine products was determined by mass spectrometry. While products like cysteine sulfonic acid incorporated nearly exclusively gas phase-derived oxygen species (atomic oxygen and/or singlet oxygen), a significant contribution of liquid phase-derived species (OH radicals) was observed for cysteine-S-sulfonate. The role, origin, and reaction mechanisms of short-lived species, namely hydroxyl radicals, singlet oxygen, and atomic oxygen, are discussed. Interactions of these species both with the target cysteine molecule as well as the interphase and the liquid bulk are taken into consideration to shed light onto several reaction pathways resulting in observed isotopic oxygen incorporation. These studies give valuable insight into underlying plasma–liquid interaction processes and are a first step to understand these interaction processes between the gas and liquid phase on a molecular level.

Cold atmospheric plasmas (CAPs) are promising medical tools producing short-lived reactive species.

Optical coherence angiography for pre-treatment assessment and treatment monitoring following photodynamic therapy: a basal cell carcinoma patient study

Microvascular networks of human basal cell carcinomas (BCC) and surrounding skin were assessed with optical coherence angiography (OCA) in conjunction with photodynamic therapy (PDT). OCA images were collected and analyzed in 31 lesions pre-treatment, and immediately/24 hours/3-12 months post-treatment. Pre-treatment OCA enabled differentiation between prevalent subtypes of BCC (nodular and superficial) and nodular-with-necrotic-core BCC subtypes with a diagnostic accuracy of 78%; this can facilitate more accurate biopsy reducing sampling error and better therapy regimen selection. Post-treatment OCA images at 24 hours were 98% predictive of eventual outcome. Additional findings highlight the importance of pre-treatment necrotic core, vascular metrics associated with hypertrophic scar formation, and early microvascular changes necessary in both tumorous and peri-tumorous regions to ensure treatment success.

Reactive Oxygen Species Explicit Dosimetry for Photofrin-mediated Pleural Photodynamic Therapy

Explicit dosimetry of treatment light fluence and implicit dosimetry of photosensitizer photobleaching are commonly used methods to guide dose delivery during clinical PDT. Tissue oxygen, however, is not routinely monitored intraoperatively even though it is one of the three major components of treatment. Quantitative information about in vivo tissue oxygenation during PDT is desirable, because it enables reactive oxygen species explicit dosimetry (ROSED) for prediction of treatment outcome based on PDT-induced changes in tumor oxygen level. Here, we demonstrate ROSED in a clinical setting, Photofrin-mediated pleural photodynamic therapy, by utilizing tumor blood flow information measured by diffuse correlation spectroscopy (DCS). A DCS contact probe was sutured to the pleural cavity wall after surgical resection of pleural mesothelioma tumor to monitor tissue blood flow (blood flow index) during intraoperative PDT treatment. Isotropic detectors were used to measure treatment light fluence and photosensitizer concentration. Blood-flow-derived tumor oxygen concentration, estimated by applying a preclinically determined conversion factor of 1.5 × 10⁹ μMs cm^-2 to the blood flow index, was used in the ROSED model to calculate the total reacted reactive oxygen species [ROS]rx. Seven patients and 12 different pleural sites were assessed and large inter- and intrapatient heterogeneities in [ROS]rx were observed although an identical light dose of 60 J cm^-2 was prescribed to all patients.

Validation of combined Monte Carlo and photokinetic simulations for the outcome correlation analysis of benzoporphyrin derivative-mediated photodynamic therapy on mice

We compare previously reported benzoporphyrin derivative (BPD)-mediated photodynamic therapy (PDT) results for reactive singlet oxygen concentration (also called singlet oxygen dose) on mice with simulations using a computational device, Dosie™, that calculates light transport and photokinetics for PDT in near real-time. The two sets of results are consistent and validate the use of the device in PDT treatment planning to predict BPD-mediated PDT outcomes in mice animal studies based on singlet oxygen dose, which showed a much better correlation with the cure index than the conventional light dose.

Wavelength optimization in the multispectral photoacoustic tomography of the lymphatic drainage in mice

Multispectral photoacoustic tomography provides mapping of the tissue chromophore distributions using sets of tunable laser wavelengths. With the overall goal of studying the dynamics of cerebrospinal fluid in mice in vivo, our work aims to minimize the number of wavelengths to reduce scanning time, improve the temporal resolution, reduce the energy deposition and avoid the tracer photobleaching while maintaining high image quality. To select small sets of wavelengths we directly searched for the combinations of wavelengths providing the best and worst image quality in comparison with a reference image obtained using 131 closely spaced wavelengths between 680 and 940 nm in terms of the peak signal-to-noise ratio (PSNR). We have shown that using the PSNR optimization method, additional improvements could be achieved over the wavelength set selected using the method of the minimization of the extinction matrix condition number.

Nanolipid Formulations of Benzoporphyrin Derivative: Exploring the Dependence of Nanoconstruct Photophysics and Photochemistry on Their Therapeutic Index in Ovarian Cancer Cells

With the rapidly emerging designs and applications of light-activated, photodynamic therapy (PDT)-based nanoconstructs, photonanomedicines (PNMs), an unmet need exists to establish whether conventional methods of photochemical and photophysical characterization of photosensitizers are relevant for evaluating new PNMs in order to intelligently guide their design. As a model system, we build on the clinical formulation of benzoporphyrin derivative (BPD), Visudyne^® , by developing a panel of nanolipid formulations entrapping new lipidated chemical variants of BPD with differing chemical, photochemical and photophysical properties. These are 16:0 and 20:0 lysophosphocholine-BPD (16:0/20:0 BPD-PC), DSPE-PEG-BPD and BPD-cholesterol. We show that Visudyne^® was the most phototoxic formulation to OVCAR-5 cells, and the least effective was liposomal DSPE-PEG-BPD. However, these differences did not match their optical, photophysical and photochemical properties, as the static BPD quenching was highest in Visudyne, which also exhibited the lowest generation of singlet oxygen. Furthermore, we establish that OVCAR-5 cell phototoxicity also does not correlate with rates of photosensitizer photobleaching and fluorescence quantum yields in any nanolipid formulations. These findings warrant critical future studies into subcellular targets and molecular mechanisms of phototoxicity of photodynamic nanoconstructs, as more reliable prognostic surrogates for predicting efficacy to appropriately and intelligently guide their design.

Visualizing Photodynamic Therapy in Transgenic Zebrafish Using Organic Nanoparticles with Aggregation-Induced Emission

Photodynamic therapy (PDT) employs accumulation of photosensitizers (PSs) in malignant tumor tissue followed by the light-induced generation of cytotoxic reactive oxygen species to kill the tumor cells. The success of PDT depends on optimal PS dosage that is matched with the ideal power of light. This in turn depends on PS accumulation in target tissue and light administration time and period. As theranostic nanomedicine is driven by multifunctional therapeutics that aim to achieve targeted tissue delivery and image-guided therapy, fluorescent PS nanoparticle (NP) accumulation in target tissues can be ascertained through fluorescence imaging to optimize the light dose and administration parameters. In this regard, zebrafish larvae provide a unique transparent in vivo platform to monitor fluorescent PS bio-distribution and their therapeutic efficiency. Using fluorescent PS NPs with unique aggregation-induced emission characteristics, we demonstrate for the first time the real-time visualization of polymeric NP accumulation in tumor tissue and, more importantly, the best time to conduct PDT using transgenic zebrafish larvae with inducible liver hyperplasia as an example.

Fluorescence-guided surgery and intervention - An AAPM emerging technology blue paper

Fluorescence-guided surgery (FGS) and other interventions are rapidly evolving as a class of technologically driven interventional approaches in which many surgical specialties visualize fluorescent molecular tracers or biomarkers through associated cameras or oculars to guide clinical decisions on pathological lesion detection and excision/ablation. The technology has been commercialized for some specific applications, but also presents technical challenges unique to optical imaging that could confound the utility of some interventional procedures where real-time decisions must be made. Accordingly, the AAPM has initiated the publication of this Blue Paper of The Emerging Technology Working Group (TETAWG) and the creation of a Task Group from the Therapy Physics Committee within the Treatment Delivery Subcommittee. In describing the relevant issues, this document outlines the key parameters, stakeholders, impacts, and outcomes of clinical FGS technology and its applications. The presentation is not intended to be conclusive, but rather to inform the field of medical physics and stimulate the discussions needed in the field with respect to a seemingly low-risk imaging technology that has high potential for significant therapeutic impact. This AAPM Task Group is working toward consensus around guidelines and standards for advancing the field safely and effectively.