In vivo tumor oxygen tension measurements for the evaluation of the efficiency of photodynamic therapy

Bromine indirubin FLIM/PLIM sensors to measure oxygen in normoxic and hypoxic PDT conditions

BACKGROUND

The induction of phototoxicity during photodynamic therapy (PDT) is dependent on oxygen availability. For this reason, the development of sensors to measure oxygen and oxygen consumption is extremely important.

APPROACH

In this project we have used Fluorescence Lifetime imaging (FLIM) and Phosphorescence Lifetime Imaging/ delayed Fluorescence Lifetime Imaging (PLIM/dFLIM) to investigate the ability of bromine indirubin derivatives as oxygen sensors.

RESULTS

The oxygen sensitivity of bromine indirubins was detected through PLIM/dFLIM. Moreover, we have observed, by measuring nicotinamide adenine dinucleotide (NADH) FLIM, that bromine indirubin has a significant impact on cellular metabolism by shifting the SCC-4 Cells metabolism from oxidative phosphorylation (OXPHOS) to glycolysis.

CONCLUSIONS

In conclusion, this study successfully achieves its goals and provides important insights into the use of indirubin as a potential oxygen consumption sensor with the capability to identify and differentiate between normoxic and hypoxic regions within the cells.

Photodynamic therapy and associated targeting methods for treatment of brain cancer

Brain tumors, including glioblastoma multiforme, are currently a cause of suffering and death of tens of thousands of people worldwide. Despite advances in clinical treatment, the average patient survival time from the moment of diagnosis of glioblastoma multiforme and application of standard treatment methods such as surgical resection, radio- and chemotherapy, is less than 4 years. The continuing development of new therapeutic methods for targeting and treating brain tumors may extend life and provide greater comfort to patients. One such developing therapeutic method is photodynamic therapy. Photodynamic therapy is a progressive method of therapy used in dermatology, dentistry, ophthalmology, and has found use as an antimicrobial agent. It has also found wide application in photodiagnosis. Photodynamic therapy requires the presence of three necessary components: a clinically approved photosensitizer, oxygen and light. This paper is a review of selected literature from Pubmed and Scopus scientific databases in the field of photodynamic therapy in brain tumors with an emphasis on glioblastoma treatment.

Microfluidic oxygen tolerability screening of nanocarriers for triplet fusion photon upconversion

The full potential of triplet fusion photon upconversion (TF-UC) of providing high-energy photons locally with low-energy excitation is limited in biomedicine and life sciences by its oxygen sensitivity. This hampers the applicability of TF-UC systems in sensors, imaging, optogenetics and drug release. Despite the advances in improving the oxygen tolerability of TF-UC systems, the evaluation of oxygen tolerability is based on comparing the performance at completely deoxygenated (0% oxygen) and ambient (20-21%) conditions, leaving the physiological oxygen levels (0.3-13.5%) neglected. This oversight is not deliberate and is only the result of the lack of simple and predictable methods to obtain and maintain these physiological oxygen levels in an optical setup. Herein, we demonstrate the use of microfluidic chips made of oxygen depleting materials to study the oxygen tolerability of four different micellar nanocarriers made of FDA-approved materials with various oxygen scavenging capabilities by screening their TF-UC performance over physiological oxygen levels. All nanocarriers were capable of efficient TF-UC even in ambient conditions. However, utilizing oxygen scavengers in the oil phase of the nanocarrier improves the oxygen tolerability considerably. For example, at the mean tumour oxygen level (1.4%), nanocarriers made of surfactants and oil phase both capable of oxygen scavenging retained remarkably 80% of their TF-UC emission. This microfluidic concept enables faster, simpler and more realistic evaluation of, not only TF-UC, but any micro or nanoscale oxygen-sensitive system and facilitates their development and implementation in biomedical and life science applications.

Photodynamic Therapy-Current Limitations and Novel Approaches

Photodynamic therapy (PDT) mostly relies on the generation of singlet oxygen, via the excitation of a photosensitizer, so that target tumor cells can be destroyed. PDT can be applied in the settings of several malignant diseases. In fact, the earliest preclinical applications date back to 1900’s. Dougherty reported the treatment of skin tumors by PDT in 1978. Several further studies around 1980 demonstrated the effectiveness of PDT. Thus, the technique has attracted the attention of numerous researchers since then. Hematoporphyrin derivative received the FDA approval as a clinical application of PDT in 1995. We have indeed witnessed a considerable progress in the field over the last century. Given the fact that PDT has a favorable adverse event profile and can enhance anti-tumor immune responses as well as demonstrating minimally invasive characteristics, it is disappointing that PDT is not broadly utilized in the clinical setting for the treatment of malignant and/or non-malignant diseases. Several issues still hinder the development of PDT, such as those related with light, tissue oxygenation and inherent properties of the photosensitizers. Various photosensitizers have been designed/synthesized in order to overcome the limitations. In this Review, we provide a general overview of the mechanisms of action in terms of PDT in cancer, including the effects on immune system and vasculature as well as mechanisms related with tumor cell destruction. We will also briefly mention the application of PDT for non-malignant diseases. The current limitations of PDT utilization in cancer will be reviewed, since identifying problems associated with design/synthesis of photosensitizers as well as application of light and tissue oxygenation might pave the way for more effective PDT approaches. Furthermore, novel promising approaches to improve outcome in PDT such as selectivity, bioengineering, subcellular/organelle targeting, etc. will also be discussed in detail, since the potential of pioneering and exceptional approaches that aim to overcome the limitations and reveal the full potential of PDT in terms of clinical translation are undoubtedly exciting. A better understanding of novel concepts in the field (e.g. enhanced, two-stage, fractional PDT) will most likely prove to be very useful for pursuing and improving effective PDT strategies.

Application of photodynamic therapy in immune-related diseases

Photodynamic therapy (PDT) is a therapeutic modality that utilizes photodamage caused by photosensitizers and oxygen after exposure to a specific wavelength of light. Owing to its low toxicity, high selectivity, and minimally invasive properties, PDT has been widely applied to treat various malignant tumors, premalignant lesions, and infectious diseases. Moreover, there is growing evidence of its immunomodulatory effects and potential for the treatment of immune-related diseases. This review mainly focuses on the effect of PDT on immunity and its application in immune-related diseases.

Nanomedicine-Based Strategies Assisting Photodynamic Therapy for Hypoxic Tumors: State-of-the-Art Approaches and Emerging Trends

Since the first clinical cancer treatment in 1978, photodynamic therapy (PDT) technologies have been largely improved and approved for clinical usage in various cancers. Due to the oxygen-dependent nature, the application of PDT is still limited by hypoxia in tumor tissues. Thus, the development of effective strategies for manipulating hypoxia and improving the effectiveness of PDT is one of the most important area in PDT field. Recently, emerging nanotechnology has benefitted progress in many areas, including PDT. In this review, after briefly introducing the mechanisms of PDT and hypoxia, as well as basic knowledge about nanomedicines, we will discuss the state of the art of nanomedicine-based approaches for assisting PDT for treating hypoxic tumors, mainly based on oxygen replenishing strategies and the oxygen dependency diminishing strategies. Among these strategies, we will emphasize emerging trends about the use of nanoscale metal-organic framework (nMOF) materials and the combination of PDT with immunotherapy. We further discuss future perspectives and challenges associated with these trends in both the aspects of mechanism and clinical translation.

Alternative methods of photodynamic therapy and oxygen consumption measurements-A review

Photooxidation generates reactive oxygen species (ROS) through the interaction of dyes or surfaces with light radiation of appropriate wavelength. The reaction is of wide utility and is highly effective in photodynamic therapy (PDT) of various types of cancer and skin disease. Understanding generation of singlet oxygen has contributed to the development of PDT and its subsequent use in vivo. However, this therapy has some limitations that prevent its use in the treatment of cancers located deep within the body. The limited depth of light penetration through biological tissue limits initiation of PDT action in deep tissue. Measurement of oxygen photo consumption is critical due to tumor hypoxia, and use of magnetic resonance imaging (MRI) is particularly attractive since it is non-invasive. This article presents bioluminescence (BL) and chemiluminescence (CL) phenomena based on publications from the last 20 years, and preliminary results from our lab in the use of MRI to measure oxygen concentration in water. Current work is aimed at improving the effectiveness of singlet oxygen delivery to deep tissue cancer.

Chemoreactive Nanotherapeutics by Metal Peroxide Based Nanomedicine

The advances of nanobiotechnology and nanomedicine enable the triggering of in situ chemical reactions in disease microenvironment for achieving disease-specific nanotherapeutics with both intriguing therapeutic efficacy and mitigated side effects. Metal peroxide based nanoparticles, as one of the important but generally ignored categories of metal-involved nanosystems, can function as the solid precursors to produce oxygen (O2) and hydrogen peroxide (H2O2) through simple chemical reactions, both of which are the important chemical species for enhancing the therapeutic outcome of versatile modalities, accompanied with the unique bioactivity of metal ion based components. This progress report summarizes and discusses the most representative paradigms of metal peroxides in chemoreactive nanomedicine, including copper peroxide (CuO2), calcium peroxide (CaO2), magnesium peroxide (MgO2), zinc peroxide (ZnO2), barium peroxide (BaO2), and titanium peroxide (TiOx) nanosystems. Their reactions and corresponding products have been broadly explored in versatile disease treatments, including catalytic nanotherapeutics, photodynamic therapy, radiation therapy, antibacterial infection, tissue regeneration, and some synergistically therapeutic applications. This progress report particularly focuses on the underlying reaction mechanisms on enhancing the therapeutic efficacy of these modalities, accompanied with the discussion on their biological effects and biosafety. The existing gap between fundamental research and clinical translation of these metal peroxide based nanotherapeutic technologies is finally discussed in depth.

Monitoring photodynamic oxygen consumption by endogenous oxygen contrast MRI

Photodynamic oxygen consumption was measured by changes in spin-lattice relaxation time (T₁) in aqueous solution in a clinical GE scanner at 1.5 T. Similar measurements were attempted in excised laryngeal and thyroid tissues that were infused with Rose Bengal. First, T₁ was measured as a function of dissolved oxygen in argon and in oxygen pre-saturated water samples that were opened to the atmosphere in a series of steps allowing air to diffuse into or out of solution; for both argon and oxygen saturated water solutions, stepwise air re-equilibration resulted in a return to air-saturated water T₁. Secondly, T₁ was measured as a function of time under type II photooxidative conditions in aqueous solution. Under type II photooxidative conditions, a 492 ± 53 ms increase in T₁ was measured following 300 s of visible light illumination of aqueous solutions containing the photosensitizer Rose Bengal (2.5 × 10^-6 M) and the singlet oxygen trap methionine (0.0012 M). The 492 ± 53 ms increase in T₁ corresponded to consumption of all the measurable dissolved oxygen (˜ 0.1 mg O₂ in 15.0 mL of H₂O) during photooxidation of methionine in air saturated water. This rapid oxygen consumption, indicated by an increase in T₁, is due to irreversible trapping of photogenerated singlet oxygen by methionine. Thirdly, an increase in T₁ was observed in Rose Bengal infused normal laryngeal tissue, and in normal and cancerous thyroid tissue samples following 20 min of exposure to visible light. An increase in T₁ was not observed after 40 min of illumination which suggests that the increases in T₁ observed after 20 min were not due to water uptake, but rather to photoconsumption of interstitial dissolved oxygen.

Ultrastable Near-Infrared Conjugated-Polymer Nanoparticles for Dually Photoactive Tumor Inhibition

It is highly desired that satisfactory photoactive agents with ideal photophysical characteristics are explored for potent cancer phototherapeutics. Herein, bifunctional nanoparticles of low-bandgap donor-acceptor (D-A)-type conjugated-polymer nanoparticles (CP-NPs) are developed to afford a highly efficient singlet-to-triplet transition and photothermal conversion for near-infrared (NIR) light-induced photodynamic (PDT)/photothermal (PTT) treatment. CP-NPs display remarkable NIR absorption with the peak at 782 nm, and perfect resistance to photobleaching. Photoexcited CP-NPs undergo singlet-to-triplet intersystem crossing through charge transfer in the excited D-A system and simultaneous nonradiative decay from the electron-deficient electron acceptor isoindigo derivative under single-wavelength NIR light irradiation, leading to distinct singlet oxygen quantum yield and high photothermal conversion efficiency. Moreover, the CP-NPs display effective cellular uptake and cytoplasmic translocation from lysosomes, as well as effective tumor accumulation, thus promoting severe light-triggered damage caused by favorable reactive oxygen species (ROS) generation and potent hyperthermia. Thus, CP-NPs achieve photoactive cell damage through their photoconversion ability for synergistic PDT/PTT treatment with tumor ablation. The proof-of-concept design of D-A-type conjugated-polymer nanoparticles with ideal photophysical characteristics provides a general approach to afford potent photoactive cancer therapy.

Strategies for optimizing the delivery to tumors of macrocyclic photosensitizers used in photodynamic therapy (PDT)

This review briefly summaries the principles and mechanisms of action of photodynamic therapy (PDT) as concerns its application in the oncological field, highlighting its drawbacks and some of the strategies that have been or are being explored to overcome them. The major aim is to increase the efficiency and selectivity of the photosensitizer (PS) uptake in the cancer cells for optimizing the PDT effects on tumors while sparing normal cells. Some attempts to achieve this are based on the conjugation of the PS to biomolecules (small ligands, peptides) functioning as carriers with the ability to efficiently penetrate cells and/or specifically recognize and bind proteins/receptors overexpressed on the surface of cancer cells. Alternatively, the PS can be entrapped in nanocarriers derived from various types of materials that can target the tumor by exploiting the enhanced permeability and retention (EPR) effects. The use of nanocarriers is particularly attractive because it allows the simultaneous delivery of more than one drug with the possibility of combining PDT with other therapeutic modalities.

Realtime Tracking of the Photobleaching Trajectory During Photodynamic Therapy

OBJECTIVE

Photodynamic therapy (PDT) is an alternative treatment for cancer, which involves the administration of a photosensitizing agent that is activated by light at a specific wavelength. This illumination causes after a sequence of photoreactions, the production of reactive oxygen species responsible for the death of the tumor cells but also the degradation of the photosensitizing agent, which then loose the fluorescence properties. The phenomenon is commonly known as the photobleaching process and can be considered as a therapy efficiency indicator.

METHODS

This paper presents the design and validation of a real-time controller able to track a preset photobleaching trajectory by modulating the light impulses width during the treatment sessions.

RESULTS

This innovative solution was validated by in vivo experiments that have shown a significantly improvement of reproducibility of the interindividual photobleaching kinetic.

CONCLUSION

We believe that this approach could lead to personalized PDT modalities.

SIGNIFICANCE

This work may open new perspectives in the control and optimization of photodynamic treatments.

Revisiting photodynamic therapy dosimetry: reductionist & surrogate approaches to facilitate clinical success

Photodynamic therapy (PDT) can be a highly complex treatment, with many parameters influencing treatment efficacy. The extent to which dosimetry is used to monitor and standardize treatment delivery varies widely, ranging from measurement of a single surrogate marker to comprehensive approaches that aim to measure or estimate as many relevant parameters as possible. Today, most clinical PDT treatments are still administered with little more than application of a prescribed drug dose and timed light delivery, and thus the role of patient-specific dosimetry has not reached widespread clinical adoption. This disconnect is at least partly due to the inherent conflict between the need to measure and understand multiple parameters in vivo in order to optimize treatment, and the need for expedience in the clinic and in the regulatory and commercialization process. Thus, a methodical approach to selecting primary dosimetry metrics is required at each stage of translation of a treatment procedure, moving from complex measurements to understand PDT mechanisms in pre-clinical and early phase I trials, towards the identification and application of essential dose-limiting and/or surrogate measurements in phase II/III trials. If successful, identifying the essential and/or reliable surrogate dosimetry measurements should help facilitate increased adoption of clinical PDT. In this paper, examples of essential dosimetry points and surrogate dosimetry tools that may be implemented in phase II/III trials are discussed. For example, the treatment efficacy as limited by light penetration in interstitial PDT may be predicted by the amount of contrast uptake in CT, and so this could be utilized as a surrogate dosimetry measurement to prescribe light doses based upon pre-treatment contrast. Success of clinical ALA-based skin lesion treatment is predicted almost uniquely by the explicit or implicit measurements of photosensitizer and photobleaching, yet the individualization of treatment based upon each patients measured bleaching needs to be attempted. In the case of ALA, lack of PpIX is more likely an indicator that alternative PpIX production methods must be implemented. Parsimonious dosimetry, using surrogate measurements that are clinically acceptable, might strategically help to advance PDT in a medical world that is increasingly cost and time sensitive. Careful attention to methodologies that can identify and advance the most critical dosimetric measurements, either direct or surrogate, are needed to ensure successful incorporation of PDT into niche clinical procedures.

Intraoperative optical assessment of photodynamic therapy response of superficial oral squamous cell carcinoma

This study investigated whether diffuse optical spectroscopy (DOS) measurements could assess clinical response to photodynamic therapy (PDT) in patients with head and neck squamous cell carcinoma (HNSCC). In addition, the correlation between parameters measured with DOS and the crosslinking of signal transducer and activator of transcription 3 (STAT3), a molecular marker for PDT-induced photoreaction, was investigated. Thirteen patients with early stage HNSCC received the photosensitizer 2-[1-hexyloxyethyl]-2-devinylpyropheophorbide-a (HPPH) and DOS measurements were performed before and after PDT in the operating room (OR). In addition, biopsies were acquired after PDT to assess the STAT3 crosslinking. Parameters measured with DOS, including blood volume fraction, blood oxygen saturation (StO2), HPPH concentration (cHPPH), HPPH fluorescence, and blood flow index (BFI), were compared to the pathologic response and the STAT3 crosslinking. The best individual predictor of pathological response was a change in cHPPH (sensitivity=60%, specificity=100%), while discrimination analysis using a two-parameter classifier (change in cHPPH and change in StO2) classified pathological response with 100% sensitivity and 100% specificity. BFI showed the best correlation with the crosslinking of STAT3. These results indicate that DOS-derived parameters can assess the clinical response in the OR, allowing for earlier reintervention if needed.

Clinical use of photodynamic therapy in ocular tumors

Although the introduction of intravitreal anti-vascular endothelial growth factor drugs reduced the indications for photodynamic therapy in ophthalmology, it may still be used in various ocular tumors. Although many studies have shown that photodynamic therapy is effective in ocular tumors, the literature consists of case reports and series. In this review, we systematically performed a meta-analysis for the use of photodynamic therapy in circumscribed choroidal hemangioma, diffuse choroidal hemangioma, retinal capillary hemangioma, von Hippel-Lindau angiomatosis, choroidal melanoma, retinal astrocytoma, retinoblastoma, eyelid tumors, conjunctival tumors, and choroidal metastasis.

Photodynamic therapy: one step ahead with self-assembled nanoparticles

Photodynamic therapy (PDT) is a promising treatment modality for cancer with possible advantages over current treatment alternatives. It involves combination of light and a photosensitizer (PS), which is activated by absorption of specific wavelength light and creates local tissue damage through generation of reactive oxygen species (ROS) that induce a cascade of cellular and molecular events. However, as of today, PDT is still in need of improvement and nanotechnology may play a role. PDT frequently employs PS with molecular structures that are highly hydrophobic, water insoluble and prone to aggregation. Aggregation of PS leads to reduced ROS generation and thus lowers the PDT activity. Some PS such as 5-aminolevulinic acid (ALA) cannot penetrate through the stratum corneum of the skin and systemic administration is not an option due to frequently encountered side effects. Therefore PS are often encapsulated or conjugated in/on nano-drug delivery vehicles to allow them to be better taken up by cells and to more selectively deliver them to tumors or other target tissues. Several nano-drug delivery vehicles including liposomes, fullerosomes and nanocells have been tested and reviewed. Here we cover non-liposomal self-assembled nanoparticles consisting of polymeric micelles including block co-polymers, polymeric micelles, dendrimers and porphysomes.

An IR Navigation System for Pleural PDT

Pleural photodynamic therapy (PDT) has been used as an adjuvant treatment with lung-sparing surgical treatment for malignant pleural mesothelioma (MPM). In the current pleural PDT protocol, a moving fiber-based point source is used to deliver the light. The light fluences at multiple locations are monitored by several isotropic detectors placed in the pleural cavity. To improve the delivery of light fluence uniformity, an infrared (IR) navigation system is used to track the motion of the light source in real-time at a rate of 20 - 60 Hz. A treatment planning system uses the laser source positions obtained from the IR camera to calculate light fluence distribution to monitor the light fluence uniformity on the surface of the pleural cavity. A novel reconstruction algorithm is used to determine the pleural cavity surface contour. A dual-correction method is used to match the calculated fluences at detector locations to the detector readings. Preliminary data from a phantom shows superior light uniformity using this method. Light fluence uniformity from patient treatments is also shown with and without the correction method.

Time-resolved insight into the photosensitized generation of singlet oxygen in endoperoxides

A synergistic approach combining high-level multiconfigurational static calculations and full-dimensional ab initio surface hopping dynamics has been employed to gain insight into the photochemistry of endoperoxides. Electronic excitation of endoperoxides triggers two competing pathways, cycloreversion and O–O homolysis, that result in the generation of singlet oxygen and oxygen diradical rearrangement products. Our results reveal that cycloreversion or the rupture of the two C–O bonds occurs via an asynchronous mechanism that can lead to the population of a ground-state intermediate showing a single C–O bond. Furthermore, singlet oxygen is directly generated in its most stable excited electronic state 1Δg. The triplet states do not intervene in this mechanism, as opposed to the O–O homolysis where the exchange of population between the singlet and triplet manifolds is remarkable. In line with recent experiments performed on the larger anthracene-9,10-endoperoxide, upon excitation to the spectroscopic ππ* electronic states, the primary photoreactive pathway that governs deactivation of endoperoxides is O–O homolysis with a quantum yield of 65%.

Influence of photoactivated tetra sulphonatophenyl porphyrin and TiO2nanowhiskers on rheumatoid arthritis infected bone marrow stem cell proliferation in vitro and oxidative stress biomarkers in vivo

Besides the lethal effects of photodynamic therapy on neoplasms, herein we report photoactivated TSPP–TiO₂nanocomposites' growth promoting effect on rheumatoid arthritis BMS cells.

The role of strong hypoxia in tumors after treatment in the outcome of bacteriochlorin-based photodynamic therapy

Blood flow and pO2 changes after vascular-targeted photodynamic therapy (V-PDT) or cellular-targeted PDT (C-PDT) using 5,10,15,20-tetrakis(2,6-difluoro-3-N-methylsulfamoylphenyl) bacteriochlorin (F2BMet) as photosensitizer were investigated in DBA/2 mice with S91 Cloudman mouse melanoma, and correlated with long-term tumor responses. F2BMet generates both singlet oxygen and hydroxyl radicals under near-infrared radiation, which consume oxygen. Partial oxygen pressure was lowered in PDT-treated tumors and this was ascribed both to oxygen consumption during PDT and to fluctuations in oxygen transport after PDT. Similarly, microcirculatory blood flow changed as a result of the disruption of blood vessels by the treatment. A novel noninvasive approach combining electron paramagnetic resonance oximetry and laser Doppler blood perfusion measurements allowed longitudinal monitoring of hypoxia and vascular function changes in the same animals, after PDT. C-PDT induced parallel changes in tumor pO2 and blood flow, i.e., an initial decrease immediately after treatment, followed by a slow increase. In contrast, V-PDT led to a strong and persistent depletion of pO2, although the microcirculatory blood flow increased. Strong hypoxia after V-PDT led to a slight increase in VEGF level 24h after treatment. C-PDT caused a ca. 5-day delay in tumor growth, whereas V-PDT was much more efficient and led to tumor growth inhibition in 90% of animals. The tumors of 44% of mice treated with V-PDT regressed completely and did not reappear for over 1 year. In conclusion, mild and transient hypoxia after C-PDT led to intense pO2 compensatory effects and modest tumor inhibition, but strong and persistent local hypoxia after V-PDT caused tumor growth inhibition.

Mechanisms in photodynamic therapy: part two-cellular signaling, cell metabolism and modes of cell death

Photodynamic therapy (PDT) has been known for over a hundred years, but is only now becoming widely used. Originally developed as a tumor therapy, some of its most successful applications are for non-malignant disease. In the second of a series of three reviews, we will discuss the mechanisms that operate in PDT on a cellular level. In Part I [Castano AP, Demidova TN, Hamblin MR. Mechanism in photodynamic therapy: part one-photosensitizers, photochemistry and cellular localization. Photodiagn Photodyn Ther 2004;1:279-93] it was shown that one of the most important factors governing the outcome of PDT, is how the photosensitizer (PS) interacts with cells in the target tissue or tumor, and the key aspect of this interaction is the subcellular localization of the PS. PS can localize in mitochondria, lysosomes, endoplasmic reticulum, Golgi apparatus and plasma membranes. An explosion of investigation and explorations in the field of cell biology have elucidated many of the pathways that mammalian cells undergo when PS are delivered in tissue culture and subsequently illuminated. There is an acute stress response leading to changes in calcium and lipid metabolism and production of cytokines and stress proteins. Enzymes particularly, protein kinases, are activated and transcription factors are expressed. Many of the cellular responses are centered on mitochondria. These effects frequently lead to induction of apoptosis either by the mitochondrial pathway involving caspases and release of cytochrome c, or by pathways involving ceramide or death receptors. However, under certain circumstances cells subjected to PDT die by necrosis. Although there have been many reports of DNA damage caused by PDT, this is not thought to be an important cell-death pathway. This mechanistic research is expected to lead to optimization of PDT as a tumor treatment, and to rational selection of combination therapies that include PDT as a component.

Accumulation and elimination of photosens and protoporphyrin IX by different types of mesenchymal cells

We studied the kinetics of accumulation and elimination of Photosens and accumulation of protoporphyrin IX in macrophages, endothelial cells, and mesenchymal stromal cells of the human adipose tissue in vitro. In all studied cells, the dynamics of Photosens accumulation was described by a multiphase curve and the maximum accumulation of the dye was observed during the second exponential phase. Elimination of Photosens did not depend on the cell function. Accumulation of protoporphyrin IX differed considerably in different cells: it was maximum in mesenchymal stromal cells was practically not detected in endothelial cells. Accumulation of the dye by macrophages depended on individual donor characteristics.

The effects of protoporphyrin IX-induced photodynamic therapy with and without iron chelation on human squamous carcinoma cells cultured under normoxic, hypoxic and hyperoxic conditions

BACKGROUND

Photodynamic therapy requires the combined interaction of a photosensitiser, light and oxygen to ablate target tissue. In this study we examined the effect of iron chelation and oxygen environment manipulation on the accumulation of the clinically useful photosensitiser protoporphyrin IX (PpIX) within human squamous epithelial carcinoma cells and the subsequent ablation of these cells on irradiation.

METHODS

Cells were incubated at concentrations of 5%, 20% or 40% oxygen for 24h prior to and for 3h following the administration of the PpIX precursors aminolevulinic acid (ALA), methyl aminolevulinate (MAL) or hexylaminolevulinate (HAL) with or without the iron chelator 1,2-diethyl-3-hydroxypyridin-4-one hydrochloride (CP94). PpIX accumulation was monitored using a fluorescence plate reader, cells were irradiated with 37 J/cm(2) red light and cell viability measured using the neutral red uptake assay.

RESULTS

Manipulation of the oxygen environment and/or co-administration of CP94 with PpIX precursors resulted in significant changes in both PpIX accumulation and photobleaching. Incubation with 5% or 40% oxygen produced the greatest levels of PpIX and photobleaching in cells incubated with ALA/MAL. Incorporation of CP94 also resulted in significant decreases in cell viability following administration of ALA/MAL/HAL, with oxygen concentration predominantly having a significant effect in cells incubated with HAL.

CONCLUSIONS

Experimentation with human squamous epithelial carcinoma cells has indicated that the iron chelator CP94 significantly increased PpIX accumulation induced by each PpIX congener investigated (ALA/MAL/HAL) at all oxygen concentrations employed (5%/20%/40%) resulting in increased levels of photobleaching and reduced cell viability on irradiation. Further detailed investigation of the complex relationship of PDT cytotoxicity at various oxygen concentrations is required. It is therefore concluded that iron chelation with CP94 is a simple protocol modification with which it may be much easier to enhance clinical PDT efficacy than the complex and less well understood process of oxygen manipulation.

Veterinary photodynamic therapy: a review

Whereas in human medicine photodynamic therapy represents a well-known and recognized treatment option for diverse indications, it is still little known and unfortunately not yet established treatment option for pets. Various photosensitizers and light sources have been used and clinical results have been published. The main indication is a frequently occurring skin tumor in cats: in situ carcinoma/squamous cell carcinoma, mainly found in not or only slightly pigmented areas of the head. For early stages of this tumor, promising results have been published, partly using new, selective drugs to decrease light sensitivity after systemic administration and to increase response rates. Other possible indications are urinary tract neoplasia of dogs and equine sarcoids, the latter representing very common tumors in horses where no effective treatment is known so far. This review article summarizes the role of photodynamic therapy in veterinary medicine.

Monitoring photodynamic therapy of head and neck malignancies with optical spectroscopies

In recent years there has been significant developments in photosensitizers (PSs), light sources and light delivery systems that have allowed decreasing the treatment time and skin phototoxicity resulting in more frequent use of photodynamic therapy (PDT) in the clinical settings. Compared to standard treatment approaches such as chemo-radiation and surgery, PDT has much reduced morbidity for head and neck malignancies and is becoming an alternative treatment option. It can be used as an adjunct therapy to other treatment modalities without any additive cumulative side effects. Surface illumination can be an option for pre-malignant and early-stage malignancies while interstitial treatment is for debulking of thick tumors in the head and neck region. PDT can achieve equivalent or greater efficacy in treating head and neck malignancies, suggesting that it may be considered as a first line therapy in the future. Despite progressive development, clinical PDT needs improvement in several topics for wider acceptance including standardization of protocols that involve the same administrated light and PS doses and establishing quantitative tools for PDT dosimetry planning and response monitoring. Quantitative measures such as optical parameters, PS concentration, tissue oxygenation and blood flow are essential for accurate PDT dosimetry as well as PDT response monitoring and assessing therapy outcome. Unlike conventional imaging modalities like magnetic resonance imaging, novel optical imaging techniques can quantify PDT-related parameters without any contrast agent administration and enable real-time assessment during PDT for providing fast feedback to clinicians. Ongoing developments in optical imaging offer the promise of optimization of PDT protocols with improved outcomes.

Single continuous wave laser induced photodynamic/plasmonic photothermal therapy using photosensitizer-functionalized gold nanostars

Chlorin e6 conjugated gold nanostars (GNS-PEG-Ce6) are used to perform simultaneous photodynamic/plasmonic photothermal therapy (PDT/PPTT) upon single laser irradiation. The early-phase PDT effect is coordinated with the late-phase PPTT effect to obtain synergistic anticancer efficiency. The prepared GNS-PEG-Ce6 shows excellent water dispersibility, good biocompatibility, enhanced cellular uptake and remarkable anticancer efficiency upon irradiation in vivo.

Unique diagnostic and therapeutic roles of porphyrins and phthalocyanines in photodynamic therapy, imaging and theranostics

Porphyrinic molecules have a unique theranostic role in disease therapy; they have been used to image, detect and treat different forms of diseased tissue including age-related macular degeneration and a number of different cancer types. Current focus is on the clinical imaging of tumour tissue; targeted delivery of photosensitisers and the potential of photosensitisers in multimodal biomedical theranostic nanoplatforms. The roles of porphyrinic molecules in imaging and pdt, along with research into improving their selective uptake in diseased tissue and their utility in theranostic applications are highlighted in this Review.

DMBA-induced hamster buccal pouch carcinoma and VX2-induced rabbit cancer as a model for human oral carcinogenesis

In this article, we have described and compared the advantages and disadvantages of two potential animal cancer models (the hamster buccal pouch cancer model and the VX2-induced rabbit cancer model) for human squamous cell carcinomas of the oral mucosa. Currently, no animal cancer model is perfectly applicable to human oral squamous cell carcinomas. This is because the hamster buccal pouch cancer model has a different etiology and genetic constitution compared with human oral carcinomas. In addition, the VX2-induced rabbit cancer model is not produced in situ and, consequently, its natural behavior is totally reliant on the location of transplantation. Nonetheless, with the use of these two animal cancer models together, researchers could evaluate different aspects of the cellular and molecular biological characteristics or assess potential novel treatment regimens for squamous cell carcinomas of the human oral mucosa.

Light delivery over extended time periods enhances the effectiveness of photodynamic therapy

PURPOSE

The rate of energy delivery is a principal factor determining the biological consequences of photodynamic therapy (PDT). In contrast to conventional high-irradiance treatments, recent preclinical and clinical studies have focused on low-irradiance schemes. The objective of this study was to investigate the relationship between irradiance, photosensitizer dose, and PDT dose with regard to treatment outcome and tumor oxygenation in a rat tumor model.

EXPERIMENTAL DESIGN

Using the photosensitizer HPPH (2-[1-hexyloxyethyl]-2-devinyl pyropheophorbide), a wide range of PDT doses that included clinically relevant photosensitizer concentrations was evaluated. Magnetic resonance imaging and oxygen tension measurements were done along with the Evans blue exclusion assay to assess vascular response, oxygenation status, and tumor necrosis.

RESULTS

In contrast to high-incident laser power (150 mW), low-power regimens (7 mW) yielded effective tumor destruction. This was largely independent of PDT dose (drug-light product), with up to 30-fold differences in photosensitizer dose and 15-fold differences in drug-light product. For all drug-light products, the duration of light treatment positively influenced tumor response. Regimens using treatment times of 120 to 240 min showed marked reduction in signal intensity in T2-weighted magnetic resonance images at both low (0.1 mg/kg) and high (3 mg/kg) drug doses compared with short-duration (6-11 min) regimens. Significantly greater reductions in pO(2) were observed with extended exposures, which persisted after completion of treatment.

CONCLUSIONS

These results confirm the benefit of prolonged light exposure, identify vascular response as a major contributor, and suggest that duration of light treatment (time) may be an important new treatment variable.

The physics, biophysics and technology of photodynamic therapy

Photodynamic therapy (PDT) uses light-activated drugs to treat diseases ranging from cancer to age-related macular degeneration and antibiotic-resistant infections. This paper reviews the current status of PDT with an emphasis on the contributions of physics, biophysics and technology, and the challenges remaining in the optimization and adoption of this treatment modality. A theme of the review is the complexity of PDT dosimetry due to the dynamic nature of the three essential components -- light, photosensitizer and oxygen. Considerable progress has been made in understanding the problem and in developing instruments to measure all three, so that optimization of individual PDT treatments is becoming a feasible target. The final section of the review introduces some new frontiers of research including low dose rate (metronomic) PDT, two-photon PDT, activatable PDT molecular beacons and nanoparticle-based PDT.

Hypericin-mediated photodynamic therapy in combination with Avastin (bevacizumab) improves tumor response by downregulating angiogenic proteins

Photodynamic therapy (PDT) is a therapeutic modality in which a photosensitizer is locally or systemically administered followed by light irradiation of suitable wavelength to achieve selective tissue damage. In addition, PDT is an oxygen-consuming reaction, that causes hypoxia mediated destruction of tumor vasculature that results in effective treatment. However, the hypoxic condition within tumors can cause stress-related release of angiogenic growth factors and cytokines and this inflammatory response could possibly diminish the efficacy of PDT by promoting tumor regrowth. In such circumstances, PDT effectiveness can be enhanced by combining angiogenesis inhibitors into the treatment regimen. Avastin (bevacizumab), a vascular endothelial growth factor (VEGF) specific monoclonal antibody in combination with chemotherapy is offering hope to patients with metastatic colorectal cancer. In this study we evaluated the combination of hypericin-mediated PDT and Avastin on VEGF levels as well as its effect on overall tumor response. Experiments were conducted on bladder carcinoma xenografts established subcutaneously in Balb/c nude mice. Antibody array, enzyme-linked immunosorbent assay (ELISA) and immunohistochemistry (IHC) were performed to assess VEGF concentrations in the various treatment groups. Our results demonstrated that the targeted therapy by Avastin along with PDT can improve tumor responsiveness in bladder tumor xenografts. Immunostaining showed minimal expression of VEGF in tumors treated with combination therapy of PDT and Avastin. Angiogenic proteins e.g., angiogenin, basic fibroblast growth factor (bFGF), epidermal growth factor (EGF) and interleukins (IL-6 and IL-8) were also found to be downregulated in groups treated with combination therapy.

The role of oxygen monitoring during photodynamic therapy and its potential for treatment dosimetry

Understanding of the biology of photodynamic therapy (PDT) has expanded tremendously over the past few years. However, in the clinical situation, it is still a challenge to match the extent of PDT effects to the extent of the disease process being treated. PDT requires drug, light and oxygen, any of which can be the limiting factor in determining efficacy at each point in a target organ. This article reviews techniques available for monitoring tissue oxygenation during PDT. Point measurements can be made using oxygen electrodes or luminescence-based optodes for direct measurements of tissue pO2, or using optical spectroscopy for measuring the oxygen saturation of haemoglobin. Imaging is considerably more complex, but may become feasible with techniques like BOLD MRI. Pre-clinical studies have shown dramatic changes in oxygenation during PDT, which vary with the photosensitizer used and the light delivery regimen. Better oxygenation throughout treatment is achieved if the light fluence rate is kept low as this reduces the rate of oxygen consumption. The relationship between tissue oxygenation and PDT effect is complex and remarkably few studies have directly correlated oxygenation changes during PDT with the final biological effect, although those that have confirm the value of maintaining good oxygenation. Real time monitoring to ensure adequate oxygenation at strategic points in target tissues during PDT is likely to be important, particularly in the image guided treatment of tumours of solid organs.

Milestones in the development of photodynamic therapy and fluorescence diagnosis

Many reviews on PDT have been published. This field is now so large, and embraces so many sub-specialties, from laser technology and optical penetration through diffusing media to a number of medical fields including dermatology, gastroenterology, ophthalmology, blood sterilization and treatment of microbial-viral diseases, that it is impossible to cover all aspects in a single review. Here, we will concentrate on a few basic aspects, all important for the route of development leading PDT to its present state: early work on hematoporphyrin and hematoporphyrin derivative, second and third generation photosensitizers, 5-aminolevulinic acid and its derivatives, oxygen and singlet oxygen, PDT effects on cell organelles, mutagenic potential, the basis for tumour selectivity, cell cooperativity, photochemical internalization, light penetration into tissue and the significance of oxygen depletion, photobleaching of photosensitizers, optimal light sources, effects on the immune system, and, finally, future trends.

Interstitial photodynamic therapy of the canine prostate using intra-arterial administration of photosensitizer and computerized pulsed light delivery

PURPOSE

We determined the feasibility of complete treatment of the canine prostate and long-term effectiveness of interstitial photodynamic therapy using the intra-arterial photosensitizer QLT0074 (benzoporphyrin derivative 1,3-diene C,D-diethylene glycol ester A ring) (QLT, Vancouver, British Columbia, Canada) administration and pulsed light delivery.

MATERIALS AND METHODS

The prostate gland of 11 dogs were infused with QLT0074 via the prostatovesical arteries (2 mg drug per artery bilaterally) under fluoroscopic guidance. Immediately following infusion the prostate was surgically exposed and 7 optical fibers with 1.5 cm cylindrical diffusers in after loading sheaths were inserted into the prostate through a template. Light was delivered sequentially to the optic fibers via a computer driven switch system. One dog was sacrificed 6 days after photodynamic therapy to assess acute tissue effects. The other 10 dogs were monitored for clinical tolerance and urinary function, and sacrificed at between 3 and 11 months. Prostate specimens were examined microscopically to evaluate long-term tissue reactions.

RESULTS

Comprehensive destruction of the prostate was noted in the acute dog. Except for urinary retention and mild hematuria no other perioperative complications were observed in the chronic dogs. Urodynamic examination did not reveal deleterious bladder and urethral function. Average prostate volume decreased 71% at 3 months and 56% after 6 months (p=0.007 and 0.014, respectively). Microscopic evaluation revealed prostate glandular epithelial atrophy, stromal fibrosis and mononuclear cell infiltration.

CONCLUSIONS

Interstitial photodynamic therapy using intra-arterial QLT0074 and pulsed light delivery is safe and feasible for comprehensive destruction of the canine prostate. Clinical trials are required to confirm it for managing prostate diseases.