The biophysical foundations of photodynamic therapy

Daylight-PDT: everything under the sun

5-Aminolevulinic acid-based photodynamic therapy (ALA-PDT) was first implemented over three decades ago and has since been mainly part of clinical practice for the management of pre-cancerous and cancerous skin lesions. Photodynamic therapy relies on the combination of a photosensitizer, light and oxygen to cause photo-oxidative damage of cellular components. 5-Aminolevulinic acid (ALA) is a natural precursor of the heme biosynthetic pathway, which when exogenously administered leads to the accumulation of the photoactivatable protoporphyrin IX. Although, effective and providing excellent cosmetic outcomes, its use has been restricted by the burning, stinging, and prickling sensation associated with treatment, as well as cutaneous adverse reactions that may be induced. Despite intense research in the realm of drug delivery, pain moderation, and light delivery, a novel protocol design using sunlight has led to some of the best results in terms of treatment response and patient satisfaction. Daylight PDT is the protocol of choice for the management of treatment of multiple or confluent actinic keratoses (AK) skin lesions. This review aims to revisit the photophysical, physicochemical and biological characteristics of ALA-PDT, and the underlying mechanisms resulting in daylight PDT efficiency and limitations.

Antitumor Immune Response Triggered by Metal-Based Photosensitizers for Photodynamic Therapy: Where Are We?

Metal complexes based on transition metals have rich photochemical and photophysical properties that are derived from a variety of excited state electronic configurations triggered by visible and near-infrared light. These properties can be exploited to produce powerful energy and electron transfer processes that can lead to oxygen-(in)dependent photobiological activity. These principles are the basis of photodynamic therapy (PDT), which is a clinically approved treatment that offers a promising, effective, and noninvasive complementary treatment or even an alternative to treat several types of cancers. PDT is based on a reaction involving a photosensitizer (PS), light, and oxygen, which ultimately generates cytotoxic reactive oxygen species (ROS). However, skin photosensitivity, due to the accumulation of PSs in skin cells, has hampered, among other elements, its clinical development and application. Therefore, these is an increasing interest in the use of (metal-based) PSs that are more specific to tumor cells. This may increase efficacy and corollary decrease side-effects. To this end, metal-containing nanoparticles with photosensitizing properties have recently been developed. In addition, several studies have reported that the use of immunogenic/immunomodulatory metal-based nanoparticles increases the antitumor efficacy of immune-checkpoint inhibitor-based immunotherapy mediated by anti-PD-(L)1 or CTLA-4 antibodies. In this review, we discuss the main metal complexes used as PDT PSs. Lastly, we review the preclinical studies associated with metal-based PDT PSs and immunotherapies. This therapeutic association could stimulate PDT.

From molecules to nanovectors: Current state of the art and applications of photosensitizers in photodynamic therapy

Photodynamic therapy (PDT) is a concept based on a selective activation by light of drugs called photosensitizers (PS) leading to reactive oxygen species production responsible for cell destruction. Mechanisms of photodynamic reaction and cell photo-destruction following direct or indirect mechanisms will be presented as well as PS classification, from first generation molecules developed in the 1960 s to third generation vectorized PS with improved affinity for tumor cells. Many clinical applications in dermatology, ophthalmology, urology, gastroenterology, gynecology, neurosurgery and pneumology reported encouraging results in human tumor management. However, this interesting technique needs improvements that are currently investigated in the field of PS excitation by the design of new PS intended for two-photon excitation or for X-ray excitation. The former excitation technique is allowing better light penetration and preservation of healthy tissues while the latter is combining PDT and radiotherapy so that external light sources are no longer needed to generate the photodynamic effect. Nanotechnology can also improve the PS to reach the tumor cells by grafting addressing molecule and by increasing its aqueous solubility and consequently its bioavailability by encapsulation in synthetic or biogenic nanovector systems, ensuring good drug protection and targeting. Co-internalization of PS with magnetic nanoparticles in multifunctional vectors or stealth nanoplatforms allows a theranostic anticancer approach. Finally, a new category of inorganic PS will be presented with promising results on cancer cell destruction.

Enhancement of photo-bactericidal effect of tetrasulfonated hydroxyaluminum phthalocyanine on Pseudomonas aeruginosa

At the present time, photodynamic inactivation (PDI) is receiving considerable interest for its potential as an antimicrobial therapy. The results of our study indicate that enhancement of the phototoxic effect on Pseudomonas aeruginosa can be achieved by combination of tetrasulfonated hydroxyaluminum phthalocyanine (AlPcS₄) and bimetallic gold/silver nanoparticles (Au/Ag-NPs) synthesized by the cell-free filtrate of Aureobasidium pullulans. The bimetallic nanoparticles were characterized by a number of techniques including UV-vis, XPS, TEM, and SEM-EDS to be 14 ± 3 nm spherical particles coated with proteins. The effect of diode lasers with the peak-power wavelength ʎ = 650 nm (output power of 10 and 40 mW; radiation intensity of 26 and 105 mW/cm²) in combination with the AlPcS₄ and the bimetallic nanoparticles mixture on the viability of P. aeruginosa rods was shown. Particularly high efficiency of killing bacterial cells was obtained for the light intensity of 105 mW/cm², after 20, 30, and 40 min of irradiation corresponding to 126, 189^, and 252 J/cm² energy fluences. For AlPcS₄+Au/Ag-NPs treatment, the viable count reduction were equal to 99.90, 99.96, and 99.975%, respectively. These results were significantly better than those accomplished for irradiated separated assays of AlPcS₄ and Au/Ag-NPs.

Antimicrobial photodynamic inactivation in nanomedicine: small light strides against bad bugs

The relentless advance of drug-resistance among pathogenic microbes, mandates a search for alternative approaches that will not cause resistance. Photodynamic inactivation (PDI) involves the combination of nontoxic dyes with harmless visible light to produce reactive oxygen species that can selectively kill microbial cells. PDI can be broad-spectrum in nature and can also destroy microbial cells in biofilms. Many different kinds of nanoparticles have been studied to potentiate antimicrobial PDI by improving photosensitizer solubility, photochemistry, photophysics and targeting. This review will cover photocatalytic disinfection with titania nanoparticles, carbon nanomaterials (fullerenes, carbon nanotubes and graphene), liposomes and polymeric nanoparticles. Natural polymers (chitosan and cellulose), gold and silver plasmonic nanoparticles, mesoporous silica, magnetic and upconverting nanoparticles have all been used for PDI.

Photodynamic therapy enhanced by hyperbaric oxygenation in palliation of malignant pleural mesothelioma: clinical experience

INTRODUCTION

Surgical debulking followed by radiotherapy/chemotherapy are the standards in the palliative treatment schedule of malignant pleural mesothelioma. The aim of this study was to evaluate the additional effect of intraoperative photodynamic therapy (PDT) under hyperbaric oxygenation (HBO) if compared to decortication alone.

PATIENTS AND METHODS

From January 1993 to August 2003, decortication was done in 34 patients (28 males, 6 females; mean age: 65 years) suffering from advanced malignant pleural mesothelioma. Twenty-two patients received additional intraoperative PDT under HBO. The surgery and PDT/HBO was done 48h after photosensitization with a polyhematoporphyrin, 2mg/kg BW using a diode laser delivering red light at 630nm through a microlens. The light dose was calculated for 300J at a distance of 1cm from the tumour surface.

RESULTS

At 6-month follow-up the Karnofsky performance status showed no significant difference (P≥0.05) between both groups. CT scans documented focal regrowth of the tumour after 6 months in 10/12 cases of the non-PDT group. However, in the PDT group tumour regrowth was detected in only 9/22 cases at 6-month follow-up. Survival analysis showed a significant advantage for the group with PDT (log-rank test: P=0.0179).

CONCLUSION

Although the study includes only a small number of patients, it indicates that additional PDT/HBO represents a safe and technically feasible approach in the palliative setting of advanced malignant mesothelioma of the pleura.

Laser technology and applications in gynaecology

The term 'laser' is an acronym for Light Amplification by Stimulated Emission of Radiation. Lasers are commonly described by the emitted wavelength, which determines the colour of the light, as well as the active lasing medium. Currently, over 40 types of lasers have been developed with a wide range of both industrial and medical uses. Gas and solid-state lasers are frequently used in surgical applications, with CO2 and Ar being the most common examples of gas lasers, and the Nd:YAG and KTP:YAG being the most common examples of solid-state lasers. At present, it appears that the CO2, Nd:YAG, and KTP lasers provide alternative methods for achieving similar results, as opposed to superior results, when compared with traditional endoscopic techniques, such as cold-cutting monopolar and bipolar energy. This review focuses on the physics, tissue interaction, safety and applications of commonly used lasers in gynaecological surgery.

Individualized, multimodal palliative treatment of inoperable esophageal cancer: clinical impact of photodynamic therapy resulting in prolonged survival

BACKGROUND AND OBJECTIVE

In esophageal carcinoma palliative treatment is often required due to advanced tumor stage or patient-related factors. The main goal of our retrospective single center study was to evaluate the effect of an individualized multimodal palliative treatment, focusing on the efficacy of different treatment options.

MATERIALS AND METHODS

Between 1999 and 2009, 640 patients suffering from esophageal carcinoma were referred to our division. Two hundred fifty out of those (39.1%) were treated with palliative intention by using a individualized, multimodal concept including endoscopic dilatation, photodynamic therapy (PDT), endoluminal brachytherapy, external radiation, chemotherapy, stenting, feeding tube, and palliative resection.

RESULTS

There were 37 women (14.9%) and 211 men (85.1%). The treatment included PDT in 171 cases (in 118 as first measure), stenting in 124 (38), dilatation in 83 (24), endoluminal brachytherapy in 92 (20), feeding enterostomy in 40 (14), external radiation in 67 (23), chemotherapy in 57 (29), and palliative resection in 3 patients. The mean number of palliative treatments per patient was 2.6. Mean survival time for the collective was 34 months. Distant metastases and nodal positivity were connected with a significantly reduced survival. If PDT was used in the first place, median survival was 50.9 months compared to 17.3 months if other options were used as initial modality (P = 0.012).

CONCLUSION

By using an individualized multimodal approach, an acceptable mean survival time can be achieved in advanced esophageal cancer treated with palliative intention. PDT, if used as initial endoluminal treatment in patients without gross tumor infiltration into the mediastinum, the great vessels or the tracheo-bronchial tree, enables a considerable beneficial effect in the palliative setting.

Evaluation of EPR monitoring of singlet oxygen production using the photosensitizer chloroboron subphthalocyanine

Singlet molecular oxygen produced in the presence of 2,2,6,6-tetramethyl-4-piperidone (TMPD) in 1,4-dioxan, by boron subphthalocyanine chloride as the sensitizer, was monitored by Electron Paramagnetic Resonance (EPR) via the oxidation of TMPD to the corresponding aminoxyl radical. This radical product is formed in low yields along the singlet oxygen pathway. A kinetic analysis of the process allows one to understand the reasons behind this, while affording more accurate quantitative insights into the mechanistic details. A crucial aspect of this reaction system, which explains the low aminoxyl radical yields along the singlet oxygen pathway, is the disappearance of the sensitizer triplet state in a reaction with TMPD, which has a rate constant of 1 × 109 M-1.s-1.

Aminolevulinic acid-photodynamic therapy combined with topically applied vascular disrupting agent vadimezan leads to enhanced antitumor responses

The tumor vascular-disrupting agent (VDA) vadimezan (5,6-dimethylxanthenone-4-acetic acid, DMXAA) has been shown to potentiate the antitumor activity of photodynamic therapy (PDT) using systemically administered photosensitizers. Here, we characterized the response of subcutaneous syngeneic Colon26 murine colon adenocarcinoma tumors to PDT using the locally applied photosensitizer precursor aminolevulinic acid (ALA) in combination with a topical formulation of vadimezan. Diffuse correlation spectroscopy (DCS), a noninvasive method for monitoring blood flow, was utilized to determine tumor vascular response to treatment. In addition, correlative CD31-immunohistochemistry to visualize endothelial damage, ELISA to measure induction of tumor necrosis factor-alpha (TNF-α) and tumor weight measurements were also examined in separate animals. In our previous work, DCS revealed a selective decrease in tumor blood flow over time following topical vadimezan. ALA-PDT treatment also induced a decrease in tumor blood flow. The onset of blood flow reduction was rapid in tumors treated with both ALA-PDT and vadimezan. CD31-immunostaining of tumor sections confirmed vascular damage following topical application of vadimezan. Tumor weight measurements revealed enhanced tumor growth inhibition with combination treatment compared with ALA-PDT or vadimezan treatment alone. In conclusion, vadimezan as a topical agent enhances treatment efficacy when combined with ALA-PDT. This combination could be useful in clinical applications.

Pharmacokinetics and biodistribution of Photolon (Fotolon) in intact and tumor-bearing rats

BACKGROUND

This paper provides the results of the non-clinical evaluation of biodistribution of the PS Photolon in inner organs and tissues of intact and tumor-bearing rats with xenograft tumors of different morphologic types.

METHODS

The accumulation studies were performed in rats by means of intravital laser fluorimetry in situ and spectrophotometric determination ex vivo.

RESULTS

The biodistribution pattern of Photolon does not depend on tumor carriage as well as on morphologic type of the xenograft tumor. We have also showed that Photolon easily crosses an intact blood-brain barrier and accumulates in tissues of central nervous system. The relative bioavailability of brain tissues for Photolon was estimated as 82%, T(max)-30 min, mean residual time (MRT)-1.6h.

CONCLUSIONS

In general, results of the experimental study of biodistribution of Photolon in inner organs and tissues of rats, performed as in real time (by means of intravital laser fluorimetry in situ) as ex vivo (spectrophotometric assay) can be utilized while optimizing existing regimens of PDT with the purpose to increase safety and efficacy of treatment as well as for the development of new PDT protocols with Photolon applied for new indications. Parameters of pharmacokinetics and biodistribution of Photolon/Fotolon as well as its' ability to cross an intact blood-brain barrier, are optimal for the majority of modern clinical applications of PDT.

Protoporphyrin IX fluorescence photobleaching increases with the use of fractionated irradiation in the esophagus

Fluorescence measurements have been used to track the dosimetry of photodynamic therapy (PDT) for many years, and this approach can be especially important for treatments with aminolevulinic-acid-induced protoporphyrin IX (ALA-PpIX). PpIX photobleaches rapidly, and the bleaching is known to be oxygen dependent, and at the same time, fractionation or reduced irradiance treatments have been shown to significantly increase efficacy. Thus, in vivo measurement of either the bleaching rate and/or the total bleaching yield could be used to track the deposited dose in tissue and determine the optimal treatment plans. Fluorescence in rat esophagus and human Barrett's esophagus are measured during PDT in both continuous and fractionated light delivery treatment, and the bleaching is quantified. Reducing the optical irradiance from 50 to 25 mWcm did not significantly alter photobleaching in rat esophagus, but fractionation of the light at 1-min on and off intervals did increase photobleaching up to 10% more (p value=0.02) and up to 25% more in the human Barrett's tissue (p value<0.001). While two different tissues and two different dosimetry systems are used, the data support the overall hypothesis that light fractionation in ALA-PpIX PDT esophageal treatments should have a beneficial effect on the total treatment effect.

Monitoring singlet oxygen in situ with delayed chemiluminescence to deduce the effect of photodynamic therapy

Singlet oxygen ((1)O(2)) is an important factor mediating cell killing in photodynamic therapy (PDT). We previously reported that chemiluminescence (CL) can be used to detect (1)O(2) production in PDT and linked the signal to the PDT-induced cytotoxicity in vitro. We develop a new CL detection apparatus to achieve in vivo measurements. The system utilizes a time-delayed CL signal to overcome the interference from scattered excitation light, thus greatly improving the accuracy of the detection. The system is tested on healthy skin of BALB/ca mouse for its feasibility and reliability. The CL measurement is made during a synchronized gating period of the irradiation light. After each PDT treatment and in situ CL measurement, the skin response is scored over a period of 2 weeks. A remarkable relationship is observed between the score and the CL, regardless of the PDT treatment protocol. Although there are many issues yet to be addressed, our results clearly demonstrate the feasibility of CL measurement during PDT and its potential for in vivo PDT dosimetry. This requires further investigations.

Plasmonic engineering of singlet oxygen generation

In this article, we report metal-enhanced singlet oxygen generation (ME(1)O2). We demonstrate a direct relationship between the singlet oxygen yield of a common photosensitizer (Rose Bengal) and the theoretical electric field enhancement or enhanced absorption of the photosensitizer in proximity to metallic nanoparticles. Using a series of photosensitizers, sandwiched between silver island films (SiFs), we report that the extent of singlet oxygen enhancement is inversely proportional to the free space singlet oxygen quantum yield. By modifying plasmon coupling parameters, such as nanoparticle size and shape, fluorophore/particle distance, and the excitation wavelength of the coupling photosensitizer, we can readily tune singlet oxygen yields for applications in singlet oxygen-based clinical therapy.

In vivo monitoring of singlet oxygen using delayed chemiluminescence during photodynamic therapy

It is known that singlet oxygen ((1)O(2)) is the main factor mediating cytotoxicity in photodynamic therapy (PDT). The effectiveness of a PDT treatment is directly linked to the (1)O(2) produced in the target. Although the luminescence from (1)O(2) is suggested as an indicator for evaluating photodynamic therapy, the inherent disadvantages limit its potential for in vivo applications. We have previously reported that chemiluminescence can be used to detect (1)O(2) production in PDT and have linked the signal to the cytotoxicity. We further our investigation for monitoring (1)O(2) production during PDT. The lifetime of 3,7-dihydro-6-{4-[2-(N(')-(5-fluoresceinyl)thioureido)ethoxy]phenyl}-2-methylimidazo {1,2-a} pyrazin-3-one-chemiluminescence (FCLA-CL) is evaluated, and the results show that it is much longer than that of direct luminescence of (1)O(2). A gated measurement algorithm is developed to fully utilize the longer lifetime for a clean measurement of the CL without the interference from the irradiation light. The results show that it is practically feasible to use the technique to monitor the (1)O(2). Compared to the direct (1)O(2) luminescence measurement, our new technique is sensitive and can be realized with a conventional optical detector with excellent signal-to-noise ratio. It thus provides a means for real-time in vivo monitoring of (1)O(2) production during PDT.

Optical properties of adenocarcinoma and squamous cell carcinoma of the gastroesophageal junction

Photodynamic therapy (PDT) is an alternative to radical surgical resection for T1a or nonresectable carcinomas of the gastroesophageal junction. Besides the concentration of the photosensitizer, the light distribution in tissue is responsible for tumor destruction. For this reason, knowledge about the behavior of light in healthy and dysplastic tissue is of great interest for careful irradiation scheduling. The aim of this study is to determine the optical parameters (OP) of healthy and carcinomatous tissue of the gastroesophageal junction in vitro to provide reproducible parameters for optimal dosimetry when applying PDT. A total of 36 tissue samples [adenocarcinoma tissue (n=21), squamous cell tissue (n=15)] are obtained from patients with carcinomas of the gastroesophageal junction. The optical parameters are measured in 10-nm steps using new integrating sphere spectrometers in the PDT-relevant wavelength range of 300 to 1140 nm and evaluated by inverse Monte-Carlo simulation. Additional examinations are done in healthy tissue from the surgical safety margin. In the wavelength range of frequently applied photosensitizers at 330, 630, and 650 nm, the absorption coefficient in tumor tissue (adenocarcinoma 1.22, 0.16, and 0.15 mm(-1); squamous cell carcinoma 1.48, 0.13, and 0.11 mm(-1)) is significantly lower than in healthy tissue (stomach 3.34, 0.26, and 0.20 mm(-1); esophagus 2.47, 0.21, and 0.18 mm(-1)). The scattering coefficient of all tissues decreases continuously with increasing wavelength (adenocarcinoma 22.8, 12.99, and 12.52 mm(-1); squamous cell carcinoma 19.44, 9.35, and 8.98 mm(-1); stomach 20.55, 13.96, and 13.94 mm(-1); esophagus 20.34, 12.56, and 12.22 mm(-1). All tissues show an anisotropy factor between 0.80 and 0.94 over the entire spectrum. The maximum optical penetration depth for all tissues is achieved in the range of 800 to 1100 nm. At the wavelength range of 330, 630, and 650 nm, the optical penetration depth is significantly higher in carcinoma tissue (adenocarcinoma 0.27, 1.54, and 1.66 mm; squamous cell carcinoma 0.23, 1.71, and 1.84 mm) than in healthy tissue (stomach 0.16, 1.10, and 1.26 mm; esophagus 0.17, 1.47, and 1.65 mm; p<0.05). Above 1000 nm, a higher absorption coefficient of tumor tissue results in a lower optical penetration depth than in healthy tissue (p<0.05). The higher absorption and scattering of the tumor tissue in the wavelength range of available photosensitizer is associated with a low optical penetration depth. This necessitates higher energy doses and long application times or repeated applications to effectively treat large tumor volumes. Photosensitizers optimized for larger wavelength range need to be developed to increase the efficacy of PDT.

The history of PDT in Norway Part one: Identification of basic mechanisms of general PDT

Photodynamic therapy (PDT) is now an established treatment of malignant and premalignant dysplasias. A number of first and second generation photosensitizers have been studied in Norway. The aim has been to improve PDT efficiency and applicability. Many critical details regarding the mechanisms of PDT were elucidated by researchers in Norway. In this review we focus on the most important findings related to these basic mechanisms, such as generation of singlet oxygen, estimations of its lifetime, the oxygen effect itself, the subcellular localization of photosensitizers with different properties, their photodegradation during PDT and their tumour selectivity.

Topical application of 5-aminolaevulinic acid, methyl 5-aminolaevulinate and hexyl 5-aminolaevulinate on normal human skin

BACKGROUND

5-Aminolaevulinic acid (ALA) and its ester derivatives are used in photodynamic therapy. Despite extensive investigations, the differences in biodistribution and pharmacokinetics of protoporphyrin IX (PpIX) induced by ALA and its derivatives are still not well understood, notably for humans.

OBJECTIVES

To study porphyrin accumulation after topical application of ALA and two of its ester derivatives in normal human skin.

METHODS

Creams containing 0.2%, 2% and 20% (w/w) of ALA, methyl 5-aminolaevulinate (MAL) and hexyl 5-aminolaevulinate (HAL) were applied on normal human skin of six volunteers. The amount and distribution of porphyrins formed in the skin was investigated noninvasively by means of fluorescence spectroscopy.

RESULTS

Fluorescence emission and excitation spectra exhibited similar spectral shapes for the all drugs, indicating that mainly PpIX was formed. Low concentrations (0.2% and 2%) of MAL induced considerably less PpIX in normal human skin than similar concentrations of ALA and HAL. A high concentration (20%) of ALA gave higher PpIX fluorescence in normal human skin than was found for MAL and HAL.

CONCLUSIONS

The concentrations inducing half of the maximal PpIX fluorescence are around 2% for ALA, 8% for MAL and 1% for HAL.

Influence of light exposure on the kinetics of protoporphyrin IX formation in normal skin of hairless mice after application of 5-aminolevulinic acid methyl ester

The rates of protoporphyrin IX (PpIX) photodegradation and reappearance after light exposure at 420 and 632 nm were measured in mouse skin at different times after 1 h topical application of 5-aminolevulinic acid methyl ester (ALA-Me). After ALA-Me application (1 h) and removal, the fluorescence of PpIX increased for about 1 h, and then reached a maximum and started to decrease. Reappearance of PpIX fluorescence after exposures (degrading 60%-80% of the PpIX) was faster for exposures 0.5 h after ALA-Me application than for exposures 3 h. The bleaching rate was largest in the former case. This indicates that PpIX is located deeper in the skin after 3 h than after 0.5 h, whereas the pool of ALA-Me in the skin is largest at 0.5 h. In all cases, the reappearance was faster at a skin temperature of 35 degrees C than at 23 degrees C. Reappearance of PpIX fluorescence was faster after exposure to light at 420 nm than at 632 nm. The rate of elimination of PpIX from the volume of detection was faster after 420 nm light irradiation than that after 632 nm. These findings are discussed in view of penetration depths of light and ALA-Me, and diffusion of PpIX.

Phototherapy and malignancy: Possible enhancement by iron administration and hyperbaric oxygen

Photodynamic therapy (PDT) is a new therapeutic approach for the treatment of malignant tumors. Hyperbaric oxygen (HBO(2)) shows beneficial effects in various modalities of cancer interventions. Tumor cells tend to accumulate large amount of iron. There is interaction between tissue content of oxygen, iron, free radical production and tissue damage. Accumulation of intracellular iron is necessary for the production of oxygen radicals. HBO(2) increases tissue oxygen and hydrogen peroxide production in the cells. Malignant cells require iron, and exhibit more transferrin receptors. The photodynamic sensitization of human leukemic cells is achieved with accumulation of porphyrins stimulated by 5-aminolaevulanic acid (ALA) plus hemin. Further, a significant improvement in tumor response is obtained when PDT is delivered during hyperoxygenation. When PDT is combined with hyperoxygenation, the hypoxic condition is improved and the cell killing rate at various time points after PDT is significantly enhanced. Photosensitization with use of porphyrins is used with HBO(2) and PDT for treatment of certain tumors. PDT with ALA is used for treatment of actinic keratosis (AK). The combination of iron administration (by injection or oral rout), hemin, or transferrin, as a source for iron, HBO(2) as a source of oxygen under pressure and PDT as a source of generating free-radical tissue damage may be useful in the treatment of tumors. The possibility of combining HBO(2), iron, light and local photosensitizers to overcome skin tumors deserve extensive laboratory and clinical research work. Conclusively, iron, HBO(2), and PDT may have synergistic effect to hamper tumor cells.

Characterization of Photofrin photobleaching for singlet oxygen dose estimation during photodynamic therapy of MLL cells in vitro

A singlet oxygen dose model is developed for PDT with Photofrin. The model is based on photosensitizer photobleaching kinetics, and incorporates both singlet oxygen and non-singlet oxygen mediated bleaching mechanisms. To test our model, in vitro experiments were performed in which MatLyLu (MLL) cells were incubated in Photofrin and then irradiated with 532 nm light. Photofrin fluorescence was monitored during treatment and, at selected fluence levels, cell viability was determined using a colony formation assay. Cell survival correlated well to calculated singlet oxygen dose, independent of initial Photofrin concentration or oxygenation. About 2 x 10(8) molecules of singlet oxygen per cell were required to reduce the surviving fraction by 1/e. Analysis of the photobleaching kinetics suggests that the lifetime of singlet oxygen in cells is 0.048 +/- 0.005 micros. The generation of fluorescent photoproducts was not a result of singlet oxygen reactions exclusively, and therefore did not yield additional information to aid in quantifying singlet oxygen dose.

Photodynamic therapy for Bowen's disease and squamous cell carcinoma of the skin

BACKGROUND

Photodynamic therapy involves the activation by visible light of a previously administered photosensitizing agent in order to cause tumor necrosis. Skin tumors can be treated with topical photosensitizers and thus avoiding systemic side effects. In this study we evaluate the immediate and long-term effects of photodynamic therapy (PDT), using aminolevulinic acid (ALA) as a photosensitizer and a non-laser light source, on Bowen's disease (intra-epithelial squamous cell carcinoma) and on frank squamous cell carcinoma (SCC) of the skin.

METHODS

ALA in cream form (20%) was topically applied on biopsy-proven Bowen's disease or SCC of the skin. The lesions were covered with occlusive and light-shielding dressing. Sixteen hours later, they were submitted to a 10-min light session using Versa-Light™, a non-laser light source (spectral output of 580-720nm and 1250-1600nm, 100J/cm(2)). The initial evaluation was done 21 days post-treatment and every 3m thereafter. Patients that did not respond to treatment after two to three sessions were referred to surgery.

RESULTS

Forty Bowen's disease lesions (24 patients) and 43 SCC lesions (18 patients) underwent treatment. Median follow-up was 21±8m. No patient had any remarkable side effects. Thirty-four Bowen's disease (85%) lesions completely responded as did 32 SCC lesions (74%).

CONCLUSIONS

Our findings showed that PDT is highly effective in treating Bowen's disease and SCC lesions and can be used as a first treatment modality in so far as its use does not preclude the subsequent surgery recommended for the small percentage of failures.

Effectiveness of different light sources for 5-aminolevulinic acid photodynamic therapy

Many medical applications, including photodynamic therapy for cancer (PDT), involve the use of lasers. However, the coherence of laser light is not necessary for PDT, and attempts have been made to construct non-coherent light sources for PDT, which are relatively inexpensive, stable and easy to operate, require simple maintenance but differ fundamentally from the lasers in their output characteristics. In the present work we compared two clinically used lamps, CureLight1, which is a broadband source (560-740 nm) based on a filtered halogen lamp, and CureLight2, which is a narrowband source based on light-emitting diodes (LEDs), with respect to several parameters of crucial significance for PDT efficiency in vivo: (a) depth of action in tissues, (b) heating effects, (c) pain generation, (d) photodegradation of PpIX in solution, in cells and in mouse skin and (e) photo-inactivation of cells in vitro. We conclude that CureLight2 (LED), relative to CureLight1 (halogen) has deeper PDT action in tissue, similar efficiency for bleaching PpIX in mouse skin, better efficiency for bleaching PpIX in cells and solutions and good efficiency for inactivating cells in vitro. CureLight2 gives less heating of the tissue and less pain in unsensitised human skin. All these differences are related to difference in the spectra of the lamps. Thus, PDT light sources with emissions that are visually similar have significantly different photobiological properties.

A comparison of photodynamic therapy using topical methyl aminolevulinate (Metvix) with single cycle cryotherapy in patients with actinic keratosis: a prospective, randomized study

BACKGROUND

Actinic keratosis (AK) is a very common condition, which has the potential of progressing to squamous cell carcinoma. The present study is a prospective, randomized study comparing the lesion response, cosmetic outcome, patient satisfaction and tolerability of a new treatment modality, photodynamic therapy (PDT), using topical methyl aminolevulinate (Metvix), with the most commonly used standard therapy for AK, cryotherapy.

METHODS

A total of 204 patients with clinically diagnosed AK were randomized to either cryotherapy or PDT. The PDT patients were further assigned to an active or placebo group in a random, double-blind manner. Cryotherapy was performed using liquid nitrogen spray in a single freeze-thaw cycle. PDT was performed using 160 mg/g methyl aminolevulinate cream or placebo, a 3-hour application time, red light (570-670 nm) and a total light dose of 75 J/cm(2). PDT was repeated after 7 days. Two sessions of PDT were undertaken, as a previous study had shown a single session had similar efficacy to cryotherapy. Lesion response was assessed clinically after 3 months (complete response or non-complete response).

RESULTS

The lesion response rate was 91% in the methyl aminolevulinate PDT group, 68% in the cryotherapy group and 30% in the placebo PDT group. Methyl aminolevulinate PDT was statistically significantly better than both cryotherapy and placebo PDT in terms of response rates and cosmetic outcome. Most patients preferred PDT to other treatments.

CONCLUSIONS

PDT with methyl aminolevulinate is an excellent treatment option, particularly for patients with widespread damage or AK lesions in cosmetically sensitive areas.

Fiber optic probes for biomedical optical spectroscopy

Fiber optic probes are a key element for biomedical spectroscopic sensing. We review the use of fiber optic probes for optical spectroscopy, focusing on applications in turbid media, such as tissue. The design of probes for reflectance, polarized reflectance, fluorescence, and Raman spectroscopy is illustrated. We cover universal design principles as well as technologies for beam deflecting and reshaping.

Noninvasive fluorescence excitation spectroscopy during application of 5-aminolevulinic acid in vivo

The fluorescence of PpIX induced by topical application of 5-aminolevulinic acid (ALA) in normal mouse skin was studied noninvasively by means of a fibre optic probe. The fluorescence excitation spectrum of PpIX exhibits five distinct peaks at around 408. 510, 543, 583 and 633 nm under fluorescence monitoring at the second emission peak of PpIX (705 nm). The transmission of the excitation light is wavelength dependent: the long wavelength light (>600 nm) penetrates deeper into the tissues by a factor of 6 compared with the short wavelength light (<590 nm). Thus, the fluorescence excitation spectrum of PpIX measured on the surface of the skin can be used to estimate the depth of the penetration of topically applied ALA. The fluorescence excitation spectra calculated for the depth 1.1 mm obtained the best fit with the experimentally measured spectra after topical application of ALA.

Temperature effect on accumulation of protoporphyrin IX after topical application of 5-aminolevulinic acid and its methylester and hexylester derivatives in normal mouse skin

Significant amounts of protoporphyrin IX (PpIX) are formed after 6 min of topical application of 5-aminolevulinic acid (ALA) and its hexylester derivative, whereas PpIX is formed after 10 min of topical application of ALA-methylester derivative in normal mouse skin at 37 degrees C. Lowering the skin temperature to 28-32 degrees C by the administration of the anesthetic Hypnorm-Dormicum reduces the PpIX fluorescence by a factor of 2-3. Practically no PpIX was formed as long as the skin temperature was kept at 12-18 degrees C. At around 30 degrees C PpIX fluorescence appears later after application of ALA-ester derivatives (14-20 min) than after application of ALA (8 min), indicating differences in their bioavailability (delayed penetration through the stratum corneum, cellular uptake, conversion to ALA, PpIX production) in mouse skin in vivo. The difference in lag time in the PpIX formation after application of ALA and ALA-esters may be partly related to deesterification of the ALA-ester molecules. The temperature dependence of PpIX production may be used for improvement of photodynamic therapy with ALA and ALA-ester derivatives, where accumulation of PpIX can be selectively enhanced by increasing the temperature of the target tissue.

Clinicopathologic studies of age-related macular degeneration with classic subfoveal choroidal neovascularization treated with photodynamic therapy

BACKGROUND

Photodynamic therapy (PDT) is a relatively new modality that is currently under clinical and experimental evaluation for treatment of subfoveal choroidal neovascularization (CNV). The authors report the case of an 82-year-old woman who underwent verteporfin-mediated PDT for classic subfoveal CNV. Fluorescein angiography performed 2 weeks after treatment disclosed reduction of the initial area of neovascularization and leakage by approximately 60%. Three weeks after PDT, however, the area of leakage was almost the same size as that before treatment. The patient underwent submacular membranectomy almost 4 weeks after treatment. The authors describe the ultrastructural vascular changes after PDT and a clinicopathologic study of classic CNV.

METHODS

The submacular membrane was studied by light and electron microscopy and immunohistochemical techniques.

RESULTS

Ultrastructural examination of the peripheral vessels showed evidence of endothelial cell degeneration with platelet aggregation and thrombus formation. Occasional occluded vessels were surrounded by macrophages, a phenomenon previously reported to describe the process of resorption of such blood vessels. The vessels in the center of the membrane were unremarkable.

CONCLUSION

Photodynamic therapy causes endothelial cell damage, thrombus formation, and vascular occlusion of classic CNV in age-related macular degeneration.

Acute effects of combined photodynamic therapy and hyperbaric oxygenation in lung cancer--a clinical pilot study

BACKGROUND AND OBJECTIVE

Photodynamic tumor therapy (PDT) is based upon a photochemical reaction that is limited by the availability of molecular oxygen in the target tissue. The use of hyperbaric oxygenation (HBO) increases the amount of oxygen available for the process may thereby enhance the efficacy of PDT. We investigated the acute effects on tumor stenosis after combined PDT/HBO.

PATIENTS AND METHODS

Thirty patients (22 males, 8 females, mean age: 68.8 years; range: 44-78 years) with inoperable non-small cell bronchogenic carcinoma and endobronchial stenosis were studied prospectively. Photosensitization was carried out using a hematoporphyrin-derivative 2 mg/kg BW 48 hours prior to PDT. The light dose was calculated as 300 J/cm fiber tip. The assessment of outcome 1 and 4 weeks after PDT/HBO was performed by endoscopy, chest X-ray, spirometry, laboratory parameters, subjective report of dyspnea, and Karnofsky performance status.

RESULTS

At one and four weeks after the treatment, the patients felt a significant improvement of dyspnea and hemoptysis along with an objective subsiding of poststenotic pneumonia, though spirometric parameters revealed no significant difference. A significant reduction of tumor stenosis (P < 0.05) and an improvement of the Karnofsky performance status (P < 0.05) were documented 1 and 4 weeks after PDT/HBO. No therapy related complications were observed.

CONCLUSIONS

Although the small number of patients does not allow to draw definitive conclusions to be drawn, the results suggests that combined PDT/HBO represents a new, safe, and technically feasible approach. It enables efficient and rapid reduction of the endoluminal tumor load and helps conditioning the patient for further treatment procedures.

Photodynamic studies of metallo 5,10,15,20-tetrakis(4-methoxyphenyl) porphyrin: photochemical characterization and biological consequences in a human carcinoma cell line

The photodynamic activities of the free-base 5,10,15,20-tetrakis(4-methoxyphenyl)porphyrin (TMP) and their metal complexes with zinc(II) (ZnTMP), copper(II) (CuTMP) and cadmium(II) (CdTMP) have been compared in two systems: reverse micelle of n-heptane/sodium bis(2-ethylhexyl)sulfosuccinate/water bearing photooxidizable substrates and Hep-2 human larynx carcinoma cell line. The quantum yields of singlet molecular oxygen, O2(1 delta g), production (phi delta) of TMP, ZnTMP and CdTMP in tetrahydrofuran, were determined yielding values of 0.65, 0.73 and 0.73, respectively, while O2(1 delta g) formation was not detected for CuTMP. In the reverse micellar system, the amino acid L-tryptophan (Trp) was used as biological substrate to analyze the O2(1 delta g)-mediated photooxidation. The observed rate constants for Trp photooxidation (kobsTrp) were proportional to the sensitizer quantum yield of O2(1 delta g). A value of approximately 2 x 10(7) s-1 M-1 was found for the second-order rate constant of Trp (krTry) in this system. The response of Hep-2 cells to cytotoxicity photoinduced by these agents in a biological medium was studied. The Hep-2 cultures were treated with 1 microM of porphyrin for 24 h at 37 degrees C and the cells exposed to visible light. The cell survival at different light exposure levels was dependent on phi delta. Under these conditions, the cytotoxic effect increases in the order: Cu-TMP << TMP < ZnTMP approximately CdTMP, correlating with the production of O2(1 delta g). A similar behavior was observed in both the chemical and biological media indicating that the O2(1 delta g) mediation appears to be mainly responsible for the cell inactivation.

Combined photodynamic therapy and hyperbaric oxygenation in carcinoma of the esophagus and the esophago-gastric junction

OBJECTIVES

The photochemical reaction of photodynamic therapy (PDT) depends on the presence of molecular oxygen. Due to anoxic regions in tumor tissue and vascular shutdown during PDT the efficiency is limited. Therefore, the use of hyperbaric oxygen which increases the oxygen in tumor tissue, as well as the amount of singlet oxygen, may enhance the efficiency of PDT.

PATIENTS AND METHODS

After diagnostic work-up, photosensitization was carried out with a hematoporphyrin-derivate 2 mg/kg BW 48 h prior to PDT. The light dose was calculated as 300 J/cm fiber tip. Thirty-one patients were treated by PDT alone and 44 patients received PDT under hyperbaric oxygen at a level of two absolute atmospheric pressure.

RESULTS

Improvement regarding stenosis-diameter could be obtained in both treatment arms with no significant difference (P=0.82). The dysphagia-score and tumor-length also decreased in both groups and showed a significant difference in favour of the PDT/HBO-group (P=0. 0064 and P=0.0002, respectively). The median overall survival for the PDT-group was 7 months and for the PDT/HBO-group 12 months (P=0. 0098).

CONCLUSION

According to this prospective non-randomized study, combined PDT/HBO represents a new approach in the treatment of esophageal and cardia cancer which appears to have enhanced the efficiency of PDT.

Increased binding of chlorin e6 to lipoproteins at low pH values

It is well known that the extracellular pH in tumors is lower than that of normal tissue. This has been proposed to be one of the reasons for the tumor selective uptake of several photosensitizers. Photosensitizers like chlorin e(6) are bound to blood components and delivered to different sites in the organism. Thus, the effect of pH on their interaction with human plasma needs to be studied in order to understand a possible role of the acidic microenvironment in tumors for the drug distribution. Increasing amounts of human plasma in the sample resulted in a gradual red shift of the fluorescence emission maxima of chlorin e(6), indicating binding of the drug to some of the plasma components. Titration showed that the drug-plasma interaction was pH-dependent. The titration curve had an inflection point at 7.4+/-0.1. The relative distribution of the drug among plasma components, as found after ultracentrifugation of chlorin e(6)-doped plasma in a salt gradient, showed more binding of the drug to nonlipoproteins than to lipoprotein classes at both pH values studied (6.5 and 7.4). A decrease in the pH was connected with a significant increase in drug-lipoprotein binding. The pH of the environment affects chlorin e(6)-plasma interaction and the distribution of the drug among different plasma components. The results of this study indicate a possible role of the acidic microenvironment in tumors for the preferential uptake and retention of several photosensitiziers.

Photodynamic therapy of superficial basal cell carcinoma with 5-aminolevulinic acid with dimethylsulfoxide and ethylendiaminetetraacetic acid: a comparison of two light sources

The aim of this prospective randomized study was to compare the clinical and cosmetic outcome of superficial basal cell carcinomas (BCC), using either laser or broadband halogen light, in photodynamic therapy with topical 5-aminolevulinic acid (ALA). A total of 83 patients with 245 superficial BCC were included in the study. Standard treatment involved 15 min of local pretreatment with 99% dimethylsulfoxide (DMSO) before topical application of 20% ALA with DMSO (2%) and ethylendiaminetetraacetic acid (2%) as cofactors for 3 h before light exposure with either laser or a broadband lamp (BL). A complete response was achieved in 95 lesions (86%) in the laser group and 110 lesions (82%) in the BL group 6 months after treatment. Of these, 80 lesions (84%) in the laser group and 101 lesions (92%) in the lamp group were independently evaluated to have an excellent or good cosmetic post-treatment score. No serious adverse events were reported. This study shows that there is no statistical significant difference in cure the rate (P = 0.49) and the cosmetic outcome (P = 0.075) with topical application of a modified ALA-cream between light exposure from a simple BL with continuous spectrum (570-740 nm) or from a red-light laser (monochromatic 630 nm). Cost and safety are further elements in favor of the BL in this setting.