The role of reperfusion injury in photodynamic therapy with 5-aminolaevulinic acid--a study on normal rat colon

Systematic Review of Photodynamic Therapy in Gliomas

Over the last 20 years, gliomas have made up over 89% of malignant CNS tumor cases in the American population (NIH SEER). Within this, glioblastoma is the most common subtype, comprising 57% of all glioma cases. Being highly aggressive, this deadly disease is known for its high genetic and phenotypic heterogeneity, rendering a complicated disease course. The current standard of care consists of maximally safe tumor resection concurrent with chemoradiotherapy. However, despite advances in technology and therapeutic modalities, rates of disease recurrence are still high and survivability remains low. Given the delicate nature of the tumor location, remaining margins following resection often initiate disease recurrence. Photodynamic therapy (PDT) is a therapeutic modality that, following the administration of a non-toxic photosensitizer, induces tumor-specific anti-cancer effects after localized, wavelength-specific illumination. Its effect against malignant glioma has been studied extensively over the last 30 years, in pre-clinical and clinical trials. Here, we provide a comprehensive review of the three generations of photosensitizers alongside their mechanisms of action, limitations, and future directions.

Altered cellular redox homeostasis and redox responses under standard oxygen cell culture conditions versus physioxia

In vivo, mammalian cells reside in an environment of 0.5-10% O₂ (depending on the tissue location within the body), whilst standard in vitro cell culture is carried out under room air. Little is known about the effects of this hyperoxic environment on treatment-induced oxidative stress, relative to a physiological oxygen environment. In the present study we investigated the effects of long-term culture under hyperoxia (air) on photodynamic treatment. Upon photodynamic irradiation, cells which had been cultured long-term under hyperoxia generated higher concentrations of mitochondrial reactive oxygen species, compared with cells in a physioxic (2% O₂) environment. However, there was no significant difference in viability between hyperoxic and physioxic cells. The expression of genes encoding key redox homeostasis proteins and the activity of key antioxidant enzymes was significantly higher after the long-term culture of hyperoxic cells compared with physioxic cells. The induction of antioxidant genes and increased antioxidant enzyme activity appear to contribute to the development of a phenotype that is resistant to oxidative stress-induced cellular damage and death when using standard cell culture conditions. The results from experiments using selective inhibitors suggested that the thioredoxin antioxidant system contributes to this phenotype. To avoid artefactual results, in vitro cellular responses should be studied in mammalian cells that have been cultured under physioxia. This investigation provides new insights into the effects of physioxic cell culture on a model of a clinically relevant photodynamic treatment and the associated cellular pathways.

The hydroxypyridinone iron chelator CP94 increases methyl-aminolevulinate-based photodynamic cell killing by increasing the generation of reactive oxygen species

Methyl-aminolevulinate-based photodynamic therapy (MAL-PDT) is utilised clinically for the treatment of non-melanoma skin cancers and pre-cancers and the hydroxypyridinone iron chelator, CP94, has successfully been demonstrated to increase MAL-PDT efficacy in an initial clinical pilot study. However, the biochemical and photochemical processes leading to CP94-enhanced photodynamic cell death, beyond the well-documented increases in accumulation of the photosensitiser protoporphyrin IX (PpIX), have not yet been fully elucidated. This investigation demonstrated that MAL-based photodynamic cell killing of cultured human squamous carcinoma cells (A431) occurred in a predominantly necrotic manner following the generation of singlet oxygen and ROS. Augmenting MAL-based photodynamic cell killing with CP94 co-treatment resulted in increased PpIX accumulation, MitoSOX-detectable ROS generation (probably of mitochondrial origin) and necrotic cell death, but did not affect singlet oxygen generation. We also report (to our knowledge, for the first time) the detection of intracellular PpIX-generated singlet oxygen in whole cells via electron paramagnetic resonance spectroscopy in conjunction with a spin trap.

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Augmentation of MAL-based photodynamic cell killing with CP94 increases necrosis.

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CP94 augmentation increases generation of ROS, likely to be mitochondria-localised.

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PpIX-generated ¹O₂ was detected in whole cells by EPR spectroscopy.

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Photodynamic cell killing was dependent primarily on ¹O₂.

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Superoxide/other ROS also contributed to the efficacy of photodynamic cell killing.

Photodynamic therapy in the management of pre-malignant head and neck mucosal dysplasia and microinvasive carcinoma

The management of head and neck mucosal dysplasia and microinvasive carcinoma is an appealing strategy to prevent the development of invasive carcinomas. While surgery remains the standard of care, photodynamic therapy (PDT) offers several advantages including the ability to provide superficial yet wide field mucosal ablative treatment. This is particularly attractive where defining the extent of the dysplasia can be difficult. PDT can also retreat the mucosa without any cumulative fibrotic complications affecting function. To date, clinical experience suggests that this treatment approach can be effective in obtaining a complete response for the treated lesion but long term follow-up is limited. Further research efforts are needed to define not only the risk of malignant transformation with PDT but also to develop site specific treatment recommendations that include the fluence, fluence rate and light delivery technique.

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.

Increasing the efficiency of photodynamic therapy by improved light delivery and oxygen supply using an anticoagulant in a solid tumor model

BACKGROUND AND OBJECTIVE

The main factors in photodynamic therapy (PDT) are: photosensitizer retention, photon absorption, and oxygen supply. Each factor has its unique set of problems that poses limitation to the treatment. Both light delivery and oxygen supply are significant bottlenecks in PDT. Vascular closure during PDT reduces oxygen supply to the targeted tissue. On the other hand, with the changes in blood perfusion, the tissue optical properties change, and result in variation in irradiation light transmission. For these reasons, it becomes very important to avoid blood coagulation and vascular closure during PDT.

STUDY DESIGN/MATERIALS AND METHODS

The efficiency of PDT combined with the anticoagulant heparin was studied in a BALB/c mouse model with subcutaneous EMT6 mammary carcinomas. Mice were randomized into three groups: control, PDT-only, and PDT with heparin. The photosensitizer Photofrin was used in our experiments. Light transmission, blood perfusion, and local production of reactive oxygen species (ROS) were monitored during the treatment. The corresponding histological examinations were performed to determine the thrombosis immediately after irradiation and to evaluate tumor necrosis 48 hours after the treatment.

RESULTS

The results clearly demonstrated that PDT combined with pre-administered heparin can significantly reduce thrombosis during light irradiation. The blood perfusion, oxygen supply, and light delivery are all improved. Improved tumor responses in the combined therapy, as shown with the histological examination and tumor growth assay, are clearly demonstrated and related to an increased local ROS production.

CONCLUSION

Transitory anticoagulation treatment significantly enhances the antitumor effect of PDT. It is mainly due to the improvement of the light delivery and oxygen supply in tumor, and ultimately the amount of ROS produced during PDT.

Continuous or fractionated photodynamic therapy? Comparison of three PDT schemes for ovarian peritoneal micrometastasis treatment in a rat model

OBJECTIVE

This experimental study aimed to compare three illumination schemes to optimize hexaminolaevulinate (HAL)-PDT in a rat tumor model with advanced ovarian cancer.

MATERIALS AND METHODS

Peritoneal carcinomatosis was induced by intraperitoneal 5×10(6)NuTu-19 cells injection in 60 female rats Fisher 344. Carcinomatosis was obtained 50 days post-tumor induction. Four hours post-intraperitoneal HAL (Photocure ASA, Oslo, Norway) injection, three different schemes of PDT were performed during 25 min on a 1cm(2) area. (A) Fractionated illumination (n=20) with an on-off cycle ("on": 2 min and "off": 1 min) at 30mW cm(-2) until a fluence of 30J cm(-2), (B) continuous illumination (n=20) at 30mW cm(-2) with a fluence of (45J cm(-2)C) continuous illumination (n=20) at 20mW cm(-2) with a fluence of 30J cm(-2). Laser light was generated using a 532nm KTP laser (Laser Quantum, Stockport, UK). Biopsies were taken 24h after treatment. Quantitative histology was performed. Necrosis value was determined: 0-no necrosis to 4-full necrosis. Depth of necrosis was then measured for each sample and correlated to Necrosis value.

RESULTS

HAL-PDT was efficient in producing necrosis irrespective of the scheme. Tumor destruction was superior with fractionated illumination compared to both continuous illumination schemes regarding to the depth of necrosis (213±113μm vs 154±133μm vs 171±155μm) (p<0.05) or to the full necrosis rate (50% vs 30% vs 10%) (p<0.0001).

CONCLUSION

Fractionated illumination during photodynamic therapy (PDT) was shown to improve tumor response. Fractionated illumination with short intervals should be considered for an effective PDT of advanced ovarian cancer.

Comparing and combining light dose fractionation and iron chelation to enhance experimental photodynamic therapy with aminolevulinic acid

BACKGROUND AND OBJECTIVES

Enhancement of photodynamic therapy (PDT) with 5-aminolevulinic acid (ALA) has been demonstrated experimentally using light dose fractionation or CP94 iron chelation. This study extends this research.

STUDY DESIGN/MATERIALS AND METHODS

In normal rat colon, CP94 administration and light dose fractionation were independently and concurrently employed to enhance ALA-PDT. In colonic rat tumors, the most successful enhancement regimes were employed separately.

RESULTS

Independent use of light dose fractionation and iron chelation produced similar results in normal colon (2.4- and 2.9-fold more necrosis than controls, respectively). Using both techniques simultaneously produced fivefold enhancement. In the colonic tumors, light dose fractionation and iron chelation (using different parameters) produced two and five times the volume of necrosis, respectively.

CONCLUSIONS

Both techniques significantly enhanced ALA-PDT in the normal and neoplastic tissues investigated and produced similar levels of enhancement when comparable parameters were employed. Concurrent use of light dose fractionation and iron chelation in normal colon produced considerably more enhancement than either technique could achieve independently.

The vascular response to photodynamic therapy with ATX-S10Na(II) in the normal rat colon

The mechanism of tissue damage from photodynamic therapy (PDT) may be cellular, vascular or both, depending on the photosensitising agent and the treatment conditions. Well established photosensitisers like porfimer sodium have an optimum drug light interval of two days and may cause skin photosensitivity lasting several weeks. ATX-S10Na(II) is a new photosensitiser that remains largely in the vasculature after systemic administration and clears from the body within a few hours. The present study looks at the factors controlling the extent of PDT necrosis using ATX-S10Na(II) and correlates these with changes in the circulation after PDT. Normal Wistar rats were sensitised with ATX-S10Na(II), 2 mg/kg. At laparotomy, a laser fibre was positioned just touching the colonic mucosa and 50 J light at 670 nm delivered varying the drug light interval (0.5-24 h) and light delivery regime (100 mW continuous, 20 mW continuous or 100 mW in five fractions). Some animals were killed at three days to document the area of necrosis, others received fluorescein shortly prior to death (from a few minutes to three days after PDT) to outline the zone of PDT induced vascular shutdown. Maximum necrosis was seen with the shortest drug light interval (0.5 h), with no effect by 6 h. Fractionating the light or lowering the power did not increase the necrosis. The area of fluorescein exclusion increased over the first 2 h after PDT (in contrast to the re-perfusion seen with other photosensitisers) and correlated with the area of necrosis. PDT with ATX-S10Na(II) is most effective with a drug light interval of less than one hour. It induces irreversible vascular shutdown that extends after completion of light delivery and which is largely independent of the light delivery regime.

Correlation of real-time haemoglobin oxygen saturation monitoring during photodynamic therapy with microvascular effects and tissue necrosis in normal rat liver

Photodynamic therapy (PDT) requires a photosensitising drug, light and oxygen. While it is known that the haemoglobin oxygen saturation (HbSat) can be altered by PDT, little has been done to correlate this with microvascular changes and the final biological effect. This report describes such studies on the normal liver of rats sensitised with aluminium disulphonated phthalocyanine. In total, 50 J of light at 670 nm, continuous or fractionated at 25 or 100 mW, was applied with a single laser fibre touching the liver surface. HbSat was monitored continuously 1.5-5.0 mm from the laser fibre using visible light reflectance spectroscopy (VLRS). Vascular shutdown was assessed by fluorescein angiography 2-40 min after light delivery. Necrosis was measured at post mortem 3 days after PDT. In all treatment groups at a 1.5 mm separation, HbSat fell to zero with little recovery after light delivery. At 2.5 mm, HbSat also decreased during light delivery, except with fractionated light, but then recovered. The greatest recovery of fluorescein perfusion after PDT was seen using 25 mW, suggesting an ischaemia/reperfusion injury. Necrosis was more extensive after low power and fractionated light than with 100 mW, continuous illumination. We conclude that VLRS is a useful technique for monitoring HbSat, although the correlation between HbSat, fluorescein exclusion and necrosis varied markedly with the light delivery regimen used.