Novel Iron-Chelating Prodrug Significantly Enhanced Fluorescence-Mediated Detection of Glioma Cells Experimentally In Vitro

(1) Background: The protoporphyrin IX (PpIX)-mediated fluorescence-guided resection and interoperative photodynamic therapy (PDT) of remaining cells may be effective adjuvants to the resection of glioma. Both processes may be enhanced by increasing intracellular PpIX concentrations, which can be achieved through iron chelation. AP2-18 is a novel combinational drug, which ester-links a PpIX precursor (aminolaevulinic acid; ALA) to an iron-chelating agent (CP94). (2) Methods: Human glioma U-87 MG cells were cultured in 96-well plates for 24 h and incubated for 3 or 6 h with various test compound combinations: ALA (±) CP94, methyl aminolevulinate (MAL) (±) CP94 and AP2-18. PpIX fluorescence was measured at 0, 3 or 6 h with a Bio-tek Synergy HT plate reader, as well as immediately after irradiation with a 635 nm red light (Aktilite CL16 LED array), representing the PDT procedure. Cell viability post-irradiation was assessed using the neutral red assay. (3) Results: AP2-18 significantly increased PpIX fluorescence compared to all other test compounds. All treatment protocols effectively achieved PDT-induced cytotoxicity, with no significant difference between test compound combinations. (4) Conclusions: AP2-18 has potential to improve the efficacy of fluorescence-guided resection either with or without the subsequent intraoperative PDT of glioma. Future work should feature a more complex in vitro model of the glioma microenvironment.

Improving in vitro photodynamic therapy through the development of a novel iron chelating aminolaevulinic acid prodrug

•

A new combined iron chelating prodrug (AP2-18) has been synthesised and evaluated.

•

AP2-18 significantly increased protoporphyrin IX accumulation in human skin cells.

•

This enhancement translated into greater cytotoxicity on irradiation.

•

Clinical AP2-18 application may improve future dermatological photodynamic therapy.

Background

Photodynamic therapy (PDT) is a light activated drug therapy that can be used to treat a number of cancers and precancers. It is particularly useful in its topical form in dermatology but improvement of efficacy is required to widen its application.

Methods

An ester between aminolaevulinic acid (ALA) and CP94 was synthesised (AP2-18) and experimentally evaluated to determine whether protoporphyrin IX (PpIX)-induced PDT effectiveness could be improved. A biological evaluation of AP2-18 was conducted in cultured human primary cells with both PpIX fluorescence and cell viability (as determined via the neutral red assay) being assessed in comparison to the PpIX prodrugs normally utilised in clinical practice (aminolaevulinic acid (ALA) or its methyl ester (MAL)) either administered alone or with the comparator iron chelator, CP94.

Results

No significant dark toxicity was observed in human lung fibroblasts but AP2-18 significantly increased PpIX accumulation above and beyond that achieved with ALA or MAL administration +/- CP94 in both human dermal fibroblasts and epithelial squamous carcinoma cells. On light exposure, the combined hydroxypyridinone iron chelating ALA prodrug AP2-18 generated significantly greater cytotoxicity than any of the other treatment parameters investigated when the lowest concentration (250 μM) was employed.

Conclusions

Newly synthesised AP2-18 is therefore concluded to be an efficacious prodrug for PpIX-induced PDT in these dermatologically relevant human cells, achieving enhanced effects at lower concentrations than currently possible with existing pharmaceuticals.

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.

An experimental investigation of a novel iron chelating protoporphyrin IX prodrug for the enhancement of photodynamic therapy

Objectives

Non‐melanoma skin cancers are the most frequently occurring type of cancer worldwide. They can be effectively treated using topical dermatological photodynamic therapy (PDT) employing protoporphyrin IX (PpIX) as the active photosensitising agent as long as the disease remains superficial. Novel iron chelating agents are being investigated to enhance the effectiveness and extend the applications of this treatment modality, as limiting free iron increases the accumulation of PpIX available for light activation and thus cell kill.

Methods

Human lung fibroblasts (MRC‐5) and epithelial squamous carcinoma (A431) cells were treated with PpIX precursors (aminolaevulinic acid [ALA] or methyl‐aminolevulinate [MAL]) with or without the separate hydroxypyridinone iron chelating agent (CP94) or alternatively, the new combined iron chelator and PpIX producing agent, AP2‐18. PpIX fluorescence was monitored hourly for 6 hours prior to irradiation. PDT effectiveness was then assessed the following day using the lactate dehydrogenase and neutral red assays.

Results

Generally, iron chelation achieved via CP94 or AP2‐18 administration significantly increased PpIX fluorescence. ALA was more effective as a PpIX‐prodrug than MAL in A431 cells, corresponding with the lower PpIX accumulation observed with the latter congener in this cell type. Addition of either iron chelating agent consistently increased PpIX accumulation but did not always convey an extra beneficial effect on PpIX‐PDT cell kill when using the already highly effective higher dose of ALA. However, these adjuvants were highly beneficial in the skin cancer cells when compared with MAL administration alone. AP2‐18 was also at least as effective as CP94 + ALA/MAL co‐administration throughout and significantly better than CP94 supplementation at increasing PpIX fluorescence in MRC5 cells as well as at lower doses where PpIX accumulation was observed to be more limited.

Conclusions

PpIX fluorescence levels, as well as PDT cell kill effects on irradiation can be significantly increased by pyridinone iron chelation, either via the addition of CP94 to the administration of a PpIX precursor or alternatively via the newly synthesized combined PpIX prodrug and siderophore, AP2‐18. The effect of the latter compound appears to be at least equivalent to, if not better than, the separate administration of its constituent parts, particularly when employing MAL to destroy skin cancer cells. AP2‐18 therefore warrants further detailed analysis, as it may have the potential to improve dermatological PDT outcomes in applications currently requiring enhancement. Lasers Surg. Med. 50:552–565, 2018. © 2018 The Authors. Lasers in Surgery and Medicine Published by Wiley Periodicals, Inc.

The importance of iron chelation and iron availability during PpIX-induced photodynamic therapy

Background:

Protoporphyrin IX (PpIX)-induced photodynamic therapy (PDT) is being utilised as a topical method of localised ablation of certain non-melanoma skin cancers and precancers. Standardised protocols have been implemented to good effect when the disease remains superficial but improvement is required to treat thicker or acrally located conditions. Concurrent administration of an iron chelator during PpIX-PDT has been demonstrated to increase cellular accumulation of PpIX by reducing its bioconversion to haem (an iron dependent process) thus increasing cell kill on subsequent irradiation. Iron however, can also play a role in reactive oxygen species (ROS) generation and limiting its availability via chemical chelation could theoretically reduce the efficacy of PpIX-PDT, so that a response less than that maximally feasible is produced.

Materials and methods:

The effects of iron availability and chelation on PpIX-PDT have therefore been investigated via fluorescence quantification of PpIX accumulation, single-cell gel electrophoresis (comet assay) measurement of ROS-induced DNA damage and trypan blue exclusion assessment of cell viability. Cultured human cells were utilised and incubated in standardised iron conditions with the PpIX precursor’s aminolaevulinic acid (ALA) or its methyl ester (MAL) in the presence or absence of either of the iron chelating agents desferrioxamine (DFO) or hydroxypyridinone (CP94), or alternatively iron sulphate as a source of iron.

Results:

ALA or MAL incubation was found to significantly increase cellular PpIX accumulation pre-irradiation as anticipated and this observation correlated with both significantly increased DNA damage and reduced cellular viability following irradiation. Co-incubation with either of the iron chelators investigated (DFO or CP94) significantly increased pre-irradiation PpIX accumulation as well as DNA damage and cell death on irradiation indicating the positive effect of iron chelation on the effectiveness of PpIX-induced PDT. The opposite effects were observed however, when the cells were co-incubated with iron sulphate, with significant reductions in pre-irradiation PpIX accumulation (ALA only) and DNA damage (ALA and MAL) being recorded indicating the negative effects excessive iron can have on PpIX-PDT effectiveness. Some dark toxicity produced by iron sulphate administration in non-irradiated control groups was also observed.

Conclusion:

Iron chelation and availability have therefore been observed to positively and adversely affect the PpIX-PDT process respectively and it is concluded that the effects of increased PpIX accumulation pre-irradiation produced via iron chelation outweigh any limitations reduced iron availability may have on the ability of iron to catalyse ROS generation/cascades following PpIX-induced PDT. Further investigation of iron chelation within dermatological applications where enhanced PpIX-PDT treatment effects would be beneficial is therefore warranted.

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.

The cellular and molecular carcinogenic effects of radon exposure: a review

Radon-222 is a naturally occurring radioactive gas that is responsible for approximately half of the human annual background radiation exposure globally. Chronic exposure to radon and its decay products is estimated to be the second leading cause of lung cancer behind smoking, and links to other forms of neoplasms have been postulated. Ionizing radiation emitted during the radioactive decay of radon and its progeny can induce a variety of cytogenetic effects that can be biologically damaging and result in an increased risk of carcinogenesis. Suggested effects produced as a result of alpha particle exposure from radon include mutations, chromosome aberrations, generation of reactive oxygen species, modification of the cell cycle, up or down regulation of cytokines and the increased production of proteins associated with cell-cycle regulation and carcinogenesis. A number of potential biomarkers of exposure, including translocations at codon 249 of TP53 in addition to HPRT mutations, have been suggested although, in conclusion, the evidence for such hotspots is insufficient. There is also substantial evidence of bystander effects, which may provide complications when calculating risk estimates as a result of exposure, particularly at low doses where cellular responses often appear to deviate from the linear, no-threshold hypothesis. At low doses, effects may also be dependent on cellular conditions as opposed to dose. The cellular and molecular carcinogenic effects of radon exposure have been observed to be both numerous and complex and the elevated chronic exposure of man may therefore pose a significant public health risk that may extend beyond the association with lung carcinogenesis.

An in vitro comparison of the effects of the iron-chelating agents, CP94 and dexrazoxane, on protoporphyrin IX accumulation for photodynamic therapy and/or fluorescence guided resection

Photodynamic therapy (PDT) utilizes the combined interaction of a photosensitizer, light and molecular oxygen to ablate tumor tissue. Maximizing the accumulation of the photosensitizer protoporphyrin IX (PpIX) within different cell types would be clinically useful. Dermatological PpIX-induced PDT regimes produce good clinical outcomes but this currently only applies when the lesion remains superficial. Also, as an adjuvant therapy for the treatment of primary brain tumors, fluorescence guided resection (FGR) and PDT can be used to highlight and destroy tumor cells unreachable by surgical resection. By employing iron chelators PpIX accumulation can be enhanced. Two iron-chelating agents, 1,2-diethyl-3-hydroxypyridin-4-one hydrochloride (CP94) and dexrazoxane, were individually combined with the porphyrin precursors aminolevulinic acid (ALA), methyl aminolevulinate (MAL) and hexyl aminolevulinate (HAL). Efficacies of the iron-chelating agents were compared by recording the PpIX fluorescence in human squamous epithelial carcinoma cells (A431) and human glioma cells (U-87 MG) every hour for up to 6 h. Coincubation of ALA/MAL/HAL with CP94 resulted in a greater accumulation of PpIX compared to that produced by coincubation of these congeners with dexrazoxane. Therefore the clinical employment of iron chelation, particularly with CP94 could potentially increase and/or accelerate the accumulation of ALA/MAL/HAL-induced PpIX for PDT or FGR.

Comparison of protoporphyrin IX accumulation and destruction during methylaminolevulinate photodynamic therapy of skin tumours located at acral and nonacral sites

BACKGROUND

Topical photodynamic therapy (PDT) is successful in the treatment of nonmelanoma skin cancers and associated precancers, but efficacy is significantly reduced in actinic keratosis lesions not located on the face or scalp.

OBJECTIVES

To compare the changes in protoporphyrin IX (PpIX) fluorescence in lesions undergoing routine methylaminolevulinate (MAL) PDT and the clinical outcome observed 3 months after treatment in lesions located at acral and nonacral sites.

METHODS

This study was a noninterventional, nonrandomized, observational study, which monitored changes in PpIX fluorescence in 200 lesions during standard dermatological MAL-PDT. These data were subsequently analysed in terms of lesions located at acral and nonacral sites.

RESULTS

Clinical clearance was significantly reduced (P < 0·01) in acral skin lesions when compared with lesions located at nonacral sites. The accumulation and destruction of PpIX fluorescence was significantly reduced in these acral lesions (P < 0·05 and P < 0·001, respectively). Specifically, lesion location at acral sites significantly reduced changes in PpIX fluorescence in actinic keratosis lesions during MAL-PDT (P < 0·01 and P < 0·05).

CONCLUSIONS

These data suggest that reduced PpIX accumulation and the subsequent reduction in PpIX photobleaching within acral lesions result in the reduced responsiveness of these lesions to MAL-PDT. Future work should therefore aim to improve photosensitizer accumulation/photobleaching within lesions located at acral sites.

The hydroxypyridinone iron chelator CP94 can enhance PpIX-induced PDT of cultured human glioma cells

Photodynamic therapy (PDT) with the pro-drugs 5-aminolevulinic acid (ALA) or methyl aminolevulinate (MAL) utilizes the combined interaction of a photosensitizer, light and molecular oxygen to ablate tumor tissue. To potentially increase accumulation of the photosensitizer, protoporphyrin IX (PpIX), within tumor cells an iron chelator can be employed. This study analyzed the effects of ALA/MAL-induced PDT combined with the iron chelator 1, 2-diethyl-3-hydroxypyridin-4-one hydrochloride (CP94) on the accumulation of PpIX in human glioma cells in vitro. Cells were incubated for 0, 3 and 6h with various concentrations of ALA/MAL with or without CP94 and the resulting accumulations of PpIX, which naturally fluoresces, were quantified prior to and following light irradiation. In addition, counts of viable cells were recorded. The use of CP94 in combination with ALA/MAL produced significant enhancements of PpIX fluorescence in human glioma cells. At the highest concentrations of each prodrug, CP94 enhanced PpIX fluorescence significantly at 3h for ALA and by more than 50% at 6h for MAL. Cells subsequently treated with ALA/MAL-induced PDT in combination with CP94 produced the greatest cytotoxicity. It is therefore concluded that with further study CP94 may be a useful adjuvant to photodiagnosis and/or PpIX-induced PDT treatment of glioma.

Monitoring the accumulation and dissipation of the photosensitizer protoporphyrin IX during standard dermatological methyl-aminolevulinate photodynamic therapy utilizing non-invasive fluorescence imaging and quantification

BACKGROUND

Dermatological methyl-aminolevulinate photodynamic therapy (MAL-PDT) is utilized to successfully treat dermatological conditions. This study monitored fluorescence changes attributed to the accumulation and destruction of the photosensitizer, protoporphyrin IX (PpIX), at several different stages during the first and second treatments of clinical dermatological MAL-PDT.

METHODS

A commercially available, non-invasive, fluorescence imaging system (Dyaderm, Biocam, Germany) was utilized to monitor fluorescence changes during the first and second MAL-PDT treatments in seventy-five lesions.

RESULTS

The clinical data indicated statistically significant increases in fluorescence within lesions following the application of MAL for both treatments (P<0.001 and P<0.01 respectively) and subsequent statistically significant decreases in fluorescence within the lesions following light irradiation for both treatments (P<0.001 and P<0.01 respectively) whilst normal skin fluorescence remained unaltered. Lesions receiving a second treatment accumulated and dissipated significantly less PpIX (P<0.05) than during the first treatment. No significant differences were noted in PpIX accumulation or dissipation during MAL-PDT when gender, age, lesion type and lesion surface area were considered.

CONCLUSIONS

It can therefore be concluded that PpIX fluorescence imaging can be used in real-time to assess PpIX levels during dermatological PDT. Similar observations were recorded from the three currently licensed indications indicating that the standard 'one size fits all' protocol currently employed appears to allow adequate PpIX accumulation, which is subsequently fully utilized during light irradiation regardless of patient age, gender or lesion surface area.

Protoporphyrin IX photobleaching during the light irradiation phase of standard dermatological methyl-aminolevulinate photodynamic therapy

BACKGROUND

Methyl-aminolevulinate photodynamic therapy (MAL-PDT) is a successful treatment for non-melanoma skin cancers in the UK. Monitoring the photobleaching of the photosensitiser, protoporphyrin IX (PpIX) during treatment has been demonstrated to indicate the efficacy of the treatment. This study investigated photobleaching during light irradiation.

METHODS

A validated non-invasive fluorescence imaging system was utilised to monitor changes in PpIX fluorescence during light irradiation. Fifty patients were recruited to this study, with patients monitored before, during (forty patients at the half way stage and ten at regular intervals in the initial phase of treatment) and after light irradiation.

RESULTS

Phased PpIX photobleaching was observed during light irradiation with a significantly greater change (P<0.001) in PpIX photobleaching during the first half of light treatment. Within the ten patients monitored periodically the phased photobleaching observed fitted a double exponential decay curve (r(2)=0.99, P<0.005) suggesting a rapid initial phase of reaction when the light treatment was commenced.

CONCLUSIONS

Photobleaching was observed to be maximal in the initial phases of treatment, however photobleaching of PpIX continued until the completion of light treatment indicating that current clinical protocols for MAL-PDT do not over-treat the lesion with light.

The genesis and collapse of third millennium north mesopotamian civilization

Archaeological and soil-stratigraphic data define the origin, growth, and collapse of Subir, the third millennium rain-fed agriculture civilization of northern Mesopotamia on the Habur Plains of Syria. At 2200 B. C., a marked increase in aridity and wind circulation, subsequent to a volcanic eruption, induced a considerable degradation of land-use conditions. After four centuries of urban life, this abrupt climatic change evidently caused abandonment of Tell Leilan, regional desertion, and collapse of the Akkadian empire based in southern Mesopotamia. Synchronous collapse in adjacent regions suggests that the impact of the abrupt climatic change was extensive.

Clinical investigation of the novel iron-chelating agent, CP94, to enhance topical photodynamic therapy of nodular basal cell carcinoma

BACKGROUND

Photodynamic therapy (PDT) involves the activation of a photosensitizer by visible light to produce activated oxygen species within target cells, resulting in their destruction. Evidence-based guidelines support the efficacy of PDT using topical 5-aminolaevulinic acid (ALA-PDT) in actinic keratoses, Bowen disease and basal cell carcinoma (BCC). Efficacy for nodular BCC appears inferior to that for superficial BCC unless prior debulking or repeat treatments are performed. Objectives The aim of this study was to assess the safety and efficacy of adding a novel iron-chelating agent, CP94 (1,2-diethyl-3-hydroxypyridin-4-one hydrochloride), to topical ALA, to temporarily increase the accumulation of the photosensitizer in the tumour.

METHODS

A mixed topical formulation of ALA + increasing concentrations of CP94 was used to carry out PDT on previously biopsied nodular BCC with no prior lesion preparation using standard light delivery. The area was assessed clinically and surgically excised 6 weeks later for histological examination.

RESULTS

Enhanced PDT using 40% CP94 resulted in significantly greater clearance rates in nodular BCC than with ALA-PDT alone, in our protocol of single-treatment PDT with no lesion preparation.

CONCLUSIONS

The results of this study demonstrate the safe and effective use of an enhanced ALA-PDT protocol for nodular BCC using CP94, with no adverse reactions to this modification. This is the first time this formulation has been used in patients. This formulation is now the focus of further study.

Biochemical manipulation via iron chelation to enhance porphyrin production from porphyrin precursors

Topical protoporphyrin IX (PPIX) induced photodynamic therapy (PDT) of basal cell carcinoma (BCC) produces good clinical outcomes with excellent cosmesis as long as the disease remains superficial. Efficacy for nodular BCC, however, appears inferior to standard treatment unless repeat treatments are performed. Enhancement is therefore required and may be possible by employing iron chelating agents to temporarily increase PPIX accumulation above the levels normally obtained using aminolaevulinic acid (ALA) or the methyl ester of ALA (MAL) alone. In vitro studies investigated the efficacies of the novel iron chelator, CP94 (1,2-diethyl-3-hydroxypyridin-4-one hydrochloride), and the established iron chelator, desferrioxamine (DFO), at increasing PPIX fluorescence in cultured human lung fibroblasts and squamous carcinoma cells incubated with ALA/MAL. CP94 was found to produce greater PPIX fluorescence when administered with ALA/MAL than either congener could produce alone. CP94 was also found to be superior to DFO in the enhancement of PPIX fluorescence and could be employed to accumulate the same levels of PPIX within a shorter time period. Clinical utilization of CP94 to enhance ALA/MAL-PDT could potentially result in greater PPIX accumulation or alternatively could be employed to reduce the length of the required drug-light interval. Clinical investigation of this is currently underway.

Direct Comparison of δ-Aminolevulinic Acid and Methyl-Aminolevulinate-Derived Protoporphyrin IX Accumulations Potentiated by Desferrioxamine or the Novel Hydroxypyridinone Iron Chelator CP94 in Cultured Human Cells

Aminolevulinic acid photodynamic therapy (ALA-PDT) is a cancer therapy that combines the selective accumulation of a photosensitizer in tumor tissue with visible light (and tissue oxygen) to produce reactive oxygen species. This results in cellular damage and ablation of tumor tissue. The use of iron chelators in combination with ALA has the potential to increase the accumulation of the photosensitizer protoporphyrin IX (PpIX) by reducing its bioconversion to heme. This study compares directly for the first time the effects of the novel hydroxypyridinone iron chelating agent CP94 and the more clinically established iron chelator desferrioxamine (DFO) on the enhancement of ALA and methyl-aminolevulinate (MAL)-induced PpIX accumulations in cultured human cells. Cultured human cells were incubated with a combination of ALA, MAL, CP94 and DFO concentrations; the resulting PpIX accumulations being quantified fluorometrically. The use of iron chelators in combination with ALA or MAL was shown to significantly increase the amount of PpIX accumulating in the fetal lung fibroblasts and epidermal carcinoma cells; while minimal enhancement was observed in the normal skin cells investigated (fibroblasts and keratinocytes). Where enhancement was observed CP94 was shown to be significantly superior to DFO in the enhancement of PpIX accumulation.

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.

UVA-induced apoptosis studied by the new apo/necro-Comet-assay which distinguishes viable, apoptotic and necrotic cells

An adaptation of the Comet-assay was developed which enables the discrimination of viable, apoptotic and necrotic single cells by use of the common Annexin-V staining and a dye exclusion test on the cells already embedded in agarose gel on glass slides. Membrane integrity (Ethidium-Homodimer exclusion), cellular esterase activity (Calcein blue-AM) as well as translocation of phosphadidyl-serine (Annexin-V) were analysed using these stains. The advantage of the 'apo/necro-Comet-assay' is that the viability status of individual cells can be determined and correlated with the DNA fragmentation pattern (comet) formed by the same cells. Hence, DNA damage can be assessed and correlated with viable cells or cells undergoing early, mid- or late stage apoptosis or necrosis as identified by the staining pattern. The staining was verified using heat and etoposide-induced apoptosis. This technique, among others, was used to study whether apoptotic fragmentation interferes with repair kinetics measured with the comet assay following UVA exposure (doses up to 1,280 kJ/m(2)) in the cultured human keratinocytes (HaCaT). Therefore, a time course of apoptotic events (phosphatidyl translocation and TUNEL fragmentation) was established and correlated to the DNA fragmentation in the comet-assay. Apoptotic cells were detected more than 8 h later. The combined three-colour staining method with the comet assay showed that there was no significant interference of DNA repair by apoptotic fragmentation processes since DNA repair was almost completed before the onset of apoptotic fragmentation. The apo/necro-Comet-assay reduces the general problem of false-positive results in genotoxicity tests using the Comet-assay.

Hg(II) exposure exacerbates UV-induced DNA damage in MRC5 fibroblasts: a comet assay study

When exposed to UVR, MRC5 fibroblasts incubated with mercuric chloride (0-15 microM) for 1 hour show increased DNA damage (as measured by the comet assay) compared to control cells (UVR irradiated but no mercuric chloride). This demonstrates that mercuric chloride and UVR in combination increase DNA damage in a synergistic manner. This may have implications to those exposed to mercury as it suggests that exposure to mercury in the environment may increase sensitivity to sunlight-induced carcinogenesis.

Photodynamic therapy using meta-tetrahydroxyphenylchlorin (Foscan) for the treatment of vulval intraepithelial neoplasia

BACKGROUND

Photodynamic therapy (PDT) has unique properties which make it suitable for the local treatment of superficial epithelial disorders; it has been suggested as a useful treatment for carcinoma in situ of the vulva.

OBJECTIVES

To evaluate the effect of the systemic photosensitizing agent meta-tetrahydroxyphenylchlorin (mTHPC or temoporfin; Foscan, Biolitec, Edinburgh, U.K.) in vulval intraepithelial neoplasia type III (VIN III).

METHODS

PDT using mTHPC was performed in six patients with VIN III. A dose of 0.1 mg kg(-1) body weight mTHPC was injected intravenously and the area of VIN irradiated 96 h later with 652-nm light from a diode laser. Patients were reviewed 1 week, 6 months and 2 years following treatment.

RESULTS

Patients experienced only minimal pain from the initial treatment but two patients subsequently developed severe pain at the treated site for up to 2 weeks following PDT. All patients developed oedema and slough formation at the treated site and one patient developed cellulitis. At 6 months two patients had developed small recurrences of VIN at the original site and one patient had an area of VIN at a new site. These were treated either with further PDT or with a small excision. At 2 years there was no recurrence of VIN at the original site in all patients reviewed.

CONCLUSIONS

This small case series demonstrates that mTHPC-PDT is a useful initial treatment for VIN III. It is relatively selective, shows good cosmesis and conserves form and function. This is a major advantage over surgery. Repeat treatments are also possible, which is important in a condition such as VIN, which tends to be multifocal. Systemic mTHPC-PDT appears to have an advantage over topical 5-aminolaevulinic acid-PDT as the photosensitizer is distributed widely in areas of disease and consequently identifies foci which may not be apparent clinically but become evident when illuminated.

The green tea polyphenol (-)-epigallocatechin gallate and green tea can protect human cellular DNA from ultraviolet and visible radiation-induced damage

BACKGROUND

Antioxidant compounds in green tea may be able to protect against skin carcinogenesis and it is of interest to investigate the mechanisms involved. A study was therefore conducted to determine whether the isolated green tea polyphenol (-)-epigallocatechin gallate (EGCG) could prevent ultraviolet radiation (UVR)-induced DNA damage in cultured human cells. This work was then extended to investigate whether drinking green tea could afford any UVR protection to human peripheral blood cells collected after tea ingestion.

METHODS

The alkaline comet assay was used to compare the DNA damage induced by UVR in cultured human cells with and without the presence of EGCG. The same assay technique was then employed to assess UVR-induced DNA damage in peripheral leucocytes isolated from 10 adult human volunteers before and after drinking 540 ml of green tea.

RESULTS

Initial trials found that EGCG afforded concentration-dependent photoprotection to cultured human cells with a maximal activity at a culture concentration of 250 microM. The cells types tested (lung fibroblasts, skin fibroblasts and epidermal keratinocytes) demonstrated varying susceptibility to the UVR insult provided. The in vivo trials of green tea also demonstrated a photoprotective effect, with samples of peripheral blood cells taken after green tea consumption showing lower levels of DNA damage than those taken prior to ingestion when exposed to 12 min ultraviolet A (UVA) radiation.

CONCLUSION

The studies showed that green tea and/or some constituents can offer some protection against UV-induced DNA damage in human cell cultures and also in human peripheral blood samples taken post-tea ingestion.

The use of comet assay data with a simple reaction mechanism to evaluate the relative effectiveness of free radical scavenging by quercetin, epigallocatechin gallate and N-acetylcysteine in UV-irradiated MRC5 lung fibroblasts

Comet assay data (tail DNA %) have been gathered for the concentration dependent role of three antioxidants (AOs); quercetin (Q), epigallocatechin gallate (EGCG) and N-acetylcysteine (NAC) in reducing UV-induced damage to DNA in normal fetal lung fibroblasts (MRC5). All three compounds demonstrate a concentration dependent reduction maximum with a pro-oxidant effect at higher (though not cytotoxic) concentrations. Manipulation of a simple 4-step reaction mechanism for free radical (FR) scavenging by AOs produced rate constant ratios which allowed the relative effectiveness (Q > EGCG > NAC) of the AOs to be evaluated.

N-acetyl-l-cysteine prevents DNA damage induced by UVA, UVB and visible radiation in human fibroblasts

The thiol N-acetyl-L-cysteine (NAC) is a source of cysteine for the synthesis of the endogenous antioxidant glutathione (GSH) which is depleted by ultraviolet radiation. It is also associated with the scavenging of reactive oxygen species (ROS). In this study the effects of NAC were examined in cultured human fibroblasts during prolonged exposure to ultraviolet B (UVB), ultraviolet A (UVA) and visible irradiation (280-700 nm), delivered by a 150 W xenon-arc lamp. The alkaline comet assay was used to assess the DNA damage in individual cells. It was found that incubating skin and lung fibroblasts at 37 degrees C for 1 h with an optimal 6 mM NAC supplement prior to light exposure, significantly reduced the level of DNA damage in both cell types, however, the skin fibroblasts were less sensitive to xenon-arc lamp irradiation than lung fibroblasts. NAC incubation resulted in an initial delay in DNA damage when the cells were irradiated. There was also a significant reduction in the overall levels of DNA damage observed with continued irradiation. NAC significantly reduced the DNA damage produced in lung fibroblasts depleted of normal GSH protection by the glutamylcysteinyl synthetase inhibitor, L-buthionine-[S,R]-sulfoximine. Although the specific mechanism of NAC protection has not yet been elucidated, these results support the hypothesis that NAC may protect the cells directly, by scavenging ROS induced by UVA and visible radiation, and indirectly by donating cysteine for GSH synthesis.

Fluorescence biodistribution and photosensitising activity of toluidine blue o on rat buccal mucosa

The antimicrobial activity of toluidine blue O (TBO) in the presence of red light has been demonstrated for a wide range of microorganisms. The response of tissues to TBO-induced photosensitisation is an important factor in assessing the clinical usefulness of this technique for the treatment of infectious diseases. The aims of this study were to determine the effect of TBO-mediated photosensitisation on rat buccal mucosa and the biodistribution of the photosensitiser in this tissue. An aqueous solution of TBO was applied to one side of the buccal mucosa of the animals. A 6 mm diameter area was then exposed to light (633 nm) from a copper vapour pumped-dye laser. The opposite, untreated, side of the buccal mucosa served as a control. TBO concentrations of 25, 50 and 200 microg/ml, laser light doses of 110, 170 and 340 J/cm(2) were assessed. Control groups of animals were subjected to 340 J/cm(2) laser light alone or to 200 microg/ml TBO alone. Serial sacrifices were performed after 72 h to obtain mucosal tissue samples for histological examination. For the determination of TBO biodistribution, additional groups received the same TBO doses and were sacrificed after 1 min or 10 min. Specimens were removed and frozen immediately for digital fluorescence imaging. No necrotic or inflammatory changes were found in the buccal mucosa of the animals with any of the treatments (using up to 200 microg/ml TBO and 340 J/cm(2) laser light). A high TBO fluorescence in the epithelium, particularly in the keratinised layer, with almost no fluorescence in the underlying connective tissue was demonstrated by the digital imaging. The results of this study suggest that TBO-mediated PDT (within the concentrations and light doses tested) could be a safe antimicrobial approach for the oral infections without damaging the adjacent normal tissue.

Optimisation of illumination for photodynamic therapy with mTHPC on normal colon and a transplantable tumour in rats

Recent reports suggest that the effect of photodynamic therapy (PDT) can be enhanced by fractionating the light dose or reducing the light fluence rate. We assessed these options on two tissues in rats (normal colon and a transplanted fibrosarcoma) using the photosensitiser meta-tetrahydroxyphenylchlorin (mTHPC). Animals were sensitised with 0.3 mg/kg mTHPC, 3 days prior to illumination with red light (652 nm) using a single fibre touching the target tissue and killed 1-3 days later for quantitative measurement of the extent of PDT necrosis. Results were similar for both tissues, although the differences between illumination regimens were less marked in tumour tissue. Using continuous illumination and a fixed low energy in colon, the extent of necrosis was up to almost three times larger with 5 mW than with 100 mW, although the maximum attainable necrosis was independent of power. The long treatment time using 5 mW could be halved without loss of effect by increasing the power during treatment. Dividing the light into two equal fractions at 100 mW increased the lesion size by up to 20% in colon (independent of the timing of the dark interval), but by only 10% in tumour and had no effect at 20 mW. Previous studies using 5-aminolaevulinic acid (ALA) showed a much larger effect of fractionation that was critically dependent on the timing of the dark interval. We postulate that enhancement of PDT by fractionation is due to improved oxygen supply to the treated area which may be due to reversal of temporary vascular occlusion (more likely with ALA) or less rapid photochemical consumption of oxygen (more likely with mTHPC). At lower fluence rates, the oxygen consumption rate is not fast enough to be improved by fractionation. We conclude that fractionated or low power light delivery can enhance PDT with mTHPC. Although the effects are not large, this may be of value for interstitial treatment of solid tumours when multiple sites are treated simultaneously.

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

Reperfusion injury can occur when blood flow is restored after a transient period of ischaemia. The resulting cascade of reactive oxygen species damages tissue. This mechanism may contribute to the tissue damage produced by 5-aminolaevulinic acid-induced photodynamic therapy, if this treatment temporarily depletes oxygen in an area that is subsequently reoxygenated. This was investigated in the normal colon of female Wistar rats. All animals received 200 mg kg(-1) 5-aminolaevulinic acid intravenously 2 h prior to 25 J (100 mW) of 628 nm light, which was delivered continuously or fractionated (5 J/150 second dark interval/20 J). Animals were recovered following surgery, killed 3 days later and the photodynamic therapy lesion measured macroscopically. The effects of reperfusion injury were removed from the experiments either through the administration of free radical scavengers (superoxide dismutase (10 mg kg(-1)) and catalase (7.5 mg kg(-1)) in combination) or allopurinol (an inhibitor of xanthine oxidase (50 mg kg(-1))). Prior administration of the free radical scavengers and allopurinol abolished the macroscopic damage produced by 5-aminolaevulinic acid photodynamic therapy in this model, regardless of the light regime employed. As the specific inhibitor of xanthine oxidase (allopurinol) protected against photodynamic therapy damage, it is concluded that reperfusion injury is involved in the mechanism of photodynamic therapy in the rat colon.

A preliminary investigation of the effects of arsenate on irradiation-induced DNA damage in cultured human lung fibroblasts

Single-cell gel electrophoresis (the comet assay) was used to assess single-strand breaks (SSBs) produced in cultured lung human fibroblasts by xenon lamp irradiation alone, various concentrations of arsenate [As(V)], alone or various combinations of the two. It was found that significantly higher levels of SSBs were observed in the irradiated cells than the nonirradiated cells and that elevating levels of arsenate enhanced the level of damage detected in both irradiated and nonirradiated cells in a concentration-dependent manner; that is, incubating cells with arsenate alone produced marked DNA damage without an irradiation insult being necessary. The results of this study indicate that arsenate is acting as a cogenotoxin with irradiation in this cell line. This additive effect may also be cocarcinogenic, and as a result it is possible that less solar irradiation may be required to induce skin cancer in arsenic-exposed populations.

Immunosuppression as adjuvant therapy for biliary atresia

BACKGROUND/PURPOSE

Despite improvements in the surgical management of biliary atresia, the long-term incidence of progressive liver failure remains high. Because chronic inflammation involving both bile ducts and liver parenchyma contributes to the pathology, the authors have hypothesized that the liver damage may be altered using immunosuppressive therapy. The aim of this study was to examine the safety and efficacy of long-term steroid therapy in patients with biliary atresia.

METHODS

A retrospective analysis of all patients with biliary atresia treated with an hepatoportoenterostomy and postoperative steroid therapy at our 3 institutions was undertaken. Patients were treated uniformly with immunosuppressive doses of oral steroids for a minimum of 6 weeks after surgery.

RESULTS

Twenty-five infants with biliary atresia were treated with steroid therapy. Overall survival rate was 22 patients (88%) with a mean follow-up period of 50 months. Nineteen patients (76%) became jaundice free with native liver function. Four patients (16%) did not respond to treatment and required transplantation. Age less than 12 weeks was a crucial predictor of success of adjuvant steroid therapy. Cholangitis developed in 8 patients (32%). There were no complications caused by steroid therapy.

CONCLUSIONS

Steroid administration at immunosuppressive doses markedly improves the clinical outcome within the first 5 years after surgery as measured by jaundice-free status and survival without liver transplantation when compared with concurrent reports. These results suggest that immunosuppressive therapy is safe and has a positive impact on the clinical course of this disease. However, a randomized study is needed to ultimately prove such an hypothesis.

Oxygen monitoring during 5-aminolaevulinic acid induced photodynamic therapy in normal rat colon. Comparison of continuous and fractionated light regimes

Currently, the clinical use of 5-aminolaevulinic acid (ALA) induced protoporphyrin IX (PPIX) for photodynamic therapy (PDT) is limited by the maximum tolerated oral ALA dose (60 mg/kg). Attempts have been made to enhance this treatment modality without increasing the administered dose of ALA. One way to do this is through light dose fractionation, where the irradiation is interrupted at a particular point for a short period of time. This can produce up to three times more necrosis than with the same light dose delivered without a break. An oxygen microelectrode was employed to study the effect of continuous and fractionated light regimes on the level of oxygen in the colon of normal Wistar rats during ALA PDT. A rapid decline in pO2 occurred close to the irradiation fibre as soon as the light dose commenced. With the fractionated regime, a partial recovery in pO2 was observed during the dark interval which was reversed soon after the second light fraction commenced. We have shown that the level of tissue oxygen at the treatment site is affected differently when the light dose is fractionated, than when continuous illumination is employed. This factor may at least partially explain the difference in outcome of these two treatment regimes. Further, oxygen measurements might prove to be a useful way of monitoring PDT treatments if they can predict whether tissue is likely to be viable following treatment.

Light dose fractionation to enhance photodynamic therapy using 5-aminolevulinic acid in the normal rat colon

5-Aminolevulinic acid (ALA) is an attractive photosensitizing agent for photodynamic therapy (PDT) as its photoactive derivative, protoporphyrin IX, is metabolized within 1-2 days, eliminating prolonged skin photosensitivity. However, at the maximum dose patients can tolerate by mouth, 60 mg/kg, only superficial effects are seen. This paper extends earlier studies on enhancing the effect by light fractionation. Experiments in the normal rat colon looked at the area of necrosis around a single light delivery fiber 3 days after PDT with a range of light-dose fractionation regimes. All animals were given 200 mg/kg ALA intravenously 2 h prior to light delivery (100 mW at 635 nm) and each interruption in illumination was for 150 s. The area of PDT necrosis (total dose 25 J) could be increased by a factor of 3 with a single interval after 5 J, compared with continuous illumination. Alternatively, with this single break, the total light dose could be reduced by 60% to achieve the same area of necrosis as with continuous illumination. This simple modification to PDT with ALA could markedly reduce current treatment times as well as increasing clinical efficacy.

Enhancement of 5-aminolaevulinic acid-induced photodynamic therapy in normal rat colon using hydroxypyridinone iron-chelating agents

Currently, the clinical use of 5-aminolaevulinic acid (ALA)-induced protoporphyrin IX (PPIX) for photodynamic therapy (PDT) is limited by the maximum tolerated oral ALA dose (60 mg kg(-1)). This study investigates whether hydroxypyridinone iron-chelating agents can be used to enhance the tissue levels of PPIX, without increasing the administered dose of ALA. Quantitative charge-coupled device (CCD) fluorescence microscopy was employed to study PPIX fluorescence pharmacokinetics in the colon of normal Wistar rats. The iron chelator, CP94, when administered with ALA was found to produce double the PPIX fluorescence in the colonic mucosa, compared with the same dose of ALA given alone and to be more effective than the other iron chelator studied, CP20. Microspectrofluorimetric studies demonstrated that PPIX was the predominant porphyrin species present. PDT studies conducted on the colonic mucosa showed that the simultaneous administration of 100 mg kg(-1) CP94 i.v. and 50 mg kg(-1) ALA i.v. produced an area of necrosis three times larger than similar parameters without the iron-chelating agent with the same light dose. It is possible, therefore, to increase the amount of necrosis produced by ALA-induced PDT substantially, without increasing the administered dose of ALA, through the simultaneous administration of the iron-chelating agent, CP94.

Aminoacyl-tRNA synthesis in Archaea

The mechanism of aminoacyl-tRNA synthesis differs substantially between Archaea, Bacteria and Eukarya. Sequencing of archaeal genomes has suggested that the asparaginyl-, cysteinyl-, glutaminyl- and lysyl-tRNA synthetases are absent from a number of organisms in this kingdom. The absence of the asparaginyl- and glutaminyl-tRNA synthetases is in agreement with the observation that Asn-tRNA and Gln-tRNA are synthesized by tRNA-dependent transamidation of Asp-tRNA and Glu-tRNA respectively in the archaeon Haloferax volcanii. Biochemical and genetic studies have now shown that while the cysteinyl- and lysyl-tRNA synthetases are present, the enzymes responsible for these activities are unique to Archaea.