The effect of EDTA and serum on endogenous porphyrin accumulation and photodynamic sensitization of human K562 leukemic cells

5-Aminolevulinic Acid as a Theranostic Agent for Tumor Fluorescence Imaging and Photodynamic Therapy

5-Aminolevulinic acid (ALA) is a naturally occurring amino acid synthesized in all nucleated mammalian cells. As a porphyrin precursor, ALA is metabolized in the heme biosynthetic pathway to produce protoporphyrin IX (PpIX), a fluorophore and photosensitizing agent. ALA administered exogenously bypasses the rate-limit step in the pathway, resulting in PpIX accumulation in tumor tissues. Such tumor-selective PpIX disposition following ALA administration has been exploited for tumor fluorescence diagnosis and photodynamic therapy (PDT) with much success. Five ALA-based drugs have now received worldwide approval and are being used for managing very common human (pre)cancerous diseases such as actinic keratosis and basal cell carcinoma or guiding the surgery of bladder cancer and high-grade gliomas, making it the most successful drug discovery and development endeavor in PDT and photodiagnosis. The potential of ALA-induced PpIX as a fluorescent theranostic agent is, however, yet to be fully fulfilled. In this review, we would like to describe the heme biosynthesis pathway in which PpIX is produced from ALA and its derivatives, summarize current clinical applications of ALA-based drugs, and discuss strategies for enhancing ALA-induced PpIX fluorescence and PDT response. Our goal is two-fold: to highlight the successes of ALA-based drugs in clinical practice, and to stimulate the multidisciplinary collaboration that has brought the current success and will continue to usher in more landmark advances.

Experimental investigation of a combinational iron chelating protoporphyrin IX prodrug for fluorescence detection and photodynamic therapy

Photodynamic therapy (PDT) is an oxygen-dependent, light-activated, and locally destructive drug treatment of cancer. Protoporphyrin IX (PpIX)-induced PDT exploits cancer cells' own innate heme biosynthesis to hyper-accumulate the naturally fluorescent and photoactive precursor to heme, PpIX. This occurs as a result of administering heme precursors (e.g., aminolevulinic acid; ALA) because the final step of the pathway (the insertion of ferrous iron into PpIX by ferrochelatase to form heme) is relatively slow. Separate administration of an iron chelating agent has previously been demonstrated to significantly improve dermatological PpIX-PDT by further limiting heme production. A newly synthesized combinational iron chelating PpIX prodrug (AP2-18) has been assessed experimentally in cultured primary human cells of bladder and dermatological origin, as an alternative photosensitizing agent to ALA or its methyl or hexyl esters (MAL and HAL respectively) for photodetection/PDT. Findings indicated that the technique of iron chelation (either through the separate administration of the established hydroxypyridinone iron chelator CP94 or the just as effective combined AP2-18) did not enhance either PpIX fluorescence or PDT-induced (neutral red assessed) cell death in human primary normal and malignant bladder cells. However, 500 µM AP2-18 significantly increased PpIX accumulation and produced a trend of increased cell death within epithelial squamous carcinoma cells. PpIX accumulation destabilized the actin cytoskeleton in bladder cancer cells prior to PDT and resulted in caspase-3 cleavage/early apoptosis afterwards. AP2-18 iron chelation should continue to be investigated for the enhancement of dermatological PpIX-PDT applications but not bladder photodetection/PDT.

Light-assisted anticancer photodynamic therapy using porphyrin-doped nanoencapsulates

Light activatable porphyrinic photosensitizers (PSs) are essential components of anticancer and antimicrobial therapy and diagnostic imaging. However, their biological applications are quite challenging due to the lack of hydrophilicity and biocompatibility. To overcome such drawbacks, photosensitizers can be doped into a biocompatible polymer such as gelatin and further can be used for biomedical applications. Herein, first, a novel A4 type porphyrin PS [5,10,15,20-tetrakis(4-pyridylamidephenyl)porphyrin; TPyAPP] was synthesized via a rational route with good yield. Further, this porphyrin was encapsulated into the gelatin nanoparticles (GNPs) to develop hydrophilic phototherapeutic nanoagents (PTNAs, A4por-GNPs). Notably, the synthesis of such porphyrin-doped GNPs avoids the use of any toxic chemicals or solvents. The nanoprobes have also shown good fluorescence quantum yield demonstrating their applicability in bioimaging. Further, the mechanistic aspects of the anticancer and antimicrobial efficacy of the developed A4por-GNPs were evaluated via singlet oxygen generation studies. Overall, our results indicated porphyrin-doped biodegradable polymeric nanoparticles act as effective phototherapeutic agents against a broad range of cancer cell lines and microbes upon activation by the low-cost LED light.

Deep proteome profiling of SW837 cells treated by photodynamic therapy (PDT) reveals the underlying mechanisms of metronomic and acute PDTs

AIM

Metronomic photodynamic therapy (mPDT) with a longer irradiation time and lower energy compared with acute (or classic) photodynamic therapy (aPDT) is a more effective treatment than aPDT for tumor cells, especially colorectal cancer. However, the underlying mechanisms of the superior effects of mPDT are unknown.

METHODS

we used SWATH-MS (sequential window acquisition of all theoretical mass spectra) to identify differentially expressed proteins (DEPs) specific to aPDT (conventional fluence rate, 20 mW/cm², 4 min 10 s), mPDT (metronomic fluence rate, 0.4 mW/cm², 3.5 h), and control groups of SW837 cells. The photosensitizer used in both PDT methods was aminolevulinic acid which were incubated with the cells before irradiation.

RESULTS

A total of 6805 proteins were identified in the three groups of SW837 cells. aPDT induced 333 DEPs and mPDT induced 1716 DEPs compared with the control. We identified 185 common DEPs in the two PDT groups, 148 different DEPs in the aPDT group, and 1531 different DEPs in the mPDT group. Most of the 185 common DEPs were involved in the extracellular component, participated in the processes of vesicle transport and secretion, binding, and hydrolase/catalytic activity. They were also involved in PI3K-Akt, cGMP-PKG, RAS, and aAMP signaling pathways. In addition, the 1531 different DEPs in the mPDT group participated in similar processes and molecular functions, but in a more complex manner than those in the aPDT group.

CONCLUSION

our proteome data suggest that mPDT has a complex tumor destruction mechanism with more involved proteins compared with aPDT, which may explain the better tumor killing effect of mPDT.

Photodynamic Therapy and the Biophysics of the Tumor Microenvironment

Targeting the tumor microenvironment (TME) provides opportunities to modulate tumor physiology, enhance the delivery of therapeutic agents, impact immune response and overcome resistance. Photodynamic therapy (PDT) is a photochemistry-based, nonthermal modality that produces reactive molecular species at the site of light activation and is in the clinic for nononcologic and oncologic applications. The unique mechanisms and exquisite spatiotemporal control inherent to PDT enable selective modulation or destruction of the TME and cancer cells. Mechanical stress plays an important role in tumor growth and survival, with increasing implications for therapy design and drug delivery, but remains understudied in the context of PDT and PDT-based combinations. This review describes pharmacoengineering and bioengineering approaches in PDT to target cellular and noncellular components of the TME, as well as molecular targets on tumor and tumor-associated cells. Particular emphasis is placed on the role of mechanical stress in the context of targeted PDT regimens, and combinations, for primary and metastatic tumors.

Impact of thiosemicarbazones on the accumulation of PpIX and the expression of the associated genes

Thiosemicarbazone derivatives are known for their broad biological activity including their antitumor potency. The aim of the current study was to examine the effect of a novel series of non-toxic iron chelators on the accumulation of protoporphyrin IX after external 5-aminolevulonic acid administration. From this series we selected one the most promising derivative which causes a pronounced increase in the concentration of protoporphyrin IX. The increase of the photosensitizer concentration is necessary for the trigger the efficient therapeutic effect of the photodynamic reaction. For selected compound 2 we performed an examination of a panel of the genes that are involved in the heme biosynthesis and degradation. Results indicated the crucial roles of ferrochelatase and heme oxygenase in the described processes. Surprisingly, there was a strict dependence on the type of the tested cell line. A decrease in the expression of the two aforementioned enzymes after incubation with compound 2 and 5-aminolevulonic acid is a commonly known fact and we detected this trend for the MCF-7 and HCT 116 cell lines. However, we noticed the upregulation of the tested targets for the Hs683 cells. These unconventional results prompted us to do a more in-depth analysis of the described processes. In conclusion, we found that compound 2 is a novel, highly effective booster of photodynamic therapy that has prospective applications.

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

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

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

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This enhancement translated into greater cytotoxicity on irradiation.

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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.

Design of Bifunctional Dendritic 5-Aminolevulinic Acid and Hydroxypyridinone Conjugates for Photodynamic Therapy

Iron chelators have recently attracted interest in the field of photodynamic therapy (PDT) owing to their role in enhancement of intracellular protoporphyrin IX (PpIX) generation induced by 5-aminolevulinic acid (ALA) via the biosynthetic heme cycle. Although ALA is widely used in PDT, cellular uptake of ALA is limited by its hydrophilicity. In order to improve ALA delivery and enhance the PpIX production, several dendrimers incorporating both ALA and 3-hydroxy-4-pyridinone (HPO) were synthesized. The ability of the dendrimers to enter cells and be metabolized to the PpIX photosensitizer was studied in several human cancer cell lines. The dendrimers were found to be significantly more efficient than ALA alone in PpIX production. The higher intracellular PpIX levels showed a clear correlation with enhanced cellular phototoxicity following light exposure. Dendritic derivatives are therefore capable of efficiently delivering both ALA and HPO, which act synergistically to amplify in vitro PpIX levels and enhance PDT efficacy.

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.

Comparing desferrioxamine and light fractionation enhancement of ALA-PpIX photodynamic therapy in skin cancer

Background:

Aminolevulinic acid (ALA)-based photodynamic therapy (PDT) provides selective uptake and conversion of ALA into protoporphyrin IX (PpIX) in actinic keratosis and squamous cell carcinoma, yet large response variations in effect are common between individuals. The aim of this study was to compare pre-treatment strategies that increase the therapeutic effect, including fractionated light delivery during PDT (fPDT) and use of iron chelator desferrioxamine (DFO), separately and combined.

Methods:

Optical measurements of fluorescence were used to quantify PpIX produced, and the total amount of PpIX photobleached as an implicit measure of the photodynamic dose. In addition, measurements of white light reflectance were used to quantify changes in vascular physiology throughout the PDT treatment.

Results:

fPDT produced both a replenishment of PpIX and vascular re-oxygenation during a 2 h dark interval between the first and second PDT light fractions. The absolute photodynamic dose was increased 57% by fPDT, DFO and their combination, as compared with PDT group (from 0.7 to 1.1). Despite that light fractionation increased oedema and scab formation during the week after treatment, no significant difference in long-term survival has been observed between treatment groups. However, outcomes stratified on the basis of measured photodynamic dose showed a significant difference in long-term survival.

Conclusions:

The assessment of implicit photodynamic dose was a more significant predictor of efficacy for ALA-PDT skin cancer treatments than prescription of an enhanced treatment strategy, likely because of high individual variation in response between subjects.

Design and synthesis of 5-aminolaevulinic acid/3-hydroxypyridinone conjugates for photodynamic therapy: enhancement of protoporphyrin IX production and photo-toxicity in tumor cells

A series of ALA-HPO conjugates was prepared. One such conjugate was found to possess high phototoxicity.

Aminolevulinic Acid-Based Tumor Detection and Therapy: Molecular Mechanisms and Strategies for Enhancement

Aminolevulinic acid (ALA) is the first metabolite in the heme biosynthesis pathway in humans. In addition to the end product heme, this pathway also produces other porphyrin metabolites. Protoporphyrin (PpIX) is one heme precursor porphyrin with good fluorescence and photosensitizing activity. Because tumors and other proliferating cells tend to exhibit a higher level of PpIX than normal cells after ALA incubation, ALA has been used as a prodrug to enable PpIX fluorescence detection and photodynamic therapy (PDT) of lesion tissues. Extensive studies have been carried out in the past twenty years to explore why some tumors exhibit elevated ALA-mediated PpIX and how to enhance PpIX levels to achieve better tumor detection and treatment. Here we would like to summarize previous research in order to stimulate future studies on these important topics. In this review, we focus on summarizing tumor-associated alterations in heme biosynthesis enzymes, mitochondrial functions and porphyrin transporters that contribute to ALA-PpIX increase in tumors. Mechanism-based therapeutic strategies for enhancing ALA-based modalities including iron chelators, differentiation agents and PpIX transporter inhibitors are also discussed.

Clearance mechanism of protoporphyrin IX from mouse skin after application of 5-aminolevulinic acid

BACKGROUND

5-Aminolevulinic acid (ALA) or its esters mediated photodynamic therapy (PDT) is the most widely practiced form of PDT in dermatology. One of its advantages is that undesirable photosensitization lasts only for 24-48 h. In order to optimize ALA-PDT it is necessary to understand the mechanisms of intracellular production and clearance of PpIX (efflux from cells into blood stream and/or its conversion into haem). The aim of this study is to investigate the factors controlling the clearance of intracellular PpIX from healthy skin of mice.

METHODS

PpIX was induced in mouse skin by topical or systemic application of ALA or by topical application of the iron chelator ethylenediaminetetraacetic acid (EDTA). Fluorescence spectroscopy was used to study PpIX kinetics in alive and dead skin.

RESULTS

Topical application of ALA or EDTA leads to porphyrin production in living skin, but not in excised skin. The clearance rates of PpIX from alive and dead skin were the same in the absence of an intracellular ALA pool. The clearance half-life of EDTA-induced PpIX was 4-7 times longer than that of PpIX after application of ALA.

CONCLUSIONS

Skin temperature and intracellular iron availability strongly affect PpIX clearance, while ALA application mode (topical versus systemic) and skin viability (dead versus alive) have no influence on PpIX decay. These results demonstrate that the clearance kinetics of PpIX from skin are determined mostly by the conversion of PpIX into haem, while the cellular efflux of PpIX into blood plays a minor role.

Modulating ALA-PDT efficacy of mutlidrug resistant MCF-7 breast cancer cells using ALA prodrug

Multi-drug resistance of breast cancer is a major obstacle in chemotherapy of cancer treatments. Recently it was suggested that photodynamic therapy (PDT) can overcome drug resistance of tumors. ALA-PDT is based on the administration of 5-aminolevulinic acid (ALA), the natural precursor for the PpIX biosynthesis, which is a potent natural photosensitizer. In the present study we used the AlaAcBu, a multifunctional ALA-prodrug for photodynamic inactivation of drug resistant MCF-7/DOX breast cancer cells. Supplementation of low doses (0.2mM) of AlaAcBu to the cells significantly increased accumulation of PpIX in both MCF-7/WT and MCF-7/DOX cells in comparison to ALA, or ALA + butyric acid (BA). In addition, our results show that MCF-7/DOX cells are capable of producing higher levels of porphyrins than MCF-7/WT cells due to low expression of the enzyme ferrochelatase, which inserts iron into the tetra-pyrrol ring to form the end product heme. Light irradiation of the AlaAcBu treated cells activated efficient photodynamic killing of MCF-7/DOX cells similar to the parent MCF-7/WT cells, depicted by low mitochondrial enzymatic activity, LDH leakage and decreased cell survival following PDT. These results indicate that the pro-drug AlaAcBu is an effective ALA derivative for PDT treatments of multidrug resistant tumors.

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.

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.

Silencing of ferrochelatase enhances 5-aminolevulinic acid-based fluorescence and photodynamic therapy efficacy

Background:

Recurrence of glioma frequently occurs within the marginal area of the surgical cavity due to invading residual cells. 5-Aminolevulinic acid (5-ALA) fluorescence-guided resection has been used as effective therapeutic modalities to improve discrimination of brain tumour margins and patient prognosis. However, the marginal areas of glioma usually show vague fluorescence, which makes tumour identification difficult, and the applicability of 5-ALA-based photodynamic therapy (PDT) is hampered by insufficient therapeutic efficacy in glioma tissues.

Methods:

To overcome these issues, we assessed the expression of ferrochelatase (FECH) gene, which encodes a key enzyme that catalyses the conversion of protoporphyrin IX (PpIX) to heme, in glioma surgical specimens and manipulated FECH in human glioma cell lines.

Results:

Prominent downregulation of FECH mRNA expression was found in glioblastoma tissues compared with normal brain tissues, suggesting that FECH is responsible for PpIX accumulation in glioblastoma cells. Depletion of FECH by small interference RNA enhanced PpIX fluorescence after exposure to 5-ALA concomitant with increased intracellular PpIX accumulation in glioma cells. Silencing of FECH caused marked growth inhibition and apoptosis induction by PDT in glioma cells.

Conclusion:

These results suggest that knockdown of FECH is a potential approach to enhance PpIX fluorescent quality for optimising the subjective discrimination of vague fluorescence and improving the effect of 5-ALA-PDT.

Rapid upregulation of cytoprotective nitric oxide in breast tumor cells subjected to a photodynamic therapy-like oxidative challenge

Many tumor cells produce nitric oxide (NO) as an antiapoptotic/progrowth molecule which also promotes antiogenesis and tumor expansion. This study was designed to examine possible antagonistic effects of endogenous NO on tumor eradication by photodynamic therapy (PDT). Using COH-BR1 breast cancer cells sensitized in mitochondria with 5-aminolevulinic acid (ALA)-generated protoporphyrin IX as a model for ALA-based PDT, we found that caspase-9 activation and apoptotic death following irradiation were strongly enhanced by 1400W, an inhibitor of inducible nitric oxide synthase (iNOS). RT-PCR and Western analyses revealed a substantial upregulation of both iNOS mRNA and protein, beginning ca 4 h after irradiation and persisting for at least 20 h. Accompanying this was a strong 1400W-inhibitable increase in intracellular NO, as detected with the NO probe, DAF-2-DA. Short hairpin RNA-based iNOS knockdown in COH-BR1 cells dramatically reduced NO production under photostress while enhancing caspase-9 activation and apoptosis. These findings suggest that cytoprotective iNOS/NO induction in PDT-treated tumor cells could reduce treatment efficacy, and point to pharmacologic intervention with iNOS inhibitors for counteracting this.

Application of 5-aminolevulinic acid and its derivatives for photodynamic therapy in vitro and in vivo

Photodynamic therapy (PDT) with 5-aminolevulinic acid (ALA) is the most widely used form of PDT in clinical practice. Topical application of ALA leads to overproduction of the endogenous photosensitizer protoporphyrin IX (PpIX). ALA-PDT is efficient treatment of superficial skin lesions, but not for thicker lesions. The main reason for this is suboptimal penetration of ALA molecules through cellular membranes and through stratum corneum of intact skin. Different approaches (formulations, mechanical and physical penetration enhancers, ALA derivatives) are currently used to increase the penetration. The content and distribution of ALA intracellularly and in tissues is difficult to measure, but PpIX content, on a relative scale, can be easily measured by fluorimetric assays.

Differential response of porcine osteoblasts and chondrocytes in cell or tissue culture after 5-aminolevulinic acid-based photodynamic therapy

OBJECTIVE

Outcome in osteochondral allografting is limited by the immunological incompatibility of the grafted tissue. Based on a resistance of chondrocytes to photodynamic therapy in cell culture it is proposed that 5-aminolevulinic acid-based photodynamic therapy (5-ALA-PDT) might be used to inactivate bone while maintaining viability of chondrocytes and thus immunomodulate bone selectively.

METHODS

Chondrocytes and osteoblasts from porcine humeral heads were either isolated (cell culture) or treated in situ (tissue culture). To quantify cytotoxic effects of 5-ALA-PDT (0-20 J/cm(2), 100 mW/cm(2)) an (3-(4,5-dimethylthiazol-2-yl)-2,5-di-phenyltetrazolium bromide) (MTT)-assay was used in cell culture and in situ hybridization in tissue culture to assess metabolic active cells (functional osteoblasts: col alpha(1)(I) mRNA, functional chondrocytes: col alpha(1)(II) mRNA).

RESULTS

In cell culture, survival after 5-ALA-PDT was significantly higher for chondrocytes (5 J/cm(2): 87+/-12% compared to untreated cells) than for osteoblasts (5J/cm(2): 12+/-11%). In tissue culture, the percentage of functional chondrocytes in cartilage showed a decrease after 5-ALA-PDT (direct fixation: 92+/-2%, 20 J/cm(2): 35+/-15%; P<0.0001). A significant decrease in the percentage of bone surfaces covered by functional osteoblasts was observed in freshly harvested (31+/-3%) compared to untreated tissues maintained in culture (11+/-4%, P<0.0001), with no further decrease after 5-ALA-PDT.

CONCLUSION

Chondrocytes were more resistant to 5-ALA-PDT than osteoblasts in cell culture, while in tissue culture a loss of functional chondrocytes was observed after 5-ALA-PDT. Since osteoblasts - but not chondrocytes - were sensitive to the tissue culture conditions, devitalized bone with functional cartilage might already be achieved by applying specific tissue culture conditions even without 5-ALA-PDT.

Enhancement of methyl-aminolevulinate photodynamic therapy by iron chelation with CP94: an in vitro investigation and clinical dose-escalating safety study for the treatment of nodular basal cell carcinoma

PURPOSE

Methyl-aminolevulinate (MAL) photodynamic therapy (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. Combining iron chelators with MAL has the potential to increase the accumulation of the photosensitizer protoporphyrin IX (PpIX) by reducing its bioconversion to heme. This paper investigates this method of enhancement both in vitro and for the first time clinically for the treatment of nodular basal cell carcinoma (BCC).

METHODS

Enhancement of MAL-induced PpIX accumulation by the iron chelator CP94 was quantified fluorometrically in human cultured cells (including three dermatological cell types). An open, dose-escalating, pilot study was then conducted in patients with nodular BCC, to determine the safety of this pharmacological modification.

RESULTS

Large enhancements in PpIX accumulation were observed in the cultured cells when co-incubated with the iron chelator CP94. Clinically the addition of CP94 was found to be feasible and safe. In addition greater reductions in tumor depth were observed in the CP94 co-incubated tumors.

CONCLUSION

Iron chelation by CP94 is an effective enhancer of MAL-induced PpIX accumulation in vitro. This method of enhancement was safely applied to a clinical PDT protocol with no unexpected adverse effects reported. Although the clinical investigation was only intended to be a small pilot to assess safety, enhancements in tumor clearance were observed both clinically and histologically when CP94 was included in the photosensitizing cream.

ALA and its clinical impact, from bench to bedside

ALA-induced protoporphyrin IX (PpIX) is used for fluorescence diagnosis (ALA-FD) and for fluorescence-guided resection of both (pre)malignant and non-malignant diseases. ALA is also applied in photodynamic therapy (ALA-PDT) of superficial (pre)malignant lesions in dermatology, urology, neurosurgery, otorhinolaryngology, gynecology and gastroenterology. Today, ALA is approved as Levulan for actinic keratoses, the ALA-methyl ester Metvix for actinic keratoses and basal cell carcinoma, the ALA-hexyl ester Hexvix for the diagnosis of bladder cancer and Gliolan for malignant glioma. The use of ALA for PDT and FD was established around 25 years ago, with most of the fundamental knowledge gained at the "bench" and implemented at the "bedside" due to the diligence of a few researchers within the first 10 years of research. After 1993 ALA research was taken up by many groups. For patient treatment, several factors are relevant. Administered mainly in a topical or oral form, ALA penetrates tissue in a sub-optimal way, which is currently improved by special techniques and the use of ALA-esters. PpIX accumulation is elevated in many malignant tissues, several tissue abnormalities, and in mucosa. It is also found at elevated levels in macrophages, dendritic cells and activated lymphocytes. Following sufficient PpIX accumulation in the target cells, irradiation is carried out which may be accompanied by a burning sensation at the treatment site. Due to a saturation process of PpIX formation and rapid photobleaching during irradiation the risk of overtreatment is relatively low. Pharmacokinetical studies have demonstrated a low systemic photosensitivity and excretion of PpIX via natural routes.

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.

Differential effects of photofrin, 5-aminolevulinic acid and calphostin C on glioma cells

The invasive nature of malignant gliomas makes treatment by surgery alone extremely difficult. However, the preferential accumulation of photosensitisers in neoplastic tissues suggests photodynamic therapy (PDT) may be useful as an adjuvant therapy following tumour resection. In this study, the potential use of three different photosensitisers, namely Photofrin, 5-aminolevulinic acid (5-ALA) and calphostin C in the treatment of glioma was investigated. The uptake, cytotoxicity on U87 and GBM6840 glioma cell lines were determined by flow cytometry and MTT assay respectively. Their effect on glioma cell invasiveness was evaluated by (1) measuring the levels of matrix degradation enzymes matrix metalloproteinase (MMP)-2 and -9 using gelatin zymography, and (2) Matrigel invasion assay. The results showed that uptake of calphostin C reached saturation within 2 h, while Photofrin and 5-ALA induced protoporphyrin IX (PpIX) levels elevated steadily up to 24 h. Photocytotoxic effect on the two glioma cell lines was similar with LD50 at optimal uptake: 1 microg/mL Photofrin at 1.5 J/cm(2); 1 mM 5-ALA at 2 J/cm(2) and 100 nM calphostin C at 2 J/cm(2). The inhibition in cell proliferation after Photofrin treatment was similar for both cell lines, which correlated to more cells being arrested in the G0/G1 phase of the cell cycle (P<0.01). By contrast, U87 was more sensitive to calphostin C whereas GBM6840 was more susceptible to 5-ALA treatment. The ability of both cell lines to migrate through the Matrigel artificial basement membrane was significantly reduced after PDT (P<0.001). This might be due to a decreased production in MMP-2 and MMP-9, together with the reduction of adhesion molecule expression. Photofrin was most superior in inhibiting cell invasion and calphostin C was least effective in reducing adhesion molecule expression. Taken together, PDT could be useful in the treatment of gliomas but the choice of photosensitisers must be taken into consideration.

In vitro phototoxicity of 5-aminolevulinic acid and its methyl ester and the influence of barrier properties on their release from a bioadhesive patch

Topical administration of excess exogenous 5-aminolevulinic acid (ALA) leads to selective accumulation of the potent photosensitiser protoporphyrin IX (PpIX) in neoplastic cells, which can then be destroyed by irradiation with visible light. Due to its hydrophilicity, ALA penetrates deep lesions, such as nodular basal cell carcinomas (BCCs) poorly. As a result, more lipophilic esters of ALA have been employed to improve tissue penetration. In this study, the in vitro release of ALA and M-ALA from proprietary creams and novel patch-based systems across normal stratum corneum and a model membrane designed to mimic the abnormal stratum corneum overlying neoplastic skin lesions were investigated. Receiver compartment drug concentrations were compared with the concentrations of each drug producing high levels of PpIX production and subsequent light-induced kill in a model neoplastic cell line (LOX). LOX cells were found to be quite resistant to ALA- and M-ALA-induced phototoxicity. However, drug concentrations achieved in receiver compartments were comparable to those required to induce high levels of cell death upon irradiation in cell lines reported in the literature. Patches released significantly less drug across normal stratum corneum and significantly more across the model membrane. This is of major significance since the selectivity of PDT for neoplastic lesions will be further enhanced by the delivery system. ALA/M-ALA will only be delivered in significant amounts to the abnormal tissue. PpIX will only then accumulate in the neoplastic cells and the normal surrounding tissue will be unharmed upon irradiation.

Phototoxicity of 5-aminolevulinic acid in the HeLa cell line as an indicative measure of photodynamic effect after topical administration to gynecological lesions of intraepithelial form

PURPOSE

The depth-resolved pattern of aminolevulinic acid (ALA) concentration in excised vaginal tissue was determined after in vitro application of an ALA-loaded bioadhesive patch. From this data, the tissue concentration of ALA achievable at a specified depth from the surface could be related to the concentration needed to elicit a photodynamic effect in a model gynecological tumor cell line (HeLa).

METHODS

Excised vaginal tissue was mounted in a modified Franz diffusion cell and exposed to a water-soluble, ALA-loaded, bioadhesive patch. After a period of time, the tissue was cryostatically sectioned and the stratal concentration of radiolabeled ALA determined using scintillation spectroscopy. HeLa cells were cultured in media containing specific concentrations of ALA and exposed to standard photodynamic protocols of light exposure.

RESULTS

An ALA concentration of 65.6 mM was achievable at 2.375 mm from the tissue surface after application of ALA-loaded patch. The photodynamic effectiveness of this concentration was demonstrated in HeLa with exposure to concentrations exceeding 1.0 mM ALA bringing about reductions in viable cell numbers by 90%. An enhancement of PpIX production using adjunctive EDTA over the clinically relevant 4 h application time interval was shown to be minimal in HeLa. Instead, PpIX production was more closely correlated with ALA concentration, with 100 mM ALA producing approximately 3100 ng PpIX mg(-1) protein in the same time period.

CONCLUSIONS

Given that vaginal intraepithelial neoplasias can extend to 2.0 mm from the lesion surface, the ALA permeability derived from a bioadhesive patch is sufficient to induce photosensitization suitable for light induced destruction at deep sites of this type of lesion.