The influence of temperature on photodynamic cell killing in vitro with 5-aminolevulinic acid

Efficacy of two different methods of cold air analgesia for pain relief in PDT of actinic keratoses of the head region - a randomized controlled comparison study

BACKGROUND

Photodynamic therapy (PDT) is an effective method for treating actinic keratosis (AK) with pain during illumination representing the major side effect. The efficacy of two different cooling methods for pain relief in PDT of AK in the head region was compared.

METHODS

Randomized, assessor-blinded, half side comparison study in 20 patients with symmetrically distributed AK on the head. Conventional PDT was performed on both halves of the scalp or face by applying 20% aminolevulinic acid cream (ALA) and subsequent illumination with incoherent red light. During illumination one side was cooled with a cold air blower (CAB) and the other with a standard fan (FAN) in a randomized fashion. Pain and skin temperature were recorded during and after PDT. The phototoxic skin reaction was evaluated up to seven days after PDT. The clearance rate of AK was assessed at 3 and 6 months after PDT.

RESULTS

Mean pain (VASmean), maximum pain intensity (VASmax) and the mean skin temperature during PDT were significantly lower with CAB as compared to FAN (VASmean: 2.7 ± 1.4 vs. 3.7 ± 2.1, p = 0.003; VASmax: 3.8 ± 2.0 vs. 4.8 ± 2.5, p = 0.002; 26.8 ± 2.0 °C vs. 32.1 ± 1.7 °C; p=<0.001). The severity of the phototoxic skin reaction and the clearance rate of AK did not differ between the two cooling methods.

CONCLUSION

Cooling with CAB during PDT has a greater analgesic effect than cooling with FAN. Patients with a lower skin temperature during illumination tended to experience less pain, however, this effect did not reach the level of statistical significance.

An insight into photodynamic therapy towards treating major dermatological conditions

Photodynamic therapy (PDT), as the name suggests is a light-based, non-invasive therapeutic treatment method that has garnered immense interest in the recent past for its efficacy in treating several pathological conditions. PDT has prominent use in the treatment of several dermatological conditions, which consequently have cosmetic benefits associated with it as PDT improves the overall appearance of the affected area. PDT is commonly used for repairing sun-damaged skin, providing skin rejuvenation, curbing pre-cancerous cells, treating conditions like acne, keratosis, skin-microbial infections, and cutaneous warts, etc. PDT mediates its action by generating oxygen species that are involved in bringing about immunomodulation, suppression of microbial load, wound-healing, lightening of scarring, etc. Although there are several challenges associated with PDT, the prominent ones being pain, erythema, insufficient delivery of the photosensitizing agent, and poor clinical outcomes, still PDT stands to be a promising approach with continuous efforts towards maximizing clinical efficacy while being cautious of the side effects and working towards lessening them. This article discusses the major skin-related conditions which can be treated or managed by employing PDT as a better or comparable alternative to conventional treatment approaches such that it also brings about aesthetic improvements thereof.

A Warp-Knitted Light-Emitting Fabric-Based Device for In Vitro Photodynamic Therapy: Description, Characterization, and Application on Human Cancer Cell Lines

Simple Summary

While photodynamic therapy appears to be a promising approach to treating cancers, the complexity of its parameters prevents wide acceptance. Accurate light dose measurement is one of the keys to photodynamic effect assessment, but it remains challenging when comparing different technologies. This work provides a complete demonstration of the technical performance of a homemade optical device, based on knitted light-emitting fabrics, called CELL-LEF. Thermal and optical distributions and related safeties are investigated. The results are discussed in relation to the requirements of photodynamic therapy. The usability of CELL-LEF is investigated on human cancer cell lines as a proof of concept. This study highlights that new light-emitting fabric-based technologies can be relevant light sources for in vitro photodynamic therapy studies of tomorrow.

Abstract

Photodynamic therapy (PDT) appears to be a promising strategy in biomedical applications. However, the complexity of its parameters prevents wide acceptance. This work presents and characterizes a novel optical device based on knitted light-emitting fabrics and dedicated to in vitro PDT involving low irradiance over a long illumination period. Technical characterization of this device, called CELL-LEF, is performed. A cytotoxic study of 5-ALA-mediated PDT on human cancer cell lines is provided as a proof of concept. The target of delivering an irradiance of 1 mW/cm² over 750 cm² is achieved (mean: 0.99 mW/cm²; standard deviation: 0.13 mW/cm²). The device can maintain a stable temperature with the mean thermal distribution of 35.1 °C (min: 30.7 °C; max: 38.4 °C). In vitro outcomes show that 5-ALA PDT using CELL-LEF consistently and effectively induced a decrease in tumor cell viability: Almost all the HepG2 cells died after 80 min of illumination, while less than 60% of U87 cell viability remained. CELL-LEF is suitable for in vitro PDT involving low irradiance over a long illumination period.

Treatment of cutaneous basal cell carcinoma with combined laser extirpation and methyl aminolevulinic acid: five-year success rates

INTRODUCTION

Basal cell carcinoma is the most common cancer. Excisional surgery is associated with a high clearance rate, at the expense of significant functional and aesthetic morbidity, especially within the T-zone or for extensive lesions. We report five-year follow-up outcomes for carbon dioxide laser extirpation of cutaneous basal cell carcinoma, assisted by immediate methyl aminolevulinate photodynamic therapy and cost-benefit considerations.

MATERIALS AND METHODS

Retrospective cohort database analysis of adult patients with biopsy-proven primary cutaneous basal cell carcinoma, completing five years of follow-up. Direct per-lesion cost was compared with conventional wide local excision. Patients with morphoeic basal cell carcinoma were excluded.

RESULTS

Treated lesions were up to 1% total body surface area and up to 3.8mm (1.38 ± 0.695cm, mean ± standard deviation) in biopsy-proven depth. At the five-year follow-up mark, 93.6% of treated areas remained free of recurrence. Nodular basal cell carcinoma was the most common subtype (41.5%). A mean tumour depth greater than 2 ± 0.872mm was significantly associated with recurrence (Mann-Whitney, p = 0.0487). For a service delivered through the NHS at 2015 prices, we report a 43% saving, equating to a saving of £235 per basal cell carcinoma or a national annualised saving of £70 million by 2025 for the NHS.

CONCLUSION

Our results suggest that CO2-assisted photodynamic therapy is non-inferior to excision but may offer better functional and cosmetic preservation at a fraction of the direct like for like cost of operative surgery. Investigation of this method by randomised controlled methodology is warranted.

Photodynamic Therapy for Photodamage, Actinic Keratosis, and Acne in the Cosmetic Practice

Photodynamic therapy is the combination of the initial application of a photosensitive chemical on the skin and then using typically a blue filter light of varying spectrums. This treatment protocol has been more useful and functional than other chemical peels and lasers for a variety of conditions. There has been efficacy in antiviral treatments, such as herpetic lesions; malignant cancers of the head and neck; and lung, bladder, and skin cancers. It has been tested for prostate cancers, cervical cancer, colorectal cancer, lung cancer, breast cancer, esophageal cancer, stomach cancer, pancreatic cancer, vaginal cancer, gliomas, and erythroplasia of Queyrat.

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.

Photodynamic therapy for skin cancer: How to enhance drug penetration?

Photodynamic therapy (PDT) induced by protoporphyrin IX (PpIX) has been widely used in dermatological practices such as treatment of skin cancers. Clearance rate depends on different factors such as light irradiation, skin oxygenation and drug penetration. The poor penetration of 5-aminolevulinic acid (5-ALA) with topical application is limited and restrains the production of PpIX which could restrict PDT outcomes. This review will focus on techniques already used to enhance drug penetration in human skin, and will present their results, advantages, and drawbacks. Chemical and physical pretreatments will be discussed. Chemical pre-treatments comprise of drug formulation modification, use of agents that modify the heme cycle, enhance PpIX formation, and the combination of differentiation-promoting agent prior to PDT. On the other hand, physical pretreatments affect the skin barrier by creating holes in the skin or by removing stratum corneum. To promote drug penetration, iontophoresis and temperature modulation are interesting alternative methods. Cellular mechanisms enrolled during chemical or physical pretreatments have been investigated in order to understand how 5-ALA penetrates the skin, why it is preferentially metabolized in PpIX in tumour cells, and how it could be accumulated in deeper skin layers. The objective of this review is to compare clinical trials that use innovative technology to conventional PDT treatment. Most of these pretreatments present good or even better clinical outcomes than usual PDT.

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.

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.

Photodynamic therapy for aesthetic-cosmetic indications

Photodynamic therapy (PDT) is a well-established, non-invasive treatment for a variety of dermatologic disorders, including actinic keratosis. Furthermore, PDT results in marked improvements in the signs of skin aging, although currently there are no standardized guidelines for PDT in skin rejuvenation. Two types of PDT are available: conventional-PDT (c-PDT) and the newly introduced daylight-PDT (DL-PDT). Both require a topical photosensitizer, a light source and oxygen, and both are comparable regarding safety and efficacy for treatment of photo-induced skin aging. Treatment is particularly effective for improvement of fine wrinkles, skin roughness, actinic elastosis and mottled hyperpigmentation. The most widely studied topical sensitizers used in PDT are 5-aminolevulinic acid (ALA) and methyl aminolevulinate (MAL). A range of pre-treatment procedures help improve skin absorption of the photosensitizer and lead to significantly improved efficacy. A variety of activating light sources can be used for c-PDT, while DL-PDT uses natural daylight, making it easier to treat larger areas of photodamaged skin. A major limitation of c-PDT is significant treatment-related pain, but DL-PDT has proved to be an almost pain-free procedure. Treatment duration is based on individual patient need but most patients receive 2 to 3 treatment cycles, with results fully evident 3-6 months post-treatment. PDT for aesthetic-cosmetic treatments has established its value in modern procedural dermatology as mono- or combination therapy. A major, unique advantage of PDT is that it is a non-invasive treatment that effectively rejuvenates photodamaged skin, while successfully treating a range of dermatologic conditions, including prevention and therapy of pre-cancerous actinic keratosis.

Temperature Influence on Myocardial Cell Cytotoxicity of the Extracellular Photosensitization Reaction with Talaporfin Sodium and Serum Proteins at 17°-37°C

BACKGROUND

We investigated the binding of talaporfin sodium with albumin and its photocytotoxicity during temperature changes by measuring absorbance spectra. The targeted tissue temperature differs according to the procedure. The photocytotoxicity efficiency should be investigated quantitatively because efficiency changes arising from temperature changes are expected.

MATERIALS AND METHODS

The temperature dependence of talaporfin sodium binding with human serum albumin (0-20 mg/mL), high-density lipoprotein (0-0.04 mg/mL), and low-density lipoprotein (0-0.14 mg/mL) was investigated at 17°C, 27°C, and 37°C by measurement of absorbance spectra. Cell lethality was measured using a water-soluble tetrazolium-8 assay at 2 h after the photosensitization reaction at 17°C and 37°C.

RESULTS

The binding ratios of talaporfin sodium with high-density lipoprotein decreased by 6.3% and those with low-density lipoprotein decreased by 12.8% when the temperature increased from 17°C to 37°C. Cell lethality increased significantly with a temperature rise from 17°C to 37°C at irradiation exposure of 20 and 40 J/cm² and talaporfin sodium concentration of 20 μg/mL.

CONCLUSIONS

From our in vitro data, we can predict that the change in photocytotoxicity efficiency would be negligible with a temperature decrease of <5°C from the body temperature in the case of photodynamic ablation with a short drug-light interval.

Efficacy of ultra short sub-30 minute incubation of 5-aminolevulinic acid photodynamic therapy in vitro

BACKGROUND AND OBJECTIVE

The estimated incidence of cutaneous squamous cell carcinoma (SCC) is 700,000 cases per year. In the US, SCC incidence is highest among fair skinned adults older than 50 years of age. Thus, as the population ages, the reported number of SCCs will likely increase in the future. Photodynamic therapy (PDT) is an FDA approved therapy for treatment of actinic keratoses (AKs), a precursor to cutaneous SCC lesions. The FDA approved incubation time of the photosensitizing agent 5-aminolevulinic acid (ALA) is 14-18 hours. Recent studies have investigated short ALA incubation times of 1-3 hours with ALA and PDT demonstrating treatment success. Therefore, the question exists whether ALA incubation periods of less than 30 minutes are efficacious. Herein, we evaluate the efficacy of short ALA incubation periods by measuring apoptosis after 10, 15, and 20 minutes of ALA incubation.

STUDY DESIGN/MATERIALS AND METHODS

AG13145 normal human dermal fibroblasts HDFs were incubated with 10, 15, or 20 minute of ALA at various concentrations (0, 0.05, 0.075, 0.1, 0.25, 0.375, 0.5, 1, and 2 mM). After ALA incubation, samples were treated with 1,000 seconds (16 minutes 40 seconds) of Blu-U fluorescent blue light (417 ± 5 nm) for a fluence of 10 J/cm² . Immediately following treatment with blue light, samples were collected and stained for apoptosis and necrosis with annexin-V and 7-aminoactinomycin D (7-AAD), and then analyzed by flow cytometry.

RESULTS

HDFs incubated with ALA for 10 minute at 36 °C followed by 10 J/cm² of blue light had no statistically significant changes in apoptosis. HDFs incubated with ALA for 15 or 20 minutes at 36 °C followed by 10 J/cm² of blue light had statistically significant increases in the percentages of cells positive for apoptosis in the 0.5, 1.0, and 2.0 mM ALA doses (P < 0.05).

CONCLUSIONS

We found that incubation of ALA for at least 15 minutes followed by 10 J/cm² of blue light resulted in a statistically significant increase in apoptosis. Lasers Surg. Med. 49:592-598, 2017. © 2017 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.

Weather conditions and daylight-mediated photodynamic therapy: protoporphyrin IX-weighted daylight doses measured in six geographical locations

BACKGROUND

Photodynamic therapy (PDT) is an attractive therapy for nonmelanoma skin cancers and actinic keratoses (AKs). Daylight-mediated methyl aminolaevulinate PDT (daylight-PDT) is a simple and painless treatment procedure for PDT. All daylight-PDT studies have been performed in the Nordic countries. To be able to apply these results in other parts of the world we have to compare the daily protoporphyrin IX (PpIX) light dose in other countries with the PpIX light doses found in Nordic countries.

OBJECTIVES

  To calculate where and when daylight-PDT of AKs was possible in six different geographical locations using ground stations measuring PpIX-weighted daylight doses.

METHODS

  PpIX-weighted daylight doses were measured using a dosimeter with a customer-specific photodiode with a detector sensitivity that mimics the PpIX absorption spectrum and measures in 'PpIX doses'. The dosimeters were built into ground stations that were placed in six geographical locations measuring from July to December 2008. Temperature data for each location were obtained from the internet. The maximal ultraviolet (UV) index for Copenhagen was obtained for the measuring period of the dosimeters.

RESULTS

  If the PpIX light dose should be above 8Jcm(-2) and the maximum temperature of the day at least 10°C, it was possible to treat patients on nearly all days until the middle of September in Reykjavik and Oslo, until the last week of October in Copenhagen and Regensburg, until the middle of November in Turin and all year in Israel.

CONCLUSIONS

  Where and when to perform daylight-PDT depends on the PpIX light dose and outdoor temperature. The PpIX light dose was influenced by the geographical location (latitude), weather condition and time of year. The UV index was not more suitable than temperature and weather to predict if the intensity of daylight would be sufficient for daylight-PDT.

Aminolevulinic Acid (ALA) as a Prodrug in Photodynamic Therapy of Cancer

Aminolevulinic acid (ALA) is an endogenous metabolite normally formed in the mitochondria from succinyl-CoA and glycine. Conjugation of eight ALA molecules yields protoporphyrin IX (PpIX) and finally leads to formation of heme. Conversion of PpIX to its downstream substrates requires the activity of a rate-limiting enzyme ferrochelatase. When ALA is administered externally the abundantly produced PpIX cannot be quickly converted to its final product - heme by ferrochelatase and therefore accumulates within cells. Since PpIX is a potent photosensitizer this metabolic pathway can be exploited in photodynamic therapy (PDT). This is an already approved therapeutic strategy making ALA one of the most successful prodrugs used in cancer treatment.

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.

Calcitriol treatment improves methyl aminolaevulinate-based photodynamic therapy in human squamous cell carcinoma A431 cells

BACKGROUND

Photodynamic therapy (PDT) using methyl aminolaevulinate (MAL) provides a new, approved method for treatment of skin cancer and its precursors. However, MAL-based PDT is not very efficient for poorly differentiated skin carcinoma. Thus, novel strategies to enhance the PDT effect are needed.

OBJECTIVES

In order to improve the efficacy of MAL-based PDT, we investigated the effect of adding calcitriol, a prodifferentiation hormone, to human squamous cell carcinoma A431 cells in vitro.

METHODS

A short course (24 h) of calcitriol pretreatment was applied in A431 cells, and, subsequently, MAL-induced protoporphyrin IX (PpIX) was measured.

RESULTS

Calcitriol pretreatment of the cells elevated their PpIX levels. Furthermore, the cell damage after exposure to blue light was significantly higher in calcitriol-treated cells. Increased photoinactivation correlated with higher levels of PpIX in the calcitriol-pretreated cells.

CONCLUSIONS

Calcitriol enhances MAL-based PDT in A431 cells.

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.

Two-photon photodynamic therapy of C6 cells by means of 5-aminolevulinic acid induced protoporphyrin IX

Photodynamic therapy (PDT) has received increased attention as a treatment modality for malignant tumors as well as non-oncologic diseases such as age-related macular degeneration (AMD). An alternative to excite the photosensitizer by the common one-photon absorption is the method of two-photon excitation (TPE). This two-photon photodynamic therapy has the potential of improving the therapeutic outcome due to a highly localized photodynamic effect. The present study investigated the two-photon excited PDT performing in vitro experiments where C6 rat glioma cells were irradiated with a pulsed and focused fs Ti:sapphire laser emitting light at 800 nm. The irradiance distribution of the laser beam was carefully analyzed before the experiment and the applied irradiance was known for each position within the irradiated cell layer. Cells were divided into four groups and one group was incubated with 5-ALA and irradiated 4-5h later. The survival of this group was tested after irradiation by means of ethidium bromide and acridine orange staining and compared to a control group, which was irradiated under the same conditions, but not incubated with 5-ALA before. Both groups showed necrotic areas depending on the applied irradiance, the value of which at the margin of the necrotic area could be deduced from its size. 5-ALA incubated cells became necrotic after irradiation with a mean irradiance above 6.1 x 10(10) W/cm(2), while non-incubated cells remained viable. Cells of both groups became necrotic when treated with an irradiance above 10.9 x 10(10) W/cm(2). The observed affected area of the cell layers was between 0.13 mm(2) and 1.10 mm(2). Since the irradiation of non-incubated cells below the mean power density of 10.9 x 10(10) W/cm(2) induced no necrosis, apparently no thermal damage was induced in the cells and necrosis of the 5-ALA incubated cells can be ascribed to the photodynamic effect induced by two-photon excitation. The successful photodynamic treatment of a large area of a monolayer cell culture induced by two-photon excitation offers new perspectives for photodynamic treatment modalities.