Topical photodynamic therapy at low fluence rates--theory and practice

Targeting Microenvironment of Melanoma and Head and Neck Cancers in Photodynamic Therapy

Background:

Photodynamic therapy (PDT), in comparison to other skin cancers, is still far less effective for melanoma, due to the strong absorbance and the role of melanin in cytoprotection. The tumour microenvironment (TME) has a significant role in tumour progression, and the hypoxic TME is one of the main reasons for melanoma progression to metastasis and its resistance to PDT. Hypoxia is also a feature of solid tumours in the head and neck region that indicates negative prognosis.

Objective:

The aim of this study was to individuate and describe systematically the main strategies in targeting the TME, especially hypoxia, in PDT against melanoma and head and neck cancers (HNC), and assess the current success in their application.

Methods:

PubMed was used for searching, in MEDLINE and other databases, for the most recent publications on PDT against melanoma and HNC in combination with the TME targeting and hypoxia.

Results:

In PDT for melanoma and HNC, it is very important to control hypoxia levels, and amongst the different approaches, oxygen self-supply systems are often applied. Vascular targeting is promising, but to improve it, optimal drug-light interval, and formulation to increase the accumulation of the photosensitiser in the tumour vasculature, have to be established. On the other side, the use of angiogenesis inhibitors, such as those interfering with VEGF signalling, is somewhat less successful than expected and needs to be further investigated.

Conclusion:

The combination of PDT with immunotherapy by using multifunctional nanoparticles continues to develop and seems to be the most promising for achieving a complete and lasting antitumour effect.

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.

The conventional protocol vs. a protocol including illumination with a fabric-based biophotonic device (the Phosistos protocol) in photodynamic therapy for actinic keratosis: a randomized, controlled, noninferiority clinical study

BACKGROUND

Topical photodynamic therapy (PDT) using methyl aminolaevulinate is a noninvasive treatment option suitable to treat clinical and subclinical actinic keratosis (AK) over a large area (field cancerization). The most widely used, conventional protocol in Europe includes illumination with a red-light lamp. This illumination commonly causes pain, and patients often cannot complete the treatment.

OBJECTIVES

The aims of this paper are twofold. The first aim is to introduce a novel protocol, the Phosistos protocol (P-PDT), which includes illumination with a fabric-based biophotonic device. The second and major aim is to assess the noninferiority, in terms of efficacy for PDT of AK, of P-PDT compared with the conventional protocol (C-PDT).

METHODS

A randomized, controlled, multicentre, intraindividual clinical study was conducted. Forty-six patients with grade I-II AK of the forehead and scalp were treated with P-PDT on one area (280 AK lesions) and with C-PDT on the contralateral area (280 AK lesions). The primary end point was the lesion complete response (CR) rate at 3 months, with an absolute noninferiority margin of -10%. Secondary end points included pain scores, incidence of adverse effects and cosmetic outcome.

RESULTS

Three months following treatment, the lesion CR rate of P-PDT was noninferior to that of C-PDT (79·3% vs. 80·7%, respectively; absolute difference -1·6%; one-sided 95% confidence interval -4·5% to infinity). The noninferiority of P-PDT to C-PDT in terms of the lesion CR rate remained at the 6-month follow-up (94·2% vs. 94·9%, respectively; absolute difference -0·6%; one-sided 95% confidence interval -2·7% to infinity). Moreover, the pain score at the end of illumination was significantly lower for P-PDT than for C-PDT (mean ± SD 0·3 ± 0·6 vs. 7·4 ± 2·3; P < 0·001).

CONCLUSIONS

P-PDT is noninferior to C-PDT in terms of efficacy for treating AK of the forehead and scalp and resulted in much lower pain scores and fewer adverse effects. What's already known about this topic? Topical photodynamic therapy using methyl aminolaevulinate is effective for treating actinic keratosis. In Europe, the conventional protocol involves illumination with a red-light lamp. Unfortunately, pain is often experienced by patients undergoing this protocol. An alternative protocol that uses daylight illumination has recently been shown to be as effective as the conventional protocol while being nearly painless. However, this alternative protocol can be conducted only in suitable weather conditions. What does this study add? The Phosistos protocol is demonstrated to be as effective as the conventional protocol, nearly as painless as the daylight protocols and suitable year round for treatment of actinic keratosis.

Photochemical internalization in bladder cancer - development of an orthotopic in vivo model

The possibility of using photochemical internalization (PCI) to enhance the effects of the cytotoxic drug bleomycin is investigated, together with photophysical determination and outlines of a possible treatment for intravesical therapy of bladder cancer. In vitro experiments indicated that the employment of PCI technology using the novel photosensitizer TPCS_2a® can enhance the cytotoxic effect of bleomycin in bladder cancer cells. Furthermore, experiments in an orthotopic in vivo bladder cancer model show an effective reduction in both the necrotic area and the bladder weight after TPCS_2a based photodynamic therapy (PDT). The tumor selectivity and PDT effects may be sufficient to destroy tumors without damaging the detrusor muscle layer. Our results present a possible new treatment strategy for non-muscle invasive bladder cancer, with the intravesical instillation of the photosensitizer and bleomycin followed by illumination through an optic fiber by using a catheter.

A prospective study of pain control by a 2-step irradiance schedule during topical photodynamic therapy of nonmelanoma skin cancer

BACKGROUND

Topical photodynamic therapy (PDT) for selected nonmelanoma skin cancer using 5-aminolevulinic acid (ALA) or methyl aminolevulinate (MAL) has yielded high long-term complete response rates with very good cosmesis. Pain during light activation of the photosensitizer can be a serious adverse event. A 2-step irradiance protocol has previously been shown to minimize ALA-PDT pain.

OBJECTIVE

To determine the irradiance-dependent pain threshold for MAL-PDT, to adapt the 2-step protocol to a light-emitting diode (LED) light source, and assess clinical response.

METHODS

In this prospective study, 25 superficial basal cell carcinoma (sBCC) received an initial irradiance by laser at 40 or 50 mW/cm², or LED at 35 mW/cm² followed by an irradiance at 70 mW/cm² for a total of 75 J/cm². Pain levels were recorded for both irradiance steps. Efficacy was assessed at 6, 12, or 24 months.

RESULTS

Pain was mild in the 40/70 mW/cm² laser cohort. Three instances of irradiance-limiting pain occurred at 50/70 mW/cm². Pain was minimal in the 35/70 mW/cm² LED cohort. Clinical response rates were 80% in the 50/70 mW/cm² laser cohort and 90% in the 35/70 mW/cm² LED cohort.

CONCLUSION

Topical PDT can be effectively delivered to sBCC with minimal treatment-related pain by a 2-step irradiance protocol.

Non-melanoma skin cancers: photodynamic therapy, cryotherapy, 5-fluorouracil, imiquimod, diclofenac, or what? Facts and controversies

Surgical modalities-excision, Mohs micrographic surgery, and electrodesiccation with curettage-are the preferred treatments for nonmelanoma skin cancer (NMSC). When used within guidelines, they have cure rates greater than 90%. Despite this, many other treatments have been studied and utilized for NMSC. We present a comprehensive review of the literature on these topical treatments. Photodynamic therapy (PDT) is administered under numerous and significantly varied regimens, and there are a wide range of cure rates reported. Even with aggressive regimens, PDT is not as effective as surgery is, and it is not a first-line therapy for NMSC. The cryotherapy regimen aggressive enough to adequately treat NMSC carries adverse effects and cosmetic outcomes poor enough to negate its usefulness. Topical 5-fluorouracil and imiquimod are efficacious and safe for the treatment of superficial basal cell carcinoma (BCC) but not other BCC subtypes or squamous cell carcinoma. They are self-administered twice daily for several weeks; therefore, patient and tumor selection are vital to ensuring adherence. There are currently insufficient data to support the use of topical diclofenac and ingenol mebutate for NMSC.

The effect of light fractionation with a 2-h dark interval on the efficacy of topical hexyl-aminolevulinate photodynamic therapy in normal mouse skin

BACKGROUND

Light fractionation with a 2-h dark interval increases the efficacy of topical aminolevulinic acid (ALA) photodynamic therapy (PDT). Hexyl-aminolevulinate (HAL) is the hexyl ester of ALA. Both HAL and ALA lead to protoporphyrin IX (PpIX) accumulation in endothelial cells and to vascular effects, which are important for light fractionation. We investigated light fractionation for HAL-PDT in a mouse skin model and compared this with ALA.

METHODS

Three illumination schemes were studied: (a) 100 J cm(-2) in a single illumination; (b) 50+50 J cm(-2) in a twofold illumination; (c) a small first light fraction until 50% of PpIX was photobleached (ca. 3 J cm(-2)), followed by 97 J cm(-2) 2h later. PpIX fluorescence was measured continuously during illumination. Efficacy was evaluated by daily visual skin damage scoring up to 7 days after PDT.

RESULTS

Light fractionation showed a trend towards increased efficacy for HAL-PDT. Both the initial PpIX synthesis and the PpIX resynthesis during the dark interval were higher for ALA, but these were not correlated with efficacy. Single HAL-PDT was more effective than single ALA-PDT. Photobleaching rates of HAL and ALA were similar indicating similar biodistributions at depth.

CONCLUSION

Our results provide evidence to support that light fractionation may be beneficial for HAL-PDT. We are cautious because we found only a non-significant increase in response. However, combining our results with literature data suggest that the illumination scheme may be further optimized for HAL-PDT to potentially enhance the effect of light fractionation.

A retrospective review of pain control by a two-step irradiance schedule during topical ALA-photodynamic therapy of non-melanoma skin cancer

BACKGROUND AND OBJECTIVE

Photodynamic therapy (PDT) with topical δ-aminolevulinic acid (ALA) of non-melanoma skin cancers is often associated with treatment-limiting pain. A previous study on basal cell carcinomas (BCCs) at Roswell Park Cancer Institute evaluated a two-step irradiance scheme as a means of minimizing pain, preserving outcomes, and limiting treatment time. We used an initial low irradiance until 90% of the protoporphyrin IX was photobleached, followed by a high irradiance interval until the prescribed fluence was delivered. Success of this pilot investigation motivated integration of the protocol into routine practice. Here, we present a retrospective review of recent clinical experience in a broad patient population.

STUDY DESIGN/MATERIALS AND METHODS

This was a retrospective review of an existing dermatology database. Fourteen caucasion patients-nine men and five women, ages 18-80, with a total of 51 superficial and 73 nodular BCCs, and three Bowen's disease lesions-were included. ALA was applied to each lesion for approximately 4 hours. Lesions received an initial irradiance of 30-50 mW/cm(2) for 20 J/cm(2) , followed by 150 mW/cm(2) for a total fluence of 200-300 J/cm(2) . Pain was assessed using a visual analog scale (VAS). Clinical outcome was determined at 6-12 months.

RESULTS

Median VAS scores were 1.0 for both irradiances. Five of 127 lesions required pain control with 1% xylocaine. Pain was strongly influenced by lesion location but not by lesion type, number, or size. Complete responses were achieved in 84.1% of BCCs, which compares favorably with reported results for single ALA-PDT treatments. Two of three Bowen's disease lesions showed a complete response. Complete responses for nodular BCCs were 37%, which are also within the range of reported outcomes.

CONCLUSIONS

A two-step irradiance protocol in ALA-PDT effectively minimizes pain, maintains excellent clinical outcomes in superficial lesions, and adds minimal treatment time.

Ambulatory photodynamic therapy using low irradiance inorganic light-emitting diodes for the treatment of non-melanoma skin cancer: an open study

BACKGROUND/PURPOSE

Conventional photodynamic therapy (PDT) can be inconvenient and uncomfortable. We studied low irradiance PDT using an ambulatory inorganic light-emitting diode.

METHODS

Fifty-three patients with 61 lesions [superficial basal cell carcinoma (n = 30), Bowen's disease (n = 30), and actinic keratosis (AK; n = 1)] were studied. Two treatments of ambulatory PDT were undertaken 1 week apart (one treatment for AK). Clinical response was determined at 3 months, and the treatment cycle was repeated if there was residual disease. The endpoints assessed were pain during treatment (numerical rating scale (NRS); 0-10) and outcome at 1 year. Twenty-three of these patients also received conventional PDT to separate lesions.

RESULTS

The median NRS pain scores during first and second treatment were 2 (range 0-9) and 4 (0-9), respectively. Lesion clearance rate at 1 year after ambulatory PDT was 84% (21/25 lesions in 22 patients). Of the twenty-three patients treated with both ambulatory and conventional PDT, the median NRS was 1 (0-7) and 5 (1.5-9), respectively, with most patients preferring ambulatory PDT.

CONCLUSION

Ambulatory PDT is effective for superficial non-melanoma skin cancer, with 1 year clearance rates comparative to conventional PDT. Low irradiance ambulatory PDT may be less painful and more convenient than conventional PDT.

Nicotinamide reduces photodynamic therapy-induced immunosuppression in humans

BACKGROUND

The immune suppressive effects of topical photodynamic therapy (PDT) are potential contributors to treatment failure after PDT for nonmelanoma skin cancer. Nicotinamide (vitamin B(3) ) prevents immune suppression by ultraviolet radiation, but its effects on PDT-induced immunosuppression are unknown.

OBJECTIVES

To determine the effects of topical and oral nicotinamide on PDT-induced immunosuppression in humans.

METHODS

Twenty healthy Mantoux-positive volunteers received 5% nicotinamide lotion or vehicle to either side of the back daily for 3 days. Another group of 30 volunteers received 500 mg oral nicotinamide or placebo twice daily for 1 week in a randomized, double-blinded, crossover design. In each study, methylaminolaevulinate cream was applied to discrete areas on the back, followed by narrowband red light irradiation (37 J cm(-2) ) delivered at high (75 mW cm(-2) ) or low (15 mW cm(-2) ) irradiance rates. Adjacent, nonirradiated sites served as controls. Delayed-type hypersensitivity (Mantoux) reactions were assessed at treatment and control sites to determine immunosuppression.

RESULTS

High irradiance rate PDT with vehicle or with placebo caused significant immunosuppression (equivalent to 48% and 50% immunosuppression, respectively; both P < 0·0001); topical and oral nicotinamide reduced this immunosuppression by 59% and 66%, respectively (both P < 0·0001). Low irradiance rate PDT was not significantly immunosuppressive in the topical nicotinamide study (15% immunosuppression, not significant), but caused 22% immunosuppression in the oral study (placebo arm; P = 0·006); nicotinamide reduced this immunosuppression by 69% (P = 0·045).

CONCLUSIONS

While the clinical relevance of these findings is currently unknown, nicotinamide may provide an inexpensive means of preventing PDT-induced immune suppression and enhancing PDT cure rates.

Photodynamic inactivation of mammalian viruses and bacteriophages

Photodynamic inactivation (PDI) has been used to inactivate microorganisms through the use of photosensitizers. The inactivation of mammalian viruses and bacteriophages by photosensitization has been applied with success since the first decades of the last century. Due to the fact that mammalian viruses are known to pose a threat to public health and that bacteriophages are frequently used as models of mammalian viruses, it is important to know and understand the mechanisms and photodynamic procedures involved in their photoinactivation. The aim of this review is to (i) summarize the main approaches developed until now for the photodynamic inactivation of bacteriophages and mammalian viruses and, (ii) discuss and compare the present state of the art of mammalian viruses PDI with phage photoinactivation, with special focus on the most relevant mechanisms, molecular targets and factors affecting the viral inactivation process.

A review of pain experienced during topical photodynamic therapy--our experience in Dundee

BACKGROUND

Topical photodynamic therapy (PDT) using 5-aminolaevulinic acid (ALA) and its methylated ester, methyl aminolevulinate (MAL) is widely used to treat superficial non-melanoma skin cancer (NMSC). It has been proposed that ALA PDT is more painful than MAL PDT. The aim of this paper was to compare pain scores of MAL PDT with ALA PDT in our patients and to analyse the relationship between various parameters and pain during PDT.

METHODS

We retrospectively reviewed case notes and electronic records for all patients with superficial NMSC treated with PDT from June 2007 to March 2009.

RESULTS

On univariate analysis of patients with single lesions only, we observed no association between pain and lesion diameter or pro-drug or dose or diagnosis. Pre-treatment PpIX fluorescence was significantly associated with pain. However on univariate analysis of all patients (whether single or multiple lesions) treated with PDT, MAL was associated with significantly less pain than ALA. When all the recorded variables were taken into account (multivariate analysis), diagnosis, pre-treatment PpIX fluorescence and lesion diameter were associated with pain.

CONCLUSIONS

Our data lends some support to previous published reports suggesting that the MAL PDT regime is less painful than that for ALA PDT. However, PDT pain is multifactorial and choice of photosensitiser is probably not a major pain determining factor. A prospective randomised study, with the same incubation periods for each pro-drug, is needed to definitively answer the question as to whether or not MAL PDT causes less pain than ALA PDT.

Photodynamic therapy-induced immunosuppression in humans is prevented by reducing the rate of light delivery

Photodynamic therapy (PDT) of non-melanoma skin cancers currently carries failure rates of 10-40%. The optimal irradiation protocol is as yet unclear. Previous studies showed profound immunosuppression after PDT, which may compromise immune-mediated clearance of these antigenic tumors. Slower irradiation prevents immunosuppression in mice, and may be at least as effective as high-fluence-rate PDT in preliminary clinical trials. The photosensitizers 5-aminolaevulinic acid and/or methyl aminolaevulinate were applied to discrete areas on the backs of healthy Mantoux-positive volunteers, followed by narrowband red light irradiation (632 nm) at varied doses and fluence rates. Delayed type hypersensitivity (Mantoux) reactions were elicited at test sites and control sites to determine immunosuppression. Human ex vivo skin received low- and high-fluence-rate PDT and was stained for oxidative DNA photolesions. PDT caused significant, dose-responsive immunosuppression at high (75 mW cm(-2)) but not low (15 or 45 mW cm(-2)) fluence rates. DNA photolesions, which may be a trigger for immunosuppression, were observed after high-fluence-rate PDT but not when light was delivered more slowly. This study demonstrates that the current clinical PDT protocol (75 mW cm(-2)) is highly immunosuppressive. Simply reducing the rate of irradiation, while maintaining the same light dose, prevented immunosuppression and genetic damage and may have the potential to improve skin cancer outcomes.

An overview of topical photodynamic therapy in dermatology

This article is a review of the use of topical photodynamic therapy in dermatology and its current role in 2009 and future developments. The content of this article was presented at the EPPM in Wroclaw, September 2009.

Irradiance-dependent photobleaching and pain in delta-aminolevulinic acid-photodynamic therapy of superficial basal cell carcinomas

PURPOSE

In superficial basal cell carcinomas treated with photodynamic therapy with topical delta-aminolevulinic acid, we examined effects of light irradiance on photodynamic efficiency and pain. The rate of singlet-oxygen production depends on the product of irradiance and photosensitizer and oxygen concentrations. High irradiance and/or photosensitizer levels cause inefficient treatment from oxygen depletion in preclinical models.

EXPERIMENTAL DESIGN

Self-sensitized photobleaching of protoporphyrin IX (PpIX) fluorescence was used as a surrogate metric for photodynamic dose. We developed instrumentation measuring fluorescence and reflectance from lesions and margins during treatment at 633 nm with various irradiances. When PpIX was 90% bleached, irradiance was increased to 150 mW/cm(2) until 200 J/cm(2) were delivered. Pain was monitored.

RESULTS

In 33 superficial basal cell carcinomas in 26 patients, photobleaching efficiency decreased with increasing irradiance above 20 mW/cm(2), consistent with oxygen depletion. Fluences bleaching PpIX fluorescence 80% (D80) were 5.7 +/- 1.6, 4.5 +/- 0.3, 7.5 +/- 0.8, 7.4 +/- 0.3, 12.4 +/- 0.3, and 28.7 +/- 7.1 J/cm(2), respectively, at 10, 20, 40, 50, 60 and 150 mW/cm(2). At 20-150 mW/cm(2), D80 doses required 2.5-3.5 min; times for the total 200 J/cm(2) were 22.2-25.3 min. No significant pain occurred up to 50 mW/cm(2); pain was not significant when irradiance then increased. Clinical responses were comparable to continuous 150 mW/cm(2) treatment.

CONCLUSIONS

Photodynamic therapy with topical delta-aminolevulinic acid using approximately 40 mW/cm(2) at 633 nm is photodynamically efficient with minimum pain. Once PpIX is largely photobleached, higher irradiances allow efficient, rapid delivery of additional light. Optimal fluence at a single low irradiance is yet to be determined.

Influence of drug-light-interval on photodynamic therapy of port wine stains--simulation and validation of mathematic models

OBJECTIVES

We established mathematical models of photodynamic therapy (PDT) on port wine stains (PWS) to observe the effect of drug-light-interval (DLI) and optimize light dose.

MATERIALS AND METHODS

The mathematical simulations included determining (1) the distribution of laser light by Monte Carlo model, (2) the change of photosensitizer concentration in PWS vessels by a pharmacokinetics equation, (3) the change of photosensitizer distribution in tissue outside the vessels by a diffuse equation and photobleaching equation, and (4) the change of tissue oxygen concentration by the Fick's law with a consideration of the oxygen consumption during PDT. The concentration of singlet oxygen in the tissue model was calculated by the finite difference method. To validate those models, a PWS lesion of the same patient was divided into two areas and subjected to different DLIs and treated with different energy density. The color of lesion was assessed 8-12 weeks later.

RESULTS

The simulation indicated the singlet oxygen concentration of the second treatment area (DLI=40 min) was lower than that of the first treatment area (DLI=0 min). However, it would be increased to a level similar to that of the first treatment area if the light irradiation time of the second treatment area was prolonged from 40 min to 55 min. Clinical results were consistent with the results predicted by the mathematical models.

CONCLUSIONS

The mathematical models established in this study are helpful to optimize clinical protocol.

Effect of photosensitizer dose on fluence rate responses to photodynamic therapy

Photodynamic therapy (PDT) regimens that conserve tumor oxygenation are typically more efficacious, but require longer treatment times. This makes them clinically unfavorable. In this report, the inverse pairing of fluence rate and photosensitizer dose is investigated as a means of controlling oxygen depletion and benefiting therapeutic response to PDT under conditions of constant treatment time. Studies were performed for Photofrin-PDT of radiation-induced fibrosarcoma tumors over fluence rate and drug dose ranges of 25-225 mW cm(-2) and 2.5-10 mg kg(-1), respectively, for 30 min of treatment. Tumor response was similar among all inverse regimens tested, and, in general, tumor hemoglobin oxygen saturation (SO2) was well conserved during PDT, although the highest fluence rate regimen (225 mWx2.5 mg) did lead to a modest but significant reduction in SO2. Regardless, significant direct tumor cell kill (>1 log) was detected during 225 mWx2.5 mg PDT, and minimal normal tissue toxicity was found. PDT effect on tumor oxygenation was highly associated with tumor response at 225 mWx2.5 mg, as well as in all other regimens tested. These data suggest that high fluence rate PDT can be carried out under oxygen-conserving, efficacious conditions at low photosensitizer dose. Clinical confirmation and application of these results will be possible through use of minimally invasive oxygen and photosensitizer monitoring technologies, which are currently under development.

Determination of the antibacterial efficacy of a new porphyrin-based photosensitizer against MRSA ex vivo

Following extensive in vitro screening of new photosensitizers the purpose of the present study was to examine penetration as well as antibacterial efficacy of a lead photosensitizer against MRSA using an ex vivo porcine skin model. Two different applications were performed: (i) preincubation of bacteria in solution with a porphyrin-based photosensitizer XF73 and subsequent application on the ex vivo porcine skin; (ii) application of pure bacteria on the explants followed by an incubation with XF73 in a water-ethanol formulation for up to 60 min under occlusion. The localisation of XF73 was restricted to the stratum corneum. Different concentrations (0-10 microM) of XF73 and different incubation times (5-60 min) were used to determine phototoxicity against methicillin-resistant and methicillin-sensitive S. aureus, which was applied on the explants. Preincubation of S. aureus with 0.1 microM XF73 in solution prior to the application of these XF73-incubated bacteria on the skin demonstrates a higher efficacy (>3 log10) after irradiation. Antibacterial photodynamic inactivation resulted in a approximately 1 log10 (0.1 microM)-3.64+/-0.035 (10 microM) log10 growth reduction independently of the antibiotic resistance pattern of used S. aureus strains. Irradiation of applied bacteria without photosensitizer incubation did not show any marked decrease (<1 log10) of bacteria cell number, indicating a significant phototoxicity of the XF73. Histological evaluations of untreated and treated skin areas upon irradiation within 24 h showed no significant degree of necrosis or apoptosis determined by TUNEL-assay indicating that the porcine skin is still vital. This study demonstrates that this XF73 porphyrin-based photosensitizer had concentration-dependent differences in killing efficacy of MRSA in comparison to skin cells using an ex vivo porcine skin model. The results described here imply that topical delivery of XF73 may be considered as a possible treatment in patients with superficial infections of the skin.

Topical 5-aminolaevulinic acid photodynamic therapy for intractable palmoplantar psoriasis

Photodynamic therapy (PDT) has been reported to be useful in treating non-melanoma skin cancers and a variety of benign skin conditions including psoriasis. However, only two reports of palmoplantar pustular psoriasis (PPP) treated with PDT have been reported. We treated three intractable cases of PPP with PDT, using 20% 5-aminolaevulinic acid and a 630+/-50 nm light-emitting diode device. The power density was 30 mW/cm2 and the fluence was 15 J/cm2. After treatment, all cases showed mild to marked improvement. Topical PDT may be an alternative therapy in the treatment of PPP, but further study is necessary to confirm the effectiveness of topical PDT in PPP.

Pharmacological Treatments for Basal Cell Carcinoma

Basal cell carcinoma (BCC) is the most common non-melanoma skin cancer, and its incidence continues to rise. Current management options are numerous and focus on tumour eradication while maximising cosmetic and functional capacity. Although surgery continues to be considered the main treatment modality, new pharmacological agents, such as immunomodulators, topical chemotherapeutic agents and photodynamic therapy, have emerged and show promising results. Pharmacological agents offer the potential for lower morbidity and improved tissue preservation compared with surgery and radiotherapy. However, pharmacological treatments possess higher failure rates when compared with surgery, and most studies have investigated only low-risk lesions. Several prospective, randomised, double-blind, vehicle-controlled studies have established the efficacy of imiquimod for superficial BCC. This review summarises the evidence regarding the mechanism, efficacy and safety of pharmacological agents based on the literature from the past 10 years. Experimental treatments that have been successfully utilised in the treatment of BCC are also discussed. Treatment of BCC with other agents, such as tazarotene, glycoalkaloid (BEC-5) cream, cidofovir and calcium dobesilate have been reported, but further studies are needed to ascertain the efficacy and adverse-effect profiles of these treatments.

Ambulatory photodynamic therapy: a new concept in delivering photodynamic therapy

BACKGROUND

Photodynamic therapy (PDT) has been shown to be effective in treating Bowen's disease, superficial basal cell carcinoma and actinic keratosis.

OBJECTIVES

To investigate the feasibility of delivering PDT using a portable light-emitting diode device.

METHODS

A prototype diode array, comprising 37 AlGaInP diodes cast in epoxy with a diffuser, and driven by a battery pack, was designed and constructed. A pilot study was carried out in five patients with histologically proven Bowen's disease who were referred for PDT with 5-aminolaevulinic acid. They were all treated in the hospital-based dermatology PDT suite such that each received the same level of supervision as patients receiving PDT with nonambulatory light sources. Patients recorded pain levels. In accordance with our usual practice, patients received two treatments at a 4-week interval.

RESULTS

Four of five patients were clear at follow-up (range 6-13 months, median 9). Pain was classified as none or mild in 80% of treatments and moderate in the remainder.

CONCLUSIONS

There are many potential benefits of ambulatory PDT, including the possibility of a much higher patient throughput, and allowing effective treatment at home. This pilot study provides early promising data of the safety and efficacy of this approach.

Topical photodynamic therapy

Topical photodynamic therapy is a therapeutic modality in development, thus arises grate interest among dermatologists worldwide. It is an effective therapy for actinic keratosis, superficial BCC and Bowenos disease. Treatment efficacy, good cosmetics, low risk of skin cancer, low invasiveness, low rate of adverse events, facility for treating multiple or large lesions, especially in poor healing sites and, for penile, digital and facial involvement, low general toxicity and possibility of repeating the treatments with the same efficiency, enable topical photodynamic therapy to become increasingly practiced treatment modality. Researching aimed topical photodynamic therapy to prove as a treatment modality for clinical use in other dermatoses, is in experimental phase. To answer the question when dermatologist should consider using topical photodynamic therapy treatment modatility, we are present available date.

Application of lower fluence rate for less microvasculature damage and greater cell-killing during photodynamic therapy

During the process of photodynamic therapy (PDT), problems arise such as stasis or occlusion of microvasculature, tumor oxygen depletion, and photosensitizer bleaching. This study shows that the first problem could be reduced by using a lower fluence rate light source in PDT. Microvasculature damage was studied experimentally in hematoporphyrin derivative-mediated PDT against light fluence rate, and, to some extent, less microvasculature damage was induced under 75 mW/cm2 illumination than under 150 mW/cm2. Histology of vessels at the end of PDT showed that vessel damage could be observed in both groups, indicating that the microvasculature would eventually be damaged as long as the administration of light fluence was sufficient and regardless of the illuminating fluence rates. Thus microvasculature damage induced by low fluence rate illumination could also be effective in tumor control after PDT. The cell-killing experiment was performed in vitro and designed so that cell-killing rate was influenced only by light characteristics. The higher cell-killing rate caused by 75 mW/cm2 illumination indicated that lower fluence rate light could enhance the light absorbency or decrease the bleaching of photosensitizer.

Endoscopic ablation of Barrett's oesophagus: a randomized-controlled trial of photodynamic therapy vs. argon plasma coagulation

BACKGROUND

Barrett's oesophagus is the major risk factor for oesophageal adenocarcinoma. 5-Aminlevulinic acid-induced photodynamic therapy and argon plasma coagulation have been shown to be effective for ablating Barrett's oesophagus, but a comparative trial of these two modalities has not been reported.

AIMS

To compare photodynamic therapy and argon plasma coagulation for the ablation of Barrett's oesophagus.

METHODS

A total of 68 patients (54 male, 14 female; median age 61) with Barrett's oesophagus were randomized to photodynamic therapy (n = 34) or argon plasma coagulation (n = 34). Photodynamic therapy was performed using 5-aminlevulinic acid (30 mg/kg) and red light. Argon plasma coagulation was administered at a power setting of 65 W. Multiple treatment sessions were performed, with follow-up to 24 months.

RESULTS

All patients showed a macroscopic reduction in the area of Barrett's oesophagus. This was greatest in the argon plasma coagulation group with 33 of 34 (97%) ablated, compared with 17 of 34 (50%) in the photodynamic therapy group; in the remainder, there was a reduction in the length of Barrett's oesophagus (median 50%, range: 5-90). Buried glands were found in 24% of photodynamic therapy patients, and in 21% of argon plasma coagulation patients. The median follow-up is 12 months (range: 6-24).

CONCLUSIONS

Photodynamic therapy and argon plasma coagulation are both effective for ablating Barrett's oesophagus. Argon plasma coagulation appears more effective than photodynamic therapy, but the impact of both on carcinoma development requires larger studies with long-term follow-up.

Application of lower fluence rate for less microvasculature damage and greater cell-killing during photodynamic therapy

During the process of photodynamic therapy (PDT), problems arise such as stasis or occlusion of microvasculature, tumor oxygen depletion, and photosensitizer bleaching. This study shows that the first problem could be reduced by using a lower fluence rate light source in PDT. Microvasculature damage was studied experimentally in hematoporphyrin derivative-mediated PDT against light fluence rate, and, to some extent, less microvasculature damage was induced under 75 mW/cm(2) illumination than under 150 mW/cm(2). Histology of vessels at the end of PDT showed that vessel damage could be observed in both groups, indicating that the microvasculature would eventually be damaged as long as the administration of light fluence was sufficient and regardless of the illuminating fluence rates. Thus microvasculature damage induced by low fluence rate illumination could also be effective in tumor control after PDT. The cell-killing experiment was performed in vitro and designed so that cell-killing rate was influenced only by light characteristics. The higher cell-killing rate caused by 75 mW/cm(2) illumination indicated that lower fluence rate light could enhance the light absorbency or decrease the bleaching of photosensitizer.

In vivo measurement of 5-aminolaevulinic acid-induced protoporphyrin IX photobleaching: a comparison of red and blue light of various intensities

BACKGROUND

In recent years, 5-aminolaevulinic acid (ALA) has become an increasingly popular photosensitizing drug for use in both photodynamic therapy (PDT) and photodetection (PD) of cancers. ALA metabolizes within tissue to form the photosensitizer protoporphyrin IX (PpIX). Like most photosensitizers, PpIX is fluorescent, and this fluorescence progressively decreases during PDT. This phenomenon is referred to as photobleaching.

AIM

Our aim in carrying out this experiment was twofold: firstly, to compare the relative capacity of red and blue light to cause photobleaching; and secondly, to compare the capacity of a fixed light dose to cause photobleaching, when delivered at different intensities.

METHOD

In this paper, we describe the implementation of a compact fluorescence spectrometer in monitoring the photobleaching of ALA-induced PpIX in vivo on the skin of healthy volunteers.

RESULTS

We have been able to show that blue light causes more rapid photobleaching than red light, and that under illumination with red or blue light, delivery of a fixed light dose at a lower intensity results in more photobleaching.

CONCLUSION

Comparison of the photobleaching rates suggests that a blue light intensity of 5 mW/cm(2) gives the same rate of photobleaching as the typical red light PDT intensity of 100 mW/cm(2). Further investigation of the correlation between PpIX photobleaching and PDT effect would be beneficial in interpreting the clinical significance of our findings.

Topical 5-aminolaevulinic acid photodynamic therapy for cutaneous lesions: outcome and comparison of light sources

BACKGROUND

Topical 5-aminolaevulinic acid (ALA) photodynamic therapy (PDT) is increasingly used for superficial non-melanoma skin cancers and their precursors.

METHODS

We report our 3-year experience of topical ALA-PDT, with a preliminary comparison of the effects of broadband and laser light sources.

RESULTS

We performed 688 treatments on 483 lesions in 207 patients. Complete clearance was achieved in 222/239 lesions of Bowen's disease (BD), superficial basal cell carcinoma (sBCC) and actinic keratosis (AK) (93%) - 117/129 BD (91%), 84/87 sBCC (97%) and 21/23 AK (91%), with a median follow up of 48 weeks. Broadband and laser light sources were of similar efficacy. Recurrences have occurred in 10.3% BD, 4.8% sBCC and 4.8% AK. Adverse effects from PDT were uncommon but included pigmentary change (2%) and minor scarring (2%). How-ever, severe pain was experienced in 16-21% of treatments using the high-output broadband and laser sources, but in only 2% with the low-output xenon arc source.

CONCLUSION

Topical ALA-PDT is effective for BD, sBCC and AK and has been an invaluable addition to our dermatology service. Efficacy is similar for broadband and laser light sources, although treatment at higher surface irradiance may be painful, and excellent cosmetic results can be achieved.

Online electrochemical monitoring of nitric oxide during photodynamic therapy

Photodynamic therapy (PDT), as a novel treatment modality, is based on the use of a photosensitizing agent with an excitation light source for the treatment of various malignancies. Its effect is mediated through reactive oxygen species and nitric oxide (NO), which are shown to be present in apoptosis. Individual differences among patients and even in different areas of the same tumor in one patient may cause a major problem with PDT: dose calculation during application of the light. An electrochemical sensor is proposed for online monitoring of NO generation as a solution of this problem. 5-Aminolevulinic acid (ALA) was administered as the photosensitizer in rat cerebellum. An amperometric sensor, selective to NO, was designed and tested both in vitro and in vivo during PDT. ALA-mediated PDT resulted in rapid generation of NO, starting as early as the application of light on the tissue. Simultaneous amperometric recordings have been carried out for 5 min during PDT. The progressive increase in NO concentration peaked at 1.10 min and then the response current began to decrease until it reached a plateau at around 70% of its peak value. This study, for the first time, electrochemically demonstrates the generation of NO during PDT. Rapid and stable responses obtained by the experimental setup confirmed that this method could be used as an online monitoring system for PDT-mediated apoptosis.

Kinetic study of delta-Ala induced porphyrins in mice using photoacoustic and fluorescence spectroscopies

The production of delta-aminolevulinic acid (ALA)-induced porphyrins in mice skin and blood was studied by photoacoustic and fluorescence spectroscopies. Mice were intraperitoneally administered with 30 mg/kg of ALA. The abdominal skin was subsequently excised at specific times within an 8-h interval and its absorption spectrum obtained by photoacoustics. The highest porphyrins concentration in skin, determined from the optical absorption of the Soret band at 410 nm, was found to occur nearly 2 h after ALA administration, but a first peak was also observed at approximately 15 min. Our hypothesis that the first peak represents the porphyrins content in blood vessels within the skin, whereas the second peak corresponds to porphyrins production in skin tissue, was confirmed by analysing the evolution of protoporphyrin IX content in plasma extracted intracardiacally. By finally applying phase resolved photoacoustic spectroscopy, we were able to evaluate the mean depth at which porphyrins are generated.

Improvement of tumor response by manipulation of tumor oxygenation during photodynamic therapy

Photodynamic therapy (PDT) requires molecular oxygen during light irradiation to generate reactive oxygen species. Tumor hypoxia, either preexisting or induced by PDT, can severely hamper the effectiveness of PDT. Lowering the light irradiation dose rate or fractionating a light dose may improve cell kill of PDT-induced hypoxic cells but will have no effect on preexisting hypoxic cells. In this study hyperoxygenation technique was used during PDT to overcome hypoxia. C3H mice with transplanted mammary carcinoma tumors were injected with 12.5 mg/kg Photofrin and irradiated with 630 nm laser light 24 h later. Tumor oxygenation was manipulated by subjecting the animals to 3 atp (atmospheric pressure) hyperbaric oxygen or normobaric oxygen during PDT light irradiation. The results show a significant improvement in tumor response when PDT was delivered during hyperoxygenation. With hyperoxygenation up to 80% of treated tumors showed no regrowth after 60 days. In comparison, when animals breathed room air, only 20% of treated tumors did not regrow. To explore the effect of hyperoxygenation on tumor oxygenation, tumor partial oxygen pressure was measured with microelectrodes positioned in preexisting hypoxic regions before and during the PDT. The results show that hyperoxygenation may oxygenate preexisting hypoxic cells and compensate for oxygen depletion induced by PDT light irradiation. In conclusion, hyperoxygenation may provide effective ways to improve PDT efficiency by oxygenating both preexisting and treatment-induced cell hypoxia.

Guidelines for topical photodynamic therapy: report of a workshop of the British Photodermatology Group

Topical photodynamic therapy (PDT) is effective in the treatment of certain non-melanoma skin cancers and is under evaluation in other dermatoses. Its development has been enhanced by a low rate of adverse events and good cosmesis. 5-Aminolaevulinic acid (ALA) is the main agent used, converted within cells into the photosensitizer protoporphyrin IX, with surface illumination then triggering the photodynamic reaction. Despite the relative simplicity of the technique, accurate dosimetry in PDT is complicated by multiple variables in drug formulation, delivery and duration of application, in addition to light-specific parameters. Several non-coherent and coherent light sources are effective in PDT. Optimal disease-specific irradiance, wavelength and total dose characteristics have yet to be established, and are compounded by difficulties comparing light sources. The carcinogenic risk of ALA-PDT appears to be low. Current evidence indicates topical PDT to be effective in actinic keratoses on the face and scalp, Bowen's disease and superficial basal cell carcinomas (BCCs). PDT may prove advantageous where size, site or number of lesions limits the efficacy and/or acceptability of conventional therapies. Topical ALA-PDT alone is a relatively poor option for both nodular BCCs and squamous cell carcinomas. Experience of the modality in other skin diseases remains limited; areas where there is potential benefit include viral warts, acne, psoriasis and cutaneous T-cell lymphoma. A recent British Photodermatology Group workshop considered published evidence on topical PDT in order to establish guidelines to promote the efficacy and safety of this increasingly practised treatment modality.

Photodynamic therapy: applications in dermatology

Photodynamic therapy (PDT) offers the potential of an effective new treatment in several areas of medicine. Topical photodynamic therapy is practical and non-invasive and is particularly suited to dermatological indications. A variety of pre-malignant and malignant skin lesions including Bowen's disease, actinic keratoses (AKs) and basal cell carcinoma (BCC) have been treated with success. The role of PDT in inflammatory dermatoses remains to be established. The currently available literature is reviewed.