Photodynamic therapy of non-melanoma malignant tumours of the skin using topical delta-amino levulinic acid sensitization and laser irradiation

Light dosimetry measurements during ALA-PDT of Barrett's oesophagus

A fibre optic probe and compact light detection system has been used to monitor the fluence-rate at the tissue surface during 5-aminolaevulinic acid based photodynamic therapy (PDT) of Barrett's oesophagous. The contributions from three specific wavelengths were recorded, corresponding to the combination of therapeutic laser light and fluorescence emission from protoporphyrin IX (635nm), the fluorescence from an oxidation product of the photosensitiser (670nm), and the protoporphyrin IX fluorescence alone (705nm). We have found that light scattering results in an enhancement of the therapeutic fluence-rate, and hence light dose, by approximately 70%. At the onset of therapy the fluorescence provides a 10% contribution to the overall fluence-rate at 635nm. The dynamics of photosensitiser bleaching could be extracted from the depletion in light signals. By defining a bleaching dose as the 635nm light fluence delivered over the period during which the photosensitiser fluorescence decays to 1/e(3) of its initial value, we find that the average ratio of bleaching to total dose is 33%. Further, the fluorescence contributes approximately 5% of the bleaching light dose. These results suggest that the prescribed period of therapeutic light exposure may be reduced with no loss in clinical efficacy, but with a consequent improvement in patient tolerance to this therapy.

Topical application of photofrin for photodynamic diagnosis of oral neoplasms

BACKGROUND

The prognosis of patients with oral cancer can be improved by early diagnosis. Exact demarcation of tumor margins could contribute to optimum results in surgical excision and reconstruction. Therefore, the purpose of this study was to evaluate Photofrin (Quadra Logic Technologics, Inc., Vancouver, British Columbia, Canada) with protoporphyrin IX fluorescence as a new diagnostic procedure: photodynamic diagnosis for the detection of hyperplastic and malignant changes in oral tissue.

METHODS

Twenty patients with oral neoplasms received 2.5 mg/ml Photofrin solution topically. After a period of 3 hours, the patients underwent fluorescence illumination (lambdaex = 370 to 450 nm). Guided by their visible fluorescence, lesions were biopsied at four suspicious sites for each patient. All specimens were analyzed and measured by a pathologist. A quantitative analysis of the fluorescence contrast between the neoplastic and healthy tissue was performed using the red, green, and blue mode and the gray scale mode. Statistical analysis was performed by means of the analysis of variance test for multiple comparisons.

RESULTS

The sensitivity of the neoplastic tissue evaluated using the red, green, and blue and the gray scale modes combined was 92.45 percent in the macroscopic study and 93.75 percent in the microscopic study. The specificity of the neoplastic tissue evaluated using the red, green, and blue and gray scale modes combined was 95.65 percent in the macroscopic study and 97.50 percent in the microscopic study. Five patients (25 percent) displayed hyperkeratosis, nine (45 percent) displayed squamous hyperplasia, and six (30 percent) displayed squamous cell carcinoma. It is likely that Photofrin induced the visible red fluorescence. Some fluorescence could be detected in the surrounding healthy tissue. The intensity of the light was much lower than that from the lesions. The difference between healthy tissue and the lesions as a group was statistically significant.

CONCLUSIONS

Light-induced fluorescence detection using topical Photofrin provides a sensitive, noninvasive technique for the early identification of malignant neoplasms in the oral cavity. Further study by the authors will evaluate fluorescence-guided photodynamic therapy for oral cancers in early stages.

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.

Photodynamic Therapy

ALA-PDT is a safe, well-tolerated, and effective treatment for many dermatologic conditions. Current data most strongly support its use in the treatment of actinic damage, but further investigation into alternative uses continues. Current efficacy is limited primarily by the depth of penetration of the photosensitizing agent and the activating light source. Even with this limitation, the potential applications of PDT are numerous. As new technology is developed to overcome current restraints, the future of PDT is wide open.

Laser-mediated photodynamic therapy

Photodynamic therapy (PDT) has evolved since its inception at the beginning of the 20th century, when it was defined as an oxygen-dependent reaction between a photosensitizing dye and light. Photosensitizers and light sources have since been continually optimized for distinct applications and tissues. Systemic porphyrins, such as hematoporphyrin, were the first photosensitizers to be used, mostly to treat tumors. The first light sources used were broad-band, noncoherent lights, such as quartz, xenon, tungsten, or halogen lamps. The wavelengths of light chosen were based upon the absorption spectrum of porphyrins: blue because the largest peak is at 400 nm (the Soret band) and red because of its greater penetration depth but lesser absorption at 650 nm (a Q band). Systemic photosensitizers caused prolonged photosensitivity, and broad-band light sources had limitations and side effects. The development of topical photosensitizers, such as 5-aminolevulinic acid, and the advent of lasers in recent years have advanced PDT for cutaneous use. In the 1990s, red lasers were applied to PDT because of their increased skin penetration despite lesser absorption by porphyrins. Broad-band blue light and red light have been studied extensively, the former achieving Food and Drug Administration approval in combination with topical aminolevulinic acid for the treatment of actinic keratosis in 1997. These lasers and light sources caused significant side effects, such as discomfort, erythema, crusting, blistering, and dyspigmentation. The recent application of the long-pulsed pulsed dye laser (595 nm) after topical aminolevulinic acid greatly minimized side effects without compromising efficacy. Long-pulsed pulsed dye laser-mediated PDT has since been shown to be effective in treatment of actinic keratosis, actinic cheilitis, sebaceous hyperplasia, lichen sclerosus, and, most recently, acne vulgaris. Finally, intense pulsed light sources have been introduced to PDT for the treatment of photodamage and acne, offering advantages of versatility in wavelengths and applications.

Successful Treatment of Lymphadenosis benigna cutis with Topical Photodynamic Therapy with Delta-Aminolevulinic Acid

BACKGROUND

Photodynamic therapy (PDT) using topical delta-aminolevulinic acid (ALA) has been used for nonmelanoma skin cancers, including malignant cutaneous T-cell lymphomas. Moreover, PDT has been tried for benign inflammatory or infectious skin lesions.

OBJECTIVE

To evaluate the effects of ALA-PDT on skin lesions of lymphadenosis benigna cutis (LABC).

PATIENTS AND METHODS

Two 16-year-old females with solitary and infiltrated nodules were treated 5 times with topical ALA-PDT.

RESULTS

Both patients responded well and showed dramatic clinical and histopathological improvement without visible scars.

CONCLUSION

The results confirm that topical ALA-PDT is an effective and safe modality for the treatment of LABC, and that such treatment may be cosmetically beneficial.

Subungual Bowen's disease treated by topical aminolevulinic acid—photodynamic therapy

A 66-year-old man presented with an 18-month history of progressive nail dystrophy involving his left index finger. A diagnostic biopsy specimen confirmed the clinical suggestion of subungual Bowen's disease (carcinoma in situ). Various treatment options were considered, and the decision was made to treat with photodynamic therapy using topical 5-aminolevulunic acid administered as two treatments 4 weeks apart. The patient was reviewed 3 months after treatment and then regularly at 6-month intervals. Thirty months after treatment there remained no clinical evidence of recurrence of the condition with preservation of a normal nail unit. Although the successful treatment of cutaneous Bowen's disease with photodynamic therapy is well documented, this is the first report of the successful treatment of subungual Bowen's disease using topical aminolevulunic acid-photodynamic therapy.

Lipid cubic phases for improved topical drug delivery in photodynamic therapy

We have evaluated the efficacy of lipid cubic phases, highly ordered self-assembly systems on the nanometer level, as drug delivery vehicles for in vivo topical administration of delta-aminolevulinic acid (ALA) and its methyl ester (m-ALA) on nude mice skin. ALA, a precursor of heme, induces the production of the photosensitizer protoporphyrin IX (PpIX) in living tissue. Measuring the PpIX fluorescence at the skin surface, after topical administration, makes indirect quantification of the penetration of ALA into the tissue possible. Cubic phases were formed of lipid (monoolein or phytantriol), water and drug. In some cases, propylene glycol was included in the cubic phase as well. The drug concentration was 3% (w/w, based on the total sample weight) in all investigated vehicles. When the formulations were applied for 1 h, the monoolein cubic systems and the three-component phytantriol sample showed higher fluorescence compared to the standard ointment during the 10 h of measurement. Both ALA and m-ALA yielded similar results, although the differences between the investigated vehicles were more pronounced when using m-ALA. For the 24-h applications, the monoolein cubic systems with m-ALA showed faster PpIX formation than the standard ointment, implying higher PpIX levels at short application times (less than 4 h). The systemic PpIX fluorescence of ALA was elevated by using the lipid cubic formulations. Notably, a small systemic effect was also observed for the monoolein cubic sample with m-ALA. These results imply improved PpIX formation when using the lipid cubic systems, most probably due to enhanced drug penetration.

Investigation of the use of the pulsed dye laser in the treatment of Bowen's disease using 5-aminolaevulinic acid phototherapy

BACKGROUND

The use of 5-aminolaevulinic acid photodynamic therapy (ALA-PDT) for the treatment of Bowen's disease is well established. However, treatment with a continuous light source has the disadvantage of prolonged treatment time during which patients often experience significant discomfort requiring the use of local anaesthetic.

OBJECTIVES

The aim of this study was to assess the efficacy and safety of the pulsed dye laser (PDL) as the light source for photoactivation of the protoporphyrin IX to treat Bowen's disease by PDT.

METHODS

Thirteen patients with a total of 17 patches of histologically proven Bowen's disease were treated with 20% 5-ALA in Unguentum M (Crookes Healthcare, Nottingham, U.K.) under occlusion for 4 h. The patches were then irradiated using a Candela SPLTL-1b (Candela Corporation, Wayland, MA, U.S.A.) PDL using a wavelength of 585 nm, with a 7-mm diameter spot at a fluence of 10 J cm(-2). The spots overlapped by 50% to cover the lesion and extend beyond the clinical margin of the patch of Bowen's disease by 0.5 cm. Patients were then followed up initially at 2 months, then at 3-monthly intervals for a period of 12 months to assess treatment success and recurrence rate.

RESULTS

Subjects consisted of 10 females and three males, between 47 and 88 years. The mean area of the patches of Bowen's disease was 315.4 mm(2) (range 36-2464 mm(2)) requiring a median of 32 pulses (range 3-260). Lesions sites were hands (two), foot (one) and lower leg (14). All patients experienced varying degrees of discomfort during treatment but none required the use of local anaesthetic. At 2 months eight treatment sites could not be assessed due to loose overlying crusts and removal of these revealed superficial erosions in seven patients. Of the 17 lesions treated, on follow-up at 1 year, 14 patches (82%) demonstrated a complete clinical response, although one of these had required a second treatment. Two patients with three lesions that would have required further therapy refused a second treatment. Prolonged crusting lasting 8 weeks occurred in eight patches and prolonged discomfort lasting 6 weeks occurred in four patients.

CONCLUSIONS

This study has shown that the PDL is an effective light source for ALA-PDT of Bowen's disease. Light source exposure times are shorter, although overall treatment time may not always be significantly reduced for larger lesions. The procedure was well tolerated. However, the post-treatment morbidity was relatively high compared with the more conventional treatment modalities. Further studies are needed to determine whether lower energy fluences can maintain similar efficacy while reducing post-treatment morbidity.

Photodynamic Therapy of Walker Tumors by Multiple Laser Irradiation

OBJECTIVE

Photodynamic therapy of Walker tumor after subcutaneous administration of 5-ALA solution using a multiple laser irradiation scheme was monitored by the fluorescence imaging technique to investigate the effectiveness of 5-ALA-PDT.

BACKGROUND DATA

Photodynamic therapy (PDT) is a localized cancer treatment based on the selective uptake and retention of photosensitizer at the tumoral level and on the activation of the photosensitizer by a specific wavelength of light, aiming to induce cytotoxic reactions. As a new photosensitizer, the heme precursor 5- aminolevulinic acid has been introduced recently for photodynamic therapy of tumors and precancerous lesions of the skin. It has been shown that the efficacy of topical 5-ALA-PDT is limited for deeper skin tumor by the depth of 5-ALA penetration through the skin. Oral or systemic administration of ALA or the use of different irradiation schemes may improve tumor response to PDT.

METHODS

Laser irradiation parameters used in this study were lambda = 635 nm, P = 3 mW, t(exp) = 300 sec, and three sessions. The fluorescence was excitated by monochromatic light of 405 nm. The temporal behavior of PpIX fluorescence was studied by processing and analyzing the fluorescence images acquired just after applying 5-ALA, just before and just after three laser irradiations.

RESULTS

The results demonstrate that PpIX is highly selective for tumors areas and a re-accumulation of PpIX appears between laser irradiations. During laser irradiation, the PpIX fluorescence intensity decreases rapidly, reflecting the photodegradation of PpIX.

CONCLUSIONS

In conclusion, the use of a multiple laser irradiation scheme, for the activation of reaccumulation of Pp IX (with three steps) is effective for photodynamic therapy of Walker tumor.

Clinical system for interstitial photodynamic therapy with combined on-line dosimetry measurements

A system for interstitial photodynamic therapy with delta-aminolaevulinic acid and multiple optical fibers has been developed. The system enables photodynamic treatment of large embedded tumor volumes and utilizes real-time measurements to allow on-line dosimetry. Important parameters such as light fluence rate, sensitizer fluorescence intensity, and changes in local blood oxygen saturation are measured with the same fibers that deliver the therapeutic light. Data from the first clinical treatments on nodular basal cell carcinomas indicate a major treatment-induced light absorption increase, rapid sensitizer photobleaching, and a relatively constant global tissue oxygen saturation level during the treatment.

Photodynamic therapy using a novel photosensitizer, ATX-S10(Na): comparative effect with 5-aminolevulinic acid on squamous cell carcinoma cell line, SCC15, ultraviolet B-induced skin tumor, and phorbol ester-induced hyperproliferative skin

Photodynamic therapy (PDT) using 5-aminolevulinic acid (ALA) is available for the treatment of actinic keratosis (AK). Recently, we developed a new PDT photosensitizer, ATX-S10(Na), and have shown that ATX-S10(Na) PDT is effective for the treatment of various human skin diseases, such as squamous cell carcinoma, Bowen's disease, basal cell carcinoma, and psoriasis. In the present study, we compared the effects of ATX-S10(Na) PDT and ALA PDT on hyperproliferative skin induced by 12-O-tetradecanoylphorbol-13-acetate (TPA), on the squamous cell carcinoma cell line, SCC15, in vitro, and on UVB-induced skin tumors in vivo. TPA treatment induced epidermal acanthosis, which was more markedly suppressed by ATX-S10(Na) PDT than by ALA PDT. ATX-S10(Na) PDT more effectively eliminated UVB-induced AK and squamous cell carcinoma (SCC) than ALA PDT. Furthermore, both ATX-S10(Na) PDT and ALA PDT induced the death of SCC15 cells, and the effect of ATX-S10(Na) PDT was greater than that of ALA PDT. Our results indicate that ATX-S10(Na) PDT might be more effective than ALA PDT for the treatment of various skin diseases.

Photodynamic therapy systems and applications

Photodynamic therapy (PDT) is a form of photochemotherapy requiring the simultaneous presence of a photosensitiser, activating light of the proper wavelength and molecular oxygen in order to produce a localised therapeutic effect thought to be due to high-energy singlet oxygen generation. Neither drug nor light alone are effective as therapeutic agents and thus PDT treatment methods should be looked upon as true, necessary, drug and device combinations ('systems'). Selectivity of treatment is imparted by a combination of factors, including accumulation of photosensitiser by the target lesion and targeted application of activating light. The most common systemic side effect of systemically administered photosensitisers is cutaneous photosensitivity of varying periods of time. Local toxicities depend on the area of treatment. Sources of light which have been used in PDT include lasers, arc lamps, light-emitting diodes and fluorescent lamps. PDT has been used for a wide variety of clinical applications. In 1995, the first PDT system, using porfimer sodium (Photofrin, Axcan Pharma, Inc.), lasers and fibre optic light delivery methods, developed by QuadraLogic Technologies, was approved in the US for endoscopic palliation of malignant dysphagia caused by oesophageal cancer. A topical PDT system, aminolevulinic acid HCL (Levulan Kerastick) and the large-area BLU-U PDT Illuminator, was developed by DUSA Pharmaceuticals, Inc. for the treatment of actinic keratoses of the face and scalp and approved in the US in 2000. Topical PDT has applicability to a wide variety of skin cancers and precancerous conditions. In 2001, Novartis launched the systemically administered verteporfin (Visudyne) laser-based PDT system in the US as the first pharmacologic treatment for age-related macular degeneration. Development programmes are continuing to investigate PDT for the potential treatment of a variety of diseases, yielding therapeutic results with minimal toxicity.

Light distribution and calibration of commercial PDT LED arrays

Commercial photodynamic therapy (PDT) light sources are supplied with no evidence of traceability to national measurements standards to validate indicated delivered dose. Also, the spatial distribution of the radiant energy is not disclosed. This means that there is no way for the user to be able to verify that the required dose is being delivered to the appropriate area of the lesion. To this end, a simple method, traceable to national standards, is described and applied to an investigation of two commercial LED arrays. In one case, the dose fell to 38% of that received at the central area at a distance of only 2 cm. In the other, the output was more uniform over a larger area but the maximum irradiance was not at the centre of the field. All of these inhomogenieties were taken into account when the actual light dose delivered to the patient was calculated in the method described. This ensured transparent traceability in PDT dosimetry.

Effect of Oil-in-Water Emulsions on 5-Aminolevulinic Acid Uptake and Metabolism to PpIX in Cultured MCF-7 Cells

PURPOSE

To identify the optimal vehicle for fast and efficient cellular production of the photosensitizer, protoporphyrin IX (PpIX), upon administration of 5-aminolevulinic acid (ALA).

METHODS

ALA in various oil/water o/w emulsions was applied to the human mammary epithelial cell line (MCF-7) cultured in microplates. Upon incubation for 14 h, the accumulated amount of PpIX was determined by fluorescence spectroscopy. Variables such as the pH and concentration of the emulsions, the temperature and duration of incubation were examined along with the importance of ALA concentration and the presence of endocytosis inhibitors.

RESULTS

An increase in the amount of produced PpIX was observed with an increase in extracellular pH, incubation temperature, and ALA concentration. A saturable mechanism of PpIX accumulation was evident, mainly as a result of the uptake mechanism for ALA. Some of the o/w emulsions increased the amount of intracellular PpIX, and the results indicated that this was not due to an increased k(m) of the extracellular ALA to intracellular PpIX conversion, but to the increased endocytotic uptake in the presence of the emulsions. In general, the increase in PpIX in the presence of emulsions relative to the control was more pronounced after 1 h as compared to after 2-4 h.

CONCLUSIONS

The formation of PpIX in MCF-7 cells exposed to ALA is improved by the presence of certain o/w emulsions, which could be explained by endocytosis.

Photodynamic therapy for Bowen's disease and squamous cell carcinoma of the skin

BACKGROUND

Photodynamic therapy involves the activation by visible light of a previously administered photosensitizing agent in order to cause tumor necrosis. Skin tumors can be treated with topical photosensitizers and thus avoiding systemic side effects. In this study we evaluate the immediate and long-term effects of photodynamic therapy (PDT), using aminolevulinic acid (ALA) as a photosensitizer and a non-laser light source, on Bowen's disease (intra-epithelial squamous cell carcinoma) and on frank squamous cell carcinoma (SCC) of the skin.

METHODS

ALA in cream form (20%) was topically applied on biopsy-proven Bowen's disease or SCC of the skin. The lesions were covered with occlusive and light-shielding dressing. Sixteen hours later, they were submitted to a 10-min light session using Versa-Light™, a non-laser light source (spectral output of 580-720nm and 1250-1600nm, 100J/cm(2)). The initial evaluation was done 21 days post-treatment and every 3m thereafter. Patients that did not respond to treatment after two to three sessions were referred to surgery.

RESULTS

Forty Bowen's disease lesions (24 patients) and 43 SCC lesions (18 patients) underwent treatment. Median follow-up was 21±8m. No patient had any remarkable side effects. Thirty-four Bowen's disease (85%) lesions completely responded as did 32 SCC lesions (74%).

CONCLUSIONS

Our findings showed that PDT is highly effective in treating Bowen's disease and SCC lesions and can be used as a first treatment modality in so far as its use does not preclude the subsequent surgery recommended for the small percentage of failures.

Time-dependent hexaminolaevulinate induced protoporphyrin IX distribution after topical application in patients with cervical intraepithelial neoplasia: A fluorescence microscopy study

BACKGROUND AND OBJECTIVES

Compared to the conventional management of cervical intraepithelial neoplasia (CIN) the potential advantage of photodynamic therapy (PDT) for the treatment of cervical human papilloma virus (HPV)-related disease encompasses a minimal invasive procedure with reduced risk of profuse bleeding as a consequence of conization, and possibly more favorable long-term results avoiding cervical stenosis. At present little is known about the precise time-dependent distribution and histological localization of hexaminolaevulinate (HAL) induced protoporphyrin IX (PPIX) fluorescence in healthy tissue and in CIN. The aim of this study was to use ex vivo fluorescence microscopy to determine whether PPIX is selectively induced by neoplastic cells of the cervical epithelium at various times after topical application.

STUDY DESIGN/MATERIALS AND METHODS

Cold cream containing 0.5% HAL was applied by means of cervical cap over various periods of time. We analyzed 52 healthy cervical mucosa and 84 CINs.

RESULTS

At time delay 100 (+/-10) minutes, high epithelial fluorescence and a significant selectivity between epithelium and underlying lamina propria was found. By contrast, no significant difference between healthy and neoplastic tissues, or between low and high-grade epithelial dysplasia (P > or = 0.05), was observed at any time point.

CONCLUSIONS

Application of HAL 0.5% cream to the cervix induced selective fluorescence in epithelial cells. The optimal ratio with a homogeneous PPIX distribution was obtained after 100 ( +/- 10) minutes cream application, which should be evaluated further for PDT.

Evaluation of the penetration of 5-aminolevulinic acid through basal cell carcinoma: a pilot study

Aminolevulinic acid (ALA) is a charged, hydrophilic molecule that penetrates poorly through cellular structures. This property has been implicated in the poor clinical response of non-superficial basal cell carcinomas (BCCs) to photodynamic therapy (PDT). Release of ALA hydrochloride from a 20% w/w formulation was found to be incomplete and that approximately 36.8% of the total dose is released during the application period of 4 h. Using scintillation spectroscopy and a precise tissue sectioning protocol, it was demonstrated that depths of penetration of at least 2 mm from the lesion surface had been reached. Using cumulative stratal ALA concentrations, it was found that 10% of the total applied dose permeated into the lesion. In spite of this, comparisons drawn with photodynamic concentrations used in tissue culture work reported elsewhere revealed that estimations of the ALA concentration at 2 mm were sufficient to elicit a possible therapeutic response. Results from this work question the reasons given for poor outcomes of PDT in nodular BCC based solely on depth as a hindering factor.

In vitro evaluation of the cytotoxic and mutagenic potential of the 5-aminolevulinic acid hexylester-mediated photodynamic therapy

Photodynamic therapy (PDT) of tumors with 5-aminolevulinic acid hexylester (h-ALA) causes photo-oxidative reactions in treated tissues. In order to study cytotoxic and/or mutagenic effects, cells of the tumor cell line RPMI 2650 as well as fibroblasts of the cell line WS 1 were given photodynamic treatment in vitro. The cells were photosensitized with a 1mM h-ALA-medium solution for 5h and illuminated with different light doses (0.5, 1.0, 1.5 and 2.0 J/cm2) using red light (633+/-20 nm). PDT-induced cytotoxic effects were determined by measurement of the mitotic index (MI) and the nuclear division index (NDI). Chromosome aberrations (CA) and micronuclei (MN) were recorded to study mutagenicity. After treatment of the photosensitized RPMI 2650 cells with a light dose of 2.0 J/cm2, the MI was significantly decreased to 16.9 per thousand in comparison with that of the h-ALA control (33.8 per thousand ). In photosensitized WS 1 cells, light doses up to 2.0 J/cm2 showed no significant effect. The NDI of photosensitized RPMI 2650 cells was significantly decreased by light doses from 1.0 to 2.0 J/cm2, whereas no significant effect was seen in WS 1 cultures. Thus, h-ALA-PDT only induced desirable cytotoxic effects in tumor cells, but not in the fibroblasts. After application of light doses from 0.5 to 2.0 J/cm2, photosensitized RPMI 2650 cultures showed CA in 7.0-7.5% of the metaphases, which was not a significant increase (h-ALA control: 5.5%). In WS 1 cultures metaphases containing CA varied non-significantly from 5.0 to 7.5%. The MN rates were approximately the same in illuminated RPMI 2650 cultures and in the corresponding h-ALA control (4.4-4.9 per thousand ). The MN rates of the illuminated WS 1 cultures also varied non-significantly from 4.5 to 5.0 per thousand in comparison with the h-ALA control (5.5 per thousand ). In the mutagenicity tests the h-ALA-PDT had no significant effect, neither on the tumor cells nor on the fibroblasts. In addition to the cytogenetic analysis, spectral karyotyping (SKY) was used to characterize the cell lines and gain more detailed information on possibly PDT-induced CA. The SKY evaluation also showed no significant increase of the CA rate, but confirmed the result of the CA test. Thus, within the scope of the experiments performed, a mutagenic potential of the h-ALA-PDT can be excluded.

Iontophoretic delivery of 5-aminolevulinic acid and its methyl ester using a carbopol gel as vehicle

The aim of this study was to evaluate a Carbopol gel as a vehicle for iontophoretic delivery of 5-aminolevulinic acid (ALA) and its methyl ester (m-ALA). The formulation was characterized rheologically and the passive diffusion of ALA and m-ALA in the gels was measured. Addition of ALA and m-ALA did not change the rheological behavior of the gel and the diffusion coefficients of ALA and m-ALA were 4.4 +/- 1.2 x 10(-6) and 3.08 +/- 0.7 x 10(-7) cm2 s(-1), respectively. The anodal iontophoretic transport of ALA and m-ALA through porcine skin in vitro was followed for 15 h at a constant current of 0.4 mA. When incorporating ALA in the gel, the steady-state was reached in 10-12 h at a flux level of approx. 65 nmol cm(-2) h(-1) compared to 2.5-4 h and a level of approximately 145 nmol cm(-2) h(-1) for m-ALA. The total amount of m-ALA delivered after 15 h of iontophoresis resulted in a six-fold enhancement over ALA delivery. Iontophoretic delivery from the gel formulation seems to be better than, or comparable to, the passive delivery from formulations commonly used clinically, in spite of the 10-20 times lower concentration of the drug in the gel formulation. The skin uptake after iontophoresis for m-ALA showed a nine-fold increase over that of ALA in the stratum corneum (SC).

Topical photodynamic therapy in clinical dermatology

The growing incidence of cutaneous malignancies each year necessitates the development of new and more effective methods for both the diagnosis and the treatment of cancerous lesions, while assuring better cosmetic results and improving patient satisfaction. With that in mind, the use of topical photodynamic therapy (PDT) has been explored in the treatment as well as the diagnosis of various cutaneous malignancies. Using the intrinsic cellular haem biosynthetic pathway and principles of photoillumination, topical PDT carries the goal of selectively targeting abnormal cells, while preserving the normal surrounding structures. This paper will discuss the various applications and data on the use of topical PDT in dermatology.

Nevoid basal cell carcinoma syndrome: a review of the literature

The nevoid basal cell carcinoma syndrome (NBCCS) or Gorlin-Goltz Syndrome is an autosomal dominant disorder principally characterized by cutaneous basal cell carcinomas, multiple keratocysts, and skeletal anomalies. The present report reviews current knowledge of this disorder that has profound relevance to specialists in Oral and Maxillo-Facial Surgery, Oral Medicine and Radiology.

Topical photodynamic therapy for patients with therapy-resistant lesions of cutaneous T-cell lymphoma

Photodynamic therapy after topical application of 5-aminolevulinic acid is an effective therapy for nonmelanoma epithelial skin cancers. It has also been used for some cases of cutaneous T-cell lymphoma. We treated 4 patients with different cutaneous T-cell lymphomas with photodynamic therapy. Those patients had previously reached a partial remission with more conventional therapies, but single lesions had remained. In all of these cases a complete remission of these lesions was achieved. We, therefore, suggest that photodynamic therapy can be a useful additional treatment modality for patients with therapy-resistant lesions of cutaneous T-cell lymphoma.

Topical photodynamic therapy in the treatment of actinic keratoses and Bowen's disease in transplant recipients

BACKGROUND

Transplant recipients (TR) have a dramatically increased risk for widespread epithelial neoplasms of the skin. Thus, there is a need to treat initial stages of these neoplasms such as actinic keratoses (AK) and Bowen's disease (BD) to prevent progression to invasive and potentially fatal squamous cell carcinoma. Topical photodynamic therapy (PDT) has been proven to be an effective treatment for AK and BD in immunocompetent patients, but no prospective trials in immunocompromised TR have been performed so far.

METHODS

Twenty TR and 20 controls with histologically confirmed AK or BD underwent either a single or two consecutive treatments of topical PDT in an open trial. The application of 20% 5-aminolevulinic acid (ALA) for 5 hours was followed by illumination with 75 J/cm2 of visible light delivered at 80 mW/cm2 by an incoherent light source.

RESULTS

The overall complete response rates in TR at 4, 12, and 48 weeks were 0.86, 0.68, and 0.48, respectively. The cure rates in both patient groups were comparable at 4 weeks but were significantly lower in TR than in controls at 12 and 48 weeks (P<0.05). Side effects included erythema, edema, and crust formation after illumination. Cosmetic results were excellent without scar formation or alterations in pigmentation.

CONCLUSIONS

Topical PDT with 20% 5-ALA is an effective and safe treatment for AK and BD in immunosuppressed TR, with initial response rates comparable with those in immunocompetent patients. It is particularly useful in TR because of the possibility for repeated treatment of large lesional areas.

A Review of Laser and Photodynamic Therapy for the Treatment of Nonmelanoma Skin Cancer

BACKGROUND

The role of laser and light sources used alone and in conjunction with photodynamic therapy (PDT) for the treatment of nonmelanoma skin cancers (NMSCs) remains unclear. PDT is a newly accepted treatment option for actinic keratoses (AKs) with clearance rates comparable to 5-flourouracil. The purpose of this study was to review literature pertaining to the use of light-emitting technologies and PDT for the treatment of basal cell carcinoma (BCC), squamous cell carcinoma (SCC), and AKs.

METHODS

A National Library of Medicine PubMed Internet search of English-language journals was performed using the terms laser, PDT, BCC, SCC, and AK. The search encompassed all English-language clinical trials on human subjects from the mid-1960s to the present using laser and light source therapy and/or topical aminolevulinic acid. Articles were excluded if they contained fewer than 10 patients, had a follow-up time of less than 1 month, used intravenous photosensitizers, or were review articles.

RESULTS

A total of 20 papers were included for review (10 for BCC, 4 for AK, and 6 for SCC). Follow-up for these patients ranged from 1 to 36 months. Clearance rates were reported up to 100% for superficial BCCs, AKs, and SCC in situ, and lower (8%) for more invasive SCC. Recurrence rates ranged from to 0% to 31% for superficial BCCs, 16% to 31% for AKs, 0% to 52% for SCC in situ, and 82% for invasive SCC.

CONCLUSION

Precise PDT and laser clearance and recurrence rates for superficial and nodular BCC and SCC treated with laser and PDT are not yet known. From the available data, it appears that PDT may be capable of achieving clearance rates comparable to radiation therapy for BCC. However, with current technology, PDT treatment of BCC remains inferior to surgical excision and Mohs surgery, for which recurrence rates have been reported to be less than 10%. The reported clearance rates currently limit the usefulness of PDT and laser therapy. However, multiple treatments and the use of penetration enhancers may significantly increase the efficacy of 5-aminolevulinic acid-PDT. With regard to SCCs, the risk of metastatic disease restricts the use of laser and PDT. Studies are currently underway with new light sources, photosensitizers, and various therapeutic regimens. At this time, because the reported recurrence rates are significantly higher than those achieved with standard therapies, laser and PDT should be reserved for only those patients who cannot undergo surgical therapy for BCC and SCC.

Topical methyl aminolaevulinate photodynamic therapy in patients with basal cell carcinoma prone to complications and poor cosmetic outcome with conventional treatment

BACKGROUND

Conventional treatment of basal cell carcinoma (BCC) causes morbidity and/or disfigurement in some patients because of the location (e.g. mid-face) and size of the lesion.

OBJECTIVES

Following reports that such difficult-to-treat BCC lesions have been treated successfully with topical methyl aminolaevulinate (MAL) photodynamic therapy (PDT), a multicentre study was performed to determine the response of such BCC to MAL-PDT.

METHODS

An open, uncontrolled, prospective, multicentre study was conducted comprising patients with superficial and/or nodular BCC who were at risk of complications, poor cosmetic outcome, disfigurement and/or recurrence using conventional therapy. Patients were given one or two cycles within 3 months of topical MAL-PDT, each consisting of two treatments 1 week apart. Tumour response was assessed clinically at 3 months after the last PDT, with histological confirmation of all lesions in clinical remission. The cosmetic outcome was rated. Patients with a BCC in remission will be followed up for 5 years for recurrence, of which the 24-month follow-up is reported here. Ninety-four patients with 123 lesions were enrolled and treated with MAL-PDT at nine European primary care and referral university hospitals. An independent blinded study review board (SRB) retrospectively excluded nine patients and a total of 15 lesions from the efficacy analysis, for not having a difficult-to-treat BCC according to the protocol.

RESULTS

The lesion remission rate at 3 months was 92% (45 of 49) for superficial BCC, 87% (45 of 52) for nodular BCC, and 57% (four of seven) for mixed BCC, as assessed by clinical examination, and 85% (40 of 47), 75% (38 of 51), and 43% (three of seven), respectively, as assessed by histological examination and verified by the SRB. At 24 months after treatment, the overall lesion recurrence rate was 18% (12 of 66). The cosmetic outcome was graded as excellent or good by the investigators in 76% of the cases after 3 months follow-up, rising to 85% at 12 months follow-up, and 94% at 24 months follow-up.

CONCLUSIONS

Topical MAL-PDT is effective in treating BCC at risk of complications and poor cosmetic outcome using conventional therapy. MAL-PDT preserves the skin and shows favourable cosmetic results.

Basal cell carcinoma

The authors of this review aim to provide a comprehensive overview of basal cell carcinoma, concentrating in particular on incidence, risk factors, molecular genetics, clinical features, and treatment

Photodynamic therapy for the treatment of skin disease

The efficacy of photodynamic therapy for the treatment of a large number of skin diseases, in particular non-malignant skin cancer, has been reported by a number of studies. It has been demonstrated to be particularly beneficial for large or multiple lesions, especially where good cosmesis is required. However for PDT to become established in routine clinical practice further comparative multi-center studies with currently accepted standard techniques are required.

Acceleration of ALA-induced PpIX fluorescence development in the oral mucosa

BACKGROUND AND OBJECTIVES

The development of 5-aminolevulinic acid (ALA)-induced tissue fluorescence is optimal 2-4 hours after ALA application. Goal of this work was to develop a means of accelerating oral topical ALA-induced tissue fluorescence.

STUDY DESIGN/MATERIALS AND METHODS

In 300 hamsters, DMBA (9,10 dimethyl-1,2-benzanthracene) cheek pouch carcinogenesis produced dysplasia in 3-5 weeks. Topical application of 20% ALA in Eucerin was followed by localized ultrasound treatment (1, 3.3 MHz) in 150 animals. In 75 animals, ALA was applied in an Oral Pluronic Lecithin Organogel (OPLO-an absorption enhancer) vehicle. Seventy-five animals received only topical ALA in Eucerin. Hamsters were sacrificed and cryosections underwent fluorescence measurements, histological evaluation, 20-180 minutes after ALA application. One-way ANOVA detected independent effects of pathology on laser-induced fluorescence (LIF). Two-way ANOVA tested for independent effect of pathology and of OPLO, ultrasound, and interaction effects.

RESULTS

Ultrasound significantly (P < 0.05) accelerated tissue fluorescence development.

CONCLUSIONS

Low-frequency ultrasound can accelerate ALA-induced fluorescence development.

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.

Detection and diagnosis of oral cancer by light-induced fluorescence

BACKGROUND AND OBJECTIVE

New techniques for non-invasive early detection and diagnosis of oral dysplasia and carcinoma are required. Our objective was to determine in the hamster cheek pouch model whether differentiation between the healthy tissue and the different stages of oral premalignancy and malignancy is possible using laser-induced fluorescence after tissue exposure to 5-Aminolevulinic acid (ALA).

STUDY DESIGN/MATERIALS AND METHODS

DMBA carcinogenesis was applied to one cheek pouch in 18 hamsters for 0-20 weeks. Prior to sacrifice, 20% ALA was applied to the cheek tissues. Excised cheek tissues were cryosectioned and imaged using fluorescence microscopy with excitation at 405 nm, detection at 635 nm. After fluorescence measurement, H&E staining and histopathological evaluation were performed.

RESULTS

Fluorescence intensity was significantly lower in healthy tissue than in pathological tissues. Significantly higher intensities and more "fluorescence hot spots" occurred in severe dysplasia and carcinoma than in healthy tissue, hyperkeratosis, mild and moderate dysplasia.

CONCLUSIONS

Light-induced fluorescence after ALA exposure can differentiate between the different stages of premalignancy and malignancy. Its ability to differentiate between healthy tissue and early pathology is particularly interesting

Terapêutica fotodinâmica com ácido delta-aminolevulínico em neoplasias queratinocíticas superficiais

FUNDAMENTOS: A terapêutica fotodinâmica (TFD) é técnica de tratamento em que são aplicadas, nos tecidos, substâncias fotossensibilizantes, posteriormente ativadas com luzes de comprimentos de onda específicos, com a finalidade de produzir destruição celular, por meio da ação de produtos citotóxicos fotoativados. Tal método tem sido utilizado em diversos tipos de neoplasias cutâneas, com resultados bastante entusiasmadores. OBJETIVOS: Avaliar o efeito de uma única sessão de terapêutica fotodinâmica (TFD) com ácido delta aminolevulínico (ALA) tópico, estimulado por luz não coerente, em ceratoses actínicas (CAC), carcinomas basocelulares (CBC) superficiais e doenças de Bowen (DB). MATERIAL E MÉTODOS: Utilizando uma fonte de luz não coerente, emitida por protótipo desenvolvido no Serviço de Engenharia Biomédica do Hospital de Clínicas de Porto Alegre (HCPA), para ativar o ácido delta-aminolevulínico (ALA) a 20%, aplicado com oclusão, foram tradadas 80 lesões cutâneas, em 52 pacientes. Entre as lesões, 32 (40%) eram carcinomas basocelulares superficiais, 37 (46,3%) ceratoses actinícas e 11 (13,7%) doenças de Bowen. Em 23 casos (28,7%), além das características clínicas, o diagnóstico foi confirmado por biópsia e exame histopatológico. RESULTADOS: Não foi possível obter o seguimento de cinco lesões tratadas. Das 75 lesões que puderam ser avaliadas, 41 (54,6%) apresentaram cura, 22 (29,4%) apresentaram melhora, e 12 (16,0%) permaneceram inalteradas, tendo o tratamento sido considerado ineficaz nestas últimas. Das 35 ceratoses actínicas, 23 (65,7%) obtiveram cura, 7 (20%) melhoraram, e cinco (14,3%) não responderam ao tratamento.Trinta carcinomas basocelulares superficiais foram tratados, com cura em 10 (33,3%), melhora em 13 (43,4%) e sem alterações em sete (23,3%). Dos 10 casos de doença de Bowen avaliados, oito (80%) curaram e dois (20%) melhoraram. Os efeitos colaterais observados foram ardência em 24 lesões (32%), dor em cinco (6,7%) e prurido em um caso (1,3%). A maioria dos casos (60%) apresentou boa tolerância ao tratamento, não havendo efeitos paralelos dignos de nota. CONCLUSÕES: Os resultados obtidos no trabalho assemelham-se, em parte, aos relatados na literatura com aplicação única da terapêutica fotodinâmica com ácido delta-aminolevulínico em neoplasias queratinocíticas superficiais, principalmente nas ceratoses actínicas e na doença de Bowen.

Optimization of aminolevulinic acid delivery by iontophoresis

The objective was to optimize aminolevulinic acid (ALA) electrotransport into and through the skin by adjustment of formulation composition and ionic strength. ALA delivery was investigated as a function of the polarity and concentrations of drug and background electrolyte in the donor solution. The anodal iontophoretic flux of ALA from a 10% solution was compared with the drug's passive flux from the same formulation to which 5% dimethyl sulphoxide (DMSO) had been added. Iontophoresis of the predominantly zwitterionic ALA from the anode is more efficient than that from the cathode. It was possible, though, to increase the electrotransport of ALA by simultaneously delivering the drug from both anode and cathode. Reduction of NaCl concentration in the anode led to a 3- to 4-fold increase in ALA flux. Transport of ALA across the skin and the amount of prodrug delivered into the skin (SC and [epidermis+dermis]) were approximately 4-fold greater with iontophoresis as compared to the passive application of the DMSO formulation.

IN CONCLUSION

(a) electroosmosis from the anode is enhanced when the background electrolyte concentration is lowered; and (b) low-level iontophoresis enhances ALA transport across and, more importantly, into the [epidermis+dermis] than a simple formulation incorporating DMSO.

Photodynamic therapy with intravesical instillation of 5-aminolevulinic acid for patients with recurrent superficial bladder cancer: a single-center study

OBJECTIVES

Photodynamic therapy (PDT) is an effective treatment option for patients with superficial bladder cancer uncontrolled by transurethral resection and/or intravesical bacille Calmette-Guérin (BCG) immunotherapy alone. We determined the efficacy and side effects of PDT in patients with recurrent superficial bladder cancer.

METHODS

Between April 1994 and July 2001, PDT was performed in 31 patients (23 men and 8 women). 5-Aminolevulinic acid (50 mL) in a 3% concentration was instilled intravesically. Patients were instructed to hold the solution as long as possible and were irradiated transurethrally with a mean light dose of 3.9 W using laser light emitting a wavelength of 633 nm for a mean time of 1260 seconds.

RESULTS

The mean patient age at the procedure was 70.2 years. At an average follow-up of 23.7 months (range 1 to 73), 16 patients were free of tumor recurrence; 15 patients had developed tumor recurrence after a mean of 8.3 months. Of 10 patients with prior BCG treatment, 4 were free of tumor recurrence. Treatment was well tolerated, with the only side effect being dysuria due to urinary tract infection in 4 patients and hematuria in 7 patients. No phototoxic skin reactions were observed.

CONCLUSIONS

PDT represents a safe, effective, and less-invasive treatment for patients with recurrent superficial bladder cancer. Because of the favorable side-effect profile, PDT can also be applied to patients with comorbidity precluding surgical treatment. Furthermore, PDT represents a second-line treatment for patients with tumor recurrence after BCG failure.

Photodynamic therapy and topical aminolevulinic acid: an overview

Photodynamic therapy is a non-invasive technique used in the treatment of skin diseases which has various advantages, one being the ability to localize treatment to the area being treated, which is common among most photosensitizers. Aminolevulinic acid is a prodrug that is metabolized intracellularly to form the photosensitizing molecule protoporphyrin IX (PpIX). When PpIX is activated by light, cytotoxic reactive oxygen species and free radicals are generated. This phototoxic effect may cause malignant and non-malignant hyperproliferative tissue to be destroyed, to decrease in size, and to eventually disappear. The application of topical aminolevulinic acid 20% followed by the use of a blue light photodynamic therapy illuminator is indicated in the US for the treatment of non-hyperkeratotic actinic keratoses of the face or scalp. There are data suggesting that aminolevulinic acid/photodynamic therapy may also be beneficial in acne vulgaris, verrucae, psoriasis, mycosis fungoides, and human papillomavirus. This treatment modality has also proven effective in the management of skin cancer such as, Bowen disease and basal cell carcinoma. Further experience in the use of photodynamic therapy will help define its utility in the management of actinic keratosis and other dermatoses.

Differentiation enhances aminolevulinic acid-dependent photodynamic treatment of LNCaP prostate cancer cells

Photodynamic therapy using 5-aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) may be applied to the treatment of neoplasms in a variety of organs. In order to enhance existing regimens of photodynamic therapy, we investigated the effects of adding differentiation therapy to photodynamic therapy in human prostate cancer cells in vitro. The objective of differentiation therapy per se is to reverse the lack of differentiation in cancer cells using pharmacological agents. The motivation for this study was to exploit the differentiation-dependent expression of some heme enzymes to enhance tumour cell toxicity of ALA-photodynamic therapy. A short course of differentiation therapy was applied to increase PpIX formation during subsequent ALA exposure. Using the synthetic androgen R1881, isomers of retinoic acid, and analogues of vitamin D for 3 to 4 days, exogenous ALA-dependent PpIX formation in LNCaP cells was increased, along with markers for growth arrest and for differentiation. As a consequence of higher PpIX levels, cytotoxic effects of visible light exposure were also enhanced. Short-term differentiation therapy increased not only the overall PpIX production but also reduced that fraction of cells that contained low PpIX levels as demonstrated by flow cytometry and fluorescence microscopy. This study suggests that it will be feasible to develop protocols combining short-term differentiation therapy with photodynamic therapy for enhanced photosensitisation.

Pain caused by photodynamic therapy of skin cancer

Pain resulting from photodynamic therapy (PDT) of skin cancer was investigated. The study included 69 lesions (60 patients) with different types of skin tumours or precursors. Protoporphyrin IX, which is produced by the topical application of delta-aminolevulinic acid, was used as a photosensitizing agent. Twenty-three of the lesions (19 patients) were examined with a fluorescence imaging system which demarcates the tumour area from the healthy skin and visualizes the contrast between the fluorescence from healthy skin and that from the tumour. EMLA is used on all patients as part of our routine PDT protocol but despite this the major side-effect of PDT is pain during treatment. There is a large variation in pain intensity experienced by the patients, as measured by a visual analogue scale (VAS). Patients with actinic keratoses experienced more pain than those with Bowen's disease or basal cell carcinoma. The mean VAS score was higher when treating lesions located on the head than when treating lesions on the torso or the extremities. Also, treatment of large skin areas resulted in more pain than treatment of small areas, and men experienced more pain than women. The pain experienced by the patients did not correlate with treatment dose, Fitzpatrick skin type, age or fluorescence intensity.

Topical 5-ALA photodynamic therapy for the treatment of cutaneous T-cell lymphoma

Therapeutic options for cutaneous T cell lymphoma (CTCL) include topical steroids, topical chemotherapy and phototherapy. Patients with limited disease that is unresponsive to these therapies present a particular challenge. We report successful treatment of a patient with two plaques of CTCL using topical photodynamic therapy (PDT). 5-aminolaevulinic acid (5-ALA) was applied 6-24 h preillumination with 100 J/cm2 red light. Treatment was repeated on four occasions with clinical and histological clearance. ALA-PDT may be a useful addition to the therapeutic options for CTCL. Further studies are required to define optimal treatment protocols.

The advantages of aminolevulinic acid photodynamic therapy in dermatology

Photodynamic therapy (PDT) is being increasingly employed in the detection and treatment of malignant and non-malignant disease. This local technique uses a photosensitizing drug activated by light to generate cell death via the production of reactive oxygen species. This review describes the fundamental processes behind PDT, focussing on the use of 5-aminolevulinic acid (ALA). ALA itself is not a photosensitizing drug, but administration of exogenous ALA induces the build-up of the natural endogenous photosensitizer protoporphyrin IX (PpIX). This form of PDT has proved promising for the treatment of a number of dermatological indications. An overview of these current and potential applications of ALA-based PDT is presented, with emphasis on the advantages of the technique that make it especially suitable for skin conditions and the problem areas on which future research should be focussed.