Topical application of 5-aminolevulinic acid, DMSO and EDTA: protoporphyrin IX accumulation in skin and tumours of mice

In vivo skin absorption dynamics of topically applied pharmaceuticals monitored by fiber-optic diffuse reflectance spectroscopy

A simple non-invasive ultra-violet/visible (UV/vis) diffusive reflectance spectroscopy combined with fiber-optics was investigated to elicit the dynamics of skin penetration in vivo of a pharmaceutical, aminolevulinic acid polyethylene glycol cream (5-ALA-PEG cream). Temporal data of the reflectance, R(lambda), were measured from a bare skin region and from a skin region treated with 5-ALA cream. The difference in apparent optical density [(DeltaAOD)=Deltalog[1/R(lambda)]] between the treated and untreated regions of the skin was gradually increased to a local maximum value with an increasing time of measurement, and then it was decreased in an oscillatory manner. This temporal increase in DeltaAOD was interpreted as a diminution of total reflectance by an increased scattering inside the skin tissue as topically applied materials penetrated gradually and temporally accumulated into the skin. A following decrease in DeltaAOD was attributed to diminished scattering effects as the penetrated materials gradually cleared out by cellular uptake of 5-ALA and circulation by epidermal capillary. In conclusion, it was possible to measure the skin absorption kinetics of the topically treated materials, including the penetration time and clearing out from the temporal course of the differential AOD.

In vitro percutaneous absorption and in vivo protoporphyrin IX accumulation in skin and tumors after topical 5-aminolevulinic acid application with enhancement using an erbium:YAG laser

5-aminolevulinic acid (ALA) is used as a precursor of protoporphyrin IX (PpIX) for photodynamic therapy (PDT) of superficial skin cancers and subcutaneous metastases of internal malignancies. The permeability of ALA across intact skin is always low, making it difficult to achieve the desired therapeutic benefits. Hence new methods for enhancing ALA permeation are urgently needed. The aim of this study was to determine the in vivo kinetics of PpIX generation in mouse tissues after topical ALA application enhanced by an erbium (Er):yttrium-aluminum-garnet (YAG) laser. The in vitro permeation of ALA was also used to screen the optimal method for the in vivo study. The efficacy of the improved drug delivery was determined as a function of various laser fluences and cancer models. ALA applied to laser-treated skin produced a higher accumulations of PpIX within superficial skin and subcutaneous tumors as compared to those of the non-treated group (t-test, p < 0.05). The enhancement ratios (ER) of laser-treated skin ranged from 1.7 to 4.9 times as compared to the control depending to the fluences used. The enhanced PpIX level of laser-treated skin was generally more pronounced in normal and lesional skin than in subcutaneous nodular tumors. Confocal laser scanning microscopy (CLSM) of laser-treated skin revealed intense red fluorescence within the epidermis and upper dermis, and a much-weaker fluorescence within the bottom layers of the skin. On the other hand, the fluorescence intensity of the control group was much lower than that of laser-treated group. The barrier properties of the skin irradiated by the laser had completely recovered within 3 days. Pretreatment of skin using an Er:YAG laser was useful in increasing the amount of Pp IX within skin tumors.

Design and evaluation of a water-soluble bioadhesive patch formulation for cutaneous delivery of 5-aminolevulinic acid to superficial neoplastic lesions

Photodynamic therapy of superficial neoplastic lesions generally uses high aminolevulinic acid (ALA) loadings (20%, w/w) in emulsion-type systems under occlusion. This approach makes ALA dosing difficult and delivery to demanding areas, such as the vulval, perineal and perianal skin, are seldom possible. This work evaluated a water-soluble bioadhesive patch, loaded with ALA, which can adhere to both intact skin and mucous surfaces. ALA loading in the patch (38 mg cm(-2)) was chosen using a simple comparative procedure. Tensile measurements showed that large ALA loadings did not adversely affect adhesion to porcine skin, achieving a mean strength of 1.7 N cm(-2). Increasing the loading was, however, shown to lower break strength and enhance percentage elongation at break. Water uptake studies showed an initial, rapid weight gain followed by gradual patch dissolution over 60 min. Drug release studies demonstrated that 57% of ALA was released across an aqueous semi-permeable membrane within 6 h, compared to 42% released from a proprietary cream formulation. The patch designed in this work is suited to definable ALA delivery to diverse regions, such as the lower female reproductive tract and lesions on exposed skin. Adhesion is sufficiently tenacious to allow photodynamic therapy (PDT), without the need to immobilise patients for up to 6 h, as was common with the cream-under-occlusion approach.

Oleic acid as optimizer of the skin delivery of 5-aminolevulinic acid in photodynamic therapy

PURPOSE

In photodynamic therapy (PDT), topically applied aminolevulinic acid (5-ALA) is converted to protoporphyrin IX (PpIX), which upon light excitation induces tumor destruction. To optimize 5-ALA-PDT via improving the highly hydrophilic 5-ALA limited penetration into the skin, we propose the use of the known skin penetration enhancer, oleic acid (OA).

METHODS

In vitro skin penetration and retention of 5-ALA (1% w/w) were measured in the presence or absence of OA (2.5, 5.0, and 10.0% w/w) in propylene glycol (PG) using porcine ear skin as the membrane. In vivo accumulation of PpIX, 4 h after application, was determined fluorometrically in healthy mice skin by chemical extraction of skin samples. In vivo PpIX fluorescence kinetics was also investigated by noninvasive techniques using an optical fiber probe, for 30 min up to 24 h after topical application of 1.0% 5-ALA + 10.0% OA in PG on hairless mice skins.

RESULTS

The flux and in vitro retention of 5-ALA in viable epidermis increased in the presence of 10.0% (w/w) OA. The amounts of PpIX, evaluated both by chemical tissue extractions and in vivo measurements by an optical fiber probe, increased after applying 5-ALA formulations containing 5.0 or 10.0% OA. Moreover, in vivo kinetic studies showed an increase in skin PpIX accumulation when formulations containing 10% OA were used; PpIX accumulation was also maintained longer compared to controls.

CONCLUSIONS

Both in vitro and in vivo results show the OA potential as an optimizer of 5-ALA skin delivery.

5-Aminolevulinic Acid Derivatives in Photomedicine: Characteristics, Application and Perspectives

The introduction of lipophilic derivatives of the naturally occurring heme precursor 5-aminolevulinic acid (5-ALA) into photomedicine has led to a true revival of this research area. 5-ALA-mediated photodynamic therapy (PDT) and fluorescence photodetection (FD) of neoplastic disease is probably one of the most selective cancer treatments currently known in oncology. To date, this method has been assessed experimentally for the treatment of various medical indications. However, the limited local bioavailability of 5-ALA has widely prevented its use in daily clinical practice. Although researchers were already aware of this drawback early during the development of 5-ALA-mediated PDT, only recently have well-established concepts in pharmaceutical science been adapted to investigate ways to overcome this drawback. Recently, two derivatives of 5-ALA, methylaminolevulinate (MAL) and hexylaminolevulinate (HAL), gained marketing authorization from the regulatory offices in Europe and Australia. MAL is marketed under the trade name Metvix for the treatment of actinic keratosis and difficult-to-treat basal cell carcinoma. HAL has recently been launched under the trade name Hexvix to improve the detection of superficial bladder cancer in Europe. This review will first present the fundamental concepts underlying the use of 5-ALA derivatives in PDT and FD from a chemical, biochemical and pharmaceutical point of view. Experimental evidences from preclinical data on the improvements and limits observed with 5-ALA derivatives will then be introduced. The state-of-the-art from clinical studies with 5-ALA esters will be discussed, with special emphasis placed on the process that led to the development of MAL in dermatology and to HAL in urology. Finally, we will discuss promising medical fields in which use of 5-ALA derivatives might potentially lead to further use of this methodology in photomedicine.

Deferoxamine photosensitizes cancer cells in vitro

Effect of the iron chelator deferoxamine (DF) on the production of endogenous porphyrins was studied in adenocarcinoma WiDr cells and erythroid K562 cells in vitro. Porphyrin fluorescence was observed in the cells in vitro incubated with DF. The fluorescence spectra recorded in the cells were similar to that of protoporphyrin IX (PpIX). The amount of PpIX generated by DF was around 5% of the ALA effect. Around 90% of the WiDr cells incubated in vitro with DF (0.5 mM, 24 h) and then exposed to light (400-460 nm, 20 min) were photodynamically inactivated. In conclusion, the present study describes a novel approach of using iron chelating agents without 5-aminolevulinic acid (ALA) to photosensitize cancer cells.

Photodynamic therapy for Staphylococcus aureus infected burn wounds in mice

The rise of multiply antibiotic resistant bacteria has led to searches for novel antimicrobial therapies to treat infections. Photodynamic therapy (PDT) is a potential candidate; it uses the combination of a photosensitizer with visible light to produce reactive oxygen species that lead to cell death. We used PDT mediated by meso-mono-phenyl-tri(N-methyl-4-pyridyl)-porphyrin (PTMPP) to treat burn wounds in mice with established Staphylococcus aureus infections The third degree burn wounds were infected with bioluminescent S. aureus. PDT was applied after one day of bacterial growth by adding a 25% DMSO/500 microM PTMPP solution to the wound followed by illumination with red light and periodic imaging of the mice using a sensitive camera to detect the bioluminescence. More than 98% of the bacteria were eradicated after a light dose of 210 J cm(-2) in the presence of PTMPP. However, bacterial re-growth was observed. Light alone or PDT both delayed the wound healing. These data suggest that PDT has the potential to rapidly reduce the bacterial load in infected burns. The treatment needs to be optimized to reduce wound damage and prevent recurrence.

5-Aminolevulinic acid ester?induced protoporphyrin IX in a murine melanoma cell line

The use of 5-aminolevulinic acid (5-ALA) ester derivatives as precursors of endogenous protoporphyrin IX (PpIX) has been proposed as a good strategy for improved drug diffusion across biological membranes. In the present work, the 5-ALA ester derivatives hexyl-ALA (h-ALA), octyl-ALA (o-ALA), and decyl-ALA (d-ALA) were synthesized, and their efficacy to induce endogenous PpIX was explored in a murine melanoma cell line (B-16) as compared with that of 5-ALA. The maximum level of PpIX induced in cells treated with 5-ALA, h-ALA, o-ALA, and d-ALA was reached at optimal concentrations of 0.3, 0.075, 0.1, and 0.075 mM, respectively. The derivatives h-ALA and o-ALA appear as the most efficient PpIX precursors in this cell line, since a higher or similar PpIX production could be achieved with a fourfold and threefold lower dose of these precursors compared with 5-ALA. The phototoxicity effect of h-ALA and o-ALA ester derivatives showed the same phototoxicity behavior detected for 5-ALA but at much lower drug doses. Our study suggests that h-ALA and o-ALA esters improve intracellular PpIX formation in B-16 cells at reduced concentrations. This should enable clinical applications at lower precursor doses with reduced effective costs.

Antimetastatic activity of the photodynamic agent hypericin in the dark

A unique property of the photodynamic signal transduction inhibitor hypericin (HY) is high functionality in the dark, which has been shown to result in portfolio of anticancer activities both in vitro and in vivo. Here we show that treatment with HY significantly reduces growth rate of metastases in 2 murine models: breast adenocarcinoma (DA3) and squamous cell carcinoma (SQ2). Focus on metastases was achieved by resection of primary tumors at stages in which micrometastases exist in lungs. Long-term animal survival in DA3 tumor-excised groups increased from 15.6% in controls to 34.5% following supplementary treatment with HY. In mice bearing SQ2 tumor metastases, therapy with HY increased animal survival from 17.7% in controls to 46.1%. Using Laser-induced fluorescence and multipixel spectral image analyses, we demonstrate that HY has a high tendency to accumulate in primary and metastatic tumors; HY content in lungs bearing metastases was approximately 2-fold higher than in the lungs of healthy animals. The tendency of HY to preferentially concentrate in lung metastases, combined with its potent antiproliferative activities, may render HY as a useful supplementary modality in the treatment of metastatic cancer irrespective of photoactivation.

The effect of an iron chelating agent on protoporphyrin IX levels and phototoxicity in topical 5-aminolaevulinic acid photodynamic therapy

BACKGROUND

In 5-aminolaevulinic acid (ALA)-photodynamic therapy (PDT), the prodrug ALA is endogenously converted to the active sensitizer protoporphyrin IX (PpIX), while further conversion of PpIX to haem requires iron.

OBJECTIVES

To explore the potential of the iron chelator desferrioxamine (DFO) to enhance PpIX levels and phototoxicity in ALA-PDT.

METHODS

A series of six doses of 2% ALA solution was iontophoresed into the healthy skin of each ventral forearm of 10 volunteers. One arm was pretreated with 20% DFO in aqueous cream, while the control arm received aqueous cream alone, for 16 h. At 5 h following iontophoresis, skin-surface PpIX fluorescence was measured, following which the forearms were simultaneously irradiated with 100 J cm-2 broadband red light. The phototoxic reaction was assessed at 24 h postirradiation as the minimal phototoxic dose (MPD) and with quantification of erythema. Next, eight patients with two superficial basal cell carcinomas or two plaques of Bowen's disease of similar appearance received 20% ALA topically to one lesion and 20% ALA with 20% DFO to the other, for 3 h. Skin-surface PpIX fluorescence was measured at 5 h, following which lesions were irradiated with 100 J cm-2 broadband red light.

RESULTS

In healthy skin, PpIX fluorescence increased with increasing ALA dose at DFO-treated and untreated sites (P < 0.0005); PpIX fluorescence peak values were consistently higher in DFO-treated compared with control sites (P < 0.02). Erythema also correlated with ALA dose (P < 0.0005), but a significant difference between active and control sites occurred only at low ALA dose (P < 0.05). The median MPD appeared lower at the DFO-treated sites, at 6 mC vs. 12 mC (P = 0.06). In contrast, in lesional skin there was no consistent difference in PpIX fluorescence levels between those treated with and without DFO.

CONCLUSIONS

While iron chelation augmented ALA-PDT phototoxicity in normal skin, this occurred only at low ALA dose. Addition of DFO does not appear to confer additional benefit in ALA-PDT of nonmelanoma skin cancers.

Final report on the safety assessment of EDTA, calcium disodium EDTA, diammonium EDTA, dipotassium EDTA, disodium EDTA, TEA-EDTA, tetrasodium EDTA, tripotassium EDTA, trisodium EDTA, HEDTA, and trisodium HEDTA

EDTA (ethylenediamine tetraacetic acid) and its salts are substituted diamines. HEDTA (hydroxyethyl ethylenediamine triacetic acid) and its trisodium salt are substituted amines. These ingredients function as chelating agents in cosmetic formulations. The typical concentration of use of EDTA is less than 2%, with the other salts in current use at even lower concentrations. The lowest dose reported to cause a toxic effect in animals was 750 mg/kg/day. These chelating agents are cytotoxic and weakly genotoxic, but not carcinogenic. Oral exposures to EDTA produced adverse reproductive and developmental effects in animals. Clinical tests reported no absorption of an EDTA salt through the skin. These ingredients are likely, however, to affect the passage of other chemicals into the skin because they will chelate calcium. Exposure to EDTA in most cosmetic formulations, therefore, would produce systemic exposure levels well below those seen to be toxic in oral dosing studies. Exposure to EDTA in cosmetic formulations that may be inhaled, however, was a concern. An exposure assessment done using conservative assumptions predicted that the maximum EDTA dose via inhalation of an aerosolized cosmetic formulation is below that shown to produce reproductive or developmental toxicity. Because of the potential to increase the penetration of other chemicals, formulators should continue to be aware of this when combining these ingredients with ingredients that previously have been determined to be safe, primarily because they were not significantly absorbed. Based on the available data, the Cosmetic Ingredient Review Expert Panel found that these ingredients are safe as used in cosmetic formulations.

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.

Topical application of ALA and ALA hexyl ester on a subcutaneous murine mammary adenocarcinoma: tissue distribution

Although 5-aminolevulinic acid (ALA)-based photodynamic therapy (PDT) has proven to be clinically beneficial for the treatment of certain cancers, including a variety of skin cancers, optimal tissue localisation still remains a problem. An approach to improve the bioavailability of protoporphyrin IX (PpIX) is the use of ALA derivatives instead of ALA. In this work, we employed a subcutaneous murine mammary adenocarcinoma to study the tissue distribution pattern of the ALA hexyl ester (He-ALA) in comparison with ALA after their topical application in different vehicles. He-ALA induced porphyrin synthesis in the skin overlying the tumour (SOT), but it did not reach the tumour tissue as efficiently. Only 5 h after He-ALA lotion application, tumour porphyrin levels surpassed control values. He-ALA delivered in cream induced a substantially lower porphyrin synthesis in SOT, reinforcing the importance of the vehicle in the use of topical PDT. Porphyrin levels in internal organs remained almost within control values when He-ALA was employed. The addition of DMSO to ALA formulation slightly increased tumour and SOT porphyrin biosynthesis, but it did not when added to He-ALA lotion.

The stability of 5-aminolevulinic acid in solution

5-Aminolevulinic acid (ALA) is being assessed for photodynamic therapy of cancer and other diseases worldwide. However, its stability properties in solution are not well understood yet. The breakdown of ALA in pH-buffered solutions was examined in this work. Solutions of ALA in PBS buffered to physiological pH were found to be unstable, leading to a breakdown product that absorbs photons around 278 nm. The ability of the solution to stimulate porphyrin production in cells is gradually lost upon breakdown, though the kinetics for this are different from those for formation of the UV absorbing product. It is likely, therefore, that several chemical pathways contribute to the breakdown of dissolved ALA at physiological pH. Temperature studies of the formation kinetics of the UV absorbing product also indicate that a complex formation process is involved.

In vitro/in vivo correlations between transdermal delivery of 5-aminolaevulinic acid and cutaneous protoporphyrin IX accumulation and effect of formulation

BACKGROUND

Photodynamic therapy (PDT) using topical application of 5-aminolaevulinic acid (ALA) has been widely reported for the treatment of a variety of neoplastic and non-neoplastic cutaneous diseases. Although different formulations containing variable amounts of ALA have been applied in PDT, the dose-response relationships between transdermal ALA delivery and cutaneous protoporphyrin IX (PpIX) accumulation have not been studied.

OBJECTIVES AND METHODS

The objectives of this study were to investigate the effect of permeability barrier function, ALA concentration and formulation on the in vitro penetration of ALA through nude mouse skin and cutaneous PpIX formation at 2 h following a 2-h application of ALA to nude mouse skin in vivo, and to delineate the relationships in between.

RESULTS

Results demonstrated that variations in barrier integrity, in addition to ALA concentration, profoundly influenced ALA delivery to generate PpIX. Saturable correlations were found to exist between PpIX concentrations in both the epidermis and dermis in vivo and its transdermal flux in vitro, and the relationships were well described by the Emax model. The established correlations based on pure aqueous solutions were applicable to different formulations containing hydroxypropylmethylcellulose as the gelling agent and ethylenediamine tetraacetic acid as the iron chelator. Moreover, incorporation of desferrioxamine, another iron chelator, in the formulation prolonged cutaneous PpIX accumulation in the skin in comparison with 3% ALA aqueous solution, but the peak PpIX levels were not increased. Application of a liposomal formulation resulted in similar prolongation in ALA-induced PpIX accumulation, as well as better epidermal targeting.

CONCLUSIONS

Knowledge of the dose-response relationships and the effect of formulation is important for designing optimal formulations and treatment schedules for topical ALA-PDT.

Fluorescence spectroscopy study of protoporphyrin IX metabolism level in cells

Fluorescence spectroscopy was used to study the protoporphyrin IX (PpIX) metabolism level in chick embryos during the cell proliferation process. The emission spectra were measured for PpIX bound to albumin from nonincubated and incubated eggs. The relative characteristic emission intensity of PpIX was used to determine the level of PpIX metabolism as a function of the embryonic development time. This technique might be used to estimate tumor development time.

Stratum corneum lipids liposomes for the topical delivery of 5-aminolevulinic acid in photodynamic therapy of skin cancer: preparation and in vitro permeation study

BACKGROUND

Photodynamic therapy (PDT) using 5-aminolevulinic acid (5-ALA) is a skin cancer therapy that still has limitations due to the low penetration of this drug into the skin. We have proposed in this work a delivery system for 5-ALA based on liposomes having lipid composition similar to the mammalian stratum corneum (SCLLs) in order to optimize its skin delivery in Photodynamic Therapy (PDT) of skin cancers.

METHODS

SCLLs were obtained by reverse phase evaporation technique and size distribution of the vesicles was determinated by photon correlation spectroscopy. In vitro permeation profile was characterized using hairless mouse skin mounted in modified Franz diffusion cell.

RESULTS

Size exclusion chromatography on gel filtration confirmed vesicle formation. SCLLs obtained by presented a degree of encapsulation of 5-ALA around 5.7%. A distribution of vesicle size centering at around 500 nm and 400 nm respectively for SCLLs and SCLLs containing 5-ALA was found. In vitro 5-ALA permeation study showed that SCLLs preparations presented higher skin retention significantly (p < 0.05) on the epidermis without SC + dermis, with a decreasing of skin permeation compared to aqueous solution.

CONCLUSIONS

The in vitro delivery performance provided by SCLLs lead to consider this systems adequate for the 5-ALA-PDT of skin cancer, since SCLLs have delivered 5-ALA to the target skin layers (viable epidermis + dermis) to be treated by topical PDT of skin cancer.

Routine experimental system for defining conditions used in photodynamic therapy and fluorescence photodetection of (non-) neoplastic epithelia

A common method to induce enhanced short-term endogenous porphyrin synthesis and accumulation in cell is the topical, systemic application of 5-aminolevulinic acid or one of its derivatives. This circumvents the intravenous administration of photosensitizers normally used for photodynamic therapy (PDT) of fluorescence photodetection. However, in the majority of potential medical indications, optimal conditions with respect to the porphyrin precursor or its pharmaceutical formulation have not yet been found. Due to ethical restrictions and animal right directives, the number of available test objects is limited. Hence, definition and use of nonanimal test methods are needed. Tissue and organ cultures are a promising approach in replacing cost intensive animal models in early stages of drug development. In this paper, we present a tissue culture, which can among others be used routinely to answer specific questions emerging in the field of photodynamic therapy and fluorescence photodetection. This technique uses mucosae excised from sheep paranasal sinuses or pig bladder, which is cultured under controlled conditions. It allows quasiquantitative testing of different protoporphyrin IX precursors with respect to dose-response curves and pharmacokinetics, as well as the evaluation of different incubation conditions and/or different drug formulations. Furthermore, this approach, when combined with the use of electron microscopy and fluorescence-based methods, can be used to quantitatively determine the therapeutic outcome following protoporphyrin IX-mediated PDT.

Is delta-aminolevulinic acid dehydratase rate limiting in heme biosynthesis following exposure of cells to delta-aminolevulinic acid?

Understanding the regulation and control of heme/porphyrin biosynthesis is critical for the optimization of the delta-aminolevulinic-acid (ALA)-mediated photodynamic therapy of cancer, in which endogenously produced protoporphyrin IX (PPIX) is the photosensitizer. The human breast cancer cell line MCF-7, the rat mammary adenocarcinoma cell line R3230AC, the mouse mammary tumor cell line EMT-6 and the human mesothelioma cell line H-MESO-1 were used to study ALA-induced PPIX levels and their relationship to delta-aminolevulinic acid dehydratase (ALA-D) activity in vitro. Incubation of these cell lines with 0.5 mM ALA for 3 h resulted in a significant increase in PPIX accumulation, compared with control cells, but there was no significant change in ALA-D activity. Exposure of cells incubated with ALA to 30 mJ/cm2 of fluorescent light, a dose that would cause a 50% reduction in cell proliferation, did not significantly alter the activity of ALA-D. Increasing the activity of porphobilinogen deaminase (PBGD), the enzyme immediately subsequent to ALA-D, by four- to seven-fold via transfection of cells with PBGD complementary DNA did not alter the activity of ALA-D. However, incubation of cells with various concentrations of succinyl acetone, a potent inhibitor of ALA-D, caused a concomitant decline in both PPIX accumulation and ALA-D activity. These data imply that when cells are exposed to exogenous ALA, ALA-D is an important early-control step in heme/porphyrin biosynthesis and that regulation of PPIX synthesis by this dehydratase may impact the effectiveness of ALA-mediated photosensitization.

Photodynamic therapy of skin cancers: sensitizers, clinical studies and future directives

Photodynamic therapy (PDT) is a new modality of skin cancer treatment. It involves the administration of photosensitizing drugs which, when localized in tumor tissue can produce its destruction by absorbing an adequate dose of light of an appropriate wavelength. A large number of photosensitizing agents have been tested in PDT experiments. Topical application of 5-aminolevulinic acid (5-ALA) followed by light irradiation is the most commonly used method. 5-ALA is a prodrug converted in situ via the heme cycle into protoporphyrin IX, an effective photosensitizer agent. Treatment of nonmelanoma skin cancers by PDT has met with varying degrees of success. In the case of 5-ALA, this therapy's main limitation is the poor penetration of 5-ALA into skin, due to hydrophilic and charge characteristics. However, the efficacy of 5-ALA-PDT may be improved by (a) development of adequate drug delivery systems; (b) use of enhancers of PpIX production and accumulation in target tissue, and (c) modifications of the 5-ALA molecule. Optimal timing, light sources, doses, and number of applications are also important factors for topical 5-ALA therapy and must be well defined. The aim of this review is to highlight recent progress in 5-ALA-PDT of skin cancer, and to present ways holding promise for its improvement.

The influence of the vehicle on the synthesis of porphyrins after topical application of 5-aminolaevulinic acid. Implications in cutaneous photodynamic sensitization

BACKGROUND

The optimal vehicle to ensure adequate penetration of 5-aminolaevulinic acid (ALA) for its use in photodynamic therapy (PDT) of skin lesions has not been determined.

OBJECTIVES

We aimed to study the effects of ALA in various vehicle formulations [saline lotion with and without dimethylsulphoxide (DMSO), cream, liposomes and vaseline] after topical application in a murine subcutaneous adenocarcinoma model.

METHODS

The effect of DMSO on porphyrin synthesis and ALA penetration through the skin was studied by measuring the uptake of 14C label from ALA, ALA and porphobilinogen accumulation, and some haem enzyme activities. The tissue distribution and kinetics of porphyrin synthesis after topical application of ALA entrapped in large multilamellar liposomes was also determined.

RESULTS

ALA in saline lotion, alone or with 10% DMSO, proved to be the most efficient vehicle for tumour porphyrin accumulation (mean +/- SD 1.75 +/- 0.25 and 2.09 +/- 0.39 microg g-1, respectively), whereas cream and liposomes induced lower levels and identical porphyrin accumulation (0.60 microg g-1). Using ALA + DMSO saline lotion, a higher porphyrin accumulation was found in skin overlying the tumour tissue and in the first 2 mm of tumour, probably due to increased ALA penetration, or greater interconversion to porphyrins, or greater retention of ALA and/or porphyrins.

CONCLUSIONS

These findings reinforce the importance of the vehicle in topical ALA-based PDT, and explain the mechanism of action of DMSO in enhancing protoporphyrin IX biosynthesis in superficial lesions.

Treatment of viral infections with 5-aminolevulinic acid and light

BACKGROUND AND OBJECTIVE

When 5-aminolevulinic acid (ALA) is exogenously supplied, protoporphyrin IX (PpIX) is accumulated in various cells and makes them light sensitive. The possibility of using such an approach for the treatment of viral infections was studied in this work.

STUDY DESIGN/MATERIALS AND METHODS

ALA was added to cultured cells infected with human immunodeficiency virus (HIV). Accumulation of PpIX in the cells as well as virus infectivity after photodynamic treatment (PDT) were assessed. For in vivo studies, guinea pigs were infected with herpes simplex virus (HSV) and then administered ALA at intervals after infection. The animals were exposed to PDT at the site of infection 3 hours after ALA administration. Clinical observations and virus titration were made daily. For clinical studies, two patients with Molluscum contagiosum and Verrucae vulgares were treated with ALA fortified with an iron chelating agent and dimethylsulfoxide, followed 4 hours later by PDT.

RESULTS

Cells that are infected with HIV accumulated PpIX upon addition of ALA in vitro. This accumulation was enhanced approximately two-fold in the presence of an iron chelator. Subsequent exposure to red light PDT drastically reduced the virus titer (> 99% for U1 cells latently infected with HIV). In guinea pigs infected with HSV, subsequent administration of ALA and exposure of the lesions to red light shortened the duration of vesicles' appearance from more than a week to a few days and reduced HSV titer in the lesions by > or = 5 log10. ALA-PDT treated AIDS patient suffering from Molluscum contagiosum or a kidney transplant patient with Verrucae vulgares showed greatly improved clinical symptoms one month after treatment.

CONCLUSION

It is concluded that ALA-PDT could be effective in treating certain viral infections, particularly those resulting in warts.

A vehicle for photodynamic therapy of skin cancer: influence of dimethylsulphoxide on 5-aminolevulinic acid in vitro cutaneous permeation and in vivo protoporphyrin IX accumulation determined by confocal microscopy

Topical application of 5-aminolevulinic acid (5-ALA) followed by light irradiation is a new concept of photodynamic therapy (PDT) of skin cancers. 5-ALA is a prodrug that can be converted by the heme biosynthetic pathway into protoporphyrin IX, an effective photosensitizer. In the present work we propose the enhancement of 5-ALA-induced protoporphyrin IX accumulation by dimethylsulphoxide (DMSO) and ethylenediamine-tetraacetic acid disodium salt (EDTA). The presence of 20% DMSO (w/w) in oil-in-water emulsions increased the in vitro permeation of 5-ALA through hairless mouse skin. In vivo studies demonstrated a significant increase in the amount of protoporphyrin IX extracted from healthy hairless mouse skin after 3 h treatment with an oil-in-water emulsion containing 10% 5-ALA (w/w), 3% EDTA (w/w) and 20% DMSO (w/w). By confocal scanning laser microscopy imaging, an observed increase in red fluorescence, at 476 nm excitation and emission detected longer than 590 nm, in skin that had received this treatment, was attributed to protoporphyrin IX accumulation. Although no effect of EDTA on short-term protoporphyrin IX accumulation in skin was detected, this chelator could protect 5-ALA from decomposition during prolonged topical administration. The results obtained indicate that association of 5-ALA, EDTA and 20% DMSO may enhance the delivery of 5-ALA to the skin in the topical PDT.

Photodynamic therapy in dermatology

The combination of light and chemicals to treat skin diseases is widely practiced in dermatology. Within this broad use of light and drugs, in recent years the concept of photodynamic therapy (PDT) has emerged. PDT is a promising modality for the management of various tumors and nonmalignant diseases, based on the combination of a photosensitizer that is selectively localized in the target tissue and illumination of the lesion with visible light, resulting in photodamage and subsequent cell death. Moreover, the fluorescence of photosensitizing compounds is also utilized as a helpful diagnostic tool for the detection of neoplastic tissue. Intensive basic and clinical research culminated in the worldwide approval of PDT for bladder, esophageal, and lung cancer. The expanding use of this relatively new therapeutic modality in dermatology at many centers around the world has revealed its efficacy for the treatment of cutaneous precancer and cancer, as well as selected benign skin disorders. The following article summarizes the main principles of PDT considering the most recent developments and provides a comprehensive synopsis of the present status of the use of PDT in dermatology. (J Am Acad Dermatol 2000;42:389-413.)

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should be able to describe the basic concepts of PDT, including fundamental knowledge of the most relevant photosensitizers, the light sources, the mechanisms involved in PDT-mediated cell destruction, as well as the indications and limitations of photodynamic treatment of skin diseases.

Delta-aminolaevulinic acid-induced photodynamic therapy inhibits protoporphyrin IX biosynthesis and reduces subsequent treatment efficacy in vitro

Recently, considerable interest has been given to photodynamic therapy of cancer using delta-aminolaevulinic acid to induce protoporphyrin IX as the cell photosensitizer. One advantage of this modality is that protoporphyrin IX is cleared from tissue within 24 h after delta-aminolaevulinic acid administration. This could allow for multiple treatment regimens because of little concern regarding the accumulation of the photosensitizer in normal tissues. However, the haem biosynthetic pathway would have to be fully functional after the first course of therapy to allow for subsequent treatments. Photosensitization of cultured R3230AC rat mammary adenocarcinoma cells with delta-aminolaevulinic acid-induced protoporphyrin IX resulted in the inhibition of porphobilinogen deaminase, an enzyme in the haem biosynthetic pathway, and a concomitant decrease in protoporphyrin IX levels. Cultured R3230AC cells exposed to 0.5 mM delta-aminolaevulinic acid for 27 h accumulated 6.07 x 10(-16) mol of protoporphyrin IX per cell and had a porphobilinogen deaminase activity of 0.046 fmol uroporphyrin per 30 min per cell. Cells cultured under the same incubation conditions but exposed to 30 mJ cm(-2) irradiation after a 3-h incubation with delta-aminolaevulinic acid showed a significant reduction in protoporphyrin IX, 2.28 x 10(-16) mol per cell, and an 80% reduction in porphobilinogen deaminase activity to 0.0088 fmol uroporphyrin per 30 min per cell. Similar effects were evident in irradiated cells incubated with delta-aminolaevulinic acid immediately after, or following a 24 h interval, post-irradiation. There was little gain in efficacy from a second treatment regimen applied within 24 h of the initial treatment, probably a result of initial metabolic damage leading to reduced levels of protoporphyrin IX. These findings suggest that a correlation may exist between the delta-aminolaevulinic acid induction of porphobilinogen deaminase activity and the increase in intracellular protoporphyrin IX accumulation.

Endogenous porphyrin accumulation and photosensitization in the yeast Saccharomyces cerevisiae in the presence of 2,2'-dipyridyl

The chelator 2,2'-dipyridyl (0.2 mM) induces a remarkable increase of protoporphyrin IX concentration as well as of its Zn-containing complex in the yeast Saccharomyces cerevisiae. Endogenous porphyrin accumulation results in five- to six-fold cell sensitization to visible light (400-600 nm). Mitochondria isolated from the cells grown in the presence of 2,2'-dipyridyl accumulate protoporphyrin IX and Zn-protoporphyrin IX, while plasma membranes besides that exhibit porphyrin-type fluorescence at 670-675 nm in chloroform extract. The protoporphyrin IX content increases more than four-fold in mitochondria and two-fold in plasma membranes isolated from chelator-treated cells. The relative contribution of subcellular structure photodestruction to photoinduced cell inactivation is discussed.

Optimum porphyrin accumulation in epithelial skin tumours and psoriatic lesions after topical application of delta-aminolaevulinic acid

Photodynamic therapy with topically applied delta-aminolaevulinic acid is used to treat skin tumours by employing endogenously formed porphyrins as photosensitizers. This study examines the time course of porphyrin metabolite formation after topical application of delta-aminolaevulinic acid. Porphyrin biosynthesis in human skin tumours (basal cell carcinoma, squamous cell carcinoma), in psoriatic lesions, and in normal skin was investigated. Skin areas were treated with delta-aminolaevulinic acid, and levels of total porphyrins, porphyrin metabolites and proteins were measured in samples excised after 1, 2, 4, 6, 9, 12 and 24 h. There was an increase in porphyrin biosynthesis in all tissues with maximum porphyrin levels in tumours between 2 and 6 h and in psoriatic lesions 6 h after treatment. The pattern of porphyrins showed no significant difference between normal and neoplastic skin, protoporphyrin being the predominant metabolite. The results suggest that optimum irradiation time for superficial epithelial skin tumours may be as soon as 2 h after application of delta-aminolaevulinic acid, whereas for treatment of psoriatic lesions an application time of 6 h is more suitable.

Differentiation-specific increase in ALA-induced protoporphyrin IX accumulation in primary mouse keratinocytes

A treatment regimen that takes advantage of the induction of intracellular porphyrins such as protoporphyrin IX (PPIX) by exposure to exogenous 5-amino-laevulinic acid (ALA) followed by localized exposure to visible light represents a promising new approach to photodynamic therapy (PDT). Acting upon the suggestion that the effectiveness of ALA-dependent PDT may depend upon the state of cellular differentiation, we investigated the effect of terminal differentiation upon ALA-induced synthesis of and the subsequent phototoxicity attributable to PPIX in primary mouse keratinocytes. Induction of keratinocyte differentiation augmented intracellular PPIX accumulation in cells treated with ALA. These elevated PPIX levels resulted in an enhanced lethal photodynamic sensitization of differentiated cells. The differentiation-dependent increase in cellular PPIX levels resulted from several factors including: (a) increased ALA uptake, (b) enhanced PPIX production and (c) decreased PPIX export into the culture media. Simultaneously, steady-state levels of coproporphyrinogen oxidase mRNA increased but aminolaevulinic acid dehydratase mRNA levels remained unchanged. From experiments using 12-o-tetradecanoylphorbol-13-acetate, transforming growth factor beta 1 and calcimycin we demonstrated that the increase in PPIX concentration in terminally differentiating keratinocytes is calcium- and differentiation specific. Stimulation of the haem synthetic capacity is seen in primary keratinocytes, but not in PAM 212 cells that fail to undergo differentiation. Interestingly, increased PPIX formation and elevated coproporphyrinogen oxidase mRNA levels are not limited to differentiating keratinocytes; these were also elevated in the C2C12 myoblast and the PC12 adrenal cell lines upon induction of differentiation. Overall, the therapeutic implications of these results are that the effectiveness of ALA-dependent PDT depends on the differentiation status of the cell and that this may enable selective targeting of several tissue types.

The kinetics of protoporphyrin fluorescence during ALA-PDT in human malignant skin tumors

Fluorescence monitoring during photodynamic therapy (PDT) with the use of topical 5-aminolevulinic acid (ALA) was carried out in patients bearing superficial and nodular basal cell carcinomas (BCC), squamous cell carcinomas (SCC) and Kaposi's sarcomas. A new diagnostic-therapeutic system based on an incoherent CW light source was used for fluorescence spectral measurements and imaging. The results showed that photoirradiation reduced ALA-induced protoporphyrin IX (PP) fluorescence in all tumors. The rate of PP photobleaching in superficial BCC and SCC tumors was significantly higher than in large nodular BCC tumors. The results showed that the differences in kinetics of fluorescence reduction could be attributed to the tumor thickness. One hour after photoirradiation with a light dose of 170 J/cm2 a phenomenon of re-appearance and recovery of PP fluorescence was observed in the large deeply penetrating BCC tumors and Kaposi's sarcoma lesions. In such cases an additional light treatment was performed. The results of the study demonstrated that fluorescence monitoring is very appropriate for the definition of an optimal ALA-PDT clinical protocol.

Effect of continuous and multiple doses of 5-aminolevulinic acid on protoporphyrin IX concentrations in the rat uterus

The objective of the present study was to determine if the concentration of protoporphyrin IX (PpIX) in the rat endometrium could be increased by administering 5-aminolevulinic acid (ALA) in multiple doses or by continuous infusion. The effect of pH, temperature and time in solution on the stability of ALA were also investigated. Estrogen-filled silastic capsules were implanted subcutaneously into ovary intact female rats (200-225 g) (n = 66). On the third day of hormonal priming, ALA (10 mg or 25 mg) dissolved in saline and adjusted to a pH of 5-5.5 was administered intrauterine either as a single bolus or as two injections 3 hours apart (n = 10). A fifth group of rats was infused with 25 mg ALA over a 12 hour period using an osmotic minipump (n = 6). In a second experiment, ALA (25 mg) was injected immediately after being dissolved in saline (pH 2) (n = 16) or after incubation at 37 degrees C for 12 hour (pH 2) (n = 7). PpIX was then extracted from the endometrium and myometrium using a 1:1 methanol/perchloric acid solution and quantified spectrofluorometrically. A dose-response relationship was observed between 10 and 25 mg of ALA and endometrial PpIX concentrations. However, no differences in endometrial PpIX concentrations were detected between rats administered ALA either as a single bolus or as two doses. Continuous infusion of 25 mg of ALA resulted in statistically lower endometrial PpIX concentrations compared to 25 mg ALA injected either as a single bolus or as two injections. Neither pH, temperature, nor time in solution affected ALA-induced PpIX accumulation. We conclude that the simplest way of achieving the highest PpIX concentration in the rat endometrium in vivo is to administer a bolus injection of 25 mg of ALA.

Pharmacokinetics of 5-aminolevulinic acid-induced protoporphyrin IX in skin and blood

The fluorescence and photosensitivity of endogenously synthesized protoporphyrin IX (PPIX) is increasingly used for the diagnosis and treatment of malignant and certain non-malignant diseases. A selective accumulation of PPIX can be induced by application of 5-aminolevulinic acid (5-ALA), which is a precursor of PPIX in the cellular biosynthetic pathway of heme. The purpose of this study was to monitor the in vivo accumulation of PPIX in different locations of the skin after oral ingestion and to determine the pharmacokinetics of 5-ALA and PPIX in human blood plasma for various routes of application. At the same time we wanted to achieve an optimal treatment scheme but also study possible side-effects of 5-ALA administration. After oral application of 5-ALA in a concentration of 40 mg kg-1 body weight, the fluorescence intensities of PPIX in the skin showed maxima between 6.5 and 9.8 h depending on the location and decreased to values lower than 5% related to the maximum after a mean time of about 40 h. The measured absolute intensities of PPIX fluorescence varied strongly between different patients and different locations on one patient. In the plasma of blood samples, PPIX could be detected via its fluorescence for all studied routes of application with the exception of the ointment, where PPIX levels were below the detection limit of 1 microgram l-1. The highest mean concentration of 742 micrograms l-1 PPIX in the plasma was measured 6.7 h after oral application. For inhalation of 5-ALA, a mean maximum concentration of 12 micrograms l-1 could be detected 4.1 h after application, for intravesical instillation, the mean maximum concentration was found to be 1 microgram l-1 2.9 h after application. The kinetics of 5-ALA in the plasma peaked much earlier with a maximum concentration of 32 mg l-1 about 30 min. after oral administration. The 5-ALA levels did not exceed normal reference values after topical application. The results of our experiments suggest that for a systemic application of 5-ALA side-effects in sensitive patients cannot be excluded.

In vivo fluorescence imaging for tissue diagnostics

Non-invasive fluorescence imaging has the potential to provide in vivo diagnostic information for many clinical specialties. Techniques have been developed over the years for simple ocular observations following UV excitation to sophisticated spectroscopic imaging using advanced equipment. Much of the impetus for research on fluorescence imaging for tissue diagnostics has come from parallel developments in photodynamic therapy of malignant lesions with fluorescent photosensitizers. However, the fluorescence of endogenous molecules (tissue autofluorescence) also plays an important role in most applications. In this paper, the possibilities of imaging tissues using fluorescence spectroscopy as a mean of tissue characterization are discussed. The various imaging techniques for extracting diagnostic information suggested in the literature are reviewed. The development of exogenous fluorophores for this purpose is also presented. Finally, the present status of clinical evaluation and future directions are discussed.

Iontophoretic delivery of ALA provides a quantitative model for ALA pharmacokinetics and PpIX phototoxicity in human skin

Photodynamic therapy (PDT) with topical 5-aminolevulinic acid (ALA) is increasingly employed for skin cancer, yet ALA dosing is crude. Using iontophoresis, we developed a rapid and quantifiable system for topical ALA delivery, with measurement of subsequent PpIX fluorescence and phototoxicity. ALA was iontophoresed from a 2% solution into upper inner arm skin of 13 healthy volunteers. Six doses of ALA were delivered with a series of charges varying from 3-120 milliCoulombs (mC); four additional doses were given with a charge of 60 mC. Five hours post-iontophoresis, sites were irradiated with broad-band yellow-red light, the series of six ALA doses receiving 100 J/cm2, while the four identical doses received 6.25, 12.5, 25, and 50 J/cm2, respectively. Resultant erythema was measured by reflectance spectroscopy. The time course of PpIX fluorescence was ALA-dose-dependent. With charge < or = 24 mC, PpIX fluorescence peaked at 3 h and returned to zero at 9-10 h, whereas charges > 24 mC had a sustained peak at 5-10 h, falling to zero by 24 h. Pre-irradiation, PpIX fluorescence correlated with ALA dose (r = 1.0). PpIX fluorescence fell immediately post-irradiation (p < 0.0001); recovery levels at 3 h correlated with ALA dose (p < 0.0001). Delayed erythema correlated with ALA dose and irradiation dose (p < 0.0001, p < 0.01, respectively). Both PpIX fluorescence intensity pre-irradiation and fall in PpIX fluorescence post-irradiation correlated with erythema (r = 0.98). Hence, PpIX synthesis is ALA-dose-dependent, and phototoxicity can be predicted from ALA dose, irradiation dose, and photobleaching of PpIX. This reproducible system allows accurate dosimetry in topical PDT and facilitates study of ALA metabolism.

Photodynamic therapy (PDT) and photodiagnosis (PD) using endogenous photosensitization induced by 5-aminolevulinic acid (ALA): mechanisms and clinical results

5-Aminolevulinic acid (ALA), when added to many tissues, results in the accumulation of sufficient quantities of the endogenous photosensitizer protoporphyrin IX (PpIX) via the heme biosynthetic pathway, to produce a photodynamic effect when exposed to activating light. Therefore, ALA is the only photodynamic therapy (PDT) agent in current clinical development that is a biochemical precursor of a photosensitizer. Topical ALA application, followed by exposure to activating light (ALA PDT), has been reported effective for the treatment of a variety of dermatologic diseases including cutaneous superficial and nodular basal cell carcinoma, Bowen's disease, and actinic (solar) keratoses. Local internal application of ALA has also been used for selective endometrial ablation in animal model systems and in human clinical studies has shown selective formation of PpIX within the endometrium. PpIX induced by ALA application has also been used as a fluorescence detection marker for photodiagnosis (PD) of cancer and dysplastic conditions of the urinary bladder and other organs. Systemic, oral administration of ALA has been used for ALA PDT of superficial head and neck cancer, various gastrointestinal cancers, and the condition known as Barrett's esophagus. The current state of knowledge of the mechanisms of endogenous topical and systemic photosensitization using ALA, the results of published clinical trials, and possible methods of increasing the efficacy of endogenous photosensitization for ALA PDT are reviewed in this paper.

Photodynamic therapy in veterinary medicine: current status and implications for applications in human disease

The historical development and published veterinary applications of photodynamic therapy are reviewed. Potential animal models, using naturally-occurring diseases in veterinary patients, for the future development of photodynamic therapy are described.

Fourier transform multipixel spectroscopy and spectral imaging of protoporphyrin in single melanoma cells

Fourier transform multipixel spectroscopy was applied to subcellular localization of endogenous protoporphyrin (endo-PP) in single living B16 melanoma cells during photosensitization. Continuous fluorescence spectra for each pixel were recorded using a Sagnac interferometer coupled to a charge-coupled device camera. Multiple frames of data were acquired for each pixel composing the image, then they were stored as interferometric data and resolved as spectra for every pixel (10(3)-4 x 10(3) point pixels in a single cell). The net result was the intensity I (x, y, gamma), for each pixel of the image (x,y), at any wave-length (gamma). The present study demonstrates the application of Fourier transformed multipixel spectroscopy for spectral imaging of melanoma cells incubated with 5-aminolevulinic acid (ALA). The fluorescence image of ALA-treated cells revealed endo-PP all over the cytosol with a vesicular distribution, which represent mitochondria and endoplasmic reticulum compartments. Two main spectral fluorescence peaks were demonstrated at 630 and 670 nm, of monomeric and aggregated protoporphyrin, with intensities that differed from one subcellular site to another. Photoirradiation of the cells induced point-specific subcellular fluorescence spectrum changes and demonstrated photoproduct formation. Spectral-image reconstruction revealed the subcellular distribution of porphyrin species in single photosensitized cells. Multipixel spectroscopy of exogenous protoporphyrin revealed an endosomal-lysosomal compartment in aggregated states, whereas monomeric porphyrin species were localized mainly on the outer membrane. Photo-products could be visualized at sites of formation in subcellular compartments.

Kinetics and localisation of PpIX fluorescence after topical and systemic ALA application, observed in skin and skin tumours of UVB-treated mice

In this study the kinetics and localisation of protoporphyrin IX (PpIX) fluorescence in skin and skin tumours were examined after topically (20% for 4h) or systemically (200 mg/kg,i.p.) administered 5-aminolaevulinic acid (ALA). As a model we used hairless mice with skin lesions (actinic keratoses and squamous cell carcinoma), which were induced by daily UVB irradiation. The epidermis of the skin surrounding the tumours (T) was altered (AS); owing to the UVB irradiation, the epidermis was thicker and less elastic. Therefore, non-UVB-irradiated mice were used to assess fluorescence of normal skin (NS). Light from a halogen lamp was used to excite at 500 +/- 20 nm and fluorescence was detected through a filter that passes light of 670 +/- 50 nm. Maximal fluorescence following i.p. ALA was observed 2 h post injection (p.i.) and was three times less than after topically applied ALA. Furthermore, after i.p. ALA a lower T selectively (T/NS) could be obtained than after topically applied ALA. Maximal fluorescence following topically applied ALA was achieved 6 h after the end of the 4 h application time. At that interval fluorescence of T was twice as high as directly after the application period. Furthermore, T selectivity (T/NS) after topical ALA at the interval of maximal fluorescence was higher than at the interval directly after application. With fluorescence cryomicroscopy localisation of fluorescence in the skin at the interval of maximal fluorescence was determined after both administration routes. For both cases fluorescence was mainly located in T, epidermis and hair follicles. Fluorescence in subcutis could only be observed at 2 h post i.p. ALA and a 6 h post topical ALA. No fluorescence could be observed in muscle. We conclude that, in this model and with these ALA doses, a higher fluorescence intensity and selectivity (T/NS) was achieved after topically applied ALA than after systemically administered ALA. These results make topically applied ALA more favourable for ALA-PDT of superficial skin tumours in this model. In general these results imply that by optimising the time after ALA application the efficacy and selectivity of topical ALA-PDT for skin tumours may be improved.

A comparative study of tissue distribution and photodynamic therapy selectivity of chlorin e6, Photofrin II and ALA-induced protoporphyrin IX in a colon carcinoma model

An in vivo study of tissue distribution kinetics and photodynamic therapy (PDT) using 5-aminolaevulinic acid (ALA), chlorin e6 (Chl) and Photofrin (PII) was performed to evaluate the selectivity of porphyrin accumulation and tissue damage effects in a tumour model compared with normal tissue. C26 colon carcinoma of mice transplanted to the foot was used as a model for selectivity assessment. Fluorescence measurements of porphyrin accumulation in the foot bearing the tumour and in the normal foot were performed by the laser-induced fluorescence (LIF) system. A new high-intensity pulsed light delivery system (HIPLS) was used for simultaneous irradiation of both feet by light in the range of 600-800 nm, with light doses from 120 to 300 J cm-2 (0.6 J cm-2 per pulse, 1 Hz). Photoirradiation was carried out 1 h after injection of ALA, 3 h after injection of Chl and 24 h after injection of PII. A ratio of porphyrin accumulation in tumour vs normal tissue was used as an index of accumulation selectivity for each agent. PDT selectivity was determined from the regression analysis of normal and tumour tissue responses to PDT as a function of the applied light dose. A normal tissue damage index was defined at various values (50, 80 and 100%) of antitumour effect. The results of the LIF measurements revealed different patterns of fluorescence intensity in tumour and normal tissues for ALA-induced protoporphyrin IX (ALA-PpIX), Chl and PII. The results of PDT demonstrated the differences in both anti-tumour efficiency and normal tissue damage for the agents used. The selectivity of porphyrin accumulation in the tumour at the time of photoirradiation, as obtained by the LIF measurements, was in the order ALA-PpIX > Chl > PII. PDT selectivity at an equal value of anti-tumour effect was in the order Chl > ALA-PpIX > PII. Histological examination revealed certain differences in structural changes of normal skin after PDT with the agents tested. The results of PDT selectivity assessment with respect to differences in mechanisms of action for ALA, Chl and PII are discussed.

Distribution of 5-aminolevulinic acid-induced porphyrins in noduloulcerative basal cell carcinoma

Microscopic fluorescence photometry incorporating a light-sensitive thermo-electrically cooled charge-coupled device (CCD) camera was employed to investigate the fluorescence distribution of 5-aminolevulinic acid (ALA)-induced porphyrins in 22 patients with a total number of 52 noduloulcerative basal cell carcinomas (BCC) after topical ALA application with or without dimethylsulfoxide (DMSO)/ethylenediaminetetraacetic acid (EDTA) or after intravenous administration of ALA. Both localization patterns and amounts of ALA-induced porphyrins in the BCC were studied. The ALA-induced porphyrins were localized only in the superficial layers of the noduloulcerative BCC lesions after topical application of 20% ALA alone for 3 h. However, both the penetration of ALA into deep lesions and the production of the ALA-induced porphyrin fluorescence were increased after topical administration of 20% ALA and 20% DMSO/4% EDTA for 3 h. Prior treatment with 99% DMSO for 15 min further enhanced the ALA penetration into the BCC lesions after topical application of the ALA/DMSO/EDTA mixture and produced more ALA-induced porphyrins by a factor of about three compared with those treated with ALA alone. The penetration of ALA into the deep BCC lesions could also be increased by prolonging the time of topical application of 20% ALA/4% EDTA to 29-48 h (without DMSO). Intravenous injection of ALA led to a more homogeneous distribution of the ALA-derived porphyrins in the whole noduloulcerative BCC lesions.