Comparison of the pharmacokinetics and phototoxicity of protoporphyrin IX metabolized from 5-aminolevulinic acid and two derivatives in human skin in vivo

Skin surface Protoporphyrin IX fluorescence is associated with epidermal but not dermal fluorescence intensities

BACKGROUND

Photodynamic therapy with Protoporphyrin IX (PpIX) is well-established for keratinocyte dysplasia. PpIX fluorescence can be quantified at the skin surface and within skin layers, but their relation is previously undescribed. The study objective was to assess the relation between skin surface PpIX fluorescence and PpIX fluorescence in epidermis and dermis.

METHODS

Normal buttocks skin was tape-stripped and incubated with 20 % methyl aminolevulinate cream and 20 % hexyl aminolevulinate cream under occlusion. After 3 h, skin surface PpIX fluorescence photographs were captured and 4 mm punch biopsies sampled. PpIX fluorescence microscopy was measured in regions of interest (ROI) in epidermis and superficial dermis. All PpIX fluorescence intensities were calculated in arbitrary units (AU).

RESULTS

Skin surface PpIX fluorescence intensity expressed a positive, linear relation to ROI-epidermis PpIX fluorescence (HAL- and MAL-incubated skin, p < 0.001, r² = 0.60), but not to PpIX fluorescence intensities in ROI-superficial dermis (p = 0.112). PpIX fluorescence microscopy identified higher fluorescence intensities in ROI-epidermis (median 92 AU) compared to lower fluorescence intensities in ROI-superficial dermis (median 37 AU) (p < 0.001). HAL reached higher median PpIX fluorescence intensities than MAL when measured by skin surface photographs (10230 vs. 5630 AU, p < 0.001), andbyfluorescence microscopy in ROI-epidermis (107 vs. 52.5 AU, p < 0.001) or ROI-superficial dermis (40 vs. 30.5 AU, p = 0.04).

CONCLUSION

The positive linear relation between skin surface PpIX fluorescence photographs and epidermal PpIX fluorescence microscopy indicates that skin surface PpIX fluorescence predominantly derives from epidermis.

Photodynamic diagnosis with 5-aminolevulinic acid for intraoperative detection of peritoneal metastases of ovarian cancer: A feasibility and dose finding study

OBJECTIVE

With a prospective feasibility study, we aimed to analyse the effect of different time points for application and dosage of preoperative oral 5-aminolevulinic acid administration for photodynamic diagnosis of peritoneal metastases in ovarian cancer patients.

MATERIALS AND METHODS

In this prospective cohort study patients were randomly divided into three different groups. 5-Aminolevulinic acid was orally administered 3-14 hours before surgery using a dosage of 1 mg/kg, 4-9 hours using 10 mg/kg, and 9-16 hours using 10 mg/kg, respectively. Fluorescence was recorded intraoperatively using endoscopic equipment. The number and localization, of fluorescing nodules were documented. To analyze sensitivity and specificity samples from fluorescent and non-fluorescent tissues were evaluated histologically. Plasma protoporphyrin concentrations as well as any adverse events were assessed perioperatively.

RESULTS

In total, 26 patients suspected for ovarian cancer underwent intraoperative photodynamic diagnosis with 5-aminolevulinic acid. Most of them suffered from advanced cancer, 72% from FIGO-Stage IIIc. No severe adverse events were observed. Orally applied 5-aminolevulinic acid with a dosage of 1 mg/kg revealed no detectable fluorescence. However, at a dosage of 10 mg/kg fluorescence of metastatic tissue was significantly stronger than of non-affected tissue. If administered 4-9 hours preoperatively best detection rates for peritoneal metastases were obtained resulting in a sensitivity of 75% and a specificity of 100%.

CONCLUSIONS

Photodynamic diagnosis with 5-aminolevulinic acid leads to safe and specific fluorescence detection of peritoneal metastases. 5-Aminolevulinic acid should be used at a dosage of at least 10 mg/kg 4-9 hours preoperatively. Further phase I-II studies are recommended. Lasers Surg. Med. 49:169-176, 2017. © 2016 Wiley Periodicals, Inc.

Daylight photodynamic therapy with 1.5% 3-butenyl 5-aminolevulinate gel as a convenient, effective and safe therapy in acne treatment: A double-blind randomized controlled trial

While daylight photodynamic therapy (PDT) is a simpler and more tolerable treatment procedure for both clinicians and patients, it has never been applied for acne treatment. In this study, we evaluated efficacy, safety and histological changes of facial acne after application of the novel variant of 5-aminolevulinate (ALA)-ester, 1.5% 3-butenyl ALA-bu gel, using daylight only as the potential visible light source. Forty-six acne patients were randomly assigned to either ALA-bu or vehicle application group in a double-blind fashion. Both groups applied the allocated gel to facial acne lesions every other day for 12 weeks. At the final 12 week, both inflammatory and non-inflammatory acne lesions had decreased significantly by 58.0% and 34.1% in the ALA-bu group, respectively. Only a few patients expressed mild adverse effects. In the histopathological analysis, attenuated inflammatory cell infiltrations were observed and immunostaining intensities for interleukin-8, interleukin-1β, matrix metalloproteinase-9 and phosphorylated nuclear factor-κB were reduced concomitantly. Changes of their mRNA expression demonstrated comparable patterns. In conclusion, this ambulatory PDT was effective, very well tolerated and convenient for treating inflammatory acne lesions. Experimental results correlated well with clinical results. This novel regimen would provide a viable option for acne therapy.

Iontophoretic skin permeation of peptides: an investigation into the influence of molecular properties, iontophoretic conditions and formulation parameters

The transdermal route offers advantages for delivery of peptides and proteins. However, these polar and large molecules do not permeate the skin barrier well. Various enhancement methods have been employed to address this problem. Iontophoresis is one of the methods that shows promise but its application to peptide delivery has yet to be fully explored. This study investigates the effects of different molecular properties and iontophoretic conditions on the skin permeation of peptides. In this study, the permeation of alanine-tryptophan dipeptide (MW 276 Da), alanine-alanine-proline-valine tetrapeptide (MW 355 Da), Argireline® (Acetyl hexapeptide-3, MW 889 Da) and Triptorelin acetate (decapeptide, MW 1311 Da) through excised human skin under passive or iontophoretic current of 0.4 mA was investigated. The effects of pH change (3.0-7.4, to provide different net negative, neutral, and positive charges) to the peptide, donor concentration (1-10 mg/ml), background electrolyte (34-137 mM NaCl and/or 5-20 mM HEPES) and current direction (anodal vs cathodal) were also studied. Peptides were analysed by high-performance liquid chromatography or liquid scintillation counting. Iontophoresis led up to a 30 times increase in peptide permeation relative to passive permeation for the peptides. Electroosmosis was an important determinant of the total flux for the high molecular weight charged peptides. Electrorepulsion was found to be considerable for low molecular weight charged moieties. Permeation was decreased at lower pH, possibly due to decreased electroosmosis. Results also showed that 10 times increase in donor peptide concentration increases permeation of peptides by about 2-4 times and decreases iontophoretic permeability coefficients by about 2.5-5 times. The addition of extra background electrolyte decreased the iontophoretic permeation coefficient of peptides by 2-60 times. This study shows that iontophoretic permeation of peptides is affected by a number of parameters that can be optimized for effective transdermal peptide delivery.

Photodynamic Therapy with 5% δ-Aminolevulinic Acid is Safe and Effective Treatment of Acne Vulgaris in Japanese Patients

BACKGROUND AND AIMS

Photodynamic therapy with aminolevulinic acid (ALA-PDT) is effective therapy for acne vulgaris; however, relatively strong side effects limit its wide usage. We have previously demonstrated that ALA-induced protoporphyrin IX distribution with lower concentrations and shorter contact time of ALA resulted in focused damage in sebaceous glands in vivo. We have formulated a protocol for ALA-PDT using 5% ALA with 2 hours contact time. The objective of this study was to establish the effectiveness and side effect profile of the new protocol in humans.

SUBJECTS AND METHODS

Eleven Japanese patients (Fitzpatrick's skin type III - IV, mean age 23.7±7.2) with facial acne received topical application of 5% ALA for 2 hours with subsequent illumination by a broadband light (600 - 1100 nm, 15J/cm(2), 60 mW/cm(2)). Subjects were evaluated prior to the procedure, 1 month, and 3 months after the treatment by a blinded dermatologist using the global acne grading system (GAGS). Side effects were monitored through the treatment period.

RESULTS

The mean GAGS score decreased from 22.1±3.8 at baseline to 19.4 at 1 month, and to 16.3 at 3 months after PDT (P<0.05). Ten of eleven patients experienced local side effects, such as erythema, which were of minimal to mild severity. However, most side effects were of minimal to mild severity, and all of them resolved within several days without post inflammatory hyper pigmentation.

CONCLUSION

Our protocol was effective for acne in Japanese and did not exhibit severe side effects.

Anticancer effect of photodynamic therapy with hexenyl ester of 5-aminolevulinic acid in oral squamous cell carcinoma

BACKGROUND

Five-aminolaevulinic acid (ALA) and its derivatives act as precursors of the photosensitizer protoporphyrin IX (PpIX). In this study, the effect of photodynamic therapy (PDT) with hexenyl ester of ALA (ALA-hx) was examined in a human oral squamous cell carcinoma, YD10B cells.

METHODS

PpIX accumulation and mRNA expression of coproporphyrinogen oxidase (CPO) by ALA and ALA-hx was examined. Cell viability was examined by MTT assay and the molecular mechanism was investigated.

RESULTS

The PpIX synthesis and mRNA expression of CPO was much higher in the cells treated with ALA-hx than ALA. At the concentration that PDT with ALA did not affect cell growth, ALA-hx PDT effectively produced reactive oxygen species (ROS) and suppressed cell growth. Growth inhibition by ALA-hx PDT was due to mitochondrial-dependent apoptosis.

CONCLUSION

Our results suggest that ALA-hx PDT effectively induced apoptosis of YD-10B cells and can be considered as a therapeutic alternative for oral cancer.

Noninvasive fluorescence monitoring of protoporphyrin IX production and clinical outcomes in actinic keratoses following short-contact application of 5-aminolevulinate

Topical 5-aminolevulinic acid (ALA) is widely used in photodynamic therapy (PDT) of actinic keratoses (AK), a type of premalignant skin lesion. However, the optimal time between ALA application and exposure to light has not been carefully investigated. Our objective is to study the kinetics of protoporphyrin IX (PpIX) accumulation in AK after short contact ALA and relate this to erythemal responses. Using a noninvasive dosimeter, PpIX fluorescence measurements (5 replicates) were taken at 20-min intervals for 2 h following ALA application, in 63 AK in 20 patients. Data were analyzed for maximal fluorescent signal obtained, kinetic slope, and changes in erythema. Our results show that PpIX accumulation was linear over time, becoming statistically higher than background in 48% of all lesions by 20 min, 92% of lesions by 1 h, and 100% of lesions by 2 h. PpIX accumulation was roughly correlated with changes in lesional erythema post-PDT. We conclude that significant amounts of PpIX are produced in all AK lesions by 2 h. The linear kinetics of accumulation suggest that shorter ALA application times may be efficacious in many patients. Noninvasive fluorescence monitoring of PpIX may be useful to delineate areas of high PpIX accumulation within precancerous areas of the skin.

Photosensitiser delivery for photodynamic therapy. Part 1: Topical carrier platforms

BACKGROUND

Photodynamic therapy (PDT) is a medical treatment in which a combination of a photosensitising drug and visible light causes destruction of selected cells. Due to the lack of true selectivity of preformed photosensitisers for neoplastic tissue and their high molecular weights, PDT of superficial skin lesions has traditionally been mediated by topical application of the porphyrin precursor 5-aminolevulinic acid (ALA).

OBJECTIVE

This article aims to review the traditional formulation-based approaches taken to topical delivery of ALA and discusses the more innovative strategies investigated for enhancement of PDT mediated by topical application of ALA and preformed photosensitisers.

METHODS

All of the available published print and online literature in this area was reviewed. As drug delivery of agents used in PDT is still something of an emerging field, it was not necessary to go beyond literature from the last 30 years.

RESULTS/CONCLUSION

PDT of neoplastic skin lesions is currently based almost exclusively on topical application of simple semisolid dosage forms containing ALA or its methyl ester. Until expiry of patents on the current market-leading products, there is unlikely to be a great incentive to engage in design and evaluation of innovative formulations for topical PDT, especially those containing the more difficult-to-deliver preformed photosensitisers.

Comparison of ALA- and ALA hexyl-ester-induced PpIX depth distribution in human skin carcinoma

Photodynamic therapy (PDT) based on the use of photoactivable porphyrins, such as protoporphyrin IX (PpIX), induced by the topical application of amino-levulinic acid (ALA) or its derivatives, ALA methyl-ester (m-ALA), is a treatment for superficial basal cell carcinoma (BCC), with complete response rates of over 80%. However, in the case of deep, nodular-ulcerative lesions, the complete response rates are lower, possibly related to a lower bioavailability of PpIX. Previous in vitro skin permeation studies demonstrated an increased penetration of amino-levulinic acid hexyl-ester (h-ALA) over ALA. In this study, we tested the validity of this approach in vivo on human BCCs. An emulsion containing 20% ALA (w/w) and preparations of h-ALA at different concentrations were applied topically to the normal skin of Caucasian volunteers to compare the PpIX fluorescence intensities with an optical fiber-based spectrofluorometer. In addition, the PpIX depth distribution and fluorescence intensity in 26 BCCs were investigated by fluorescence microscopy following topical application of 20% ALA and 1% h-ALA. We found that, for application times up to 24h, h-ALA is identical to ALA as a PpIX precursor with respect to PpIX fluorescence intensity, depth of penetration, and distribution in basal cell carcinoma, but has the added advantage that much smaller h-ALA concentrations can be used (up to a factor 13). We observed a non-homogenous distribution in BCCs with both precursors, independent of the histological type and depth of invasion in the dermis.

Derivatives of 5-Aminolevulinic Acid for Photodynamic Therapy

Photodynamic therapy (PDT) is a clinical treatment that combines the effects of visible light irradiation with subsequent biochemical events that arise from the presence of a photosensitising drug (possessing no dark toxicity) to cause destruction of selected cells. Today, the most common agent used in dermatological PDT is 5-aminolevulinic acid (ALA). As a result of its hydrophilic character, ALA penetrates skin lesions poorly when applied topically. Its systemic bioavailability is limited and it is known to cause significant side effects when given orally or intravenously. Numerous chemical derivatives of ALA have been synthesised with the aims of either improving topical penetration or enhancing systemic bioavailability, while reducing side effects. In vitro cell culture experiments with ALA derivatives have yielded promising results. However, if ALA derivatives are to demonstrate meaningful clinical benefits, a rational approach to topical formulation design is required, along with a systematic study aimed at uncovering the true potential of ALA derivatives in photodynamic therapy. With respect to systemic ALA delivery, more study is required in the developing area of ALA-containing dendrons and dendrimers.

Fluorescence staining of human ovarian cancer tissue following application of 5-aminolevulinic acid: fluorescence microscopy studies

BACKGROUND AND OBJECTIVES

Application of 5-aminolevulinic acid (ALA) for fluorescence-guided second-look laparoscopy has been shown to be a promising new procedure in the early diagnosis of ovarian carcinoma metastases. However, for assessing the reliability of this method, information on the microscopic distribution of protoporphyrin IX (PP IX) in the tissue is needed. Additionally, the selectivity of PP IX uptake is essential for a potential photodynamic therapy (PDT) of ovarian cancer metastases.

STUDY DESIGN/MATERIALS AND METHODS

Thirty-six patients with epithelial ovarian cancer and two patients suffering from fallopian tube carcinoma underwent a laparoscopic second-look procedure 5 hours after the application of ALA. In 17 patients 36 fluorescence-guided biopsies were taken from fluorescing and non-fluorescing tissues for further evaluation. Fluorescence microscopy and digital image processing were utilized to determine the presence of PP IX fluorescence.

RESULTS

A specificity of 88% and a sensitivity of 100% with a negative predictive value of 100% and a positive predictive value of 91% were calculated for PP IX fluorescence on a microscopic level as marker for ovarian cancer metastases.

CONCLUSIONS

On a microscopic scale, ALA-induced PP IX fluorescence is confined to ovarian cancer tumor tissue sparing stromal tissues.

Topical application of 5-aminolaevulinic acid, methyl 5-aminolaevulinate and hexyl 5-aminolaevulinate on normal human skin

BACKGROUND

5-Aminolaevulinic acid (ALA) and its ester derivatives are used in photodynamic therapy. Despite extensive investigations, the differences in biodistribution and pharmacokinetics of protoporphyrin IX (PpIX) induced by ALA and its derivatives are still not well understood, notably for humans.

OBJECTIVES

To study porphyrin accumulation after topical application of ALA and two of its ester derivatives in normal human skin.

METHODS

Creams containing 0.2%, 2% and 20% (w/w) of ALA, methyl 5-aminolaevulinate (MAL) and hexyl 5-aminolaevulinate (HAL) were applied on normal human skin of six volunteers. The amount and distribution of porphyrins formed in the skin was investigated noninvasively by means of fluorescence spectroscopy.

RESULTS

Fluorescence emission and excitation spectra exhibited similar spectral shapes for the all drugs, indicating that mainly PpIX was formed. Low concentrations (0.2% and 2%) of MAL induced considerably less PpIX in normal human skin than similar concentrations of ALA and HAL. A high concentration (20%) of ALA gave higher PpIX fluorescence in normal human skin than was found for MAL and HAL.

CONCLUSIONS

The concentrations inducing half of the maximal PpIX fluorescence are around 2% for ALA, 8% for MAL and 1% for HAL.

Topical Iontophoresis of Valaciclovir Hydrochloride Improves Cutaneous Aciclovir Delivery

PURPOSE

To investigate the topical iontophoresis of valaciclovir (VCV) as a means to improve cutaneous aciclovir (ACV) delivery.

METHODS

ACV and VCV electrotransport experiments were conducted using excised porcine skin in vitro.

RESULTS

While the charged nature of the prodrug, VCV, enabled it to be more efficiently iontophoresed into the skin than the parent molecule, ACV, only the latter was detectable in the receptor chamber, suggesting that VCV was enzymatically cleaved into the active metabolite during skin transit. Iontophoresis of VCV was significantly more efficient than that of ACV; the cumulative permeation of ACV after 1, 2 and 3 h of VCV iontophoresis at 0.5 mA cm(-2) and using an aqueous 2 mM (approximately 0.06%) formulation was 20+/-10, 104+/-47 and 194+/- 82 microg cm( -2), respectively (cf. non-quantifiable levels, 0.1 and 1.0+/-0.7 microg cm(-2) after ACV iontophoresis).

CONCLUSIONS

These delivery rates provide ample room to reduce either current density or the duration of current application. Preliminary in vitro data serve to emphasize the potential of VCV iontophoresis to improve the topical therapy of cutaneous herpes simplex infections and merit further investigation to demonstrate clinical efficacy.

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

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

On the Role of Iron and one of its Chelating Agents in the Production of Protoporphyrin IX Generated by 5-Aminolevulinic Acid and its Hexyl Ester Derivative Tested on an Epidermal Equivalent of Human Skin

Photodynamic therapy (PDT) with 5-aminolevulinic acid (ALA) or its derivatives as precursors of protoporphyrin IX (PPIX) is routinely used in dermatology for the treatment of various pathologies. However, this methodology suffers to some extent from a limited efficacy. Therefore, the main goal of this study was to investigate the modulation and pharmacokinetics of PPIX buildup after a 5 h incubation with ALA (1.5 mM) and one of its derivatives, the hexyl ester of ALA (h-ALA) (1.5 mM), on the human epidermal equivalent Epidex. PPIX production was modulated with (L+) ascorbic acid iron (II) salt (LAI) or the iron (II)-specific chelating agent deferoxamine (DFO). PPIX fluorescence from the Epidex layers was measured up to 150 h after the precursor administration using a microspectrofluorometer (lambda(ex): 400 +/- 20 nm; lambda(det): 635 nm). The maximum PPIX fluorescence intensity induced by h-ALA was about 1.7 x larger than that induced by ALA. The addition of DFO resulted in a more than 50% increase in PPIX fluorescence for both precursors. The decay half life measured for PPIX fluorescence is 30 and 42.5 h, respectively, for ALA and h-ALA. These half lives are doubled when the samples contain DFO. In the samples with the highest fluorescence intensity, a modified fluorescence spectrum was observed after 10 h, with the emergence of a peak at 590 nm, which is attributed to zinc protoporphyrin IX (Zn PPIX).

Enhanced porphyrin accumulation using dendritic derivatives of 5-aminolaevulinic acid for photodynamic therapy: An in vitro study

Intracellular porphyrin generation following administration of 5-aminolaevulinic acid has been widely used in photodynamic therapy for a range of malignant and certain non-malignant lesions. However, cellular uptake of 5-aminolaevulinic acid is limited by its hydrophilic nature and improved means of delivery are therefore being sought. Highly branched polymeric drug carriers known as dendrimers are a promising new approach to drug delivery. The aim of this study was to investigate the efficacy of dendrimers conjugated with 5-aminolaevulinic acid for porphyrin production in the transformed PAM 212 keratinocyte cell line and skin explants. Each dendritic derivative incorporated three 5-aminolaevulinic acid residues which were conjugated as esters via methyl or propyl linkers to a central tertiary carbon whose remaining terminal bore an amino, aminobenzyloxycarbonyl or nitro group. In the cell line, all compounds were more efficient at low concentrations compared to equimolar 5-aminolaevulinic acid for porphyrin production, with the most efficient incorporating the longer propyl linker. This compound was also the most lipophilic according to partition coefficient measurements. The intracellular porphyrin fluorescence levels showed good correlation with cellular phototoxicity following light exposure for all the compounds, together with minimal dark toxicity. Our findings indicate that the key factors influencing the efficacy of the dendritic derivatives are lipophilicity and steric hindrance within the dendritic structure which could restrict access to intracellular esterases for liberation of 5-aminolaevulinic acid. These findings should be taken into account in the design of larger dendrimers of 5-aminolaevulinic acid.

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.

Comparative in vitro percutaneous penetration of 5-aminolevulinic acid and two of its esters through excised hairless mouse skin

BACKGROUND AND OBJECTIVES

ALA esters have been developed to improve PpIX production in ALA-PDT, but they do not perform as well in skin as they do in cells and the bladder.

STUDY DESIGN/MATERIALS AND METHODS

The in vitro penetration across normal mouse skin of ALA and its methyl and hexyl ester was determined for different application concentrations. ALA and the esters were also applied to tape stripped skin to determine the effect of the stratum corneum.

RESULTS

The penetration of ALA and the esters was higher through tape stripped skin than through normal skin (P < 0.01), showing that the stratum corneum is an important barrier. The experiments with different application concentrations indicated that the skin penetration through normal skin and tape stripped skin is highest for ALA and lowest for the hexyl ester.

CONCLUSIONS

The differences in skin penetration properties could be (co-)responsible for the finding that ALA esters do not induce substantially higher PpIX levels in in vivo skin.

Photodynamic Therapy of oral dysplasia with topical 5-aminolevulinic acid and light-emitting diode array

BACKGROUND AND OBJECTIVES

In Taiwan, more than two million people have the betel quid (BQ) chewing habit which is a risk factor related to premalignant lesion and squamous cell carcinoma of oral cavity. We developed a light-emitting diode (LED) array combined with topical 5-aminolevulinic acid (ALA) for photodynamic therapy (PDT) and evaluated its effectiveness for the treatment of oral lesions.

STUDY DESIGN/MATERIALS AND METHODS

We compared the ALA-PDT effect of the homemade LED array to that of a commercial light source on cultured Ca9-22 human gingival carcinoma cells and the DMBA-induced hamster buccal pouch carcinoma model. Furthermore, we treated several patients having an oral lesion using a topical ALA delivery system and the LED array.

RESULTS

The LED array light source was as effective as the commercial light source for ALA-PDT in cultured Ca9-22 cells with LD(50) of 4.5 and 4.3 J/cm(2), respectively, using an MTT assay. This light source was also effective in the DMBA-induced hamster buccal pouch carcinoma model, and in the patients of oral leukoplakia.

CONCLUSIONS

ALA-PDT is effective for premalignant lesions such as mucosal dysplasia and carcinoma in situ of oral cavity. Good results could be obtained by using the homemade LED array as light source. The LED array has the advantages of low cost, high reliability, and portability. It is safe, convenient and easy to use for the treatment of oral dysplasia.

Enhanced delivery of 5-aminolevulinic acid esters by iontophoresis in vitro

The goals of this study were to quantitatively evaluate the iontophoretic delivery of a homologous series of cationic aminolevulinic acid (ALA) esters and to determine the contributions of electromigration and electroosmosis to their overall electrotransport in vitro. Anodal iontophoretic transport of ALA esters through porcine skin in vitro was followed for 2 h at a constant current of 0.5 mA/cm2. To deduce the mechanism, the concomitant transport of an electroosmotic marker, mannitol, was also assessed. Positively charged ALA esters of moderate lipophilicity showed increased iontophoretic flux through the skin. A more than 50-fold enhancement as compared with the zwitterionic parent ALA was observed for the methyl ester. As the size and lipophilicity of the ester increased, the efficiency of electrotransport decreased. The most lipophilic esters reduced the electroosmotic flow presumably because of the association of these cations with negative charges in the skin. Iontophoresis of methyl-ALA and hexyl-ALA also increased the amount of prodrug delivered into the skin. In summary, significant topical delivery of ALA esters can be achieved by iontophoresis, and transport into and across the skin was greatly enhanced compared with that of ALA itself. It remains to be seen whether this enhanced local bioavailability of the protoporphyrin prodrug can allow improved photodynamic therapy for the treatment of skin cancer.

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.

Pharmacology of protoporphyrin IX in nude mice after application of ALA and ALA esters

Aminolevulinic acid (ALA), ALA methylester (ALA-Me) and ALA hexylester (ALA-Hex) were topically applied for 5 and 20 hr, respectively, on normal skin of mice. The distribution of protoporphyrin IX (PpIX) induced in 7 different tissues by these drugs was determined either by spectrofluorometric measurements with an optical fibre probe or by chemical extraction of PpIX from the tissues. The results from these 2 types of measurements were compared. Both methods showed that ALA and the esters induced similar amounts of PpIX at the skin spot where they were applied and that the esters produced much less PpIX at remote skin spots (i.e., spots outside the location where the drugs were applied) than ALA did, notably after 20 hr application. After 20 hr of drug application ALA produced much more PpIX in liver, intestine and lungs than the esters did. In contrast with the direct fluorescence measurements, the extraction method showed detectable amounts of PpIX in liver, intestine and lung after application of the esters, notably of ALA-Me. The discrepancy is probably related to the fact that the pigmented tissues absorb light and, therefore, the direct fluorescence readings are misleading. Notably in the liver, which contains high concentration of light-absorbing pigments, very weak direct fluorescence was seen. In no case there was any accumulation of PpIX in muscle tissue nor in brain. The esters seem to penetrate less into the circulation than ALA, and PpIX formed by them in the skin is faster cleared than PpIX formed from ALA. This is also true after oral and i.p. administration of the drugs.

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

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

Noninvasive fluorescence excitation spectroscopy during application of 5-aminolevulinic acid in vivo

The fluorescence of PpIX induced by topical application of 5-aminolevulinic acid (ALA) in normal mouse skin was studied noninvasively by means of a fibre optic probe. The fluorescence excitation spectrum of PpIX exhibits five distinct peaks at around 408. 510, 543, 583 and 633 nm under fluorescence monitoring at the second emission peak of PpIX (705 nm). The transmission of the excitation light is wavelength dependent: the long wavelength light (>600 nm) penetrates deeper into the tissues by a factor of 6 compared with the short wavelength light (<590 nm). Thus, the fluorescence excitation spectrum of PpIX measured on the surface of the skin can be used to estimate the depth of the penetration of topically applied ALA. The fluorescence excitation spectra calculated for the depth 1.1 mm obtained the best fit with the experimentally measured spectra after topical application of ALA.

Topical application of 5-aminolevulinic acid and its methylester, hexylester and octylester derivatives: considerations for dosimetry in mouse skin model

Ester derivatives of 5-aminolevulinic acid (ALA-esters) have been proposed as alternative drugs for ALA in photodynamic therapy. After topical application of creams containing ALA, ALA methylester (ALA-Me), ALA hexylester (ALA-Hex) and ALA octylester (ALA-Oct) on mouse skin, typical fluorescence excitation and emission spectra of protoporphyrin IX (PpIX) were recorded, exhibiting a similar spectral shape for all the drugs in the range of concentrations (0.5-20%) studied. The accumulation kinetics of PpIX followed nearly a similar profile for all the drug formulations. The fluorescence of PpIX peaked at around 6-12 h of continuous cream application. Nevertheless, some differences in pharmacokinetics were noticed. For ALA cream, the highest PpIX fluorescence was achieved using 20% of ALA in an ointment. Conversely, 10% of ALA-Me and ALA-Hex, but not of ALA-Oct, in the cream was more efficient (P < 0.05) than was 20%. The cream becomes rather fluid when 20% of any of these ALA-esters is used in ointment, whereas 10% and lower concentrations of ALA-esters do not significantly increase fluidity of the cream. The dependence of PpIX accumulation on the concentration of ALA and ALA-ester in the applied cream followed (P < 0.002) kinetics as described by a mathematical model based on the Michaelis-Menten equation for enzymatic processes. Under the present conditions, the PpIX amount in the skin increased by around 50% by the application of ALA-Me, ALA-Hex or ALA-Oct for 4-12 h as compared with ALA for the same period. Observations of the mice under exposure to blue light showed that after 8-24 h of continuous application of ALA, the whole mouse was fluorescent, whereas in the case of ALA-Me, ALA-Hex and ALA-Oct the fluorescence of PpIX was located only at the area of initial cream application. The amount of the active compound in the applied cream necessary to induce 90% of the maximal amount of PpIX was determined for normal mouse skin. Optimal PpIX fluorescence can be attained using around 5% ALA, 10% ALA-Me and 5% ALA-Hex creams during short application times (2-4 h). Topical application of ALA-Oct may not gain optimal PpIX accumulation for short applications (<5 h). For long application times (8-12 h), it seems that around 1% ALA, 4% ALA-Me, 6% ALA-Hex and 16% ALA-Oct can give optimal PpIX fluorescence. But for long application times and high concentrations, systemic effect of ALA applied topically on relatively large areas should be considered.

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.

Protoporphyrin IX fluorescence kinetics in UV-induced tumours and normal skin of hairless mice after topical application of 5-aminolevulinic acid methyl ester

Accumulation of protoporphyrin IX (PpIX) was investigated in normal skin and UV-induced tumours in hairless mice after topical application of a cream containing 2, 8 or 16% of 5-aminolevulinic acid methyl ester (ALA-Me). Higher levels of PpIX were measured in tumours compared to normal skin. The maximal amount of PpIX was reached at 1.5, 3 and 4 h after 2, 8 and 16% ALA-Me application, respectively. Higher tumour to normal skin PpIX fluorescence ratios were measured after application of 8 and 16% ALA-Me than after application of 2%. After irradiation with a broad spectrum of visible light from a slide projector, more than 90% of PpIX was bleached by fluences of 36 and 48 J/cm2, at fluence rates of 10 and 40 mW/cm2 respectively. At these fluences, the PpIX photobleaching rate was significantly higher (P<0.05) in normal mouse skin than in tumours. In addition, for a given fluence, more PpIX was photobleached at the lower fluence rate (10 mW/cm2) than at the higher fluence rate (40 mW/cm2) in normal skin (P<0.001) as well as in tumours (P<0.05) after exposure to 24 J/cm2 of light. In conclusion, the highest tumour to normal skin PpIX ratio was observed 3 h after application of 8% ALA-Me, suggesting that light exposure should be performed at this time in order to achieve an optimal PDT effect in this tumour model.

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

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

Quantification of topically delivered 5-aminolevulinic acid by lontophoresis across ex vivo human stratum corneum

Iontophoretic transport of the prodrug 5-aminolevulinic acid (ALA), which is used for photodynamic therapy (PDT), across human stratum corneum (SC) was studied quantitatively in vitro. The experiments were carried out in a three-compartment iontophoresis cell consisting of two electrode chambers equipped with Ag-AgCl electrodes, each separated from a central acceptor chamber by a sheet of SC, supported by a dialysis membrane, to mimic the side-by-side configuration normally used in vivo. Acceptor fluid samples were collected every hour for a period of 30 h in a fraction collector and analyzed by high-performance liquid chromatography-fluorometry after derivatization of the ALA. The iontophoretic ALA flux was studied as a function of the applied current density and the ALA concentration in the donor solution (1, 2.5 or 10% ALA). Depending on the ALA concentration in the donor cell, iontophoresis enhances the flux from close to the detection limit of 0.23 nmol cm(-2) h(-1) at zero current density (passive diffusion) to several hundred or thousand nanomoles per square centimeter per hour at current densities ranging from 100 to 1000 microA cm(-2). For example, interpolating our data we find that with an ALA concentration of 2% in the donor chamber, a current density of 0.255 mA cm(-2) transports 0.065 micromol cm(-2) ALA across the SC in 10 min (conditions of Rhodes et al. (1997), J. Invest. Dermatol. 108, 87-91). For passive diffusion we find that a 5 h topical application of 20% ALA results in the transport of 0.05 micromol cm(-2). Thus, the amount of ALA that passively diffuses through the SC in several hours, leading to therapeutic levels of protoporphyrin IX (PpIX) in the epidermis, can be delivered by iontophoresis in 10 min or less. However, because the formation of sufficient PpIX also requires several hours and also because the SC overlying skin lesions such as basal cell carcinoma (BCC) is not intact, the clinical benefit of topical ALA delivery by iontophoresis for PDT of BCC is yet to be established.

Photodynamic effects induced by aminolevulinic acid esters on human cervical carcinoma cells in culture

Fluorescence diagnosis and photodynamic therapy using 5-aminolevulinic acid (ALA) provide new methods for the detection and treatment of cervical cancer and especially its precursors. However, these techniques are restricted by the rate of uptake of the hydrophilic ALA, its poor diffusion through the bilayer of biological membranes or both. In this study we evaluated the effect of some esterified ALA derivatives on the induction of the endogenous photosensitizer, protoporphyrin IX (PpIX), and the photodamage in cultured human cervical cells (C33-A and CaSki). The kinetics of PpIX accumulation showed that ALA esters, especially the ALA-hexylester (h-ALA), induced significantly faster PpIX formation than ALA at the same concentration (0.5 mM). The PpIX induction showed a dose-dependent characteristic. The highest PpIX values could be achieved by an up to 1.3-13-fold lower concentration of ALA esters than with ALA. Using the Annexin V assay, apoptosis was found to be induced rapidly after irradiation in both ALA- and ALA esters-treated cells. On measuring mitochondrial activity, the incubation with h-ALA induced a more pronounced photodamage. The results indicate that improved or at least comparable photodynamic effects can be achieved by using remarkably lower doses of ALA esters.

Selective distribution of porphyrins in skin thick basal cell carcinoma after topical application of methyl 5-aminolevulinate

Topical photodynamic therapy (PDT) of superficial basal cell carcinoma (BCC) with 5-aminolevulinic acid (ALA) has achieved promising clinical results. However, the efficacy of this therapy for thick BCC is dramatically decreased by a limited diffusion of hydrophilic ALA into the tumor. Lipophilic esters of ALA may enhance their penetration into the lesion. In this randomized, open clinical study, microscopic fluorescence photometry incorporating a light-sensitive thermo-electrically cooled charge-coupled device (CCD) camera was employed to investigate the penetration of methyl 5-aminolevulinate-induced porphyrin fluorescence in thick BCC lesions. Both the distribution pattern and the amount of porphyrins in 32 lesions of 16 patients were studied after topical application of 16, 80 or 160 mg/g of methyl 5-aminolevulinate for 3 or 18 h. A highly selective and homogeneous distribution of methyl 5-aminolevulinate-induced porphyrin fluorescence was seen in all lesions studied, with much less fluorescence in the adjacent normal skin tissues. In lesions of up to 2 mm thickness the application of 160 mg/g methyl 5-aminolevulinate for 3 h showed the highest ratio of porphyrin fluorescence depth to tumor depth (0.98+/-0.04), thus providing a biologic rationale for a clinical PDT trial with this regimen.