Aminolevulinic acid: pharmacological profile and clinical indication

Trends and targets in antiviral phototherapy

Photodynamic therapy (PDT) is a well-established treatment option in the treatment of certain cancerous and pre-cancerous lesions. Though best-known for its application in tumor therapy, historically the photodynamic effect was first demonstrated against bacteria at the beginning of the 20^th century. Today, in light of spreading antibiotic resistance and the rise of new infections, this photodynamic inactivation (PDI) of microbes, such as bacteria, fungi, and viruses, is gaining considerable attention. This review focuses on the PDI of viruses as an alternative treatment in antiviral therapy, but also as a means of viral decontamination, covering mainly the literature of the last decade. The PDI of viruses shares the general action mechanism of photodynamic applications: the irradiation of a dye with light and the subsequent generation of reactive oxygen species (ROS) which are the effective phototoxic agents damaging virus targets by reacting with viral nucleic acids, lipids and proteins. Interestingly, a light-independent antiviral activity has also been found for some of these dyes. This review covers the compound classes employed in the PDI of viruses and their various areas of use. In the medical area, currently two fields stand out in which the PDI of viruses has found broader application: the purification of blood products and the treatment of human papilloma virus manifestations. However, the PDI of viruses has also found interest in such diverse areas as water and surface decontamination, and biosafety.

Investigational drugs currently in phase II clinical trials for actinic keratosis

INTRODUCTION

Actinic keratoses (AKs) are limited areas of irregular epidermal growth on a background of excessive solar exposure. The entire sun-damaged skin is considered a field of cancerization with multiple visible and subclinical lesions. AK management requires field-directed therapies to block lesion relapse and prevent squamous cell carcinoma (SCC).

AREAS COVERED

In this review, we focused on phase II clinical trials for AKs, involving well-known agents and newer molecules such as proapoptotic drugs (VDA-1102, SR-T100, oleogel-S10, ICVT, eflornithine), immunomodulants (isotretinoin, tretinoin) and chemopreventive agents (nicotinamide, perillyl alcohol, liposomal T4N5). We used the website 'ClinicalTrials.Gov' as main reference. We selected and discussed completed and ongoing trials and analysed chemical structure and mechanism of action of the investigated molecules.

EXPERT OPINION

AK therapy should be tailored on the patient's profile considering first of all the age and site of the AKs, which are relevant parameters for local immune response. The new molecules could be combined to obtain a synergic effect blocking the different steps of skin tumorigenesis. Phase II trials highlight a new therapeutic opportunity to block selectively cell proliferation regulators and work both on the field of cancerization and on the AKs currently present.

High-level soluble expression of the hemA gene from Rhodobacter capsulatus and comparative study of its enzymatic properties

The Rhodobacter capsulatus hemA gene, which encodes 5-aminolevulinic acid synthase (ALAS), was expressed in Escherichia coli Rosetta (DE3) and the enzymatic properties of the purified recombinant ALAS (RC-ALAS) were studied. Compared with ALASs encoded by hemA genes from Agrobacterium radiobacter (AR-ALAS) and Rhodobacter sphaeroides (RS-ALAS), the specific activity of RC-ALAS reached 198.2 U/mg, which was about 31.2% and 69.5% higher than those of AR-ALAS (151.1 U/mg) and RS-ALAS (116.9 U/mg), respectively. The optimum pH values and temperatures of the three above mentioned enzymes were all pH 7.5 and 37 °C, respectively. Moreover, RC-ALAS was more sensitive to pH, while the other two were sensitive to temperature. The effects of metals, ethylene diamine tetraacetic acid (EDTA), and sodium dodecyl sulfate (SDS) on the three ALASs were also investigated. The results indicate that they had the same effects on the activities of the three ALASs. SDS and metal ions such as Co(2+), Zn(2+), and Cu(2+) strongly inhibited the activities of the ALASs, while Mn(2+) exerted slight inhibition, and K(+), Ca(2+), Ba(2+), Mg(2+), or EDTA had no significant effect. The specificity constant of succinyl coenzyme A [(kcat/Km)(S-CoA)] of RC-ALAS was 1.4989, which was higher than those of AR-ALAS (0.7456) and RS-ALAS (1.1699), showing its high catalytic efficiency. The fed-batch fermentation was conducted using the recombinant strain containing the R. capsulatus hemA gene, and the yield of 5-aminolevulinic acid (ALA) achieved was 8.8 g/L (67 mmol/L) under the appropriate conditions.

Apoptosis mechanisms related to the increased sensitivity of Jurkat T-cells vs A431 epidermoid cells to photodynamic therapy with the phthalocyanine Pc 4

To examine the clinical applicability of Pc 4, a promising second-generation photosensitizer, for the photodynamic treatment of lymphocyte-mediated skin diseases, we studied the A431 and Jurkat cell lines, commonly used as surrogates for human keratinocyte-derived carcinomas and lymphocytes, respectively. As revealed by ethyl acetate extraction and absorption spectrophotometry, uptake of Pc 4 into the two cell lines was linear with Pc 4 concentration and similar on a per cell basis but greater in Jurkat cells on a per mass basis. Flow cytometry showed that uptake was linear at low doses; variations in the dose-response for uptake measured by fluorescence supported differential aggregation of Pc 4 in the two cell types. As detected by confocal microscopy, Pc 4 localized to mitochondria and endoplasmic reticulum in both cell lines. Jurkat cells were much more sensitive to the lethal effects of phthalocyanine photodynamic therapy (Pc 4-PDT) than were A431 cells, as measured by a tetrazolium dye reduction assay, and more readily underwent morphological apoptosis. In a search for molecular factors to explain the greater photosensitivity of Jurkat cells, the fate of important Bcl-2 family members was monitored. Jurkat cells were more sensitive to the induction of immediate photodamage to Bcl-2, but the difference was insufficient to account fully for their greater sensitivity. The antiapoptotic protein Mcl-1 was extensively cleaved in a dose- and caspase-dependent manner in Jurkat, but not in A431, cells exposed to Pc 4-PDT. Thus, the greater killing by Pc 4-PDT in Jurkat compared with A431 cells correlated with greater Bcl-2 photodamage and more strongly to the more extensive Mcl-1 degradation. Pc 4-PDT may offer therapeutic advantages in targeting inflammatory cells over normal keratinocytes in the treatment of T-cell-mediated skin diseases, such as cutaneous lymphomas, dermatitis, lichenoid tissue reactions and psoriasis, and it will be instructive to evaluate the role of Bcl-2 family proteins, especially Mcl-1, in the therapeutic response.

The dual face of endogenous alpha-aminoketones: pro-oxidizing metabolic weapons

Amino metabolites with potential prooxidant properties, particularly alpha-aminocarbonyls, are the focus of this review. Among them we emphasize 5-aminolevulinic acid (a heme precursor formed from succinyl-CoA and glycine), aminoacetone (a threonine and glycine metabolite), and hexosamines and hexosimines, formed by Schiff condensation of hexoses with basic amino acid residues of proteins. All these metabolites were shown, in vitro, to undergo enolization and subsequent aerobic oxidation, yielding oxyradicals and highly cyto- and genotoxic alpha-oxoaldehydes. Their metabolic roles in health and disease are examined here and compared in humans and experimental animals, including rats, quail, and octopus. In the past two decades, we have concentrated on two endogenous alpha-aminoketones: (i) 5-aminolevulinic acid (ALA), accumulated in acquired (e.g., lead poisoning) and inborn (e.g., intermittent acute porphyria) porphyric disorders, and (ii) aminoacetone (AA), putatively overproduced in diabetes mellitus and cri-du-chat syndrome. ALA and AA have been implicated as contributing sources of oxyradicals and oxidative stress in these diseases. The end product of ALA oxidation, 4,5-dioxovaleric acid (DOVA), is able to alkylate DNA guanine moieties, promote protein cross-linking, and damage GABAergic receptors of rat brain synaptosome preparations. In turn, methylglyoxal (MG), the end product of AA oxidation, is also highly cytotoxic and able to release iron from ferritin and copper from ceruloplasmin, and to aggregate proteins. This review covers chemical and biochemical aspects of these alpha-aminoketones and their putative roles in the oxidative stress associated with porphyrias, tyrosinosis, diabetes, and cri-du-chat. In addition, we comment briefly on a side prooxidant behaviour of hexosamines, that are known to constitute building blocks of several glycoproteins and to be involved in Schiff base-mediated enzymatic reactions.

Vitamin D Enhances ALA-Induced Protoporphyrin IX Production and Photodynamic Cell Death in 3-D Organotypic Cultures of Keratinocytes

Photodynamic therapy (PDT) with 5-aminolevulinic acid (ALA) is based upon the intracellular synthesis of protoporphyrin IX (PpIX), which absorbs light and targets metabolically active cells. We tested the hypothesis that levels of PpIX within keratinocytes might be increased by vitamin D (Vit D), a differentiation-promoting hormone. Vit D promoted terminal differentiation in monolayer cultures of rat epidermal keratinocytes (REKs), but high PpIX signals were found only in stratifying islands. To simulate a normal epidermis, REKs were grown in organotypic cultures. The presence of Vit D (10(-10) M for 4 days) led to heightened expression of terminal differentiation markers (stratum corneum, K10, and loricrin). PpIX levels, at 4 hours after addition of ALA (1 mM), were significantly increased in the Vit D-preconditioned cultures by confocal fluorescence microscopy and semiquantitative image analysis. Maximal PpIX induction was seen at (Vit D) 10(-12)-10(-10) M. Phototoxic cell killing after exposure to 635 nm light was significantly higher in Vit D-preconditioned cultures. No differences in apoptotic markers between Vit D and control cultures were seen, suggesting that Vit D augments photodynamic cell death via alternative pathways (e.g., necrosis). In summary, Vit D may be useful as a biological enhancer of ALA-based PDT.

Photodynamic ultradeformable liposomes: Design and characterization

Hydrophobic ([tetrakis(2,4-dimetil-3-pentyloxi)-phthalocyaninate]zinc(II)) (ZnPc) and hydrophilic ([tetrakis(N,N,N-trimethylammoniumetoxi)-phthalocyaninate]zinc(II) tetraiodide) (ZnPcMet) phthalocyanines were synthesized and loaded in ultradeformable liposomes (UDL) of soybean phosphatidylcholine and sodium cholate (6:1, w/w, ratio), resulting 100 nm mean size vesicles of negative Zeta potential, with encapsulation efficiencies of 85 and 53%, enthalpy of phase transition of 5.33 and 158 J/mmol for ZnPc and ZnPcMet, respectively, indicating their deep and moderate partition into UD matrices. Matrix elasticity of UDL-phthalocyanines resulted 28-fold greater than that of non-UDL, leaking only 25% of its inner aqueous content after passage through a nanoporous barrier versus 100% leakage for non-UDL. UDL-ZnPc made ZnPc soluble in aqueous buffer while kept the monomeric state, rendering singlet oxygen quantum yield (Phi(Delta)) similar to that obtained in ethanol (0.61), whereas UDL-ZnPcMet had a four-fold higher Phi(Delta) than that of free ZnPcMet (0.21). Free phthalocyanines were non-toxic at 1 and 10 microM, both in dark or upon irradiation at 15 J/cm2 on Vero and J-774 cells (MTT assay). Only liposomal ZnPc at 10 microM was toxic for J-774 cells under both conditions. Additionally, endo-lysosomal confinement of the HPTS dye was kept after irradiation at 15 J/cm2 in the presence of UDL-phtalocyanines. This could lead to improve effects of singlet oxygen against intra-vesicular pathogen targets inside the endo-lysosomal system.

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.

Clinical and immunohistochemical evaluation of psoriatic plaques treated with topical 5-aminolaevulinic acid photodynamic therapy

BACKGROUND/PURPOSE

The aims of this study were to investigate the clinical and immunohistochemical events of psoriatic plaques during photodynamic therapy (PDT) using topical application of 5-aminolaevulinic acid (ALA).

METHODS

Twelve psoriatic patients were recruited for this study. Four of them dropped out because of pain during treatment. The effect of PDT was evaluated in the remaining eight. One plaque was selected in each patient and treated once weekly with PDT 10-30 J/cm(2) two to five times. It was evaluated by using the scale, erythema and induration (SEI) index (maximal score per patient=9). Pain during treatment was assessed by a visual analogue scale (VAS), ranging from 0 to 10. Skin biopsies were taken before treatment, after two treatments and after completion of treatment, and were evaluated by immunohistochemistry.

RESULTS

Median SEI scores were significantly reduced from 7 (range 5-9) before to 1.5 (range 0-3) following treatment (P<0.0001). The median pain during PDT was 7. The number of vessels in the subpapillary dermis, identified by antibodies against Factor VIII and endoglin, increased during and/or after treatment in six of eight patients. Before treatment, the epidermal growth factor (EGF) receptor was displayed throughout the epidermis, keratin 16 suprabasally, involucrin from the stratum granulosum to the lower spinous layers and filaggrin in stratum granulosum with focal absence. There was a moderate dermal infiltrate of CD4(+) cells and a sparse one of CD8(+). Following treatment, the EGF receptor was still displayed throughout the epidermis in seven of eight specimens. Cytokeratin 16 expression decreased markedly. Involucrin was not seen as deep in the spinous layers as before PDT. Filaggrin was expressed throughout the stratum granulosum and often weakly in the upper stratum spinosum. The number of CD4(+) and CD8(+) dermal cells decreased.

CONCLUSION

PDT improved psoriasis and induced dermal neovascularization. Although a good clinical response was seen in most of our patients, the high frequency of discomfort during treatment limits the usefulness of ALA-PDT for psoriasis. The mechanism of the neovascularization is unknown. It may be owing to an indirect effect of PDT on the microvasculature and immune system or recovery phenomena.

Emerging drugs in psoriasis

Psoriasis is a relatively common, chronic skin disease affecting 1-2% of the population in the developed countries. It is an inflammatory, autoimmune skin disorder characterised by an accelerated rate of epidermal proliferation and disordered differentiation. Since our last review in 1999, considerable progress has been made in understanding the immunopathogenesis of this disease, and new drugs have become available for its treatment. Recent clinical trials showed the efficacy of novel biotechnology approaches, such as blocking tumour necrosis factor-alpha or T-cell-mediated immune response by the anti-CD2, anti-CD11a, anti-B7, anti-CD4 or anti-CD25 approaches. Agents which block type 1 cytokines or skew immune reactions into type 2 are other promising approaches. Other possible targets are chemokines and their receptors, the cytokines and receptors involved in T cell trafficking into the skin, and peroxisome proliferator-activated receptors. Relatively little development is reported of the drugs targeting the keratinocyte or the classical antipsoriatic compounds which include glucocorticoids, vitamin D derivatives and cytostatic agents.

Aminolevulinic acid: from its unique biological function to its star role in photodynamic therapy

Porphyrins are molecules essential for life. They are involved in the key processes of photosynthesis and respiration. The biosynthesis of tetrapyrroles in all living cells occurs through several steps where the formation of aminolevulinic acid (ALA) is the first committed intermediate. Two alternative routes for the formation of ALA have been proposed: one involves the condensation of Succinyl CoA and glycine catalyzed by ALA synthetase taking place in the mitochondria, and the second one is the so called 5-carbon route, occurring in the stroma of plastids. Eight molecules of ALA are used in the formation of protoporphyrin IX. Specific deficiencies in one of the enzymes of the heme pathway produce the porphyrias. In the acute porphyrias, the pathogenesis of the neurological dysfunction is attributed to the accumulation of ALA. Fluorescent and photosensitizing properties of protoporphyrin accumulated after the exogenous administration of ALA, can be used to visualize and destroy malignant cells in the so-called photodynamic diagnosis (PDD) and photodynamic therapy (PDT) of cancer. Many clinical ALA-PDT applications to malignant and non-malignant pathologies are currently in use. Different approaches to enhance ALA penetration in cells are under investigation, including the use of more lipophilic ALA derivatives and studies of the transport mechanisms of ALA. ALA has also been proposed to be used as a biodegradable herbicide, as an insecticide and as a plant growth regulator.

Photodynamic therapy systems and applications

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

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Treatment of cutaneous leishmaniasis by photodynamic therapy

BACKGROUND

Cutaneous leishmaniasis represents a common health problem and standard treatments are often ineffective or yield poor cosmetic results.

OBJECTIVE

We compared the efficacy of photodynamic therapy (PDT) with paromomycin sulfate in 10 lesions of cutaneous leishmaniasis.

METHODS

Five lesions were treated by PDT with Metvix (Photocure, Oslo, Norway) and 75 J/cm(2) red light. PDT was performed twice weekly and, after 12 weeks, once weekly. The other 5 lesions were treated with paromomycin sulfate once daily. All nonresponding lesions of the paromomycin-treated plaques finally also underwent PDT.

RESULTS

All 5 lesions treated by PDT and 2 of the paromomycin sulfate-treated plaques were clinically and histologically Leishmania free. Three lesions with poor response to paromomycin sulfate finally responded to subsequent PDT. Ten months after therapy there was no recurrence, and cosmetic outcome after PDT was excellent.

CONCLUSION

PDT may be an effective therapeutic alternative in cutaneous leishmaniasis.