Novel development of 5-aminolevurinic acid (ALA) in cancer diagnoses and therapy

Early detection and intervention are needed for optimal outcomes in cancer therapy. Improvements in diagnostic technology, including endoscopy, photodynamic diagnosis (PDD), and photodynamic therapy (PDT), have allowed substantial progress in the treatment of cancer. 5-Aminolevulinic acid (ALA) is a natural, delta amino acid biosynthesized by animal and plant mitochondria. ALA is a precursor of porphyrin, heme, and bile pigments, and it is metabolized into protoporphyrin IX (PpIX) in the course of heme synthesis. PpIX preferentially accumulates in tumor cells resulting in a red fluorescence following irradiation with violet light and the formation of singlet oxygen. This reaction, utilized to diagnose and treat cancer, is termed ALA-induced PDD and PDT. In this review, the biological significance of heme metabolites, the mechanism of PpIX accumulation in tumor cells, and the therapeutic potential of ALA-induced PDT alone and combined with hyperthermia and immunotherapy are discussed.

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.

5-aminolevulinic acid, but not 5-aminolevulinic acid esters, is transported into adenocarcinoma cells by system BETA transporters

5-aminolevulinic acid (5-ALA) and its ester derivatives are used in photodynamic therapy as precursors for the formation of photosensitizers. This study relates to the mechanisms by which 5-ALA is transported into cells. The transport of 5-ALA has been studied in a human adenocarcinoma cell line (WiDr) by means of [14C]-labeled 5-ALA. The rate of uptake was saturable following Michaelis-Menten kinetics (K(m) = 8-10 mM and Vmax = 18-20 nmol.(mg protein x h)-1), and Arrhenius plot of the temperature-dependent uptake of 5-ALA was characterized by a single discontinuity at 32 degrees C. The activation energy was 112 kJ.mol-1 in the temperature range 15 degrees-32 degrees C and 26 kJ.mol-1 above 32 degrees C. Transport of 5-ALA was Na+ and partly Cl(-)-dependent. Stoichiometric analysis revealed a Na+:5-ALA coupling ratio of 3:1. With the exception of valine, methionine and threonine, zwitterionic and basic amino acids inhibited the transport of 5-ALA. 5-ALA methyl ester was not an inhibitor of 5-ALA uptake. The transport was most efficiently inhibited, i.e. by 65-75%, by the beta-amino acids, beta-alanine and taurine and by gamma-aminobutyric acid (GABA). Accordingly, 5-ALA, but not 5-ALA methyl ester, was found to inhibit cellular uptake of [3H]-GABA and [14C]-beta-alanine. Protoporphyrin IX (PpIX) accumulation in the presence of 5-ALA (0.3 mM) was attenuated 85% in the presence of 10 mM beta-alanine, while PpIX formation in cells treated with 5-ALA methyl ester (0.3 mM) or 5-ALA hexyl ester (4 microM) was not significantly influenced by beta-alanine. Thus, 5-ALA, but not 5-ALA esters, is transported by beta-amino acid and GABA carriers in this cell line.

CP-MAS 13C-NMR dipolar correlation spectroscopy of 13C-enriched chlorosomes and isolated bacteriochlorophyll c aggregates of Chlorobium tepidum: the self-organization of pigments is the main structural feature of chlorosomes

Magic angle spinning (MAS) NMR dipolar correlation spectroscopy was applied for the first time to a biologically intact system, the light-harvesting chlorosomes of the green photosynthetic bacterium Chlorobium tepidum. The MAS spectra provide evidence that the self-organization of many thousands of bacteriochlorophyll c (BChl c) molecules is the predominant structural feature of the chlorosome. 13C-Enriched chlorosomes were prepared from nonuniformly labeled cultures grown with NaH13CO3 as the main carbon source and from a uniformly 13C-labeled culture grown with NaH13CO3 as the sole carbon source. For the nonuniformly labeled samples, the positions of the chlorin macrocycle originating from C-4 and C-5 of 5-aminolevulinic acid contained > 95% 13C while the remaining positions, which could have originated also from unlabeled acetate, were labeled to approximately 60% with 13C. The 1-D and 2-D MAS data of the labeled chlorosomes, when compared with data on the isolated labeled BChl c aggregated in n-hexane, show that the major component of the MAS signals in the chlorosomes is from BChl c, and only minor signal contributions arise from lipids and proteins. The 13C MAS signals of the BChl c aggregates were fully assigned by MAS 2-D dipolar correlation spectroscopy, using data on monomeric BChl c in CDCl3/CD3OD as reference. The 2(1)-, 3-, 3(2-), 5-, 12(1)-, 13-, and 13(1)-carbons are shifted by 2.5 ppm or more upfield with respect to the solution data.(ABSTRACT TRUNCATED AT 250 WORDS)

Statistics of the Comet assay: a key to discriminate between genotoxic effects

The alkaline Comet assay is a widely used single cell gel electrophoresis technique for the quantification of DNA strand breaks, crosslinks and alkali-labile sites induced by a series of physical and chemical agents. DNA migration in an electric field, supposed proportional to strand breakage, is a proposed estimation of genotoxicity. Breaks are quantified from geometric and fluorescence measurements by image analysis of comet-shaped DNA, often reported parameters being tail DNA and tail moment. Although a variety of statistical approaches have been used in the literature, most of these do not take into account the distribution patterns of comet data. In order to investigate a methodology for statistically demonstrating a comet effect, two different experiments, a reproducibility study and a trend analysis, were undertaken on a murine lymphoma cell line (P388D1) photodynamically stressed after induction of porphyrins with delta-aminolaevulinic acid. This treatment results in significant heterogeneity of DNA damage, producing values ranging from 0 to 100% tail DNA in the same sample. The comparison of distribution curves for stressed and non-stressed samples shows that none of the application conditions are verified, either for parametric tests (which require normal distributions), or non-parametric tests (which assume essentially similar distributions). Meaningful statistics (median and 75th percentile) were consequently extracted from repeated experiments and found suitable for comparing stress conditions in an ANOVA and in a trend analysis; the 75th percentile is theoretically more sensitive but tends to more rapidly saturate at extensive stress levels. We conclude that a trend analysis of median comet metrics from repeated experiments at different stress levels is certainly an efficient way to statistically demonstrate a genotoxic effect. Whether the considered comet parameter is tail DNA or tail moment had no influence on the conclusions of our experiments, which were carried up to stress levels leading to a median 70% tail DNA.

On the selectivity of 5-aminolevulinic acid-induced protoporphyrin IX formation

Due to its capability to induce accumulation of protoporphyrin IX (PpIX) selectively in a multitude of different pathologies, 5-aminolevulinic acid (ALA) and its derivatives have attracted enormous attention in the field of photodynamic therapy (PDT) in the past two decades. The photochemical and photophysical properties of PpIX have been used for the fluorescence photodetection and photodynamic treatment of neoplasms in several medical indications in which conversion of ALA into PpIX seems to take place preferentially. Recently, this has led to the approval of this therapy for the treatment of actinic keratosis and basal cell carcinoma. When applied topically or systemically, ALA bypasses the negative feedback control that haem exerts on the enzyme ALA synthase (ALAS), which catalyses the natural production of this delta-amino acid, thereby temporarily boosting the generation of PpIX, the direct precursor of haem. Despite considerable interest in this treatment methodology, only little is known concerning the reasons for the selective accumulation of PpIX in neoplastic tissue upon ALA administration. Following an introduction into the biochemical as well as the chemical principles of haem synthesis, the present review tries to summarise experimental evidences of the mechanisms underlying preferential production of PpIX in neoplastic tissues. Thereby, morphological, environmental, enzymatic, as well as cell-specific factors will be discussed.

Targeted delivery of 5-aminolevulinic acid by multifunctional hollow mesoporous silica nanoparticles for photodynamic skin cancer therapy

5-Aminolevulinic acid (5-ALA) is a precursor of a strong photosensitizer, protoporphyrin IX (PphIX), for photodynamic therapy (PDT). Developing appropriate delivery carriers that can assist 5-ALA in bypassing the lipophilic barrier to directly enter into cancer cells is a research focus. The improved delivery of 5-ALA is even important for skin cancer therapy through PDT process. In this work, targeting ligand folic acid (FA)-functionalized hollow mesoporous silica nanoparticles (HMSNPs) were fabricated to deliver 5-ALA for PDT against B16F10 skin cancer cells. The FA targeting ligand enabled selective endocytosis of 5-ALA loaded HMSNPs into cancer cells. PphIX formed from delivered 5-ALA exhibited high photocytotoxicity to the cancer cells in vitro.

The regulation of enzymes involved in chlorophyll biosynthesis

All living organisms contain tetrapyrroles. In plants, chlorophyll (chlorophyll a plus chlorophyll b) is the most abundant and probably most important tetrapyrrole. It is involved in light absorption and energy transduction during photosynthesis. Chlorophyll is synthesized from the intact carbon skeleton of glutamate via the C5 pathway. This pathway takes place in the chloroplast. It is the aim of this review to summarize the current knowledge on the biochemistry and molecular biology of the C5-pathway enzymes, their regulated expression in response to light, and the impact of chlorophyll biosynthesis on chloroplast development. Particular emphasis will be placed on the key regulatory steps of chlorophyll biosynthesis in higher plants, such as 5-aminolevulinic acid formation, the production of Mg(2+)-protoporphyrin IX, and light-dependent protochlorophyllide reduction.

Light scattering from intact cells reports oxidative-stress-induced mitochondrial swelling

Angularly resolved light scattering measurements were performed on suspensions of EMT6 cells and on mitochondria isolated from rabbit liver. Mie theory analysis of the scattering from intact cells indicated that mitochondrial-sized organelles dominated scattering in the range 5-90 degrees . This interpretation was supported by the analysis of scattering from isolated mitochondria. Intact cells were subjected to oxidative stress by photodynamic insult. After 3 h of incubation in the heme precursor aminolevulinic acid hexylester, EMT6 cells accumulated abundant protoporphyrin IX, an endogenous photosensitizer formed in mitochondria. Irradiation of aminolevulinic acid/protoporphyrin IX-sensitized cells with 10 J cm(-2) of 514 nm light led to pronounced changes in angularly resolved light scattering consistent with mitochondrial swelling. Electron microscopy of similarly treated EMT6 cell monolayers showed significant changes in mitochondrial morphology, which included distension of the outer unit membrane and bloating of the internal mitochondrial compartment. Informed by these electron microscopy results, we implemented a coated sphere model to interpret the scattering from intact cells subjected to oxidative stress. The coated sphere interpretation was compatible with the scattering measurements from these cells, whereas simpler Mie theory models based on homogenous swelling were dramatically unsuccessful. Thus, in this system, angularly resolved light scattering reports oxidative-stress-induced changes in mitochondrial morphology.

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.

Macromolecular delivery of 5-aminolaevulinic acid for photodynamic therapy using dendrimer conjugates

Intracellular porphyrin generation following administration of 5-aminolaevulinic acid (5-ALA) has been widely used in photodynamic therapy. However, cellular uptake of 5-ALA is limited by its hydrophilicity, and improved means of delivery are therefore being sought. Highly branched polymeric drug carriers known as dendrimers present a promising new approach to drug delivery because they have a well-defined structure capable of incorporating a high drug payload. In this work, a dendrimer conjugate was investigated, which incorporated 18 aminolaevulinic acid residues attached via ester linkages to a multipodent aromatic core. The ability of the dendrimer to deliver and release 5-ALA intracellularly for metabolism to the photosensitizer, protoporphyrin IX, was studied in the transformed PAM 212 murine keratinocyte and A431 human epidermoid carcinoma cell lines. Up to an optimum concentration of 0.1 mmol/L, the dendrimer was significantly more efficient compared with 5-ALA for porphyrin synthesis. The intracellular porphyrin fluorescence levels showed good correlation with cellular phototoxicity following light exposure, together with minimal dark toxicity. Cellular uptake of the dendrimer occurs through endocytic routes predominantly via a macropinocytosis pathway. In conclusion, macromolecular dendritic derivatives are capable of delivering 5-ALA efficiently to cells for sustained porphyrin synthesis.

Synthesis and biological studies of 5-aminolevulinic acid-containing dendrimers for photodynamic therapy

Using a convergent growth approach, a series of novel 5-aminolevulinic acid (ALA)-containing dendrimers have been synthesized. In these molecules, ALA residues are attached to the periphery by ester linkages, with amide bonds connecting the dendrons. Three first-generation dendrimers, bearing either 6 or 9 ALA residues, were synthesized by attachment of a tris(Boc-protected ALA)-containing wedge (1) to a di- or tripodent aromatic, or tripodent aliphatic core. Two second generation 18-ALA-containing dendrimers were also synthesized using a 3,3'-iminodipropionic acid spacer unit between wedge 1 and the aromatic core. These compounds differed only in the distance between the core and the linker unit. The Boc-protected dendrimers were deprotected using trifluoroacetic acid and isolated as their TFA salts. The potential of these ALA ester dendrimers as macromolecular prodrugs for photodynamic therapy has been demonstrated in the tumorigenic keratinocyte PAM 212 cell line.

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.

Heme mediates cytotoxicity from artemisinin and serves as a general anti-proliferation target

Heme (Fe2+ protoporphyrin IX) is an essential molecule that has been implicated the potent antimalarial action of artemisinin and its derivatives, although the source and nature of the heme remain controversial. Artemisinins also exhibit selective cytotoxicity against cancer cells in vitro and in vivo. We demonstrate that intracellular heme is the physiologically relevant mediator of the cytotoxic effects of artemisinins. Increasing intracellular heme synthesis through the addition of aminolevulinic acid, protoporphyrin IX, or transferrin-bound iron increased the cytotoxicity of dihydroartemisinin, while decreasing heme synthesis through the addition of succinyl acetone decreased its cytotoxic activity. A simple and robust high throughput assay was developed to screen chemical compounds that were capable of interacting with heme. A natural products library was screened which identified the compound coralyne, in addition to artemisinin, as a heme interacting compound with heme synthesis dependent cytotoxic activity. These results indicate that cellular heme may serve a general target for the development of both anti-parasitic and anti-cancer therapeutics.

Sequentially self-assembled polysaccharide-based nanocomplexes for combined chemotherapy and photodynamic therapy of breast cancer

Combination of chemotherapy and photodynamic therapy has emerged as a promising anticancer strategy. Polysaccharide-based nanoparticles are being intensively explored as drug carriers for different forms of combination therapy. In this study, novel multifunctional polysaccharide-based nanocomplexes were prepared from aldehyde-functionalized hyaluronic acid and hydroxyethyl chitosan via sequential self-assembly method. Stable nanocomplexes were obtained through both Schiff's base bond and electrostatic interactions. Chemotherapeutics doxorubicin and pro-photosensitizer 5-aminolevulinic acid were chemically conjugated onto the nanocomplexes via Schiff base linkage. Anti-HER2 antibody as targeting moiety was decorated onto the surface of nanocomplexes. The obtained near-spherical shaped nanocomplexes had an average size of 140 nm and a zeta potential of -24.6 mV, and displayed pH-responsive surface charge reversal and drug release. Active targeting strategy significantly enhanced the cellular uptake of nanocomplexes and combined anticancer efficiency of chemo-photodynamic dual therapy in breast cancer MCF-7 cells. These results suggested that the nanocomplexes had great potential for targeted combination therapy of breast cancer.

Stability of 5-aminolevulinic acid in aqueous solution

The chemical stability of 5-aminolevulinic acid (ALA) was studied in aqueous solution as a function of concentration, pH, temperature and in the presence of ethylenediaminetetraacetic acid (EDTA). The degradation of ALA was followed by reversed-phase liquid chromatography using a pH where ALA is protonated (pKa1=3.90; pKa2=8. 05, as determined potentiometrically). ALA was degraded by a reaction following second order kinetics. Stock solutions of 1% (60 mM) ALA were incubated at 50 degrees C. At pH 2.35, ALA was stable during the whole incubation period (37 days). The half-lives for the second-order decomposition of 1% ALA at pH 4.81 and 7.42 were 257 and 3.0 h, respectively. The degradation rate increased about 1.5 times with each 10 degrees C rise in temperature at pH 7.53 within the range studied (37-85 degrees C). The energy of activation, Ea, for the second-order decomposition of ALA was 43.7 kJmol-1. EDTA did not influence the degradation of ALA when a mixture of 1% ALA and 1% EDTA was incubated at pH 7.42.

5-Aminolevulinic acid induces iron release from ferritin

5-Aminolevulinic acid (ALA), a heme precursor accumulated in acute intermittent porphyria (AIP) and lead poisoning, undergoes metal-catalyzed oxidation in air-equilibrated solutions buffered at neutral pH, yielding free radicals (O2, HO. and ALA.). The capacity of ALA to release iron from horse spleen and rat liver ferritin in vitro and to concomitantly initiate liposome lipid peroxidation was characterized. ALA induced iron release from ferritin in normally aerated solutions, in a dose (0.05-1 mM)- and time (0-120 min)-dependent manner; no reaction occurs under nitrogen. Superoxide dismutase partially inhibited (50% at 100 U/ml) iron release by 0.5 mM ALA, whereas the addition of catalase (50 U/ml) had no effect under these conditions. In phosphatidylcholine: cardiolipin (80:20) liposomes, and in the presence of 2 microM EDTA, ALA (0.025-1 mM) per se had a subtle effect on lipid peroxidation, while after addition of ferritin (0.25 mg/ml) there was a significant increase in lipid peroxidation as evaluated by dose-dependent formation of 2-thiobarbituric-reactive substances and diene conjugation. In vivo, iron accumulation in the liver of ALA-treated rats was observed. Altogether, these data demonstrate the ability of ALA-generated free radicals to release iron from ferritin and to affect iron metabolism in vivo. ALA-mediated iron release from ferritin, therefore, may aggravate oxidative damage to cell components and contribute to the pathology observed in AIP (eg., primary liver cancer) and lead poisoning.

Iontophoretic delivery of 5-aminolevulinic acid (ALA): effect of pH

PURPOSE

To examine the iontophoretic delivery of ALA as a function of pH and to determine the principal mechanisms responsible for its electrotransport.

METHODS

Anodal iontophoretic transport of ALA was measured as a function of its concentration and pH of the donor solution. Experiments were performed in vitro using skin excised from porcine ears as the membrane. To deduce mechanism, the concomitant transport of the electroosmotic marker, mannitol, was also assessed.

RESULTS

ALA iontophoresis at pH 7.4 is a linear function of concentration over the range 1-100 mM. The mechanism was deduced to be electroosmosis. By reducing the pH from 7.4 to 4.0, the dominant mechanism of ALA transport was shifted from electroosmosis to electrorepulsion as the skin's net negative charge was progressively neutralized. However, the total delivery of the compound was not altered by lowering the pH suggesting that the increased electrorepulsive contribution was essentially balanced by the concomitantly reduced electroosmosis.

CONCLUSIONS

Significant ALA delivery at pH 7.4 can be achieved by increasing the drug concentration in the anodal formulation to 100 mM. Lowering the pH does not result in increased ALA transport. Alternative strategies are therefore required to maximize and optimize ALA delivery by iontophoresis.

Fluorescence image-guided brain tumour resection with adjuvant metronomic photodynamic therapy: pre-clinical model and technology development

Fluorescence-guided resection (FGR) and photodynamic therapy (PDT) have previously been investigated separately with the objectives, respectively, of increasing the extent of brain tumour resection and of selectively destroying residual tumour post-resection. Both techniques have demonstrated trends towards improved survival, pre-clinically and clinically. We hypothesize that combining these techniques will further delay tumour re-growth. In order to demonstrate technical feasibility, we here evaluate fluorescence imaging and PDT treatment techniques in a specific intracranial tumour model. The model was the VX2 carcinoma grown by injection of tumour cells into the normal rabbit brain. An operating microscope was used for white light imaging and a custom-built fluorescence imaging system with co-axial excitation and detection was used for FGR. PDT treatment light was applied by intracranially-implanted light emitting diodes (LED). The fluorescent photosensitizer used for both FGR and PDT was ALA-induced PpIX. For PDT, ALA (100 mg kg(-1)) and low light doses (15 and 30 J) were administered over extended periods, which we refer to as metronomic PDT (mPDT). Eighteen tumour bearing rabbits were divided equally into three groups: controls (no resection); FGR; and FGR followed by mPDT. Histological whole brain sections (H&E stain) showed primary and recurrent tumours. No bacteriological infections were found by Gram staining. Selective tumour cell death through mPDT-induced apoptosis was demonstrated by TUNEL stain. These results demonstrate that the combined treatment is technically feasible and this model is a candidate to evaluate it. Further optimization of mPDT treatment parameters (drug/light dose rates) is required to improve survival.

Chemical instability of 5-aminolevulinic acid used in the fluorescence diagnosis of bladder tumours

Aqueous solutions of 5-aminolevulinic acid (ALA) prepared for intravesical instillation in the framework of a clinical study on the fluorescence diagnosis of urothelial bladder cancer were found to be unstable. This chemical instability of ALA was studied in aqueous solution of 37 degrees C as a function of concentration, pH and reaction time. Our investigations showed that the reaction of ALA is an irreversible process, which yields at least two reaction products in the pH range studied (pH lower than 8): the 2,5-(beta-carboxyethyl)dihydropyrazine and the 2,5-(beta-carboxyethyl)pyrazine. As a result of these studies, the conditions for the preparation of ALA solutions to be used for intravesical instillation were optimized: solution of ALA in phosphate-buffered saline at a concentration of 0.18 M (3 g of ALA in 100 ml) neutralized to pH 5, were prepared and stored on ice until use. Solutions prepared under these conditions were stable and were used for fluorescence diagnosis of bladder tumours with successful results. The effect of the pH and the composition of the urine on the extent of the reaction of ALA and on the nature of its reaction products formed during instillation was investigated by comparing the urine of patients before and immediately after instillation of ALA.

Bioadhesive patch-based delivery of 5-aminolevulinic acid to the nail for photodynamic therapy of onychomycosis

The in vitro penetration of 5-aminolevulinic acid (ALA) across human nail and into neonate porcine hoof when released from a novel bioadhesive patch containing 50 mg cm(-2) ALA is described. ALA is a naturally occurring precursor of the photosensitiser protoporphyrin IX (PpIX). Topical application of excess ALA bypasses negative feedback inhibition and yields photosensitising concentrations of PpIX at the application site. ALA-based photodynamic therapy (PDT) has been extensively investigated in the topical treatment of various skin neoplasias. Recently, its use has been extended to the microbiological field. If sufficient concentrations of ALA could be achieved within the nail matrix, and at the nail bed, PDT may prove to be a useful treatment for onychomycosis. Patch application for 24 h allowed an ALA concentration of 2.8 mM to be achieved on the ventral side of excised human nail. Application for 48 h induced a concentration of 6.9 mM. Application time had no significant effect on the ALA concentration at mean depths of 2.375 mm in neonate porcine, with application times of 24, 48 and 72 h all producing concentrations of 0.1 mM. Incubation of Candida albicans and Trichophyton interdigitale with ALA concentrations of 10.0 mM for 30 min and 6 h, respectively, caused reductions in viability of 87% and 42%, respectively, following irradiation with red light. Incubation with 0.1 mM ALA for 30 min and 6 h, respectively, caused reductions in viability of 32% for Candida albicans and 6% for Trichophyton interdigitale, following irradiation. Drug penetration across nail may be improved using penetration enhancers, or by filing of the impenetrable dorsal surface of the nail. Moreover, iron chelators can be used to increase PpIX production for a given ALA dose. Therefore, with suitable modifications, ALA-PDT may prove to be a viable alternative in the treatment of onychomycosis.

Design and Proof of Programmed 5-Aminolevulinic Acid Prodrug Nanocarriers for Targeted Photodynamic Cancer Therapy

5-Aminolevulinic acid (ALA), the precursor of photosensitizer protoporphyrin IX (PpIX), is a U.S. FDA-approved photodynamic therapeutic agent. However, realizing efficient delivery of ALA is still a big challenge as it is hydrophilic and cannot be recognized and selectively accumulated in tumor cells. In this study, matrix metalloproteinase-2 (MMP-2) and pH dual-sensitive ALA prodrug nanocarriers were constructed as a programmed delivery strategy for the targeted delivery of ALA. The nanocarriers were prepared by the co-modification of gold nanoparticles (AuNPs) with hydrazone-linked ALA and MMP-2-activatable cell-penetrating peptides (CPPs). Cationic CPP RRRRRRRR (R8) was shielded by zwitterionic stealth peptide EKEKEKEKEKEKEKEKEKEK (EK10) via MMP-2 substrate peptide PLGLAG. The zwitterionic stealth peptide EK10 is designed to endow ALA prodrug nanocarriers with strong antifouling ability and prolonged circulation time. Upon arriving at the tumor tissue, the shielded cationic CPP R8 can be activated by tumor-microenvironment-overexpressed MMP-2, which enabled enhanced cellular uptake of ALA. The results of drug loading and release, cellular uptake, PpIX generation and accumulation, photodynamic cytotoxicity, and photodynamic tumor inhibition demonstrated that such tumor-microenvironment-sensitive ALA prodrug nanocarriers could be considered as potential candidates for targeted photodynamic cancer therapy.

Degradation mechanism and stability of 5-aminolevulinic acid

The physiological substance and precursor of the heme synthesis 5-aminolevulinic acid (ALA) is a promising prodrug for photodiagnosis and photodynamic therapy of epithelial tumors, particularly in urological and gynecological tissues. For the clinical use of this substance, a chemically stable and sterile drug formulation is required. In the present study, degradation mechanism of ALA in aqueous solution and possibilities to improve its stability were examined. A capillary electrophoretic method was developed that was suitable for the quantification of ALA and of two degradation products. The intermediate degradation product was 2, 5-dicarboxyethyl-3,6-dihydropyrazine, which was further oxidized to 2,5-dicarboxyethylpyrazine. The structures of the degradation products were proven by (1)H and (13)C nuclear magnetic resonance spectroscopy. ALA degradation was very efficiently inhibited by adjusting the pH of the aqueous solution to a value <5 and by purging with nitrogen. Additives such as antioxidants did not improve the ALA stability. These results demonstrated that low pH ALA aqueous solution may be one possible dosage form to be considered for market introduction.

Ethylene glycol and amino acid derivatives of 5-aminolevulinic acid as new photosensitizing precursors of protoporphyrin IX in cells

Protoporphyrin IX (PpIX) is used as a photosensitizing agent in photodynamic detection and therapy (PDT) of cancer and is synthesized intracellularly from aminolevulinic acid (ALA) precursors. To evaluate means to specifically target ALA derivatives to defined cells, we have synthesized and characterized ethylene glycol esters and amino acid pseudodipeptide derivatives of ALA as potential specific substrates for cellular esterases and aminopeptidases, respectively. The PpIX formation induced by these products was investigated using cultures of human and rat cell lines of carcinoma and endothelial origins. The cytotoxicity of these compounds in the absence of light was also controlled. The results have shown that ethylenglycol esters can induce high levels of PpIX and are useful at concentrations below their cytotoxicity threshold. From the ALA-amino acid derivatives which were evaluated, the highest PpIX production was obtained using ALA derivatives of neutral amino acids, as compared to acidic or basic amino acids.

Reactions of Pseudomonas 7A glutaminase-asparaginase with diazo analogues of glutamine and asparagine result in unexpected covalent inhibitions and suggests an unusual catalytic triad Thr-Tyr-Glu

Pseudomonas 7A glutaminase-asparaginase (PGA) catalyzes the hydrolysis of D and L isomers of glutamine and asparagine. Crystals of PGA were reacted with diazo analogues of glutamine (6-diazo-5-oxo-L-norleucine, DON) and asparagine (5-diazo-4-oxo-L-norvaline, DONV), which are known inhibitors of the enzyme. The derivatized crystals remained isomorphous to native PGA crystals. Their structures were refined to crystallographic R = 0.20 and R(free) = 0.24 for PGA-DON and R = 0.19 and R = 0.23 for PGA-DONV. Difference Fourier electron density maps clearly showed that both DON and DONV inactivate PGA through covalent inhibition. Continuous electron density connecting the inhibitor to both Thr20 and Tyr34 of the flexible loop was observed providing strong evidence that Thr20 is the primary catalytic nucleophile and that Tyr34 plays an important role in catalysis as well. The unexpected covalent binding observed in the PGA-DON and PGA-DONV complexes shows that a secondary reaction involving the formation of a Tyr34-inhibitor bond takes place with concomitant inactivation of PGA. The predicted covalent linkage is not seen, however, suggesting an alternative method of inhibition not yet seen for these diazo analogues. These surprising results give insight as to the role of the flexible loop Thr and Tyr in the catalytic mechanism.