Vladimir Iani

Microneedle-mediated intradermal delivery of 5-aminolevulinic acid: potential for enhanced topical photodynamic therapy.

Photodynamic therapy of deep or nodular skin tumours is currently limited by the poor tissue penetration of the porphyrin precursor 5-aminolevulinic acid (ALA). In this study, silicon microneedle arrays were used, for the first time, to enhance skin penetration of ALA in vitro and in vivo. Puncturing excised murine skin with 6 x 7 arrays of microneedles 270 microm in height, with a diameter of 240 mum at the base and an interspacing of 750 microm led to a significant increase in transdermal delivery of ALA released from a bioadhesive patch containing 19 mg ALA cm(-2). Microneedle puncture enhanced ALA delivery to the upper regions of excised porcine skin but, at mean depths of 1.875 mm, ALA concentrations were similar to control values, possibly reflecting binding of ALA by tissue components. However, and importantly, in vivo experiments using nude mice showed that microneedle puncture could reduce application time and ALA dose required to induce high levels of the photosensitizer protoporphyrin IX in skin. This clearly has implications for clinical practice, as shorter application times would mean improved patient and clinician convenience and also that more patients could be treated in the same session. As ALA is expensive and degrades rapidly via a second order reaction, reducing the required dose is also a notable advantage.

Topical Application of 5‐Aminolevulinic Acid Hexyl Ester and 5‐Aminolevulinic Acid to Normal Nude Mouse Skin: Differences in Protoporphyrin IX Fluorescence Kinetics and the Role of the Stratum Corneum¶

Abstract An important limitation of topical 5-aminolevulinic acid (ALA)-based photodetection and photodynamic therapy is that the amount of the fluorescing and photosensitizing product protoporphyrin IX (PpIX) formed is limited. The reason for this is probably the limited diffusion of ALA through the stratum corneum. A solution to this problem might be found in the use of ALA derivatives, as these compounds are more lipophilic and therefore might have better penetration properties than ALA itself. Previous studies have shown that ALA hexyl ester (ALAHE) is more successful than ALA for photodetection of early (pre)malignant lesions in the bladder. However, ALA pentyl ester slightly increased the in vivo PpIX fluorescence in early (pre)malignant lesions in hairless mouse skin compared to ALA. The increased PpIX fluorescence is located in the stratum corneum and not in the dysplastic epidermal layer. In the present study, ALA- and ALAHE-induced PpIX fluorescence kinetics are compared in the normal nude mouse skin, of which the permeability properties differ from the bladder. Application times and ALA(HE) concentrations were varied, the effect of a penetration enhancer and the effect of tape stripping the skin before or after application were investigated. Only during application for 24 h, did ALAHE induce slightly more PpIX fluorescence than ALA. After application times ranging from 1 to 60 min, ALA-induced PpIX fluorescence was higher than ALAHE-induced PpIX fluorescence. ALA also induced higher PpIX production than ALAHE after 10 min of application with concentrations ranging from 0.5 to 40%. The results of experiments with the penetration enhancer and tape stripping indicated that the stratum corneum acts a barrier against ALA and ALAHE. Use of penetration enhancer or tape stripping enhanced the PpIX production more in the case of ALAHE application than in the case of ALA application. This, together with the results from the different application times and concentrations indicates that ALAHE diffuses more slowly across the stratum corneum than ALA.

On the pharmacokinetics of topically applied 5-aminolevulinic acid and two of its esters

The kinetics of protoporphyrin IX (PpIX) production in normal tissues and WiDr tumors of mice were studied after topical application of 5‐aminolevulinic acid (ALA) and its methyl ester and hexyl ester. ALA and ALA esters were applied on a spot of 1.0 cm diameter on normal skin and on skin overlaying tumors. PpIX production was studied by fluorescence measurements. ALA induced PpIX not only on the spot of application but also on remote skin areas. This was not found for the ALA esters. They produced PpIX only on the spot of application. Thus, ALA, but neither its esters nor PpIX, is passing into the circulation. The time needed for ALA to enter the circulation through normal skin was about 5 hr. Even when looking normal, the skin overlaying tumors was more permeable to ALA than normal skin. Thus, when applied on the tumor, ALA induced PpIX on remote skin areas without any lag phase. Mainly, PpIX was found in all tissues although small amounts of a porphyrin with an excitation peak at about 400 nm, supposedly uroporphyrin and/or coproporphyrin, were found, notably in remote skin areas. An altered stratum corneum of the skin overlaying tumors probably contributes to the tumorselectivity, although in the present tumor system less PpIX was found in tumors than in muscles. This is probably related to biochemical and physiological conditions in this particular tumor, since i.p. injection of ALA also leads to less PpIX formation in the tumor than in skin/muscle tissue. Nevertheless, it seems evident that ALA can diffuse more easily from the skin surface and down to the vasculature in the tumor than in the normal tissue and that this leads to a higher concentration of PpIX in the tumor than would have been found if the physiological factors relevant for drug diffusion were the same for tumors as for skin/muscles.

Phototransformations of 5-Aminolevulinic Acid–induced Protoporphyrin IX in vitro: A Spectroscopic Study¶

Abstract Human adenocarcinoma cells of the line WiDr were incubated with 5-aminolevulinic acid to induce protoporphyrin IX (PpIX) and then exposed to laser light of wavelength 635 nm. The PpIX fluorescence decreased with increasing exposure. The decay rate was slightly dependent on the initial PpIX concentration. The PpIX fluorescence was halved by a fluence of about 40 J/cm2. Several fluorescing photoproducts were formed. The main one, supposedly the chlorin-type photoprotoporphyrin (Ppp), had a fluorescence excitation spectrum stretching out to about 680 nm with a maximum at around 668 nm. The formation kinetics of this product was dependent on the initial PpIX concentration. Moreover, it was selectively bleached by exposure to light at 670 nm. A photoproduct with an emission maximum at 652 nm, different from Ppp, remained after this exposure. Traces of a photoproduct(s) with fluorescence emission slightly blueshifted compared with that of PpIX, supposedly water-soluble porphyrins, were also detected after light exposure.

Topical Application of 5-Aminolevulinic Acid and its Methylester, Hexylester and Octylester Derivatives: Considerations for Dosimetry in Mouse Skin Model¶

Abstract 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.

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.

Intracellular Localisation of Hypericin in Human Glioblastoma and Carcinoma Cell Lines

Abstract. Hypericin, a natural polycyclic quinone extracted from Hypericum perforatum, has been recently shown to be a powerful sensitiser for photodynamic therapy (PDT). However, its intracellular localisation remains unclear and contradictory. In the present work we compared the intracellular localisation of hypericin in three cultured cell lines (adenocarcinoma cells WiDr, carcinoma cells NHIK 3025 and glioblastoma cells D54Mg) with the distribution of fluorescent probes specific to lysosomes (LysoTracker Blue DND-22), mitochondria (MitoTracker Green FM) and endoplasmic reticulum (ERTracker Blue-White DPX). It was shown that the hypericin staining pattern was different compared to the intracellular distribution of mitochondria or lysosomes. Hypericin was concentrated in the perinucleolar cytoplasmic area mainly on one side of the nucleus – the region rich in endoplasmic reticulum and Golgi. Sometimes nuclear envelope was also stained. Plasma membrane was not stained but the dye was often accumulated in the intercellular space between the tightly contacting WiDr cells in colonies. Hypericin concentrations of 10 μM or less were not toxic for WiDr cells in the dark. Orange light (λmax≈600 nm; 6 mW/cm2) killed the cells stained with 1 μM hypericin with LD50∼ 1J/cm2.

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.

Microneedle arrays permit enhanced intradermal delivery of a preformed photosensitizer

Silicon microneedle (MN) arrays were used to puncture excised murine and porcine skin in vitro and transdermal and intradermal delivery of meso‐tetra (N‐methyl‐4‐pyridyl) porphine tetra tosylate (TMP) investigated using topical application of a bioadhesive patch containing 19 mg TMP cm−2. Animal studies, using nude mice, were then conducted to investigate the in vivo performance of the bioadhesive patch following MN puncture of skin. MN puncture significantly enhanced both intradermal and transdermal delivery of TMP in vitro, though the total amounts of drug delivered (25.22% into porcine skin and 0.07% across murine skin) were still quite small in each case. Notwithstanding this, in vivo experiments showed that MN puncture was capable of permitting a prolonged increase in TMP fluorescence at the site of application. Importantly, fluorescence was negligible at distant sites, meaning systemic delivery of the drug was not sufficient to induce TMP accumulation other than at the application site. In this study we have conclusively demonstrated proof of principle; MN puncture allows true intradermal delivery of a preformed photosensitizer in animal skin models in vitro and in vivo. Importantly, transdermal delivery was much reduced in each case. Increasing MN density would allow increased amounts of photosensitizer to be delivered. However, as MNs create aqueous pores in the stratum corneum, a preformed photosensitizer must possess at least some degree of water solubility in order to permit enhanced intradermal delivery in this way. We believe that use of MN array technology in this way has the potential to significantly improve topical photodynamic therapy of skin tumors.

Fluorescence spectroscopy of normal mouse skin exposed to 5-aminolaevulinic acid and red light.

Photobleaching and phototransformation of protoporphyrin IX (PpIX) was investigated in normal mouse skin. The PpIX was induced by topical application of 5-aminolaevulinic acid (ALA). Exposure to laser light (635 nm) caused photobleaching of PpIX fluorescence and formation of fluorescent products. Analysis of the fluorescence spectra revealed appearance of new fluorescent photoproducts during light exposure. The main photoproduct, supposedly chlorin-type photoprotoporphyrin (PPp), exhibited fluorescence with an emission maximum at 675 nm. The other products exhibited main fluorescence peaks at around 588 and 623 nm that can presumably be attributed to an endogenous metallo-porphyrin and water-soluble porphyrin(s), respectively. Our results indicate that light exposure causes alterations in the enzymatic pathway of PpIX synthesis from ALA and leads to accumulation of intermediate water-soluble porphyrins. ALA-induced porphyrins are transported away from the treated area and partly deposited in remote skin sites.