Hydrogel-forming and dissolving microneedles for enhanced delivery of photosensitizers and precursors.

We present "one-step application" dissolving and hydrogel-forming microneedle arrays (MN) for enhanced delivery of photosensitizers/precursors. MN (280 µm) prepared from 20% w/w poly(methylvinylether/maelic acid) and cross-linked with glycerol by esterification to form hydrogels upon skin insertion, or allowed to dissolve rapidly in skin, were combined with patches containing 19 mg cm(-2) of 5-aminolevulinic acid (ALA) or meso-tetra (N-methyl-4-pyridyl) porphine tetra tosylate (TMP) for drug delivery. Both MN types were mechanically robust, with compression forces of 20.0 N only causing height reductions of 14%. Application forces as low as 8.0 N per array allowed >95% of the MN in each array type to penetrate excised porcine skin, with the MN penetrating to approximately 220 µm. MN significantly enhanced transdermal delivery of ALA and TMP in vitro, with the hydrogel-forming system comparable with the dissolving system for ALA delivery (approximately 3000 nmol cm(-2) over 6 h), but superior for delivery of the much larger TMP molecule (approximately 14 nmol cm(-2) over 24 h, compared to 0.15 nmol cm(-2)). As this technology clearly has potential in enhanced photodynamic therapy of neoplastic skin lesions, we are currently planning animal studies, to be followed by preliminary human evaluations. GMP manufacturing scale-up is ongoing.

Fast-drying multi-laminate bioadhesive films for transdermal and topical drug delivery.

No bioadhesive patch-based system is currently marketed. This is despite an extensive number of literature reports on such systems detailing their advantages over conventional pressure sensitive adhesive-based patches in wet environments and describing successful delivery of a diverse array of drug substances. This lack of proprietary bioadhesive patches is largely due to the fact that such systems are exclusively water-based, meaning drying is difficult. In this paper we describe, for the first time, a novel multiple lamination method for production of bioadhesive patches. In contrast to patches produced using a conventional casting approach, which took 48 hours to dry, bioadhesive films prepared using the novel multiple lamination method were dried in 15 min and were folded into formed patches in a further 10 min. Patches prepared by both methods had comparable physicochemical properties. The multiple lamination method allowed supersaturation of 5-aminolevulinic acid to be achieved in formed patch matrices. However, drug release studies were unable to show an advantage for supersaturation with this particular drug, due to its water high solubility. The multiple lamination method allowed greater than 90% of incorporated nicotine to remain within formed patches, in contrast to the 48% achieved for patches prepared using a conventional casting approach. The procedure described here could readily be adapted for automation by industry. Due to the reduced time, energy and ensuing finance now required, this could lead to bioadhesive patch-based drug delivery systems becoming commercially viable. This would, in turn, mean that pathological conditions occurring in wet or moist areas of the body could now be routinely treated by prolonged site-specific drug delivery, as mediated by a commercially produced bioadhesive patch.

Characterization of BMS-911543, a functionally selective small-molecule inhibitor of JAK2.

We report the characterization of BMS-911543, a potent and selective small-molecule inhibitor of the Janus kinase (JAK) family member, JAK2. Functionally, BMS-911543 displayed potent anti-proliferative and pharmacodynamic (PD) effects in cell lines dependent upon JAK2 signaling, and had little activity in cell types dependent upon other pathways, such as JAK1 and JAK3. BMS-911543 also displayed anti-proliferative responses in colony growth assays using primary progenitor cells isolated from patients with JAK2(V617F)-positive myeloproliferative neoplasms (MPNs). Similar to these in vitro observations, BMS-911543 was also highly active in in vivo models of JAK2 signaling, with sustained pathway suppression being observed after a single oral dose. At low dose levels active in JAK2-dependent PD models, no effects were observed in an in vivo model of immunosuppression monitoring antigen-induced IgG and IgM production. Expression profiling of JAK2(V617F)-expressing cells treated with diverse JAK2 inhibitors revealed a shared set of transcriptional changes underlying pharmacological effects of JAK2 inhibition, including many STAT1-regulated genes and STAT1 itself. Collectively, our results highlight BMS-911543 as a functionally selective JAK2 inhibitor and support the therapeutic rationale for its further characterization in patients with MPN or in other disorders characterized by constitutively active JAK2 signaling.

Electrically enhanced solute permeation across poly(ethylene glycol)-crosslinked poly(methyl vinyl ether-co-maleic acid) hydrogels: effect of hydrogel crosslink density and ionic conductivity.

Swelling kinetics, ionic conductivity and electrically assisted solute permeation (theophylline, methylene blue and fluorescein sodium) of poly(ethylene glycol) (PEG) crosslinked poly(methyl vinyl ether-co-maleic acid) (PMVE/MA) hydrogels are presented. The effects of PMVE/MA concentration and PEG molecular weight (MW) on swelling behaviour and network parameters were investigated in phosphate buffered saline (pH 7.4). The percentage swelling of hydrogels increased, and the crosslink density decreased, with a decrease in PMVE/MA content and with an increase in PEG MW. The ionic conductivity of the formulation was found to increase with an increase in PEG MW. The application of an electrical current led to a significant enhancement in the rate and extent of solute permeation across the swollen hydrogels. Furthermore, it was found that the extent of solute permeation enhancement following current application was dependent upon the crosslink density and ionic conductivity of the formulation. In general, a decrease in crosslink density and an increase in ionic conductivity led to a greater enhancement in solute permeation following current application. The electro-responsive nature of these hydrogels suggests that have a potential application in electrically controlled drug delivery systems.

Microneedle-mediated intradermal nanoparticle delivery: Potential for enhanced local administration of hydrophobic pre-formed photosensitisers.

INTRODUCTION: To date, 5-aminolevulinic acid (ALA) has been the most widely used agent in topical photodynamic therapy (PDT). However, owing to the poor penetration of ALA into skin, ALA-PDT is inappropriate for difficult-to-treat deep skin neoplasias, such as nodular basal cell carcinoma. An alternative strategy to ALA-PDT is to use pre-formed photosensitisers, which can be activated at longer wavelengths, facilitating enhanced light penetration into skin. Owing to their relatively high molecular weights and often high lipophilicities, these compounds cannot be effectively administered topically. This study aimed to deliver a model hydrophobic dye, Nile red, into the skin using novel microneedle (MN) technology. MATERIALS AND METHODS: Nile red was incorporated into poly-lactide-co-glycolic acid (PLGA) nanoparticles using an emulsion and salting-out process. Polymeric MN arrays were prepared from aqueous blends of the mucoadhesive copolymer Gantrez(®) AN-139 and tailored to contain 1.0mg of Nile red-loaded PLGA nanoparticles. Intradermal delivery of Nile red was determined in vitro. RESULTS: Uniform 150nm diameter PLGA nanoparticles were prepared containing 3.87µg Nile red / mg of PLGA. Tissue penetration studies using excised porcine skin revealed that high tissue concentrations of Nile red were observed at 1.125mm (382.63ng cm(-3)) following MN delivery. CONCLUSION: For the first time, polymeric microneedles (MN) have been employed to deliver a model lipophilic dye, Nile red, into excised porcine skin. Importantly, this is a one-step delivery strategy for the local delivery of highly hydrophobic agents, which overcomes many of the disadvantages of current delivery strategies.

Influence of penetration enhancers on topical delivery of 5-aminolevulinic acid from bioadhesive patches.

OBJECTIVES: The inclusion of chemical penetration enhancers in a novel patch-based system for the delivery of 5-aminolevulinic acid (ALA) was examined in vitro and in vivo. Poor penetration of ALA has been implicated as the primary factor for low response rates achieved with topical ALA-based photodynamic therapy of thicker neoplastic lesions, such as nodular basal cell carcinomas. METHODS: Several chemical permeation enhancers (dimethylsulfoxide, Labrafac CC, Labrafac PG and Labrafil M1944CS) were incorporated into bioadhesive patches tailored to deliver 19 mg ALA/cm(2). KEY FINDINGS: In-vitro depth penetration studies into excised porcine skin showed that high concentrations of ALA (>9 micromol/cm(3)) could be delivered to a depth of 1.875 mm. However, inclusion of permeation enhancers did not significantly increase ALA delivery, relative to the control (P > 0.05). In-vivo studies were in strong agreement with in-vitro results, with formulations containing chemical enhancers showing no improvement in delivery compared with the control. CONCLUSIONS: The patches designed in this work are suited to defineable ALA delivery without the need to immobilise patients for up to 6 h, as is common with the cream-under-occlusion approach. Overall, permeation enhancers were not found to markedly enhance the topical delivery of ALA. However, chemical penetration enhancers may have a greater effect on the delivery of more lipophilic ALA prodrugs, which are thought to primarily permeate the stratum corneum via the intercellular pathway.

Investigation of solute permeation across hydrogels composed of poly(methyl vinyl ether-co-maleic acid) and poly(ethylene glycol).

OBJECTIVES: Swelling kinetics and solute permeation (theophylline, vitamin B(12) and fluorescein sodium) of hydrogels composed of poly(methyl vinyl ether-co-maleic acid) (PMVE/MA) and poly(ethylene glycol) (PEG) are presented. METHODS: The effects of PMVE/MA and PEG 10 000 content on swelling behaviour (percentage swelling, the type of diffusion and swelling rate constant) were investigated in 0.1 m phosphate buffer. Network parameters, such as average molecular weight between crosslinks (M(c)) and crosslink density, were evaluated. KEY FINDINGS: The percentage swelling and M(c) of hydrogels increased with decrease in PMVE/MA content, where the water diffusion mechanism into the hydrogels was Class-II type. In contrast, increase in PMVE/MA content caused an increase in the crosslink density. Permeation of theophylline, vitamin B(12) and fluorescein sodium, with increasing hydrodynamic radii, was studied through the equilibrium swollen hydrogels composed of PMVE/MA and PEG. In general, the permeability and diffusion coefficients of all three solutes decreased with increase in the PMVE/MA content. In addition, permeability and diffusion coefficient values increased with decreases in the hydrodynamic radii of the solute molecules. CONCLUSIONS: The hydrogels have shown a change in swelling behaviour, crosslink density, M(c) and solute permeation with change in PMVE/MA content, thus suggesting a potential application in controlled drug-delivery systems.

Novel patch-based systems for the localised delivery of ALA-esters.

In photodynamic therapy (PDT) a combination of visible light and a sensitising drug causes the destruction of selected cells. Aminolaevulinic acid (ALA) has been widely used in topical PDT for over 15 years. However, ALA does not possess favourable physicochemical properties for skin penetration. Consequently, the clearance rates for difficult to treat lesions, such as nodular basal cell carcinomas are relatively low. For the first time, equimolar concentrations of ALA, methyl-ALA (m-ALA) and hexyl-ALA (h-ALA) have been incorporated into a bioadhesive patch-based system. In vitro penetration studies into excised porcine skin revealed that ALA patches containing relatively high loadings (226.7 micromol cm(-2)) were associated with significantly greater tissue concentrations (70.7 micromol cm(-3)) than patches containing m-ALA (16.3 micromol cm(-3)) or h-ALA (17.4 micromol cm(-3)). ALA was also found to be the most efficient inducer of protoporphyrin (PpIX) fluorescence in mice, in vivo (maximum mean fluorescence: ALA=236.2 a.u., m-ALA=175.1 a.u., h-ALA=193.5 a.u.). However, when the lipophilic hexylester was formulated in a pressure sensitive adhesive (PSA) patch, significantly higher PpIX levels were achieved compared to all bioadhesive systems tested. Of major importance, PSA patches containing relatively low h-ALA loadings induced high PpIX levels, which were localised to the application area. This study has highlighted the importance of rational selection of both the active agent and the delivery system. Bioadhesive preparations containing ALA are ideal for delivery to moist environments; whereas h-ALA-loaded PSA systems may facilitate enhanced delivery to dry areas of skin. In addition, owing to the relatively low loadings of h-ALA required in PSA patches, the costs of clinical PDT may potentially be reduced.

Hexyl aminolaevulinate is a more effective topical photosensitiser precursor than methyl aminolaevulinate and 5-aminolaevulinic acids when applied in equimolar doses.

Aminolaevulinic acid (ALA) is known to poorly penetrate into thick lesions, such as nodular basal cell carcinomas. Short chain ALA esters, possessing increased lipophilicity relative to their hydrophilic parent, have previously been shown to be highly efficient at inducing protoporphyrin IX (PpIX) production in cell culture, at equimolar concentrations. In contrast, in vitro skin permeation and in vivo animal studies, which up to now have compared prodrugs on a % w/w basis, have failed to demonstrate such benefits. For the first time, equimolar concentrations of ALA, methyl-ALA (m-ALA) and hexyl-ALA (h-ALA) have been incorporated into an o/w cream preparation. In vitro penetration studies into excised porcine skin revealed that increased levels of h-ALA, compared to ALA and m-ALA were found in the upper skin layers, at all drug loadings studied. Topical application of the formulations to nude murine skin in vivo, revealed that creams containing h-ALA induced significantly higher levels of peak PpIX fluorescence (F(max) = 289.0) at low concentrations compared to m-ALA (F(max) = 159.2) and ALA (F(max) = 191.9). Importantly, this study indicates that when compared on an equimolar basis, h-ALA has improved skin penetration, leading to enhanced PpIX production compared to the parent drug and m-ALA.

Freeze-dried, mucoadhesive system for vaginal delivery of the HIV microbicide, dapivirine: optimisation by an artificial neural network.

Dapivirine mucoadhesive gels and freeze-dried tablets were prepared using a 3x3x2 factorial design. An artificial neural network (ANN) with multi-layer perception was used to investigate the effect of hydroxypropyl-methylcellulose (HPMC): polyvinylpyrrolidone (PVP) ratio (X1), mucoadhesive concentration (X2) and delivery system (gel or freeze-dried mucoadhesive tablet, X3) on response variables; cumulative release of dapivirine at 24h (Q(24)), mucoadhesive force (F(max)) and zero-rate viscosity. Optimisation was performed by minimising the error between the experimental and predicted values of responses by ANN. The method was validated using check point analysis by preparing six formulations of gels and their corresponding freeze-dried tablets randomly selected from within the design space of contour plots. Experimental and predicted values of response variables were not significantly different (p>0.05, two-sided paired t-test). For gels, Q(24) values were higher than their corresponding freeze-dried tablets. F(max) values for freeze-dried tablets were significantly different (2-4 times greater, p>0.05, two-sided paired t-test) compared to equivalent gels. Freeze-dried tablets having lower values for X1 and higher values for X2 components offered the best compromise between effective dapivirine release, mucoadhesion and viscosity such that increased vaginal residence time was likely to be achieved.

Development and evaluation of a vaginal ring device for sustained delivery of HIV microbicides to non-human primates.

BACKGROUND: There is considerable interest in developing coitally independent, sustained release formulations for long-term administration of HIV microbicides. Vaginal ring devices are at the forefront of this formulation strategy. METHODS: Non-medicated silicone elastomer vaginal rings were prepared having a range of appropriate dimensions for testing vaginal fit in pig-tailed and Chinese rhesus macaques. Cervicovaginal proinflammatory markers were evaluated. Compression testing was performed to compare the relative flexibility of various macaque and commercial human rings. RESULTS: All rings remained in place during the study period and no tissue irritation or significant induction of cervicovaginal proinflammatory markers or signs of physical discomfort were observed during the 8-week study period. CONCLUSIONS: Qualitative evaluation suggests that the 25 x 5-mm ring provided optimal fit in both macaque species. Based on the results presented here, low-consistency silicone elastomers do not cause irritation in macaques and are proposed as suitable materials for the manufacture of microbicide-loaded vaginal rings.

Clinical and immunohistochemical assessment of vulval intraepithelial neoplasia following photodynamic therapy using a novel bioadhesive patch-type system loaded with 5-aminolevulinic acid.

BACKGROUND: The work in this study appraised photodynamic treatment (PDT) as a treatment method for vulval intraepithelial neoplasia (VIN) using a novel bioadhesive patch to deliver aminolevulinic acid. An analysis of changes in expression of apoptotic and cell cycle proteins (p53, p21, Mdm2, Blc-2, Bax, Ki-67) in response to PDT was evaluated. METHODS: PDT was performed using non-laser light, either as a one or two-cycle treatment, with clinical and pathological assessment following after 6 weeks. Twenty-three patients with 25 VIN lesions underwent 49 cycles of PDT. Patches were designed to conform to uneven vulval skin and contained 38 mg cm(-2) aminolevulinic acid. Assessment was carried out at 6 weeks post-treatment. Patient-based treatment assessment, along with clinical and pathological changes, were monitored. Immunohistochemical staining was used to elucidate a possible biomolecular basis for induced cellular changes. RESULTS: Most patients (52%) reported a symptomatic response, with normal pathology restored in 38% of lesions. The patch was easy to apply and remove, causing minimal discomfort. Fluorescence inspection confirmed protoporphyrin accumulation. Pain during implementation of PDT was problematic, necessitating some form of local analgesia. Changes in expression of cell cycle and apoptotic-related proteins suggested involvement of apoptotic pathways. Down regulation of p21 and inverse changes in Bcl-2 and Bax were key findings. CONCLUSION: Treatment of VIN lesions using a novel bioadhesive patch induced changes in cell cycle and apoptotic proteins in response to PDT with possible utilisation of apoptotic pathways. The efficacy of PDT in treating VIN could be improved by a better understanding of these apoptotic mechanisms, the influence of factors, such as HPV status, and of the need for effective pain management.

Influence of formulation factors on PpIX production and photodynamic action of novel ALA-loaded microparticles.

A novel 5-aminolevulinic acid (ALA)-containing microparticulate system was produced recently, based on incorporation of ALA into particles prepared from a suppository base that maintains drug stability during storage and melts at skin temperature to release its drug payload. The novel particulate system was applied to the skin of living animals, followed by study of protoporphyrin IX (PpIX) production. The effect of formulating the microparticles in different vehicles was investigated and also the phototoxicity of the PpIX produced using a model tumour.Particles formulated in propylene glycol gels (10% w/w ALA loading) generated the highest peak PpIX fluorescence levels in normal mouse skin. Peak PpIX levels induced in skin overlying subcutaneously implanted WiDr tumours were significantly lower than in normal skin for both the 10% w/w ALA microparticles alone and the 10% w/w ALA microparticles in propylene glycol gels during continuous 12 h applications. Tumours not treated with photodynamic therapy continued to grow over the 17 days of the anti-tumour study. However, those treated with 12 h applications of either the 10% w/w ALA microparticles alone or the 10% w/w ALA microparticles in propylene glycol gel followed by a single laser irradiation showed no growth. The gel formulation performed slightly better once again, reducing the tumour growth rate by approximately 105%, compared with the 89% reduction achieved using particles alone. Following the promising results obtained in this study, work is now going on to prepare particle-loaded gels under GMP conditions with the aim of initiating an exploratory clinical trial.

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.

Photosensitiser delivery for photodynamic therapy. Part 2: systemic carrier platforms.

BACKGROUND: The treatment of solid tumours and angiogenic ocular diseases by photodynamic therapy (PDT) requires the injection of a photosensitiser (PS) to destroy target cells through a combination of visible light irradiation and molecular oxygen. There is currently great interest in the development of efficient and specific carrier delivery platforms for systemic PDT. OBJECTIVE: This article aims to review recent developments in systemic carrier delivery platforms for PDT, with an emphasis on target specificity. METHODS: Recent publications, spanning the last five years, concerning delivery carrier platforms for systemic PDT were reviewed, including PS conjugates, dendrimers, micelles, liposomes and nanoparticles. RESULTS/CONCLUSION: PS conjugates and supramolecular delivery platforms can improve PDT selectivity by exploiting cellular and physiological specificities of the targeted tissue. Overexpression of receptors in cancer and angiogenic endothelial cells allows their targeting by affinity-based moieties for the selective uptake of PS conjugates and encapsulating delivery carriers, while the abnormal tumour neovascularisation induces a specific accumulation of heavy weighted PS carriers by enhanced permeability and retention (EPR) effect. In addition, polymeric prodrug delivery platforms triggered by the acidic nature of the tumour environment or the expression of proteases can be designed. Promising results obtained with recent systemic carrier platforms will, in due course, be translated into the clinic for highly efficient and selective PDT protocols.

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.

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.

Autoradiographic and scintillation analysis of 5-aminolevulinic acid permeation through epithelialised tissue: implications for topical photodynamic therapy of superficial gynaecological neoplasias.

PURPOSE: Aminolevulinic acid (5-ALA) diffusion through both keratinised and non-keratinised tissue, used as a model tissue substrates, was evaluated, together with the depth of permeation and the concentration achieved following delivery from bioadhesive patch and proprietary cream formulations. MATERIALS AND METHODS: Moisture-activated, bioadhesive patches loaded with 5-ALA at concentrations of 19.0, 38.0 and 50.0 mg cm(-2) and an o/w cream (20% w/w 5-ALA) were radiolabelled with C14 5-ALA and applied to excised human vaginal tissue and porcine skin. After 1, 2 and 4 h, tissue was sectioned in two orientations and the 5-ALA concentration at specific depths determined using autoradiography and liquid scintillation counting (LSC). RESULTS: The stratum corneum was a significant barrier to 5-ALA permeation, with concentrations in tissue dependent on application time and drug loading. 5-ALA was detected at 6 mm using autoradiography after 2 h, with LSC showing phototoxic concentrations at 2.375 mm after 4 h of application. Inclusion of oleic acid and dimethyl sulphoxide in bioadhesive patches increased 5-ALA significantly in neonate porcine tissue, but only for patches cast from blends containing 5% w/w oleic acid. CONCLUSIONS: The bioadhesive patch described delivered 5-ALA to depths of at least 2.5 mm in tissue types indicative of vulval skin, suggesting that photodynamic therapy of deep vulval intraepithelial neoplasia is feasible using this means of bioadhesive 5-ALA delivery.

Influence of solution viscosity and injection protocol on distribution patterns of jet injectors: application to photodynamic tumour targeting.

Photodynamic therapy of deep or nodular skin tumours is currently limited by the poor tissue penetration of the porphyrin precursor 5-aminolevulinic acid (ALA) and preformed photosensitisers. In this study, we investigated the potential of jet injection to deliver both ALA and a preformed photosensitiser (meso-tetra (N-methyl-4-pyridyl) porphine tetra tosylate, TMP) into a defined volume of skin. Initial studies using a model hydrogel showed that as standoff distance is increased, injection depth decreases. As the ejected volume is increased, injection depth increases. It was also shown, for the first time, that, as injection solution viscosity was increased, for a given injection setting and standoff distance, both total depth of jet penetration, L(t), and depth at which the maximum width of the penetration pattern occurred, L(m), decreased progressively. For a standoff distance of zero, the maximum width of the penetration pattern, L(w), increased progressively with increasing viscosity at each of the injection settings. Conversely, when the standoff distance was 2.5 mm, L(w) decreased progressively with increasing viscosity. Studies with neonate porcine skin revealed that an injection protocol comprising an 8.98 mPas solution, an arbitrary injection setting of 8 and a standoff distance of zero was capable of delivering photosensitisers to a volume of tissue (L(t) of 2.91 mm, L(m) of 2.14 mm, L(w) of 5.10 mm) comparable to that occupied by a typical nodular basal cell carcinoma. Both ALA and TMP were successfully delivered using jet injection, with peak tissue concentrations (67.3 mg cm(-3) and 5.6 mg cm(-3), respectively) achieved at a depth of around 1.0mm and substantial reductions in drug concentration seen at depths below 3.0 mm. Consequently, jet injection may be suitable for selective targeting of ALA or preformed photosensitisers to skin tumours.