Search

Hair follicle-penetrating nanoparticles offer a promising avenue for targeted antibiotic delivery, especially in challenging infections like acne inversa or folliculitis decalvans. However, demonstrating their efficacy with existing preclinical models remains difficult. This study presents an innovative approach using a 3D in vitro organ culture system with human hair follicles to investigate the hypothesis that antibiotic nanocarriers may reach bacteria within the follicular cleft more effectively than free drugs. Living human hair follicles were transplanted into a collagen matrix within a 3D printed polymer scaffold to replicate the follicle's microenvironment. Hair growth kinetics over 7 days resembled those of simple floating cultures. In the 3D model, fluorescent nanoparticles exhibited some penetration into the follicle, not observed in floating cultures. Staphylococcus aureus bacteria displayed similar distribution profiles postinfection of follicles. While rifampicin-loaded lipid nanocapsules were as effective as free rifampicin in floating cultures, only nanoencapsulated rifampicin achieved the same reduction of CFU/mL in the 3D model. This underscores the hair follicle microenvironment's critical role in limiting conventional antibiotic treatment efficacy. By mimicking this microenvironment, the 3D model demonstrates the advantage of topically administered nanocarriers for targeted antibiotic therapy against follicular infections.

Biofilm-associated infections are causing over half a million deaths each year, raising the requirement for innovative therapeutic approaches. For developing novel therapeutics against bacterial biofilm infections, complex in vitro models that allow to study drug effects on both pathogens and host cells as well as their interaction under controlled, physiologically relevant conditions appear as highly desirable. Nonetheless, building such models is quite challenging because (1) rapid bacterial growth and release of virulence factors may lead to premature host cell death and (2) maintaining the biofilm status under suitable co-culture requires a highly controlled environment. To approach that problem, we chose 3D bioprinting. However, printing living bacterial biofilms in defined shapes on human cell models, requires bioinks with very specific properties. Hence, this work aims to develop a 3D bioprinting biofilm method to build robust in vitro infection models. Based on rheology, printability and bacterial growth, a bioink containing 3% gelatin and 1% alginate in Luria-Bertani-medium was found optimal for Escherichia coli MG1655 biofilms. Biofilm properties were maintained after printing, as shown visually via microscopy techniques as well as in antibiotic susceptibility assays. Metabolic profile analysis of bioprinted biofilms showed high similarity to native biofilms. After printing on human bronchial epithelial cells (Calu-3), the shape of printed biofilms was maintained even after dissolution of non-crosslinked bioink, while no cytotoxicity was observed over 24 h. Therefore, the approach presented here may provide a platform for building complex in vitro infection models comprising bacterial biofilms and human host cells., (Creative Commons Attribution license.)

The steady improvement and optimization of transdermal permeation is a constant and challenging pharmaceutical task. In this study the influence of poly(lactide-co-glycolide) (PLGA) nanoparticles on the dermal permeation of the anti-inflammatory drug flufenamic acid (FFA) was investigated. For this aim, different vehicles under non-buffered and buffered conditions and different skin models (human heat separated epidermis and reconstructed human epidermis equivalents) were tested. Permeation experiments were performed using static Franz diffusion cells under infinite dosing conditions. Already the presence of drug-free nanoparticles increased drug permeation across the skin. Drug permeation was even enhanced when applying drug-loaded nanoparticles. In contrast, buffered vehicles with different pH values (pH 5.4-7.4) revealed the influence of the pH on the permeation of FFA. The change of the surrounding pH of the biodegradable nanoparticulate system was demonstrated and visualized using pH-sensitive fluorescent probes. While a potential contribution of hair follicles could be ruled out, our data suggest that the enhanced permeation of FFA through human skin in the presence of PLGA nanoparticles is mediated by a locally decreased pH during hydrolytic degradation of this polymer. This hypothesis is supported by the observation that skin permeation of the weak base caffeine was not affected.

Tofacitinib (TFB), a Janus kinase inhibitor, has shown excellent success off-label in treating various dermatological diseases, especially alopecia areata (AA). However, TFB's safe and targeted delivery into hair follicles (HFs) is highly desirable due to its systemic adverse effects. Nanoparticles (NPs) can enhance targeted follicular drug delivery and minimize interfollicular permeation and thereby reduce systemic drug exposure. In this study, we report a facile method to assemble the stable and uniform 240 nm TFB loaded squalenyl derivative (SqD) nanoparticles (TFB SqD NPs) in aqueous solution, which allowed an excellent loading capacity (LC) of 20%. The SqD NPs showed an enhanced TFB delivery into HFs compared to the aqueous formulations of plain drug in an ex vivo pig ear model. Furthermore, the therapeutic efficacy of the TFB SqD NPs was studied in a mouse model of allergic dermatitis by ear swelling reduction and compared to TFB dissolved in a non-aqueous mixture of acetone and DMSO (7:1 v / v ). Whereas such formulation would not be acceptable for use in the clinic, the TFB SqD NPs dispersed in water illustrated a better reduction in inflammatory effects than plain TFB's aqueous formulation, implying both encouraging good in vivo efficacy and safety. These findings support the potential of TFB SqD NPs for developing a long-term topical therapy of AA.

Limited drug loading capacity (LC), mostly below 5% w/w, is a significant drawback of nanoparticulate drug delivery systems (DDS). Squalenoylation technology, which employs bioconjugation of squalenyl moiety and drug, allows self-assemble of nanoparticles (NPs) in aqueous media with significantly high LC (>30% w/w). The synthesis and particle preparation of squalenoylated prodrugs are, however, not facile for molecules with multiple reactive groups. Taking a different approach, we describe the synthesis of amphiphilic squalenyl derivatives (SqDs) as well as the physicochemical and biopharmaceutical characterizations of their self-assembled NPs as DDSs. The SqDs included in this study are (i) cationic squalenyl diethanolamine (ii) PEGylated SqD (PEG 750 Da), (iii) PEGylated SqD (PEG 3,000 Da), and (iv) anionic squalenyl hydrogen sulfate. All four SqDs self-assemble into NPs in a size range from 100 to 200 nm in an aqueous solution. Furthermore, all NP derivatives demonstrate appropriate biocompatibility and adequate colloidal stability in physiological relevant pH environments. The mucoprotein binding of PEGylated NPs is reduced compared to the charged NPs. Most importantly, this technology allows excellent LC (at maximum of 45% w/w) of a wide range of multifunctional compounds, varying in physicochemical properties and molecular weight. Interestingly, the drug release profile can be tuned by different loading methods. In summary, the SqD-based NPs appear as versatile drug delivery platforms., (Copyright © 2020 Ho, Christmann, Murgia, De Rossi, Frisch, Koch, Schaefer, Loretz, Desmaele, Couvreur and Lehr.)

The conducting airways of the human lungs are lined by mucus, which lubricates the lung epithelium and provides a first-line protection against airborne threats. As a novel approach for visualization of the human mucus microstructure, we applied confocal Raman microscopy as a label-free and chemically selective technique. We were successfully able to chemically resolve the pulmonary surfactant from the mucus matrix and show its spatial distribution, as well as to visualize the structural changes within the freeze-dried mucus mesh upon chemical mucolysis. Subsequently, we performed rheological measurements before and after mucolysis and correlated morphology and chemical structure of the mucus with its rheological characteristics. These results do not only enrich the knowledge about the mucus microstructure, but can also, significantly contribute to rational development of future lung therapeutics., (Copyright © 2017 Elsevier B.V. All rights reserved.)

Native horse mucus is characterized with micro- and macrorheology and compared to hydroxyethylcellulose (HEC) gel as a model. Both systems show comparable viscoelastic properties on the microscale and for the HEC the macrorheology is in good agreement with the microrheology. For the mucus, the viscoelastic moduli on the macroscale are several orders of magnitude larger than on the microscale. Large amplitude oscillatory shear experiments show that the mucus responds nonlinearly at much smaller deformations than HEC. This behavior fosters the assumption that the mucus has a foam like structure on the microscale compared to the typical mesh like structure of the HEC, a model that is supported by cryogenic-scanning-electron-microscopy (CSEM) images. These images allow also to determine the relative amount of volume that is occupied by the pores and the scaffold. Consequently, we can estimate the elastic modulus of the scaffold. We conclude that this particular foam like microstructure should be considered as a key factor for the transport of particulate matter which plays a central role in mucus function with respect to particle penetration., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

In this study we have applied a model to explain the reported subdiffusion of particles in mucus, based on the measured mean squared displacements (MSD). The model considers Brownian diffusion of particles in a confined geometry, made from permeable membranes. The applied model predicts a normal diffusive behavior at very short and long time lags, as observed in several experiments. In between these timescales, we find that the "subdiffusive" regime is only a transient effect, MSD∝τ α ,α<1. The only parameters in the model are the diffusion-coefficients at the limits of very short and long times, and the distance between the permeable membranes L. Our numerical results are in agreement with published experimental data for realistic assumptions of these parameters. Finally, we show that only particles with a diameter less than 40 nm are able to pass through a mucus layer by passive Brownian motion., (Copyright © 2017. Published by Elsevier Inc.)

Lung lining fluid is the first biological barrier nanoparticles (NPs) encounter during inhalation. As previous inhalation studies revealed considerable differences between surface functionalized NPs with respect to deposition and toxicity, our aim was to investigate the influence of lipid and/or protein binding on these processes. Thus, we analyzed a set of surface functionalized NPs including different SiO2 and ZrO2 in pure phospholipids, CuroSurf(TM) and purified native porcine pulmonary surfactant (nS). Lipid binding was surprisingly low for pure phospholipids and only few NPs attracted a minimal lipid corona. Additional presence of hydrophobic surfactant protein (SP) B in CuroSurf(TM) promoted lipid binding to NPs functionalized with Amino or PEG residues. The presence of the hydrophilic SP A in nS facilitated lipid binding to all NPs. In line with this the degree of lipid and protein affinities for different surface functionalized SiO2 NPs in nS followed the same order (SiO2 Phosphate ∼ unmodified SiO2 < SiO2 PEG < SiO2 Amino NPs). Agglomeration and biomolecule interaction of NPs in nS was mainly influenced by surface charge and hydrophobicity. Toxicological differences as observed in short-term inhalation studies (STIS) were mainly influenced by the core composition and/or surface reactivity of NPs. However, agglomeration in lipid media and lipid/protein affinity appeared to play a modulatory role on short-term inhalation toxicity. For instance, lipophilic NPs like ZrO2, which are interacting with nS to a higher extent, exhibited a far higher lung burden than their hydrophilic counterparts, which deserves further attention to predict or model effects of respirable NPs.

Aim of this study was to investigate the similarities and differences at macro- and microscale in the viscoelastic properties of mucus that covers the epithelia of the intestinal and respiratory tract. Natural mucus was collected from pulmonary and intestinal regions of healthy pigs. Macro-rheological investigations were carried out through conventional plate-plate rheometry. Microrheology was investigated using optical tweezers. Our data revealed significant differences both in macro- and micro-rheological properties between respiratory and intestinal mucus., (Copyright © 2016 Elsevier B.V. All rights reserved.)

We investigated the rheological properties and the penetration of differently sized carboxylated nanoparticles in pig pulmonary mucus, on different distance and time scales. Nanoparticles were either mechanically mixed into the mucus samples or deposited as an aerosol, the latter resembling a more physiologically relevant delivery scenario. After mechanical dispersion, 500 nm particles were locally trapped; a fraction of carboxylated tracer particles of 100 or 200 nm in diameter could however freely diffuse in these networks over distances of approximately 20 μm. In contrast, after aerosol deposition on top of the mucus layer only particles with a size of 100 nm were able to penetrate into mucus, suggesting the presence of smaller pores at the air-mucus interface compared to within mucus. These findings are relevant to an understanding of the fate of potentially harmful aerosol particles, such as pathogens, pollutants, and other nanomaterials after incidental inhalation, as well as for the design of pulmonary drug delivery systems.

The treatment of various hair disorders has become a central focus of good dermatologic patient care as it affects men and women all over the world. For many inflammatory-based scalp diseases, glucocorticoids are an essential part of treatment, even though they are known to cause systemic as well as local adverse effects when applied topically. Therefore, efficient targeting and avoidance of these side effects are of utmost importance. Optimizing the balance between drug release, interfollicular permeation, and follicular uptake may allow minimizing these adverse events and simultaneously improve drug delivery, given that one succeeds in targeting a sustained release formulation to the hair follicle. To test this hypothesis, three types of polymeric nanocarriers (nanospheres, nanocapsules, lipid-core nanocapsules) for the potent glucocorticoid clobetasol propionate (CP) were prepared. They all exhibited a sustained release of drug, as was desired. The particles were formulated as a dispersion and hydrogel and (partially) labeled with Rhodamin B for quantification purposes. Follicular uptake was investigated using the Differential Stripping method and was found highest for nanocapsules in dispersion after application of massage. Moreover, the active ingredient (CP) as well as the nanocarrier (Rhodamin B labeled polymer) recovered in the hair follicle were measured simultaneously, revealing an equivalent uptake of both. In contrast, only negligible amounts of CP could be detected in the hair follicle when applied as free drug in solution or hydrogel, regardless of any massage. Skin permeation experiments using heat-separated human epidermis mounted in Franz Diffusion cells revealed equivalent reduced transdermal permeability for all nanocarriers in comparison to application of the free drug. Combining these results, nanocapsules formulated as an aqueous dispersion and applied by massage appeare to be a good candidate to maximize follicular targeting and minimize drug penetration into the interfollicular epidermis. We conclude that such nanotechnology-based formulations provide a viable strategy for more efficient drug delivery to the hair follicle. Moreover, they present a way to minimize adverse effects of potent glucocorticoids by releasing the drug in a controlled manner and simultaneously decreasing interfollicular permeation, offering an advantage over conventional formulations for inflammatory-based skin/scalp diseases., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Follicular penetration has gained increasing interest regarding (i) safety concerns about (environmentally born) xenobiotics available to the hair follicle (HF), e.g. nanomaterials or allergens which should not enter the skin, and (ii) the possibility for non-invasive follicular drug and antigen delivery. However, not much is known about barriers in the HF which have to be surpassed upon uptake and/or penetration into surrounding tissue. Thus, aim of this work was a detailed investigation of this follicular barrier function, as well as particle uptake into the HF of porcine skin which is often used as a model system for human skin for such purposes. We show that follicular tight junctions (TJs) form a continuous barrier from the infundibulum down to the suprabulbar region, complementary to the stratum corneum in the most exposed upper follicular region, but remaining as the only barrier in the less accessible lower follicular regions. In the bulbar region of the HF no TJ barrier was found, demonstrating the importance of freely supplying this hair-forming part with e.g. nutrients or hormones from the dermal microenvironment. Moreover, the dynamic character of the follicular TJ barrier was shown by modulating its permeability using EDTA. After applying polymeric model-nanoparticles (154 nm) to the skin, transmission electron microscopy revealed that the majority of the particles were localized in the upper part of the HF where the double-barrier is present. Only few penetrated deeper, reaching regions where TJs act as the only barrier, and no particles were observed in the bulbar, barrier-less region. Lastly, the equivalent expression and distribution of TJ proteins in human and porcine HF further supports the suitability of porcine skin as a predictive model to study the follicular penetration and further biological effects of dermally applied nanomaterials in humans., (Copyright © 2016 Elsevier GmbH. All rights reserved.)

Pulmonary surfactant (PS) constitutes the first line of host defense in the deep lung. Because of its high content of phospholipids and surfactant specific proteins, the interaction of inhaled nanoparticles (NPs) with the pulmonary surfactant layer is likely to form a corona that is different to the one formed in plasma. Here we present a detailed lipidomic and proteomic analysis of NP corona formation using native porcine surfactant as a model. We analyzed the adsorbed biomolecules in the corona of three NP with different surface properties (PEG-, PLGA-, and Lipid-NP) after incubation with native porcine surfactant. Using label-free shotgun analysis for protein and LC-MS for lipid analysis, we quantitatively determined the corona composition. Our results show a conserved lipid composition in the coronas of all investigated NPs regardless of their surface properties, with only hydrophilic PEG-NPs adsorbing fewer lipids in total. In contrast, the analyzed NP displayed a marked difference in the protein corona, consisting of up to 417 different proteins. Among the proteins showing significant differences between the NP coronas, there was a striking prevalence of molecules with a notoriously high lipid and surface binding, such as, e.g., SP-A, SP-D, DMBT1. Our data indicate that the selective adsorption of proteins mediates the relatively similar lipid pattern in the coronas of different NPs. On the basis of our lipidomic and proteomic analysis, we provide a detailed set of quantitative data on the composition of the surfactant corona formed upon NP inhalation, which is unique and markedly different to the plasma corona.

For some time, in-silico models to address substance transport into and through the skin are gaining more and more importance in different fields of science and industry. In particular, the mathematical prediction of in-vivo skin absorption is of great interest to overcome ethical and economical issues. The presented work outlines a strategy to address this problem and in particular, investigates in-vitro and in-vivo skin penetration experiments of the model compound flufenamic acid solved in an ointment by means of a mathematical model. Experimental stratum corneum concentration-depth profiles (SC-CDP) for various time intervals using two different in-vitro systems (Franz diffusion cell, Saarbruecken penetration model) were examined and simulated with the help of a highly optimized three compartment numerical diffusion model and compared to the findings of SC-CDPs of the in-vivo scenario. Fitted model input parameters (diffusion coefficient and partition coefficient with respect to the stratum corneum) for the in-vitro infinite dose case could be used to predict the in-use conditions in-vitro. Despite apparent differences in calculated partition coefficients between in-vivo and in-vitro studies, prediction of in-vivo scenarios from input parameters calculated from the in-vitro case yielded reasonable results., (Copyright © 2015 Elsevier B.V. All rights reserved.)

Introduction: Mathematical models of dermal transport offer the advantages of being much faster and less expensive than in vitro or in vivo studies. The number of methods used to create such models has been increasing rapidly, probably due to the steady rise in computational power. Although each of the various approaches has its own virtues and limitations, it may be difficult to decide which approach is best suited to address a given problem., Areas Covered: Here we outline the basic ideas, drawbacks and advantages of compartmental and quantitative structure-activity relationship models, as well as of analytical and numerical approaches for solving the diffusion equation. Examples of special applications of the different approaches are given., Expert Opinion: Although some models are sophisticated and might be used in future to predict transport through damaged or diseased skin, the comparatively low availability of suitable and accurate experimental data limits extensive usage of these models and their predictive accuracy. Due to the lack of experimental data, the possibility of validating mathematical models is limited.

Appropriate setting of dissolution specification of extended release (ER) formulations should include precise definition of a multidimensional space of complex definition and interpretation, including limits in dissolution parameters, lag time (t-lag), variability, and goodness of fit. This study aimed to set dissolution specifications of ER by developing drug-specific dissolution profile comparison tests (DPC tests) that are able to detect differences in release profiles between ER formulations that represent a lack of bioequivalence (BE). Dissolution profiles of test formulations were simulated using the Weibull and Hill models. Differential equations based in vivo-in vitro correlation (IVIVC) models were used to simulate plasma concentrations. BE trial simulations were employed to find the formulations likely to be declared bioequivalent and nonbioequivalent (BE space). Customization of DPC tests was made by adjusting the delta of a recently described tolerated difference test (TDT) or the limits of rejection of f2. Drug ka (especially if ka is small), formulation lag time (t-lag), the number of subjects included in the BE studies, and the number of sampled time points in the DPC test were the factors that affected the most these setups of dissolution specifications. Another recently described DPC test, permutation test (PT), showed excellent statistical power. All the formulations declared as similar with PT were also bioequivalent. Similar case-specific studies may support the biowaiving of ER drug formulations based on customized DPC tests.

Drug delivery via the hair follicle (HF) especially with nanoparticles (NP) recently gained attention due to a depot effect and facilitated absorption conditions within the lower HF. With the prospect of transdermal drug delivery, it is of interest to optimize the follicular uptake of NP. In this study, a method was developed to quantify NP uptake into HF and applied in vitro in a pig ear model and in vivo in human volunteers. The influence of NP material on HF uptake was investigated using fluorescence-labeled NP based on poly(D,L-lactide-co-glycolide) (PLGA). All NP had similar hydrodynamic sizes (163-170 nm) but different surface modifications: (i) plain PLGA, (ii) chitosan-coated PLGA (Chit.-PLGA), and (iii) Chit.-PLGA coated with different phospholipids (PL) (DPPC (100), DPPC:Chol (85:15), and DPPC:DOTAP (92:8). Differential stripping was performed, including complete mass balance. The samples were extracted for fluorescence quantification. An effect of the PL coating on follicular uptake was observed as DPPC (100) and DPPC:DOTAP (92:8) penetrated into HF to a higher extent than the other tested NP. The effect was observed both in the pig ear model as well as in human volunteers, although it was statistically significant only in the in vitro model. An excellent in vitro-in vivo correlation (IVIVC, r(2)=0.987) between both models was demonstrated, further supporting the suitability of the pig ear model as a surrogate for the in vivo situation in humans for quantifying NP uptake into HF. These findings may help to optimize NP for targeting the HF and to improve transdermal delivery., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Aim of this study was to implement a modified phospholipid vesicle-based permeation assay (PVPA) barrier as alternative to Caco-2 cell monolayers in a combined dissolution and permeation system for testing of solid dosage forms. Commercially available Transwell® inserts were coated with egg phospholipids (Lipoid E 80) and characterized by confocal Raman microscopy. The modified PVPA barrier was then evaluated in permeation studies with solutions of different drugs as well as in combined dissolution and permeation studies utilizing an immediate and an extended release tablet formulation. Raman cross section images demonstrated complete filling of the membrane pores with lipids and the formation of a continuous lipid layer of increasing thickness on top of the membrane during the stepwise coating procedure. Furthermore, it could be shown that this lipid coating remains intact for at least 18h under dynamic flow conditions, significantly exceeding the viability of Caco-2 cell monolayers. Permeability data for both drug solutions as well as for a fast and slow release tablet formulation were in excellent correlation with those data obtained for Caco-2 cell monolayers. Especially under the dynamic flow conditions prevailing in such a setup, the modified PVPA barrier is more robust and easier to handle than epithelial cell monolayers and can be prepared rather easily at a fraction of costs and time. The modified PVPA barrier may therefore represent a valuable alternative to Caco-2 cell monolayers in such context., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Transfollicular vaccination aims to reach the peri-follicular antigen presenting cells without impairing the stratum corneum (SC) barrier. This would be an optimal vaccination strategy under critical hygienic conditions. Nanoparticles (NPs) are the ideal vehicles for transfollicular delivery of vaccines as they are able to (i) penetrate deeper into the hair follicles than molecules in solution, (ii) can help to stabilize protein based antigen and (iii) improve and modulate the immune response. This study investigates the potential of transfollicular delivery of polymeric NPs using ovalbumin (OVA) as a model antigen. NPs were prepared by a double emulsion method from pharmaceutically well characterized biocompatible and biodegradable polymers poly(lactide-co-glycolide) (PLGA) or chitosan-coated PLGA (Chit-PLGA) using polyvinyl alcohol as stabilizer. The NP formulations are available as freeze dried product which can be re-constituted with water or cell culture medium before use to yield any desired OVA/NP concentration. OVA was protected from cleavage or aggregation inside the NPs and retained its biological activity to 74% (PLGA) and 64% (Chit-PLGA). Thus, when applying a typical dose of 8.5 μl/cm(2) NP formulation (50mg NPs/ml, 54.3±0.047 and 66.5±0.044 μg OVA/mg NPs for PLGA and Chit-PLGA NPs, respectively) an effective dose of 17 μg/cm(2) (PLGA) or 18 μg/cm(2) (Chit-PLGA) of active OVA is administered. In a cell culture assay encapsulated OVA stimulated the proliferation of CD4+ (PLGA and Chit-PLGA) and CD8+ T-cells (only Chit-PLGA) to a larger extent than OVA in solution. An adoptive transfer experiment demonstrated that the model antigen OVA can be delivered via the transfollicular route. This preliminary experiment is a proof of concept that by this transfollicular immunization approach it is possible to deliver antigens, thereby stimulating antigen-specific T cells. Both NP formulations improved the delivery efficiency of OVA into the hair follicles on excised pig ears by a factor of 2-3 compared to OVA solution. This delivery efficiency could further be increased by increasing the number of NPs applied per skin area by a factor of ≈2-2.4. Consequently formulation of OVA into PLGA and Chit-PLGA NPs may offer to reduce the dose which needs to be applied for transfollicular immunization., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

Understanding the penetration behaviour of drugs into human skin is a prerequisite for the rational development and evaluation of effective dermal drug delivery. The general procedure for the acquisition of quantitative drug penetration profiles in human skin is performed by sequential segmentation and extraction. Unfortunately, this technique is destructive, laborious and lacks spatial resolution. Confocal Raman microscopy bares the potential of a chemically selective, label free and nondestructive analysis. However, the acquisition of quantitative drug depth profiles within skin by Raman microscopy is impeded by imponderable signal attenuation inside the tissue. In this study, we present a chemical semi-solid matrix system simulating the optical properties of human skin. This system serves as a skin surrogate for investigation of Raman signal attenuation under controlled conditions. Caffeine was homogeneously incorporated within the skin surrogate, and Raman intensity depth profiles were acquired. A mathematical algorithm describing the Raman signal attenuation within the surrogate was derived from these profiles. Human skin samples were incubated with caffeine, and Raman intensity depth profiles were similarly acquired. The surrogate algorithm was successfully applied to correct the drug profiles in human skin for signal attenuation. For the first time, a mathematical algorithm was established, which allows correction of Raman signal attenuation in human skin, thus facilitating reliable drug quantification in human skin by confocal Raman spectroscopy., (Copyright © 2012 Elsevier B.V. All rights reserved.)

This special issue compiles invited and contributed papers of the 9th International Conference and Workshop "Biological Barriers", 29 February-9 March 2012 at Saarland University, Saarbrücken Germany., (Copyright © 2013. Published by Elsevier B.V.)

Due to the increased demand for reliable data regarding penetration into and permeation across human skin, assessment of the absorption of xenobiotics has been gaining in importance steadily. In vitro experiments allow for determining these data faster and more easily than in vivo experiments. However, the experiments described in literature and the subsequent evaluation procedures differ considerably. Here we will give an overview on typical finite and infinite dose experiments performed in fundamental research and on the evaluation of the data. We will point out possible difficulties that may arise and give a short overview on attempts at predicting skin absorption in vitro and in vivo., (Copyright © 2012 Elsevier B.V. All rights reserved.)

To use a diffusion model for predicting skin absorption requires accurate estimates of input parameters on model geometry, affinity and transport characteristics. This review summarizes methods to obtain input parameters for diffusion models of skin absorption focusing on partition and diffusion coefficients. These include experimental methods, extrapolation approaches, and correlations that relate partition and diffusion coefficients to tabulated physico-chemical solute properties. Exhaustive databases on lipid-water and corneocyte protein-water partition coefficients are presented and analyzed to provide improved approximations to estimate lipid-water and corneocyte protein-water partition coefficients. The most commonly used estimates of lipid and corneocyte diffusion coefficients are also reviewed. In order to improve modeling of skin absorption in the future diffusion models should include the vertical stratum corneum heterogeneity, slow equilibration processes, the absorption from complex non-aqueous formulations, and an improved representation of dermal absorption processes. This will require input parameters for which no suitable estimates are yet available., (Copyright © 2012 Elsevier B.V. All rights reserved.)

The most popular way of comparing oral solid forms of drug formulations from different batches or manufacturers is through dissolution profile comparison. Usually, a similarity factor known as (f2) is employed; However, the level of confidence associated with this method is uncertain and its statistical power is low. In addition, f2 lacks the flexibility needed to perform in special scenarios. In this study two new statistical tests based on nonparametrical Permutation Test theory are described, the Permutation Test (PT), which is very restrictive to confer similarity, and the Tolerated Difference Test (TDT), which has flexible restrictedness to confer similarity, are described and compared to f2. The statistical power and robustness of the tests were analyzed by simulation using the Higuchi, Korsmayer, Peppas and Weibull dissolution models. Several batches of oral solid forms were simulated while varying the velocity of dissolution (from 30 min to 300 min to dissolve 85% of the total content) and the variability within each batch (CV 2-30%). For levels of variability below 10% the new tests exhibited better statistical power than f2 and equal or better robustness than f2. TDT can also be modified to distinguish different levels of similarity and can be employed to obtain customized comparisons for specific drugs. In conclusion, two new methods, more versatile and with a stronger statistical basis than f2, are described and proposed as viable alternatives to that method. Additionally, an optimized time sampling strategy and an experimental design-driven strategy for performing dissolution profile comparisons are described., (Copyright © 2012 Elsevier B.V. All rights reserved.)

This work investigates in vitro finite dose skin absorption of the model compounds flufenamic acid and caffeine experimentally and mathematically. The mass balance in different skin compartments (donor, stratum corneum (SC), deeper skin layers (DSL), lateral skin parts and acceptor) is analyzed as a function of time. For both substances high amounts were found in the lateral skin compartment after 6h of incubation, which emphasizes not to elide these parts in the modeling. Here, three different mathematical models were investigated and tested with the experimental data: a pharmacokinetic model (PK), a detailed microscopic two-dimensional diffusion model (MICRO) and a macroscopic homogenized diffusion model (MACRO). While the PK model was fitted to the experimental data, the MICRO and the MACRO models employed input parameters derived from infinite dose studies to predict the underlying diffusion process. All models could satisfyingly predict or describe the experimental data. The PK model and MACRO model also feature the lateral parts., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Skin penetration of nanoparticles is a recent research area in focus for the aim of development of topical nanoparticulate delivery systems as well as for health risk analysis. So far, monitoring skin penetration of nanoparticles is mostly based on qualitative microscopical examination. Here, we describe an experimental approach for extracting semiquantitative data from multiphoton images of skin specimens treated with gold nanoparticles. This will aid in depicting the factors responsible for enhancing or limiting nanoparticle penetration through the skin barrier.

This review presents an overview of German and Dutch research institutions and their studies in the field of skin drug delivery and adjacent topics. In the Netherlands, the involved research groups are mainly localized in Leiden, whereas in Germany the skin research institutions are spread over the whole country. The scientific studies in the Netherlands focus on the in-depth analysis of human skin composition and its individual components as well as on the development and characterization of dermal drug delivery systems ranging from liquid crystalline systems and vesicles up to microneedles with an emphasis on examining the interactions of these drug delivery systems with the human skin in vitro and in vivo. In Germany, the individual areas of research span from in-depth investigations on various drug delivery systems intended for skin application and the development of novel in vitro models for skin absorption testing up to in vivo studies focusing on the biological performance of topically applied actives. Furthermore, sophisticated analytical techniques are applied for the elucidation of skin assembly and transport processes. In addition, experimentally derived data are correlated with advanced computational modelling. Even though the individual research topics in the Netherlands and Germany are quite diverse, the exchange of knowledge and interdisciplinary collaborations between the two neighbouring countries were and are still frequently made. In this context, the review aims at highlighting crosslinks between the different institutions and individual persons to complete the picture. For each institution, the principal investigators and their studies are presented and the upcoming young scientists are introduced as an outlook for the field. This review does not claim completeness, but is rather intended to give a general overview of Dutch and German research in the field of skin drug delivery and adjacent topics., (© 2013 S. Karger AG, Basel.)

In this study, the mobility of nanoparticles in mucus and similar hydrogels as model systems was assessed to elucidate the link between microscopic diffusion behavior and macroscopic penetration of such gels. Differences in particle adhesion to mucus components were strongly dependent on particle coating. Particles coated with 2 kDa PEG exhibited a decreased adhesion to mucus components, whereas chitosan strongly increased the adhesion. Despite such mucoinert properties of PEG, magnetic nanoparticles of both coatings did not penetrate through native respiratory mucus, resisting high magnetic forces (even for several hours). However, model hydrogels were, indeed, penetrated by both particles in dependency of particle coating, obeying the theory of particle mobility in an external force field. Comparison of penetration data with cryogenic scanning EM images of mucus and the applied model systems suggested particularly high rigidity of the mucin scaffold and a broad pore size distribution in mucus as reasons for the observed particle immobilization. Active probing of the rigidity of mucus and model gels with optical tweezers was used in this context to confirm such properties of mucus on the microscale, thus presenting the missing link between micro- and macroscopical observations. Because of high heterogeneity in the size of the voids and pores in mucus, on small scales, particle mobility will depend on adhesive or inert properties. However, particle translocation over distances larger than a few micrometers is restricted by highly rigid structures within the mucus mesh.

Pulmonary delivery of drugs, particularly in the treatment of lung cancer, is an attractive strategy for future targeted therapy. In this context, inhalation of nanoplexes might offer a new mode for drug delivery in gene therapy. However, limited data are currently available demonstrating pulmonary delivery, cellular uptake as well as local tolerability in lung tissue. The aim of this study was to elucidate the pulmonary delivery, tissue distribution and local tolerability of aerosolized chitosan-coated poly(lactide-co-glycolide) based nanoplexes containing antisense 2'-O-Methyl RNA (OMR). Therefore, an aerosol of OMR-nanoplexes or OMR alone was administered intra-tracheally using the model of the isolated perfused and ventilated rat lung. Localization of OMR in rat lung tissue was examined by immunohistochemistry. Administration of the OMR-nanoplex formulation resulted in significantly higher cellular OMR uptake of the respiratory epithelium in contrast to the administration of OMR alone, indicating that drug administration via aerosolized nanoplexes is able to target lung tissue. No prominent changes in lung physiology parameters were observed following inhalation, suggesting good local tolerability of OMR-nanoplex formulation., (Copyright © 2012 Elsevier B.V. All rights reserved.)

Upon contact with the human body, nanomaterials are known to interact with the physiological surroundings, especially with proteins. In this context, we explored analytical methods to provide biologically relevant information, in particular for manufactured nanomaterials as produced by the chemical industry. For this purpose, we selected two batches of SiO(2) nanoparticles as well as four batches of CeO(2) nanoparticles, each of comparably high chemical purity and similar physicochemical properties. Adsorption of serum proteins and bovine serum albumin (BSA) was quantified by SDS-PAGE in combination with densitometry and further investigated by atomic force microscopy (AFM) and analytical ultracentrifugation (AUC). The protein adsorption to SiO(2) nanoparticles was below the limit of detection, regardless of adjusting pH or osmolality to physiological conditions. In contrast, the four CeO(2) nanomaterials could be classified in two groups according to half-maximal protein adsorption. Measuring the work of adhesion and indention by AFM for the BSA-binding CeO(2) nanomaterials revealed the same classification, pointing to alterations in shape of the adsorbed protein. The same trend was also reflected in the agglomeration behavior/dispersibility of the four CeO(2) nanomaterials as revealed by AUC. We conclude that even small differences in physicochemical particle properties may nevertheless lead to differences in protein adsorption, possibly implicating a different disposition and other biological responses in the human body. Advanced analytical methods such as AFM and AUC may provide valuable additional information in this context.

The fate of inhaled particles after deposition onto the pulmonary mucosa is far from being solved, in particular with respect to mucociliary clearance and mucus penetration. Due to the fact that these phenomena govern pulmonary residence time and thus bioavailability, they are highly relevant for any kind of controlled release formulation delivered via that route. This study applies ex vivo and in silico approaches to investigate the dependency of muciliary clearance of micro-, submicrometer and nanoparticles on size, shape, charge and surface chemistry of such particles. In addition, measurement of mucociliary clearance of different particles also provided information about their penetration into mucus. Surprisingly, no significant differences in mucociliary clearance could be found for any type of particle under investigation. As revealed by computational modeling, particle penetration into the mucus gel layer was negligible at least within the time frame allowed by horizontal mucus transport. These data suggest that the observed lack of difference in mucociliary clearance is caused by the lack of immediate penetration of deposited aerosol particles through the mucus blanket., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Antisense oligonucleotide, 2'-O-Methyl-RNA (OMR), is known as potent telomerase inhibitor for the treatment of lung cancer but limited by poor intracellular uptake. Chitosan-coated polymeric nanoparticles were compared to chitosan solution as non-viral vectors for OMR. The study investigated the role of chitosan properties and concentration in improving the efficiency of the nanocarriers in terms of loading, viability, cellular uptake, and telomerase inhibition in human lung cancer cell lines. Certain concentration of chitosan on nanoparticle surface is necessary to significantly increase the cellular uptake. However, excessive chitosan negatively affected the transfection efficiency. Self-assembled nanoplexes with chitosan polymer are preferentially adsorbed to the cell membrane rather than being internalized. Thus, polymeric nanoparticles proved to be superior to cationic polymers as carrier for antisense oligonucleotides. Charge cannot be considered the principle factor behind improved transfection. Uptake studies carried out on air-interface cell cultures to mimic in vivo conditions supported the results on normal cultures showing enhanced uptake of nanoplexes over naked oligonucleotides. OMR nanoplexes reduced telomerase activity by ∼50% in A549 cells concluding the potential of the system as a safe, non-invasive, and efficient treatment for lung carcinoma. These data are prerequisites for the ongoing studies on lung perfusion model and in vivo experiments., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The peripheral lungs are a potential entrance portal for nanoparticles into the human body due to their large surface area. The fact that nanoparticles can be deposited in the alveolar region of the lungs is of interest for pulmonary drug delivery strategies and is of equal importance for toxicological considerations. Therefore, a detailed understanding of nanoparticle interaction with the structures of this largest and most sensitive part of the lungs is important for both nanomedicine and nanotoxicology. Astonishingly, there is still little known about the bio-nano interactions that occur after nanoparticle deposition in the alveoli. In this study, we compared the effects of surfactant-associated protein A (SP-A) and D (SP-D) on the clearance of magnetite nanoparticles (mNP) with either more hydrophilic (starch) or hydrophobic (phosphatidylcholine) surface modification by an alveolar macrophage (AM) cell line (MH-S) using flow cytometry and confocal microscopy. Both proteins enhanced the AM uptake of mNP compared with pristine nanoparticles; for the hydrophilic ST-mNP, this effect was strongest with SP-D, whereas for the hydrophobic PL-mNP it was most pronounced with SP-A. Using gel electrophoretic and dynamic light scattering methods, we were able to demonstrate that the observed cellular effects were related to protein adsorption and to protein-mediated interference with the colloidal stability. Next, we investigated the influence of various surfactant lipids on nanoparticle uptake by AM because lipids are the major surfactant component. Synthetic surfactant lipid and isolated native surfactant preparations significantly modulated the effects exerted by SP-A and SP-D, respectively, resulting in comparable levels of macrophage interaction for both hydrophilic and hydrophobic nanoparticles. Our findings suggest that because of the interplay of both surfactant lipids and proteins, the AM clearance of nanoparticles is essentially the same, regardless of different intrinsic surface properties.

The blood-air barrier formed by the alveolar epithelium of the peripheral lung is crucial for the pulmonary delivery of drugs. Most existing in vitro models mimicking the blood-air barrier are represented by tumor cells or immortalized cells and lack biological relevance due to their genetic alterations and underexpressed essential physiological functions. However, the increasing interest of aerosol administration of medicines to the respiratory system requires the development and use of representative in vitro models. Thereby, human alveolar epithelial cells (hAEpC) are a suitable test system allowing standardized toxicity and transport studies for newly developed compounds and delivery systems. The isolation, purification, and cultivation of hAEpC are described as well as their possible application in the so-called Pharmaceutical Aerosol Deposition Device On Cell Cultures (PADDOCC) mimicking the complete inhalation process of a powder aerosol in vitro.

Understanding the bio-nano interactions in the lungs upon the inhalation of nanoparticles is a major challenge in both pulmonary nanomedicine and nanotoxicology. To investigate the effect of pulmonary surfactant protein A (SP-A) on the interaction between nanoparticles and alveolar macrophages, we used magnetite nanoparticles (110-180 nm in diameter) coated with different polymers (starch, carboxymethyldextran, chitosan, poly-maleic-oleic acid, phosphatidylcholine). Cellular binding and uptake of nanoparticles by alveolar macrophages was increased for nanoparticles treated with SP-A, whereas albumin, the prevailing protein in plasma, led to a significant decrease. A significantly different adsorption pattern of SP-A, compared to albumin was found for these five different nanomaterials. This study provides evidence that after inhalation of nanoparticles, a different protein coating and thus different biological behavior may result compared to direct administration to the bloodstream., From the Clinical Editor: In this nano-toxicology study of inhaled nanoparticles, the authors investigated the effect of pulmonary surfactant protein A on the interaction between nanoparticles and alveolar macrophages utilizing magnetite nanoparticles coated with different polymers (starch, carboxymethyldextran, chitosan, poly-maleic-oleic acid, phosphatidylcholine). Cellular binding and uptake of nanoparticles increased for nanoparticles treated with SP-A, whereas albumin, the prevailing protein in plasma, led to a significant decrease., (Copyright © 2011 Elsevier Inc. All rights reserved.)

Nanoparticles delivery of oligonucleotides represents a potential approach for cancer treatment. However, most of the experiments were based on established cancer cell lines and may not reflect the original solid tumor in vivo. Both, tumor microenvironment and tumor cell biological properties in the tumor can influence the delivery efficiency of oligonucleotides. Therefore, it is important to understand the effect of nanoparticles delivery of oligonucleotides on tumor response in intact tissue architecture of individual tumors. We used freshly isolated human tumor tissue slices and primary lung cancer cells from non-small cell lung cancer patients to evaluate this nanocarrier system. Chitosan-coated poly(lactide-co-glycolide) (PLGA) nanoparticles were used to form oligonucleotide-nanoparticle-complexes (nanoplexes) with antisense 2'-O-methyl-RNA (OMR) that can inhibit telomerase activity by binding to the RNA component of telomerase. OMR cellular uptake was strongly enhanced by nanoplexes mediated delivery in both, primary cells and tissue slices. More than 80% of primary cancer cells and 50% of cells in tissue slices showed OMR uptake. Telomerase activity was inhibited by approximately 45% in primary cancer cells and about 40% in tissue slices. Nanoplexes could penetrate into tumor tissue without influencing tissue architecture and the delivered OMR was able to inhibit telomerase activity with relatively low cytotoxicity., (Copyright © 2011 Elsevier B.V. All rights reserved.)

The aims of this work were to increase the photostability and to reduce the skin permeation of tretinoin through nanoencapsulation. Tretinoin is widely used in the topical treatment of various dermatological diseases such as acne, psoriasis, skin cancer, and photoaging. Tretinoin-loaded lipid-core polymeric nanocapsules were prepared by interfacial deposition of a preformed polymer. Carbopol hydrogels containing nanoencapsulated tretinoin presented a pH value of 6.08±0.14, a drug content of 0.52±0.01 mg g(-1), pseudoplastic rheological behavior, and higher spreadability than a marketed formulation. Hydrogels containing nanoencapsulated tretinoin demonstrated a lower photodegradation (24.17±3.49%) than the formulation containing the non-encapsulated drug (68.64±2.92%) after 8h of ultraviolet A irradiation. The half-life of the former was seven times higher than the latter. There was a decrease in the skin permeability coefficient of the drug by nanoencapsulation, independently of the dosage form. The liquid suspension and the semisolid form provided K(p)=0.31±0.15 and K(p)=0.33±0.01 cm s(-1), respectively (p≤0.05), while the samples containing non-encapsulated tretinoin showed K(p)=1.80±0.27 and K(p)=0.73±0.12 cm s(-1) for tretinoin solution and hydrogel, respectively. Lag time was increased two times by nanoencapsulation, meaning that the drug is retained for a longer time on the skin surface., (Copyright © 2011 Elsevier B.V. All rights reserved.)

Diffusion modeling of dermal absorption relies in large part on high quality input data. Currently, estimates of corneocyte-phase partitioning are based on an analysis of a dataset of limited size and diversity. Therefore, we have updated and broadened the analysis. For this purpose, binding coefficients to different keratins, namely, bovine hoof and horn, human delipidized callus, human delipidized stratum corneum (SC), human nail, human hair, and sheep wool were collected from the literature. In addition, binding coefficients to hoof/horn and delipidized SC were measured for eight hydrophilic compounds including three ionizable compounds that were measured at different pH values. Important results are: (i) only hoof/horn, callus, and delipidized SC are suitable keratins for estimating corneocyte protein binding; (ii) binding coefficients to hoof/horn, callus, and delipidized SC can be predicted from the octanol-water partition coefficients log K(o/w) confirming the analysis of the limited dataset; (iii) binding of ionizable compounds can be predicted by correcting log K(o/w) for pH; (iv) the correlation derived for the extended database is steeper than the relationship derived for the limited dataset. This has consequences for the estimates of SC partition and diffusion coefficients for diffusion modeling of dermal absorption. ., (Copyright © 2010 Wiley-Liss, Inc.)

The alveolar lining fluid (ALF) covering the respiratory epithelium of the deep lung is the first biological barrier encountered by nanoparticles after inhalation. We here report for the first time significant differences for metal oxide nanoparticles to the binding of surfactant protein A (SP-A), the predominant protein component of ALF. SP-A is a physiologically most relevant protein and provides important biological signals. Also, it is involved in the lung's immune defence, controlling e.g. particle binding, uptake or transcytosis by epithelial cells and macrophages. In our study, we could prove different particle-protein interaction for eight different nanoparticles, whereas particles of the same bulk material revealed different adsorption patterns. In contrast to other proteins as bovine serum albumin (BSA), SP-A does not seem to significantly deagglomerate large agglomerates of particles, indicating different adsorption mechanisms as in the well-investigated model protein BSA. These findings may have important consequences for biological fate and toxicological effects of inhaled nanomaterials., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Absorption studies with aerosol formulation delivered by metered dose inhalers across cell- and tissue-based in vitro models of the pulmonary epithelia are not trivial due to the complexity of the processes involved: (i) aerosol generation and deposition, (ii) drug release from the carrier, and (iii) absorption across the epithelial air-blood barrier. In contrast to the intestinal mucosa, pulmonary epithelia are only covered by a thin film of lining fluid. Submersed cell culture systems would not allow to studying the deposition of aerosol particles and their effects on this delicate epithelial tissue. We developed a new Pharmaceutical Aerosol Deposition Device on Cell Cultures (PADDOCC) to mimic the inhalation of a single metered aerosol dose and its subsequent deposition on filter-grown pulmonary epithelial cell monolayers exposed to an air-liquid interface. The reproducibility of deposition of these dry powder aerosols and subsequent drug transport across Calu-3 monolayers with commercially available dry powder inhalers containing salbutamol sulphate or budesonide could be demonstrated. In the context of developing new dry powder aerosol formulations, PADDOCC appears as a useful tool, allowing reducing animal testing and faster translation into clinical trials., (Copyright © 2010 Elsevier B.V. All rights reserved.)

Highly optimized methods for skin segmentation are provided using tape stripping in combination with infrared absorption measurements for stratum corneum (SC) and cryosectioning for deeper skin layers. Furthermore, an example is calculated for demonstration of the respective procedures.

The skin is a large and accessible area of the body, offering the possibility to be used as an alternative route for drug delivery. In the last few years strong progress has been made on the developing of nanoparticulate systems for specific applications. The interaction of such small particles with human skin and their possible penetration attracted some interest from toxicological as well as from drug delivery perspectives. As size is assumed to play a key role, the aim of the present work was to investigate the penetration profile of very small model particles (approximately 4 nm) into excised human skin under conditions chosen to mimic the in vivo situation. Possible application procedures such as massaging the formulation (5 to 10 minutes) were analyzed by non-invasive multiphoton- and confocal laser scanning microscopy (MPM, CLSM). Furthermore, the application on damaged skin was taken into account by deliberately removing parts of the stratum corneum. Although it was clearly observed that the mechanical actions affected the distribution pattern of the QDs on the skin surface, there was no evidence of penetration into the skin in all cases tested. QDs could be found in deeper layers only after massaging of damaged skin for 10 min. Taking these data into account, obtained on the gold standard human skin, the potential applications of nanoparticulate systems to act as carrier delivering drugs into intact skin might be limited and are only of interest for partly damaged skin.

Telomerase as an enzyme is responsible for the renewal of the chromosomal ends, the so-called telomeres. By preventing them from shortening with each cell cycle, telomerase is able to inhibit cellular senescence and apoptosis. Telomerase activity, which is detectable in the majority of cancer cells, allows them to maintain their proliferative capacity. The thus obtained immortality of those cells again is a key to their malignancy. Based on these discoveries, it is obvious that telomerase inhibitors would represent an innovative approach to fight cancer, and a variety of such candidate molecules are currently in the pipeline. Telomerase inhibitors largely fall in two classes of compounds: small synthetic molecules and nucleotide-based biologicals. For several candidates, some proof of concept studies have been demonstrated, either on cell cultures or in animal models. But the same studies also revealed that inefficient delivery is largely limiting the translational step into the clinic. The most appealing feature of telomerase inhibitors, which distinguishes them from conventional anticancer drugs, is probably seen in their intrinsic non-toxicity to normal cells. Nevertheless, efficient delivery to the target cells, i.e. to the tumor, is still required. Here, some well-known biopharmaceutical problems such as insufficient solubility, permeability or even metabolic stability are frequently encountered. To address these challenges, there is a clear need for adequate delivery technologies, for example by using nanomedicines, that would allow to overcome their biopharmaceutical shortcomings and to warrant a sufficient bioavailability at the target side. This review first briefly explains the concept of telomerase and telomerase inhibition in cancer therapy. It secondly aims to provide an overview of the different currently known telomerase inhibitors. Finally, the biopharmaceutical limitations of these molecules are discussed as well as the possibilities to overcome those limits by novel drug carrier systems and formulation approaches., (Copyright 2010 Elsevier B.V. All rights reserved.)

The development of aerosol medicines typically involves numerous tests on animals, due to the lack of adequate in vitro models. A new in vitro method for testing pharmaceutical aerosol formulations on cell cultures was developed, consisting of an aerosolisation unit fitting a commercial dry powder inhaler (HandiHaler(c), Boehringer Ingelheim, Germany), an air-flow control unit (Akita(c), Activaero, Germany) and a custom-made sedimentation chamber. This chamber holds three Snapwell(c) inserts with monolayers of pulmonary epithelial cells. The whole set-up, referred to as the Pharmaceutical Aerosol Deposition Device On Cell Cultures (PADDOCC) system, aims to mimic the complete process of aerosol drug delivery, encompassing aerosol generation, aerosol deposition onto pulmonary epithelial cells and subsequent drug transport across this biological barrier, to facilitate the investigation of new aerosol formulations in the early stages of development. We describe here, the development of the design and the protocol for this device. By testing aerosol formulations of budesonide and salbutamol sulphate, respectively, reproducible deposition of aerosol particles on, and the integrity of, the pulmonary cell monolayer could be demonstrated., (2010 FRAME.)