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Inhalation therapy has been reported as the most effective treatment for respiratory bacterial infections due to the increasing relevance of drug bioavailability. Drug delivery systems (DDS) have the capacity to overcome pulmonary biological barriers limiting the bioavailability of inhaled anti-infectives. This is important to eradicate bacterial infections and to prevent the development of bacterial resistance. Despite substantial efforts in the field, the current state-of-the-art often fails to achieve those goals, and we still observe increasing bacterial resistance. We give a brief insight on benefits and challenges in pulmonary delivery of anti-infectives. In the context of drug delivery development for pulmonary infections, particularly focusing on Pseudomonas aeruginosa (PA) infections, this mini review will critically discuss the main requirements, as well as the recent strategies of drug delivery system synthesis and preparation. Finally, interaction of DDS with crucial pulmonary biological barriers will be of great importance for the success of future applications of the developed DDS.

Mucus covers all wet epithelia and acts as a protective barrier. In the airways of the lungs, the viscoelastic mucus meshwork entraps and clears inhaled materials and efficiently removes them by mucociliary escalation. In addition to physical and chemical interaction mechanisms, the role of macromolecular glycoproteins (mucins) and antimicrobial constituents in innate immune defense are receiving increasing attention. Collectively, mucus displays a major barrier for inhaled aerosols, also including therapeutics. This review discusses the origin and composition of tracheobronchial mucus in relation to its (barrier) function, as well as some pathophysiological changes in the context of pulmonary diseases. Mucus models that contemplate key features such as elastic-dominant rheology, composition, filtering mechanisms and microbial interactions are critically reviewed in the context of health and disease considering different collection methods of native human pulmonary mucus. Finally, the prerequisites towards a standardization of mucus models in a regulatory context and their role in drug delivery research are addressed.

Current treatment strategies for inflammatory bowel disease (IBD) seek to alleviate the undesirable symptoms of the disorder. Despite the higher specificity of newer generation therapeutics, e.g. monoclonal antibodies, adverse effects still arise from their interference with non-specific systemic immune cascades. To circumvent such undesirable effects, both conventional and newer therapeutic options can benefit from various targeting strategies. Of course, both the development and the assessment of the efficiency of such targeted delivery systems necessitate the use of suitable in vivo and in vitro models representing relevant pathophysiological manifestations of the disorder. Accordingly, the current review seeks to provide a comprehensive discussion of the available preclinical models with emphasis on human in vitro models of IBD, along with their potentials and limitations. This is followed by an elaboration on the advancements in the field of biology- and nanotechnology-based targeted drug delivery systems and the potential rooms for improvement to facilitate their clinical translation.

The airway epithelium together with the mucus layer coating it forms a protective system that efficiently filters and removes potentially harmful particles contained in inhaled air. The same mechanism, however, serves to entrap particulate drug carriers, precluding their interaction with their target. The mucus barrier is often neglected in in vitro testing setups employed for the assessment of pulmonary drug delivery strategies. Therefore, our aim was to more accurately model the bronchial barrier, by developing an in vitro system comprising a tight epithelial cell layer which may be optionally supplemented with a layer of human tracheal mucus. To form the epithelium in vitro, we used the cystic fibrosis cell line CFBE41o-, which can be grown as monolayers on Transwell® supports, expressing tight junctions as well as relevant transport proteins. In contrast to the cell line Calu-3, however, CFBE41o- does not produce mucus. Therefore, native human mucus, obtained from tracheal tubes of patients undergoing elective surgery, was used as a supplement. The compatibility of CFBE41o- cells with the human mucus was addressed with the MTT assay, and confirmed by fluorescein diacetate/propidium iodide live/dead staining. Moreover, the CFBE41o- cells retained their epithelial barrier properties after being supplemented with mucus, as evidenced by the high trans-epithelial electrical resistance values (∼1000Ωcm(2)) together with a continued low level of paracellular transport of sodium fluorescein. Fluorescently-labeled chitosan-coated PLGA nanoparticles (NP, ∼168nm) were used as a model drug delivery system to evaluate the suitability of this in vitro model for studying mucus permeation and cell uptake. Comparing CFBE41o- cell monolayers with and without mucus, resp., showed that the NP uptake was dramatically reduced in the presence of mucus. This model may therefore be used as a tool to study potential mucus interactions of aerosolized drugs, and more specifically NP-based drug delivery systems designed to exert their effect in the bronchial region.

A series of cyclodextrin-based star polymers were synthesized using β-cyclodextrin (CD) as hydrophilic core, methyl methacrylate (MMA) and tert-butyl acrylate (tBA) as hydrophobic arms. Star polymers, either homopolymers or random/block copolymers, showed narrow molecular weight distributions. Grafting hydrophobic arms created CD-based nanoparticles (CD-NPs) in the size range (130-200nm) with narrow PdI

In contrast to drugs for therapeutic use, there are only few data available concerning interactions between P-glycoprotein (P-gp) and drugs of abuse (DOA). In this work, interactions between structurally diverse DOA and P-gp were investigated using different strategies. First, the effect on the P-gp ATPase activity was studied by monitoring of ATP consumption after addition to recombinant, human P-gp. Second, DOA showing an increased ATP consumption were further characterized regarding their transport across filter grown Caco-2- monolayers. Analyses were performed by luminescence and liquid chromatography-mass spectrometry, respectively. Among the nine DOA initially screened, benzedrone, diclofensine, glaucine, JWH-200, MDBC, WIN-55,212-2 showed an increase of ATP consumption in the ATPase stimulation assay. In Caco-2 transport studies, Glaucine, JWH-200, mitragynine, WIN-55,212-2 could moreover be identified as non-transported substrates, but inhibitors of P-gp activity. Thus, drug-drug or drug-food interactions should be very likely for these compounds.

Biodegradable polymeric nanoparticles (NP) made from poly (lactid-co-glycolide) acid (PLGA) and chitosan (CS) hold promise as innovative formulations for targeted delivery. Since interactions of such NP with primary human immune cells have not been characterized, yet, here we assessed the effect of PLGA or CS-PLGA NP treatment on human peripheral blood mononuclear cells (PBMC), as well as on monocyte-derived DC (moDC). Amongst PBMC, antigen presenting cells (APC) showed higher uptake of both NP preparations than lymphocytes. Furthermore, moDC internalized CS-PLGA NP more efficiently than PLGA NP, presumably because of receptor-mediated endocytosis. Consequently, CS-PLGA NP were delivered mostly to endosomal compartments, whereas PLGA NP primarily ended up in lysosomes. Thus, CS-PLGA NP confer enhanced delivery to endosomal compartments of APC, offering new therapeutic options to either induce or modulate APC function and to inhibit pathogens that preferentially infect APC.

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.

Enhanced intracellular internalization of the anti-cancer active idarubicin (IDA) was achieved through appropriate surface modification of IDA loaded propyl starch nanoparticles. This was conducted by synthesizing pteroic acid modified polyvinyl alcohol (ptPVA) and employing this stabilizer for formulating the said nanoparticles. Pteroic acid attached at the nanoparticles improved the surface protein adsorption of the nanoparticle, a condition which the nanoparticles would largely experience in vitro and in vivo and hence improve their cellular internalization. Spherical, homogenous IDA nanoparticles (214 ± 5 nm) with surface modified by ptPVA were formulated using the solvent emulsification-diffusion technique. The encapsulation efficiency and drug loading amounted around 85%. In vitro release studies indicated a controlled release of IDA. Safety and efficacy of the nanoparticles was confirmed by suitable cellular cytotoxicity assays. Protein binding studies indicated a higher adsorption of the model protein on nanoparticles formulated with ptPVA as compared to PVA. Cellular uptake studies by confocal laser scanning microscopy revealed a higher cellular uptake of ptPVA stabilized nanoparticles thus confirming the proposed hypothesis of higher protein adsorption being responsible for higher cellular internalization.

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.

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.

It was the aim of this study to investigate the influence of the amount of thiol groups being covalently attached to poly(acrylic acid) 450 kDa on its properties. Five different PAA 450 – l -cysteine conjugates (PAA 450 –Cys) were synthesized bearing 53.0 (PAA I), 113.4 (PAA II), 288.8 (PAA III), 549.1 (PAA IV) and 767.0 (PAA V) μmol immobilized thiol groups per gram polymer. Mucoadhesion studies utilizing the rotating cylinder method, tensile studies and disintegration studies were performed. Self-crosslinking properties were measured by the increase in viscosity. Permeation studies were performed on rat small intestine and Caco-2 monolayers using sodium fluorescein as model drug. Following residence times on the rotating cylinder could be identified: PAA I 3.1; PAA II 5.2; PAA III 22.0; PAA IV 33.8; PAA V 53.7; control 1.3 [h]. The disintegration time of all PAA 450 –Cys tablets was strongly dependent on the degree of thiolation of the polymer. Self-crosslinking studies showed that the different PAA 450 –Cys conjugates (3% m/v) in phosphate buffer, pH 6.8, formed intramolecular disulfide bonds. In case of Caco-2 monolayer transport studies following P app -values could be identified: PAA I 9.8; PAA II 10.1; PAA III 11.1; PAA IV 8.9; PAA V 8.2; control 6.4 [ P app × 10 −6 , cm s −1 ]. Mucoadhesive and self-crosslinking properties are strongly dependent on the degree of thiolation of the polymer and with respect to transport studies, an optimum amount of covalently attached l -cysteine could be identified.

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, Saarbrucken Germany.

We are grateful to Prof. Bernd M. Rode from the ASEA-UNINET who supported this work. Also the Austrian Nano-Initiative co-financed this work as part of the Nano-Health project (No. 0200), the sub-project NANO-N-0204 being financed by the Austrian FWF (Fonds zur Forderung der Wissenschaftlichen Forschung). We also thank Prof. Prapon Wilairat for his kind assistance in the preparation of the manuscript. This work was partially supported by a grant from Thailand Research Fund granted to Wilai Noonpakdee.