Recent advances in oral delivery of biologics: nanomedicine and physical modes of delivery.

INTRODUCTION: Research into oral delivery of biologics has a long and rich history but has not produced technologies used in the clinic. The area has evolved in terms of strategies to promote oral biologics delivery from early chemical absorption enhancers to nanomedicine to devices. Continued activity in this area is justifiable considering the remarkable proliferation of biologics. AREAS COVERED: The article discusses some physiological barriers to oral delivery of biologics, with a special focus on less characterized barriers such as the basement membrane. Recent progress in oral delivery of biologics via nanomedicine is subsequently covered. Finally, the emerging field of device-mediated gastrointestinal delivery of biotherapeutics is discussed EXPERT OPINION: Oral delivery of biologics is considered a 'panacea' in drug delivery. Almost century-old approaches of utilizing chemical absorption enhancers have not produced clinically translated technologies. Nanomedicine for oral biologics delivery has demonstrated potential, but the field is relatively new, and technologies have not progressed to the clinic. Device-mediated oral biologics delivery (e.g. ultrasound or microneedles) is in its infancy. However, this space is likely to intensify owing to advances in electronics and materials, as well as the challenges and history related to clinical translation of alternative approaches.

PEGylated nanomedicines: recent progress and remaining concerns.

INTRODUCTION: Recent biopharma deals related to nanocarrier drug delivery technologies highlight the emergence of nanomedicine. This is perhaps an expected culmination of many years of research demonstrating the potential of nanomedicine as the next generation of therapeutics with improved performance. PEGylated nanocarriers play a key role within this field. AREAS COVERED: The drug delivery advantages of nanomedicines in general are discussed, focusing on nanocarriers and PEGylated nanomedicines, including products under current development/clinical evaluation. Well-established drug delivery benefits of PEGylation (e.g., prolonged circulation) are only briefly covered. Instead, attention is deliberately made to less commonly reported advantages of PEGylation, including mucosal delivery of nanomedicines. Finally, some of the issues related to the safety of PEGylated nanomedicines in clinical application are discussed. EXPERT OPINION: The advent of nanomedicine providing therapeutic options of refined performance continues. Although PEGylation as a tool to improve the pharmacokinetics of nanomedicines is well established and is used clinically, other benefits of 'PEGnology', including enhancement of physicochemical properties and/or biocompatibility of actives and/or drug carriers, as well as mucosal delivery, have attracted less attention. While concerns regarding the clinical use of PEGylated nanomedicines remain, evidence suggests that at least some safety issues may be controlled by adequate designs of nanosystems.

Uptake and transport of B12-conjugated nanoparticles in airway epithelium.

Non-invasive delivery of biotherapeutics, as an attractive alternative to injections, could potentially be achieved through the mucosal surfaces, utilizing nanoscale therapeutic carriers. However, nanoparticles do not readily cross the mucosal barriers, with the epithelium presenting a major barrier to their translocation. The transcytotic pathway of vitamin B12 has previously been shown to 'ferry' B12-decorated nanoparticles across intestinal epithelial (Caco-2) cells. However, such studies have not been reported for the airway epithelium. Furthermore, the presence in the airways of the cell machinery responsible for transepithelial trafficking of B12 is not widely reported. Using a combination of molecular biology and immunostaining techniques, our work demonstrates that the bronchial cell line, Calu-3, expresses the B12-intrinsic factor receptor, the transcobalamin II receptor and the transcobalamin II carrier protein. Importantly, the work showed that sub-200 nm model nanoparticles chemically conjugated to B12 were internalised and transported across the Calu-3 cell layers, with B12 conjugation not only enhancing cell uptake and transepithelial transport, but also influencing intracellular trafficking. Our work therefore demonstrates that the B12 endocytotic apparatus is not only present in this airway model, but also transports ligand-conjugated nanoparticles across polarised epithelial cells, indicating potential for B12-mediated delivery of nanoscale carriers of biotherapeutics across the airways.

Nanoparticle transport in epithelial cells: pathway switching through bioconjugation.

The understanding and control of nanoparticle transport into and through cellular compartments is central to biomedical applications of nanotechnology. Here, it is shown that the transport pathway of 50 nm polystyrene nanoparticles decorated with vitamin B12 in epithelial cells is different compared to both soluble B12 ligand and unmodified nanoparticles, and this is not attributable to B12 recognition alone. Importantly, the study indicates that vitamin B12 -conjugated nanoparticles circumnavigate the lysosomal compartment, the destination of soluble vitamin B12 ligand. Whereas cellular trafficking of soluble B12 is confirmed to occur via the clathrin-mediated pathway, transport of B12 -conjugated nanoparticles appears to predominantly take place by a route that is perturbed by caveolae-specific inhibitors. This data suggests that, following its conjugation to nanoparticles, in addition to dramatically increasing the cellular uptake of nanoparticles, the normal cell trafficking of B12 is switched to an alternative pathway, omitting the lysosomal stage: a result with important implications for oral delivery of nanoparticulate diagnostics and therapeutics.

Epithelial toxicity of alkylglycoside surfactants.

Alkylglycoside surfactants have been proposed as drug delivery excipients with the potential to enhance mucosal drug absorption of therapeutic macromolecules. Previous work reported their drug absorption-promoting potential by demonstrating that several compounds within this class of surfactants improve mucosal absorption of peptides, proteins and other macromolecules. However, detailed investigation of their toxicity has not been conducted. Using Calu-3 epithelial cell layers as a model of the airway mucosa, and liposomes as models of cell membranes, this work investigates the cytotoxicity of dodecylmaltoside, tridecylmaltoside and tetradecylmaltoside, as representative alkylglycosides. A combination of different toxicity assays and other tests indicating cell membrane disruption were used to assess cytotoxicity. The alkylglycosides tested induced a dramatic reduction in cell viability, cell membrane and liposome-disruptive effects, as well as abrogation of transepithelial electrical resistance that did not recover completely. Importantly, these phenomena were noted at concentrations markedly lower than those typically used in the literature studies demonstrating the absorption-enhancing properties of alkylglycosides. This work therefore demonstrates that alkylglycosides exhibit significant toxicity towards airway epithelial cells, most likely resulting from a membrane-damaging effect, highlighting a need for further evaluation of their safety as absorption-enhancing excipients.

Absorption-promoting effects of chitosan in airway and intestinal cell lines: a comparative study.

This work explored the interaction of chitosan with Calu-3 and Caco-2 cell lines, as models of the airway and intestinal epithelium, respectively. The toxicity, tight junction opening and mucoadhesive effects of chitosan were compared in the two cell lines. Additionally, the role of mucus in the absorption-promoting activity of chitosan was studied systematically. Notably, chitosan exhibited a different degree of toxicity on the Calu-3 and Caco-2 cells. Chitosan's tight junction-opening effect, observed in terms of reduction of transepithelial electrical resistance and permeability enhancement, was apparent in both cell lines, though somewhat lower in Caco-2 compared to Calu-3 cell layers (though overall permeability was higher in the former). Tight junction opening and association of chitosan with the epithelial cell layers were more prominent in mucus-containing than in mucus-depleted Calu-3 cells and non mucus-excreting Caco-2 monolayers. Overall, the work suggests that chitosan exhibits a different level of toxicity in airway, as compared to intestinal cells and although absorption enhancement is apparent in both cell lines, enabling its potential use as an absorption-promoting excipient in both pulmonary and oral macromolecular delivery, the magnitude and the duration of the effect are dependent on the level of mucus present on the epithelial surfaces.

Barrier characteristics of epithelial cultures modelling the airway and intestinal mucosa: a comparison.

The barrier characteristics of polarized layers of Calu-3 and Caco-2 cell lines, as commonly used in vitro models of intestinal and airway mucosa, respectively, were investigated by assessing the translocation of model macromolecules and nanoparticles. The barrier capacity of the cell layers towards the movement of macromolecules and nanoparticulates differed considerably between the cell lines. Permeability studies revealed the existence of a notably larger solute molecular weight limit for paracellular diffusion in Caco-2 monolayers compared to Calu-3 cells. Removal of mucus in Calu-3 cells resulted in cell layers exhibiting a larger macromolecular permeability, in addition to improved nanoparticle translocation. Microscopic examination of the tight junctions, as cellular features that play a major role in preventing transepithelial movement of macromolecules, revealed that the appearance of cell-cell boundaries was notably different in the two cell lines, which could explain the differences in macromolecular permeability. The data overall showed that epithelial layers of airway Calu-3 and intestinal Caco-2 cell cultures in vitro exhibit a different level of restrictiveness and this is due to the cell morphology and the presence of mucus.