Phage display screening of epithelial cell monolayers treated with EGTA: identification of peptide FDFWITP that modulates tight junction activity

The Basic Requirement of Tight Junction Proteins in Blood-Brain Barrier Function and Their Role in Pathologies

This review addresses the role of tight junction proteins at the blood-brain barrier (BBB). Their expression is described, and their role in physiological and pathological processes at the BBB is discussed. Based on this, new approaches are depicted for paracellular drug delivery and diagnostics in the treatment of cerebral diseases. Recent data provide convincing evidence that, in addition to its impairment in the course of diseases, the BBB could be involved in the aetiology of CNS disorders. Further progress will be expected based on new insights in tight junction protein structure and in their involvement in signalling pathways.

Storming the gate: New approaches for targeting the dynamic tight junction for improved drug delivery

As biologics used in the clinic outpace the number of new small molecule drugs, an important challenge for their efficacy and widespread use has emerged, namely tissue penetrance. Macromolecular drugs - bulky, high-molecular weight, hydrophilic agents - exhibit low permeability across biological barriers. Epithelial and endothelial layers, for example within the gastrointestinal tract or at the blood-brain barrier, present the most significant obstacle to drug transport. Within epithelium, two subcellular structures are responsible for limiting absorption: cell membranes and intercellular tight junctions. Previously considered impenetrable to macromolecular drugs, tight junctions control paracellular flux and dictate drug transport between cells. Recent work, however, has shown tight junctions to be dynamic, anisotropic structures that can be targeted for delivery. This review aims to summarize new approaches for targeting tight junctions, both directly and indirectly, and to highlight how manipulation of tight junction interactions may help usher in a new era of precision drug delivery.

Post-synthetic functionalization of tryptophan protected peptide sequences through indole (C-2) photocatalytic alkylation

We report a selective, mild, and efficient C-H functionalization of tryptophan and tryptophan-containing peptides with activated α-bromo-carbonyl compounds under visible-light irradiation. The protocol efficiency is outlined by the wide substrate scope and excellent tolerance of sensitive functional groups present in the amino acid side chains. The method can be successfully extended to access pharmaco-peptide conjugate scaffolds.

Lipid polymeric nanoparticles modified with tight junction-modulating peptides promote afatinib delivery across a blood–brain barrier model

Background

Brain metastases from non-small cell lung cancer (NSCLC) remain one of the most challenging malignancies. Afatinib (Afa) is an orally administered irreversible ErbB family blocker approved for epidermal growth factor receptor (EGFR)-mutated NSCLC. However, the incidence of brain metastases in patients with NSCLC and EGFR mutation is high. One of the major obstacles in the treatment of brain metastases is to transport drugs across the blood–brain barrier (BBB). A lipid polymeric nanoparticle (LPN) modified with a tight junction-modulating peptide is a potential formulation to deliver therapeutics across the BBB. FD7 and CCD are short peptides that perturb the tight junctions (TJs) of the BBB. In this study, the use of LPN modified with FD7 or CCD as a delivery platform was explored to enhance Afa delivery across the BBB model of mouse brain-derived endothelial bEnd.3 cells.

Results

Our findings revealed that Afa/LPN-FD7 and Afa/LPN-CCD exhibited a homogeneous shape, a uniform nano-scaled particle size, and a sustained-release profile. FD7, CCD, Afa/LPN-FD7, and Afa/LPN-CCD did not cause a significant cytotoxic effect on bEnd.3 cells. Afa/LPN-FD7 and Afa/LPN-CCD across the bEnd.3 cells enhanced the cytotoxicity of Afa on human lung adenocarcinoma PC9 cells. FD7 and CCD-modulated TJ proteins, such as claudin 5 and ZO-1, reduced transendothelial electrical resistance, and increased the permeability of paracellular markers across the bEnd.3 cells. Afa/LPN-FD7 and Afa/LPN-CCD were also partially transported through clathrin- and caveolae-mediated transcytosis, revealing the effective activation of paracellular and transcellular pathways to facilitate Afa delivery across the BBB and cytotoxicity of Afa on PC9 cells.

Conclusion

TJ-modulating peptide-modified LPN could be a prospective platform for the delivery of chemotherapeutics across the BBB to the brain for the potential treatment of the BM of NSCLC.

The Effect of Sodium Bicarbonate, a Beneficial Adjuvant Molecule in Cystic Fibrosis, on Bronchial Epithelial Cells Expressing a Wild-Type or Mutant CFTR Channel

Clinical and experimental results with inhaled sodium bicarbonate as an adjuvant therapy in cystic fibrosis (CF) are promising due to its mucolytic and bacteriostatic properties, but its direct effect has not been studied on respiratory epithelial cells. Our aim was to establish and characterize co-culture models of human CF bronchial epithelial (CFBE) cell lines expressing a wild-type (WT) or mutant (deltaF508) CF transmembrane conductance regulator (CFTR) channel with human vascular endothelial cells and investigate the effects of bicarbonate. Vascular endothelial cells induced better barrier properties in CFBE cells as reflected by the higher resistance and lower permeability values. Activation of CFTR by cAMP decreased the electrical resistance in WT but not in mutant CFBE cell layers confirming the presence and absence of functional channels, respectively. Sodium bicarbonate (100 mM) was well-tolerated by CFBE cells: it slightly reduced the impedance of WT but not that of the mutant CFBE cells. Sodium bicarbonate significantly decreased the more-alkaline intracellular pH of the mutant CFBE cells, while the barrier properties of the models were only minimally changed. These observations indicate that sodium bicarbonate is beneficial to deltaF508-CFTR expressing CFBE cells. Thus, sodium bicarbonate may have a direct therapeutic effect on the bronchial epithelium.

Bio-hybrid gold nanoparticles as SERS probe for rapid bacteria cell identification

This study reports the utilization of engineered molecular networks between bacteriophage (or phage) and gold nanoparticles (AuNPs) prepared ablating a high purity gold target in water by nanosecond laser source. Gold colloids are assembled with P9b phage clone, displaying the specific peptide (QRKLAAKLT), able to bind P. aeruginosa. The single components and assembled systems were characterized by spectroscopic and electronic techniques, such as the conventional optical absorption and micro-Raman spectroscopies as well as the Dynamic Light Scattering (DLS) and Scanning Transmission Electron Microscopy (STEM) techniques. The performance of the AuNPs-phage assembly as substrate for Surface-Enhanced Raman Spectroscopy (SERS) was tested against the detection of the characteristics Raman vibrational features of the Pseudomonas aeruginosa bacteria.

Self-Assembled Peptide-Based Nanomaterials for Biomedical Imaging and Therapy

Peptide-based materials are one of the most important biomaterials, with diverse structures and functionalities. Over the past few decades, a self-assembly strategy is introduced to construct peptide-based nanomaterials, which can form well-controlled superstructures with high stability and multivalent effect. More recently, peptide-based functional biomaterials are widely utilized in clinical applications. However, there is no comprehensive review article that summarizes this growing area, from fundamental research to clinic translation. In this review, the recent progress of peptide-based materials, from molecular building block peptides and self-assembly driving forces, to biomedical and clinical applications is systematically summarized. Ex situ and in situ constructed nanomaterials based on functional peptides are presented. The advantages of intelligent in situ construction of peptide-based nanomaterials in vivo are emphasized, including construction strategy, nanostructure modulation, and biomedical effects. This review highlights the importance of self-assembled peptide nanostructures for nanomedicine and can facilitate further knowledge and understanding of these nanosystems toward clinical translation.

Peptides and Drug Delivery

Peptides have been used as drugs to treat various health conditions, and they are also being developed as diagnostic agents. Due to their receptor selectivity, peptides have recently been utilized for drug delivery to target drug molecules to specific types of cells (i.e. cancer cells, immune cells) to lower the side effects of the drugs. In this case, the drug is conjugated to the carrier peptide for directing the drug to the target cells (e.g. cancer cells) with higher expression of a specific receptor that recognizes the carrier peptide. As a result, the drug is directed to the target diseased cells without affecting the normal cells. Peptides are also being developed for improving drug delivery through the intestinal mucosa barrier (IMB) and the blood-brain barrier (BBB). These peptides were derived from intercellular junction proteins such as occludins, claudins, and cadherins and improve drug delivery through the IMB and BBB via the paracellular pathways. It is hypothesized that the peptides modulate protein-protein interactions in the intercellular junctions of the IMB and BBB to increase the porosity of paracellular pathways of the barriers. These modulator peptides have been shown to enhance brain delivery of small molecules and medium-sized peptides as well as a large protein such as 65 kDa albumin. In the future, this method has the potential to improve oral and brain delivery of therapeutic and diagnostic peptides and proteins.

Intestinal permeation enhancers for oral peptide delivery

Intestinal permeation enhancers (PEs) are one of the most widely tested strategies to improve oral delivery of therapeutic peptides. This article assesses the intestinal permeation enhancement action of over 250 PEs that have been tested in intestinal delivery models. In depth analysis of pre-clinical data is presented for PEs as components of proprietary delivery systems that have progressed to clinical trials. Given the importance of co-presentation of sufficiently high concentrations of PE and peptide at the small intestinal epithelium, there is an emphasis on studies where PEs have been formulated with poorly permeable molecules in solid dosage forms and lipoidal dispersions.

Update on in vitro cytotoxicity assays for drug development

BACKGROUND

in vitro cytotoxicity testing provides a crucial means of ranking compounds for consideration in drug discovery. The choice of using a particular viability or cytotoxicity assay technology may be influenced by specific research goals.

OBJECTIVE

Although the high-throughput screening (HTS) utility is typically dependent upon sensitivity and scalability, it is also impacted by signal robustness and resiliency to assay interferences. Further consideration should be given to data quality, ease-of-use, reagent stability, and matters of cost-effectiveness.

METHODS

Here we focus on three main classes of assays that are at present the most popular, useful, and practical for HTS drug discovery efforts. These methods measure: i) viability by metabolism reductase activities; ii) viability by bioluminescent ATP assays; or iii) cytotoxicity by enzymes 'released' into culture medium. Multi-parametric technologies are also briefly discussed.

RESULTS/CONCLUSION

Each of these methods has its relative merits and detractions; however multi-parametric methods using both viability and cytotoxicity markers may mitigate the inherent shortcomings of single parameter measures.

Oral delivery of macromolecules: rationale underpinning Gastrointestinal Permeation Enhancement Technology (GIPET)

Oral delivery of macromolecular drugs, particularly peptides and proteins, is the focus of many academic and industrial laboratories. Armed with an increased understanding of the structure and regulation of intestinal epithelial junctional complexes of the paracellular barrier, the development of permeation enhancement technology initially focused on the specific and reversible opening of tight junctions in order to enable oral delivery. Despite intense research, none of these specific tight junction-opening technologies has yet been approved in an oral drug product, likely because of poor efficacy. Less specific enhancer technologies with a long history of safe use in man have additional surfactant-like effects on the transcellular pathway that lead to improved efficacy. These are likely to be the first to market for selected poorly permeable peptides. This review presents a summary of some approaches taken to intestinal permeation enhancement and explores in detail the oral delivery system developed by Merrion Pharmaceuticals, Gastrointestinal Permeation Enhancement Technology (GIPET).

Enhanced pulmonary absorption of a macromolecule through coupling to a sequence-specific phage display-derived peptide

With the aim of identifying a peptide sequence that promotes pulmonary epithelial transport of macromolecule cargo we used a stringent peptide-phage display library screening protocol against rat lung alveolar epithelial primary cell cultures. We identified a peptide-phage clone (LTP-1) displaying the disulphide-constrained 7-mer peptide sequence, C-TSGTHPR-C, that showed significant pulmonary epithelial translocation across highly restrictive polarised cell monolayers. Cell biological data supported a differential alveolar epithelial cell interaction of the LTP-1 peptide-phage clone and the corresponding free synthetic LTP-1 peptide. Delivering select phage-clones to the intact pulmonary barrier of an isolated perfused rat lung (IPRL) resulted in 8.7% of lung deposited LTP-1 peptide-phage clone transported from the IPRL airways to the vasculature compared (p<0.05) to the cumulative transport of less than 0.004% for control phage-clone groups. To characterise phage-independent activity of LTP-1 peptide, the LTP-1 peptide was conjugated to a 53kDa anionic PAMAM dendrimer. Compared to respective peptide-dendrimer control conjugates, the LTP-1-PAMAM conjugate displayed a two-fold (bioavailability up to 31%) greater extent of absorption in the IPRL. The LTP-1 peptide-mediated enhancement of transport, when LTP-1 was either attached to the phage clone or conjugated to dendrimer, was sequence-dependent and could be competitively inhibited by co-instillation of excess synthetic free LTP-1 peptide. The specific nature of the target receptor or mechanism involved in LTP-1 lung transport remains unclear although the enhanced transport is enabled through a mechanism that is non-disruptive with respect to the pulmonary transport of hydrophilic permeability probes. This study shows proof-of principle that array technologies can be effectively exploited to identify peptides mediating enhanced transmucosal delivery of macromolecule therapeutics across an intact organ.

Tight junction modulator and drug delivery

Recent progress in pharmaceutical technology based on genomic and proteomic research has provided many drug candidates, including not only chemicals but peptides, antibodies and nucleic acids. These candidates do not show pharmaceutical activity without their absorption into systemic flow and movement from the systemic flow into the target tissue. Epithelial and endothelial cell sheets play a pivotal role in the barrier between internal and external body and tissues. Tight junctions (TJs) between adjacent epithelial cells limit the movement of molecules through the intercellular space in epithelial and endothelial cell sheets. Thus, a promising strategy for drug delivery is the modulation of TJ components to allow molecules to pass through the TJ-based cellular barriers. In this review, we discuss recent progress in the development of TJ modulators and the possibility of absorption enhancers and drug-delivery systems based on TJ components.

Dynamic regulation of epithelial cell fate and barrier function by intercellular junctions

In the intestine, a single layer of epithelial cells effectively separates potentially harmful luminal content from the underlying tissue. The importance of an intact mucosal layer is highlighted by pathological disorders of the gut such as inflammatory bowel disease, in which disruption of the epithelial barrier leads to severe inflammation of the submucosal tissue compartments. Epithelial barrier function is provided by tightly regulated intercellular junctions, which consist of a plethora of membrane-associated and transmembrane proteins organized in discreet, spatially restricted complexes. Classically, these complexes are known to be dynamic seals for fluids and small molecules, as well as to provide mechanical strength by anchoring cell-cell contacts to the cytoskeleton. Rather than just acting as simple gates and adapters, however, junctional complexes themselves can relay extracellular stimuli to the epithelium and initiate cellular responses such as differentiation and apoptosis. In this review, we will highlight recent studies by our group and others which discuss how junctional proteins can promote outside-to-inside signaling and modulate epithelial cell fate. Unraveling the complex crosstalk between epithelial cells and their intercellular junctions is essential to understanding how epithelial barrier function is maintained in vivo and might provide new strategies for the treatment of inflammatory disorders of the intestine.

Early embryonic lethality of mice lacking ZO-2, but Not ZO-3, reveals critical and nonredundant roles for individual zonula occludens proteins in mammalian development

ZO-1, ZO-2, and ZO-3 are closely related scaffolding proteins that link tight junction (TJ) transmembrane proteins such as claudins, junctional adhesion molecules, and occludin to the actin cytoskeleton. Even though the zonula occludens (ZO) proteins are among the first TJ proteins to have been identified and have undergone extensive biochemical analysis, little is known about the physiological roles of individual ZO proteins in different tissues or during vertebrate development. Here, we show that ZO-3 knockout mice lack an obvious phenotype. In contrast, embryos deficient for ZO-2 die shortly after implantation due to an arrest in early gastrulation. ZO-2(-)(/)(-) embryos show decreased proliferation at embryonic day 6.5 (E6.5) and increased apoptosis at E7.5 compared to wild-type embryos. The asymmetric distribution of prominin and E-cadherin to the apical and lateral plasma membrane domains, respectively, is maintained in cells of ZO-2(-)(/)(-) embryos. However, the architecture of the apical junctional complex is altered, and paracellular permeability of a low-molecular-weight tracer is increased in ZO-2(-/-) embryos. Leaky TJs and, given the association of ZO-2 with connexins and several transcription factors, effects on gap junctions and gene expression, respectively, are likely causes for embryonic lethality. Thus, ZO-2 is required for mouse embryonic development, but ZO-3 is dispensable. This is to our knowledge the first report showing that an individual ZO protein plays a nonredundant and critical role in mammalian development.