Transcytosis of GCSF-transferrin across rat alveolar epithelial cell monolayers

Oral inhalation for delivery of proteins and peptides to the lungs

Oral inhalation is the preferred route for delivery of small molecules to the lungs, because high tissue levels can be achieved shortly after application. Biologics are mainly administered by intravenous injection but inhalation might be beneficial for the treatment of lung diseases (e.g. asthma). This review discusses biological and pharmaceutical challenges for delivery of biologics and describes promising candidates. Insufficient stability of the proteins during aerosolization and the biological environment of the lung are the main obstacles for pulmonary delivery of biologics. Novel nebulizers will improve delivery by inducing less shear stress and administration as dry powder appears suitable for delivery of biologics. Other promising strategies include pegylation and development of antibody fragments, while carrier-encapsulated systems currently play no major role in pulmonary delivery of biologics for lung disease. While development of various biologics has been halted or has shown little effects, AIR DNase, alpha1-proteinase inhibitor, recombinant neuraminidase, and heparin are currently being evaluated in phase III trials. Several biologics are being tested for the treatment of coronavirus disease (COVID)-19, and it is expected that these trials will lead to improvements in pulmonary delivery of biologics.

Pulmonary Delivery of Biological Drugs

In the last decade, biological drugs have rapidly proliferated and have now become an important therapeutic modality. This is because of their high potency, high specificity and desirable safety profile. The majority of biological drugs are peptide- and protein-based therapeutics with poor oral bioavailability. They are normally administered by parenteral injection (with a very few exceptions). Pulmonary delivery is an attractive non-invasive alternative route of administration for local and systemic delivery of biologics with immense potential to treat various diseases, including diabetes, cystic fibrosis, respiratory viral infection and asthma, etc. The massive surface area and extensive vascularisation in the lungs enable rapid absorption and fast onset of action. Despite the benefits of pulmonary delivery, development of inhalable biological drug is a challenging task. There are various anatomical, physiological and immunological barriers that affect the therapeutic efficacy of inhaled formulations. This review assesses the characteristics of biological drugs and the barriers to pulmonary drug delivery. The main challenges in the formulation and inhalation devices are discussed, together with the possible strategies that can be applied to address these challenges. Current clinical developments in inhaled biological drugs for both local and systemic applications are also discussed to provide an insight for further research.

More Than Just a Barrier: The Immune Functions of the Airway Epithelium in Asthma Pathogenesis

Allergic bronchial asthma is a chronic disease of the airways that is characterized by symptoms like respiratory distress, chest tightness, wheezing, productive cough, and acute episodes of broncho-obstruction. This symptom-complex arises on the basis of chronic allergic inflammation of the airway wall. Consequently, the airway epithelium is central to the pathogenesis of this disease, because its multiple abilities directly have an impact on the inflammatory response and thus the formation of the disease. In turn, its structure and functions are markedly impaired by the inflammation. Hence, the airway epithelium represents a sealed, self-cleaning barrier, that prohibits penetration of inhaled allergens, pathogens, and other noxious agents into the body. This barrier is covered with mucus that further contains antimicrobial peptides and antibodies that are either produced or specifically transported by the airway epithelium in order to trap these particles and to remove them from the body by a process called mucociliary clearance. Once this first line of defense of the lung is overcome, airway epithelial cells are the first cells to get in contact with pathogens, to be damaged or infected. Therefore, these cells release a plethora of chemokines and cytokines that not only induce an acute inflammatory reaction but also have an impact on the alignment of the following immune reaction. In case of asthma, all these functions are impaired by the already existing allergic immune response that per se weakens the barrier integrity and self-cleaning abilities of the airway epithelium making it more vulnerable to penetration of allergens as well as of infection by bacteria and viruses. Recent studies indicate that the history of allergy- and pathogen-derived insults can leave some kind of memory in these cells that can be described as imprinting or trained immunity. Thus, the airway epithelium is in the center of processes that lead to formation, progression and acute exacerbation of asthma.

An ‘all in one’ approach for simultaneous chemotherapeutic, photothermal and magnetic hyperthermia mediated by hybrid magnetic nanoparticles

Trimodal (chemo-photothermal and MHT) lethality imparted by triple targeted dual drug loaded hybrid MNPs.

Mass spectrometry-guided optimization and characterization of a biologically active transferrin-lysozyme model drug conjugate

Transferrin is a promising drug carrier that has the potential to deliver metals, small organic molecules and therapeutic proteins to cancer cells and/or across physiological barriers (such as the blood-brain barrier). Despite this promise, very few transferrin-based therapeutics have been developed and reached clinical trials. This modest success record can be explained by the complexity and heterogeneity of protein conjugation products, which also pose great challenges to their analytical characterization. In this work, we use lysozyme conjugated to transferrin as a model therapeutic that targets the central nervous system (where its bacteriostatic properties may be exploited to control infection) and develop analytical protocols based on electrospray ionization mass spectrometry to characterize its structure and interactions with therapeutic targets and physiological partners critical for its successful delivery. Mass spectrometry has already become an indispensable tool facilitating all stages of the protein drug development process, and this work demonstrates the enormous potential of this technique in facilitating the development of a range of therapeutically effective protein-drug conjugates.

Intestinal receptor targeting for peptide delivery: an expert's personal perspective on reasons for failure and new opportunities

The technology has been available more than 25 years that would enable the oral delivery of vaccines, proteins and peptides, thus avoiding the need for injection. To this day, injection is still the mode of delivery, yet not the main mode of choice. This review focuses on several of the potential modes for oral delivery of peptides, proteins and vaccines. Additionally, the review will provide the reader with an insight into the problems and potential solutions for several of these modes of oral delivery of peptides and proteins.

Strategies for non-invasive delivery of biologics

Macromolecular therapeutics, in particular, many biologics, is the most advancing category of drugs over conventional chemical drugs. The potency and specificity of the biologics for curing certain disease made them to be a leading compound in the pharmaceutical industry. However, due to their intrinsic nature, including high molecular weight, hydrophilicity and instability, they are difficult to be administered via non-invasive route. This is a major quest especially in biologics, as they are frequently used clinically for chronic disorders, which requires long-term administration. Therefore, many efforts have been made to develop formulation for non-invasive administration, in attempt to improve patient compliance and convenience. In this review, strategies for non-invasive delivery, in particular, oral, pulmonary and nasal delivery, that are recently adopted for delivery of biologics are discussed. Insulin, calcitonin and heparin were mainly focused for the discussion as they could represent protein, polypeptide and polysaccharide drugs, respectively. Many recent attempts for non-invasive delivery of biologics are compared to provide an insight of developing successful delivery system.

Primary alveolar epithelial cell surface membrane microdomain function is required for Pneumocystis β-glucan-induced inflammatory responses

Intense lung inflammation characterizes respiratory failure associated with Pneumocystis pneumonia. Our laboratory has previously demonstrated that alveolar epithelial cells (AECs) elaborate inflammatory cytokines and chemokines in response to the Pneumocystis carinii cell wall constituent β-(1→3)-glucan (PCBG), and that these responses require lactosylceramide, a prominent glycosphingolipid constituent of certain cell membrane microdomains. The relevance of membrane microdomains, also termed plasma membrane lipid rafts, in cell signaling and macromolecule handling has been increasingly recognized in many biologic systems, but their role in P. carinii-induced inflammation is unknown. To investigate the mechanisms of microdomain-dependent P. carinii-induced inflammation, we challenged primary rat AECs with PCBG with or without pre-incubation with inhibitors of microdomain function. Glycosphingolipid and cholesterol rich microdomain inhibition resulted in significant attenuation of P. carinii-induced expression of TNF-α and the rodent C-X-C chemokine MIP-2, as well as their known inflammatory secondary signaling pathways. We have previously shown that protein kinase C (PKC) is activated by PCBG challenge and herein show that PKC localizes to AEC microdomains. We also demonstrate by conventional microscopy, fluorescence microscopy, confocal microscopy and spectrophotofluorimetry that AECs internalize fluorescently-labeled PCBG by microdomain-mediated mechanisms, and that anti-microdomain pretreatments prevent internalization. Taken together, these data suggest an important role for AEC microdomain function in PCBG-induced inflammatory responses. This offers a potential novel target for therapeutics for a condition that continues to exert unacceptable morbidity and mortality among immunocompromised populations.

Transferrin-conjugated curcumin-loaded superparamagnetic iron oxide nanoparticles induce augmented cellular uptake and apoptosis in K562 cells

Superparamagnetic iron oxide nanoparticles are currently used for precise drug delivery and as an image contrast agent. In the present study, the potentiality of curcumin-loaded magnetic nanoparticles (Cur-MNPs) for the treatment of chronic myeloid leukemia (CML) was investigated. For active therapy, transferrin (Tf) ligand was further conjugated to Cur-MNPs, which demonstrated enhanced uptake compared to Cur-MNPs in p210bcr/abl-positive cell line (K562). Cur-MNPs demonstrated greater and sustained anti-proliferative activity in a dose- and time-dependent manner; however, with the advent of a magnetic field the anti-proliferative activity of Cur-MNPs as well as Tf-Cur-MNPs was enhanced due to higher cellular uptake with enhanced cytotoxicity activity. Down-regulation of Bcr-Abl protein activates intrinsic apoptotic pathways for promoting anti-leukemic responses. Our in vitro results advocate potential clinical applications of Cur-MNPs by activating multiple signaling pathways for provoking the anti-leukemic activity.

Transferrin conjugation confers mucosal molecular targeting to a model HIV-1 trimeric gp140 vaccine antigen

The generation of effective immune responses by mucosal vaccination without the use of inflammatory adjuvants, that compromise the epithelial barrier and recruit new cellular targets, is a key goal of vaccines designed to protect against sexually acquired pathogens. In the present study we use a model HIV antigen (CN54gp140) conjugated to transferrin (Tf) and evaluate the ability of the natural transferrin receptor CD71 to modulate immunity. We show that the conjugated transferrin retained high affinity for its receptor and that the conjugate was specifically transported across an epithelial barrier, co-localizing with MHC Class II⁺ cells in the sub-mucosal stroma. Vaccination studies in mice revealed that the Tf-gp140 conjugate elicited high titres of CN54gp140-specific serum antibodies, equivalent to a systemic vaccination, when conjugate was applied topically to the nasal mucosae whereas gp140 alone was poorly immunogenic. Moreover, the Tf-gp140 conjugate elicited both IgG and IgA responses and significantly higher gp140-specific IgA titre in the female genital tract than unconjugated antigen. These responses were achieved after mucosal application of the conjugated protein alone, in the absence of any pro-inflammatory adjuvant and suggest a potentially useful and novel molecular targeting approach, delivering a vaccine cargo to directly elicit or enhance pathogen-specific mucosal immunity.

Arf6-dependent intracellular trafficking of Pasteurella multocida toxin and pH-dependent translocation from late endosomes

The potent mitogenic toxin from Pasteurella multocida (PMT) is the major virulence factor associated with a number of epizootic and zoonotic diseases caused by infection with this respiratory pathogen. PMT is a glutamine-specific protein deamidase that acts on its intracellular G-protein targets to increase intracellular calcium, cytoskeletal, and mitogenic signaling. PMT enters cells through receptor-mediated endocytosis and then translocates into the cytosol through a pH-dependent process that is inhibited by NH₄Cl or bafilomycin A1. However, the detailed mechanisms that govern cellular entry, trafficking, and translocation of PMT remain unclear. Co-localization studies described herein revealed that while PMT shares an initial entry pathway with transferrin (Tfn) and cholera toxin (CT), the trafficking pathways of Tfn, CT, and PMT subsequently diverge, as Tfn is trafficked to recycling endosomes, CT is trafficked retrograde to the ER, and PMT is trafficked to late endosomes. Our studies implicate the small regulatory GTPase Arf6 in the endocytic trafficking of PMT. Translocation of PMT from the endocytic vesicle occurs through a pH-dependent process that is also dependent on both microtubule and actin dynamics, as evidenced by inhibition of PMT activity in our SRE-based reporter assay, with nocodazole and cytochalasin D, respectively, suggesting that membrane translocation and cytotoxicity of PMT is dependent on its transfer to late endosomal compartments. In contrast, disruption of Golgi-ER trafficking with brefeldin A increased PMT activity, suggesting that inhibiting PMT trafficking to non-productive compartments that do not lead to translocation, while promoting formation of an acidic tubulovesicle system more conducive to translocation, enhances PMT translocation and activity.

Nanomaterial interactions with and trafficking across the lung alveolar epithelial barrier: implications for health effects of air-pollution particles

Studies on the health effects of air-pollution particles suggest that injury may result from inhalation of airborne ultrafine particles (<100 nm in diameter). Engineered nanomaterials (<100 nm in at least one dimension) may also be harmful if inhaled. Nanomaterials deposited on the respiratory epithelial tract are thought to cross the air-blood barrier, especially via the expansive alveolar region, into the systemic circulation to reach end organs (e.g., myocardium, liver, pancreas, kidney, and spleen). Since ambient ultrafine particles are difficult to track, studies of defined engineered nanomaterials have been used to obtain valuable information on how nanomaterials interact with and traffic across the air-blood barrier of mammalian lungs. Since specific mechanistic information on how nanomaterials interact with the lung is difficult to obtain using in vivo or ex vivo lungs due to their complex anatomy, in vitro alveolar epithelial models have been of considerable value in determining nanomaterial-lung interactions. In this review, we provide information on mechanisms underlying lung alveolar epithelial injury caused by various nanomaterials and on nanomaterial trafficking across alveolar epithelium that may lead to end-organ injury.

Design of an in vivo cleavable disulfide linker in recombinant fusion proteins

In order to achieve optimal biological activity and desired pharmacokinetic profiles, a dithiocyclopeptide linker was designed for in vivo release of protein domains from a recombinant fusion protein. This novel in vivo cleavable disulfide linker, based on a dithiocyclopeptide containing a thrombin-sensitive sequence and an intramolecular disulfide bond, was inserted between transferrin and granulocyte colony-stimulating factor (G-CSF) recombinant fusion protein domains. After expression of the fusion protein, G-C-T, from HEK293 cells, thrombin treatment in vitro generated a fusion protein linked via a reversible disulfide bond that was quickly cleaved in vivo, separating the protein domains. After release from the fusion protein, free G-CSF exhibited an improved biological activity in a cell proliferation assay. Although reversible disulfide bonds are commonly used in protein chemical conjugation methods, to our knowledge this report is the first example of the construction of a recombinant fusion protein with a disulfide linkage for the release of the functional domain. This linker design can be adapted to diverse recombinant fusion proteins in which in vivo separation of protein domains is required to achieve an improved therapeutic effect and a desirable pharmacokinetic profile and biodistribution of the functional domain.

Human growth hormone-transferrin fusion protein for oral delivery in hypophysectomized rats

Transferrin (Tf)-based recombinant fusion protein approach was investigated to achieve oral delivery for human growth hormone (hGH). Plasmid constructs expressing the fusion proteins were established by fusing coding sequences of both hGH and Tf in frame. Fusion proteins were produced in serum free media by transient transfection of human embryonic kidney HEK293 cells. The SDS-PAGE analysis of conditioned media showed that fusion proteins expressed at high purity with a 100 kDa molecular weight; the Western blot analysis with anti-hGH and anti-Tf antibodies verified the identity of fusion proteins. The Nb2 cell proliferation and Caco-2 cell Tf receptor (TfR) binding assays demonstrated that fusion proteins retained bioactivity of both hGH and Tf, respectively. A helical linker was inserted as spacer between hGH- and Tf-domain to enhance the bioactivity and the yield of the fusion protein. Two fusion proteins, hGH-Tf (GT) and hGH-(H4)(2)-Tf (GHT) were obtained and assessed in hGH-deficient hypophysectomized rats for in vivo biological activity. Results from seven-day subcutaneous dosing (1.25mg/kg/day) demonstrated that both GT and GHT fusion proteins were bioactive in vivo, comparable to native hGH. However, only the GHT, but not GT, fusion protein promoted a modest but statistically significant weight gain after oral dosing with 12.5mg/kg/day.

Surface-functionalized nanoparticles for targeted gene delivery across nasal respiratory epithelium

The objective of this study was to determine whether surface-modified nanoparticles enhance permeability across nasal mucosa, while retaining the effectiveness of the payload. The uptake and permeability of polystyrene nanoparticles (PS-NPs; FluoSpheres) was evaluated across the various regions of the bovine nasal epithelia following conjugation with deslorelin and transferrin. Uptake and transport of PS-NPs, deslorelin-PS-NPs, and transferrin-PS-NPs exhibited regional differences in the order: inferior turbinate posterior (ITP) > medium turbinate posterior (MTP) > medium turbinate anterior (MTA). Uptake and transport also exhibited directionality and temperature dependence in these tissues. Further, uptake as well as transport of functionalized nanoparticles could be inhibited by excess free functionalizing ligand. Confocal microscopy indicated the presence of functionalized nanoparticles in respiratory epithelial cells, as well as other cell types of the nasal tissue. We chose the ITP region for further studies with deslorelin or transferrin-conjugated poly-l-lactide-co-glycolide nanoparticles (PLGA-NPs) encapsulating an anti-VEGF intraceptor (Flt23k) plasmid. Transport of the nanoparticles, as well as the plasmid from the nanoparticles, exhibited the following order: transferrin-PLGA-NPs > deslorelin-PLGA-NPs > PLGA-NPs >> plasmid. The ability of the nanoparticles transported across the nasal tissue to retain the effectiveness of the Flt23k plasmid was evaluated by measuring transfection efficiency (percentage of cells expressing GFP) and VEGF inhibition in LNCaP and PC-3 prostate cancer cells. Transfection efficiencies and VEGF inhibition in LNCaP and PC-3 cells exhibited the following trend: transferrin-PLGA-NPs >or= deslorelin-PLGA-NPs > PLGA-NPs >> plasmid. Further, functionalized nanoparticles exhibited transfection efficiencies and VEGF inhibition significantly superior compared with the routinely used transfecting agent, lipofectamine. Formulating plasmids into nanoparticulate delivery systems enhances the transnasal delivery and gene therapy at remote target cancer cells, which can be further enhanced by nanoparticle functionalization with deslorelin or transferrin.

Mechanisms of alveolar epithelial translocation of a defined population of nanoparticles

To explore mechanisms of nanoparticle interactions with and trafficking across lung alveolar epithelium, we utilized primary rat alveolar epithelial cell monolayers (RAECMs) and an artificial lipid bilayer on filter model (ALBF). Trafficking rates of fluorescently labeled polystyrene nanoparticles (PNPs; 20 and 100 nm, carboxylate (negatively charged) or amidine (positively charged)-modified) in the apical-to-basolateral direction under various experimental conditions were measured. Using confocal laser scanning microscopy, we investigated PNP colocalization with early endosome antigen-1, caveolin-1, clathrin heavy chain, cholera toxin B, and wheat germ agglutinin. Leakage of 5-carboxyfluorescein diacetate from RAECMs, and trafficking of (22)Na and (14)C-mannitol across ALBF, were measured in the presence and absence of PNPs. Results showed that trafficking of positively charged PNPs was 20-40 times that of negatively charged PNPs across both RAECMs and ALBF, whereas translocation of PNPs across RAECMs was 2-3 times faster than that across ALBF. Trafficking rates of PNPs across RAECMs did not change in the presence of EGTA (which decreased transepithelial electrical resistance to zero) or inhibitors of endocytosis. Confocal laser scanning microscopy revealed no intracellular colocalization of PNPs with early endosome antigen-1, caveolin-1, clathrin heavy chain, cholera toxin B, or wheat germ agglutinin. Leakage of 5-carboxyfluorescein diacetate from alveolar epithelial cells, and sodium ion and mannitol flux across ALBF, were not different in the presence or absence of PNPs. These data indicate that PNPs translocate primarily transcellularly across RAECMs, but not via known major endocytic pathways, and suggest that such translocation may take place by diffusion of PNPs through the lipid bilayer of cell plasma membranes.

Characterization of protein factor(s) in rat bronchoalveolar lavage fluid that enhance insulin transport via transcytosis across primary rat alveolar epithelial cell monolayers

The aim of this study was to characterize factor(s) in rat bronchoalveolar lavage fluid (BALF) that enhance(s) insulin transport across primary rat alveolar epithelial cell monolayers (RAECM) in primary culture. BALF was concentrated 7.5-fold using the Centricon device and the retentate was used to characterize the factor(s) involved in enhancing apical-to-basolateral transport of intact 125I-insulin across various epithelial cell monolayers. These factor(s) enhanced transport of intact insulin across type II cell-like RAECM (3-fold increase) and type I cell-like RAECM (2-fold increase), but not across Caco-2 or MDCK cell monolayers. The insulin transport-enhancing factor(s) were temperature- and trypsin-sensitive. The mechanism of enhancement did not seem to involve paracellular transport or fluid-phase endocytosis, since fluxes of sodium fluorescein and FITC-dextran (70 kDa) were not affected by the factor(s) in the apical bathing fluid. BALF enhancement of intact 125I-insulin transport was abolished at 4 degrees C and in the presence of monensin, suggesting involvement of transcellular pathways. Sephacryl S-200 purification of BALF retentate, followed by LC-MS/MS, indicated that the high molecular weight (>100 kDa) fractions (which show some homology to alpha-1-inhibitor III, murinoglobulin gamma 2, and pregnancy-zone protein) appear to facilitate transcellular transport of insulin across RAECM.

Enhancement of insulin transport across primary rat alveolar epithelial cell monolayers by endogenous cellular factor(s)

PURPOSE

To characterize factor(s) contained in apical medium of primary cultured rat alveolar epithelial type II cell-like monolayers (RAECM-II) that enhance insulin absorption across alveolar epithelial cells.

MATERIALS AND METHODS

Primary rat alveolar epithelial cell monolayers cultured on Transwells in the presence and absence of 10 ng/ml keratinocyte growth factor for 6 days were dosed from the apical compartment with radiolabeled insulin in: newborn bovine serum-containing medium (SM), conditioned medium from apical compartment of rat alveolar epithelial type I cell-like monolayers (RAECM-I) (CMI), or conditioned medium from apical compartment of RAECM-II (CMII). At the end of 2 h incubation, basolateral medium was collected and amounts of transported radiolabeled insulin were determined using a gamma counter. In order to determine the molecular size range of the enhancing factor(s), CMII was centrifuged in 50 kDa molecular weight cut-off Centricon tubes, and both retentate and filtrate were used as separate dosing solutions. Heat denaturation and ammonium sulphate precipitation were used to determine if the involved factor(s) represent proteins or other smaller soluble factors. Transalveolar transport rates of a paracellular marker, (14)C-mannitol, and fluid-phase marker, horseradish peroxidase, were determined in the presence and absence of the factors. Effects of temperature (4, 16 and 37 degrees C) on radiolabeled insulin fluxes were also measured.

RESULTS

Conditioned medium obtained from the apical compartment of RAECM-II, CMII, increased transport of insulin across the monolayers when compared to SM or CMI. The enhancing effect of CMII was retained in the precipitate following ammonium sulfate treatment and in the retentate after Centricon filtration. The enhancing effect of CMII was significantly decreased when heated at 80 degrees C for 15 min. CMII did not affect the transport of (14)C-mannitol or HRP, while its effect on insulin transport was decreased by 87% when temperature was lowered to 4 degrees C from 37 degrees C.

CONCLUSIONS

Conditioned medium from type II cell-like monolayer cultures appears to contain protein factor(s) which seem to be involved in facilitating active transcellular transport of insulin across primary cultured RAECM-II.

Accumulation of transferrin in Caco-2 cells: a possible mechanism of intestinal transferrin absorption

Transferrin receptor (TfR)-mediated endocytosis and transcytosis in enterocyte-like Caco-2 cells was investigated in order to elucidate the transport mechanism of orally administered Tf-fusion proteins. Cellular uptake and pulse chase studies were performed in Caco-2, MCF-7 and bladder carcinoma (5637) cells using 125I-labeled Tf (125I-Tf). Co-localization studies of Rab 11 and FITC-Tf endocytosed at either the apical or basolateral membrane were performed in polarized Caco-2 cells grown on Transwells, using confocal laser scanning microscopy (LSM510, Zeiss). Unlike in MCF-7 or 5637 cells, where rapid recycling of Tf was observed, a significant amount of endocytosed 125I-Tf accumulated in Caco-2 cells. This accumulation was especially noticeable with the internalization of 125I-Tf from the apical membrane of polarized Caco-2 cells. Confocal microscopy studies showed that apically, but not basolaterally, endocytosed FITC-Tf was delivered to a Rab11-positive compartment. Our results suggest that a significant amount of apically endocytosed Tf in intestinal epithelial cells is transported to a Rab11-positive compartment, possibly a late endosomal and slow recycling compartment. The Rab11-positive compartment may control the release of apically internalized Tf for either slow recycling to apical membrane or processing to transcytotic compartments.

In vivo, in vitro and ex vivo models to assess pulmonary absorption and disposition of inhaled therapeutics for systemic delivery

Despite the interest in systemic delivery of therapeutic molecules including macromolecular proteins and peptides via the lung, the accurate assessment of their pulmonary biopharmaceutics is a challenging experimental task. This article reviews in vivo, in vitro and ex vivo models currently available for studying lung absorption and disposition for inhaled therapeutic molecules. The general methodologies are discussed with recent advances, current challenges and perspectives, especially in the context of their use in systemic pulmonary delivery research. In vivo approaches in small rodents continue to be the mainstay of assessment by virtue of the acquisition of direct pharmacokinetic data, more meaningful when attention is given to reproducible dosing and control of lung-regional distribution through use of more sophisticated lung-dosing methods, such as forced instillation, microspray, nebulization and aerosol puff. A variety of in vitro lung epithelial cell lines models and primary cultured alveolar epithelial (AE) cells when grown to monolayer status offer new opportunity to clarify the more detailed kinetics and mechanisms of transepithelial drug transport. While continuous cell lines, Calu-3 and 16HBE14o-, show potential, primary cultured AE cell models from rat and human origins may be of greater use, by virtue of their universally tight intercellular junctions that discriminate the transport kinetics of different therapeutic entities. Nevertheless, the relevance of using these reconstructed barriers to represent complex disposition of intact lung may still be debatable. Meanwhile, the intermediate ex vivo model of the isolated perfused lung (IPL) appears to resolve deficiencies of these in vivo and in vitro models. While controlling lung-regional distributions, the preparation alongside a novel kinetic modeling analysis enables separate determinations of kinetic descriptors for lung absorption and non-absorptive clearances, i.e., mucociliary clearance, phagocytosis and/or metabolism. This ex vivo model has been shown to be kinetically predictive of in vivo, with respect to macromolecular disposition, despite limitations concerning short viable periods of 2-3 h and likely absence of tracheobronchial circulation. Given the advantages and disadvantages of each model, scientists must make appropriate selection and timely exploitation of the best model at each stage of the research and development program, affording efficient progress toward clinical trials for future inhaled therapeutic entities for systemic delivery.

Improving the Oral Efficacy of Recombinant Granulocyte Colony-Stimulating Factor and Transferrin Fusion Protein by Spacer Optimization

PURPOSE

To improve the oral efficacy of the recombinant fusion protein containing granulocyte colony-stimulating factor (G-CSF) and transferrin (Tf) by inserting a linker between the two protein domains.

MATERIALS AND METHODS

Oligonucleotides encoding flexible and helix-forming peptides were inserted to the recombinant plasmids. The fusion protein without linker insertion was used for comparison. The G-CSF cell-proliferation and Tf receptor-binding activities of the fusion proteins were tested in NFS-60 cells and Caco-2 cells, respectively, and in vivo myelopoietic assay with both subcutaneous and oral administration was performed in BDF1 mice.

RESULTS

All fusion proteins produced from transfected HEK293 cells were positive in Western-blotting assay with anti-G-CSF and anti-Tf antibodies. Among them, the fusion protein with a long helical (H4-2) linker showed the highest activity in NFS-60 cell proliferation assay, with an EC50 about ten-fold lower than that of the non-linker fusion protein. The fusion protein with H4-2 linker also showed a significantly higher myelopoietic effect when administered either subcutaneously or orally in BDF1 mice.

CONCLUSION

The insertion of a linker peptide, such as the helix linker H4-2, between G-CSF and Tf domains in the recombinant fusion protein can improve significantly both in vitro and in vivo myelopoietic activity over the non-linker fusion protein.

Assessment of transport rates of proteins and peptides across primary human alveolar epithelial cell monolayers

In this study, we investigated bi-directional fluxes (i.e., in absorptive and secretive directions) of human serum proteins [albumin (HSA), transferrin (TF), and immunoglobulin G (IgG)] and peptides/proteins of potential therapeutic relevance [insulin (INS), glucagon-like peptide-1 (GLP-1), growth hormone (GH), and parathyroid hormone (PTH)] across tight monolayers of human alveolar epithelial cells (hAEpC) in primary culture. Apparent permeability coefficients (P(app); x10(-7)cm/s, mean+/-S.D.) for GLP-1 (6.13+/-0.87 (absorptive) versus 1.91+/-0.51 (secretive)), HSA (2.45+/-1.02 versus 0.21+/-0.31), TF (0.88+/-0.15 versus 0.30+/-0.03), and IgG (0.36+/-0.22 versus 0.15+/-0.16) were all strongly direction-dependent, i.e., net absorptive, while PTH (2.20+/-0.30 versus 1.80+/-0.77), GH (8.33+/-1.24 versus 9.02+/-3.43), and INS (0.77+/-0.15 versus 0.72+/-0.36) showed no directionality. Trichloroacetic acid precipitation analysis of tested molecules collected from donor and receiver fluids exhibited very little degradation. This is the first study on permeability data for a range of peptides and proteins across an in vitro model of the human alveolar epithelial barrier. These data indicate that there is no apparent size-dependent transport conforming to passive restricted diffusion for the tested substances across human alveolar barrier, in part confirming net absorptive transcytosis. The obtained data differ significantly from previously published reports utilising monolayers from different species. It can be concluded that the use of homologous tissue should be preferred to avoid species differences.

Cell culture models of the respiratory tract relevant to pulmonary drug delivery

The respiratory tract holds promise as an alternative site of drug delivery due to fast absorption and rapid onset of drug action, with avoidance of hepatic and intestinal first-pass metabolism as an additional benefit compared to oral drug delivery. At present, the pharmaceutical industry increasingly relies on appropriate in vitro models for the faster evaluation of drug absorption and metabolism as an alternative to animal testing. This article reviews the various existing cell culture systems that may be applied as in vitro models of the human air-blood barrier, for instance, in order to enable the screening of large numbers of new drug candidates at low cost with high reliability and within a short time span. Apart from such screening, cell culture-based in vitro systems may also contribute to improve our understanding of the mechanisms of drug transport across such epithelial tissues, and the mechanisms of action how advanced drug carriers, such as nanoparticles or liposomes, can help to overcome these barriers. After all, the increasing use and acceptance of such in vitro models may lead to a significant acceleration of the drug development process by facilitating the progress into clinical studies and product registration.

Recombinant granulocyte colony-stimulating factor-transferrin fusion protein as an oral myelopoietic agent

An expression construct harboring granulocyte colony-stimulating factor (G-CSF)-transferrin (Tf) fusion protein (G-CSF-Tf) was engineered by fusing human cDNAs encoding G-CSF and Tf to explore the feasibility of using Tf as a carrier moiety for oral delivery of therapeutic proteins. The recombinant protein, G-CSF-Tf, was harvested from protein-free, conditioned medium of transfected HEK293 cells. The in vitro studies demonstrated that the purified G-CSF-Tf fusion protein possesses the activity of both Tf receptor (TfR) binding in Caco-2 cells and G-CSF-dependent stimulation of NFS-60 cell proliferation. Subcutaneous administration of G-CSF-Tf fusion protein to BDF1 mice demonstrated a pharmacological effect comparable to the commercial G-CSF on the increase of absolute neutrophil counts (ANC). However, the fusion protein elicited a significant increase in ANC upon oral administration to BDF1 mice, whereas G-CSF had no effect. This study also showed that orally administered G-CSF-Tf elicits a sustained myelopoietic effect up to 3 days, whereas the s.c. administered G-CSF or G-CSF-Tf lasts only 1 day. Furthermore, coadministration of free Tf abolished the increase of ANC by orally delivered G-CSF-Tf, suggesting that the recombinant protein is absorbed via a TfR-mediated process in the gastrointestinal tract. Taken together, we conclude that the Tf-based recombinant fusion protein technology represents a promising approach for future development of orally effective peptide and protein drugs.

Induction of epithelial-mesenchymal transition in alveolar epithelial cells by transforming growth factor-beta1: potential role in idiopathic pulmonary fibrosis

The hallmark of idiopathic pulmonary fibrosis (IPF) is the myofibroblast, the cellular origin of which in the lung is unknown. We hypothesized that alveolar epithelial cells (AECs) may serve as a source of myofibroblasts through epithelial-mesenchymal transition (EMT). Effects of chronic exposure to transforming growth factor (TGF)-beta1 on the phenotype of isolated rat AECs in primary culture and a rat type II cell line (RLE-6TN) were evaluated. Additionally, tissue samples from patients with IPF were evaluated for cells co-expressing epithelial (thyroid transcription factor (TTF)-1 and pro-surfactant protein-B (pro-SP-B), and mesenchymal (alpha-smooth muscle actin (alpha-SMA)) markers. RLE-6TN cells exposed to TGF-beta1 for 6 days demonstrated increased expression of mesenchymal cell markers and a fibroblast-like morphology, an effect augmented by tumor necrosis factor-alpha (TNF-alpha). Exposure of rat AECs to TGF-beta1 (100 pmol/L) resulted in increased expression of alpha-SMA, type I collagen, vimentin, and desmin, with concurrent transition to a fibroblast-like morphology and decreased expression of TTF-1, aquaporin-5 (AQP5), zonula occludens-1 (ZO-1), and cytokeratins. Cells co-expressing epithelial markers and alpha-SMA were abundant in lung tissue from IPF patients. These results suggest that AECs undergo EMT when chronically exposed to TGF-beta1, raising the possibility that epithelial cells may serve as a novel source of myofibroblasts in IPF.

Net absorption of IgG via FcRn-mediated transcytosis across rat alveolar epithelial cell monolayers

We characterized immunoglobulin G (IgG) transport across rat alveolar epithelial cell monolayers cultured on permeable supports. Unidirectional fluxes of biotin-labeled rat IgG (biot-rIgG) were measured in the apical-to-basolateral ( ab) and opposite ( ba) directions as functions of [rIgG] in upstream fluids at 37 and 4°C. We explored specificity of IgG transport by measuring fluxes in the presence of excess Fc, Fab, F(ab′)2, or chicken Ig (IgY). Expression of the IgG receptor FcRn and the effects of dexamethasone on FcRn expression and biot-rIgG fluxes were determined. Results show that ab flux of biot-rIgG is about fivefold greater than ba flux at an upstream concentration of 25 nM biot-rIgG at 37°C. Both ab and ba fluxes of rIgG saturate, resulting in net absorption with half-maximal concentration and maximal flow of 7.1 nM and 1.3 fmol·cm−2·h−1. At 4°C, both ab and ba fluxes significantly decrease, nearly collapsing net absorption. The presence of excess unlabeled Fc [but not Fab, F(ab′)2, or IgY] significantly reduces biot-rIgG fluxes. RT-PCR demonstrates expression of α- and β-subunits of rat FcRn. Northern analysis further confirms the presence of α-subunit of rat FcRn mRNA of ∼1.6 kb. Dexamethasone exposure for 72 h decreases the steady-state level of mRNA for rat FcRn α-subunit and the ab (but not ba) flux of biot-rIgG. These data indicate that IgG transport across alveolar epithelium takes place via regulable FcRn-mediated transcytosis, which may play an important role in alveolar homeostasis in health and disease.

Mechanisms of TfR-mediated transcytosis and sorting in epithelial cells and applications toward drug delivery

Transferrin receptor has been an important protein for many of the advances made in understanding the intricacies of the intramolecular sorting pathways of endocytosed molecules. The unique internalization and recycling functions of transferrin receptor have also made it an attractive choice for drug targeting and delivery of large protein-based therapeutics and toxins. Recent advances in elucidating the role of the intracellular controllers of transferrin recycling and sorting, such as Rab proteins and their effectors, have led to enhancement of transferrin receptor as a drug delivery vehicle. This review focuses on the use of transferrin receptor as an agent for facilitating drug delivery and targeting, and the role that mechanisms of transferrin receptor sorting and transcytosis play in these events.