Sustained Delivery of GLP-1 Receptor Agonists from Injectable Biomimetic Hydrogels Improves Treatment of Diabetes.

Glucagon-like peptide-1 (GLP-1) is an incretin hormone and neurotransmitter secreted from intestinal L-cells in response to nutrients to stimulate insulin and block glucagon secretion in a glucose-dependent manner. GLP-1 in itself is rapidly degraded, but long-acting GLP-1 receptor agonists (GLP-1 RAs) have become central in the treatment of T2D because of the beneficial effects extending also beyond glucose control. Currently, these therapeutics must be injected either daily or weekly or taken daily orally, leaving room for technological innovations that enable less frequent administrations, which will reduce patient burden and increase patient compliance. An ideal GLP-1 RA drug product would provide continuous therapy for upwards of four months from a single administration to match the cadence with which T2D patients typically visit their physician. In this work, we leveraged an injectable hydrogel depot technology to develop a long-acting GLP-1 RA drug product. By modulating the hydrogel properties to tune GLP-1 RA retention within the hydrogel depot, we engineered formulations capable of months-long GLP-1 RA delivery. Using a rat model of T2D, we confirmed that a single injection of hydrogel-based therapies exhibits sustained exposure of GLP-1 RA over 42 days, corresponding to a once-every four month therapy in humans. Moreover, these hydrogel therapies maintained optimal management of blood glucose and weight comparable to daily injections of a leading GLP-1 RA drug molecule. The pharmacokinetics and pharmacodynamics of these hydrogel-based long-acting GLP-1 RA treatments are promising for development of novel therapies reducing treatment burden for more effective management of T2D. Progress and Potential: While insufficient access to quality healthcare is problematic for consistent management of Type II diabetes (T2D), poor adherence to burdensome treatment regimens is one of the greatest challenges for disease management. Glucagon-like peptide 1 (GLP1) drugs have become central to the treatment of T2D due to their many beneficial effects beyond improving glucose control. Unfortunately, while optimization of GLP1 drugs has reduced treatment frequency from daily to weekly, significant patient burden still leads to poor patience compliance. In this work we developed an injectable hydrogel technology to enable GLP1 drugs only requiring administration once every four months. We showed in a rat model of T2D that one injection of a hydrogel-based therapy improves management of blood glucose and weight when compared with daily injections of the leading drug used clinically. These hydrogel-based GLP1 treatments are promising for reducing treatment burden and more effectively managing T2D. Future Impact: A GLP-1-based drug product providing four months of continuous therapy per administration could be transformational for the management of Type II diabetes (T2D). One of the most challenging aspects of diabetes management with GLP-1 mimics is maintenance of consistent levels of the drugs in the body, which is complicated by poor patient compliance on account of the high frequency of dosing required for current treatments. By leveraging a unique sustained release hydrogel depot technology we develop a months-long GLP-1 drug product candidate that has the potential to reduce patient burden and improving diabetes management. Overall, the hydrogel technology we describe here can dramatically reduce the frequency of therapeutic interventions, significantly increasing patient quality of life and reducing complications of diabetes management.Our next steps will focus on optimization of the drug formulations in a swine model of T2D, which is the most advanced and translationally-relevant animal model for these types of therapeutics. The long-term vision for this work is to translate lead candidate drug products towards clinical evaluation, which will also require comprehensive safety evaluation in multiple species and manufacturing our these materials according to Good Manufacturing Practices. The months-long-acting GLP-1 drug product that will come from this work has the potential to afford thus far unrealized therapeutic impact for the hundreds of millions of people with diabetes worldwide.

Use of a biomimetic hydrogel depot technology for sustained delivery of GLP-1 receptor agonists reduces burden of diabetes management.

Glucagon-like peptide-1 (GLP-1) is an incretin hormone and neurotransmitter secreted from intestinal L cells in response to nutrients to stimulate insulin and block glucagon secretion in a glucose-dependent manner. Long-acting GLP-1 receptor agonists (GLP-1 RAs) have become central to treating type 2 diabetes (T2D); however, these therapies are burdensome, as they must be taken daily or weekly. Technological innovations that enable less frequent administrations would reduce patient burden and increase patient compliance. Herein, we leverage an injectable hydrogel depot technology to develop a GLP-1 RA drug product capable of months-long GLP-1 RA delivery. Using a rat model of T2D, we confirm that one injection of hydrogel-based therapy sustains exposure of GLP-1 RA over 42 days, corresponding to a once-every-4-months therapy in humans. Hydrogel therapy maintains management of blood glucose and weight comparable to daily injections of a leading GLP-1 RA drug. This long-acting GLP-1 RA treatment is a promising therapy for more effective T2D management.

The upregulated intestinal folate transporters direct the uptake of ligand-modified nanoparticles for enhanced oral insulin delivery.

Transporters are traditionally considered to transport small molecules rather than large-sized nanoparticles due to their small pores. In this study, we demonstrate that the upregulated intestinal transporter (PCFT), which reaches a maximum of 12.3-fold expression in the intestinal epithelial cells of diabetic rats, mediates the uptake of the folic acid-grafted nanoparticles (FNP). Specifically, the upregulated PCFT could exert its function to mediate the endocytosis of FNP and efficiently stimulate the traverse of FNP across enterocytes by the lysosome-evading pathway, Golgi-targeting pathway and basolateral exocytosis, featuring a high oral insulin bioavailability of 14.4% in the diabetic rats. Conversely, in cells with relatively low PCFT expression, the positive surface charge contributes to the cellular uptake of FNP, and FNP are mainly degraded in the lysosomes. Overall, we emphasize that the upregulated intestinal transporters could direct the uptake of ligand-modified nanoparticles by mediating the endocytosis and intracellular trafficking of ligand-modified nanoparticles via the transporter-mediated pathway. This study may also theoretically provide insightful guidelines for the rational design of transporter-targeted nanoparticles to achieve efficient drug delivery in diverse diseases.

Multivariate analysis of phenol in freeze-dried and spray-dried insulin formulations by NIR and FTIR.

Dehydration is a commonly used method to stabilise protein formulations. Upon dehydration, there is a significant risk the composition of the formulation will change especially if the protein formulation contains volatile compounds. Phenol is often used as excipient in insulin formulations, stabilising the insulin hexamer by changing the secondary structure. We have previously shown that it is possible to maintain this structural change after drying. The aim of this study was to evaluate the residual phenol content in spray-dried and freeze-dried insulin formulations by Fourier transform infrared (FTIR) spectroscopy and near infrared (NIR) spectroscopy using multivariate data analysis. A principal component analysis (PCA) and partial least squares (PLS) projections were used to analyse spectral data. After drying, there was a difference between the two drying methods in the phenol/insulin ratio and the water content of the dried samples. The spray-dried samples contained more water and less phenol compared with the freeze-dried samples. For the FTIR spectra, the best model used one PLS component to describe the phenol/insulin ratio in the powders, and was based on the second derivative pre-treated spectra in the 850-650 cm(-1) region. The best PLS model based on the NIR spectra utilised three PLS components to describe the phenol/insulin ratio and was based on the standard normal variate transformed spectra in the 6,200-5,800 cm(-1) region. The root mean square error of cross validation was 0.69% and 0.60% (w/w) for the models based on the FTIR and NIR spectra, respectively. In general, both methods were suitable for phenol quantification in dried phenol/insulin samples.

Engineering of Orally Available, Ultralong-Acting Insulin Analogues: Discovery of OI338 and OI320.

Recently, the first basal oral insulin (OI338) was shown to provide similar treatment outcomes to insulin glargine in a phase 2a clinical trial. Here, we report the engineering of a novel class of basal oral insulin analogues of which OI338, 10, in this publication, was successfully tested in the phase 2a clinical trial. We found that the introduction of two insulin substitutions, A14E and B25H, was needed to provide increased stability toward proteolysis. Ultralong pharmacokinetic profiles were obtained by attaching an albumin-binding side chain derived from octadecanedioic (C18) or icosanedioic acid (C20) to the lysine in position B29. Crucial for obtaining the ultralong PK profile was also a significant reduction of insulin receptor affinity. Oral bioavailability in dogs indicated that C18-based analogues were superior to C20-based analogues. These studies led to the identification of the two clinical candidates OI338 and OI320 (10 and 24, respectively).

Molecular engineering of safe and efficacious oral basal insulin.

Recently, the clinical proof of concept for the first ultra-long oral insulin was reported, showing efficacy and safety similar to subcutaneously administered insulin glargine. Here, we report the molecular engineering as well as biological and pharmacological properties of these insulin analogues. Molecules were designed to have ultra-long pharmacokinetic profile to minimize variability in plasma exposure. Elimination plasma half-life of ~20 h in dogs and ~70 h in man is achieved by a strong albumin binding, and by lowering the insulin receptor affinity 500-fold to slow down receptor mediated clearance. These insulin analogues still stimulate efficient glucose disposal in rats, pigs and dogs during constant intravenous infusion and euglycemic clamp conditions. The albumin binding facilitates initial high plasma exposure with a concomitant delay in distribution to peripheral tissues. This slow appearance in the periphery mediates an early transient hepato-centric insulin action and blunts hypoglycaemia in dogs in response to overdosing.

Overcoming Poor Tabletability of Bulky Absorption Enhancers by Spray Drying Technology.

Absorption enhancers are often a major component of solid oral peptide formulations as compared to the active pharmaceutical ingredient and excipients. This commonly results in poor tabletability that is hard to mitigate in direct compaction by addition of small amounts of excipients. To improve the tabletability of bulky absorption enhancers, the model absorption enhancers, sodium cholate and deoxycholic acid, were co-spray-dried with hydroxypropyl methylcellulose E5, where the percentage of absorption enhancers was not lower than 90% (w/w). The physicochemical properties of the resulting powders were assessed by laser diffraction, scanning electron microscopy, X-ray powder diffraction, thermogravimetric analysis, and differential scanning calorimetry. The powders were compressed into tablets, and the tabletability was evaluated. Co-spray drying with 10% of hydroxypropyl methylcellulose significantly improved the tabletability of the both absorption enhancers. Moreover, it was demonstrated that small particle size and amorphous state rather than high moisture content contributed to the improved tabletability of the spray-dried powders. The study suggests that spray drying technology can be promising to overcome the poor tabletability of oral peptide formulation consisting of large amounts of absorption enhancers.

Quality by design - Spray drying of insulin intended for inhalation.

Quality by design (QBD) refers to a holistic approach towards drug development. Important parts of QBD include definition of final product performance and understanding of formulation and process parameters. Inhalation of proteins for systemic distribution requires specific product characteristics and a manufacturing process which produces the desired product. The objective of this study was to understand the spray drying process of insulin intended for pulmonary administration. In particular, the effects of process and formulation parameters on particle characteristics and insulin integrity were investigated. Design of experiments (DOE) and multivariate data analysis were used to identify important process parameters and correlations between particle characteristics. The independent parameters included the process parameters nozzle, feed, and drying air flow rate and drying air temperature along with the insulin concentration as a formulation parameter. The dependent variables included droplet size, geometric particle size, aerodynamic particle size, yield, density, tap density, moisture content, outlet temperature, morphology, and physical and chemical integrity. Principal component analysis was performed to find correlations between dependent and independent variables. Prediction equations were obtained for all dependent variables including both interaction and quadratic terms. Overall, the insulin concentration was found to be the most important parameter, followed by inlet drying air temperature and the nozzle gas flow rate. The insulin concentration mainly affected the particle size, yield and tap density, while the inlet drying air temperature mainly affected the moisture content. No change was observed in physical and chemical integrity of the insulin molecule.

Solvent diversity in polymorph screening.

Selecting a diverse set of solvents to be included in polymorph screening assignments can be a challenging task. As an aid to decision making, a database of 218 organic solvents with 24 property descriptors was explored and visualized using multivariate tools. The descriptors included, among others, log P, vapor pressure, hydrogen bond formation capabilities, polarity, number of pi-bonds and descriptors derived from molecular interaction field calculations (e.g., size/shape parameters and hydrophilic/hydrophobic regions). The data matrix was initially analyzed using principal component analysis (PCA). Results from the PCA showed 57% cumulative variance being explained in the first two principal components (PCs), although relevant information was also found in the third, fourth and fifth component, revealing distinct clusters of solvents. Since five dimensions were not suitable for visual presentation, a nonlinear method, self-organizing maps (SOMs), was applied to the dataset. The constructed SOM displayed features of clusters observed in the first three PCs, however in a more compelling way. Thus, the SOM was chosen as the visually most convenient way to display the diversity of the 218 solvents. In addition, it was demonstrated how safety aspects can be considered by labeling a large fraction of the solvents in the SOM with toxicological information.

Characterization and physical stability of spray dried solid dispersions of probucol and PVP-K30.

The main purpose of this study was to obtain stable, well-characterized solid dispersions (SDs) of amorphous probucol and polyvinylpyrrolidone K-30 (PVP-K30) with improved dissolution rates. A secondary aim was to investigate the flow-through dissolution method for in-vitro dissolution measurements of small-sized amorphous powders dispersed in a hydrophilic polymer. SDs were prepared by spray drying solutions of probucol and different amounts of PVP-K30. The obtained SDs were characterized by dissolution rate measurements in a flow-through apparatus, X-ray Powder Diffraction (XRPD), Differential Scanning Calorimetry (DSC), Scanning Electron Microscopy (SEM), particle sizing (laser diffraction) and Brunauer-Emmett-Teller Method (BET) and results were compared with starting material and a physical mixture. The physical stability was monitored after storage at 25 degrees C and 60% RH for up to 12 weeks. The flow-through method was found suitable as dissolution method. All SDs showed improved in-vitro dissolution rates when compared to starting material and physical mixtures. The greatest improvement in the in-vitro dissolution rate was observed for the highest polymer to drug ratio. By means of the results from XRPD and DSC, it was argued that the presence of amorphous probucol improved the dissolution rate, but the amorphous state could not fully account for the difference in dissolution profiles between the SDs. It was suggested that the increase in surface area due to the reduction in particle size contributed to an increased dissolution rate as well as the presence of PVP-K30 by preventing aggregation and drug re-crystallization and by improving wettability during dissolution. The stabilizing effect of the polymer was verified in the solid state, as all the SDs retained probucol in the amorphous state throughout the entire length of the stability study.

Functional nanoparticles exploit the bile acid pathway to overcome multiple barriers of the intestinal epithelium for oral insulin delivery.

Oral absorption of protein/peptide-loaded nanoparticles is often limited by multiple barriers of the intestinal epithelium. In addition to mucus translocation and apical endocytosis, highly efficient transepithelial absorption of nanoparticles requires successful intracellular trafficking, especially to avoid lysosomal degradation, and basolateral release. Here, the functional material, deoxycholic acid-conjugated chitosan, is synthesized and loaded with the model protein drug insulin into deoxycholic acid-modified nanoparticles (DNPs). The DNPs designed in this study are demonstrated to overcome multiple barriers of the intestinal epithelium by exploiting the bile acid pathway. In Caco-2 cell monolayers, DNPs are internalized via apical sodium-dependent bile acid transporter (ASBT)-mediated endocytosis. Interestingly, insulin degradation in the epithelium is significantly prevented due to endolysosomal escape of DNPs. Additionally, DNPs can interact with a cytosolic ileal bile acid-binding protein that facilitates the intracellular trafficking and basolateral release of insulin. In rats, intravital two-photon microscopy also reveals that the transport of DNPs into the intestinal villi is mediated by ASBT. Further pharmacokinetic studies disclose an oral bioavailability of 15.9% in type I diabetic rats after loading freeze-dried DNPs into enteric-coated capsules. Thus, deoxycholic acid-modified chitosan nanoparticles can overcome multiple barriers of the intestinal epithelium for oral delivery of insulin.

Helium pycnometry as a tool for assessment of sealing efficiency in microencapsulation.

There is a need for a fast and reliable method to evaluate the development in coating quality during coating, especially for fast dissolving coatings. In the present study, pycnometric density was evaluated as a tool for assessment of coating quality in terms of sealing efficiency for microspheres coated with polymeric aqueous solutions. Further, it was investigated if the method could be used to study effects of spray variables on the sealing efficiency of coated microspheres. The microcrystalline cellulose particles Ethispheres250 were coated with aqueous solutions of Hypromellose 5 and Povidone K-90F by Wurster bottom-spray technique. End products and samples drawn during coating were analysed in terms of pycnometric helium density and scanning electron microscopy (SEM). Experiments constituted a 2(3) factorial design with the following spray related variables: atomisation air flow, polymer type, and solution concentration/viscosity. Helium pycnometric density was seen to lower gradually during coating in all experiments and to follow a common pattern. The quantitative lowering in density was further seen to correlate to sealing of voids by gradual covering of the microsphere surface and thus the sealing efficiency. Hence, the present data suggests helium pycnometry as a tool for assessment of coating quality in terms of sealing efficiency. This goes particularly for testing of products coated with water-soluble coatings, where dissolution testing obviously is compromised. The specific data on sealing efficiency might also add to other analytical methods in the analysis of coating quality, in general. End point densities of coated microspheres were seen to reveal differences in sealing efficiency between polymers. Measured densities of final products were also generally seen to reflect differences in coating permeability caused by variations in spray conditions. Thus, the measurement of density is a potential a tool for evaluation of spray conditions with respect to sealing of microspheres and identification of critical spray conditions.

Computational prediction of solubilizers' effect on partitioning.

A computational model for the prediction of solubilizers' effect on drug partitioning has been developed. Membrane/water partitioning was evaluated by means of immobilized artificial membrane (IAM) chromatography. Four solubilizers were used to alter the partitioning in the IAM column. Two types of molecular descriptors were calculated: 2D descriptors using the MOE software and 3D descriptors using the Volsurf software. Structure-property relationships between each of the two types of descriptors and partitioning were established using partial least squares, projection to latent structures (PLS) statistics. Statistically significant relationships between the molecular descriptors and the IAM data were identified. Based on the 2D descriptors structure-property relationships R(2)Y=0. 99 and Q(2)=0.82-0.83 were obtained for some of the solubilizers. The most important descriptor was related to logP. For the Volsurf 3D descriptors models with R(2)Y=0.53-0.64 and Q(2)=0.40-0.54 were obtained using five descriptors. The present study showed that it is possible to predict partitioning of substances in an artificial phospholipid membrane, with or without the use of solubilizers.

Determination of surface-adsorbed excipients of various types on drug particles prepared by antisolvent precipitation using HPLC with evaporative light scattering detection.

A common challenge in the development of new drug substances is poor dissolution characteristics related to low aqueous solubility. One approach to overcome this problem is antisolvent precipitation in the presence of polymers or surfactants, which may enhance the dissolution rate through reduced particle size and increased wettability. In this study, a simple method based on size exclusion chromatography (SEC) with evaporative light scattering detection (ELSD) was developed for the determination of polymers and surfactants adsorbed to drug particles prepared by antisolvent precipitation of the poorly water-soluble model drug Lu 28-179. Detection of many polymeric excipients and surfactants is problematic due to the lack of UV-absorbing chromophores, but ELSD proved successful for the direct determination of the investigated compounds. A mixed mode column was used to effectively separate each of the excipient structures from the drug. The mobile phase comprised acetonitrile-ammonium formate (20mM; pH 6.5) (50:50, v/v) at a flow-rate of 0.6 ml/min. Qualification studies showed that the method was adequately sensitive and precise with limits of detection between 0.72 and 4.32 microg/ml. Linearity of the calibration curves was achieved by log-log modelling. The method was applied for determination of nine polymeric excipients and surfactants adsorbed to particles of the model drug. The extent of excipient adsorption varied between 0.07 and 1.39% (w/w) of the total particle weight.

Inhibition of tumor necrosis factor-alpha reduces atherosclerosis in apolipoprotein E knockout mice.

OBJECTIVE: Inflammation plays an important role in atherosclerosis. One of the most potent pro-inflammatory cytokines is tumor necrosis factor-alpha (TNF-alpha), a cytokine identified to have a pathogenic role in chronic inflammatory diseases such as rheumatoid arthritis (RA). The aim of the study was to evaluate the importance of TNF-alpha in atherogenesis. METHODS AND RESULTS: Mice deficient in both apolipoprotein E (apoE) and TNF-alpha were compared regarding their atherosclerotic burden. Mice were fed a Western-style diet (WD) or normal chow. Mice deficient in both apoE and TNF-alpha exhibited a 50% (P=0.035) reduction of relative lesion size after 10 weeks of WD. Bone marrow transplantation of apoE(o) mice with apoE(o)tnf-alpha(o) bone marrow resulted in a 83% (P=0.021) reduction after 25 weeks on WD. In apoE knockout mice treated with recombinant soluble TNF receptor I releasing pellets, there was a reduction in relative lesion size after 25 weeks of 75% (P=0.018). CONCLUSIONS: These findings demonstrate that TNF-alpha is actively involved in the progression of atherosclerosis. Accordingly, TNF-alpha represents a possible target for prevention of atherosclerosis. This may be of particular importance in rheumatoid arthritis because these patients have an increased risk for cardiovascular disease.

Liposomes containing cholesterol analogues of botanical origin as drug delivery systems to enhance the oral absorption of insulin.

In fear of animal-associated diseases, there is a trend in searching for non-animal derived substitutes for existing excipients in the pharmaceutical industries. This paper aimed to screen cholesterol analogues as membrane stabilizers of liposomes from botanical sterols, including ß-sitosterol, stigmasterol, ergosterol and lanosterol. Liposomes containing four kinds of sterols were prepared and evaluated in vitro and in vivo as oral delivery system of insulin. Liposomes containing ß-sitosterol (Si-Lip), stigmasterol (St-Lip) and lanosterol (La-Lip) was found not to protect insulin against degradation. Only 10% of the initial insulin in liposomes was preserved after a 30 min exposure to simulated gastric fluids. However, the protective ability of liposomes containing ergosterol (Er-Lip) was similar to that of liposomes containing sodium glycocholate (Sgc-Lip) and superior to that of liposomes containing cholesterol (Ch-Lip). In addition, the blood glucose level can decrease to about 50% of initial level after oral Er-Lip which was significantly superior to the in vivo performance of Si-Lip and Ch-Lip and similar to Sgc-Lip. Er-Lips of ergosterol/phospholipids ratios of 1:4 or 1:6 exerts more pronounced protective ability of insulin in simulated gastrointestinal fluids and hypoglycemic effects in rats than other formulations. Furthermore, Er-Lips exerted low toxicity to Caco-2 cells through a cell viability study. Meahwhile, insulin permeability was significantly increased across Caco-2 monolayers by encapsulating in Er-Lip. It was concluded that ergosterol could be used as a substitute for cholesterol and bile salt derivatives in liposomes to enhance oral bioavailability of insulin.

In silico modelling of permeation enhancement potency in Caco-2 monolayers based on molecular descriptors and random forest.

Structural traits of permeation enhancers are important determinants of their capacity to promote enhanced drug absorption. Therefore, in order to obtain a better understanding of structure-activity relationships for permeation enhancers, a Quantitative Structural Activity Relationship (QSAR) model has been developed. The random forest-QSAR model was based upon Caco-2 data for 41 surfactant-like permeation enhancers from Whitehead et al. (2008) and molecular descriptors calculated from their structure. The QSAR model was validated by two test-sets: (i) an eleven compound experimental set with Caco-2 data and (ii) nine compounds with Caco-2 data from literature. Feature contributions, a recent developed diagnostic tool, was applied to elucidate the contribution of individual molecular descriptors to the predicted potency. Feature contributions provided easy interpretable suggestions of important structural properties for potent permeation enhancers such as segregation of hydrophilic and lipophilic domains. Focusing on surfactant-like properties, it is possible to model the potency of the complex pharmaceutical excipients, permeation enhancers. For the first time, a QSAR model has been developed for permeation enhancement. The model is a valuable in silico approach for both screening of new permeation enhancers and physicochemical optimisation of surfactant enhancer systems.

Application of confocal laser scanning microscopy in characterization of chemical enhancers in drug-in-adhesive transdermal patches.

The purpose of this study was to evaluate the application of confocal laser scanning microscopy (CLSM) in the examination of the embedment and the release characteristics of chemical permeation enhancers from transdermal drug delivery systems (TDDSs) of the "drug-in-adhesive" type. The enhancer lauric acid and a lauric acid fluorescing probe of the Bodipy type were incorporated into TDDSs consisting of an acrylic, a polyisobutylene, or a silicone polymer adhesive. Three-dimensional confocal images of the distribution were obtained before and during release into an aqueous medium. The images showed that the lauric acid fluorescing probe was homogeneously embedded in all the adhesives except for 1 polyisobutylene. The release profiles and release rate constants of the lauric acid fluorescing probe were consistent with data from a release study of lauric acid performed using conventional measurements of the released amounts. This indicated that lauric acid was distributed in a homogeneous manner. Furthermore, it was possible to illustrate the mechanics of the diffusion process inside the TDDS and compare these patterns with theoretically drawn profiles, based on Fick's law of diffusion. CLSM was demonstrated to be an excellent tool to study how enhancers are incorporated and diffuse into a TDDS.

Orally active-targeted drug delivery systems for proteins and peptides.

INTRODUCTION: In the past decade, extensive efforts have been devoted to designing 'active targeted' drug delivery systems (ATDDS) to improve oral absorption of proteins and peptides. Such ATDDS enhance cellular internalization and permeability of proteins and peptides via molecular recognition processes such as ligand-receptor or antigen-antibody interaction, and thus enhance drug absorption. AREAS COVERED: This review focuses on recent advances with orally ATDDS, including ligand-protein conjugates, recombinant ligand-protein fusion proteins and ligand-modified carriers. In addition to traditional intestinal active transport systems of substrates and their corresponding receptors, transporters and carriers, new targets such as intercellular adhesion molecule-1 and ß-integrin are also discussed. EXPERT OPINION: ATDDS can improve oral absorption of proteins and peptides. However, currently, no clinical studies on ATDDS for proteins and peptides are underway, perhaps due to the complexity and limited knowledge of transport mechanisms. Therefore, more research is warranted to optimize ATDDS efficiency.