Transport of macromolecules across the capillary walls

Microphysiological Conditions Do Not Affect MDR1-Mediated Transport of Rhodamine 123 above an Artificial Proximal Tubule

Despite disadvantages, such as high cost and their poor predictive value, animal experiments are still the state of the art for pharmaceutical substance testing. One reason for this problem is the inability of standard cell culture methods to emulate the physiological environment necessary to recapitulate in vivo processes. Microphysiological systems offer the opportunity to close this gap. In this study, we utilize a previously employed microphysiological system to examine the impact of pressure and flow on the transportation of substances mediated by multidrug resistance protein 1 (MDR1) across an artificial cell-based tubular barrier. By using a miniaturized fluorescence measurement device, we could continuously track the MDR1-mediated transport of rhodamine 123 above the artificial barrier over 48 h. We proved that applying pressure and flow affects both active and passive transport of rhodamine 123. Using experimental results and curve fittings, the kinetics of MDR1-mediated transport as well as passive transport were investigated; thus, a kinetic model that explains this transport above an artificial tubular barrier was identified. This kinetic model demonstrates that the simple Michaelis-Menten model is not an appropriate model to explain the MDR1-mediated transport; instead, Hill kinetics, with Hill slope of n = 2, is a better fit. The kinetic values, K_m, V_max, and apparent permeability (P_app), obtained in this study are comparable with other in vivo and in vitro studies. Finally, the presented proximal tubule-on-a-chip can be used for pharmaceutical substance testing and to investigate pharmacokinetics of the renal transporter MDR1.

Fibroblast Growth Factor 2 Conjugated with Monomethyl Auristatin E Inhibits Tumor Growth in a Mouse Model

Worldwide, cancer is the second leading cause of death. Regardless of the continuous progress in medicine, we still do not have a fully effective anti-cancer therapy. Therefore, the search for new targeted anti-cancer drugs is still an unmet need. Here, we present novel protein–drug conjugates that inhibit tumor growth in a mouse model of human breast cancer. We developed conjugates based on fibroblast growth factor (FGF2) with improved biophysical and biological properties for the efficient killing of cancer cells overproducing fibroblast growth factor receptor 1 (FGFR1). We used hydrophilic and biocompatible PEG4 or PEG27 molecules as a spacer between FGF2 and the toxic agent monomethyl auristatin E. All conjugates exhibited a cytotoxic effect on FGFR1-positive cancer cell lines. The conjugate with the highest hydrodynamic size (42 kDa) and cytotoxicity was found to efficiently inhibit tumor growth in a mouse model of human breast cancer.

Transglutaminase and Sialyltransferase Enzymatic Approaches for Polymer Conjugation to Proteins

Proteins hold a central role in medicine and biology, also confirmed by the several therapeutic applications based on biologic drugs. Such therapies are of great relevance thanks to high potency and safety of proteins. Nevertheless, many proteins as therapeutics might present issues like fast kidney clearance, rapid enzymatic degradation, or immunogenicity. Such defects implicate frequent administrations or administrations at high doses of the therapeutics, thus yielding or exacerbating potential side effects. A successful technology for improving the clinical profiles of proteins is the conjugation of polymers to the protein surface. The design of a protein-polymer conjugate presents critical aspects that determine the efficacy and safety of the final product. The control over stoichiometry and conjugation site is a strict criterion on which researchers have been intensively focused during the years, in order to obtain homogeneous and batch-to-batch reproducible products. An innovative site-specific conjugation strategy relies on the use of enzymes as tools to mediate polymer conjugation. Enzymatic approaches are attractive because they allow site-selective polymer conjugation at specific protein amino acids. In these reactions, the polymer is a substrate analog that replaces the native substrate. Furthermore, enzymes can count other advantages such as high yields of conversion and physiological conditions of reaction. This chapter provides a meaningful description of protein-polymer conjugation through transglutaminase-mediated and sialyltransferase-mediated enzymatic strategies, reporting the mechanism of action and some relevant examples.

Two-Pore Minimum Physiologically-based Pharmacokinetic Model to Describe the Disposition of Therapeutic Monoclonal IgG Antibody in Humans

PURPOSE

The aim of this study was to develop a two-pore minimum physiologically-based pharmacokinetic (mPBPK) model in describing the pharmacokinetic (PK) of therapeutic monoclonal antibody (TMAb) in human subjects.

METHODS

PK data used in this study were endogenous/exogenous native IgG and two TMAbs (palivizumab and Motavizumab-YTE) in normal volunteer or familial hypercatabolic hypoproteinemia (FIHH) patient. Several important components were implemented to overcome the limitations of the early mPBPK model, e.g. two-pore model to describe the transcapillary transport of IgG from vascular to interstitial space. Six mPBPK models with different osmotic reflection coefficient (OFC) of transcapillary transport, endocytosis rates (ETR) and plasma clearance for the TMAbs/IgG were tested and the best model was selected using AICc values.

RESULTS

The final model consisted of different OFC and ETR values for native IgG and TMAbs, supporting the hypothesis that the dynamics in the endosomal space had an important role in the compliant FcRn salvage mechanism to determine the clearance of TMAbs. The estimated FcRn concentration of FIHH subjects was 2.72 μmol/l. The final two-pore mPBPK model has a better performance for native IgG than previously developed mPBPK model.

CONCLUSIONS

The final two-pore mPBPK model not only overcome the limitations of the early mPBPK model but also has a better performance to describe the disposition of the IgG antibody in human subjects.

Strategies to combine ROP with ATRP or RAFT polymerization for the synthesis of biodegradable polymeric nanoparticles for biomedical applications

The available strategies to combine CRPs and ROP in the synthesis of highly engineered polymer nanoparticles are here critically discussed.

Site-Specific In Vivo Bioorthogonal Ligation via Chemical Modulation

A critical limitation of bioorthogonal click chemistry for in vivo applications has been its low reaction efficiency due to the pharmacokinetic barriers, such as blood distribution, circulation, and elimination in living organisms. To identify key factors that dominate the efficiency of click chemistry, here a rational design of near-infrared fluorophores containing tetrazine as a click moiety is proposed. Using trans-cyclooctene-modified cells in live mice, it is found that the in vivo click chemistry can be improved by subtle changes in lipophilicity and surface charges of intravenously administered moieties. By controlling pharmacokinetics, biodistribution, and clearance of click moieties, it is proved that the chemical structure dominates the fate of in vivo click ligation.

Efficient hepatic delivery of drugs: novel strategies and their significance

Liver is a vital organ responsible for plethora of functions including detoxification, protein synthesis, and the production of biochemicals necessary for the sustenance of life. Therefore, patients with chronic liver diseases such as viral hepatitis, liver cirrhosis, and hepatocellular carcinoma need immediate attention to sustain life and as a result are often exposed to the prolonged treatment with drugs/herbal medications. Lack of site-specific delivery of these medications to the hepatocytes/nonparenchymal cells and adverse effects associated with their off-target interactions limit their continuous use. This calls for the development and fabrication of targeted delivery systems which can deliver the drug payload at the desired site of action for defined period of time. The primary aim of drug targeting is to manipulate the whole body distribution of drugs, that is, to prevent distribution to non-target cells and concomitantly increase the drug concentration at the targeted site. Carrier molecules are designed for their selective cellular uptake, taking advantage of specific receptors or binding sites present on the surface membrane of the target cell. In this review, various aspects of liver targeting of drug molecules and herbal medications have been discussed which elucidate the importance of delivering the drugs/herbal medications at their desired site of action.

Nanotechnology and site-targeted drug delivery

Nanotechnology, building on its ability to control or manipulate structures at the atomic level, promises to develop effective drug-delivery systems. This is to be achieved through creating structures that have novel properties because of their small size. This is not an entirely new concept in site-targeted drug delivery, and this critical review examines recent contributions made by 'nanotechnology' to solve critical issues concerning the development of therapeutically effective and acceptable site-targeted drug delivery systems. It is shown that very little progress has been made. For nanotechnology rationally to generate materials useful in human therapy it will need to progress in full recognition of all the requirements biology places on the acceptability of exogenous materials.

Hemoconcentration caused by microvascular dysfunction after blast injuries to the chest and abdomen of rabbits

BACKGROUND

One of the important causes of death after blast injuries is reduced blood volume, which typically results from hemorrhage but may also result from nonhemorrhagic causes. Hemoconcentration is one such alternate cause of reduced blood volume, but its mechanism is unclear. Because blood is condensed after chest-abdomen blast injuries in rabbits, a series of experiments was conducted to clarify this phenomenon.

METHODS

Chest-abdomen blast injuries from different distances (10 cm, 15 cm, 20 cm, and 30 cm) were induced in male rabbits. ¹²⁵I-albumin was injected into the blood, and its concentration in different organs was tested at various times after the blast injury. The residual radioactivity in different organs and the pre- and postinjury hematocrit was also tested. Histologic evaluations were conducted to detect the injuries to the different organs.

RESULTS

After injury, ¹²⁵I-albumin leaked out of the vessels into organs such as the lungs, liver, and kidneys. The volume of leakage was highly correlated with the distance from the blast. At a distance of 10 cm, the rate of leakage was the highest. The hematocrit was higher for 30 minutes and 3 hours after the injury; 6 hours after the injury, the hematocrit began to return to normal levels. The residual radioactivity of ¹²⁵I-albumin was increased in the heart, brain, lungs, and kidneys, especially at a distance of 10 cm. Histologic evaluation results showed that the cells, microvessels, and organelles of the microvessel endothelial cells in the vital organs, such as the kidneys, were damaged.

CONCLUSION

The preliminary results indicate that microvessels in the lungs and kidneys are the key targets of blast injuries. The damage to the microvessels leads to leakage of albumin, which is one of the important reasons for hemoconcentration in the absence of active bleeding after a blast injury. Treatment should be initiated in victims of blast injuries who are severely wounded as soon as possible after the explosion during the earliest stages of the injury to avoid the occurrence of shock or other severe complications.

State of the art in PEGylation: the great versatility achieved after forty years of research

In the recent years, protein PEGylation has become an established and highly refined technology by moving forward from initial simple random coupling approaches based on conjugation at the level of lysine ε-amino group. Nevertheless, amino PEGylation is still yielding important conjugates, currently in clinical practice, where the degree of homogeneity was improved by optimizing the reaction conditions and implementing the purification processes. However, the current research is mainly focused on methods of site-selective PEGylation that allow the obtainment of a single isomer, thus highly increasing the degree of homogeneity and the preservation of bioactivity. Protein N-terminus and free cysteines were the first sites exploited for selective PEGylation but currently further positions can be addressed thanks to approaches like bridging PEGylation (disulphide bridges), enzymatic PEGylation (glutamines and C-terminus) and glycoPEGylation (sites of O- and N-glycosylation or the glycans of a glycoprotein). Furthermore, by combining the tools of genetic engineering with specific PEGylation approaches, the polymer can be basically coupled at any position on the protein surface, owing to the substitution of a properly chosen amino acid in the sequence with a natural or unnatural amino acid bearing an orthogonal reactive group. On the other hand, PEGylation has not achieved the same success in the delivery of small drugs, despite the large interest and several studies in this field. Targeted conjugates and PEGs for combination therapy might represent the promising answers for the so far unmet needs of PEG as carrier of small drugs. This review presents a thorough panorama of recent advances in the field of PEGylation.

PEGylation: Posttranslational bioengineering of protein biotherapeutics

Polymer conjugation, especially by poly(ethylene glycol), has become a leading technology for the delivery of proteins. Nowadays, biotech drugs represent an increasing share of the new approved drugs, but their use is often prevented by drawbacks and safety concern. In particular, short in vivo half-life and immunogenicity are significant problems faced by the researchers dealing with the development of protein and peptide drugs. The chemical linking of a polymer to the protein surface has proved effective in prolonging protein blood circulation and reducing the immunogenicity by decreasing renal clearance and shielding immunogenic epitopes, respectively. So far, PEGylation has already led to nine marketed conjugates with great therapeutic success.:

Essential properties of drug-targeting delivery systems

How, if at all, can drug delivery help to create ideal drugs? After four decades of trying, an effective site-specific drug-delivery system has not yet been developed. This review draws attention to the pharmacokinetic conditions that must be met to achieve a successful performance by site-selective drug-carrier delivery systems. In a drug-carrier approach, a drug is attached to a macromolecular carrier via a chemically labile linker. The carrier transports the drug to its site of action and releases it at the target site. For this simple approach to work, several fundamental conditions (nonspecific interactions, target site access, drug release and drug suitability) must be satisfied. The importance of these essential requirements, not always recognized in the development of drug-delivery systems, is discussed and illustrated by recent examples selected from the literature.

Release from polymeric prodrugs: linkages and their degradation

Polymeric prodrugs have evolved into a very useful class of drug delivery agents. Numerous polymeric prodrugs have been prepared for applications ranging from passive drug targeting to controlled release. The mechanistic aspects of the release processes, however, have not been clearly delineated. This review highlights the salient features of the chemical reactions that are responsible for drug release from these systems. The mechanisms of release from polymeric prodrugs employing various chemical linkages, esters, carbonates, carbamates, C=N linkage and amides, are discussed.

Synthesis and characterization of branched poly(l-glutamic acid) as a biodegradable drug carrier

Polymeric drug delivery systems are used not only to improve aqueous solubility of drug molecules but also to achieve desirable pharmacokinetics and an enhanced therapeutic index. New biodegradable polymers are needed to improve the biodistribution and targeting-ability of polymeric carriers. In this study, the synthesis and characterization of branched poly(L-glutamic acid) (PG) containing multiple PG chains centered on a poly(amidoamine) (PAMAM) dendrimer or polyethyleneimine (PEI) cores were described. The branched PG polymers were obtained by ring-opening polymerization of benzyl ester of L-glutamic acid N-carboxyanhydride using PAMAM or PEI as the initiator. These polymers were degradable in the presence of the lysosomal enzyme cathepsin B, albeit more slowly than linear PG. Unlike conventional linear PG, each branched PG possessed multiple terminal amino groups. This made it possible to attach multiple targeting moieties selectively to the termini of branched PG. Conjugation of monofunctional or heterodifunctional polyethylene glycol to the chain ends of branched PG was demonstrated in the presence of side chain carboxyl groups. Furthermore, folic acid, a model targeting moiety, and the near-infrared dye indocyanine green, a model diagnostic agent, were successfully conjugated to the terminal amino groups and the side chain carboxyl groups of branched PG, respectively. The resulting conjugate had reduced nonspecific interaction and bound selectively to tumor cells expressing folate receptors. Thus, branched PG may be useful as a polymeric carrier for targeted drug delivery.

Extravasation of macromolecules

Macromolecules can extravasate across the normal endothelium by transcapillary pinocytosis as well as by passage through interendothelial cell junctions, gaps or fenestrae. The main biological factors that control extravasation of a solute include regional differences in the capillary structures, the disease state of the organ or tissue, and the rate of blood and lymph supply. Physicochemical properties that are of profound significance in the extravasation of macromolecules are molecular size, shape, charge and hydrophilic/lipophilic balance (HLB) characteristics. Extravasation of small drugs, proteins, oligonucleotides and genes can be controlled by conjugating or forming complexes with macromolecular carriers. This requires a thorough understanding of the relationship between the chemical structures, physicochemical properties and the pharmacokinetics of both carrier and active molecules. This review article discusses the extravasation of macromolecules from the view points of pharmacokinetics and drug delivery systems, with the main emphasis on the extravasation across the liver, kidney and tumor capillaries.

Fate of water-soluble polymers administered via different routes

The biological fate of synthetic water-soluble polymers administered to mice by injection at different sites is described. After intraperitoneal (ip), subcutaneous (sc), and intramuscular (im) injections of 125I-labeled poly(vinyl alcohol) (PVA) and poly(ethylene glycol) (PEG) with various molecular weights, the time-course of polymer concentration in the blood was measured and analyzed pharmacokinetically. The location of PVA in the body was similar to that of PEG; that is, the elimination from the injection sites and the translocation from the injection sites into the blood circulation were similar for both polymers. The elimination rate of both polymers from the injection sites increased in the order ip > sc > im. After sc and im injections of polymers, the elimination rate decreased with an increase in the molecular weight, whereas the elimination rate of polymers injected showed no molecular weight dependence over the range studied, regardless of the type of polymers used. The time-course of polymer concentration in the blood depended largely on the injection route of the polymers, and the polymer elimination from the blood circulation was enhanced with the decreasing molecular weight of polymers injected. It was concluded that the molecular weight and the injection site are the important factors that affect the concentration profile of polymers in the blood circulation.

R-[N-acetyl]eglin c:poly(oxyethylene) conjugates: preparation, plasma persistence, and urinary excretion

In this paper, we describe the preparation, purification, and characterization of conjugates of R-[N-acetyl]eglin c (Eglin c) with poly(oxyethylene) (POE; Eglin c:POE). The plasma profile and urinary excretion of the conjugates has been determined after iv administration in mice. The modification of Eglin c with POE does not significantly impair the ability of Eglin c to bind elastase as measured by an in vitro assay. In the best example, 79% of theoretical activity was retained by the conjugate. The in vivo results clearly show that the amount of Eglin c:POE in plasma after iv administration is much higher than comparative doses of unconjugated Eglin c. The time course of the plasma concentration of the conjugate matches closely that of the corresponding free polymer. Consequently, we can expect that higher plasma concentration could be achieved, if and when required, by selecting polymers of appropriate size.