Enhanced cellular uptake and in vivo biodistribution of a monoclonal antibody following cationization

Exit pathways of therapeutic antibodies from the brain and retention strategies

Treating brain diseases requires therapeutics to pass the blood-brain barrier (BBB) which is nearly impermeable for large biologics such as antibodies. Several methods now facilitate crossing or circumventing the BBB for antibody therapeutics. Some of these exploit receptor-mediated transcytosis, others use direct delivery bypassing the BBB. However, successful delivery into the brain does not preclude exit back to the systemic circulation. Various mechanisms are implicated in the active and passive export of antibodies from the central nervous system. Here we review findings on active export via transcytosis of therapeutic antibodies - in particular, the role of the neonatal Fc receptor (FcRn) - and discuss a possible contribution of passive efflux pathways such as lymphatic and perivascular drainage. We point out open questions and how to address these experimentally. In addition, we suggest how emerging findings could aid the design of the next generation of therapeutic antibodies for neurologic diseases.

Optimization of Drug-Linker to Enable Long-term Storage of Antibody-Drug Conjugate for Subcutaneous Dosing

To facilitate subcutaneous dosing, biotherapeutics need to exhibit properties that enable high-concentration formulation and long-term stability in the formulation buffer. For antibody-drug conjugates (ADCs), the introduction of drug-linkers can lead to increased hydrophobicity and higher levels of aggregation, which are both detrimental to the properties required for subcutaneous dosing. Herein we show how the physicochemical properties of ADCs could be controlled through the drug-linker chemistry in combination with prodrug chemistry of the payload, and how optimization of these combinations could afford ADCs with significantly improved solution stability. Key to achieving this optimization is the use of an accelerated stress test performed in a minimal formulation buffer.

Physiologically Based Pharmacokinetic Modeling to Characterize the Effect of Molecular Charge on Whole-Body Disposition of Monoclonal Antibodies

Motivated by a series of work demonstrating the effect of molecular charge on antibody pharmacokinetics (PK), physiological-based pharmacokinetic (PBPK) models are emerging that relate in silico calculated charge or in vitro measures of polyspecificity to antibody PK parameters. However, only plasma data has been used for model development in these studies, leading to unvalidated assumptions. Here, we present an extended platform PBPK model for antibodies that incorporate charge-dependent endothelial cell pinocytosis rate and nonspecific off-target binding in the interstitial space and on circulating blood cells, to simultaneously characterize whole-body disposition of three antibody charge variants. Predictive potential of various charge metrics was also explored, and the difference between positive charge patches and negative charge patches (i.e., PPC-PNC) was used as the charge parameter to establish quantitative relationships with nonspecific binding affinities and endothelial cell uptake rate. Whole-body disposition of these charge variants was captured well by the model, with less than 2-fold predictive error in area under the curve of most plasma and tissue PK data. The model also predicted that with greater positive charge, nonspecific binding was more substantial, and pinocytosis rate increased especially in brain, heart, kidney, liver, lung, and spleen, but remained unchanged in adipose, bone, muscle, and skin. The presented PBPK model contributes to our understanding of the mechanisms governing the disposition of charged antibodies and can be used as a platform to guide charge engineering based on desired plasma and tissue exposures.

Cell Penetrating Peptides Conjugated to Anti-Carcinoembryonic Antigen "Catch-and-Release" Monoclonal Antibodies Alter Plasma and Tissue Pharmacokinetics in Colorectal Cancer Xenograft Mice

Cell penetrating peptides conjugated to delivery vehicles, such as nanoparticles or antibodies, can enhance the cytosolic delivery of macromolecules. The present study examines the effects of conjugation to cell penetrating and endosomal escape peptides (i.e., TAT, GALA, and H6CM18) on the pharmacokinetics and distribution of an anti-carcinoembryonic antigen "catch-and-release" monoclonal antibody, 10H6, in a murine model of colorectal cancer. GALA and TAT were conjugated to 10H6 using SoluLINK technology that allowed the evaluation of peptide-to-antibody ratio by ultraviolet spectroscopy. H6CM18 was conjugated to either NHS or maleimide-modified 10H6 using an azide-modified valine-citrulline linker and copper-free click chemistry. Unmodified and peptide-conjugated 10H6 preparations were administered intravenously at 6.67 nmol/kg to mice-bearing MC38^CEA+ tumors. Unconjugated 10H6 demonstrated a clearance of 19.9 ± 1.36 mL/day/kg, with an apparent volume of distribution of 62.4 ± 7.78 mL/kg. All antibody-peptide conjugates exhibited significantly decreased plasma and tissue exposure, increased plasma clearance, and increased distribution volume. Examination of tissue-to-plasma exposure ratios showed an enhanced selectivity of 10H6-TAT for the GI tract (+25%), kidney (+24%), liver (+38%), muscle (+3%), and spleen (+33%). 10H6-GALA and 10H6-H6CM18 conjugates demonstrated decreased exposure in all tissues, relative to unmodified 10H6. All conjugates demonstrated decreased tumor exposure and selectivity; however, differences in tumor selectivity between 10H6 and 10H6-H6CM18 (maleimide) were not statistically significant. Relationships between the predicted peptide conjugate isoelectric point (pI) and pharmacokinetic parameters were bell-shaped, where pI values around 6.8-7 exhibit the slowest plasma clearance and smallest distribution volume. The data and analyses presented in this work may guide future efforts to develop immunoconjugates with cell penetrating and endosomal escape peptides.

CPPs to the Test: Effects on Binding, Uptake and Biodistribution of a Tumor Targeting Nanobody

Nanobodies are well-established targeting ligands for molecular imaging and therapy. Their short circulation time enables early imaging and reduces systemic radiation exposure. However, shorter circulation time leads to lower tracer accumulation in the target tissue. Cell-penetrating peptides (CPPs) improve cellular uptake of various cargoes, including nanobodies. CPPs could enhance tissue retention without compromising rapid clearance. However, systematic investigations on how the functionalities of nanobody and CPP combine with each other at the level of 2D and 3D cell cultures and in vivo are lacking. Here, we demonstrate that conjugates of the epidermal growth factor receptor (EGFR)-binding nanobody 7D12 with different CPPs (nonaarginine, penetratin, Tat and hLF) differ with respect to cell binding and induction of endocytosis. For nonaarginine and penetratin we compared the competition of EGF binding and performance of L- and D-peptide stereoisomers, and tested the D-peptide conjugates in tumor cell spheroids and in vivo. The D-peptide conjugates showed better penetration into spheroids than the unconjugated 7D12. Both in vivo and in vitro, the behavior of the agent reflects the combination of both functionalities. Although CPPs cause promising increases in in vitro uptake and 3D penetration, the dominant effect of the CPP in the control of biodistribution warrants further investigation.

Not so innocent: Impact of fluorophore chemistry on the in vivo properties of bioconjugates

The combination of targeting ligands and fluorescent dyes is a powerful strategy to observe cell types and tissues of interest. Conjugates of peptides, proteins, and, in particular, monoclonal antibodies (mAbs) exhibit excellent tumor targeting in various contexts. This approach has been translated to a clinical setting to provide real-time molecular insights during the surgical resection of solid tumors. A critical element of this approach is the generation of highly fluorescent bioconjugates that maintain the properties of the parent targeting ligand. A number of studies have found that fluorophores can dramatically impact the pharmacokinetic and tumor-targeting properties of the bioconjugates they are meant to only innocently observe. In this review, we summarize several examples of these effects and highlight strategies that have been used to mitigate them. These include the application of site-specific labeling chemistries, modulating label density, and altering the structure of the fluorescent probe itself. In particular, we point out the significant potential of fluorophores with hydrophilic but net-neutral structures. Overall, this review highlights recent progress in refining the in vivo properties of fluorescent bioconjugates, and we hope, will inform future efforts in this area.

An Inside Job: Applications of Intracellular Single Domain Antibodies

Sera of camelid species contain a special kind of antibody that consists only of heavy chains. The variable antigen binding domain of these heavy chain antibodies can be expressed as a separate entity, called a single domain antibody that is characterized by its small size, high solubility and oftentimes exceptional stability. Because of this, most single domain antibodies fold correctly when expressed in the reducing environment of the cytoplasm, and thereby retain their antigen binding specificity. Single domain antibodies can thus be used to target a broad range of intracellular proteins. Such intracellular single domain antibodies are also known as intrabodies, and have proven to be highly useful tools for basic research by allowing visualization, disruption and even targeted degradation of intracellular proteins. Furthermore, intrabodies can be used to uncover prospective new therapeutic targets and have the potential to be applied in therapeutic settings in the future. In this review we provide a brief overview of recent advances in the field of intracellular single domain antibodies, focusing on their use as research tools and potential therapeutic applications. Special attention is given to the available methods that allow delivery of single domain antibodies into cells.

The biodistribution of therapeutic proteins: Mechanism, implications for pharmacokinetics, and methods of evaluation

Therapeutic proteins (TPs) are a diverse drug class that include monoclonal antibodies (mAbs), recombinantly expressed enzymes, hormones and growth factors, cytokines (e.g. chemokines, interleukins, interferons), as well as a wide range of engineered fusion scaffolds containing IgG1 Fc domain for half-life extension. As the pharmaceutical industry advances more potent and selective protein-based medicines through discovery and into the clinical stages of development, it has become widely appreciated that a comprehensive understanding of the mechanisms of TP biodistribution can aid this endeavor. This review aims to highlight the literature that has advanced our understanding of the determinants of TP biodistribution. A particular emphasis is placed on the multi-faceted role of the neonatal Fc receptor (FcRn) in mAb and Fc-fusion protein disposition. In addition, characterization of the TP-target interaction at the cell-level is discussed as an essential strategy to establish pharmacokinetic-pharmacodynamic (PK/PD) relationships that may lead to more informed human dose projections during clinical development. Methods for incorporation of tissue and cell-level parameters defining these characteristics into higher-order mechanistic and semi-mechanistic PK models will also be presented.

Photoimmunotherapy of Ovarian Cancer: A Unique Niche in the Management of Advanced Disease

Ovarian cancer (OvCa) is the leading cause of gynecological cancer-related deaths in the United States, with five-year survival rates of 15-20% for stage III cancers and 5% for stage IV cancers. The standard of care for advanced OvCa involves surgical debulking of disseminated disease in the peritoneum followed by chemotherapy. Despite advances in treatment efficacy, the prognosis for advanced stage OvCa patients remains poor and the emergence of chemoresistant disease localized to the peritoneum is the primary cause of death. Therefore, a complementary modality that is agnostic to typical chemo- and radio-resistance mechanisms is urgently needed. Photodynamic therapy (PDT), a photochemistry-based process, is an ideal complement to standard treatments for residual disease. The confinement of the disease in the peritoneal cavity makes it amenable for regionally localized treatment with PDT. PDT involves photochemical generation of cytotoxic reactive molecular species (RMS) by non-toxic photosensitizers (PSs) following exposure to non-harmful visible light, leading to localized cell death. However, due to the complex topology of sensitive organs in the peritoneum, diffuse intra-abdominal PDT induces dose-limiting toxicities due to non-selective accumulation of PSs in both healthy and diseased tissue. In an effort to achieve selective damage to tumorous nodules, targeted PS formulations have shown promise to make PDT a feasible treatment modality in this setting. This targeted strategy involves chemical conjugation of PSs to antibodies, referred to as photoimmunoconjugates (PICs), to target OvCa specific molecular markers leading to enhanced therapeutic outcomes while reducing off-target toxicity. In light of promising results of pilot clinical studies and recent preclinical advances, this review provides the rationale and methodologies for PIC-based PDT, or photo-immunotherapy (PIT), in the context of OvCa management.

Selecting and engineering monoclonal antibodies with drug-like specificity

Despite the recent explosion in the use of monoclonal antibodies (mAbs) as drugs, it remains a significant challenge to generate antibodies with a combination of physicochemical properties that are optimal for therapeutic applications. We argue that one of the most important and underappreciated drug-like antibody properties is high specificity - defined here as low levels of antibody non-specific and self-interactions - which is linked to low off-target binding and slow antibody clearance in vivo and high solubility and low viscosity in vitro. Here, we review the latest advances in characterizing antibody specificity and elucidating its molecular determinants as well as using these findings to improve the selection and engineering of antibodies with extremely high, drug-like specificity.

Influence of protein properties and protein modification on biodistribution and tumor uptake of anticancer antibodies, antibody derivatives, and non-Ig scaffolds

Newly developed protein drugs that target tumor-associated antigens are often modified in order to increase their therapeutic effect, tumor exposure, and safety profile. During the development of protein drugs, molecular imaging is increasingly used to provide additional information on their in vivo behavior. As a result, there are increasing numbers of studies that demonstrate the effect of protein modification on whole body distribution and tumor uptake of protein drugs. However, much still remains unclear about how to interpret obtained biodistribution data correctly. Consequently, there is a need for more insight in the correct way of interpreting preclinical and clinical imaging data. Summarizing the knowledge gained to date may facilitate this interpretation. This review therefore provides an overview of specific protein properties and modifications that can affect biodistribution and tumor uptake of anticancer antibodies, antibody fragments, and nonimmunoglobulin scaffolds. Protein properties that are discussed in this review are molecular size, target interaction, FcRn binding, and charge. Protein modifications that are discussed are radiolabeling, fluorescent labeling drug conjugation, glycosylation, humanization, albumin binding, and polyethylene glycolation.

Use of PEGylated Immunoliposomes to Deliver Dopamine Across the Blood-Brain Barrier in a Rat Model of Parkinson's Disease

AIM

To treat neurodegenerative disorders such as Parkinson's disease (PD), drugs must be able to cross the blood-brain barrier (BBB). Patients with PD are deficient in dopamine (DA), a neurotransmitter that cannot pass through the BBB. Liposomes modified by adding polyethylene glycol (PEGylated liposomes (PLs)) can be conjugated with antibody to form DA-PEGylated immunoliposomes (DA-PILs), and we tested their use as carriers of DA for treating PD.

METHODS

PEGylated liposomes (PLs) were prepared by evaporation method, and [(3) H]dopamine was encapsulated within the dried lipid film using a freeze/thaw cycle to form DA-PL. Thiolated OX26 MAb, an antitransferrin receptor monoclonal antibody, was then conjugated to 46-nm PEGylated liposomes. Particle size, zeta potential, and stability were assessed, and in vivo effects were determined after the intravenous injection of DA, DA-PL, and DA-PIL by examining brain tissue in normal rats and rats that underwent transection of the medial forebrain bundle to induce PD.

RESULTS

The uptake of DA-PIL in the brains of this PD rat model increased about 8-fold compared with that of DA alone and about 3-fold compared with that of encapsulated DA-PEGylated liposomes (DA-PL). The volume of distribution of DA-PIL in the brain by the perfusion method was 4-fold higher than that of DA-PL, indicating that conjugation of OX26 MAb to the transferrin receptor of brain capillary endothelium mediated the effective delivery of DA to brain tissue.

CONCLUSIONS

Dopamine can be effectively delivered to the brain by means of a PIL-based drug delivery system in PD rats.

Balancing charge in the complementarity-determining regions of humanized mAbs without affecting pI reduces non-specific binding and improves the pharmacokinetics

Lowering the isoelectric point (pI) through engineering the variable region or framework of an IgG can improve its exposure and half-life via a reduction in clearance mediated through non-specific interactions. As such, net charge is a potentially important property to consider in developing therapeutic IgG molecules having favorable pharmaceutical characteristics. Frequently, it may not be possible to shift the pI of monoclonal antibodies (mAbs) dramatically without the introduction of other liabilities such as increased off-target interactions or reduced on-target binding properties. In this report, we explored the influence of more subtle modifications of molecular charge on the in vivo properties of an IgG1 and IgG4 monoclonal antibody. Molecular surface modeling was used to direct residue substitutions in the complementarity-determining regions (CDRs) to disrupt positive charge patch regions, resulting in a reduction in net positive charge without affecting the overall pI of the mAbs. The effect of balancing the net positive charge on non-specific binding was more significant for the IgG4 versus the IgG1 molecule that we examined. This differential effect was connected to the degree of influence on cellular degradation in vitro and in vivo clearance, distribution and metabolism in mice. In the more extreme case of the IgG4, balancing the charge yielded an ∼7-fold improvement in peripheral exposure, as well as significantly reduced tissue catabolism and subsequent excretion of proteolyzed products in urine. Balancing charge on the IgG1 molecule had a more subtle influence on non-specific binding and yielded only a modest alteration in clearance, distribution and elimination. These results suggest that balancing CDR charge without affecting the pI can lead to improved mAb pharmacokinetics, the magnitude of which is likely dependent on the relative influence of charge imbalance and other factors affecting the molecule's disposition.

Evaluating the Use of Antibody Variable Region (Fv) Charge as a Risk Assessment Tool for Predicting Typical Cynomolgus Monkey Pharmacokinetics

The pharmacokinetic (PK) behavior of monoclonal antibodies in cynomolgus monkeys (cynos) is generally translatable to that in humans. Unfortunately, about 39% of the antibodies evaluated for PKs in cynos have fast nonspecific (or non-target-mediated) clearance (in-house data). An empirical model relating variable region (Fv) charge and hydrophobicity to cyno nonspecific clearance was developed to gauge the risk an antibody would have for fast nonspecific clearance in the monkey. The purpose of this study was to evaluate the predictability of this empirical model on cyno nonspecific clearance with antibodies specifically engineered to have either high or low Fv charge. These amino acid changes were made in the Fv region of two test antibodies, humAb4D5-8 and anti-lymphotoxin α. The humAb4D5-8 has a typical nonspecific clearance in cynos, and by making it more positively charged, the antibody acquires fast nonspecific clearance, and making it less positively charged did not impact its clearance. Anti-lymphotoxin α has fast nonspecific clearance in cynos, and making it more positively charged caused it to clear even faster, whereas making it less positively charged caused it to clear slower and within the typical range. These trends in clearance were also observed in two other preclinical species, mice and rats. The effect of modifying Fv charge on subcutaneous bioavailability was also examined, and in general bioavailability was inversely related to the direction of the Fv charge change. Thus, modifying Fv charge appears to impact antibody PKs, and the changes tended to correlate with those predicted by the empirical model.

Transendothelial Transport and Its Role in Therapeutics

Present review paper highlights role of BBB in endothelial transport of various substances into the brain. More specifically, permeability functions of BBB in transendothelial transport of various substances such as metabolic fuels, ethanol, amino acids, proteins, peptides, lipids, vitamins, neurotransmitters, monocarbxylic acids, gases, water, and minerals in the peripheral circulation and into the brain have been widely explained. In addition, roles of various receptors, ATP powered pumps, channels, and transporters in transport of vital molecules in maintenance of homeostasis and normal body functions have been described in detail. Major role of integral membrane proteins, carriers, or transporters in drug transport is highlighted. Both diffusion and carrier mediated transport mechanisms which facilitate molecular trafficking through transcellular route to maintain influx and outflux of important nutrients and metabolic substances are elucidated. Present review paper aims to emphasize role of important transport systems with their recent advancements in CNS protection mainly for providing a rapid clinical aid to patients. This review also suggests requirement of new well-designed therapeutic strategies mainly potential techniques, appropriate drug formulations, and new transport systems for quick, easy, and safe delivery of drugs across blood brain barrier to save the life of tumor and virus infected patients.

Recent progress in generating intracellular functional antibody fragments to target and trace cellular components in living cells

In biomedical research there is an ongoing demand for new technologies, which help to elucidate disease mechanisms and provide the basis to develop novel therapeutics. In this context a comprehensive understanding of cellular processes and their pathophysiology based on reliable information on abundance, localization, posttranslational modifications and dynamic interactions of cellular components is indispensable. Besides their significant impact as therapeutic molecules, antibodies are arguably the most powerful research tools to study endogenous proteins and other cellular components. However, for cellular diagnostics their use is restricted to endpoint assays using fixed and permeabilized cells. Alternatively, live cell imaging using fluorescent protein-tagged reporters is widely used to study protein localization and dynamics in living cells. However, only artificially introduced chimeric proteins are visualized, whereas the endogenous proteins, their posttranslational modifications as well as non-protein components of the cell remain invisible and cannot be analyzed. To overcome these limitations, traceable intracellular binding molecules provide new opportunities to perform cellular diagnostics in real time. In this review we summarize recent progress in the generation of intracellular and cell penetrating antibodies and their application to target and trace cellular components in living cells. We highlight recent advances in the structural formulation of recombinant antibody formats, reliable screening protocols and sophisticated cellular targeting technologies and propose that such intrabodies will become versatile research tools for real time cell-based diagnostics including target validation and live cell imaging. This article is part of a Special Issue entitled: Recent advances in molecular engineering of antibody.

Amination of enzymes to improve biocatalyst performance: coupling genetic modification and physicochemical tools

Improvement of the features of an enzyme is in many instances a pre-requisite for the industrial implementation of these exceedingly interesting biocatalysts.

Modeling approach to investigate the effect of neonatal Fc receptor binding affinity and anti-therapeutic antibody on the pharmacokinetic of humanized monoclonal anti-tumor necrosis factor-α IgG antibody in cynomolgus monkey

PURPOSE

Several neonatal Fc receptor (FcRn) variants of an anti-tumor necrosis factor (TNF)-α humanized monoclonal IgG antibodies (mAbs) were developed but the effect of their differential FcRn binding affinities on pharmacokinetic (PK) behavior were difficult to be definitively measured in vivo due to formation of anti-therapeutic antibody (ATA). A semi-mechanistic model was developed to investigate the quantitative relationship between the FcRn binding affinity and PK of mAbs in cynomolgus monkey with the presence of ATA.

METHODS

PK and ATA data from cynomolgus monkeys which received a single intravenous dose of adalimumab, wild-type or two FcRn variant (N434H and N434A) anti-TNF-α mAbs were included in the analysis. Likelihood-based censored data handling method was used to include many PK observations with BQL values for model development. A fully integrated PK-ATA model was developed and used to fit simultaneously to the PK/ATA data.

RESULTS AND CONCLUSIONS

The PK and ATA time-profiles and effect of FcRn-binding affinity on PK of mAbs were well described by the model and the parameters were estimated with good precision. The model was used successfully to construct quantitative relationships between FcRn binding affinity and PK of anti-TNF-α mAbs in the presence of the ATA-mediated elimination and interferences.

Cationized IVIg as a potential substitute to IVIg for the treatment of experimental immune thrombocytopenia

In this study, we evaluated the possibility of using cationized IVIg (cIVIg) instead of IVIg as a more effective therapy for the treatment of experimental immune thrombocytopenia in mice. The pharmacokinetics (PK) and biodistribution of cIVIg and IVIg in mice were compared. cIVIg displayed a shorter plasma half-life and an increased organ uptake in both the spleen and liver compared to IVIg, suggesting that cIVIg could be more potent than IVIg to prevent platelet clearance in a mouse model of thrombocytopenia. However, although the biodistribution of cIVIg in the spleen and liver was improved, its ability to prevent platelet clearance in mice remained similar to that of IVIg. Altogether, our data demonstrate the possibility of using chemical cationization of IVIg preparations to increase organ uptake, and also highlight the challenges of developing effective substitutes to IVIg.

Exploiting protein cationization techniques in future drug development

The development of a method for the efficient intracellular delivery of inherently non-permeable proteins is needed for manipulation of cellular phenotypes or the discovery of protein-based drugs. It has been demonstrated that proteins artificially cationized by chemical conjugation show efficient intracellular delivery via adsorptive-mediated endocytosis and then can exert their biological activity in cells. Studies have also revealed that cationic peptides known as cell-penetrating peptides (CPPs) provide a means to deliver molecules into mammalian cells. Although the internalization mechanisms remain controversial, it is now becoming clear that the main port of entry into cells by CPPs also involves adsorptive-mediated endocytosis rather than the direct penetration of the plasma membrane. As the mammalian cell membrane possesses an abundance of negatively charged glycoproteins and glycosphingolipids, cationization of proteins is a reasonable choice to endow them with the ability for intracellular delivery. Cationization of proteins is usually accompanied by drastic changes in protein properties, structure and biological activities. Recently developed sophisticated protein chemistry can minimize these side effects. Therefore, protein cationization techniques will hopefully prove to be powerful tools for innovative research and drug discovery. In this review, techniques for cationization of proteins and their intracellular delivery, as well as some of their potential therapeutic applications, are discussed.

Cell-penetrating anti-GFAP VHH and corresponding fluorescent fusion protein VHH-GFP spontaneously cross the blood-brain barrier and specifically recognize astrocytes: application to brain imaging

Antibodies normally do not cross the blood-brain barrier (BBB) and cannot bind an intracellular cerebral antigen. We demonstrate here for the first time that a new class of antibodies can cross the BBB without treatment. Camelids produce native homodimeric heavy-chain antibodies, the paratope being composed of a single-variable domain called VHH. Here, we used recombinant VHH directed against human glial fibrillary acidic protein (GFAP), a specific marker of astrocytes. Only basic VHHs (e.g., pI=9.4) were able to cross the BBB in vitro (7.8 vs. 0% for VHH with pI=7.7). By intracarotid and intravenous injections into live mice, we showed that these basic VHHs are able to cross the BBB in vivo, diffuse into the brain tissue, penetrate into astrocytes, and specifically label GFAP. To analyze their ability to be used as a specific transporter, we then expressed a recombinant fusion protein VHH-green fluorescent protein (GFP). These "fluobodies" specifically labeled GFAP on murine brain sections, and a basic variant (pI=9.3) of the fusion protein VHH-GFP was able to cross the BBB and to label astrocytes in vivo. The potential of VHHs as diagnostic or therapeutic agents in the central nervous system now deserves attention.

Covalent modifications of antitetanus F(ab')2 fragments with natural and synthetic polyamines and their effects on the antibody endocytosis in cultured HL60 cells

For antibody therapeutics to succeed when intracellular target molecules are involved, a strategy must be applied to increase the delivery of antibodies into cells to reach their targets. Antibody cationization by chemical conjugation of a polyamine could be one such strategy. Both natural polyamines with increasing net charge valencies (putrescine, PUT; spermidine, SPD; and spermine, SPM) and a synthetic polyamine (hexamethylenediamine, HMD) can be used to cationize antibodies, but no comparison of the respective effects of these polyamines on intracellular delivery of antibodies has been performed yet. This study describes the covalent modification of antitetanus F(ab') 2 with these four polyamines using different reaction conditions, and compares the effects of these modifications on antibody interaction with cultured HL60 cells. The cationized antibodies retained > or =80% of the binding activity of the unmodified F(ab') 2 with regard to tetanus toxin, as measured by an antigen-binding capture enzyme immunoassay. This same method was used to quantify the amount of cell-associated F(ab') 2 following incubation with HL60 cells. Cationization was shown to enhance cell interaction of the F(ab') 2 : the higher the number of coupled polyamine molecules, the greater the amount of antibody associated with the cells. Moreover, coupling the F(ab') 2 to the SPD and SPM polyamines had greater effect on cell interaction than coupling the F(ab') 2 to the PUT and HMD diamines. Internalization of the cationized antibodies by the HL60 cells was demonstrated by confocal microscopy. This technique also showed that SPD and SPM were more effective than PUT and HMD in terms of intracellular delivery of the F(ab') 2 . It follows from all these results that electrostatic interaction involving charge density plays a predominant role in the endocytic transport mechanism of the F(ab') 2 modified with these polyamines. However, coupling the F(ab') 2 to SPM and SPD yielded the same maximum effects in terms of cell interaction, although coupling SPM was expected to increase the antibody net charge valency more than coupling SPD. This finding suggests that the effective global charge for the cell interaction and uptake of polyamine-modified antibodies does not simply correspond to the addition of the ionizable amine functions on the coupled polyamines, and that other factors may come into play.

Intracellular delivery of glutathione S-transferase-fused proteins into mammalian cells by polyethylenimine-glutathione conjugates

The glutathione S-transferase (GST)-fused protein expression system has been extensively used to generate a large quantity of proteins and has served for functional analysis in vitro. In this study, we developed a novel approach for the efficient intracellular delivery of GST-fused proteins into living cells to expand their usefulness up to in vivo use. Since protein cationization techniques are powerful strategies for efficient intracellular uptake by adsorptive-mediated endocytosis, GST-fused proteins were cationized by forming a complex with a polycationic polyethylenimine (PEI)-glutathione conjugate. On screening of protein transduction, optimized PEI-glutathione conjugate for protein transduction was characterized by a partly oligomerized mixture of PEI with average molecular masses of 600 (PEI600) modified with multiple glutathiones, which could have sufficient avidity for GST. Furthermore, enhanced endosomal escape of transduced GST-fused proteins was observed when they were delivered with a glutathione-conjugated PEI600 derivative possessing a hydroxybutenyl moiety. These results were confirmed by both intracellular confocal imaging of GST-fused green fluorescent protein and activation of an endogenous growth signal transduction pathway by a GST-fused constitutively active mutant of a kinase protein. These PEI-glutathione conjugates seem to be convenient molecular tools for protein transduction of widely used GST-fused proteins.

pH-responsive nanoparticles for cancer drug delivery

Solid tumors have an acidic extracellular environment and an altered pH gradient across their cell compartments. Nanoparticles responsive to the pH gradients are promising for cancer drug delivery. Such pH-responsive nanoparticles consist of a corona and a core, one or both of which respond to the external pH to change their soluble/insoluble or charge states. Nanoparticles whose coronas become positively charged or become soluble to make their targeting groups available for binding at the tumor extracellular pH have been developed for promoting cellular targeting and internalization. Nanoparticles whose cores become soluble or change their structures to release the carried drugs at the tumor extracellular pH or lysosomal pH have been developed for fast drug release into the extracellular fluid or cytosol. Such pH-responsive nanoparticles have therapeutic advantages over the conventional pH-insensitive counterparts.

Intracellular delivery of proteins into mammalian living cells by polyethylenimine-cationization

In the post-genomic era, there is pressing need for development of protein manipulation methodology to analyze functions of proteins in living cells. For this purpose, techniques to deliver functional proteins into living cells are currently being evaluated as alternative approaches to the introduction of transcriptionally active DNA. Here, we describe a novel method for efficient protein transduction into living cells in which a protein is simply cationized with polyethylenimine (PEI) by limited chemical conjugation. PEI-cationized proteins appear to adhere to the cell surface by ionic charge interaction and then internalize into cells in a receptor- and transporter-independent fashion. Since PEI is an organic macromolecule with a high cationic-charge density, limited coupling with PEI results in endowment of sufficient cationic charge to proteins without causing serious decline in their fundamental functions. A number of PEI-cationized proteins, such as ribonuclease (RNase), green fluorescent protein (GFP) and immunoglobulin (IgG), efficiently entered cells and functioned in the cytosol. Our results suggest that protein cationization techniques using PEI will be useful for the development of protein transduction technology.

Development and validation of an antigen-binding capture ELISA for native and putrescine-modified anti-tetanus F(ab')2 fragments for the assessment of the cellular uptake and plasma kinetics of the antibodies

Cationization is a strategy to enhance the permeability of antibodies to physiological membranes for potential therapeutic and diagnostic applications of these proteins, with one of its crucial points being the retention of antigen binding activity. Here, we describe the cationization of horse polyclonal anti-tetanus F(ab')(2) fragments and the development and validation of an ELISA for quantitative measurements of the binding activity of the native and cationized F(ab')(2) in cell lysates and rat plasma samples, assessing the cellular uptake and plasma kinetics of these antibodies, respectively. The method used tetanus anatoxin coated on microtitre plates as capture antigen to bind sample or standard F(ab')(2), the amount of antibody binding being quantified using, first, a secondary biotinylated anti-horse antibody/streptavidin-alkaline phosphatase complex in situ and then a measurement of the substrate product. Cationization of the F(ab')(2) was performed with putrescine at pH 4.5 using soluble carbodiimide as carboxyl activator. The average substitution ratio was determined at 3 putrescine molecules per F(ab')(2) molecule. The cationized F(ab')(2) retained roughly 80% of the initial antigen binding activity and was stable over a 1 year period of storage at -20 degrees C. The ELISA validation data showed that the method was linear for both the native and cationized F(ab')(2) using Hanks' balanced saline solution with 0.2% bovine serum albumin as assay diluent for the cell lysate samples. The useful F(ab')(2) concentration range was 2.5-25 ng/ml and the limit of quantification was 2.5 ng/ml. With rat blank plasma used as assay diluent for the rat plasma samples the useful F(ab')(2) concentration range was 3.5-25 ng/ml and the limit of quantification was 3.5 ng/ml. Specific requirements for the limits of quantification were fulfilled: precision < or =20% CV and accuracy within +/-20% of the nominal values. Intra- and inter-assay coefficients of variation were within 9% and accuracies within +/-10% of the nominal values. The validated method was applied to the study of the cellular uptake of native and cationized anti-tetanus F(ab')(2) in an HL 60 cell model, and of plasma kinetics after i.v. administration to rats.

Monoclonal antibody radiopharmaceuticals: cationization, pegylation, radiometal chelation, pharmacokinetics, and tumor imaging

The 528 murine monoclonal antibody (MAb) to the human epidermal growth factor receptor (EGFR) was sequentially cationized with hexamethylenediamine and conjugated with diethylenetriaminepentaacetic acid (DTPA) as a potential antibody radiopharmaceutical for imaging EGFR-expressing cancer. The cationized 528 MAb was characterized with isoelectric focusing and electrophoresis, and an immunoradiometric assay, which showed the affinity of the 528 MAb for the human EGFR was retained following cationization. The native or cationized 528 MAb, labeled with (111)In, was injected intravenously in scid mice bearing human U87 flank tumors, which express the EGFR, and tumor imaging was performed with both external detection in live animals and with whole body autoradiography. However, the tumor signal was not increased with the cationized MAb, relative to the native MAb, and this was due to a serum inhibition phenomenon that was confirmed by a pharmacokinetics analysis in control mice. In an attempt to block the serum inhibition, the cationized 528 MAb was pegylated with 2000 Da poly(ethylene glycol), and the cationized/pegylated MAb was conjugated with DTPA and labeled with (111)In. However, a pharmacokinetics analysis showed the pegylation did not reverse the serum inhibition of the cationic charge on the MAb. These studies describe methods for reformulating monoclonal antibodies to develop improved radiopharmaceuticals, but show that radiolabeling a cationized MAb with DTPA produces a serum neutralization of the initial cationization modification.

De novo synthesis of a new diethylenetriaminepentaacetic acid (DTPA) bifunctional chelating agent

Diethylene triamine pentaacetic acid (DTPA) has been in extensive use as a metal chelator in the development of radiopharmaceuticals and contrast agents. The former application uses DTPA mostly as a bifunctional chelating agent (BCA) conjugated to tumor-targeting vehicles (TTVs) such as monoclonal antibodies (MAbs) and receptor-directed peptides. A new bifunctional DTPA derivative was synthesized by a fully organic scheme. This compound, N(4),N(alpha),N(alpha),N(epsilon),N(epsilon)-[pentakis(carboxymethyl)]-N(4)-(carboxymethyl)-2,6-diamino-4-azahexanoic hydrazide (20) was prepared by a convergent synthesis strategy using N(alpha)-benzyloxycarbonyl-2,3-diaminopropionic acid as the starting compound. This commercially available material was used to build a functionalized triamine which served as the molecular core template for assembling the target molecule. To evaluate the conjugation and radiolabeling capabilities of this new molecule, it was covalently attached to the anti-TAG-72 MAb, Delta CH2HuCC49, and the conjugate was radiolabeled in near-quantitative yields with yttrium-90 ((90)Y) and lutetium-177 ((177)Lu). Biodistribution of the (177)Lu-labeled DTPA-Delta CH2HuCC49 in tumor-bearing nude mice demonstrated preservation of the immunoreactivity of the MAb as indicated by high tumor uptake. In addition to the introduction of a new bifunctional DTPA, this work reports on a novel synthetic approach for preparation of this useful metal chelator and introduces a new conjugation protocol.

Preparation of potent cytotoxic ribonucleases by cationization: enhanced cellular uptake and decreased interaction with ribonuclease inhibitor by chemical modification of carboxyl groups

Carboxyl groups of bovine RNase A were amidated with ethylenediamine (to convert negative charges of carboxylate anions to positive ones), 2-aminoethanol (to eliminate negative charges), and taurine (to keep negative charges), respectively, by a carbodiimide reaction. Human RNase 1 was also modified with ethylenediamine. Surprisingly, the modified RNases were all cytotoxic toward 3T3-SV-40 cells despite their decreased ribonucleolytic activity. However, their enzymatic activity was not completely eliminated by the presence of excess cytosolic RNase inhibitor (RI). As for native RNase A and RNase 1 which were not cytotoxic, they were completely inactivated by RI. More interestingly, within the cytotoxic RNase derivatives, cytotoxicity correlated well with the net positive charge. RNase 1 and RNase A modified with ethylenediamine were more cytotoxic than naturally occurring cytotoxic bovine seminal RNase. An experiment using the fluorescence-labeled RNase derivatives indicated that the more cationic RNases were more efficiently adsorbed to the cells. Thus, it is suggested that the modification of carboxyl groups could change complementarity of RNase to RI and as a result endow RNase cytotoxicity and that cationization enhances the efficiency of cellular uptake of RNase so as to strengthen its cytotoxicity. The finding that an extracellular human enzyme such as RNase 1 could be effectively internalized into the cell by cationization suggests that cationization is a simple strategy for efficient delivery of a protein into cells and may open the way of the development of new therapeutics.

Enhanced cellular uptake and transport of polyclonal immunoglobulin G and fab after their cationization

Antibodies are poorly transported across cell membranes and biological barriers in vivo. Cationization of antibody molecules by the derivatization of surface carboxyl groups generating primary amino groups could represent a strategy for intracellular antibody delivery. Before cationization of polyclonal colchicine-specific IgG and Fab, using hexamethylenediamine the isoelectric point (pl) of native IgG and Fab (nIgG and nFab) was in the range of 5.9 9.0 and 8.7-9.3, respectively. The pI of cationized IgG and Fab (cIgG and cFab) were both higher at 8.7, 10.3 and 9.5 -11, respectively. The affinity and specificity of both IgG and Fab were not modified by cationization. When HL 60 cells were incubated with the native or cationized 125I-BSA. -IgG and -Fab, the maximal cellular uptake of clgG and cFab was 3.2 and 2.4 times higher than that of nIgG and nFab at an extracellular concentration of 500 ng/ml. Results also indicated that the uptake was dose- and temperature-dependent suggesting absorptive-mediated endocytosis of cationized antibodies by HL 60 cells. Confocal microscopy analysis indicated that the cationized antibodies were present in the plasma membranes and cytoplasm of HL 60 cells. Finally, a study with bovine arterial endothelial monolayer cells showed that the transport of cIgG and cFab through the monolayer cells was 3.3- and 4.3-fold higher for 125I-cIgG and 125I-cFab than those of the corresponding native forms.

Electroporation of antibodies, DNA, and other macromolecules into cells: a highly efficient method

While antibodies are a major extracellular tool of the highest specificity to answer important biomedical questions, the improvements in electroporation discussed below may make it feasible to also use antibodies as an intracellular deletion tool to study (a) viruses inside the cell, (b) cancer cells, (c) signal transduction, (d) genetics, (e) metabolism, and (f) other structures and mechanisms. Already, others have succeeded in depositing macromolecules, including antibodies (Abs), and nucleic acids inside cells, using many techniques, including electroporation (EP). However, EP has limitations that have precluded its widespread use, particularly its high kill rate for cells and the low percentage of cells that are able to incorporate macromolecules. If these limitations could be overcome for Abs and nucleic acids, then it would be practical to use them as highly specific probes for intracellular molecules. In our experiments using EP, we were able to largely prevent lethality for cells during EP by employing a commercially available cold-storage solution for organ transplants containing high K(+) and Mg(++) (ViaSpan, Belzer UW cold-storage solution, DuPont Pharmaceuticals). This solution decreased cell death after standard EP by an average of 50% for a number of cell lines. Viability of WISH cells after EP approached 100%. In transfection studies, ViaSpan medium strongly increased both P3HR1 cell survival as well as the total number of cells transfected with DNA for green fluorescent protein (GFP). In additional experiments with Abs, we were able to strongly increase the percent of cells that incorporated Ab by using two serial EPs. This enhanced the intracellular protection by Abs against viruses in Vero cells from 64% to a maximum of 98%. We were able to further simplify the EP technique by using unpurified antiserum in place of purified IgG. Thus, this EP technique offers multiple advantages: simplicity, high cell viability, high effectiveness, high specificity, rapid action, usefulness with adherent or non-adherent cells, and no requirement for purification of antibodies from antiserum.

Assessment of stereoselectivity of trimethylphenylalanine analogues of delta-opioid [D-Pen(2),D-Pen(5)]-enkephalin

[D-Pen(2),D-Pen(5)]-Enkephalin (DPDPE) is an enzymatically stable delta-opioid receptor-selective peptide, which was modified by the trimethylation of the Phe(4) residue to give beta-methyl-2', 6'-dimethylphenylalanine (TMP), resulting in four conformations : (2R,3S)-beta-Phe-DPDPE, (2R,3R)-beta-Phe-DPDPE, (2R, 3S)-beta-Phe-DPDPE, and (2S,3R)-beta-Phe-DPDPE. Synthesis was by solid-phase techniques using enantiomerically pure amino acids to give the four optically pure diastereoisomer peptides. The potency and selectivity (delta- versus mu-opioid receptor) were evaluated by radioreceptor binding in rat brain, with a mu/delta ratio decrease for all TMP conformations, compared with the parent compound (DPDPE). Octanol/buffer distribution analysis showed enhanced lipophilicity of all TMP forms, with a sixfold enhancement associated with (2S,3S)-TMP. In situ vascular perfusion in anesthetized rats showed a 1.6-fold (p < 0.01) increase in the ratio of brain uptake for (2S,3S)-TMP and a 1.5-fold (p < 0.01) decrease in uptake for (2R,3R)-TMP. Saturability of (2S,3S)-TMP was shown (p < 0.01) against 100 microM unlabeled DPDPE, showing a shared nondiffusionary transport system. P-glycoprotein affinity was shown in situ for the parent and (2S,3S)-TMP (p < 0.01). Protein binding capacity of the TMP compounds in rat plasma and in situ mammalian bovine serum albumin-Ringer showed (2R,3S)-TMP and (2S,3R)-TMP with the lowest degree of protein binding (p < 0.01), and (2S,3S)-TMP and (2R,3R)-TMP with comparable affinities to DPDPE. Analgesia, via intravenous administration, showed significantly reduced (p < 0.01) end effect and time course for (2R,3R)-TMP, (2R,3S)-TMP, and (2S, 3R)-TMP as compared with DPDPE. These results demonstrate that topographical modification in a conformationally restricted peptide can significantly modulate potency and receptor selectivity, binding capacity, enzymatic stability, lipophilicity, P-glycoprotein affinity, and blood-brain barrier permeability, resulting in a change of bioavailability, and thereby provides insight for future peptide drug design.

Reduction of the Nonspecific Animal Toxicity of Anti-Tac(Fv)-PE38 by Mutations in the Framework Regions of the Fv Which Lower the Isoelectric Point

Anti-Tac(Fv)-PE38, also called LMB-2, is a very active recombinant immunotoxin that has produced eight responses, including a durable clinical complete remission in a recently completed phase I trial of leukemias and lymphomas. Dose escalation was limited by liver toxicity. We have noted that the Fv of anti-Tac has an isoelectric point (pI) of 10.2. We hypothesize that the overall positive charge on the Fv portion of anti-Tac(Fv)-PE38 contributes to nonspecific binding to liver cells and results in dose-limiting liver toxicity. We have used a mouse model to investigate the basis of this toxicity and found that lowering the pI of the Fv of anti-Tac from 10.2 to 6.82 by selective mutation of surface residues causes a 3-fold decrease in animal toxicity and hepatic necrosis. This change in pI did not significantly alter the CD25 binding affinity, the cytotoxic activity toward target cells, or antitumor activity, resulting in a 3-fold improvement in the therapeutic index. If this decreased toxicity occurs in humans, it should greatly increase the clinical utility of this immunotoxin.

Pharmacokinetics and organ distribution of cationized colchicine-specific IgG and Fab fragments in rat

Pharmacokinetics of cationized goat colchicine-specific polyclonal immunoglobulin G (IgG) and antigen binding fragment (Fab) (cIgG and cFab, respectively) were studied in male adult Sprague-Dawley rats and compared with those of the native proteins (nIgG and nFab). All proteins were radioiodinated by the Iodogen method, and kinetics were investigated following trichloroacetic acid (TCA) precipitation or immunoprecipitation. Deiodination and catabolism were more pronounced with the cationized than the native proteins, especially for cFab. Both cIgG and cFab in plasma decreased more rapidly than nIgG and nFab. The elimination half-lives were 52.9 and 81.8 h for cIgG and nIgG, respectively. In addition, there was a 74-fold increase in the volume of distribution and a 114-fold increase in the systemic clearance of cIgG compared with nIgG. For cFab, the volume of distribution and systemic clearance were increased 6.4- and 3.5-fold, respectively. Organ uptake of cIgG and cFab was markedly increased compared with that of nIgG and nFab, especially in kidney, liver, spleen, and lung. Renal clearance of cIgG and cFab was also increased 30- and 10-fold compared with that of nIgG and nFab, respectively. The present data suggest that cationization of colchicine-specific IgG and Fab fragments increased the organ distribution and greatly altered their pharmacokinetics. Nevertheless, the smaller molecular size of Fab versus IgG did not enhance the distribution and clearance of cFab. These data pave the way for evaluating the biological efficacy of these more tissue-organ-interactive antibodies.

Avidin targeting of intraperitoneal tumor xenografts

BACKGROUND

Lectins (proteins that bind specific sugar molecules on glycoproteins and glycolipids) are expressed at various levels on the surface of tumor cells. Conjugation of cytotoxic agents to glycoproteins recognized by lectins could be useful in the treatment of tumors. Avidin (a highly glycosylated, positively charged protein found in egg white) contains terminal N-acetylglucosamine and mannose residues that bind to some lectins. In this study, we tested the ability of avidin, labeled through conjugation to radioactive biotin (a B vitamin), to target intraperitoneal tumors.

METHODS

Biotin was radioactively labeled with 111In. Four tumor models (one ovarian, one lung, and two colon) were established in nude mice by intraperitoneal injection of cultured cancer cells. The following two approaches were used in the intraperitoneal administration of avidin: 1) radioactive biotin-avidin conjugates were injected and 2) avidin was injected 1-24 hours before the injection of radioactive biotin (avidin pretargeting; avidin-biotin conjugates formed in vivo). The distribution of injected radioactivity in the tissues of treated animals was assessed.

RESULTS

Radiolabeled avidin localized highly and rapidly in the tumors. More than 50% of the administered dose of avidin-biotin conjugate accumulated per gram of tumor tissue 2 hours after injection; high tumor uptake of radioactivity was observed up to 24 hours after conjugate injection. In contrast, accumulation of radioactivity in normal tissues was low, yielding high tumor to nontumor ratios. With avidin pretargeting, accumulation of radioactivity in the liver, kidney, and spleen was reduced to a greater extent than that in the tumor, and tumor to nontumor ratios were increased.

CONCLUSIONS

Avidin may be a promising vehicle for the delivery of radioisotopes, drugs, toxins, or therapeutic genes to intraperitoneal tumors.