Tuning the serum persistence of human serum albumin domain III:diabody fusion proteins

Binding of Apo and Glycated Human Serum Albumins to an Albumin-Selective Aptamer-Bound Graphene Quantum Dot Complex

Diabetes mellitus is a chronic metabolic disease involving continued elevated blood glucose levels. It is a leading cause of mortality and reduced life expectancy. Glycated human serum albumin (GHSA) has been reported to be a potential diabetes biomarker. A nanomaterial-based aptasensor is one of the effective techniques to detect GHSA. Graphene quantum dots (GQDs) have been widely used in aptasensors as an aptamer fluorescence quencher due to their high biocompatibility and sensitivity. GHSA-selective fluorescent aptamers are first quenched upon binding to GQDs. The presence of albumin targets results in the release of aptamers to albumin and consequently fluorescence recovery. To date, the molecular details on how GQDs interact with GHSA-selective aptamers and albumin remain limited, especially the interactions of an aptamer-bound GQD (GQDA) with an albumin. Thus, in this work, molecular dynamics simulations were used to reveal the binding mechanism of human serum albumin (HSA) and GHSA to GQDA. The results show the rapid and spontaneous assembly of albumin and GQDA. Multiple sites of albumins can accommodate both aptamers and GQDs. This suggests that the saturation of aptamers on GQDs is required for accurate albumin detection. Guanine and thymine are keys for albumin-aptamer clustering. GHSA gets denatured more than HSA. The presence of bound GQDA on GHSA widens the entrance of drug site I, resulting in the release of open-chain glucose. The insight obtained here will serve as a base for accurate GQD-based aptasensor design and development.

Fused human paraoxonase 1 as a prophylactic agent against organophosphate poisoning

Organophosphates (OPs) are highly neurotoxic compounds and certain OP-compounds are also exploited as a weapon of mass destruction and chemical warfare in terrorist attacks. Available prophylactic and post-exposure treatments are less effective and also have serious side-effects. Thus, there is a dire need to develop effective and safe prophylactic agent(s) against OP-poisoning. Human Paraoxonase 1 (hPON1) can hydrolyze a wide range of OP molecules and can be developed as an effective and safe prophylactic agent. Thus, there is a dire need in the art to develop variant(s) of rhPON1 that not only possess 'good' OP-hydrolyzing activity but also have improved pharmacokinetic properties. In this report, we describe the characterization of the fused hPON1 (FHP) variant that not only exhibit enhanced in vivo pharmacokinetic properties but also delay / prevent the symptoms of OP-poisoning and prevents OP-induced mortality in rats.

Computation-Aided Design of Albumin Affibody-Inserted Antibody Fragment for the Prolonged Serum Half-Life

Single-chain variable fragments (scFvs) have been recognized as promising agents in cancer therapy. However, short serum half-life of scFvs often limits clinical application. Fusion to albumin affibody (ABD) is an effective and convenient half-life extension strategy. Although one terminus of scFv is available for fusion of ABD, it is also frequently used for fusion of useful moieties such as small functional proteins, cytokines, or antibodies. Herein, we investigated the internal linker region for ABD fusion instead of terminal region, which was rarely explored before. We constructed two internally ABD-inserted anti-HER2 4D5scFv (4D5-ABD) variants, which have short (4D5-S-ABD) and long (4D5-L-ABD) linker length respectively. The model structures of these 4D5scFv and 4D5-ABD variants predicted using the deep learning-based protein structure prediction program (AlphaFold2) revealed high similarity to either the original 4D5scFv or the ABD structure, implying that the functionality would be retained. Designed 4D5-ABD variants were expressed in the bacterial expression system and characterized. Both 4D5-ABD variants showed anti-HER2 binding affinity comparable with 4D5scFv. Binding affinity of both 4D5-ABD variants against albumin was also comparable. In a pharmacokinetic study in mice, the 4D5-ABD variants showed a significantly prolonged half-life of 34 h, 114 times longer than that of 4D5scFv. In conclusion, we have developed a versatile scFv platform with enhanced pharmacokinetic profiles with an aid of deep learning-based structure prediction.

A portable SERS sensor for pyocyanin detection in simulated wound fluid and through swab sampling

A portable surface-enhanced Raman spectroscopy (SERS) sensor for detecting pyocyanin (PYO) in simulated wound fluid and from bacteria samples was developed. Solution-phase SERS detection protocols are designed to be compatible with two different clinical practices for wound exudate collection, namely negative pressure liquid collection and swabbing. For citrate-coated metal nanoparticles of three different compositions, i.e. gold (AuNPs), alloyed silver/gold (AgAuNPs), and silver (AgNPs), we firstly confirmed their interaction with PYO in the complex wound fluid, using fluorescence quenching experiments, which rationalized the Raman enhancement effects. We then demonstrated the Raman enhancement effects of the metal nanoparticles in the order of AgNPs > AgAuNPs > AuNPs. The limit of detection (LOD) achieved for PYO is 1.1 μM (in a linear range of 0.1-25 μM by the AgNPs), 10.9 μM (in a linear range of 5-100 μM, by the AgAuNPs), and 17.7 μM (in a linear range of 10-100 μM by the AuNPs). The AgNP and AgAuNP sensors together cover the sensitivity and dynamic range requirements for the clinical detection of wound infection, where PYO is present at a concentration of 1-50 μM. In addition, sterilized cotton swabs were used to collect wound fluid and transfer samples into AgNP solution for SERS measurements. This detection protocol was completed within 5 minutes with a LOD of 23.1 μM (in a linear range of 15-100 μM). The SERS sensing protocol was validated by its successful detection of PYO in cultured Pseudomonas aeruginosa bacteria. The findings presented in this work pave the way towards point-of-care diagnostics of wound infections.

Albumin Fusion at the N-Terminus or C-Terminus of HM-3 Leads to Improved Pharmacokinetics and Bioactivities

HM-3, an integrin antagonist, exhibits anti-tumor biological responses and therefore has potential as a therapeutic polypeptide. However, the clinical applications of HM-3 are limited by its short half-life. In this study, we genetically fused human serum albumin (HSA) to the N or C-terminus of HM-3 to improve HM-3 pharmacokinetics. HM-3/HSA proteins were successfully expressed in Pichia pastoris and displayed improved pharmacokinetic properties and stability. Among them, the half-life of HM-3-HSA was longer than HSA-HM-3. In vitro, the IC₅₀ values of HSA-HM-3 and HM-3-HSA were 0.38 ± 0.14 μM and 0.25 ± 0.08 μM in B16F10 cells, respectively. In vivo, the inhibition rates of B16F10 tumor growth were 36% (HSA-HM-3) and 56% (HM-3-HSA), respectively, indicating antitumor activity of HM-3-HSA was higher than HSA-HM-3. In conclusion, these results suggested that the HM-3/HSA fusion protein might be potential candidate HM-3 agent for treatment of melanoma and when HSA was fused at the C-terminus of HM-3, the fusion protein had a higher stability and activity.

Structure Prediction and Expression of Modified rCTLA4-Ig as a Blocker for B7 Molecules

CTLA4-Ig (Abatacept) has been produced to suppress immune response by inhibition of T cells functions in autoimmune disease. A new drug, which is called belatacept, has recently been recently developed that is more efficient. The development has been occurred by two substitutions (A29Y, L104E) in the extracellular domain of CTLA4. In the present study, the bioinformatics analysis was used in order to make a new structure that has a better function in comparison with belatacept. Firstly, eight different structures were designed. Thereafter, the secondary and 3D structures, mRNA structure, docking of chimeric proteins with CD80/CD86, antigenicity and affinity of designed chimeric molecules were predicted. Based on the criteria, a new candidate molecule was selected and its gene synthesized. The gene was cloned and expressed in E. coli BL21 (DE3) successfully. The purified rCTLA4-Ig was analyzed by SDS-PAGE, western blotting, and ELISA. Circular dichroism analysis (CD analysis) was used for characterization of the rCTLA4-Ig. Affinity of rCTLA4-Ig was also evaluated by the flow cytometry method. Finally, its biological activity was determined by T cell inhibition test. The results showed rCTLA4-Ig and the belatacept protein have some similarities in structure and function. In addition, rCTLA4-Ig was able to bind CD80/CD86 and inhibit T cell function. Although flow cytomery results showed that the standard protein (CTLA4-Ig), represented better affinity than rCTLA4-Ig, the recombinant protein was able to inhibit T cell proliferation as well as CTLA4-Ig.

Development of a novel prostate apoptosis response-4 (Par-4) protein entity with an extended duration of action for therapeutic treatment of cancer

Prostate apoptosis response-4 (Par-4) is a tumor suppressor which protects against neoplastic transformation. Remarkably, Par-4 is capable of inducing apoptosis selectively in cancer cells without affecting the normal cells. In this study, we found that recombinant Par-4 protein had limited serum persistence in mice that may diminish its anti-tumor activity in vivo. To improve the in vivo performance of the short-lived Par-4 protein, we aimed to develop a novel, long-lasting form of Par-4 with extended sequence, denoted as Par-4Ex, without affecting the desirable molecular function of the natural Par-4. We demonstrate that the Par-4Ex protein entity, produced by using the Escherichia coli expression system suitable for large-scale production, fully retains the desirable pro-apoptotic activity of Par-4 protein, but with ~7-fold improved biological half-life. Further in vivo tests confirmed that, due to the prolonged biological half-life, the Par-4Ex protein is indeed more potent in suppressing metastatic tumor growth in mice.

Truncated domains of human serum albumin improves the binding efficiency of uremic toxins: A surface plasmon resonance and computational approach

Albumin binding is the major cause for the toxicity of protein bound uremic toxins (PBUTs) in uremic patients. Albumin binding property is exploited to address this issue, as some of the extracorporeal dialysis systems use albumin as dialysate. In this line, a detailed study about binding of PBUTs to human serum albumin (HSA) and its domains gives valuable information. The focus of this work emphasizes the mechanism of binding of HSA and its domains with a few selected PBUTs such as hippuric acid (HA), indole acetic acid (IAA) and melatonin. The HSA domains (D2, D3 and D2-3) were expressed in Pichia pastoris and purified by using Albupure matrix. The binding of the expressed domains and HSA, with PBUTs, was measured using surface plasmon resonance and analyzed. All the three domains have significant affinity towards PBUTs, while D3 had greater affinity for all the three selected PBUTs. Docking studies showed that the basic amino acid, lysine, was forming hydrogen bond with PUBTs inorder to stabile these complex. This study would be having therapeutic importance for preparing the extracorporeal dialysis systems, in combination of different domains of HSA to remove the PBUTs.

Human and mouse albumin bind their respective neonatal Fc receptors differently

Albumin has a serum half-life of three weeks in humans and is utilized to extend the serum persistence of drugs that are genetically fused or conjugated directly to albumin or albumin-binding molecules. Responsible for the long half-life is FcRn that protects albumin from intracellular degradation. An in-depth understanding of how FcRn binds albumin across species is of importance for design and evaluation of albumin-based therapeutics. Albumin consists of three homologous domains where domain I and domain III of human albumin are crucial for binding to human FcRn. Here, we show that swapping of two loops in domain I or the whole domain with the corresponding sequence in mouse albumin results in reduced binding to human FcRn. In contrast, humanizing domain I of mouse albumin improves binding. We reveal that domain I of mouse albumin plays a minor role in the interaction with the mouse and human receptors, as domain III on its own binds with similar affinity as full-length mouse albumin. Further, we show that P573 in domain III of mouse albumin is required for strong receptor binding. Our study highlights distinct differences in structural requirements for the interactions between mouse and human albumin with their respective receptor, which should be taken into consideration in design of albumin-based drugs and evaluation in mouse models.

A Macropinocytosis-Intensifying Albumin Domain-Based scFv Antibody and Its Conjugate Directed against K-Ras Mutant Pancreatic Cancer

Enhanced macropinocytosis has been found in K-Ras mutant pancreatic cancer cells, through which albumin can massively enter into the K-Ras-driven cancer cells, suggesting its role in serving as a macropinocytosis-intensifying drug delivery carrier. In the present study, a novel recombinant protein Fv-LDP-D3 and its reconstituted analogue Fv-LDP-D3-AE were designed and prepared. Fv is the fragment of an anti-EGFR antibody, D3 is the domain III of human serum albumin (HSA), LDP is the apoprotein of the antitumor antibiotic lidamycin (LDM), and AE is an extremely cytotoxic enediyne chromophore derived from LDM. As shown, the recombinant protein Fv-LDP-D3 presented intensive and selective binding capacity to pancreatic cancer cells and inhibited cell proliferation by blocking EGFR signaling. Moreover, Fv-LDP-D3 showed prominent tumor imaging in pancreatic carcinoma xenograft. The reconstituted, enediyne-integrated analogue Fv-LDP-D3-AE displayed highly potent cytotoxicity to pancreatic cancer cells through apoptosis induction and G2/M arrest. Fv-LDP-D3 and Fv-LDP-D3-AE markedly inhibited the tumor growth of the pancreatic carcinoma AsPC-1 xenograft. Study results indicated that the novel recombinant protein displays both EGFR-targeting and macropinocytosis-intensifying attributes, presenting a new format of scFv antibody that integrates with albumin domain III. It might be a feasible strategy to develop targeted drugs for K-Ras mutant pancreatic cancer.

Learning from nature: the role of albumin in drug delivery

Graphical Abstract

[Formula: see text]

New pathogen-specific immunoPET/MR tracer for molecular imaging of a systemic bacterial infection

The specific and rapid detection of Enterobacteriaceae, the most frequent cause of gram-negative bacterial infections in humans, remains a major challenge. We developed a non-invasive method to rapidly detect systemic Yersinia enterocolitica infections using immunoPET (antibody-targeted positron emission tomography) with [64Cu]NODAGA-labeled Yersinia-specific polyclonal antibodies targeting the outer membrane protein YadA. In contrast to the tracer [18F]FDG, [64Cu]NODAGA-YadA uptake co-localized in a dose dependent manner with bacterial lesions of Yersinia-infected mice, as detected by magnetic resonance (MR) imaging. This was accompanied by elevated uptake of [64Cu]NODAGA-YadA in infected tissues, in ex vivo biodistribution studies, whereas reduced uptake was observed following blocking with unlabeled anti-YadA antibody. We show, for the first time, a bacteria-specific, antibody-based, in vivo imaging method for the diagnosis of a Gram-negative enterobacterial infection as a proof of concept, which may provide new insights into pathogen-host interactions.

Fab-dsFv: A bispecific antibody format with extended serum half-life through albumin binding

An antibody format, termed Fab-dsFv, has been designed for clinical indications that require monovalent target binding in the absence of direct Fc receptor (FcR) binding while retaining substantial serum presence. The variable fragment (Fv) domain of a humanized albumin-binding antibody was fused to the C-termini of Fab constant domains, such that the VL and VH domains were individually connected to the Cκ and CH1 domains by peptide linkers, respectively. The anti-albumin Fv was selected for properties thought to be desirable to ensure a durable serum half-life mediated via FcRn. The Fv domain was further stabilized by an inter-domain disulfide bond. The bispecific format was shown to be thermodynamically and biophysically stable, and retained good affinity and efficacy to both antigens simultaneously. In in vivo studies, the serum half-life of Fab-dsFv, 2.6 d in mice and 7.9 d in cynomolgus monkeys, was equivalent to Fab'-PEG.

Expression and bioactivity of recombinant human serum albumin and dTMP fusion proteins in CHO cells

The 14-amino acid (IEGPTLRQWLAARA) thrombopoietin mimetic peptide (TMP) shares no sequence homology with native thrombopoietin (TPO). When dimerized, it displays a high-binding affinity for the TPO receptor and has equipotent bioactivity with recombinant human TPO (rhTPO) in stimulating proliferation and maturation of megakaryocytes in vitro. However, TMP is limited for clinical usage because of its short half-life in vivo. In this study, fusion proteins that composed of tandem dimer of TMP (dTMP) genetically fused at the C- or N-terminus of human serum albumin (HSA) were separately expressed in Chinese hamster ovary (CHO) cells. In vitro bioactivity assays showed that purified fusion proteins promoted the proliferation of megakaryocytes in a dose-dependent manner and activated signal transducer and activator of transcription (STAT) pathway in TPO receptor-dependent manner. Following subcutaneous administration, both HSA-dTMP and dTMP-HSA significantly elevated peripheral platelet counts in normal mice in a dose-dependent manner. In addition, fusion with HSA successfully prolonged dTMP half-life in mice. However, when HSA was fused at the C-terminus of dTMP, the bioactivity of dTMP-HSA was about half of that of HSA-dTMP. In conclusion, these results suggested that HSA/dTMP fusion proteins might be potential drugs for thrombocytopenia and, when HSA was fused at the N-terminus of dTMP, the fusion protein had a higher activity.

Fusion protein of single-chain variable domain fragments for treatment of myasthenia gravis

Single-chain variable domain fragment (scFv) 637 is an antigen-specific scFv of myasthenia gravis. In this study, scFv and human serum albumin genes were conjugated and the fusion protein was expressed in Pichia pastoris. The affinity of scFv-human serum albumin fusion protein to bind to acetylcholine receptor at the neuromuscular junction of human intercostal muscles was detected by immunofluorescence staining. The ability of the fusion protein to block myasthenia gravis patient sera binding to acetylcholine receptors and its stability in healthy serum were measured by competitive ELISA. The results showed that the inhibition rate was 2.0-77.4%, and the stability of fusion protein in static healthy sera was about 3 days. This approach suggests the scFv-human serum albumin is a potential candidate for specific immunosuppressive therapy of myasthenia gravis.

Pharmacokinetics and PET imaging properties of two recombinant anti-PSMA antibody fragments in comparison to their parental antibody

BACKGROUND

Radioimmunoimaging with disease-specific tracers can be advantageous compared to that with nonspecific tracers for the imaging of glucose metabolism and cell proliferation. Monoclonal antibodies (mAbs) or their fragments are excellent tools for immuno-positron emission tomography (PET). In this study, PSMA-specific mAb 3/F11 and its recombinant fragments were compared for the imaging of prostate cancer in xenografts.

METHODS

Recombinant anti-PSMA antibody fragments D7-Fc and D7-CH3 were constructed by genetically fusing the binding domains of mAb 3/F11 (D7) to the human IgG3 CH3 or CH2-CH3 (Fc) domain. The fragments and the mAb 3/F11 were DOTA conjugated, tested in vitro, and radiolabeled with (64) Cu. PSMA-positive C4-2 and PSMA-negative DU 145 prostate cancer xenografts were used for PET-MR imaging and for ex vivo biodistribution.

RESULTS

The constructs showed strong and specific binding to PSMA-positive C4-2 cells in vitro which did not decrease after DOTA conjugation. Both tested fragments showed stable accumulation in PSMA-positive C4-2 tumors at all measured time points but reduced uptake compared to the full-length antibody. Other organs and PSMA-negative tumors showed a very low tracer uptake only 3 hr after injection, with the exception of the kidneys, which demonstrated high radioactivity uptake due to rapid renal clearance of the mAb fragments.

CONCLUSION

Stable tumor uptake and fast serum clearance of the tested radiolabeled fragments was observed in this preclinical study compared to the full length mAb. Since the fragments show rapid and specific tumor uptake, the tested fragments might serve as tools for theranostic imaging with suitable isotopes for radioimmunotherapy.

Extending the serum half-life of G-CSF via fusion with the domain III of human serum albumin

Protein fusion technology is one of the most commonly used methods to extend the half-life of therapeutic proteins. In this study, in order to prolong the half-life of Granulocyte colony stimulating factor (G-CSF), the domain III of human serum albumin (3DHSA) was genetically fused to the N-terminal of G-CSF. The 3DHSA-G-CSF fusion gene was cloned into pPICZαA along with the open reading frame of the α-factor signal under the control of the AOX1 promoter. The recombinant expression vector was transformed into Pichia pastoris GS115, and the recombinant strains were screened by SDS-PAGE. As expected, the 3DHSA-G-CSF showed high binding affinity with HSA antibody and G-CSF antibody, and the natural N-terminal of 3DHSA was detected by N-terminal sequencing. The bioactivity and pharmacokinetic studies of 3DHSA-G-CSF were respectively determined using neutropenia model mice and human G-CSF ELISA kit. The results demonstrated that 3DHSA-G-CSF has the ability to increase the peripheral white blood cell (WBC) counts of neutropenia model mice, and the half-life of 3DHSA-G-CSF is longer than that of native G-CSF. In conclusion, 3DHSA can be used to extend the half-life of G-CSF.

Are hepatic impairment studies necessary for therapeutic proteins?

OBJECTIVE

This study assessed whether trials to investigate the effect of hepatic impairment on the pharmacokinetics of therapeutic proteins (TPs), which are conducted for small molecule drugs, are necessary.

METHODS

The product labeling for 91 TPs that have been approved by the US Food and Drug Administration were reviewed. A PubMed search was also conducted to identify completed studies that assessed the effect of hepatic impairment on the pharmacokinetics of TPs. Biologic License Applications were subsequently reviewed to gather further descriptions of the trials conducted in patients with hepatic impairment and data analyses.

RESULTS

No dedicated pharmacokinetics trials were conducted in patients with hepatic impairment for these approved TPs, but subgroup (n = 2 [2.2%]) or population (n = 5 [5.5%]) pharmacokinetic analyses were performed for 7 TPs. The pharmacokinetics of these proteins were not affected by the hepatic dysfunction, with the exception that the clearance of drotrecogin alfa seemed 25% higher in patients with hepatic impairment than in patients without hepatic impairment; however, no dose reduction was recommended. Thus, the effect of hepatic impairment on the pharmacokinetics of TPs is unclear based on the limited analyses completed to date.

CONCLUSIONS

A dedicated pharmacokinetics trial for TPs in patients with hepatic impairment is not necessary. Recognizing that the data are very limited, it would be important to continue collecting pharmacokinetic data of TP in patients with hepatic impairment and using population pharmacokinetic analyses to evaluate the effect of hepatic impairment on the pharmacokinetics of TP.

Albumin as a versatile platform for drug half-life extension

BACKGROUND

Albumin is the most abundant plasma protein, is highly soluble, very stable and has an extraordinarily long circulatory half-life as a direct result of its size and interaction with the FcRn mediated recycling pathway. In contrast, many therapeutic molecules are smaller than the renal filtration threshold and are rapidly lost from the circulation thereby limiting their therapeutic potential. Albumin can be used in a variety of ways to increase the circulatory half-life of such molecules.

SCOPE OF REVIEW

This article will review the mechanisms which underpin albumin's extraordinarily long circulatory half-life and how the understanding of these processes are currently being employed to extend the circulatory half-life of drugs which can be engineered to bind to albumin, or are conjugated to, or genetically fused to, albumin.

MAJOR CONCLUSIONS

The recent and growing understanding of the pivotal role of FcRn in maintaining the extended circulatory half-life of albumin will necessitate a greater and more thorough investigation of suitable pre-clinical model systems for assessing the pharmacokinetic profiles of drugs associated, conjugated or fused to albumin.

GENERAL SIGNIFICANCE

Association, conjugation or fusion of therapeutic drugs to albumin is a well-accepted and established half-life extension technology. The manipulation of the albumin-FcRn interaction will facilitate the modulation of the circulatory half-life of albumin-enabled drugs, leading to superior pharmacokinetics tailored to the disease state and increased patient compliance. This article is part of a Special Issue entitled Serum Albumin.

Fc engineering: serum half-life modulation through FcRn binding

Controlling the half-life of pharmaceuticals through Fc engineering is a desirable approach to achieve optimal exposure and targeting. The long serum residence time of gamma immunoglobulins is attributed to the Fc binding to the neonatal Fc receptor (FcRn). The residues in the Fc region that interact with FcRn have been mapped and individual mutations of these residues have demonstrated reduced affinity to FcRn and faster blood clearance. Here, we describe site-specific mutagenesis of Fc residues in a scFv-Fc fusion protein, as well as the mammalian production, purification, characterization, and the in vivo pharmacokinetics of these antibody fragments.

Structure-based mutagenesis reveals the albumin-binding site of the neonatal Fc receptor

Albumin is the most abundant protein in blood where it has a pivotal role as a transporter of fatty acids and drugs. Like IgG, albumin has long serum half-life, protected from degradation by pH-dependent recycling mediated by interaction with the neonatal Fc receptor, FcRn. Although the FcRn interaction with IgG is well characterized at the atomic level, its interaction with albumin is not. Here we present structure-based modelling of the FcRn–albumin complex, supported by binding analysis of site-specific mutants, providing mechanistic evidence for the presence of pH-sensitive ionic networks at the interaction interface. These networks involve conserved histidines in both FcRn and albumin domain III. Histidines also contribute to intramolecular interactions that stabilize the otherwise flexible loops at both the interacting surfaces. Molecular details of the FcRn–albumin complex may guide the development of novel albumin variants with altered serum half-life as carriers of drugs.

Albumin transport proteins circulate in the blood and are protected from degradation by interaction with the neonatal Fc receptor. Andersen et al. investigate the albumin binding site of the neonatal Fc receptor and find pH sensitive ionic networks at the binding interface.

Design and production of multimeric antibody fragments, focused on diabodies with enhanced clinical efficacy

Multimeric antibody fragments, particularly dimers (diabodies), trimers (triabodies), and tetramers (tetrabodies) of single-chain Fv molecules (scFv), provide high avidity through multivalent binding to the target antigen. The combination of their smaller size and avid binding can provide desirable biological characteristics for tumor targeting applications in vivo; for example, diabodies can have greater tumor penetration and faster blood clearance rates compared to intact full-size antibodies (IgGs). The pharmacokinetic and biodistribution characteristics can further be optimized by the addition of specific thiolation sites for conjugation of PEG molecules to regulate molecular weight and reduce kidney uptake. Thiolation sites can also be used for precise loading of therapeutic payloads. This protocol describes our method for construction and bacterial production of soluble multimeric antibody scFv fragments, focusing on diabodies (scFv dimers).

Neonatal Fc receptor and IgG-based therapeutics

The majority of potent new biologics today are IgG-based molecules that have demonstrated tissue-targeting specificity with favorable clinical response. Several factors determine the efficacy of these products, including target specificity, serum half-life and effector functions via complement-dependent cytotoxicity, antibody-dependent cell-mediated cytotoxicity or drug conjugates. In this review, we will focus on the interaction between therapeutic antibody and neonatal Fc receptor (FcRn), which is one of the critical factors in determining the circulating antibody half-life. Specifically, we will review the fundamental biology of FcRn, FcRn functions in various organs, Fc mutations designed to modulate binding to FcRn, IgG-based therapeutics that directly exploit FcRn functions and tools and strategies used to study FcRn-IgG interactions. Comprehensive understanding of FcRn-IgG interactions not only allows for development of effective therapeutics, but also avoidance of potential adverse effects.

Strategies for extended serum half-life of protein therapeutics

With a growing number of protein therapeutics being developed, many of them exhibiting a short plasma half-life, half-life extension strategies find increasing attention by the biotech and pharmaceutical industry. Extension of the half-life can help to reduce the number of applications and to lower doses, thus are beneficial for therapeutic but also economic reasons. Here, a comprehensive overview of currently developed half-life extension strategies is provided including those aiming at increasing the hydrodynamic volume of a protein drug but also those implementing recycling processes mediated by the neonatal Fc receptor.

Prostaglandin E₂ protects murine lungs from bleomycin-induced pulmonary fibrosis and lung dysfunction

Prostaglandin E(2) (PGE(2)) is a lipid mediator that is produced via the metabolism of arachidonic acid by cyclooxygenase enzymes. In the lung, PGE(2) acts as an anti-inflammatory factor and plays an important role in tissue repair processes. Although several studies have examined the role of PGE(2) in the pathogenesis of pulmonary fibrosis in rodents, results have generally been conflicting, and few studies have examined the therapeutic effects of PGE(2) on the accompanying lung dysfunction. In this study, an established model of pulmonary fibrosis was used in which 10-12-wk-old male C57BL/6 mice were administered a single dose (1.0 mg/kg) of bleomycin via oropharyngeal aspiration. To test the role of prostaglandins in this model, mice were dosed, via surgically implanted minipumps, with either vehicle, PGE(2) (1.32 μg/h), or the prostacyclin analog iloprost (0.33 μg/h) beginning 7 days before or 14 days after bleomycin administration. Endpoints assessed at 7 days after bleomycin administration included proinflammatory cytokine levels and measurement of cellular infiltration into the lung. Endpoints assessed at 21 days after bleomycin administration included lung function assessment via invasive (FlexiVent) analysis, cellular infiltration, lung collagen content, and semiquantitative histological analysis of the degree of lung fibrosis (Ashcroft method). Seven days after bleomycin administration, lymphocyte numbers and chemokine C-C motif ligand 2 expression were significantly lower in PGE(2)- and iloprost-treated animals compared with vehicle-treated controls (P < 0.05). When administered 7 days before bleomycin challenge, PGE(2) also protected against the decline in lung static compliance, lung fibrosis, and collagen production that is associated with 3 wk of bleomycin exposure. However, PGE(2) had no therapeutic effect on these parameters when administered 14 days after bleomycin challenge. In summary, PGE(2) prevented the decline in lung static compliance and protected against lung fibrosis when it was administered before bleomycin challenge but had no therapeutic effect when administered after bleomycin challenge.