Extending serum half-life of albumin by engineering neonatal Fc receptor (FcRn) binding.

A major challenge for the therapeutic use of many peptides and proteins is their short circulatory half-life. Albumin has an extended serum half-life of 3 weeks because of its size and FcRn-mediated recycling that prevents intracellular degradation, properties shared with IgG antibodies. Engineering the strictly pH-dependent IgG-FcRn interaction is known to extend IgG half-life. However, this principle has not been extensively explored for albumin. We have engineered human albumin by introducing single point mutations in the C-terminal end that generated a panel of variants with greatly improved affinities for FcRn. One variant (K573P) with 12-fold improved affinity showed extended serum half-life in normal mice, mice transgenic for human FcRn, and cynomolgus monkeys. Importantly, favorable binding to FcRn was maintained when a single-chain fragment variable antibody was genetically fused to either the N- or the C-terminal end. The engineered albumin variants may be attractive for improving the serum half-life of biopharmaceuticals.

Single-chain variable fragment albumin fusions bind the neonatal Fc receptor (FcRn) in a species-dependent manner: implications for in vivo half-life evaluation of albumin fusion therapeutics.

Albumin has a serum half-life of 3 weeks in humans. This has been utilized to extend the serum persistence of biopharmaceuticals that are fused to albumin. In light of the fact that the neonatal Fc receptor (FcRn) is a key regulator of albumin homeostasis, it is crucial to address how fusion of therapeutics to albumin impacts binding to FcRn. Here, we report on a detailed molecular investigation on how genetic fusion of a short peptide or an single-chain variable fragment (scFv) fragment to human serum albumin (HSA) influences pH-dependent binding to FcRn from mouse, rat, monkey, and human. We have found that fusion to the N- or C-terminal end of HSA only slightly reduces receptor binding, where the most noticeable effect is seen after fusion to the C-terminal end. Furthermore, in contrast to the observed strong binding to human and monkey FcRn, HSA and all HSA fusions bound very poorly to mouse and rat versions of the receptor. Thus, we demonstrate that conventional rodents are limited as preclinical models for analysis of serum half-life of HSA-based biopharmaceuticals. This finding is explained by cross-species differences mainly found within domain III (DIII) of albumin. Our data demonstrate that although fusion, particularly to the C-terminal end, may slightly reduce the affinity for FcRn, HSA is versatile as a carrier of biopharmaceuticals.

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.

Collection of family health history for assessment of chronic disease risk in primary care.

BACKGROUND: Family health history can predict a patient's risk for common complex diseases. This project assessed the completeness of family health history data in medical charts and evaluated the utility of these data for performing risk assessments in primary care. METHODS: Family health history data were collected and analyzed to determine the presence of quality indicators that are necessary for effective and accurate assessment of disease risk. RESULTS: More than 99% of the 390 paper charts analyzed contained information about family health history, which was usually scattered throughout the chart. Information on the health of the patient's parents was collected more often than information on the health of other relatives. Key information that was often not collected included age of disease onset, affected side of the family, and second-degree relatives affected. Less than 4% of patient charts included family health histories that were informative enough to accurately assess risk for common complex diseases. LIMITATIONS: Limitations of this study include the small number of charts reviewed per provider, the fact that the sample consisted of primary care providers in a single geographic location, and the inability to assess ethnicity, consanguinity, and other indicators of the informativeness of family health history. CONCLUSIONS: The family health histories collected in primary care are usually not complete enough to assess the patient's risk for common complex diseases. This situation could be improved with use of tools that analyze the family health history information collected and provide risk-stratified decision support recommendations for primary care.

Exploring the Readability of Ingredients Lists of Food Labels with Existing Metrics.

Healthy diet and dietary behaviors are key components in prevention of chronic disease and management of chronic illness. Nutritional literacy has been associated with dietary behaviors and consumer choice of healthy foods. Nutritional literacy can be measured, for example, by examining consumer food label use, but current research focuses largely on the Nutrition Facts panel of a food product. Ingredients lists are critical for communicating food composition but are relatively unstudied in existing literature. The goal of this work is to measure the readability of ingredients lists on branded food products in the United States using existing metrics. We examined ingredients lists for all 495,646 products listed in the USDA Food Data Central database using four existing readability measures for text written in natural language. Each of these indices approximates the grade level that would be expected to comprehend a text; comparatively, patient consent forms are considered acceptable at an 8th grade reading level or lower. We report a broad variability for in readability using different metrics: ingredients lists recorded at a 9th grade reading level or higher to comprehend are found at rates of 16.5% (Automated Reading Index) to 74.9% (Gunning-Fog Index). Ingredients lists recorded at a 10th grade reading level or higher to comprehend are found at rates of 84.2% (using FRE Index). These results demonstrate the need to further explore how ingredients lists can be measured for readability, both for the purposes of consumer understanding as well as for supporting future nutrition research involving text mining.

The production, characterisation and enhanced pharmacokinetics of scFv-albumin fusions expressed in Saccharomyces cerevisiae.

An expression system is described for the production of monomeric scFvs and scFv antibody fragments genetically fused to human albumin (at either the N- or C-terminus or both). Based upon strains of Saccharomyces cerevisiae originally developed for the production of a recombinant human albumin (Recombumin) this system has delivered high levels of secreted product into the supernatant of shake flask and high cell density fed-batch fermentations. Specific binding to the corresponding ligand was demonstrated for each of the scFvs and scFv-albumin fusions and pharmacokinetic studies showed that the fusion products had greatly extended circulatory half-lives. The system described provides an attractive alternative to other microbial systems for the manufacture of this type of product.

Generation of a double transgenic humanized neonatal Fc receptor (FcRn)/albumin mouse to study the pharmacokinetics of albumin-linked drugs.

Human serum albumin (HSA) is a natural carrier protein possessing multiple ligand binding sites with a plasma half-life ~19days, facilitated by interaction with the human neonatal Fc receptor (FcRn), that promotes it as a highly attractive drug delivery technology. A lack of adequate rodent models, however, is a major challenge in the preclinical development of albumin-linked therapeutics. This work describes the first double transgenic mouse model bearing both human FcRn and HSA genes (hFcRn(+/+), hAlb(+/+)) under the control of an endogenous promoter. Human FcRn was shown by immunohistochemical and qPCR analysis to be ubiquitously expressed in the major organs. Physiological levels of HSA were detected in the blood that exhibited similar FcRn binding kinetics to recombinant or human serum-derived HSA. The circulatory half-life (t1/2) was shown to be dependent on FcRn binding affinity that increased from low affinity (t1/2 29h), to wild type (t1/2 50h), to high affinity (t1/2 80h) variants, that validates the application of the model for optimizing the pharmacokinetics of drug carriers who's circulatory half-life is dependent in some manner upon interaction with endogenous FcRn. This study presents a novel mouse model that better mimics the human physiological conditions and, thus, has potential wide applications in the development of albumin-linked drugs or conventional drugs whose action is influenced by reversible binding to endogenous HSA.

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.

Deep venous thrombosis in gynecological oncology: incidence and clinical symptoms study.

OBJECTIVE: Cancer patients have increased risks of leg deep venous thrombosis (DVT). We studied the incidence, risk factors and most predictive symptoms of leg DVT in gynecologic oncology patients. STUDY DESIGNS: Gynecologic oncology patients with any leg DVT symptoms were recruited and screened using Doppler sonogram. All hospitalized surgery and non-ambulating patients received thigh-high sequential compression devices (SCDs) without heparin as a prophylactic method against thrombosis. Statistical analysis was done using chi-square or Fisher's exact tests. RESULTS: Out of 1974 patients, 134 complained of lower limb symptoms. Doppler studies found 38 patients with leg DVT. Incidence of leg DVT was 36/853 (4.2%) in patients with cancer and 2/1121 (0.2%) in patients without cancer (odds ratio 2.8 with a diagnosis of cancer). Leg edema, erythema, fever, and warm leg were significant symptoms in diagnosing leg DVT (p<0.01). The cost of finding a leg DVT was $747.54. CONCLUSIONS: Clinical exam is less accurate than Doppler sonogram in diagnosing leg DVT. The incidence of leg DVT using SCD seems to be comparable with other studies. Finally, the cost of identifying leg DVT seems reasonable.

Monocarboxylate transporter MCT1 is a target for immunosuppression.

Current immunosuppressive therapies act on T lymphocytes by modulation of cytokine production, modulation of signaling pathways or by inhibition of the enzymes of nucleotide biosynthesis. We have identified a previously unknown series of immunomodulatory compounds that potently inhibit human and rat T lymphocyte proliferation in vitro and in vivo in immune-mediated animal models of disease, acting by a novel mechanism. Here we identify the target of these compounds, the monocarboxylate transporter MCT1 (SLC16A1), using a strategy of photoaffinity labeling and proteomic characterization. We show that inhibition of MCT1 during T lymphocyte activation results in selective and profound inhibition of the extremely rapid phase of T cell division essential for an effective immune response. MCT1 activity, however, is not required for many stages of lymphocyte activation, such as cytokine production, or for most normal physiological functions. By pursuing a chemistry-led target identification strategy, we have discovered that MCT1 is a previously unknown target for immunosuppressive therapy and have uncovered an unsuspected role for MCT1 in immune biology.