Alison Joyce

Emerging Technologies to Increase Ligand Binding Assay Sensitivity

Ligand binding assays (LBAs) have been the method of choice for protein analyte measurements for more than four decades. Over the years, LBA methods have improved in sensitivity and achieved larger dynamic ranges by using alternative detection systems and new technologies. As a consequence, the landscape and application of immunoassay platforms has changed dramatically. The introduction of bead-based methods, coupled with single molecule detection standardization and the ability to amplify assay signals, has improved the sensitivity of many immunoassays, in some cases by several logs of magnitude. Three promising immunoassay platforms are described in this article: Single Molecule Counting (SMC™) from Singulex Inc, Single Molecule Arrays (Simoa™) from Quanterix Corporation, and Immuno-PCR (Imperacer®) from Chimera Biotec GmbH. These platforms have the potential to significantly improve immunoassay sensitivity and thereby address the bioanalytical needs and challenges faced during biopharmaceutical drug development.

Pharmacokinetic, biodistribution, and biophysical profiles of TNF nanobodies conjugated to linear or branched poly(ethylene glycol).

Covalent attachment of poly(ethylene glycol) (PEG) to therapeutic proteins has been used to prolong in vivo exposure of therapeutic proteins. We have examined pharmacokinetic, biodistribution, and biophysical profiles of three different tumor necrosis factor alpha (TNF) Nanobody-40 kDa PEG conjugates: linear 1 × 40 KDa, branched 2 × 20 kDa, and 4 × 10 kDa conjugates. In accord with earlier reports, the superior PK profile was observed for the branched versus linear PEG conjugates, while all three conjugates had similar potency in a cell-based assay. Our results also indicate that (i) a superior PK profile of branched versus linear PEGs is likely to hold across species, (ii) for a given PEG size, the extent of PEG branching affects the PK profile, and (iii) tissue penetration may differ between linear and branched PEG conjugates in a tissue-specific manner. Biophysical analysis (R(g)/R(h) ratio) demonstrated that among the three protein-PEG conjugates the linear PEG conjugate had the most extended time-average conformation and the most exposed surface charges. We hypothesized that these biophysical characteristics of the linear PEG conjugate accounts for relatively less optimal masking of sites involved in elimination of the PEGylated Nanobodies (e.g., intracellular uptake and proteolysis), leading to lower in vivo exposure compared to the branched PEG conjugates. However, additional studies are needed to test this hypothesis.

Bioanalytical platform comparison using a generic human IgG PK assay format.

A comparison of four different ligand-binding assay technology platforms (ELISA, Meso Scale Discovery®, Gyros® and AlphaLISA®) was conducted using quantitative assays for the measurement of a human IgG₁ monoclonal antibody (MAb) in rat serum. The assays used common reagents for Fc-specific measurement to determine total levels of a human IgG MAb drug analyte, and all were fully optimized for use on each platform. Mock MAb study samples were prepared and analyzed using all platforms to assess assay performance. Assay parameters such as sensitivity, dynamic range, minimum required dilution and sample volume as well as other considerations such as per-run cost, technology availability, requisite equipment and necessary reagent modifications were evaluated toward the determination of a default go-to assay platform for monoclonal antibody biotherapeutics in this laboratory. Based primarily on superior assay performance, Meso Scale Discovery and Gyros were selected from the four technologies evaluated as our default platforms for non-regulated (discovery) study support. As an adjunct, immunoaffinity LC-MS/MS was explored as an alternate platform for generic Fc quantitation and was found to perform similarly to the ligand-binding assays.

Engineering a Monomeric Fc Domain Modality by N-Glycosylation for the Half-life Extension of Biotherapeutics

Background: The bivalency of IgG and Fc fusion could cause undesired therapeutic properties. Results: We developed a stable monomeric Fc modality by N-glycosylation engineering, enabling the generation of crystal structure. Conclusion: The monomeric Fc prolonged the half-life of Fab domain through the interaction with neonatal Fc receptor. Significance: The monomeric Fc will be used for pharmacokinetics enhancement of biotherapeutics that require monovalent properties. Human IgG is a bivalent molecule that has two identical Fab domains connected by a dimeric Fc domain. For therapeutic purposes, however, the bivalency of IgG and Fc fusion proteins could cause undesired properties. We therefore engineered the conversion of the natural dimeric Fc domain to a highly soluble monomer by introducing two Asn-linked glycans onto the hydrophobic CH3-CH3 dimer interface. The monomeric Fc (monoFc) maintained the binding affinity for neonatal Fc receptor (FcRn) in a pH-dependent manner. We solved the crystal structure of monoFc, which explains how the carbohydrates can stabilize the protein surface and provides the rationale for molecular recognition between monoFc and FcRn. The monoFc prolonged the in vivo half-life of an antibody Fab domain, and a tandem repeat of the monoFc further prolonged the half-life. This monoFc modality can be used to improve the pharmacokinetics of monomeric therapeutic proteins with an option to modulate the degree of half-life extension.

Utility of a human FcRn transgenic mouse model in drug discovery for early assessment and prediction of human pharmacokinetics of monoclonal antibodies

ABSTRACT Therapeutic antibodies continue to develop as an emerging drug class, with a need for preclinical tools to better predict in vivo characteristics. Transgenic mice expressing human neonatal Fc receptor (hFcRn) have potential as a preclinical pharmacokinetic (PK) model to project human PK of monoclonal antibodies (mAbs). Using a panel of 27 mAbs with a broad PK range, we sought to characterize and establish utility of this preclinical animal model and provide guidance for its application in drug development of mAbs. This set of mAbs was administered to both hemizygous and homozygous hFcRn transgenic mice (Tg32) at a single intravenous dose, and PK parameters were derived. Higher hFcRn protein tissue expression was confirmed by liquid chromatography-high resolution tandem mass spectrometry in Tg32 homozygous versus hemizygous mice. Clearance (CL) was calculated using non-compartmental analysis and correlations were assessed to historical data in wild-type mouse, non-human primate (NHP), and human. Results show that mAb CL in hFcRn Tg32 homozygous mouse correlate with human (r2 = 0.83, r = 0.91, p < 0.01) better than NHP (r2 = 0.67, r = 0.82, p < 0.01) for this dataset. Applying simple allometric scaling using an empirically derived best-fit exponent of 0.93 enabled the prediction of human CL from the Tg32 homozygous mouse within 2-fold error for 100% of mAbs tested. Implementing the Tg32 homozygous mouse model in discovery and preclinical drug development to predict human CL may result in an overall decreased usage of monkeys for PK studies, enhancement of the early selection of lead molecules, and ultimately a decrease in the time for a drug candidate to reach the clinic.

Challenges in selectivity, specificity and quantitation range of ligand-binding assays: case studies using a microfluidics platform

BACKGROUND Method developers of plate-based ligand-binding assays (LBAs) often face challenges establishing selectivity, specificity and range of quantitation to meet the needs of a particular study. Case studies are presented to compare different ligand-binding immunoassay platforms (plate-based vs microfluidic system) in method development to support pharmacokinetic and pharmacodynamic studies. RESULTS Studies highlight the challenges of plate-based LBAs to establish selectivity, specificity and range of quantitation as a result of nonspecific background signal, matrix interference, lack of linearity and drug interference. The fast assay kinetics of a microfluidic immunoassay system was shown to generally reduce nonspecific background and matrix effects, while increasing assay linear range and drug tolerance. CONCLUSION The short incubation times with microfluidics can be beneficial for LBAs burdened by matrix effects and in these cases had superior assay performance compared with widely used immunoassay platforms in bioanalysis, for example, Meso Scale Discovery(®) and enzyme-linked immunosorbent assay.

Use of response surface methods and path of steepest ascent to optimize ligand-binding assay sensitivity.

Response surface methods (RSM) combined with a steepest ascent approach is a powerful technique to optimize assay performance. In this case, a ligand-binding assay (LBA) to quantitate a peptide biotherapeutic was optimized for improved sensitivity using this technique. Conditions were elucidated to enable pg/mL quantitation of the peptide in human plasma using steepest ascent to efficiently optimize assay factors. Instead of relying solely on assay development experience and intuition to improve assay sensitivity, this systematic approach takes advantage of a predictive mathematical model generated through response surface methods that defines a specific path towards greater predicted assay sensitivity. The actual response observed along the steepest ascent path was in good agreement with the model for several steps, until reagent concentrations moved beyond the physical limits of the system, and model breakdown occurred. RSM combined with steepest ascent method proved a useful tool for sensitivity optimization in three ways: (1) The required LBA sensitivity performance (approximately 200 pg/mL), measured as a signal-to-noise ratio (SNR) at the targeted lower limit of quantitation (LLOQ), was efficiently achieved in only two optimization experiments; (2) Steepest ascent confirmed that the desired sensitivity was found within the initial RSM design space, and no further gain in sensitivity was found venturing beyond this design space along the steepest ascent path; (3) The desired assay sensitivity was maintained over a reasonable range of reagent concentrations along the steepest ascent path, indicating assay robustness for this parameter.

Feasibility of Singlet Analysis for Ligand Binding Assays: a Retrospective Examination of Data Generated Using the Gyrolab Platform

ABSTRACTThere are many sources of analytical variability in ligand binding assays (LBA). One strategy to reduce variability has been duplicate analyses. With recent advances in LBA technologies, it is conceivable that singlet analysis is possible. We retrospectively evaluated singlet analysis using Gyrolab data. Relative precision of duplicates compared to singlets was evaluated using 60 datasets from toxicokinetic (TK) or pharmacokinetic (PK) studies which contained over 23,000 replicate pairs composed of standards, quality control (QC), and animal samples measured with 23 different bioanalytical assays. The comparison was first done with standard curve and QCs followed by PK parameters (i.e., Cmax and AUC). Statistical analyses were performed on combined duplicate versus singlets using a concordance correlation coefficient (CCC), a measurement used to assess agreement. Variance component analyses were conducted on PK estimates to assess the relative analytical and biological variability. Overall, 97.5% of replicate pairs had a %CV of <11% and 50% of the results had a %CV of ≤1.38%. There was no observable bias in concentration comparing the first replicate with the second (CCC of 0.99746 and accuracy value of 1). The comparison of AUC and Cmax showed no observable difference between singlet and duplicate (CCC for AUC and Cmax >0.99999). Analysis of variance indicated an AUC inter-subject variability 35.3-fold greater than replicate variability and 8.5-fold greater for Cmax. Running replicates from the same sample will not significantly reduce variation or change PK parameters. These analyses indicated the majority of variance was inter-subject and supported the use of a singlet strategy.

Faster in vivo clearance of human embryonic kidney than Chinese hamster ovary cell derived protein: Role of glycan mediated clearance

This investigation used in vivo and in vitro tools to study pharmacokinetics and glycosylation of two monomeric antibodies produced either transiently by HEK293 cells or stably by Chinese hamster ovary cells, and demonstrated that higher in vivo clearance of human embryonic kidney antibody was due to higher glycosylation, thus higher mannose receptor mediated uptake.

Preclinical Pharmacokinetics, Pharmacodynamics, Tissue Distribution, and Interspecies Scaling of Recombinant Human Coagulation Factor XaI16L

FXaI16L is a recombinant human FXa variant which is currently being evaluated in the clinic for treating intracerebral hemorrhage. The aim of our studies is to investigate overall pharmacokinetics, pharmacodynamics, and distribution of FXaI16L in preclinical species, and to understand its potential implication in human. Pharmacokinetics of FXaI16L was examined using active site probes and the results showed that FXaI16L displayed fast clearance, low volume of distribution, and a very short plasma resident time in mice, rats, and monkeys. When pharmacodynamics was examined in monkeys, concentration effects of FXaI16L on shortening of active partial prothrombin time and formation of thrombin-antithrombin complex were observed. Furthermore, biodistribution study was conducted in mice using radiolabeled FXaI16L, and showed that 125I-FXaI16L has high plasma protein binding and significant liver and kidney distribution. Human pharmacokinetic prediction for first-in-human dosing was evaluated using allometric scaling, liver blood flow, and a fixed coefficient method, and single species allometric scaling using monkey data was most predictive for human pharmacokinetics of FXaI16L.