A survey of pharmacokinetic bioanalytical methods in biosimilar biological license applications for the assessment of target and antidrug antibody effects.

The presence of circulating targets and antidrug antibodies can influence the ability of a bioanalytical method to measure therapeutic protein (TP) concentration relevant to exposure-response evaluations. This project surveyed biosimilar submissions for their bioanalytical methods. Survey results revealed that 97% of pharmacokinetic methods designed to measure theoretically free or partial-free TPs with respect to target indeed measured free or partial-free TPs when considering experimental testing results for target effects. Antidrug antibody effect is less often evaluated. The observed trend of measuring biologically active forms of TP is consistent with the scientific understanding that pharmacokinetics of biologically active forms is more likely to be relevant to the clinical responses and evaluation of clinically meaningful differences to contribute to biosimilarity assessments.

Non-clinical similarity of biosimilar ABP 798 with rituximab reference product.

ABP 798 is a biosimilar to Rituxan® (rituximab reference product [RP]). Non-clinical assessments relevant to the primary and secondary mechanisms of action (MOA) contribute to the totality of the evidence (TOE) in supporting biosimilarity and are critical in providing scientific evidence for extrapolation of indications. Similarity of ABP 798 with rituximab RP was investigated across a range of biological activities which have potential impact on pharmacokinetics and clinical efficacy with non-clinical assessments relevant to MOA such as CD20 internalization, trogocytosis, binding to primary human natural killer (NK) cells as well as the ability to induce antibody-dependent cellular phagocytosis (ADCP) in peripheral blood mononuclear cells. Additionally, in vitro synergy of ABP 798 or RP with chemotherapeutic agents, in vivo xenograft studies in mice, and toxicological assessments in cynomolgus monkeys (including B cell depletion and toxicokinetics) were also conducted. Results from these non-clinical assessments contribute to the TOE supporting the biosimilarity between ABP 798 and rituximab RP across a range of primary and secondary MOAs and support justification for extrapolation to all indications of use for ABP 798 for which the RP is approved.

A Simulation Approach to Evaluate the Impact of Patterns of Bioanalytical Bias Difference on the Outcome of Pharmacokinetic Similarity Studies.

Pharmacokinetic (PK) similarity studies are vital to assess the biosimilarity of a biosimilar to a reference product. Systematic bias in a bioanalytical method that quantify products could be a potential source of error affecting the variability of the data and influencing the outcome of a PK similarity study. We investigated the impact of six varying patterns of bioanalytical bias difference (biasdiff ) between the similar products on the probability passing the PK similarity test. A population PK model was used to simulate concentration-time profiles for a biosimilar and a reference product and added biasdiff ranging from 030%. The probability of achieving the PK similarity criteria (90% confidence interval between 0.8 and 1.25) for the maximum serum concentration (Cmax ) and area under the curve (AUC) was assessed. The data indicate that an increase in absolute biasdiff between products of ≥ 10% would decrease the power to assess the similarity criteria for Cmax and AUC.

Retrospective Analysis of Bioanalytical Method Validation Approaches in Biosimilar Biological Product Development.

Development and validation of a bioanalytical method for biosimilar biological product development (BPD) can be challenging. It requires the development of a bioanalytical method that reliably and accurately measures both proposed biosimilar and reference products in a biological matrix. This survey summarizes the current state of bioanalysis in BPD. Bioanalytical data from 28 biosimilar biologic license applications submitted to U.S. Food and Drug Administration (FDA) up to December 2018 were analyzed. The aim of the analysis was to provide (i) a summary of the bioanalytical landscape for BPD, (ii) a cumulative review of bioanalytical method validation approaches to aid in understanding how a specific method was selected, and (iii) a summary of data regarding bioanalytical bias differences between products. Results show diversity of the bioanalytical approaches used, as well as the observed differences in bioanalytical bias. Our findings highlight the need for understanding the critical aspects of BPD bioanalysis and clarifying BPD bioanalytical best practices, which could help ensure consistent method validation approaches in the BPD community.

Role of Modeling and Simulation in the Development of Novel and Biosimilar Therapeutic Proteins.

Modeling and simulation (M&S) is an important enabler of knowledge integration in novel biological product development programs. Given the volume of data generated from clinical trials and the complexity of pharmacokinetic (PK) and pharmacodynamic (PD) properties for reference products, extending the use of M&S to biosimilar development is logical. Assessing PK and PD similarity is normally a critical part of demonstrating biosimilarity to a reference product. Thoughtful considerations are necessary in study design to minimize the PK and PD variability, thereby increasing the sensitivity for detecting potential differences between products. In addition, the sensitivity of PD biomarkers depends partly on their relevance to the mechanism(s) of action and the dynamic range of PD response(s), including the impact of certain structural differences on PD in the relevant population. As such, opportunities exist for leveraging the available M&S knowledgebase to maximize the efficiency in the design and interpretation of PK and PD similarity studies. This article describes M&S applications which have contributed to and can continue to enhance biosimilar development programs.

Utility of a Bayesian Mathematical Model to Predict the Impact of Immunogenicity on Pharmacokinetics of Therapeutic Proteins.

The impact of an anti-drug antibody (ADA) response on pharmacokinetic (PK) of a therapeutic protein (TP) requires an in-depth understanding of both PK parameters and ADA characteristics. The ADA and PK bioanalytical assays have technical limitations due to high circulating levels of TP and ADA, respectively, hence, significantly hindering the interpretation of this assessment. The goal of this study was to develop a population-based modeling and simulation approach that can identify a more relevant PK parameter associated with ADA-mediated clearance. The concentration-time data from a single dose PK study using five monoclonal antibodies were modeled using a non-compartmental analysis (NCA), one-compartmental, and two-compartmental Michaelis-Menten kinetic model (MMK). A novel PK parameter termed change in clearance time of the TP (α) derived from the MMK model could predict variations in α much earlier than the time points when ADA could be bioanalytically detectable. The model could also identify subjects that might have been potentially identified as false negative due to interference of TP with ADA detection. While NCA and one-compartment models can estimate loss of exposures, and changes in clearance, the two-compartment model provides this additional ability to predict that loss of exposure by means of α. Modeling data from this study showed that the two-compartment model along with the conventional modeling approaches can help predict the impact of ADA response in the absence of relevant ADA data.

Fundamentals of large-molecule protein therapeutic bioanalysis using ligand-binding assays.

This article provides an overview of ligand-binding assays, including the origin and evolution of the primary concepts, in addition to reviewing commonly used assay formats. The birth of ligand-binding assays began with a radioimmunoassay developed to measure insulin in 1960. Fundamental to ligand-binding assay design is the requirement of at least one protein that interacts with the analyte of interest. Enzyme immunoassay has largely supplanted radioimmunoassay as the ligand-binding assay of choice in today's laboratory environment. This article illustrates various assay formats such as competitive, sandwich and bridging, in addition to, describing critical reagents necessary for their design. The utility of ligand-binding assays in therapeutic protein development and comparison to alternative bioanalysis platforms is discussed.

Measurement of Free Versus Total Therapeutic Monoclonal Antibody in Pharmacokinetic Assessment is Modulated by Affinity, Incubation Time, and Bioanalytical Platform.

Decisions about efficacy and safety of therapeutic proteins (TP) designed to target soluble ligands are made in part by their ex vivo quantification. Ligand binding assays (LBAs) are critical tools in measuring serum TP levels in pharmacokinetic, toxicokinetic, and pharmacodynamic studies. This study evaluated the impact of reagent antibody affinities, assay incubation times, and analytical platform on free or total TP quantitation. An ELISA-based LBA that measures monoclonal anti-sclerostin antibody (TPx) was used as the model system. To determine whether the method measures free or total TPx, the effects of K on, K off, and K D were determined. An 8:1 molar ratio of sclerostin (Scl) to TPx compared to a 1:1 molar ratio produced by rabbit polyclonal antibodies to TPx was required to achieve IC50, a measure of TPx interference effectiveness, making it unclear whether the ELISA truly measured free TPx. Kinetic analysis revealed that Scl had a rapid dissociation rate (K off) from TPx and that capture and detection antibodies had significantly higher binding affinities (K D) to TPx. These kinetic limitations along with long ELISA incubation times lead to the higher molar ratios (8:1) required for achieving 50% inhibition of TPx. However, a microfluidic platform with the same reagent pairs required shorter incubations to achieve a lower Scl IC50 molar ratio (1:1). The findings from this study provide the bioanalytical community with a deeper understanding of how reagent and platform selection for LBAs can affect what a particular method measures, either free or total TP concentrations.

In Silico Evaluation of the Potential Impact of Bioanalytical Bias Difference between Two Therapeutic Protein Formulations for Pharmacokinetic Assessment in a Biocomparability Study.

Formulation changes at later stages of biotherapeutics development require biocomparability (BC) assessment. Using simulation, this study aims to determine the potential effect of bias difference observed between the two formulations after spiking into serum in passing or failing of a critical BC study. An ELISA method with 20% total error was used to assess any bias differences between a reference (RF) and test formulations (TF) in serum. During bioanalytical comparison of these formulations, a 9% difference in bias was observed between the two formulations in sera. To determine acceptable level of bias difference between the RF and TF bioanalytically, two in silico simulations were performed. The in silico analysis showed that the likelihood of the study meeting the BC criteria was >90% when the bias difference between RF and TF in serum was 9% and the number of subjects was ≥20 per treatment arm. An additional simulation showed that when the bias difference was increased to 13% and the number of subjects was <40, the likelihood of meeting the BC criteria decreased to 80%. The result from in silico analysis allowed the bioanalytical laboratory to proceed with sample analysis using a single calibrator and quality controls made from the reference formulation. This modeling approach can be applied to other BC studies with similar situations.

Validation of a microfluidic platform to measure total therapeutic antibodies and incurred sample reanalysis performance.

BACKGROUND: A microfluidic platform-based assay was validated to measure a humanized or fully human IgG in rat serum samples. MATERIALS & METHODS: The cumulative assessment for accuracy and precision was performed with three accuracy and precision runs. RESULTS: The inter-assay accuracy (mean %bias) ranged from -4.3 to 3.8%, and inter-batch %CV ranged from 5.0 to 9.2%. The method acceptance criterion was determined as 15% total error. The assay dynamic range was 50 to 10000 ng/ml. Incurred sample reanalysis passed with 95% of samples meeting incurred sample reanalysis acceptance criteria. Potential carryover effect was not observed. CONCLUSION: This study demonstrated the need for evaluating additional platform-specific processes when new technologies are employed to ensure the reproducibility of a successfully validated microfluidic platform method.

Impact of anti-drug antibodies in preclinical pharmacokinetic assessment.

The administration of human biotherapeutics is often associated with a higher incidence of immunogenicity in preclinical species. The presence of anti-drug antibodies (ADAs) in the test samples can affect the accurate measurement of therapeutic protein (TP) in bioanalytical methods designed to support pharmacokinetic (PK) and toxicokinetic (TK) assessments. The impact can vary depending on the bioanalytical method platform and study dosing design. The goal of this study is to evaluate the impact of ADA response on the bioanalytical methods in support of PK/TK and the associated study data interpretation. Sprague Dawley rats were administered with four weekly doses of 50 mg/kg TP, a humanized monoclonal antibody. The TP in serum samples was measured using three bioanalytical methods that quantified bound and/or unbound TP to ADA. The ADA response in the animals was classified into negative, low, medium, and high based on the magnitude of the response. The presence of ADA in samples led to discrepant TP measurements between the methods, especially at time points where the TP concentrations were low. This could be due to ADA interference to the accurate measurement of ADA-bound TP concentrations. The TP concentration at last time point (C last) was reduced by 82.8%, 98.6%, and 99.8%, respectively, for samples containing low, medium, and high levels of ADA. The interfering effects of the ADA on bioanalytical methods and exposure were evident as early as 2 weeks post-dosing. This modeling approach can provide the better understanding of ADA impact on PK exposure in multiple doses.

Model-based strategy for bioanalytical method comparison: measurement of a soluble ligand as a biomarker.

Ligand binding assays (LBAs) are often the method of choice for quantification of protein biomarkers and therapeutic biologics during drug development. Soluble ligand X is a glycoprotein. To understand the role of circulating ligand X in drug-target relationship, an analytical method (Method 1) was developed and validated to measure circulating ligand X and to support early clinical studies. Change in the detection reagent led to the development and validation of a second method (Method 2). Both methods measure total circulating ligand X levels. To ensure that the method specificities and data were consistent upon method change, the two methods were cross-validated using three distinct sample types: (1) recombinant ligand X (rLIGX) spiked in buffer, (2) authentic serum samples containing endogenous ligand X (eLIGX), and (3) serum samples collected from patients being dosed with the therapeutic antibody (incurred samples). Methods were considered comparable if the 90% confidence interval (90% CI) fell within 0.80-1.25 for all sample types. The results from the comparison reveal that two methods were comparable for rLIGX samples with the 90% CI of 0.90-1.07. However, with eLIGX samples, Method 1 produced higher mean (± SD) concentrations 675 (± 316 pg/mL) than Method 2 195 (± 97 pg/mL) and the two methods were considered not comparable as the 90% CI was 0.27-0.29. With the incurred samples, the comparison results also indicated the incomparability of these two methods as the 90% CI was 0.57-0.65. To describe the statistically relevant relationship between two methods in analyzing the serum samples, linear and quadratic regression models were applied to derive two conversion equations; one each for eLIGX and incurred samples. The applicability of the equations was verified with independent study data to indicate that the equations can be used to relate two different sets of study data. A model-based strategy presented here can serve as an explicatory paradigm for other analogous situations in the future.

Method transfer for ligand-binding assays: recommendations for best practice.

To support clinical trials, bioanalytical methods are often transferred from one laboratory to another. With the rising number of large-molecule therapeutic proteins submitted for US FDA approval, the demand for large-molecule bioanalytical support and, subsequently, method transfer increases. Ligand-binding assays are the methods most commonly used to quantify endogenous and therapeutic proteins for the assessment of biomarkers and pharmacokinetic parameters. The goal of this review is to provide an overview of ligand-binding assay method transfer, essential parameters for partial method validation and to lay out a strategy to increase the chance of success. The recommendations herein are based on a summary of current publications and the authors' specific experiences, to help increase workload efficiency, maintain positive collaborations with partners and meet program timelines.

Assessment of incurred sample reanalysis for macromolecules to evaluate bioanalytical method robustness: effects from imprecision.

Incurred sample reanalysis (ISR) is recommended by regulatory agencies to demonstrate reproducibility of validated methods and provide confidence that methods used in pharmacokinetic and toxicokinetic assessments give reproducible results. For macromolecules to pass ISR, regulatory recommendations require that two thirds of ISR samples be within 30% of the average of original and reanalyzed values. A modified Bland-Altman (mBA) analysis was used to evaluate whether total error (TE), the sum of precision and accuracy, was predictive of a method's passing ISR and to identify potential contributing parameters for ISR success. Simulated studies determined minimum precision requirements for methods to have successful ISR and evaluated the relationship between precision and the probability of a method's passing ISR acceptance criteria. The present analysis evaluated ISRs conducted for 37 studies involving ligand-binding assays (LBAs), with TEs ranging from 15% to 30%. An mBA approach was used to assess accuracy and precision of ISR, each with a threshold of 30%. All ISR studies met current regulatory criteria; using mBA, all studies met the accuracy threshold of 30% or less, but two studies (5%) failed to meet the 30% precision threshold. Simulation results showed that when an LBA has ≤15% imprecision, the ISR criteria for both the regulatory recommendation and mBA would be met in 99.9% of studies. Approximately 71% of samples are expected to be within 1.5 times the method imprecision. Therefore, precision appears to be a critical parameter in LBA reproducibility and may also be useful in identifying methods that have difficulty passing ISR.

Bioanalytical method requirements and statistical considerations in incurred sample reanalysis for macromolecules.

BACKGROUND: Incurred sample reanalysis (ISR) is the most recent in-study validation parameter that regulatory agencies have mandated to ensure reproducibility of bioanalytical methods supporting pharmacokinetic/toxicokinetic and clinical studies. The present analysis describes five representative case studies for macromolecule therapeutics. METHOD: Single ISR acceptance criteria (within 30% of the averaged or original concentration) and a modified Bland-Altman (BA) approach were used to assess accuracy and precision of ISR results. General concordance between the two criteria was examined using simulation studies. RESULTS: All five methods met the ISR criteria. The results indicated that thorough method development and prestudy validation were prerequisites for a successful ISR. The overall agreement between the original and reanalyzed results as determined by BA was within 20%. Simulation studies indicated that concordance between the ISR criteria and BA was observed in 95% of the cases. Dilution factors had no significant impact on the ISR, even for C(max) samples where 1:100 or higher dilutions were used. CONCLUSION: The current ISR acceptance criteria for macromolecules was scientifically and statistically meaningful for methods with a total error of 25% or less.

Inhibition of sclerostin by monoclonal antibody increases bone formation, bone mass, and bone strength in aged male rats.

The purpose of this study was to evaluate the effects of sclerostin inhibition by treatment with a sclerostin antibody (Scl-AbII) on bone formation, bone mass, and bone strength in an aged, gonad-intact male rat model. Sixteen-month-old male Sprague-Dawley rats were injected subcutaneously with vehicle or Scl-AbII at 5 or 25 mg/kg twice per week for 5 weeks (9-10/group). In vivo dual-energy X-ray absorptiometry (DXA) analysis showed that there was a marked increase in areal bone mineral density of the lumbar vertebrae (L(1) to L(5) ) and long bones (femur and tibia) in both the 5 and 25 mg/kg Scl-AbII-treated groups compared with baseline or vehicle controls at 3 and 5 weeks after treatment. Ex vivo micro-computed tomographic (µCT) analysis demonstrated improved trabecular and cortical architecture at the fifth lumbar vertebral body (L(5) ), femoral diaphysis (FD), and femoral neck (FN) in both Scl-AbII dose groups compared with vehicle controls. The increased cortical and trabecular bone mass was associated with a significantly higher maximal load of L(5) , FD, and FN in the high-dose group. Bone-formation parameters (ie, mineralizing surface, mineral apposition rate, and bone-formation rate) at the proximal tibial metaphysis and tibial shaft were markedly greater on trabecular, periosteal, and endocortical surfaces in both Scl-AbII dose groups compared with controls. These results indicate that sclerostin inhibition by treatment with a sclerostin antibody increased bone formation, bone mass, and bone strength in aged male rats and, furthermore, suggest that pharmacologic inhibition of sclerostin may represent a promising anabolic therapy for low bone mass in aged men.

Experimental and statistical approaches in method cross-validation to support pharmacokinetic decisions.

A case study of experimental and statistical approaches for cross-validating and examining the equivalence of two ligand binding assay (LBA) methods that were employed in pharmacokinetic (PK) studies is presented. The impact of changes in methodology based on the intended use of the methods was assessed. The cross-validation processes included an experimental plan, sample size selection, and statistical analysis with a predefined criterion of method equivalence. The two methods were deemed equivalent if the ratio of mean concentration fell within the 90% confidence interval (0.80-1.25). Statistical consideration of method imprecision was used to choose the number of incurred samples (collected from study animals) and conformance samples (spiked controls) for equivalence tests. The difference of log-transformed mean concentration and the 90% confidence interval for two methods were computed using analysis of variance. The mean concentration ratios of the two methods for the incurred and spiked conformance samples were 1.63 and 1.57, respectively. The 90% confidence limit was 1.55-1.72 for the incurred samples and 1.54-1.60 for the spiked conformance samples; therefore, the 90% confidence interval was not contained within the (0.80-1.25) equivalence interval. When the PK parameters of two studies using each of these two methods were compared, we determined that the therapeutic exposure, AUC((0-168)) and C(max), from Study A/Method 1 was approximately twice that of Study B/Method 2. We concluded that the two methods were not statistically equivalent and that the magnitude of the difference was reflected in the PK parameters in the studies using each method. This paper demonstrates the need for method cross-validation whenever there is a switch in bioanalytical methods, statistical approaches in designing the cross-validation experiments and assessing results, or interpretation of the impact of PK data.

Antibodies from preeclamptic patients stimulate increased intracellular Ca2+ mobilization through angiotensin receptor activation.

BACKGROUND: Preeclampsia is a serious disorder of pregnancy characterized by hypertension, proteinuria, edema, and coagulation and vascular abnormalities. At the cellular level, abnormalities include increased calcium concentration in platelets, lymphocytes, and erythrocytes. Recent studies have shown that antibodies directed against angiotensin II type I (AT1) receptors are also highly associated with preeclampsia. METHODS AND RESULTS: We tested the hypothesis that AT1 receptor-agonistic antibodies (AT1-AAs) could activate AT1 receptors, leading to an increased intracellular concentration of free calcium and to downstream activation of Ca2+ signaling pathways. Sera of 30 pregnant patients, 16 diagnosed with severe preeclampsia and 14 normotensive, were examined for the presence of IgG capable of stimulating intracellular Ca2+ mobilization. IgG from all preeclamptic patients activated AT1 receptors and increased intracellular free calcium. In contrast, none of the normotensive individuals had IgG capable of activating AT1 receptors. The specific mobilization of intracellular Ca2+ by AT1-AAs was blocked by losartan, an AT1 receptor antagonist, and by a 7-amino-acid peptide that corresponds to a portion of the second extracellular loop of the AT1 receptor. In addition, we have shown that AT1-AA-stimulated mobilization of intracellular Ca2+ results in the activation of the transcription factor, nuclear factor of activated T cells. CONCLUSIONS: These results suggest that maternal antibodies capable of activating AT1 receptors are likely to account for increased intracellular free Ca2+ concentrations and changes in gene expression associated with preeclampsia.