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1.  Specific Method Validation and Sample Analysis Approaches for Biocomparability Studies of Denosumab Addressing Method and Manufacture Site Changes 
The AAPS Journal  2012;15(1):70-77.
Manufacturing changes during a biological drug product life cycle occur often; one common change is that of the manufacturing site. Comparability studies may be required to ensure that the changes will not affect the pharmacokinetic properties of the drug. In addition, the bioanalytical method for sample analysis may evolve during the course of drug development. This paper illustrates the scenario of both manufacturing and bioanalytical method changes encountered during the development of denosumab, a fully human monoclonal antibody which inhibits bone resorption by targeting RANK Ligand. Here, we present a rational approach to address the bioanalytical method changes and provide considerations for method validation and sample analysis in support of biocomparability studies. An updated and improved ELISA method was validated, and its performance was compared to the existing method. The analytical performances, i.e., the accuracy and precision of standards and validation samples prepared from both manufacturing formulation lots, were evaluated and found to be equivalent. One of the lots was used as the reference standard for sample analysis of the biocomparability study. This study was sufficiently powered using a parallel design. The bioequivalence acceptance criteria for small molecule drugs were adopted. The pharmacokinetic parameters of the subjects dosed with both formulation lots were found to be comparable.
Electronic supplementary material
The online version of this article (doi:10.1208/s12248-012-9414-x) contains supplementary material, which is available to authorized users.
PMCID: PMC3535110  PMID: 23054973
biocomparability; denosumab; ligand binding assay; method validation; pharmacokinetics
2.  Assessment of Incurred Sample Reanalysis for Macromolecules to Evaluate Bioanalytical Method Robustness: Effects from Imprecision 
The AAPS Journal  2011;13(2):291-298.
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.
PMCID: PMC3085709  PMID: 21461973
incurred sample reanalysis; LBA; sample size selection; statistical analysis; total error
3.  Ligand-Binding Mass Spectrometry to Study Biotransformation of Fusion Protein Drugs and Guide Immunoassay Development: Strategic Approach and Application to Peptibodies Targeting the Thrombopoietin Receptor 
The AAPS Journal  2010;12(4):576-585.
The knowledge of in vivo biotransformation (e.g., proteolysis) of protein therapeutic candidates reveals structural liabilities that impact stability. This information aids the development and confirmation of ligand-binding assays with the required specificity for bioactive moieties (including intact molecule and metabolites) for appropriate PK profiling. Furthermore, the information can be used for re-engineering of constructs to remove in vivo liabilities in order to design the most stable candidates. We have developed a strategic approach of ligand-binding mass spectrometry (LBMS) to study biotransformation of fusion proteins of peptides fused to human Fc (“peptibodies”) using anti-human Fc immunoaffinity capture followed by tiered mass spectrometric interrogation. LBMS offers the combined power of selectivity of ligand capture with the specificity and detailed molecular-level information of mass spectrometry. In this paper, we demonstrate the preclinical application of LBMS to three peptibodies, AMG531 (romiplostim), AMG195(linear), and AMG195(loop), that target the thrombopoietin receptor. The data show that ligand capture offers excellent sample cleanup and concentration of intact peptibodies and metabolites for subsequent query by matrix-assisted laser desorption ionization time-of-flight mass spectrometry for identification of in vivo proteolytic points. Additional higher-resolution analysis by nanoscale liquid chromatography interfaced with electrospray ionization mass spectrometry is required for identification of heterogeneous metabolites. Five proteolytic points are accurately identified for AMG531 and two for AMG195(linear), while AMG195(loop) is the most stable construct in rats. We recommend the use of LBMS to assess biotransformation and in vivo stability during early preclinical phase development for all novel fusion proteins.
PMCID: PMC2976999  PMID: 20625864
fusion protein biotransformation; in vivo stability of biopharmaceuticals; immunoaffinity-mass spectrometry; ligand-binding assay; peptibodies
4.  “Fit-for-Purpose” Method Validation and Application of a Biomarker (C-terminal Telopeptides of Type 1 Collagen) in Denosumab Clinical Studies 
The AAPS Journal  2009;11(2):385-394.
Biomarkers are used to study drug effects, exposure–response relationships, and facilitate early decision making during development. Denosumab, a fully human monoclonal antibody against receptor activator of nuclear factor-κB ligand, profoundly inhibits bone resorption. C-terminal telopeptides of type I collagen (CTx), a bone resorption biomarker, provides early indications of denosumab effectiveness and informs protracted clinical outcomes (e.g., bone mineral density). Because of the dynamic relationship between denosumab and CTx, a precise and robust assay was desired. Thus, we adopted a fit-for-purpose approach to modify and validate a commercial CTx diagnostic kit to meet the intended applications of a quantitative pharmacodynamic biomarker for denosumab development. Seven standards were prepared to replace five calibrators provided in the kit. Three quality controls (QC) and two sample controls were used to characterize and monitor assay performance. Robotic workstations were used for standard and QC preparation and assay execution. Method validation experiments were conducted with rigor and procedures similar to those used for drug bioanalysis. The method demonstrated a linear range of 0.0490–2.34 ng/mL with four-parameter logistic regression. Inter-assay total error of validation samples in serum was ≤26.7%. Extensive tests were conducted on selectivity in sera from target populations, specificity, stability, parallelism, and dilutional linearity. Applications to samples from numerous clinical studies confirmed that the CTx method was reliable, robust, and fit for use as an early indicator of denosumab effectiveness. Refinement supported the confidence for use in pharmacokinetic/pharmacodynamic modeling, dose selections, correlation to clinical effects, and formulation bioequivalence work.
PMCID: PMC2691475  PMID: 19462251
bone resorption marker; commercial immunoassay kit; method validation; pharmacodynamic (PD) biomarker; serum C-terminal telopeptides of type 1 (CTx)
5.  Key elements of bioanalytical method validation for macromolecules 
The AAPS Journal  2007;9(2):E156-E163.
The Third American Association of Pharmaceutical Scientists/US Food and Drug Administration (FDA) Bioanalytical Workshop, which was held May 1 and 2, 2006, in Arlington, VA, addressed bioanalytical assays that are being used for the quantification of therapeutic candidates in support of pharmacokinetic evaluations. One of the main goals of this workshop was to discuss best practices used in bioanalysis regardless of the size of the therapeutic candidates. Since the last bioanalytical workshop, technological advancements in the field and in the statistical understanding of the validation issues have generated a variety of interpretations to clarify and understand the practicality of using the current FDA guidance for assaying macromolecular therapeutics. This article addresses some of the key elements that are essential to the validation of macromolecular therapeutics using ligand binding assays. Because of the nature of ligand binding assays, attempts have been made within the scientific community to use statistical approaches to interpret the acceptance criteria that are aligned with the prestudy validation and in-study validation (sample analysis) processes. We discuss, among other topics, using the total error criterion or confidence interval approaches for acceptance of assays and using anchor calibrators to fit the nonlinear regression models.
PMCID: PMC2751404  PMID: 17614356
Bioanalytical validation; ligand binding assays; macromolecules; biological matrices; immunoassay

Results 1-5 (5)