Combining pharmacometric models with predictive and prognostic biomarkers for precision therapy in Crohn's disease: A case study of brazikumab.

Pharmacometric models were used to investigate the utility of biomarkers in predicting the efficacy (Crohn's Disease Activity Index [CDAI]) of brazikumab and provide a data-driven framework for precision therapy for Crohn's disease (CD). In a phase IIa trial in patients with moderate to severe CD, treatment with brazikumab, an anti-interleukin 23 monoclonal antibody, was associated with clinical improvement. Brazikumab treatment effect was determined to be dependent on the baseline IL-22 (BIL22) or baseline C-reactive protein (BCRP; predictive biomarkers), and placebo effect was found to be correlated with the baseline CDAI (a prognostic biomarker). A maximal total inhibition on CDAI input function of 50.6% and 42.4% was predicted for patients with extremely high BIL22 or BCRP, compared to a maximal total inhibition of 20.9% and 17.8% for patients with extremely low BIL22 or BCRP, respectively, which were mainly due to the placebo effect. We demonstrated that model-derived baseline biomarker levels that achieve 50% of maximum unbound systemic concentration of 22.8 pg/mL and 8.03 mg/L for BIL22 and BCRP as the cutoffs to select subpopulations can effectively identify high-response subgroup patients with improved separation of responders when compared to using the median values as the cutoff. This work exemplifies the utility of pharmacometrics to quantify biomarker-driven responses in biologic therapies and distinguish between predictive and prognostic biomarkers, complementing clinical efforts of identifying subpopulations with higher likelihood of response to brazikumab.

Neutralizing Antibody Validation Testing and Reporting Harmonization.

Evolving immunogenicity assay performance expectations and a lack of harmonized neutralizing antibody validation testing and reporting tools have resulted in significant time spent by health authorities and sponsors on resolving filing queries. A team of experts within the American Association of Pharmaceutical Scientists' Therapeutic Product Immunogenicity Community across industry and the Food and Drug Administration addressed challenges unique to cell-based and non-cell-based neutralizing antibody assays. Harmonization of validation expectations and data reporting will facilitate filings to health authorities and are described in this manuscript. This team provides validation testing and reporting strategies and tools for the following assessments: (1) format selection; (2) cut point; (3) assay acceptance criteria; (4) control precision; (5) sensitivity including positive control selection and performance tracking; (6) negative control selection; (7) selectivity/specificity including matrix interference, hemolysis, lipemia, bilirubin, concomitant medications, and structurally similar analytes; (8) drug tolerance; (9) target tolerance; (10) sample stability; and (11) assay robustness.

Anti-drug Antibody Sample Testing and Reporting Harmonization.

A clear scientific and operational need exists for harmonized bioanalytical immunogenicity study reporting to facilitate communication of immunogenicity findings and expedient review by industry and health authorities. To address these key bioanalytical reporting gaps and provide a report structure for documenting immunogenicity results, this cross-industry group was formed to establish harmonized recommendations and a develop a submission template to facilitate agency filings. Provided here are recommendations for reporting clinical anti-drug antibody (ADA) assay results using ligand-binding assay technologies. This publication describes the essential bioanalytical report (BAR) elements such as the method, critical reagents and equipment, study samples, results, and data analysis, and provides a template for a suggested structure for the ADA BAR. This publication focuses on the content and presentation of the bioanalytical ADA sample analysis report. The interpretation of immunogenicity data, including the evaluation of the impact of ADA on safety, exposure, and efficacy, is out of scope of this publication.

A Novel Pharmacodynamic Biomarker and Mechanistic Modeling Facilitate the Development of Tovetumab, a Monoclonal Antibody Directed Against Platelet-Derived Growth Factor Receptor Alpha, for Cancer Therapy.

Tovetumab (MEDI-575) is a fully human IgG2κ monoclonal antibody that specifically binds to human platelet-derived growth factor receptor alpha (PDGFRα) and blocks receptor signal transduction by PDGF ligands. The affinity of tovetumab determined using surface plasmon resonance technology and flow cytometry demonstrated comparable binding affinity for human and monkey PDGFRα. In single and repeat-dose monkey pharmacokinetic-pharmacodynamic (PK-PD) studies, tovetumab administration resulted in dose-dependent elevation of circulating levels of PDGF-AA, a member of the PDGF ligand family, due to displacement of PDGF-AA from PDGFRα by tovetumab and subsequent blockade of PDGFRα-mediated PDGF-AA degradation. As such, PDGF-AA accumulation is an indirect measurement of receptor occupancy and is a novel PD biomarker for tovetumab. The nonlinear PK of tovetumab and dose-dependent increase in circulating PDGF-AA profiles were well described by a novel mechanistic model, in which tovetumab and PDGF-AA compete for the binding to PDGFRα. To facilitate translational simulation, the internalization half-lives of PDGF-AA and tovetumab upon binding to PDGFRα were determined using confocal imaging to be 14 ± 4 min and 30 ± 8 min, respectively. By incorporating PDGFRα internalization kinetics, the model not only predicted the target receptor occupancy by tovetumab, but also the biologically active agonistic ligand-receptor complex. This work described a novel PD biomarker approach applicable for anti-receptor therapeutics and the first mechanistic model to delineate the in vivo tri-molecular system of a drug, its target receptor, and a competing endogenous ligand, which collectively have been used for optimal dose recommendation supporting clinical development of tovetumab.

Molecular Mechanism of HER2 Rapid Internalization and Redirected Trafficking Induced by Anti-HER2 Biparatopic Antibody.

Amplification and overexpression of HER2 (human epidermal growth factor receptor 2), an ErbB2 receptor tyrosine kinase, have been implicated in human cancer and metastasis. A bispecific tetravalent anti-HER2 antibody (anti-HER2-Bs), targeting two non-overlapping epitopes on HER2 in domain IV (trastuzumab) and domain II (39S), has been reported to induce rapid internalization and efficient degradation of HER2 receptors. In this study, we investigated the molecular mechanism of this antibody-induced rapid HER2 internalization and intracellular trafficking. Using quantitative fluorescent imaging, we compared the internalization kinetics of anti-HER2-Bs and its parental arm antibodies, alone or in combinations and under various internalization-promoting conditions. The results demonstrated that concurrent engagement of both epitopes was necessary for rapid anti-HER2-Bs internalization. Cellular uptake of anti-HER2-Bs and parental arm antibodies occurred via clathrin-dependent endocytosis; however, inside the cells antibodies directed different trafficking pathways. Trastuzumab dissociated from HER2 in 2 h, enabling the receptor to recycle, whereas anti-HER2-Bs stayed associated with the receptor throughout the entire endocytic pathway, promoting receptor ubiquitination, trafficking to the lysosomes, and efficient degradation. Consistent with routing HER2 to degradation, anti-HER2-Bs significantly reduced HER2 shedding and altered its exosomal export. Collectively, these results enable a better understanding of the mechanism of action of anti-Her2-Bs and can guide the rational design of anti-HER2 therapeutics as well as other bispecific molecules.

Results from an international phase 2 study of the anti-CD22 immunotoxin moxetumomab pasudotox in relapsed or refractory childhood B-lineage acute lymphoblastic leukemia.

BACKGROUND: In a multicenter phase 1 study of children with relapsed/refractory acute lymphoblastic leukemia (ALL), moxetumomab pasudotox, an anti-CD22 immunotoxin, demonstrated a manageable safety profile and preliminary evidence of clinical activity. A phase 2 study further evaluated efficacy. PROCEDURE: This international, multicenter, phase 2 study enrolled children with relapsed/refractory B-cell precursor ALL who received moxetumomab pasudotox 40 µg/kg intravenously every other day, for six doses per 21-day cycle. The primary objective was to evaluate the complete response (CR) rate. Secondary objectives included safety, pharmacokinetics, and immunogenicity evaluations. RESULTS: Thirty-two patients (median age, 10 years) were enrolled at 16 sites; 30 received study drug and were evaluable for safety; 28 were evaluable for response. The objective response rate was 28.6%, with three patients (10.7%) achieving morphologic CR, and five patients (17.9%) achieving partial response. Disease progression occurred in 11 patients (39.3%). Ten patients (33.3%) experienced at least one treatment-related serious adverse event, including capillary leak syndrome (CLS; n = 6), hemolytic uremic syndrome (HUS; n = 4), and treatment-related death (n = 1) from pulmonary edema. No differences were observed in inflammatory markers in patients who did or did not develop CLS or HUS. CONCLUSIONS: Despite a signal for clinical activity, this phase 2 study was terminated at interim analysis for a CR rate that did not reach the stage 1 target. Preclinical data suggest enhanced efficacy of moxetumomab pasudotox via continuous infusion or in combination regimens; thus, further studies designed to optimize the efficacy and safety of moxetumomab pasudotox in pediatric ALL may be warranted.

A novel approach to assess domain specificity of anti-drug antibodies to moxetumomab pasudotox, an immunotoxin with two functional domains.

Biologics are potentially immunogenic and can elicit immune response. Complex biologics, such as bispecific antibodies or multi-domain molecules can induce anti-drug antibodies (ADA) with specificity to different domains. Domain specific ADAs may differently affect drug efficacy and safety, and thus, characterization of ADA domain specificity has become a regulatory expectation for multi-domain biologics. Unlike well-established methods for screening, confirmation, titer and neutralizing ADA detection, characterization of ADA domain specificity is an emerging field. The conventional approach for determination of ADA domain specificity is a competitive inhibition with domain-containing molecules. When developing a conventional domain specificity assay for moxetumomab pasudotox, a recombinant anti-CD22 immunotoxin, comprised of two functional domains (CD22-binding fragment and truncated Pseudomonas exotoxin A (PE38), we encountered a bioanalytical challenge. The method was able to detect immunodominant anti-PE38 (ADA-PE) but generated false negative results for low abundant CD22-binding domain ADA (ADA-BD) in a polyclonal sample. Troubleshooting experiments using control samples with varying levels of each ADA subtype demonstrated that a major factor for successful ADA identification was the ratio of the ADA signals contributed by each ADA subtype. To overcome this unique bioanalytical challenge, we developed a novel approach, which ensures detection of a domain-specific ADA subtype regardless of its relative level in a polyclonal ADA sample by evaluating signal inhibition by a respective domain-containing molecule at the condition when signals from all other ADAs are fully blocked. The method has been used for characterization of ADA domain specificity in moxetumomab pasudotox clinical trials, including study 1053, the pivotal Phase III study in hairy cell leukemia patients. It allowed for successful detection of ADA-BD in the presence of immunodominant ADA-PE, enabling accurate determination of domain specificity for moxetumomab pasudotox. The results demonstrated that the method was superior than the conventional approach. The method could be applied broadly to other biologics with two or more domains when there is a need to detect a minor ADA subtype in polyclonal samples.

Characterisation of anifrolumab, a fully human anti-interferon receptor antagonist antibody for the treatment of systemic lupus erythematosus.

OBJECTIVE: We investigated the mechanistic and pharmacological properties of anifrolumab, a fully human, effector-null, anti-type I interferon (IFN) alpha receptor 1 (IFNAR1) monoclonal antibody in development for SLE. METHODS: IFNAR1 surface expression and internalisation on human monocytes before and after exposure to anifrolumab were assessed using confocal microscopy and flow cytometry. The effects of anifrolumab on type I IFN pathway activation were assessed using signal transducer and activator of transcription 1 (STAT1) phosphorylation, IFN-stimulated response element-luciferase reporter cell assays and type I IFN gene signature induction. The ability of anifrolumab to inhibit plasmacytoid dendritic cell (pDC) function and plasma cell differentiation was assessed by flow cytometry and ELISA. Effector-null properties of anifrolumab were assessed in antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC) assays with B cells. RESULTS: Anifrolumab reduced cell surface IFNAR1 by eliciting IFNAR1 internalisation. Anifrolumab blocked type I IFN-dependent STAT1 phosphorylation and IFN-dependent signalling induced by recombinant and pDC-derived type I IFNs and serum of patients with SLE. Anifrolumab suppressed type I IFN production by blocking the type I IFN autoamplification loop and inhibited proinflammatory cytokine induction and the upregulation of costimulatory molecules on stimulated pDCs. Blockade of IFNAR1 suppressed plasma cell differentiation in pDC/B cell co-cultures. Anifrolumab did not exhibit CDC or ADCC activity. CONCLUSIONS: Anifrolumab potently inhibits type I IFN-dependent signalling, including the type I IFN autoamplification loop, and is a promising therapeutic for patients with SLE and other diseases that exhibit chronic dysfunctional type I IFN signalling.

Development and analytical performance of a new ARCHITECT automated dipeptidyl peptidase-4 immunoassay.

BACKGROUND: Dipeptidyl peptidase-4 (DPP-4) may be a suitable biomarker to identify people with severe asthma who have greater activation of the interleukin-13 (IL-13) pathway and may therefore benefit from IL-13-targeted treatments. We report the analytical performance of an Investigational Use Only immunoassay and provide data on the biological range of DPP-4 concentrations. METHODS: We assessed assay performance, utilising analyses of precision, linearity and sensitivity; interference from common endogenous assay interferents, and from asthma and anti-diabetic medications, were also assessed. The assay was used to measure the range of serum DPP-4 concentrations in healthy volunteers and subjects with diabetes and severe, uncontrolled asthma. RESULTS: The total precision of DPP-4 concentration measurement (determined using percentage coefficient of variation) was ≤5% over 20 days. Dilution analysis yielded linear results from 30 to 1305 ng/mL; the limit of quantitation was 19.2 ng/mL. No notable endogenous or drug interferences were observed at the expected therapeutic concentration. Median DPP-4 concentrations in healthy volunteers and subjects with asthma or Type 1 diabetes were assessed, with concentrations remaining similar in subjects with diabetes and asthma across different demographics. CONCLUSION: These analyses indicate that the ARCHITECT DPP-4 Immunoassay is a reliable and robust method for measuring serum DPP-4 concentration.

A CD80-Biased CTLA4-Ig Fusion Protein with Superior In Vivo Efficacy by Simultaneous Engineering of Affinity, Selectivity, Stability, and FcRn Binding.

Affinity- and stability-engineered variants of CTLA4-Ig fusion molecules with enhanced pharmacokinetic profiles could yield improved therapies with the potential of higher efficacy and greater convenience to patients. In this study, to our knowledge, we have, for the first time, used in vitro evolution to simultaneously optimize CTLA4 affinity and stability. We selected for improved binding to both ligands, CD80 and CD86, and screened as dimeric Fc fusions directly in functional assays to identify variants with stronger suppression of in vitro T cell activation. The majority of CTLA4 molecules showing the largest potency gains in primary in vitro and ex vivo human cell assays, using PBMCs from type 1 diabetes patients, had significant improvements in CD80, but only modest gains in CD86 binding. We furthermore observed different potency rankings between our lead molecule MEDI5265, abatacept, and belatacept, depending on which type of APC was used, with MEDI5265 consistently being the most potent. We then created fusions of both stability- and potency-optimized CTLA4 moieties with human Fc variants conferring extended plasma t1/2 In a cynomolgus model of T cell-dependent Ab response, the CTLA4-Ig variant MEDI5265 could be formulated at >100 mg/ml for s.c. administration and showed superior efficacy and significantly prolonged serum t1/2 The combination of higher stability and potency with prolonged pharmacokinetics could be compatible with very infrequent, s.c. dosing while maintaining a similar level of immune suppression to more frequently and i.v. administered licensed therapies.

An immunoinhibition approach to overcome the impact of pre-existing antibodies on cut point establishment for immunogenicity assessment of moxetumomab pasudotox.

Immunogenicity can impact PK, PD, efficacy and safety of biopharmaceuticals, and is often evaluated as a secondary objective in clinical studies. Methods to detect anti-drug antibodies (ADA) and neutralizing ADA (NAb) are semi-quantitative and utilize cut points to determine positive or negative samples. Assay cut points are established by the statistical analysis of treatment-naïve subject specimens that are assumed ADA and NAb-negative. Pre-existing antibodies to various biopharmaceuticals have been observed in treatment-naïve subjects and may artificially elevate the cut point, resulting in compromised assay sensitivities, inaccuracy in immunogenicity reporting and ultimately misleading assessment of the impact of immunogenicity on clinical outcomes. Although several approaches such as removal of pre-existing antibody samples or increasing the sample dilution could be used for cut point establishment to mitigate impact of pre-existing antibodies, they each have limitations, especially when a high prevalence of pre-existing antibodies is observed. Here we describe an innovative approach used to establish cut points for ADA and NAb assays of moxetumomab pasudotox (moxetumomab), a recombinant anti-CD22 immunotoxin, to which a high prevalence of pre-existing antibodies was observed. In order to overcome the challenges associated with this high prevalence and prevent establishment of an artificially elevated cut point, we developed an immunoinhibition approach that allowed generation of pseudo ADA and NAb-negative populations for cut point determination. Immunoinhibition was performed by adding excess moxetumomab (for ADA) or a non-CD22 binding PE38-containing immunotoxin, CAT-5001 (for NAb), to treatment-naive samples prior to evaluating samples for cut point establishment. This approach successfully eliminated pre-existing antibody activity in treatment-naive samples, enabling establishment of more accurate ADA and NAb assay cut points. A comparative analysis of the clinical immunogenicity results using cut points derived with immunoinhibition and without immunoinhibition (conventional method) demonstrated that the immunoinhibition approach markedly improved detection sensitivity and accuracy of immunogenicity characterization in patient samples. This innovative approach provides an alternative, practical solution for immunogenicity assay cut point establishment when biopharmaceuticals have a high prevalence of pre-existing antibodies.

Evaluation of assay interference and interpretation of CXCR4 receptor occupancy results in a preclinical study with MEDI3185, a fully human antibody to CXCR4.

BACKGROUND: Receptor occupancy (RO) assays provide a means to measure the direct interaction of therapeutics with their cell surface targets. Free receptor assays quantify cell-surface receptors not bound by a therapeutic while total receptor assays quantify the amount of target on the cell surface. METHODS: We developed both a flow cytometry-based free RO assay to detect free surface CXCR4, and a total surface CXCR4 assay. In an effort to evaluate potential displacement interference, we performed in vitro experiments to compare on-cell affinity with the IC50 values from in vitro and in vivo from the free CXCR4 assay. We determined free and total surface CXCR4 on circulating blood cells in cynomolgus monkeys dosed with MEDI3185, a fully human monoclonal antibody to CXCR4. RESULTS: We devised an approach to evaluate displacement interference during assay development and showed that our free assay demonstrated little to no displacement interference. After dosing cynomolgus monkeys with MEDI3185, we observed dose-dependence in the magnitude and duration of receptor occupancy and found CXCR4 to increase on lymphocytes, monocytes, and granulocytes. In a multiple dose study, we observed time points where surface CXCR4 appeared fully occupied but MEDI3185 was not detectable in serum. These paradoxical results represented a type of assay interference, and by comparing pharmacokinetic, ADA and total CXCR4 results, the most likely reason for the free CXCR4 results was the emergence of neutralizing anti-drug antibodies (ADA). The total CXCR4 assay was unaffected by ADA and provided a reliable marker of target modulation in both in vivo studies.

Multiplexing of receptor occupancy measurements for pharmacodynamic biomarker assessment of biopharmaceuticals.

BACKGROUND: Receptor occupancy (RO) assays measure drug target engagement, and are used as pharmacodynamic (PD) biomarkers. RO assays are commonly performed by flow cytometry and often require multiplexing for assessment of multiple PD biomarkers when specimen volumes are limited. We present multiplexed RO assays for an IGF1R-EGFR bispecific antibody (Bs-Ab) and a CTLA4-Ig recombinant fusion protein to demonstrate key considerations for accurate RO assessment. METHODS: RO in cynomolgus monkeys was determined in whole blood using flow cytometry. Free and total receptors were measured using anti-receptor fluorescence-labeled detection reagents, competitive and noncompetitive to drug, respectively. RESULTS: RO of IGF1R was examined as PD for Bs-Ab, since IGF1R was expressed on blood cells. Multiplexed measurements of free and total IGF1R showed that IGF1R expression measured by total receptor was highly variable, impacting interpretation of free-IGF1R. Normalization of free-over-total IGF1R measurements compensated for variability of receptor expression allowing for accurate RO assessment. RO of CTLA4-Ig, a recombinant fusion protein targeting CD80 and CD86 receptors, was multiplexed to simultaneously measure target engagements for both receptors. Both RO methods demonstrated specificity of receptor measurements without cross-reactivity to each other in multiplexed formats. RO methods were used for evaluation of PD activity of Bs-Ab and CTLA4-Ig in cynomolgus monkeys. In both cases, RO results showed dose-dependent target engagement, corresponding well to the pharmacokinetics. CONCLUSIONS: Multiplexed RO methods allowed accurate assessment of PD activity for Bs-Ab and CTLA4-Ig, facilitating development of these biopharmaceuticals from preclinical to clinical stages.

Receptor occupancy assessment by flow cytometry as a pharmacodynamic biomarker in biopharmaceutical development.

Receptor occupancy (RO) assays are designed to quantify the binding of therapeutics to their targets on the cell surface and are frequently used to generate pharmacodynamic (PD) biomarker data in nonclinical and clinical studies of biopharmaceuticals. When combined with the pharmacokinetic (PK) profile, RO data can establish PKPD relationships, which are crucial for informing dose decisions. RO is commonly measured by flow cytometry on fresh blood specimens and is subject to numerous technical and logistical challenges. To ensure that reliable and high quality results are generated from RO assays, careful assay design, key reagent characterization, data normalization/reporting, and thorough planning for implementation are of critical importance during development. In this article, the authors share their experiences and perspectives in these areas and discuss challenges and potential solutions when developing and implementing a flow cytometry-based RO method in support of biopharmaceutical drug development.

Quantitative measurement of the target-mediated internalization kinetics of biopharmaceuticals.

PURPOSE: Measurement of internalization of biopharmaceuticals targeting cell surface proteins can greatly facilitate drug development. The objective of this study was to develop a reliable method for determination of internalization rate constant (kint) and to demonstrate its utility. METHODS: This method utilized confocal imaging to record the internalization kinetics of fluorescence-tagged biopharmaceuticals in live-cells and a quantitative image-analysis algorithm for kint determination. Kint was incorporated into a pharmacokinetic-pharmacodynamic (PK-PD) model for simulation of the drug PK profiles, target occupancy and the displacement of endogenous ligand. RESULTS: The method was highly sensitive, allowing kint determination in cells expressing as low as 5,000 receptors/cell, and was amenable to adherent and suspension cells. Its feasibility in a mixed cell population, such as whole blood, was also demonstrated. Accurate assessment of the kint was largely attributed to continuous monitoring of internalization in live cells, rapid confocal image acquisition and quantitative image-analysis algorithm. Translational PK-PD simulations demonstrated that kint is a major determinant of the drug PK profiles, target occupancy, and the displacement of endogenous ligand. CONCLUSIONS: The developed method is robust for broad cell types. Reliable kint assessment can greatly expedite biopharmaceutical development by facilitating target evaluation, drug affinity goal setting, and clinical dose projection.

Interference in immunoassays to support therapeutic antibody development in preclinical and clinical studies.

During preclinical and clinical studies, immunoassays are used to measure the concentration of the therapeutic antibody, anti-drug antibodies and soluble protein biomarkers. The reliability of these assays is crucial since the results are routinely used for safety assessment and dose selection. Furthermore, soluble protein biomarkers can provide information about target engagement, proof of mechanism, proof of principle and prediction of response. Study samples mostly consist of complex matrices that can exhibit considerable interference, resulting in inaccurate measurements. This perspective discusses the source of interference and strategies to mitigate or eliminate interference in immunoassays used during preclinical and clinical drug development of drugs with a focus on the development of therapeutic antibodies.

Pharmacokinetic and pharmacodynamic comparability study of moxetumomab pasudotox, an immunotoxin targeting CD22, in cynomolgus monkeys.

Moxetumomab pasudotox is an immunotoxin currently being investigated in patients for the treatment of CD22-expressing B-cell malignancies. A single-cycle pharmacokinetic (PK)-pharmacodynamic (PD) study was conducted in cynomolgus monkeys for PK comparability assessment and population PK-PD modeling after major manufacturing process and site changes. Primates were randomized by body weight and baseline CD22 lymphocyte counts to receive intravenous administrations of 1 mg/kg moxetumomab pasudotox (n = 12/group) on Days 1, 3, and 5. PK and B-lymphocyte count data were modeled using a population approach. The 90% confidence intervals of the geometric mean ratios of PK exposure were within the 80%-125% range. The B lymphocytes were depleted to a similar extent, and the immunogenicity incidences were similar across the two groups. The B-cell depletion was described by a novel lifespan model in which moxetumomab pasudotox induced random destruction of B cells in each aging compartment. The endogenous de novo influx from bone marrow was subject to a negative feedback mechanism. The estimated B cell apparent lifespan was 51 days. Covariate analysis confirmed that the manufacturing change had no impact on PK or PD of moxetumomab pasudotox. Results from this study supported continued clinical investigation of moxetumomab pasudotox using the new material.

Mechanistic modeling of antigen sink effect for mavrilimumab following intravenous administration in patients with rheumatoid arthritis.

Mavrilimumab is a fully human monoclonal antibody that binds to granulocyte-macrophage colony stimulating factor receptor α (GM-CSFRα) with high affinity and specificity and has potential application in various inflammatory diseases. The objective of this investigation was to develop a mechanistic population model to characterize the pharmacokinetics of mavrilimumab, the GM-CSFRα-mediated clearance, and receptor occupancy following single intravenous dosing to patients with rheumatoid arthritis. The internalization rate of mavrilimumab-GM-CSFRα complex was fixed to a value determined from quantitative confocal fluorescent imaging. The estimated typical first-order clearance and the central and peripheral distribution volumes were 3.79 mL/kg/d, 39.6 mL/kg, and 50.3 mL/kg, respectively. The systemic GM-CSFRα expression level was estimated to be 0.0782 nM, and the equilibrium dissociation constant (0.103 nM) was in good agreement with the monovalent affinity determined by surface plasmon resonance. By fitting to the observed pharmacokinetic data, the mechanistic model predicted that systemically greater than 90% GM-CSFRα blockade by mavrilimumab was achieved and maintained up to 4, 7, and 11 weeks following single 1-, 3-, and 10-mg/kg administrations, respectively. Posterior visual predictive check and bootstrapping suggest that the mechanistic model is reasonably robust and can be used to predict mavrilimumab exposure under various scenarios for future clinical trial design.