Impact of Shed/Soluble targets on the PK/PD of approved therapeutic monoclonal antibodies

Deciphering the Exact Sequence of Endogenous Soluble B Cell Maturation Antigen and Unbiased Quantitation in Multiple Myeloma Patient Samples by LC-MS

BACKGROUND

B-cell maturation antigen is a pivotal therapeutic target for multiple myeloma (MM). Membrane-bound BCMA can be cleaved by γ-secretase and shed as soluble BCMA (sBCMA). sBCMA can act as a neutralizing sink to compete with drug, as well as serve as a diagnostic/prognostic biomarker for MM. Antibody-capture based methods, such as enzyme-linked immunosorbent assay (ELISA) and immunoaffinity-liquid chromatography-multiple reaction monitoring (IA-LC-MRM), have been reported and well adopted to measure sBCMA in clinical samples. However, both methods are biased by capturing antibodies.

METHODS

We have used various LC-MS workflows to characterize and quantify endogenous sBCMA in MM patient samples, including bottom-up peptide mapping, intact analysis, IA-based, and reagent-free (RF)-LC-MRM quantitation.

RESULTS

We have confirmed that sBCMA contains a variable N-terminus and a C-terminus that extends to the transmembrane domain, ending at amino acid 61. Leveraging an in-house synthesized G-1-61 sBCMA recombinant standard, we developed a RF-LC-MRM method for unbiased sBCMA quantitation in MM patient samples. By comparing the results from RF-LC-MRM with ELISA and IA-LC-MRM, we demonstrated that RF-LC-MRM measures a more complete pool of endogenous sBCMA compared to the antibody-based methods.

CONCLUSIONS

This work fills the knowledge gap of the exact sequence of endogenous sBCMA for the first time, which differs from the current commercially available standard. Additionally, this work highlights the necessity of identifying the actual sequence of an endogenous soluble target such as sBCMA, both for bioanalytical purposes and to underpin pharmacodynamic measurements.

Time-dependent clearance can confound exposure-response analysis of therapeutic antibodies: A comprehensive review of the current literature

Exposure-response (ER) analysis is used to optimize dose and dose regimens during clinical development. Characterization of relationships between drug exposure and efficacy or safety outcomes can be utilized to make dose adjustments that improve patient response. Therapeutic antibodies typically show predictable pharmacokinetics (PK) but can exhibit clearance that decreases over time due to treatment. Moreover, time-dependent changes in clearance are frequently associated with drug response, with larger decreases in clearance and increased exposure seen in patients who respond to treatment. This often confounds traditional ER analysis, as drug response influences exposure rather than the reverse. In this review, we survey published population PK analyses for reported time-dependent drug clearance effects across 158 therapeutic antibodies approved or in regulatory review. We describe the mechanisms by which time-dependent clearance can arise, and evaluate trends in frequency, magnitude, and time scale of changes in clearance with respect to indication, mechanistic interpretation of time-dependence, and PK modeling techniques employed. We discuss the modeling and simulation strategies commonly used to characterize time-dependent clearance, and examples where time-dependent clearance has impeded ER analysis. A case study using population model simulation was explored to interrogate the impact of time-dependent clearance on ER analysis and how it can lead to spurious conclusions. Overall, time-dependent clearance arises frequently among therapeutic antibodies and has spurred erroneous conclusions in ER analysis. Appropriate PK modeling techniques aid in identifying and characterizing temporal shifts in exposure that may impede accurate ER assessment and successful dose optimization.

Factors contributing to the nonlinear pharmacokinetics of astegolimab: a close examination of potential causes

Aim: This paper describes a case study of an antibody therapeutic targeting a membrane-bound receptor, also present in systemic circulation, as a soluble receptor. During phase I studies of astegolimab, nonlinear pharmacokinetics (PKs) were observed. We investigated the potential contribution of antidrug antibodies, target-mediated drug disposition and assay format. Materials & methods: A more target-tolerant assay was developed, and a subset of phase I samples were evaluated in both free and total PK assay formats. Results & conclusion: Our results demonstrate that there were two main contributors to PK nonlinearity: soluble target interference in the free PK assay, in addition to target-mediated drug disposition. Antidrug antibody status did not significantly impact PK.

Review of the Existing Translational Pharmacokinetics Modeling Approaches Specific to Monoclonal Antibodies (mAbs) to Support the First-In-Human (FIH) Dose Selection

The interest in therapeutic monoclonal antibodies (mAbs) has continuously growing in several diseases. However, their pharmacokinetics (PK) is complex due to their target-mediated drug disposition (TMDD) profiles which can induce a non-linear PK. This point is particularly challenging during the pre-clinical and translational development of a new mAb. This article reviews and describes the existing PK modeling approaches used to translate the mAbs PK from animal to human for intravenous (IV) and subcutaneous (SC) administration routes. Several approaches are presented, from the most empirical models to full physiologically based pharmacokinetic (PBPK) models, with a focus on the population PK methods (compartmental and minimal PBPK models). They include the translational approaches for the linear part of the PK and the TMDD mechanism of mAbs. The objective of this article is to provide an up-to-date overview and future perspectives of the translational PK approaches for mAbs during a model-informed drug development (MIDD), since the field of PK modeling has gained recently significant interest for guiding mAbs drug development.

Targeting the immune checkpoint B7-H3 for next-generation cancer immunotherapy

Immune checkpoint inhibitors (ICIs) for programmed death-1 (PD-1) and programmed cell death-ligand 1 (PD-L1) have become preferred treatment strategies for several advanced cancers. However, response rates for these treatments are limited, which encourages the search for new ICI candidates. Recent reports have underscored significant roles of B7 homolog 3 protein (B7-H3) in tumor immunity and disease progression. While its multifaceted roles are being elucidated, B7-H3 has already entered clinical trials as a therapeutic target. In this review, we overview the recent results of clinical trials evaluating the antitumor activity and safety of B7-H3 targeting drugs. On this basis, we also discuss the challenges and opportunities arising from the application of these drugs. Finally, we point out current gaps to address in the understanding of B7-H3 function and regulation in order to fully unleash the future clinical utility of B7-H3-based therapies for the treatment of cancer.

Pharmacokinetics and Determination of Tumor Interstitial Distribution of a Therapeutic Monoclonal Antibody Using Large-Pore Microdialysis

R7072 is a fully human monoclonal antibody (mAb) exerting anti-tumor activity via blockade of insulin like growth factor 1 receptor. The tumoral interstitial concentrations are anticipated to be better surrogates of active site concentrations than commonly used serum concentrations for pharmacokinetic-pharmacodynamic correlation of anti-tumor mAbs. Previously, a large-pore microdialysis technique for measuring tissue interstitial concentrations of R7072 in non-tumor bearing mice was established. In the current studies, the serum pharmacokinetics of R7072 were assessed and tissue interstitial concentrations were measured by large-pore microdialysis following intravenous and intraperitoneal administration of R7072 in tumor bearing mice. R7072 exhibited nonlinear pharmacokinetics in the studied dose range. Tumor and subcutaneous interstitial concentration data suggested some delay in tissue distribution after dosing. A dose-dependent increase in the ratio of tumor interstitial to serum concentration was observed indicating target-mediated drug disposition in tumor tissue. However, subcutaneous interstitial to serum concentration ratios were similar across the doses as observed previously in non-tumor bearing mice. A two-compartment population pharmacokinetic model with subcutaneous and tumor as open-loop compartments comprising of parallel linear and non-linear elimination from serum, linear disposition from subcutaneous interstitium and non-linear disposition from tumor interstitium was developed to simultaneously describe the pharmacokinetic data from all matrices.

A Flexible Multiplatform Bioanalytical Strategy for Measurement of Total Circulating Shed Target Receptors: Application to Soluble B Cell Maturation Antigen Levels in the Presence of a Bispecific Antibody Drug

B cell maturation antigen (BCMA) is a membrane-bound receptor that is overexpressed on multiple myeloma cells and can be targeted with biotherapeutics. Soluble shed forms of membrane-associated receptors in circulation can act as a drug sink, especially when it is present in high molar ratio compared to drug concentration, potentially derailing the intended pharmacological mechanism and impacting pharmacokinetic (PK) measurements and efficacious dose predictions. In this study, we present a bioanalytical strategy for assessing dynamic levels of total soluble BCMA before and during treatment with a bispecific antibody targeting BCMA and CD3. Implementation of a ligand binding assay was not successful due to extensive bispecific antibody interference. Instead, we explored two types of immunoaffinity (IA) liquid chromatography-tandem mass spectrometry (LC-MS/MS) assays, one at the protein level and one at the surrogate peptide level. Ultimately, the protein-level IA-LC-MS/MS method was optimized for use in a cynomolgus monkey PK/pharmacodynamic study. In addition, we demonstrated that the method was easily adapted for use with human samples in preparation for translation to the clinic. This work demonstrates the benefit of flexibility and agility in bioanalytical method development in early drug development. Multiplatform suitability assessments enable rapid, resource-sparing identification and qualification of clinically translatable assays. We recommend early adoption of this strategy to provide enough time for critical reagent development and assay validation for analysis of shed targets.

Approaching sites of action of drugs in clinical pharmacology: New analytical options and their challenges

Clinical pharmacology is an important discipline for drug development aiming to define pharmacokinetics (PK), pharmacodynamics (PD) and optimum exposure to drugs, i.e. the concentration-response relationship and its modulators. For this purpose, information on drug concentrations at the anatomical, cellular and molecular sites of action is particularly valuable. In pharmacological assays, the limited accessibility of target cells in readily available samples (i.e. blood) often hampers mass spectrometry-based monitoring of the absolute quantity of a compound and the determination of its molecular action at the cellular level. Recently, new sample collection methods have been developed for the specific capture of rare circulating cells, especially for the diagnosis of circulating tumour cells. In parallel, new advances and developments in mass spectrometric instrumentation now allow analyses to be scaled down to the cellular level. Together, these developments may permit the monitoring of minute drug quantities and show their effect at the cellular level. In turn, such PK/PD associations on a cellular level would not only enrich our pharmacological knowledge of a given compound but also expand the basis for PK/PD simulations. In this review, we describe novel concepts supporting clinical pharmacology at the anatomical, cellular and molecular sites of action, and highlight the new challenges in mass spectrometry-based monitoring. Moreover, we present methods to tackle these challenges and define future needs.

Mechanistic Quantitative Pharmacology Strategies for the Early Clinical Development of Bispecific Antibodies in Oncology

Bispecific antibodies (bsAbs) have become an integral component of the therapeutic research strategy to treat cancer. In addition to clinically validated immune cell re‐targeting, bsAbs are being designed for tumor targeting and as dual immune modulators. Explorative preclinical and emerging clinical data indicate potential for enhanced efficacy and reduced systemic toxicity. However, bsAbs are a complex modality with challenges to overcome in early clinical trials, including selection of relevant starting doses using a minimal anticipated biological effect level approach, and predicting efficacious dose despite nonintuitive dose response relationships. Multiple factors can contribute to variability in the clinic, including differences in functional affinity due to avidity, receptor expression, effector to target cell ratio, and presence of soluble target. Mechanistic modeling approaches are a powerful integrative tool to understand the complexities and aid in clinical translation, trial design, and prediction of regimens and strategies to reduce dose limiting toxicities of bsAbs. In this tutorial, the use of mechanistic modeling to impact decision making for bsAbs is presented and illustrated using case study examples.

Automated, Generic Reagent and Ultratargeted 2D-LC-MS/MS Enabling Quantification of Biotherapeutics and Soluble Targets down to pg/mL Range in Serum

Mass spectrometry has recently emerged as a powerful analytical tool for the assessment of pharmacokinetics and biomarkers in drug development. Compared with ligand binding assays, a major advantage of mass spectrometry-based assays is that they are less dependent on high quality binding reagents, while a key limitation is the relatively lower sensitivity. To address the sensitivity issue, we have developed a generic reagent, ultratargeted two-dimensional liquid chromatography-tandem mass spectrometry (2D-LC-MS/MS) method which combines commercially available protein A affinity capture, targeted analyte isolation by 2D-LC, and targeted detection by multiple reaction monitoring (MRM). A targeted-2D-with-dilution configuration was designed to automate 2D-LC-MS/MS. This method was systematically evaluated using an anti-CD22 monoclonal antibody spiked into monkey and human serum, where lower limits of quantification (LLOQ) of 0.78 and 1.56 ng/mL were achieved, respectively. This represents an over 100-fold improvement in assay sensitivity compared to the conventional LC-MS/MS method. The performance of the method was further confirmed by analyzing another monoclonal antibody, bevacizumab, as well as a soluble antigen, circulating PD-L1. The results indicate that our method enables quantification of antibody therapeutics and antigen biomarkers in both clinical and nonclinical samples in the pg/mL to low ng/mL range. Protein A affinity capture was employed as a universal sample preparation procedure applicable to both full-length antibody therapeutics and antibody-antigen complexes. This novel method is also fully automated and proven to be highly robust for routine bioanalysis in drug development.

Bioanalytical challenges and unique considerations to support pharmacokinetic characterization of bispecific biotherapeutics

Compared with conventional (monospecific) therapeutics, bispecific protein therapeutics present unique challenges for pharmacokinetic (PK) characterization – namely, the characterization of multiple functional domains as well as the consideration of biotransformation or interference by the formation of antitherapeutic antibodies against each functional domain. PK characterization is essential to the success of the overall drug development plan and for molecules with multiple binding domains; multiple bioanalytical methods may be needed to answer critical questions for each phase of drug development. The number of bispecific protein therapeutics entering drug development continues to increase, and therefore, a bioanalytical strategy for the PK characterization of bispecific molecules and study of their in vivo structure–function relationship is needed. This review presents case studies and a regulatory perspective.

Pharmacokinetic Evaluation of Nimotuzumab in Patients With Autosomal Dominant Polycystic Kidney Disease

Autosomal dominant polycystic kidney disease (ADPKD) is a genetic disease characterized by an overexpression and mislocalization of epidermal growth factor receptor (EGFR) to the apical membranes of cystic epithelial cells. Nimotuzumab is a humanized antibody that recognizes an extracellular domain III of human EGFR. The aim of this study was to assess the pharmacokinetic behavior of nimotuzumab in patients with ADPKD given as a single dose. A phase I, single-center, and noncontrolled open clinical study was conducted. Five patients were enrolled at each of the following fixed-dose levels: 50, 100, 200, and 400 mg. Intravenous continuous infusions of nimotuzumab were administered every 14 days during a year, except the first administration, when blood samples were drawn during 28 days for pharmacokinetic assessments. Subjects were closely monitored during the trial and at completion of the administration of nimotuzumab, including the anti-idiotypic response. For the first time, nimotuzumab was used for treating a nononcological disease. The administration of nimotuzumab showed dose-dependent kinetics. Nimotuzumab does not develop anti-idiotypic response against the murine portion present in the hypervariable region of the antibody present in the serum of the patients treated. No significant differences were found in the systemic clearance between the 100- and 400-mg dose, which indicates that the optimal biological dose is in this range of dose.

Monoclonal Antibodies: Past, Present and Future

Monoclonal antibodies (mAbs) are immunoglobulins designed to target a specific epitope on an antigen. Immunoglobulins of identical amino-acid sequence were originally produced by hybridomas grown in culture and, subsequently, by recombinant DNA technology using mammalian cell expression systems. The antigen-binding region of the mAb is formed by the variable domains of the heavy and light chains and contains the complementarity-determining region that imparts the high specificity for the target antigen. The pharmacokinetics of mAbs involves target-mediated and non-target-related factors that influence their disposition.Preclinical safety evaluation of mAbs differs substantially from that of small molecular (chemical) entities. Immunogenicity of mAbs has implications for their pharmacokinetics and safety. Early studies of mAbs in humans require careful consideration of the most suitable study population, route/s of administration, starting dose, study design and the potential difference in pharmacokinetics in healthy subjects compared to patients expressing the target antigen.Of the ever-increasing diversity of therapeutic indications for mAbs, we have concentrated on two that have proved dramatically successful. The contribution that mAbs have made to the treatment of inflammatory conditions, in particular arthritides and inflammatory bowel disease, has been nothing short of revolutionary. Their benefit has also been striking in the treatment of solid tumours and, most recently, as immunotherapy for a wide variety of cancers. Finally, we speculate on the future with various new approaches to the development of therapeutic antibodies.