Review on modeling anti-antibody responses to monoclonal antibodies

Selection of positive controls and their impact on anti-drug antibody assay performance

Development of assays to reliably identify and characterize anti-drug antibodies (ADAs) depends on positive control anti-idiotype (anti-id) reagents, which are used to demonstrate that the standards recommended by regulatory authorities are met. This work employs a set of therapeutic antibodies under clinical development and their corresponding anti-ids to investigate how different positive control reagent properties impact ADA assay development. Positive controls exhibited different response profiles and apparent assay analytical sensitivity values depending on assay format. Neither anti-id affinity for drug, nor sensitivity in direct immunoassays related to sensitivity in ADA assays. Anti-ids were differentially able to detect damage to drug conjugates used in bridging assays and were differentially drug tolerant. These parameters also failed to relate to assay sensitivity, further complicating selection of anti-ids for use in ADA assay development based on functional characteristics. Given this variability among anti-ids, alternative controls that could be employed across multiple antibody drugs were investigated as a more uniform means to define ADA detection sensitivity across drug products and assay protocols, which could help better relate assay results to clinical risks of ADA responses. Overall, this study highlights the importance of positive control selection to reliable detection and clinical interpretation of the presence and magnitude of ADA responses.

Challenging the Norm: A Multidisciplinary Perspective on Intravenous to Subcutaneous Bridging Strategies for Biologics

The transition from intravenous (i.v.) to subcutaneous (s.c.) administration of biologics is a critical strategy in drug development aimed at improving patient convenience, compliance, and therapeutic outcomes. Focusing on the increasing role of model-informed drug development (MIDD) in the acceleration of this transition, an in-depth overview of the essential clinical pharmacology, and regulatory considerations for successful i.v. to s.c. bridging for biologics after the i.v. formulation has been approved are presented. Considerations encompass multiple aspects beginning with adequate pharmacokinetic (PK) and pharmacodynamic (i.e., exposure-response) evaluations which play a vital role in establishing comparability between the i.v. and s.c. routes of administrations. Selected key recommendations and points to consider include: (i) PK characterization of the s.c. formulation, supported by the increasing preclinical understanding of the s.c. absorption, and robust PK study design and analyses in humans; (ii) a thorough characterization of the exposure-response profiles including important metrics of exposure for both efficacy and safety; (iii) comparability studies designed to meet regulatory considerations and support approval of the s.c. formulation, including noninferiority studies with PK and/or efficacy and safety as primary end points; and (iv) comprehensive safety package addressing assessments of immunogenicity and patients' safety profile with the new route of administration. Recommendations for successful bridging strategies are evolving and MIDD approaches have been used successfully to accelerate the transition to s.c. dosing, ultimately leading to improved patient experiences, adherence, and clinical outcomes.

A Comprehensive review on Pharmacokinetic Studies of Vaccines: Impact of delivery route, carrier-and its modulation on immune response

The lack of knowledge about the absorption, distribution, metabolism, and excretion (ADME) of vaccines makes former biopharmaceutical optimization difficult. This was shown during the COVID-19 immunization campaign, where gradual booster doses were introduced.. Thus, understanding vaccine ADME and its effects on immunization effectiveness could result in a more logical vaccine design in terms of formulation, method of administration, and dosing regimens. Herein, we will cover the information available on vaccine pharmacokinetics, impacts of delivery routes and carriers on ADME, utilization and efficiency of nanoparticulate delivery vehicles, impact of dose level and dosing schedule on the therapeutic efficacy of vaccines, intracellular and endosomal trafficking and in vivo fate, perspective on DNA and mRNA vaccines, new generation sequencing and mathematical models to improve cancer vaccination and pharmacology, and the reported toxicological study of COVID-19 vaccines. Altogether, this review will enhance the reader's understanding of the pharmacokinetics of vaccines and methods that can be implied in delivery vehicle design to improve the absorption and distribution of immunizing agents and estimate the appropriate dose to achieve better immunogenic responses and prevent toxicities.

Perspective for Discovery of Small Molecule IL-6 Inhibitors through Study of Structure–Activity Relationships and Molecular Docking

Interleukin-6 (IL-6) is a proinflammatory cytokine that plays a key role in the pathogenesis and physiology of inflammatory and autoimmune diseases, such as coronary heart disease, cancer, Alzheimer's disease, asthma, rheumatoid arthritis, and most recently COVID-19. IL-6 and its signaling pathway are promising targets in the treatment of inflammatory and autoimmune diseases. Although, anti-IL-6 monoclonal antibodies are currently being used in clinics, huge unmet medical needs remain because of the high cost, administration-related toxicity, lack of opportunity for oral dosing, and potential immunogenicity of monoclonal antibody therapy. Furthermore, nonresponse or loss of response to monoclonal antibody therapy has been reported, which increases the importance of optimizing drug therapy with small molecule drugs. This work aims to provide a perspective for the discovery of novel small molecule IL-6 inhibitors by the analysis of the structure-activity relationships and computational studies for protein-protein inhibitors targeting the IL-6/IL-6 receptor/gp130 complex.

Assessing the Impact of Immunogenicity and Improving Prediction of Trough Concentrations: Population Pharmacokinetic Modeling of Adalimumab in Patients with Crohn's Disease and Ulcerative Colitis

BACKGROUND AND OBJECTIVE

Predicting adalimumab pharmacokinetics (PK) for patients impacted by anti-drug antibodies (ADA) has been challenging. The present study assessed the performance of the adalimumab immunogenicity assays in predicting which patients with Crohn's disease (CD) and ulcerative colitis (UC) have low adalimumab trough concentrations; and aimed to improve predictive performance of adalimumab population PK (popPK) model in CD and UC patients whose PK was impacted by ADA.

METHODS

Adalimumab PK and immunogenicity data obtained from 1459 patients in SERENE CD (NCT02065570) and SERENE UC (NCT02065622) were analyzed. Adalimumab immunogenicity was assessed using electrochemiluminescence (ECL) and enzyme-linked immunosorbent (ELISA) assays. From these assays, three analytical approaches (ELISA concentrations, titer, and signal-to-noise [S/N] measurements) were tested as predictors for classifying patients with/without low concentrations potentially affected by immunogenicity. The performance of different thresholds for these analytical procedures was assessed using receiver operating characteristic curves and precision-recall curves. Based on the results from the most sensitive immunogenicity analytical procedure, patients were classified into PK-not-ADA-impacted and PK-ADA-impacted subpopulations. Stepwise popPK modeling was implemented to fit the PK data to an empirical adalimumab two-compartment model with linear elimination and ADA delay compartments to account for the time delay to generate ADA. Model performance was assessed by visual predictive checks and goodness-of-fit plots.

RESULTS

The classical ELISA-based classification (with 20 ng/mL ADA as lower threshold) showed a good balance of precision and recall, to determine which patients had at least 30% adalimumab concentrations below 1 µg/mL. Titer-based classification with the lower limit of quantitation (LLOQ) as threshold showed higher sensitivity to classify these patients compared to the ELISA-based approach. Therefore, patients were classified as PK-ADA-impacted or PK-not-ADA impacted using the LLOQ titer threshold. In the stepwise modeling approach ADA-independent parameters were first fit using PK data from titer-PK-not-ADA-impacted population. The identified ADA-independent covariates included the effect of indication, weight, baseline fecal calprotectin, baseline C-reactive protein, baseline albumin on clearance; and sex and weight on volume of distribution of the central compartment. Pharmacokinetic-ADA-driven dynamics were characterized using PK data for the PK-ADA-impacted population. The categorical covariate based on the ELISA classification was the best at describing the additional effect of immunogenicity analytical approaches on ADA synthesis rate. The model was able to adequately describe the central tendency and variability for PK-ADA-impacted CD/UC patients.

CONCLUSIONS

The ELISA assay was found to be optimal for capturing impact of ADA on PK. The developed adalimumab popPK model is robust in predicting PK profiles for CD and UC patients whose PK was impacted by ADA.

A PBPK model recapitulates early kinetics of anti-PEG antibody-mediated clearance of PEG-liposomes

PEGylation is routinely used to extend the systemic circulation of various protein therapeutics and nanomedicines. Nonetheless, mounting evidence is emerging that individuals exposed to select PEGylated therapeutics can develop antibodies specific to PEG, i.e., anti-PEG antibodies (APA). In turn, APA increase both the risk of hypersensitivity to the drug as well as potential loss of efficacy due to accelerated blood clearance of the drug. Despite the broad implications of APA, the timescales and systemic specificity by which APA can alter the pharmacokinetics and biodistribution of PEGylated drugs remain not well understood. Here, we developed a physiologically based pharmacokinetic (PBPK) model designed to resolve APA's impact on both early- and late-phase pharmacokinetics and biodistribution of intravenously administered PEGylated drugs. Our model accurately recapitulates PK and biodistribution data obtained from PET/CT imaging of radiolabeled PEG-liposomes and PEG-uricase in mice with and without APA, as well as serum levels of PEG-uricase in humans. Our work provides another illustration of the power of high-resolution PBPK models for understanding the pharmacokinetic impacts of anti-drug antibodies and the dynamics with which antibodies can mediate clearance of foreign species.

A population physiologically-based pharmacokinetic model to characterize antibody disposition in pediatrics and evaluation of the model using infliximab

AIMS

In order to better predict the pharmacokinetics (PK) of antibodies in children, and to facilitate dose optimization of antibodies in paediatric patients, there is a need to develop systems PK models that integrate ontogeny-related changes in human physiological parameters.

METHODS

A population-based physiological-based PK (PBPK) model to characterize antibody PK in paediatrics has been developed, by incorporating age-related changes in body weight, organ weight, organ blood flow rate and interstitial volumes in a previously published platform model. The model was further used to perform Monte Carlo simulations to investigate clearance vs. age and dose-exposure relationships for infliximab.

RESULTS

By estimating only one parameter and associated interindividual variability, the model was able to characterize clinical PK of infliximab from two paediatric cohorts (n = 141, 4-19 years) reasonably well. Model simulations demonstrated that only 50% of children reached desired trough concentrations when receiving FDA-labelled dosing regimen for infliximab, suggesting that higher doses and/or more frequent dosing are needed to achieve target trough concentrations of this antibody.

CONCLUSION

The paediatric PBPK model presented here can serve as a framework to characterize the PK of antibodies in paediatric patients. The model can also be applied to other protein therapeutics to advance precision medicine paradigm and optimize antibody dosing regimens in children.

Modeling approaches for reducing safety-related attrition in drug discovery and development: a review on myelotoxicity, immunotoxicity, cardiovascular toxicity, and liver toxicity

Introduction:Safety and tolerability is a critical area where improvements are needed to decrease the attrition rates during development of new drug candidates. Modeling approaches, when smartly implemented, can contribute to this aim.Areas covered:The focus of this review was on modeling approaches applied to four kinds of drug-induced toxicities: hematological, immunological, cardiovascular (CV) and liver toxicity. Papers, mainly published in the last 10 years, reporting models in three main methodological categories - computational models (e.g., quantitative structure-property relationships, machine learning approaches, neural networks, etc.), pharmacokinetic-pharmacodynamic (PK-PD) models, and quantitative system pharmacology (QSP) models - have been considered.Expert opinion:The picture observed in the four examined toxicity areas appears heterogeneous. Computational models are typically used in all areas as screening tools in the early stages of development for hematological, cardiovascular and liver toxicity, with accuracies in the range of 70-90%. A limited number of computational models, based on the analysis of drug protein sequence, was instead proposed for immunotoxicity. In the later stages of development, toxicities are quantitatively predicted with reasonably good accuracy using either semi-mechanistic PK-PD models (hematological and cardiovascular toxicity), or fully exploited QSP models (immuno-toxicity and liver toxicity).

Pharmacokinetic Modelling of Human Recombinant Protein, p75ECD-Fc: A Novel Therapeutic Approach for Treatment of Alzheimer's Disease, in Serum and Tissue of Sprague Dawley Rats

BACKGROUND AND OBJECTIVE

p75ECD-Fc is a novel antagonist of toxic amyloid beta protein and other neurodegenerative factors with potential for the treatment of Alzheimer's disease (AD). Preclinical studies showed that it can alleviate the AD pathologies in animal models of dementia. In a previous paper, we used non-compartmental pharmacokinetic analysis to obtain preliminary pharmacokinetic data for p75ECD-Fc in Sprague Dawley (SD) rats. We also studied the tissue distribution in terms of drug metabolism that helped us to understand possible mechanisms of action. Here, we aim to develop population pharmacokinetic models that can describe the pharmacokinetics of p75ECD-Fc in serum and tissues.

METHODS

p75ECD-Fc was delivered to SD rats via two routes (intravenous and subcutaneous) at a single dose of 3 mg/kg (n = 15). Blood (n = 12) and tissue samples (n = 10-15) were then separated at different time points for a total duration of 42 days post dosage. The concentration of p75ECD-Fc in serum and tissues was measured using an enzyme-linked immunosorbent assay.

RESULTS

Data were best fitted to a 2-compartment model with linear elimination kinetics. The population parameter estimates for clearance, and volume of central and peripheral compartments were 0.000176 L/h, 0.0145 L and 0.0263 L, respectively. The presence of anti-drug antibodies was added to the final model as a covariate on clearance. The subcutaneous bioavailability was estimated to be 53.5% with a first-order absorption rate constant of 0.00745 1/h. By modeling of individual tissue concentrations, p75ECD-Fc was found to exhibit modest tissue distribution with estimated tissue/plasma partition coefficients (R) ranging from 0.004 to 0.2.

CONCLUSION

This is the first report of a pharmacokinetic model for p75ECD-Fc and these results may facilitate the ongoing development of p75ECD-Fc and translation to clinical studies.

Allometric scaling of therapeutic monoclonal antibodies in preclinical and clinical settings

Constant technological advancement enabled the production of therapeutic monoclonal antibodies (mAbs) and will continue to contribute to their rapid expansion. Compared to small-molecule drugs, mAbs have favorable characteristics, but also more complex pharmacokinetics (PK), e.g., target-mediated nonlinear elimination and recycling by neonatal Fc-receptor. This review briefly discusses mAb biology, similarities and differences in PK processes across species and within human, and provides a detailed overview of allometric scaling approaches for translating mAb PK from preclinical species to human and extrapolating from adults to children. The approaches described here will remain vital in mAb drug development, although more data are needed, for example, from very young patients and mAbs with nonlinear PK, to allow for more confident conclusions and contribute to further growth of this field. Improving mAb PK predictions will facilitate better planning of (pediatric) clinical studies and enable progression toward the ultimate goal of expediting drug development.

Generation and Characterization of a Novel Anti-Rat TLR4/MD2 Antibody with Potent Neutralizing Activity In Vivo

Toll-like receptor 4 (TLR4) plays a critical role in the innate immune system and is involved in the pathogenesis of multiple diseases. Here, we report the antagonistic and ratized antibody, 52-1H4 e2 (e2), which completely inhibited lipopolysaccharide-induced interleukin-6 secretion in vitro. The average serum drug concentration was above 10 μg/mL for 28 days in rats injected with e2. The novel anti-rat TLR4/myeloid differentiation factor 2 antibody, e2, may be a useful tool for investigating the role of TLR4 in rat disease models.

Stem Cell as Vehicles of Antibody in Treatment of Lymphoma: a Novel and Potential Targeted Therapy

Lymphoma is a heterogeneous malignancy and its incidence is increasing in the past decades all over the world. Although more than half of lymphoma patients achieve complete or partial remission from the standard first-line ABVD or R-CHOP based therapy, patients who fail to respond to these regimens will give rise to relapsed or refractory (R/R) lymphoma and may lead to a worse prognosis. Developing novel agents is important for R/R lymphoma. Based on the homing ability and being genetically modified easily, stem cells are usually used as vehicles in cell-based anti-tumor therapy, which can not only retain their own biological characteristics, but also make anti-tumor agents secrete constantly in tumor environment, to eventually kill the tumor cells more effectively. In this review, we will briefly introduce the properties of antibody therapy carried by stem cells, especially the hopes and hurdles of stem cell-mediated antibody secretion in the treatment of lymphoma.

Antibodies Inhibiting the Type III Secretion System of Gram-Negative Pathogenic Bacteria

Pathogenic bacteria are a global health threat, with over 2 million infections caused by Gram-negative bacteria every year in the United States. This problem is exacerbated by the increase in resistance to common antibiotics that are routinely used to treat these infections, creating an urgent need for innovative ways to treat and prevent virulence caused by these pathogens. Many Gram-negative pathogenic bacteria use a type III secretion system (T3SS) to inject toxins and other effector proteins directly into host cells. The T3SS has become a popular anti-virulence target because it is required for pathogenesis and knockouts have attenuated virulence. It is also not required for survival, which should result in less selective pressure for resistance formation against T3SS inhibitors. In this review, we will highlight selected examples of direct antibody immunizations and the use of antibodies in immunotherapy treatments that target the bacterial T3SS. These examples include antibodies targeting the T3SS of Pseudomonas aeruginosa, Yersinia pestis, Escherichia coli, Salmonella enterica, Shigella spp., and Chlamydia trachomatis.

Toward comparability of anti-drug antibody assays: is the amount of anti-drug antibody–reagent complexes at cut-point (CP-ARC) the missing piece?

Immunogenicity testing is a mandatory and critical activity during the development of therapeutic proteins. Multiple regulatory guidelines provide clear recommendations on appropriate immunogenicity testing strategies and required bioanalytical assay performances. Unfortunately, it is still generally accepted that a comparison of the immunogenicity of different compounds is not possible due to apparent performance differences of the used bioanalytical methods. In this perspective, we propose the ‘cut-point anti-drug antibody–reagents complex’ (CP-ARC) concept for technical comparability of the bioanalytical methods. The feasibility and implementation in routine assay development is discussed as well as the potential improvement of reporting of bioanalytical immunogenicity data to allow comparison across drugs. Scientific sound comparability of the bioanalytical methods is the first step toward comparability of clinical immunogenicity.

Physiologic constraints of using exosomes in vivo as systemic delivery vehicles

Systemic delivery of exosomes meets hurdles which had not been elucidated using live molecular imaging for their biodistribution. Production and uptake of endogenous exosomes are expected to be nonspecific and specific, respectively, where external stimuli of production of exosomes and their quantitative degree of productions are not understood. Despite this lack of understanding of basic physiology of in vivo behavior of exosomes including their possible paracrine or endocrine actions, many engineering efforts are taken to develop therapeutic vehicles. Especially, the fraction of exosomes’ taking the routes of waste disposal and exerting target actions are not characterized after systemic administration. Here, we reviewed the literature about in vivo distribution and disposal/excretion of exogenous or endogenous exosomes and, from these limited resources of knowledge currently available, summarized the knowledge and the uncertainties of exosomes on physiologic standpoints. An eloquent example of the investigations to understand the roles and confounders of exosomes’ action in the brain was highlighted with emphasis on the recent discovery of brain lymphatics and hypothesis of glymphatic/lymphatic clearance pathways in diseases as well as in physiologic processes. The possibility of delivering therapeutic exosomes through the systemic circulation, across blood-brain barriers and finally to target cells such as microglia, astrocytes and/or neurons is a good testbed in which the investigators can formulate problems to solve for both understanding (science) and application (engineering).

PKPD Assessment of the Anti-CD20 Antibody Obinutuzumab in Cynomolgus Monkey is Feasible Despite Marked Anti-Drug Antibody Response in This Species

The pharmacokinetics (PK) of the anti-CD20 monoclonal antibody obinutuzumab was assessed after single intravenous dosing to cynomolgus monkeys. In addition, the pharmacokinetic-pharmacodynamic (PKPD) relationship for B-cell depletion was characterized. The PKPD model was used to estimate the B-cell repopulation during the recovery phase of chronic toxicology studies, thereby supporting the study design, in particular planning the recovery phase duration. Marked immunogenicity against obinutuzumab was observed approximately 10 days after single dose, leading to an up to ∼30-fold increase in obinutuzumab clearance in the affected monkeys. Despite this accelerated clearance, the PK could be characterized, either by disregarding the clearance in noncompartmental PK analysis or by capturing it explicitly as an additional time-dependent clearance process in compartmental modeling. This latter step was crucial to model the PKPD of B-cells as an indirect response to obinutuzumab exposure, showing that-without immune response-the limiting factor is obinutuzumab elimination with concentrations below 0.02 μg/mL required for initiation of B-cell recovery. Overall, the results demonstrate that despite a marked anti-drug antibody response in the nonclinical animal species, the PK and PKPD of obinutuzumab could be characterized successfully by appropriately addressing the immune-modulated clearance pathway in data analysis and modeling.

Evaluating a Multiscale Mechanistic Model of the Immune System to Predict Human Immunogenicity for a Biotherapeutic in Phase 1

A mechanistic model of the immune response was evaluated for its ability to predict anti-drug antibody (ADA) and their impact on pharmacokinetics (PK) and pharmacodynamics (PD) for a biotherapeutic in a phase 1 clinical trial. Observed ADA incidence ranged from 33 to 67% after single doses and 27-50% after multiple doses. The model captured the single dose incidence well; however, there was overprediction after multiple dosing. The model was updated to include a T-regulatory (Treg) cell mediated tolerance, which reduced the overprediction (relative decrease in predicted incidence rate of 21.5-59.3% across multidose panels) without compromising the single dose predictions (relative decrease in predicted incidence rate of 0.6-13%). The Treg-adjusted model predicted no ADA impact on PK or PD, consistent with the observed data. A prospective phase 2 trial was simulated, including co-medication effects in the form of corticosteroid-induced immunosuppression. Predicted ADA incidences were 0-10%, depending on co-medication dosage. This work demonstrates the utility in applying an integrated, iterative modeling approach to predict ADA during different stages of clinical development.

Antibody therapeutics and immunoregulation in cancer and autoimmune disease

Cancer and autoimmune disease are closely related, and many therapeutic antibodies are widely used in clinics for the treatment of both diseases. Among them, the anti-CD20 antibody has proven to be effective against both lymphoid malignancy and autoimmune disease. Moreover, immune checkpoint blockade using the anti-PD1/PD-L1/CTLA4 antibody has improved the prognosis of patients with refractory solid tumors. At the same time, however, over-enhancement of immunoreaction can induce autoimmune reaction. Although anti-TNF antibody therapies represent a breakthrough in the treatment of autoimmune diseases, optimal management is required to control the serious associated issues, including development and progression of cancer, and it is becoming more and more important to control the immunoreaction. In addition, next-generation antibody therapeutics such as antibody-drug conjugates and bispecific antibodies, are anticipated to treat uncontrolled cancer and autoimmune disease. IL-7R signaling plays an important role in the development and progression of both lymphoid malignancy and autoimmune disease. In addition, abnormal homing activity and steroid resistance caused by IL-7R signaling may worsen prognosis. Therefore, anti-IL-7R targeting antibody therapies that enable suppression of such pathophysiological status have the potential to be beneficial for the treatment of both diseases. In this review, we discuss current antibody therapeutics in cancer and autoimmune disease, and describe a new therapeutic strategy for immunoregulation including IL-7R targeting antibodies.

Immunogenicity of Protein Pharmaceuticals

Protein therapeutics have drastically changed the landscape of treatment for many diseases by providing a regimen that is highly specific and lacks many off-target toxicities. The clinical utility of many therapeutic proteins has been undermined by the potential development of unwanted immune responses against the protein, limiting their efficacy and negatively impacting its safety profile. This review attempts to provide an overview of immunogenicity of therapeutic proteins, including immune mechanisms and factors influencing immunogenicity, impact of immunogenicity, preclinical screening methods, and strategies to mitigate immunogenicity.

Monoclonal Antibodies and Fc-Fusion Proteins for Pediatric Use: Dosing, Immunogenicity, and Modeling and Simulation in Data Submitted to the US Food and Drug Administration

The experience with the use of monoclonal antibodies and Fc-fusion proteins (mAb/Fc) in the pediatric population is limited. The objective of this study is to review those factors impacting the clinical efficacy and product safety of mAb/Fc products in pediatric patients during drug development. We reviewed the list of biologic products in the US Food and Drug Administration's Purple Book as of March 2018 with a focus on mAb/Fc products that are indicated for use in both adults and pediatric patients. Of 68 mAb/Fc products in the Purple Book (excluding biosimilars), 20 products have approved indications in both adults and children. Thirteen products had concurrent approval for both adult and pediatric populations. The sample size of pediatric studies generally ranged from approximately 2% to 70% of the sample size of adult studies with the same indication. In general, pediatric dosing regimens were found to be more based on body weight and weight tiered than the regimens for adults. Modeling and simulation techniques comprised mainly population pharmacokinetic and pharmacodynamic models. A review of the immunogenicity incidence did not reveal any notable difference in the 5 products having data on both pediatric and adult patients. In conclusion, most of the mAb/Fc products have a different weight-based dosing regimen for pediatric patients versus adults. An understanding of the comparative experience in drug development for mAb/Fc products between adult and pediatric patients coupled with the application of advanced modeling and simulation methods should assist future development of new mAb/Fc products for pediatric patients.

Rituximab Serum Concentrations and Anti-Rituximab Antibodies During B-Cell Depletion Therapy for Myalgic Encephalopathy/Chronic Fatigue Syndrome

PURPOSE

Previous Phase II trials indicated clinical benefit from B-cell depletion using the monoclonal anti-CD20 antibody rituximab in patients with myalgic encephalopathy/chronic fatigue syndrome (ME/CFS). The association between rituximab serum concentrations and the effect and clinical relevance of antidrug antibodies (ADAs) against rituximab in ME/CFS is unknown. We retrospectively measured rituximab concentrations and ADAs in serum samples from patients included in an open-label Phase II trial with maintenance rituximab treatment (KTS-2-2010) to investigate possible associations with clinical improvement and clinical and biochemical data.

METHODS

Patients with ME/CFS fulfilling the Canadian criteria received rituximab (500 mg/m²) infusions: 2 infusions 2 weeks apart (induction), followed by maintenance treatment at 3, 6, 10, and 15 months. The measured rituximab concentrations and ADAs in serum samples included 23 of 28 patients from the trial.

FINDINGS

There were no significant differences in mean serum rituximab concentrations between 14 patients experiencing clinical improvement versus 9 patients with no improvement. Female patients had higher mean serum rituximab concentrations than male patients at 3 months (P = 0.05). There was a significant negative correlation between B-cell numbers in peripheral blood at baseline and rituximab serum concentration at 3 months (r = -0.47; P = 0.03). None of the patients had ADAs at any time point.

IMPLICATIONS

Clinical improvement of patients with ME/CFS in the KTS-2-2010 trial was not related to rituximab serum concentrations or ADAs. This finding is also in line with a recent randomized trial questioning the efficacy of rituximab in ME/CFS. Rituximab concentrations and ADAs still offer supplemental information when interpreting the results of these trials.

A Model-Based Approach to Quantify the Time-Course of Anti-Drug Antibodies for Therapeutic Proteins

A mathematical antidrug antibody (ADA) model was developed to quantitatively assess immunogenicity for therapeutic proteins. The ADA model was built with antibody titer data in subjects from 10 clinical trials. The time course of the antibody titers was quantitatively characterized with a two-component semimechanistic model describing the double peaks of ADA titers. The relationship between antibody titer and incidence was also explored. The ADA incidences in subjects from 12 clinical trials were used for internal and external validations. The ADA titers reasonably predicted the incidence of antibody. The model-predicted elimination rate constant for antibody titer was 14.1 × 10^-3  day^-1 and 8.1 × 10^-3  day^-1 in healthy subjects and patients, respectively. This research provided a useful tool to quantitatively evaluate immunogenicity and its impact for therapeutic proteins.

A minimal physiologically based pharmacokinetic model that predicts anti-PEG IgG-mediated clearance of PEGylated drugs in human and mouse

Circulating antibodies that specifically bind polyethylene glycol (PEG), a polymer routinely used in protein and nanoparticle therapeutics, have been associated with reduced efficacy and increased adverse reactions to some PEGylated therapeutics. In addition to acute induction of anti-PEG antibodies (APA) by PEGylated drugs, typically low but detectable levels of APA are also found in up to 70% of the general population. Despite the broad implications of APA, the dynamics of APA-mediated clearance of PEGylated drugs, and why many patients continue to respond to PEGylated drugs despite the presence of pre-existing APA, remains not well understood. Here, we developed a minimal physiologically based pharmacokinetic (mPBPK) model that incorporates various properties of APA and PEGylated drugs. Our mPBPK model reproduced clinical PK data of APA-mediated accelerated blood clearance of pegloticase, as well as APA-dependent elimination of PEGyated liposomes in mice. Our model predicts that the prolonged circulation of PEGylated drugs will be compromised only at APA concentrations greater than ~500 ng/mL, providing a quantitative explanation to why the effects of APA on PEGylated treatments appear to be limited in most patients. This mPBPK model is readily adaptable to other PEGylated drugs and particles to predict the precise levels of APA that could render them ineffective, providing a powerful tool to support the development and interpretation of preclinical and clinical studies of various PEGylated therapeutics.

Correlation between anti-PD-L1 tumor concentrations and tumor-specific and nonspecific biomarkers in a melanoma mouse model

Blockade of PD-L1 with specific monoclonal antibodies (anti-PD-L1) represents a therapeutic strategy to increase the capability of the immune system to modulate the tumor immune-resistance. The relationship between anti-PD-L1 tumor exposition and anti-tumor effect represents a challenge that has been addressed in this work through the identification of certain biomarkers implicated in the antibody's mechanism of action, using a syngeneic melanoma mouse model. The development of an in-vitro/in-vivo platform has allowed us to investigate the PD-L1 behavior after its blockage with anti-PD-L1 at cellular level and in animals. In-vitro studies showed that the complex PD-L1/anti-PD-L1 was retained mainly at the cell surface. The antibody concentration and time exposure affected directly the recycling or ligand turnover. In-vivo studies showed that anti-PD-L1 was therapeutically active at all stage of the disease, with a rapid onset, a low but durable efficacy and non-relevant toxic effect. This efficacy measured as tumor shrinkage correlated with tumor-specific infiltrating lymphocytes (TILs), which increased as antibody tumor concentrations increased. Both, TILS and antibody concentrations followed similar kinetic patterns, justifying the observed anti-PD-L1 rapid onset. Interestingly, peripheral lymphocytes (PBLs) behave as infiltrating lymphocytes, suggesting that these PBLs might be considered as a possible biomarker for antibody activity.

Translational pharmacokinetics and pharmacodynamics of monoclonal antibodies

Monoclonal antibodies (mAbs) are an important therapeutic class with complex pharmacology and interdependent pharmacokinetic (PK) and pharmacodynamics (PD) properties. Understanding the PK and PD of mAbs and their biological and mechanistic underpinnings are crucial in enabling their design and selection, designing appropriate efficacy and toxicity studies, translating PK/PD parameters to humans, and optimizing dose and regimen to maximize success in the clinic. Significant progress has been made in this field however many critical questions still remain. This article gives a brief overview of the PK and PD of mAbs, factors that influence them, and areas of ongoing inquiry. Current tools and translational approaches to predict the PK/PD of mAbs in humans are also discussed.

Antidrug Antibody Formation in Oncology: Clinical Relevance and Challenges

: In oncology, an increasing number of targeted anticancer agents and immunotherapies are of biological origin. These biological drugs may trigger immune responses that lead to the formation of antidrug antibodies (ADAs). ADAs are directed against immunogenic parts of the drug and may affect efficacy and safety. In other medical fields, such as rheumatology and hematology, the relevance of ADA formation is well established. However, the relevance of ADAs in oncology is just starting to be recognized, and literature on this topic is scarce. In an attempt to fill this gap in the literature, we provide an up-to-date status of ADA formation in oncology. In this focused review, data on ADAs was extracted from 81 clinical trials with biological anticancer agents. We found that most biological anticancer drugs in these trials are immunogenic and induce ADAs (63%). However, it is difficult to establish the clinical relevance of these ADAs. In order to determine this relevance, the possible effects of ADAs on pharmacokinetics, efficacy, and safety parameters need to be investigated. Our data show that this was done in fewer than 50% of the trials. In addition, we describe the incidence and consequences of ADAs for registered agents. We highlight the challenges in ADA detection and argue for the importance of validating, standardizing, and describing well the used assays. Finally, we discuss prevention strategies such as immunosuppression and regimen adaptations. We encourage the launch of clinical trials that explore these strategies in oncology.

IMPLICATIONS FOR PRACTICE

Because of the increasing use of biologicals in oncology, many patients are at risk of developing antidrug antibodies (ADAs) during therapy. Although clinical consequences are uncertain, ADAs may affect pharmacokinetics, patient safety, and treatment efficacy. ADA detection and reporting is currently highly inconsistent, which makes it difficult to evaluate the clinical consequences. Standardized reporting of ADA investigations in the context of the aforementioned parameters is critical to understanding the relevance of ADA formation for each drug. Furthermore, the development of trials that specifically aim to investigate clinical prevention strategies in oncology is needed.

The Role of Aggregates of Therapeutic Protein Products in Immunogenicity: An Evaluation by Mathematical Modeling

Therapeutic protein products (TPP) have been widely used to treat a variety of human diseases, including cancer, hemophilia, and autoimmune diseases. However, TPP can induce unwanted immune responses that can impact both drug efficacy and patient safety. The presence of aggregates is of particular concern as they have been implicated in inducing both T cell-independent and T cell-dependent immune responses. We used mathematical modeling to evaluate several mechanisms through which aggregates of TPP could contribute to the development of immunogenicity. Modeling interactions between aggregates and B cell receptors demonstrated that aggregates are unlikely to induce T cell-independent immune responses by cross-linking B cell receptors because the amount of signal transducing complex that can form under physiologically relevant conditions is limited. We systematically evaluate the role of aggregates in inducing T cell-dependent immune responses using a recently developed multiscale mechanistic mathematical model. Our analysis indicates that aggregates could contribute to T cell-dependent immune response by inducing high affinity epitopes which may not be present in the nonaggregated TPP and/or by enhancing danger signals to break tolerance. In summary, our computational analysis is suggestive of novel insights into the mechanisms underlying aggregate-induced immunogenicity, which could be used to develop mitigation strategies.

Pharmacokinetics and pharmacokinetic-pharmacodynamic relationships of monoclonal antibodies in children

Monoclonal antibodies (mAbs) constitute a therapeutically and economically important drug class with increasing use in both adult and paediatric patients. The rather complex pharmacokinetic and pharmacodynamic properties of mAbs have been extensively reviewed in adults. In children, however, limited information is currently available. This paper aims to comprehensively review published pharmacokinetic and pharmacokinetic-pharmacodynamic studies of mAbs in children. The current status of mAbs in the USA and in Europe is outlined, including a critical discussion of the dosing strategies of approved mAbs. The pharmacokinetic properties of mAbs in children are exhaustively summarised along with comparisons to reports in adults: for each pharmacokinetic process, we discuss the general principles and mechanisms of the pharmacokinetic/pharmacodynamic characteristics of mAbs, as well as key growth and maturational processes in children that might impact these characteristics. Throughout this review, considerable knowledge gaps are identified, especially regarding children-specific properties that influence pharmacokinetics, pharmacodynamics and immunogenicity. Furthermore, the large heterogeneity in the presentation of pharmacokinetic/pharmacodynamic data limited clinical inferences in many aspects of paediatric mAb therapy. Overall, further studies are needed to fully understand the impact of body size and maturational changes on drug exposure and response. To maximise future knowledge gain, we propose a 'Guideline for Best Practice' on how to report pharmacokinetic and pharmacokinetic-pharmacodynamic results from mAb studies in children which also facilitates comparisons. Finally, we advocate the use of more sophisticated modelling strategies (population analysis, physiology-based approaches) to appropriately characterise pharmacokinetic-pharmacodynamic relationships of mAbs and, thus, allow for a more rational use of mAb in the paediatric population.