A Fab of trastuzumab to treat HER2 overexpressing breast cancer brain metastases.

Despite major therapeutic advances for two decades, including the most recently approved anti-HER2 drugs, brain metastatic localizations remain the major cause of death for women with metastatic HER2 breast cancer. The main reason is the limited drug passage of the blood-brain barrier after intravenous injection and the significant efflux of drugs, including monoclocal antibodies, after administration into the cerebrospinal fluid. We hypothesized that this efflux was linked to the presence of a FcRn receptor in the blood-brain barrier. To overcome this efflux, we engineered two Fab fragments of trastuzumab, an anti-HER2 monoclonal antibody, and did a thorough preclinical development for therapeutic translational purpose. We demonstrated the safety and equal efficacy of the Fabs with trastuzumab in vitro, and in vivo using a patient-derived xenograft model of HER2 overexpressing breast cancer. For the pharmacokinetic studies of intra-cerebrospinal fluid administration, we implemented original rat models with catheter implanted into the cisterna magna. After intraventricular administration in rats, we demonstrated that the brain-to-blood efflux of Fab was up to 10 times lower than for trastuzumab, associated with a two-fold higher brain penetration compared to trastuzumab. This Fab, capable of significantly reducing brain-to-blood efflux and enhancing brain penetration after intra-cerebrospinal fluid injection, could thus be a new and original effective drug in the treatment of HER2 breast cancer brain metastases, which will be demonstrated by a phase I clinical trial dedicated to women in resort situations.

Eculizumab dose tapering should take into account the nonlinearity of its pharmacokinetics.

AIMS: Eculizumab is a monoclonal antibody targeting complement protein C5 used in renal diseases. As recommended dosing regimen leads to unnecessarily high concentrations in some patients, tailored dosing therapeutic drug monitoring was proposed to reduce treatment cost. The objectives of the present work were (i) to investigate the target-mediated elimination of eculizumab and (ii) whether a pharmacokinetic model integrating a nonlinear elimination allows a better prediction of eculizumab concentrations than a linear model. METHODS: We analysed 377 eculizumab serum concentrations from 44 patients treated for atypical haemolytic uraemic syndrome and C3 glomerulopathy with a population pharmacokinetic approach. Critical concentrations (below which a non-log-linear decline of concentration over time is evidenced) were computed to estimate the relevance of the target-mediated elimination. Simulations of dosing regimens were then performed to predict probabilities of target attainment (i.e. trough >100 mg/L). RESULTS: Pharmacokinetics of eculizumab was nonlinear and followed a mixture of first-order (CL = 1.318 mL/day/kg) and Michaelis-Menten elimination (Vmax = 26.07 mg/day, Km = 24.06 mg/L). Volume of distribution (72.39 mL/kg) and clearance were weight-dependent. Critical concentrations (Vmax/CL) ranged from 144.7 to 759.7 mg/L and were inversely related to body weight (P = .013). Nonlinearity was thus noticeable at therapeutic concentrations. Simulations predicted that 1200 mg of eculizumab every 21 days would allow 85% and 76% of patients to maintain a therapeutic exposure, for 50 or 90 kg body weight, respectively. CONCLUSIONS: Our study investigates the nonlinear elimination of eculizumab and discusses the importance of accounting for eculizumab target-mediated elimination in therapeutic drug monitoring.

Confounding mitigation for the exposure-response relationship of bevacizumab in colorectal cancer patients.

AIMS: The exposure-response relationship of bevacizumab may be confounded by various factors, including baseline characteristics, time-dependent target engagement and recursive relationships between exposure and response, requiring effective mitigation. This study aimed to investigate the exposure-response relationships of bevacizumab in metastatic colorectal cancer (mCRC) patients while mitigating potential biases. METHODS: Bevacizumab pharmacokinetics was described using target-mediated drug disposition modelling. Relationships between target kinetics, progression-free (PFS) and overall (OS) survivals were assessed using joint pharmacokinetic and parametric hazard function models. Both prognostic-driven and response-driven potential biases were mitigated. These models evaluated the impact of increased antigen target levels, clearance and intensified dosing regimen on survival. RESULTS: Estimated target-mediated pharmacokinetic parameters in 130 assessed patients were baseline target levels (R0 = 8.4 nM), steady-state dissociation constant (KSS = 10 nM) and antibody-target complexes elimination constant (kint = 0.52 day-1). The distribution of R0 was significantly associated with increased baseline concentrations of carcinoembryonic antigen, circulating vascular endothelial growth factor and the presence of extrahepatic metastases. Unbound target levels (R) significantly influenced both progression and death hazard functions. Increasing baseline target levels and/or clearance values led to decreased bevacizumab unbound concentrations, increased R levels and shortened PFS and OS, while increasing bevacizumab dose led to decreased R and longer survival. CONCLUSION: This study is the first to demonstrate the relationship between bevacizumab concentrations, target involvement and clinical efficacy by effectively mitigating potential sources of bias. Most of the target amount may be tumoural in mCRC. Future studies should provide a more in-depth description of this relationship.

Efficacy and safety of intravenous bevacizumab on severe bleeding associated with hemorrhagic hereditary telangiectasia: A national, randomized multicenter trial.

BACKGROUND: Bevacizumab-a humanized monoclonal antibody-has been widely used to treat patients with hereditary hemorrhagic telangiectasia (HHT), but no randomized trial has yet been conducted. METHODS: This study is a double-blind multicenter randomized phase 2 trial with a 1:1 active-treatment-to-placebo ratio. We included patients over the age of 18 with a confirmed diagnosis and the need for at least four red blood cell (RBC) units transfused in the 3 months before study enrollment. Bevacizumab was administered at a dose of 5 mg/kg every 14 days with a total of six injections. The primary efficacy criterion was a decrease of at least 50% in the cumulative number of RBC units transfused in a 3-month period before and after treatment. RESULTS: A total of 24 patients (12 in each group) were included and randomized at 4 different centers. In intention-to-treat analysis, 63.6% of patients (7/11) in the bevacizumab group versus 33.3% of patients (4/12) in the placebo group decreased the number of blood transfusions by at least 50% (p = 0.22). Hemoglobin levels significantly improved at 6 months in the bevacizumab versus placebo group (p = 0.02). The pharmacokinetics study revealed that patients with high exposure to bevacizumab had a significant decrease in RBC transfusions (p = 0.03). Fifty-nine adverse events were observed, 34 in the placebo arm versus 25 in the bevacizumab arm. CONCLUSION: Though the present trial was underpowered, patients with HHT receiving bevacizumab required numerically fewer red blood cell transfusions than those receiving placebo, particularly those with high exposure.

Relationship Between Cetuximab Target-Mediated Pharmacokinetics and Progression-Free Survival in Metastatic Colorectal Cancer Patients.

BACKGROUND AND OBJECTIVE: Cetuximab, an anti-epidermal growth factor receptor (EGFR) monoclonal immunoglobulin (Ig)G1 antibody, has been approved for the treatment of metastatic colorectal cancer (mCRC). The influence of target-antigen on cetuximab pharmacokinetics has never been investigated using target-mediated drug disposition (TMDD) modelling. This study aimed to investigate the relationship between cetuximab concentrations, target kinetics and progression-free survival (PFS). METHODS: In this ancillary study (NCT00559741), 91 patients with mCRC treated with cetuximab were assessed. Influence of target levels on cetuximab pharmacokinetics was described using TMDD modelling. The relationship between cetuximab concentrations, target kinetics and time-to-progression (TTP) was described using a joint pharmacokinetic-TTP model, where unbound target levels were assumed to influence hazard of progression by an Emax model. Mitigation strategies of concentration-response relationship, i.e., time-varying endogenous clearance and mutual influences of clearance and time-to-progression were investigated. RESULTS: Cetuximab concentration-time data were satisfactorily described using the TMDD model with quasi-steady-state approximation and time-varying endogenous clearance. Estimated target parameters were baseline target levels (R0 = 43 nM), and complex elimination rate constant (kint = 0.95 day-1). Estimated time-varying clearance parameters were time-invariant component of CL (CL0= 0.38 L/day-1), time-variant component of CL (CL1= 0.058 L/day-1) and first-order rate of CL1 decreasing over time (kdes = 0.049 day-1). Part of concentration-TTP was TTP-driven, where clearance and TTP were inversely correlated. In addition, increased target occupancy was associated with increased TTP. CONCLUSION: This is the first study describing the complex relationship between cetuximab target-mediated pharmacokinetics and PFS in mCRC patients using a joint PK-time-to-progression model. Further studies are needed to provide a more in-depth description of this relationship.

The Influence of Underlying Disease on Rituximab Pharmacokinetics May be Explained by Target-Mediated Drug Disposition.

BACKGROUND AND OBJECTIVES: Rituximab is an anti-CD20 monoclonal antibody approved in several diseases, including chronic lymphocytic leukemia (CLL), diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL), rheumatoid arthritis (RA), and anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV). The influence of underlying disease on rituximab pharmacokinetics has never been investigated for several cancer and non-cancer diseases simultaneously. This study aimed at assessing this influence using an integrated semi-mechanistic model accounting for target-mediated elimination of rituximab. METHODS: Rituximab concentration-time data from five studies previously published in patients with CLL, DLBCL, FL, RA, and AAV were described using a two-compartment model with irreversible binding of rituximab to its target antigen. Both underlying disease and target antigen measurements were assessed as covariates. RESULTS: Central volume of distribution was [95% confidence interval] 1.7-fold [1.6-1.9] higher in DLBCL than in RA, FL, and CLL, and it was 1.8-fold [1.6-2.1] higher in RA, FL, and CLL than in AAV. First-order elimination rate constants were 1.8-fold [1.7-2.0] and 1.3-fold [1.2-1.5] higher in RA, DLBCL, and FL than in CLL and AAV, respectively. Baseline latent antigen level (L0) was 54-fold [30-94], 20-fold [11-36], and 29-fold [14-64] higher in CLL, DLBCL, and FL, respectively, than in RA and AAV. In lymphoma, L0 increased with baseline total metabolic tumor volume (p = 6.10-7). In CLL, the second-order target-mediated elimination rate constant (kdeg) increased with baseline CD20 count on circulating B cells (CD20cir, p = 0.0081). CONCLUSIONS: Our results show for the first time that rituximab pharmacokinetics is strongly influenced by underlying disease and disease activity. Notably, neoplasms are associated with higher antigen amounts that result in decreased exposure to rituximab compared to inflammatory diseases. Our model might be used to estimate unbound target amounts in upcoming studies.

Infliximab Efficacy May Be Linked to Full TNF-α Blockade in Peripheral Compartment-A Double Central-Peripheral Target-Mediated Drug Disposition (TMDD) Model.

Infliximab is an anti-TNF-α monoclonal antibody approved in chronic inflammatory bowel diseases (IBD). This study aimed at providing an in-depth description of infliximab target-mediated pharmacokinetics in 133 IBD patients treated with 5 mg/kg infliximab at weeks 0, 2, 14, and 22. A two-compartment model with double target-mediated drug disposition (TMDD) in both central and peripheral compartments was developed, using a rich database of 26 ankylosing spondylitis patients as a reference for linear elimination kinetics. Population approach and quasi-steady-state (QSS) approximation were used. Concentration-time data were satisfactorily described using the double-TMDD model. Target-mediated parameters of central and peripheral compartments were respectively baseline TNF concentrations (RC0 = 3.3 nM and RP0 = 0.46 nM), steady-stated dissociation rates (KCSS = 15.4 nM and KPSS = 0.49 nM), and first-order elimination rates of complexes (kCint = 0.17 day-1 and kPint = 0.0079 day-1). This model showed slower turnover of targets and infliximab-TNF complex elimination rate in peripheral compartment than in central compartment. This study allowed a better understanding of the multi-scale target-mediated pharmacokinetics of infliximab. This model could be useful to improve model-based therapeutic drug monitoring of infliximab in IBD patients.

Association of IgG1 Antibody Clearance with FcγRIIA Polymorphism and Platelet Count in Infliximab-Treated Patients.

The FcγRIIA/CD32A is mainly expressed on platelets, myeloid and several endothelial cells. Its affinity is considered insufficient for allowing significant binding of monomeric IgG, while its H131R polymorphism (histidine > arginine at position 131) influences affinity for multimeric IgG2. Platelet FcγRIIA has been reported to contribute to IgG-containing immune-complexe clearance. Given our finding that platelet FcγRIIA actually binds monomeric IgG, we investigated the role of platelets and FcγRIIA in IgG antibody elimination. We used pharmacokinetics analysis of infliximab (IgG1) in individuals with controlled Crohn's disease. The influence of platelet count and FcγRIIA polymorphism was quantified by multivariate linear modelling. The infliximab half-life increased with R allele number (13.2, 14.4 and 15.6 days for HH, HR and RR patients, respectively). It decreased with increasing platelet count in R carriers: from ≈20 days (RR) and ≈17 days (HR) at 150 × 109/L, respectively, to ≈13 days (both HR and RR) at 350 × 109/L. Moreover, a flow cytometry assay showed that infliximab and monomeric IgG1 bound efficiently to platelet FcγRIIA H and R allotypes, whereas panitumumab and IgG2 bound poorly to the latter. We propose that infliximab (and presumably any IgG1 antibody) elimination is partly due to an unappreciated mechanism dependent on binding to platelet FcγRIIA, which is probably tuned by its affinity for IgG2.

Panitumumab and cetuximab affect differently miRNA expression in colorectal cancer cells.

Background & aim: Resistance to anti-EGFR monoclonal antibodies in metastatic colorectal cancer (CRC) is frequent and prognostic biomarkers are lacking. MicroRNAs (miR) are good candidates in this context. We aimed to characterize cetuximab and panitumumab exposure influence on miR expression in colorectal cancer cells to identify those regulating the EGFR pathway and implicated in resistance to treatment. Finally, we aimed to identify miR expression in serum of patients with advanced CRC treated with cetuximab or panitumumab. Results: Cetuximab and panitumumab exposure induced significant expression variations of 17 miR out of a miRnome panel of 752. Six of those miR interacted with at least one downstream element of the EGFR pathway. Conclusion: After the bioinformatics two-phase process, five miR rarely described before could be potential actors of anti-EGFR monoclonal antibody resistance: miR-95-3p, miR-139-5p, miR-145-5p, miR-429 and miR-1247-5p. In vivo, we detected the expression of miR-139-5p and miR-145-5p in serum of patients with metastatic CRC.

A robust enzyme-linked immunosorbent assay to measure serum ramucirumab concentrations.

Aim: Ramucirumab, an anti-VEGFR2 monoclonal antibody, has been approved for the treatment of metastatic gastric and colorectal cancer. An assay measuring ramucirumab serum concentrations was needed to investigate its pharmacokinetics and concentration-response relationship. Results: An ELISA was developed and validated according to the international guidelines for ligand-binding assays. Ramucirumab calibration standards ranged from 0.125 to 40 mg/l. Low, middle and high quality controls were spiked at 0.2, 4 and 8 mg/l, respectively. The limits of quantification were established to be 0.125 and 10 mg/l for LLOQ and ULOQ, respectively. No cross-reactivity with anti-VEGF or anti-EGFR was detected. Conclusion: This in-house-developed ELISA is sensitive, accurate, reproducible and suitable for pharmacokinetic studies of ramucirumab.

Antigen Mass May Influence Trastuzumab Concentrations in Cerebrospinal Fluid After Intrathecal Administration.

Intravenous administration of monoclonal antibodies leads to low concentrations in the central nervous system, which is a serious concern in neuro-oncology, especially in leptomeningeal carcinomatosis of HER2-overexpressing breast cancer. Case reports of i.t. administrations of trastuzumab have shown promising results in these patients but dosing regimens are empirical in absence of pharmacokinetic (PK) study. With a population PK approach, we described the fate of trastuzumab after i.t. administration in 21 women included in a phase I-II clinical trial. Trastuzumab was administered by i.t. route every week for 8 weeks and both cerebrospinal fluid (CSF) and serum were sampled to measure trough concentrations. Some patients showed noticeable CSF concentration fluctuations predicted using a target-mediated drug disposition. This target was latent and produced with a delayed feedback. Apparent volumes of distribution were close to physiological volumes (V1  = 3.25 L, V2  = 0.644 L, for serum and CSF, respectively). Estimated (constant) transfer from serum to CSF was very slow (k12  = 0.264 mg/day) whereas estimated half-life of transfer from CSF to serum was rapid (2.2 days). From the individual parameters of patients, a single i.t. administration of 150 mg of trastuzumab corresponded to median mean residence times of 3.8 days and 15.6 days in CSF and serum, respectively. Survival without neurological relapse was not related to trastuzumab exposure. This study confirms that transfer of trastuzumab from serum to CSF is very limited and that this monoclonal antibody, when administered by i.t. route, is rapidly transferred to the serum.

Methotrexate effect on immunogenicity and long-term maintenance of adalimumab in axial spondyloarthritis: a multicentric randomised trial.

OBJECTIVES: Anti-drug antibodies (ADA) are responsible for decreased adalimumab efficacy in axial spondyloarthritis (SpA). We aimed to evaluate the ability of methotrexate (MTX) to decrease adalimumab immunisation. METHODS: A total of 110 patients eligible to receive adalimumab 40 mg subcutaneously (s.c.) every other week were randomised (1:1 ratio) to receive, 2 weeks before adalimumab (W-2) and weekly, MTX 10 mg s.c. (MTX+) or not (MTX-). ADA detection and adalimumab serum concentration were assessed at weeks 4 (W4), 8 (W8), 12 (W12) and 26 (W26) after starting adalimumab (W0). The primary outcome was the proportion of patients with ADA at W26. Four years after the study completion, we retrospectively analysed adalimumab maintenance in relation with MTX co-treatment duration. RESULTS: We analysed data for 107 patients (MTX+; n=52; MTX-; n=55). ADA were detected at W26 in 39/107 (36.4%) patients: 13/52 (25%) in the MTX+ group and 26/55 (47.3%) in the MTX- group (p=0.03). Adalimumab concentration was significantly higher in the MTX+ than MTX- group at W4, W8, W12 and W26. The two groups did not differ in adverse events or efficacy. In the follow-up study, MTX co-treatment >W26 versus no MTX or ≤W26 was significantly associated with adalimumab long-term maintenance (p=0.04). CONCLUSION: MTX reduces the immunogenicity and ameliorate the pharmacokinetics of adalimumab in axial SpA. A prolonged co-treatment of MTX>W26 seems to increase adalimumab long-term maintenance.

A successful compartmental approach for the treatment of breast cancer brain metastases.

BACKGROUND: Brain metastases are challenging daily practice in oncology and remain a compartmental problem since most anti-cancer drugs do not cross the blood-brain barrier at relevant pharmacological concentrations. METHODS: In a young woman with HER2-overexpressing breast cancer resistant to standard treatments, at the time of brain metastases progression, a ventricular reservoir was implanted for intrathecal drug injections and detailed pharmacokinetic studies. RESULTS: A first association of intrathecal trastuzumab with intravenous cisplatin was offered to the patient. For trastuzumab, the mean cerebrospinal fluid trough concentration of 53.4 mg/L reached relevant levels, enabling the stabilization of the metastases. Adding intravenous cisplatin was not beneficial, since the cerebrospinal fluid exposure was almost undetectable under 0.08 mg/L. We then offered the patient an intrathecal combination of trastuzumab and methotrexate, because of their in vitro synergic cytotoxicity. The cerebrospinal fluid peak of methotrexate was 1037 µmol/L at 2 h, and the concentrations remained above the theoretical therapeutic concentration. After 2 months of this drug combination, we obtained an excellent response on the brain metastases. CONCLUSION: Our preliminary study supports the interest of a compartmental approach through a direct administration of drugs into the cerebrospinal fluid for the treatment of breast cancer brain metastases.

Phase I feasibility study for intrathecal administration of trastuzumab in patients with HER2 positive breast carcinomatous meningitis.

PURPOSE: Leptomeningeal carcinomatosis (MC) is commonly associated with HER2-positive breast cancer (HER2-BC), with a poor prognosis and no standardised treatment. We conducted a phase I dose-escalation study of intrathecal (IT) administration of trastuzumab in HER2-BC patients with MC to determine the maximum tolerated dose (MTD), which was based on both the achievement of a trastuzumab intra-cerebrospinal fluid concentration close to a conventional therapeutic plasma concentration (30 mg/L) and/or dose-limiting toxicity (DLT). METHODS: The protocol planned IT administration of trastuzumab (30 mg, 60 mg, 100 mg or 150 mg dose levels) once a week, over the course of at least 4 weeks. Sixteen patients with MC from HER2-BC received IT trastuzumab. Intra-cerebrospinal fluid samples were obtained before each injection for pharmacokinetics. RESULTS: We did not observe DLT of IT trastuzumab. Eleven patients had no toxicity attributed to IT trastuzumab. For 60 mg or higher dose levels, minor toxicities attributed to IT trastuzumab included headache (2 patients), nausea (2 patients), vomiting (1 patient), cervical pain (1 patient) and peripheral neuropathy (1 patient). Two patients experienced immediate toxicity including headache or vomiting. The mean residual intra-cerebrospinal fluid concentration of trastuzumab was 27.9 mg/L for the 150 mg dose level. Three patients achieved a clinical response, seven patients had stable disease and four patients had progressive disease. CONCLUSIONS: The MTD and recommended phase II weekly dose of IT trastuzumab in patients with HER2-BC and MC is 150 mg. A phase II trial using this dose regimen in MC from HER2-BC is ongoing. REGISTRATION IDENTIFICATION: ClinicalTrials.gov Identifier: NCT01373710 (https://clinicaltrials.gov/ct2/show/NCT01373710?term=trastuzumab+intrathecal&rank=1).

Development and validation of an ELISA to study panitumumab pharmacokinetics.

AIM: Panitumumab is a monoclonal antibody directed against EGFR that is approved for the treatment of metastatic colorectal cancer. To investigate its pharmacokinetics and concentration-response relationship, a validated assay is required. RESULTS: An ELISA assay was developed and validated according to international recommendations. Six calibrators (ranging from 0.1 to 20 mg/l) plus one anchor point (50 mg/l) and three quality controls (0.45, 2 and 8 mg/l) were defined. The limit of detection, lower limit of quantification and upper limit of quantification were 0.033, 0.112 and 10 mg/l, respectively. CONCLUSION: This method is validated and can be used to study pharmacokinetics of panitumumab or to perform therapeutic drug monitoring.

Model-Based Therapeutic Drug Monitoring of Infliximab Using a Single Serum Trough Concentration.

BACKGROUND AND OBJECTIVES: The pharmacokinetics of infliximab are highly variable and influence clinical response in chronic inflammatory diseases. The goal of this study was to build a Bayesian model allowing predictions of upcoming infliximab concentrations and dosing regimen adjustment, using only one concentration measurement and information regarding the last infliximab infusion. METHODS: This retrospective study was based on data from 218 patients treated with infliximab in Tours University Hospital who were randomly assigned to learning (two-thirds) or validation (one-third) data subsets. One-compartment pharmacokinetic and time since last dose (TLD) models were built and compared using learning and validation subsets. From these models, Bayesian pharmacokinetic and TLD models using one concentration measurement (1C-PK and 1C-TLD) were designed. The predictive performances of the 1C-TLD model were tested on two external validation cohorts. RESULTS: Pharmacokinetic and TLD models described the data satisfactorily and provided accurate parameter estimations. Comparable predictions of infliximab concentrations were obtained from pharmacokinetic versus TLD models, as well as from Bayesian 1C-PK versus 1C-TLD models. The 1C-TLD model showed satisfactory prediction of future infliximab concentrations and provided satisfactory predictions of infliximab steady-state concentration for up to three upcoming visits after a blood sample. CONCLUSIONS: Accurate individual concentration predictions can be obtained using a single infliximab concentration measurement and information regarding only the last infusion. The 1C-TLD model may help to optimize the dosing regimen of infliximab in routine therapeutic drug monitoring.

Development and validation of an enzyme-linked immunosorbent assay to measure free eculizumab concentration in serum.

AIM: Eculizumab is a monoclonal antibody toward C5 fraction of the complement system. It is approved to treat paroxysmal nocturnal hemoglobinuria and atypical hemolytic uremic syndrome. To perform pharmacokinetic studies and therapeutic drug monitoring, a validated assay is required. MATERIALS & METHODS: An indirect ELISA with recombinant human C5 sensitized microtiter plates were developed. RESULTS: The assay allows the measurement of free eculizumab concentration in human serum. The LOD, LLOQ and ULOQ were 0.091, 0.25 and 82.35 mg/l, respectively. The assay meets EMA and US FDA guidelines criteria for the validation of a ligand-binding assay. CONCLUSION: This method is validated and can be used in PK and PK-PD studies as well as to perform therapeutic drug monitoring of free eculizumab.

Immunoassays for Measuring Serum Concentrations of Monoclonal Antibodies and Anti-biopharmaceutical Antibodies in Patients.

Monoclonal antibodies (mAbs) may be used as biopharmaceuticals to treat various diseases, ranging from oncology to inflammatory and cardiovascular affections. Trustworthy analytical methods are necessary to study their pharmacokinetics, both during their development and in post-marketing studies. Because biopharmaceuticals are macromolecules, ligand-binding assays (both immunoassays and bioassays) are methods of choice to measure their concentrations. Immunoassays are based on the capture of biopharmaceuticals by their target, which may be a circulating or membrane antigen or by an antibody recognizing their structure. Bioassays measure the activity of the biopharmaceutical in a specific in vitro test. A number of techniques have been reported, but their limits of detection and quantification vary widely. Anti-drug antibodies (ADA) against biopharmaceuticals are often formed and sometimes interfere with clinical efficacy. Accurate and reliable detection of ADA is therefore necessary. Binding of ADA is dependent on affinity and avidity, which makes quantification challenging. In this review, we discuss the benefits and limitations of each method to determine mAb levels and carefully compare ADA assays.

Crucial Role for Immune Complexes but Not FcRn in Immunization against Anti-TNF-α Antibodies after a Single Injection in Mice.

The immunogenicity of infliximab and adalimumab is a major concern because patients may develop Abs also called antidrug Abs (ADA), directed against these anti-TNF-α Abs after just a few weeks of treatment. These ADAs can lead to a decrease in biologic concentration, which is associated with lower treatment efficacy. Our aim was to study the involvement of immune complexes and neonatal Fc receptor (FcRn) in the emergence of ADAs in the case of anti-TNF-α Abs. Wild type and FcRn knockout mice were injected once with either infliximab or adalimumab, alone or preincubated with TNF-α. Adalimumab cross-reacts with murine TNF-α whereas infliximab is species specific. When injected alone, only adalimumab elicited a humoral response. By preforming immune complexes with TNF-α, an anti-infliximab response was elicited. Surprisingly, both wild type and FcRn knockout mice were able to mount an immune response against anti-TNF-α Abs, suggesting that immune complexes are a major determinant of this immunization.

Antigenic burden and serum IgG concentrations influence rituximab pharmacokinetics in rheumatoid arthritis patients.

AIMS: Rituximab is a monoclonal antibody directed against CD20, which is approved in rheumatoid arthritis (RA). This study aimed at assessing the influence of CD19+ cell counts as target-antigen amount, and of immunoglobulin G (IgG) serum concentrations on rituximab pharmacokinetics in RA patients. METHODS: In a cohort of 64 RA patients who had received repetitive courses of rituximab, the influence of CD19+ cell count, IgG serum concentration, body surface area, sex and disease activity score in 28 joints on rituximab pharmacokinetic parameters was assessed using a population pharmacokinetic analysis. RESULTS: A two-compartment model, with first-order distribution and elimination best described the data. The volume of distribution of central compartment and clearance of rituximab were estimated at 4.7 l and 0.56 l day-1 , respectively. Distribution and elimination half-lives were 0.9 days and 17.3 days, respectively. As expected, the central volume of distribution increased with body surface area (P = 0.012) and was higher in male than in female (P = 0.004). We found that the elimination rate constant (k10 ) increased with CD19+ count (P = 0.00022) and IgG concentration (P = 7.4 × 10-8 ), and that k10 decreased with time (P = 0.00015), partly explained by a change in target-antigen amount. CONCLUSIONS: The association between CD19+ count and k10 may be explained by target-mediated drug disposition, while the association between IgG serum concentration and k10 may be explained by a saturation of the neonatal Fc receptor at high IgG concentrations, resulting in decreased recycling of rituximab.