Rituximab Immunomonitoring Predicts Remission in Membranous Nephropathy.

Primary membranous nephropathy (pMN) is an autoimmune kidney disease and a common cause of nephrotic syndrome in adults. Rituximab is becoming a first line therapy for patients with persistent nephrotic syndrome with proven safety and efficacy, achieving remission in 60%-80% of cases. For the remaining 20%-40% of patients there is an urgent need to identify early biomarkers of resistance to rituximab to adapt therapeutic management. In nephrotic patients, rituximab is found in the blood more transiently than in other autoimmune diseases without proteinuria, due to rituximab wasting in the urine. However, rituximab immunomonitoring is not routinely performed. We evaluated the predictive value of serum rituximab levels in patients with pMN three months after rituximab injection (month-3) on clinical remission rates six months (month-6) and 12 months (month-12) after injection and investigated predictive factors for serum rituximab levels at month-3. Sixty-eight patients treated with rituximab between July 2015 and January 2020 from two French nephrology centers were included. We identified residual rituximab levels at month-3 as a novel early predictor of remission at month-6 (p <0.0001) and month-12 (p = 0.001). Reduced likelihood of remission in patients with undetectable rituximab at month-3 was associated with lower serum albumin and higher anti-PLA2R1 titers at baseline and with lower serum albumin, higher proteinuria, higher CD19+ counts and higher anti-PLA2R1 titers during follow-up. In multivariate analysis, high baseline proteinuria and undetectable rituximab levels at month-3 were independent risk factors for treatment failure at month-6 and high baseline weight and undetectable rituximab levels at month-3 were independent risk factors for treatment failure at month-12. We identified serum albumin at baseline as a predictive factor for serum rituximab levels at month-3. Patients with serum albumin below 22.5 g/L at baseline had an 8.66-fold higher risk of having undetectable rituximab levels at month-3. Therefore, rituximab immunomonitoring in pMN patients treated with rituximab would allow the detection of patients at risk of treatment failure as early as month-3. Studies are needed to assess whether patients with low residual rituximab levels at month-3 may benefit from an early additional course of rituximab.

Development, Validation, and Comparison of Two Mass Spectrometry Methods (LC-MS/HRMS and LC-MS/MS) for the Quantification of Rituximab in Human Plasma.

Rituximab is a chimeric immunoglobulin G1-kappa (IgG1κ) antibody targeting the CD20 antigen on B-lymphocytes. Its applications are various, such as for the treatment of chronic lymphoid leukemia or non-Hodgkin's lymphoma in oncology, and it can also be used in the treatment of certain autoimmune diseases. Several studies support the interest in therapeutic drug monitoring to optimize dosing regimens of rituximab. Thus, two different laboratories have developed accurate and reproductive methods to quantify rituximab in human plasma: one using liquid chromatography quadripolar tandem mass spectrometer (LC-MS/MS) and the other, liquid chromatography orbitrap tandem mass spectrometer (LC-MS/HRMS). For both assays, quantification was based on albumin depletion or IgG-immunocapture, surrogate peptide analysis, and full-length stable isotope-labeled rituximab. With LC-MS/MS, the concentration range was from 5 to 500 µg/mL, the within- and between-run precisions were <8.5%, and the limit of quantitation was 5 µg/mL. With LC-MS/HRMS, the concentration range was from 10 to 200 µg/mL, the within- and between-run accuracy were <11.5%, and the limit of quantitation was 2 µg/mL. Rituximab plasma concentrations from 63 patients treated for vasculitis were compared. Bland-Altman analysis and Passing-Bablok regression showed the interchangeability between these two methods. Overall, these methods were robust and reliable and could be applied to routine clinical samples.

Simultaneous quantification of rituximab and eculizumab in human plasma by liquid chromatography-tandem mass spectrometry and comparison with rituximab ELISA kits.

OBJECTIVES: Specific and sensitive analytical techniques to quantify therapeutic monoclonal antibodies (mAbs) are required for therapeutic drug monitoring. The quantification of mAbs has been historically performed using enzyme-linked immunosorbent assays (ELISAs), for which the limitations in terms of specificity have led to the development of alternative analytical strategies. METHODS: Here, we describe the validation of a liquid chromatography tandem mass-spectrometry (LC-MS/MS) method for the simultaneous quantification of rituximab (RTX - anti-CD20) and eculizumab (ECU - anti-C5). Sample preparation was based on our previously published method, using protein G purification and trypsin digestion. A new specific peptide for RTX, containing an N-terminal pyroglutamine and a trypsin miss-cleavage, enables better sensitivity, while peptide of ECU was chosen thanks to an in silico trypsin digestion and the Skyline® software. Full-length stable-isotope-labeled adalimumab was added to plasma samples as an internal standard. RTX in 50 human serum samples was quantified by LC-MS/MS and the concentrations obtained compared to those obtained with two commercial ELISA kits (Lisa Tracker® and Promonitor®). RESULTS: Calibration curves were linear from 1 to 200 µg.mL-1 for RTX and 5 to 200 µg.mL-1 for ECU, and within-day and between-day accuracy and precision fulfilled Food and Drug Administration validation criteria. Comparison of the LC-MS/MS method with ELISA showed a negligible bias with the Lisa Tracker® kit (4%), but significant bias with the Promonitor® assay (mean underestimation of 69% for the Promonitor® assay). CONCLUSIONS: This new LC-MS/MS method allows the simultaneous quantification of RTX and ECU in human samples and could be used for therapeutic drug monitoring.

A phase II Japanese trial of fludarabine, cyclophosphamide and rituximab for previously untreated chronic lymphocytic leukemia.

OBJECTIVE: Fludarabine, cyclophosphamide and rituximab (FCR) is the standard regimen for fit patients with untreated CD20-positive chronic lymphocytic leukemia (CLL). However, this combination is unavailable in Japan because rituximab is not approved for CLL. We investigated the efficacy and safety of FCR in this single-arm, multicenter study designed as a bridging study to the CLL8 study by the German CLL Study Group. METHODS: The study enrolled previously untreated patients with CLL of Binet stage B or C with active disease. Patients with a Cumulative Illness Rating Scale score of ≤6 and creatinine clearance of ≥70 ml/min were eligible. Patients received 6 cycles of FCR every 28 days and were followed for up to 1 year. RESULTS: Seven patients were enrolled. The best overall response rate according to the 1996 NCI-WG Guidelines, the primary endpoint of the study, was 71.4% (95% confidence interval, 29.0-96.3%), with one patient achieving complete response. No deaths or progression occurred during follow-up. The main adverse event was hematotoxicity. CD4-positive T-cell count decreased in all patients; most patients showed no reduction in serum immunoglobulin G. CONCLUSION: Although the number of patients was limited, FCR appears to be effective with manageable toxicity for treatment-naïve fit Japanese patients with CD20-positive CLL. CLINICAL TRIAL NUMBER: JapicCTI-132285.

A Randomized, Double-Blind Study Comparing Pharmacokinetics and Pharmacodynamics of Proposed Biosimilar ABP 798 With Rituximab Reference Product in Subjects With Moderate to Severe Rheumatoid Arthritis.

ABP 798 is a proposed biosimilar to rituximab reference product (RP), an anti-CD20 monoclonal antibody. Pharmacokinetics (PK), pharmacodynamics (PD), and safety results from the comparative clinical study that evaluated the PK, PD, safety, efficacy, and immunogenicity of ABP 798 versus rituximab RP are presented here. Subjects with moderate to severe rheumatoid arthritis (RA) received 2 doses of ABP 798, United States-sourced RP (rituximab US) or European Union-sourced RP (rituximab EU), each consisting of two 1000-mg infusions 2 weeks apart. For the second dose (week 24), ABP 798- and rituximab EU-treated subjects received the same treatment; rituximab US-treated subjects transitioned to ABP 798. End points included area under the serum concentration-time curve from time 0 extrapolated to infinity and maximum observed serum concentration following the second infusion of the first dose (PK) and percentage of subjects with complete CD19+ cell depletion days 1-33 (PD). Primary analysis established PK similarity between ABP 798 and rituximab RP based on 90% confidence intervals of the adjusted geometric mean ratios being within a prespecified equivalence margin of 0.8 and 1.25. Complete CD19+ B-cell depletion on day 3 among groups confirmed PD similarity. These findings demonstrated PK/PD similarity between ABP 798 and rituximab RP in subjects with moderate to severe RA.

Pharmacokinetics and safety of IBI301 versus rituximab in patients with CD20+ B-cell lymphoma: a multicenter, randomized, double-blind, parallel-controlled study.

This multicenter, randomized, double-blind, parallel-controlled trial aimed to compare the pharmacokinetics (PK) of IBI301 with rituximab in patients with CD20-positive (CD20+) B-cell lymphoma, who achieved a complete response/unconfirmed complete response after standard treatments. Patients were randomized (1:1) to receive IBI301 or rituximab (375 mg/m2, IV). Patients who continuously benefitted from the trial after the PK phase underwent the extension phase to receive up to three cycles of 3-month-cycle of rituximab/IBI301 maintenance therapy. PK was described using the area under the serum concentration-time curve from time zero to infinity (AUC0-inf), AUC from time zero to last quantifiable concentration (AUC0-t), and maximum serum concentration (Cmax). Pharmacodynamics (PD), incidence of adverse events and immunogenicity were evaluated. PK was defined equivalent, if 90% confidence intervals (CIs) for geometric mean ratios of PK endpoints fell within the margin of 0.8-1.25. Overall, 181 patients were enrolled in IBI301 (n = 89) and rituximab (n = 92) groups. Geometric mean ratios of AUC0-inf, AUC0-t, and Cmax were 0.91 (90% CI 0.85, 0.97), 0.91 (90% CI 0.86, 0.97), and 0.96 (90% CI 0.92, 1.01) between treatment groups, all within the bioequivalence range. Peripheral CD19+ and CD20+ B-cell counts were similar at each prespecified time point between the groups. No difference in immunogenicity was observed. The incidences of treatment-emergent adverse events (84.3% vs. 83.5%) and treatment-related AEs (56.2% vs. 61.5%) were comparable (IBI301 vs. rituximab). IBI301 was PK bioequivalent to rituximab in patients with CD20+ B-cell lymphoma. The PD, safety, and immunogenicity profiles of IBI301 were similar to those of rituximab.

DSA-FXM: Accelerated Donor-specific Flow Crossmatch Discriminating Class I and II Antibody Specifically and Only to Donor HLA for Determining True Incompatibility.

BACKGROUND: Worldwide, a final crossmatch is the gold standard for determining compatibility between patient and donor before solid organ transplantation and preventing hyperacute rejection. In the absence of autoantibodies, an incompatible crossmatch in a sensitized patient is attributed to mismatched donor HLA. However, current physical crossmatch methods cannot distinguish reactivity to HLA from other clinically irrelevant cell surface targets nor the class of HLA if it is the target. Result interpretation is difficult or impossible when autoantibodies, alloantibodies, or therapeutic antibodies coexist. METHODS: Herein, we describe a unique donor-specific flow crossmatch (DSA-FXM) that distinguishes HLA class I or II donor-specific antibody bound to HLA antigens on the donor cell surface in their native conformation that is not impacted by rituximab, anti-thymocyte globulin (after absorption), or autoantibodies. It is HLA specific. RESULTS: We compared the results of single-antigen antibody testing, autoreactive and alloreactive flow cytometry crossmatches (FXM) using traditional FXM and our DSA-FXM method from 94 patients (enriched for auto+/allo+ pairs; n = 64) against 110 donors (338 tests) and show that, in our cohort, positive traditional FXM results are not directed to donor HLA 60.25% of the time and negative traditional FXM results are missing HLA donor-specific antibody 36.2% of the time based on the DSA-FXM. CONCLUSIONS: We demonstrate that the DSA-FXM is able to define categorically distinct and clinically important HLA antibody profiles in half the time required for the standard FXM, potentially shortening cold ischemia time and providing clinicians with unambiguous essential information regarding HLA compatibility when time is critical.

Randomized, Double-Blind, Pharmacokinetic Equivalence Trial Comparing DRL-Rituximab With MabThera in Patients With Diffuse Large B-Cell Lymphoma.

PURPOSE: We sought to compare the pharmacokinetics (PKs) of DRL-rituximab (DRL_RI; potential biosimilar) and innovator rituximab MabThera (Roche, Grenzach-Wyhlen, Germany; reference medicinal product [RMP]) in patients with diffuse large B-cell lymphoma (DLBCL). Efficacy, pharmacodynamics (PDs), safety, and immunogenicity were also compared. PATIENTS AND METHODS: We conducted a double-blind, parallel-group study in patients with untreated DLBCL who were eligible to receive cyclophosphamide, doxorubicin, vincristine, and prednisone (CHOP) therapy. Patients were randomly assigned at a one-to-one ratio to receive DRL_RI or RMP for six 21-day cycles of rituximab plus CHOP, with 18 months of follow-up after day 1, cycle 6 (C6). Primary end point was C1 PKs, measured as area under the plasma concentration-time curve from day 0 to 21 (AUC0-21 days) and maximum plasma concentration (Cmax). Equivalence was defined as 90% CIs for the DRL_RI/RMP geometric mean ratios (GMRs) within 80% and 125%. Secondary end points included efficacy noninferiority measured by objective response rate (ORR) at C6 and event-free survival and overall survival at 87 weeks, PK equivalence at C6 and PD equivalence (rate of B-cell depletion and repletion), safety, and immunogenicity. The trial was stopped after sufficient patients for primary end point evaluation were enrolled. Secondary end points are reported as observed. RESULTS: A total of 151 patients were randomly assigned (DRL_RI, n = 76; RMP, n = 75). DRL_RI/RMP GMRs for AUC0-21 days and Cmax in C1 were 99.77 (90% CI, 87.60 to 113.63) and 96.19 (90% CI, 88.65 to 104.38), respectively. ORR at C6 for DRL_RI and RMP were 82.0% and 84.8%, respectively. Rates of B-cell depletion/repletion, immunogenicity, and adverse events were comparable in both groups. CONCLUSION: DRL_RI and RMP had equivalent PKs, with comparable efficacy, PDs, safety, and immunogenicity.

CD4+ count-dependent concentration-effect relationship of rituximab in rheumatoid arthritis.

AIMS: Rituximab is approved in rheumatoid arthritis (RA). A substantial decrease in CD4+ count was observed in responders after a single cycle of treatment. This study aimed to describe and quantifying the influence of CD4+ count depletion on the concentration-response relationship of rituximab in RA patients. METHODS: In this retrospective monocentric observational study, 52 patients were assessed. Repeated measurements of rituximab concentrations (pharmacokinetics), CD4+ counts (biomarker) and disease activity score in 28 joints (DAS28, clinical response) were made. Rituximab pharmacokinetics was described using a 2-compartment model, and CD4+ cell counts and DAS28 measurements were described using indirect turnover and direct Emax pharmacokinetic-pharmacodynamic models, respectively. Delay between rituximab concentrations and responses was accounted for by including biophase compartments. RESULTS: Elimination half-life of rituximab was 18 days. The pharmacokinetic-pharmacodynamic model showed that DAS28 response to rituximab was partly associated with CD4+ cell depletion. At 6 months, a deeper DAS28 decrease was observed in patients when CD4+ cell count is decreased: median [interquartile range] of DAS28 was 3.7 [2.9-4.4] and 4.5 [3.7-5.3] in patients with and without CD4+ decrease, respectively. CONCLUSIONS: This is the first study to quantify the relationship between rituximab concentrations, CD4+ count and DAS28 in RA patients. This model showed that approximately 75% of patients had CD4+ count decrease, and that the clinical improvement is 2-fold higher in patients with CD4+ cells decrease than in others.

High-Dose Rituximab and Early Remission in PLA2R1-Related Membranous Nephropathy.

BACKGROUND AND OBJECTIVES: Different rituximab protocols are used to treat membranous nephropathy. We compared two rituximab protocols in patients with membranous nephropathy. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Twenty-eight participants from the NICE cohort received two infusions of 1-g rituximab at 2-week intervals, whereas 27 participants from the Prospective Randomized Multicentric Open Label Study to Evaluate Rituximab Treatment for Membranous Nephropathy (GEMRITUX) cohort received two infusions of 375 mg/m2 at 1-week interval. We measured serum rituximab levels and compared remission at month 6 and before any treatment modification and analyzed factors associated with remission and relapses. RESULTS: Remissions occurred in 18 (64%) versus eight (30%) from the NICE and GEMRITUX cohort (P=0.02) at month 6, respectively, and in 24 (86%) versus 18 (67%) participants (P=0.12) before treatment modification, respectively. Median time to remission was 3 [interquartile range (IQR), 3-9] and 9 [IQR, 6-12] months for NICE and GEMRITUX cohorts respectively (P=0.01). Participants from the NICE cohort had higher circulating level of rituximab and lower CD19 counts (3.3 µg/L [IQR, 0.0-10.8] versus 0.0 [IQR, 0.0-0.0] P<0.001 and 0.0 [IQR, 0.0-2.0] versus 16.5 [IQR, 2.5-31.0] P<0.001) at month 3, lower level of anti-PLA2R1 antibodies at month 6 (0.0 [IQR, 0.0-8.0] versus 8.3 [IQR, 0.0-73.5] P=0.03). In the combined study population, lower epitope spreading at diagnosis and higher rituximab levels at month 3 were associated with remissions at month 6 (13/26 (50%) versus 22/29 (76%) P=0.05 and 2.2 µg/ml [IQR, 0.0-10.9] versus 0.0 µg/ml [IQR, 0.0-0.0] P<0.001 respectively). All non-spreaders entered into remission whatever the protocol. Eight of the 41 participants who reached remission had relapses. Epitope spreading at diagnosis (8/8 (100%) versus 16/33 (48%) P=0.01) and incomplete depletion of anti-PLA2R1 antibodies at month 6 (4/8 (50%) versus 5/33 (9%) P=0.05) were associated with relapses. CONCLUSIONS: Our work suggests that higher dose rituximab protocol is more effective on depletion of B-cells and lack of epitope spreading is associated with remission of membranous nephropathy.

Rituximab Exhibits Altered Pharmacokinetics in Patients With Membranous Nephropathy.

BACKGROUND: Rituximab (RTX) is a chimeric monoclonal anti-CD20 antibody used off-label in the treatment of membranous nephropathy (MN). Unfortunately, limited information is available on the pharmacokinetics of therapeutic proteins such as RTX in patients with glomerular kidney diseases. OBJECTIVE: The current study evaluated RTX pharmacokinetics in patients with MN (n = 20) who received 4 RTX weekly intravenous infusions (375 mg/m2) over a month, with a repeat of the identical treatment at 6 months. Baseline patient characteristics were gender (17 male/3 female), age (49 ± 13 years), and body surface area (2.2 ± 0.24 m2). METHODS: Compartmental pharmacokinetic analyses were conducted using Phoenix, and comparisons of these parameters were made between the MN patients and published data from 2 reference populations without kidney diseases (follicular lymphoma and autoimmune disorders). RESULTS: Patients with MN exhibited a shorter half-life, reduced volume of central compartment, decreased area under the serum concentration-time curve (exposure), and increased RTX clearance from the central compartment versus previous reports in the reference patient populations. CONCLUSIONS AND RELEVANCE: These results suggest that shorter half-life and lower exposures to RTX in patients with MN may necessitate higher doses and/or changes to dosing frequency to optimize the relationships between serum concentrations and therapeutic effects.

Improved flow cytometry crossmatching in kidney transplantation.

Flow cytometry crossmatching (FC-XM) assay is the most sensitive cell-based method for detecting donor-specific antibodies (DSAs). However, the use of FC-XM remains limited by methodological and clinical variations. This basic assay cannot discriminate between complement-fixing and noncomplement-fixing antibodies. FC-XM also detects patient all antibodies bound to donor cells and not only DSAs against to HLA molecules. Pretest factors associated with a donor's medical care can affect test results by changing the number, viability and target on lymphocytes (such as rituximab on CD20+ B-cells). Assay adjustment can be performed to improve the sensitivity and specificity of FC-XM. Pronase treatment (0.5-1 mg/mL) prevents false-positive B-cell FC-XM due to nonspecific immunoglobulin binding by Fc receptors and binding of surface immunoglobulins onto the surface of B-cells. Pronase treatment (2 mg/mL) or a serum incubation step with an anti-rituximab monoclonal antibody (Ab) prevents the interference induced by rituximab therapy. The use of 7 aminoactinomycin-D (7-AAD) or fluorochrome-conjugated C4d Ab, after complement incubation, allows complement-fixing antibodies to be distinguished from noncomplement-fixing antibodies. The use of donor endothelial precursor cells as target cells allows the detection of nonmajor histocompatibility complex Ab-binding endothelial cells. However, lymphocyte crossmatches still had some limits in specificity and sensitivity. This implies that this assay must be interpreted with the virtual crossmatch.

Evaluation of the Effects of Animal Growth and Previous Exposure on the Pharmacokinetics of Rituximab in Rats.

With a long half-life, pharmacokinetic (PK) evaluation of monoclonal antibodies in rodents lasts multiple weeks during which the animals may grow significantly. We evaluated the impact of weight, age, and previous drug exposure on the PK of rituximab. Serum concentrations of rituximab were measured after intravenous and subcutaneous dosing in Sprague Dawley rats aged between 7 and 21 weeks and weighing between 200 and 600 g. The growth of rats during the study was incorporated into the model through the increase of the volumes of compartments in relation to the rats total body weight. The final model successfully captured all the data; and no difference was observed in the rituximab PK profiles between exposure naïve and redosed or young and older rats. Incorporating the rodent growth over the time course of the study into the PK model was shown to be important for providing a more physiological description of the disposition of rituximab, especially when young and rapidly growing animals are used. Redosing the same rats with monoclonal antibodies might be a viable strategy for reducing the use of laboratory animals in accordance with the 3R principles.

Dual-Color Bioluminescent Sensor Proteins for Therapeutic Drug Monitoring of Antitumor Antibodies.

Monitoring the levels of therapeutic antibodies in individual patients would allow patient-specific dose optimization, with the potential for major therapeutic and financial benefits. Our group recently developed a new platform of bioluminescent sensor proteins (LUMABS; LUMinescent AntiBody Sensor) that allow antibody detection directly in blood plasma. In this study, we targeted four clinically important therapeutic antibodies, the Her2-receptor targeting trastuzumab, the anti-CD20 antibodies rituximab and obinutuzumab, and the EGFR-blocking cetuximab. A strong correlation was found between the affinity of the antibody binding peptide and sensor performance. LUMABS sensors with physiologically relevant affinities and decent sensor responses were obtained for trastuzumab and cetuximab using mimotope and meditope peptides, respectively, with affinities in the 10-7 M range. The lower affinity of the CD20-derived cyclic peptide employed in the anti-CD20 LUMABS sensor ( Kd = 10-5 M), translated in a LUMABS sensor with a strongly attenuated sensor response. The trastuzumab and cetuximab sensors were further characterized with respect to binding kinetics and their performance in undiluted blood plasma. For both antibodies, LUMABS-based detection directly in plasma compared well to the analytical performance of commercial ELISA kits. Besides identifying important design parameters for the development of new LUMABS sensors, this work demonstrates the potential of the LUMABS platform for point-of-care detection of therapeutic antibodies.

Optimization of rituximab for the treatment of DLBCL: increasing the dose for elderly male patients.

Male sex is associated with unfavourable pharmacokinetics and prognosis in elderly patients with diffuse large B-cell lymphoma (DLBCL). We investigated higher rituximab doses for elderly male DLBCL patients. Elderly patients (61-80 years) received 6 cycles CHOP-14 (cyclophosphamide, doxorubicin, vincristine and prednisone at 14-day intervals) and were randomized to 8 cycles rituximab (males 500 mg/m2 , females 375 mg/m2 ) every 2 weeks or according to an upfront dose-dense schedule. In 268 (120 females, 148 males) no difference between the standard and the upfront dose-dense rituximab schedule was found (3-year PFS 72% vs. 74%; OS 74% vs. 77%; P = 0.651). The 500 mg/m2 dose of rituximab for male patients was associated with serum levels and exposure times slightly better than in females and a male/female hazard ratio of 0.9 for progression-free survival (PFS) and 0.8 for overall survival. For elderly males, 500 mg/m2 was not more toxic than 375 mg/m2 rituximab, but improved PFS by 32.5% (P = 0.039), with a trend for a (30%) better overall survival (P = 0.076) in a planned subgroup analysis adjusting for International Prognostic Index risk factors. We conclude that the higher rituximab dose for elderly male patients abrogated the adverse prognosis of male sex without increasing toxicity. In the era of personalized medicine, sex-specific pharmacokinetics and toxicities should be investigated for all drugs where these parameters impact on outcome.

Time-Dependent Structural Alteration of Rituximab Analyzed by LC/TOF-MS after a Systemic Administration to Rats.

Therapeutic monoclonal antibodies (mAbs) have heterogeneities in their structures. Multiple studies have reported that the variety of post-translational modifications could affect the pharmacokinetic profiles or pharmacological potencies of therapeutic mAbs. Taking into the account that the structural modification of mAbs would affect the efficacy, it is worth investigating the structural alteration of therapeutic mAbs in the blood and the relationship between their structures and pharmacological effects. Herein, we have developed the method to isolate rituximab from plasma in which endogenous IgGs interfere the detection of rituximab, and successfully developed the analytical method with a liquid chromatograph time-of-flight mass spectrometer to detect the structure of rituximab in plasma with errors less than 30 parts per millions. Eight types of carbohydrate chains in rituximab were detected by this method. Interestingly, time-dependent changes in carbohydrate chains such as AAF (G2F) and GnGn (G0) were observed in rats, although the amino acids were stable. Additionally, these structural changes were observed via incubation in plasma as in the rat experiment, suggesting that a certain type of enzyme in plasma caused the alterations of the carbohydrate chains. The present analytical methods could clarify the actual pharmacokinetics of therapeutic mAbs, and help to evaluate the interindividual variations in pharmacokinetics and efficacy.

Influence of FCGR3A-158V/F Genotype and Baseline CD20 Antigen Count on Target-Mediated Elimination of Rituximab in Patients with Chronic Lymphocytic Leukemia: A Study of FILO Group.

BACKGROUND AND OBJECTIVES: Rituximab is an anti-CD20 monoclonal antibody approved in the first-line treatment of patients with chronic lymphocytic leukemia (CLL). Rituximab pharmacokinetics shows a time dependency possibly related to changes in the target antigen amount over time. The purpose of this study was to quantify the influence of both CD20 antigenic mass and the FcγRIIIA genetic polymorphism on rituximab pharmacokinetics in CLL. METHODS: Rituximab pharmacokinetics was described in 118 CLL patients using a semi-mechanistic model including a latent target antigen turnover, which allowed the estimation of rituximab target-mediated elimination in addition to the endogenous clearance. RESULTS: Target-mediated elimination rate constant increased with the baseline CD20 count on circulating B cells (p = 0.00046) and in patients with the FCGR3A-158VV genotype (p = 0.0016). Physiologic elimination of antigen was lower in the Binet C disease stage (p = 0.00018). The effects of these covariates on rituximab concentrations were mainly visible at the beginning of treatment. Body surface area also increased central and peripheral volumes of distribution (p = 1.3 × 10-5 and 0.0015, respectively). CONCLUSIONS: A pharmacokinetic model including target-mediated elimination accurately described rituximab concentrations in CLL and showed that rituximab 'consumption' (target-mediated elimination) increases with increasing baseline antigen count on circulating B cells and in FCGR3A-158VV patients. CLINICAL TRIAL REGISTRATION: NCT01370772.

Using Mass Spectrometry to Quantify Rituximab and Perform Individualized Immunoglobulin Phenotyping in ANCA-Associated Vasculitis.

Therapeutic monoclonal immunoglobulins (mAbs) are used to treat patients with a wide range of disorders including autoimmune diseases. As pharmaceutical companies bring more fully humanized therapeutic mAb drugs to the healthcare market analytical platforms that perform therapeutic drug monitoring (TDM) without relying on mAb specific reagents will be needed. In this study we demonstrate that liquid-chromatography-mass spectrometry (LC-MS) can be used to perform TDM of mAbs in the same manner as smaller nonbiologic drugs. The assay uses commercially available reagents combined with heavy and light chain disulfide bond reduction followed by light chain analysis by microflow-LC-electrospray ionization-quadrupole-time-of-flight mass spectrometry (ESI-Q-TOF MS). Quantification is performed using the peak areas from multiply charged mAb light chain ions using an in-house developed software package developed for TDM of mAbs. The data presented here demonstrate the ability of an LC-MS assay to quantify a therapeutic mAb in a large cohort of patients in a clinical trial. The ability to quantify any mAb in serum via the reduced light chain without the need for reagents specific for each mAb demonstrates the unique capabilities of LC-MS. This fact, coupled with the ability to phenotype a patient's polyclonal repertoire in the same analysis further shows the potential of this approach to mAb analysis.

Validated LC/MS Bioanalysis of Rituximab CDR Peptides Using Nano-surface and Molecular-Orientation Limited (nSMOL) Proteolysis.

Presently, monoclonal antibodies (mAbs) therapeutics have big global sales and are starting to receive competition from biosimilars. We previously reported that the nano-surface and molecular-orientation limited (nSMOL) proteolysis which is optimal method for bioanalysis of antibody drugs in plasma. The nSMOL is a Fab-selective limited proteolysis, which utilize the difference of protease nanoparticle diameter (200 nm) and antibody resin pore diameter (100 nm). In this report, we have demonstrated that the full validation for chimeric antibody Rituximab bioanalysis in human plasma using nSMOL proteolysis. The immunoglobulin fraction was collected using Protein A resin from plasma, which was then followed by the nSMOL proteolysis using the FG nanoparticle-immobilized trypsin under a nondenaturing condition at 50°C for 6 h. After removal of resin and nanoparticles, Rituximab signature peptides (GLEWIGAIYPGNGDTSYNQK, ASGYTFTSYNMHWVK, and FSGSGSGTSYSLTISR) including complementarity-determining region (CDR) and internal standard P14R were simultaneously quantified by multiple reaction monitoring (MRM). This quantification of Rituximab using nSMOL proteolysis showed lower limit of quantification (LLOQ) of 0.586 µg/mL and linearity of 0.586 to 300 µg/mL. The intra- and inter-assay precision of LLOQ, low quality control (LQC), middle quality control (MQC), and high quality control (HQC) was 5.45-12.9% and 11.8, 5.77-8.84% and 9.22, 2.58-6.39 and 6.48%, and 2.69-7.29 and 4.77%, respectively. These results indicate that nSMOL can be applied to clinical pharmacokinetics study of Rituximab, based on the precise analysis.

The effects of intrathecal rituximab on biomarkers in multiple sclerosis.

OBJECTIVES: Clinical trials of IV-rituximab have proved successful. It is unclear whether intrathecal (IT)-rituximab is more efficacious at lower doses. We examine its effects on B-cell biomarkers. METHODS: MS patients received IT-rituximab at 3 time-points. CSF and serum samples were obtained at up to 5 time-points (days 0, 7, 14, 56 and 112). Serum and CSF BAFF and CXCL13, and CSF kappa and lambda free light chains (FLC) were measured. Flow cytometry was performed, examining effects on lymphocytes, CD3-19+ and CD3-20+ cells. RESULTS: CSF BAFF fell following rituximab (p=0.0091 absolute values, p=0.0284 change from baseline) whilst serum BAFF increased across time-points 1-4 (p=0.0005 absolute values, p=0.0017 change from baseline). There were significant reductions in CD20+ and CD19+ cells in blood from baseline (p<0.0001) but not in CSF. CSF kappa FLC levels significantly increased (p=0.0480). CONCLUSIONS: BAFF levels fall in CSF but increase in serum following IT-rituximab. Rituximab appears to act peripherally with dramatic decreases in peripheral CD20+ and CD19+ cells. It is likely that CSF B-cell counts were too low to enable differences to be seen. The rapid reduction in B-cells suggests rituximab has immediate effects. The profound depletion of B-cells, despite low doses of rituximab, underlines rituximab's efficacy.