Rituximab pharmacokinetic and pharmacokinetic-pharmacodynamic evaluation based on a study in diffuse large B-cell lymphoma: Influence of tumor size on pharmacokinetic and assessment of pharmacokinetic similarity.

Dr. Reddy's Laboratories rituximab (DRL_RI; Dr. Reddy's Laboratories SA, Basel, Switzerland) is under development as a rituximab biosimilar. Study RI-01-002 (Clinical Trials Registry - India/2012/11/003129), comparing DRL_RI to the reference medicinal product (RMP) MabThera® (Roche, Grenzach-Wyhlen, Germany), demonstrated pharmacokinetic (PK) equivalence and showed comparable pharmacodynamic, efficacy, safety, and immunogenicity profiles. We used data from the same study to perform population PK and PK-pharmacodynamic analyses: first exploring possible factors influencing the PK similarity assessment between products and then performing simulations to investigate the impact of tumor size on rituximab PK. Nonlinear mixed-effects models for PK, tumor size, tumor size-PK, and tumor response were developed independently. The final PK model included drug product as a dose-scaling parameter and predicted a 6.75% higher dose reaching the system in RMP-treated patients. However, when tumor size was included in the tumor size-PK model, the drug product effect was no longer observed. The model rather indicated that patients with larger tumor size have higher clearance. Further simulations confirmed that higher baseline tumor size is associated to slightly lower rituximab exposure. Tumor response, described by a continuous-time Markov model, did not differ between drug products. Both had higher effects during the first 20 weeks of treatment. Also, the model described a subpopulation of nonresponders to treatment (42%) with faster transitions to a worse state. The different rituximab exposure initially detected between drug products (6.75%) was shown using PK/PK-pharmacodynamic analysis to be attributed to a tumor size imbalance between treatment groups. PK/PK-pharmacodynamic analyses may contribute to PK similarity assessments.

A Modified Hybrid Wald's Approximation Method for Efficient Covariate Selection in Population Pharmacokinetic Analysis.

One important objective of population pharmacokinetic (PPK) analyses is to identify and quantify relationships between covariates and model parameters such as clearance and volume. To improve upon existing covariate model development methods including stepwise procedures and Wald's approximation method (WAM), this paper introduces an innovative method named the hybrid first-order conditional estimation (FOCE)/Monte-Carlo parametric expectation maximization (MCPEM)-based Wald's approximation method with backward elimination (BE), or H-WAM-BE. Compared with WAM, this new method uses MCPEM to obtain full covariance matrix after running FOCE to obtain full model parameter estimates, followed by BE to select the final covariate model. Two groups of datasets (simulation datasets and rituximab datasets) were used to compare the performance of H-WAM-BE with two other methods, likelihood ratio test (LRT)-based stepwise covariate method (SCM) and H-WAM with full subset approach (H-WAM-F) in NONMEM. Different scenarios with different sample sizes and sampling schemes were used for simulating datasets. The nominal model was used as the reference to evaluate the three methods for their ability to accurately identify parameter-covariate relationships. The methods were compared using the number of true and false positive covariates identified, number of times that they identified the reference model, computation times, and predictive performance. Best-performing H-WAM-BE methods (M2 and M4) showed comparable results with LRT-based SCM. H-WAM-BE required shorter or comparable computation times than LRT-based SCM and H-WAM-F regardless of the model structure, sample size, or sampling design used in this study.

Low initial trough concentration of rituximab is associated with unsatisfactory response of first-line R-CHOP treatment in patients with follicular lymphoma with grade 1/2.

For follicular lymphoma (FL) with grade 1/2, the complete response (CR) rate of the first-line R-CHOP treatment was significantly low. In this study, we assessed the rationality of the administration of rituximab for FL patients with grade 1/2 based on concentration-response relationship analyses. Thus, we conducted a prospective pharmacokinetic (PK) study in 68 FL patients with grades 1-3 treated with R-CHOP at 21-day intervals. Plasma rituximab concentrations were quantified using ELISA and the population PK modeling was established with Phoenix® NLMETM. The first cycle trough concentration (C1-trough) of rituximab was a significant independent risk factor for achieving CR in matched-pair logistic regression analysis, rather than the concentrations in later cycles; the recommendatory minimum optimal C1-trough was 13.60 µg/mL. Patients with grade 1/2 had significantly lower C1-trough compared with grade 3 (12.21 µg/mL vs. 23.45 µg/mL, P < 0.001), only 30% patients with grade 1/2 could reach 13.60 µg/mL, compared with 91.67% in patients with grade 3, which was in accord with its unsatisfactory CR rates (43.33% vs. 76.32%). The stage indicating the tumor burden (the target) was a crucial influence factor for C1-trough, accounting for 40.70% of its variability, 70% patients with grade 1/2 were stage IV in this study, since the systemic therapy only started at the disseminated disease stage. The initial dose of 1800 mg was recommended by Monte Carlo simulation for patients with grade 1/2. In summary, low C1-trough accounted for low-grade FL's unsatisfactory CR rate, designing the first dosage of rituximab should be a very important component of individualized therapy for FL.

Rituximab in the management of acute lymphoblastic leukemia.

INTRODUCTION: The anti-CD20 chimeric monoclonal antibody rituximab has revolutionized the treatment of B-cell malignancies, significantly improving patient clinical outcome. Recently, some single-group studies have suggested that adding rituximab to chemotherapy can improve the outcome of CD20-positive B-cell acute lymphoblastic leukemia (ALL) patients. Areas covered: An overview of the current insights of rituximab in adult ALL patients is presented here. In particular, we focused on results of multicenter randomized phase III trial (GRAALL-2005 - Group for Research on Adult Acute Lymphoblastic Leukemia) that evaluated the benefit of associating rituximab to chemotherapy in Ph-negative, B-lineage ALL expressing the CD20 antigen. Expert opinion: Data from clinical trials confirm that rituximab enhances the efficacy of chemotherapy without additive toxicity in ALL. However, results of GRAAL 2005 study represent only a modest incremental improvement in the treatment of ALL. Other promising compounds as single agent or in combination with chemotherapy are currently in different stages of clinical development. The GRAALL 2005 study sets the stage for other prospective studies which will further elucidate the role of monoclonal antibodies in the management of ALL.

Comparative assessment of pharmacokinetics, and pharmacodynamics between RTXM83™, a rituximab biosimilar, and rituximab in diffuse large B-cell lymphoma patients: a population PK model approach.

PURPOSE: The main objective was to quantify any potential differences in pharmacokinetic (PK) parameters (AUC and Cmax) between RTXM83, a proposed rituximab biosimilar, and its reference product, using a population PK model approach. METHODS: Rituximab PK and PD data were obtained from a randomized, double-blind, phase III clinical study (RTXM83-AC-01-11) in patients with diffuse large B-cell lymphoma (DLBCL) that received 375 mg/m2 intravenous RTXM83 or its reference product with CHOP regimen, every 3 weeks, for six cycles. Rituximab levels were quantified by Meso Scale Discovery assay. PK analysis was performed using NONMEM 7.3.0. The effect of disease and patient covariates on RXTM83 PK was investigated. Model was evaluated using visual predictive check and non-parametric bootstrap. RESULTS: In total, 251 DLBCL patients (127 and 124 in RXTM83-CHOP and rituximab-CHOP arms, respectively) and 5341 serum concentrations (2703 for RXTM83 and 2638 for rituximab, respectively) were available for the population PK analysis. The volume of distribution of the central compartment (V1) and clearance of RXTM83 were estimated at 3.19 L and 12.5 mL/h, respectively. Body surface area allowed to explain the interindividual variability for V1. A statistical analysis showed that systemic exposure (AUC and Cmax) of RTXM83 was similar to rituximab. The 90% confidence intervals for all pairwise comparisons were within the predefined bioequivalence interval of 0.80-1.25. PD similarity of B-cell depletion and recovery was also observed. CONCLUSIONS: The time course of RTXM83 was well characterized by the model developed. The systemic exposure of RTXM83 and its associated variability were similar to those for rituximab reference in DLBCL patients, demonstrating PK similarity. The PD similarity of RTXM83 and rituximab reference product was also demonstrated.

SMABcare study: subcutaneous monoclonal antibody in cancer care: cost-consequence analysis of subcutaneous rituximab in patients with follicular lymphoma.

Rituximab is used as a standard of care for follicular lymphoma and is usually administered intravenously. A novel subcutaneous formulation recently showed non-inferior efficacy with similar pharmacokinetic and safety profiles compared to intravenous rituximab in patients with follicular lymphoma. This new approach is promising in terms of comfort for patients and time-saving for hospital staff. To evaluate the real-life economic impact of subcutaneous rituximab as maintenance therapy in patients with follicular lymphoma in real life, we conducted a cost-consequence analysis from the hospital's point of view in three French teaching hospitals. Health-related quality of life (EQ-5D-3L) was investigated as well as patients' and nurses' perception. Compared to intravenous rituximab, subcutaneous administration showed an estimated cost-saving of €109.20 per patient per cycle (p < 0.001), 78.6% of which could be attributed to the rituximab cost. Health-related quality of life showed no significant difference between the two groups despite tendencies for greater pain in the subcutaneous group and greater anxiety in the intravenous group. Thus, subcutaneous rituximab had a favorable pharmacoeconomic profile, with clinical efficacy similar to that of intravenous rituximab. The subcutaneous form was preferred by almost all patients, but further consideration should be given to improve the patients' experience: a dedicated day unit with trained medical, nursing, and pharmaceutical staff could be helpful.

Ultra-low dose of rituximab in rheumatoid arthritis: study protocol for a randomised controlled trial.

BACKGROUND: A standard low-dosing schedule of rituximab (RTX; 2 × 500 mg or 1 × 1000 mg) is as effective for active rheumatoid arthritis (RA) as the registered dose (2 × 1000 mg). Moreover, several small uncontrolled studies suggest that even lower-dosed treatment with RTX also leads to good treatment response in patients with RA. Retreatment with such an 'ultra-low' dose RTX in patients who responded well to RTX induction treatment is of special interest, as long-term use of lower RTX doses may lead to shorter infusion duration, lower risk of adverse events and lower costs. However, the effect of ultra-low dose of RTX has not been investigated using a controlled trial of proper design and dimensions. METHODS/DESIGN: REDO is an investigator driven six-month pragmatic, double-blind, randomised controlled non-inferiority trial on the effects of ultra-low-dose RTX (1 × 500 or 1 × 200 mg) compared to standard low dose (1 × 1000 mg) in RA patients who are being retreated with RTX. A total of 140 RA patients, having reached low disease activity (DAS28CRP < 2.9) after the previous RTX infusion and DAS28CRP < 3.5 at moment of retreatment, are randomised in a ratio of 1:2:2 to 1 × 1000 mg, 1 × 500 mg or 1 × 200 mg. The primary objective is testing non-inferiority of the ultra-low-dose vs. standard low-dose RTX, by comparing mean change in DAS28CRP from baseline to six months to the non-inferiority margin of 0.6. Secondary outcomes over the same period are: function; quality of life; safety; costs; and pharmacokinetics and dynamics as process measures. DISCUSSION: This study protocol shares characteristics of both early dose finding trials as well as late pragmatic clinical studies. Several choices in the design of this trial are described and possible consequences for RA treatment and expected biosimilar introduction are discussed. TRIAL REGISTRATION: Dutch Trial Register, NTR6117 . Registered on 15 November 2016 (CMO NL57520.091.16 , 8 November 2016).

Realistic multi-cellular dosimetry for 177Lu-labelled antibodies: model and application.

Current preclinical dosimetric models often fail to take account of the complex nature of absorbed dose distribution typical of in vitro clonogenic experiments in targeted radionuclide therapy. For this reason, clonogenic survival is often expressed as a function of added activity rather than the absorbed dose delivered to cells/cell nuclei. We designed a multi-cellular dosimetry model that takes into account the realistic distributions of cells in the Petri dish, for the establishment of survival curves as a function of the absorbed dose. General-purpose software tools were used for the generation of realistic, randomised 3D cell culture geometries based on experimentally determined parameters (cell size, cell density, cluster density, average cluster size, cell cumulated activity). A mixture of Monte Carlo and analytical approaches was implemented in order to achieve as accurate as possible results while reducing calculation time. The model was here applied to clonogenic survival experiments carried out to compare the efficacy of Betalutin®, a novel 177Lu-labelled antibody radionuclide conjugate for the treatment of non-Hodgkin lymphoma, to that of 177Lu-labelled CD20-specific (rituximab) and non-specific antibodies (Erbitux) on lymphocyte B cells. The 3D cellular model developed allowed a better understanding of the radiative and non-radiative processes associated with cellular death. Our approach is generic and can also be applied to other radiopharmaceuticals and cell distributions.

Comparative assessment of clinical response in patients with rheumatoid arthritis between PF-05280586, a proposed rituximab biosimilar, and rituximab.

AIMS: To evaluate potential differences between PF-05280586 and rituximab sourced from the European Union (rituximab-EU) and USA (rituximab-US) in clinical response (Disease Activity Score in 28 Joints [DAS28] and American College of Rheumatology [ACR] criteria), as part of the overall biosimilarity assessment of PF-05280586. METHODS: A randomised, double-blind, pharmacokinetic similarity trial was conducted in patients with active rheumatoid arthritis refractory to anti-tumour necrosis factor therapy on a background of methotrexate. Patients were treated with 1000 mg of PF-05280586, rituximab-EU or rituximab-US on days 1 and 15 and followed over 24 weeks for pharmacokinetic, clinical response and safety assessments. Key secondary end points were the areas under effect curves for DAS28 and ACR responses. Mean differences in areas under effect curves were compared against respective reference ranges established by observed rituximab-EU and rituximab-US responses using longitudinal nonlinear mixed effects models. RESULTS: The analysis included 214 patients. Demographics were similar across groups with exceptions in some baseline disease characteristics. Baseline imbalances and group-to-group variation were accounted for by covariate effects in each model. Predictions from the DAS28 and ACR models tracked the central tendency and distribution of observations well. No point estimates of mean differences were outside the reference range for DAS28 or ACR scores. The probabilities that the predicted differences between PF-05280586 vs. rituximab-EU or rituximab-US lie outside the reference ranges were low. CONCLUSIONS: No clinically meaningful differences were detected in DAS28 or ACR response between PF-05280586 and rituximab-EU or rituximab-US as the differences were within the pre-specified reference ranges. TRIAL REGISTRATION NUMBER: NCT01526057.