Feasibility and safety of tailored dosing schedule for eculizumab based on therapeutic drug monitoring: Lessons from a prospective multicentric study

High-throughput, low-cost quantification of 11 therapeutic antibodies using caprylic acid precipitation and LC-MS/MS

BACKGROUND

Therapeutic drug monitoring of treatment with therapeutic antibodies is hampered by the application of a wide range of different methods in the quantification of serum levels. LC-MS based methods could significantly improve comparability of results from different laboratories, but such methods are often considered complicated and costly. We developed a method for LC-MS/MS based quantification of 11 therapeutic antibodies concomitantly measured in a single run, with emphasis on simplicity in sample preparation and low cost.

RESULTS

After a single-step sample purification using caprylic acid precipitation to remove interfering proteins, the sample underwent proteolysis followed by LC-MS/MS analysis. Infliximab is used as internal standard for sample preparation while isotope-labeled signature peptides identified for each analyte are internal standards for the LC-MS/MS normalization. The method was validated according to recognized guidelines, and pipetting steps can be performed by automated liquid handling systems. The total precision of the method ranged between 2.7 and 7.3 % (5.1 % average) across the quantification range of 4-256 μg/ml for all 11 drugs, with an average accuracy of 96.3 %. Matrix effects were xamined in 55 individual patient samples instead of the recommended 6, and 147 individual patient samples were screened for interfering compounds.

SIGNIFICANCE AND NOVELTY

Our method for simultaneous quantification of 11 t-mAb in human serum allows an unprecedented integration of robustness, speed and reduced complexity, which could pave the way for uniform use in research projects and clinical settings alike. In addition, the first LC-MS protocol for signature peptide-based quantification of durvalumab is described. This high throughput method can be readily adapted to a drug panel of choice.

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.

[Translated article] Pharmacokinetics of eculizumab in adult and pediatric patients with atypical hemolytic uremic syndrome and C3 glomerulopathy

OBJECTIVE

The objective of the study was to analyze and describe the concentrations of eculizumab and the complement blockade in patients with atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy, and to define a therapeutic margin where there is a high probability of achieving therapeutic efficacy.

METHODS

Observational, ambispective, and multicenter study that included adult and pediatric patients diagnosed with aHUS and C3 glomerulopathy from September 2020 to October 2022 in 5 hospitals in Spain. Eculizumab was administered at the doses recommended by the data sheet according to the European Medicines Agency (EMA). Pre- and post-dose concentrations of eculizumab were determined, as well as blockade of the classical complement pathway (CH50). Sociodemographic and clinical data were collected, and pharmacokinetic parameters were calculated. To establish the cut-off point for eculizumab concentrations that predicted complement blockade, Receiver Operating Characteristic (ROC) curve analysis was performed. Lastly, the Kruskal-Wallis test was used to contrast the differences in different parameters according to eculizumab concentrations.

RESULTS

Twenty-five patients were included, 19 adults (76.0%) and 6 pediatrics (24.0%), with median ages of 43.4 (interquartile range (IQR) 35.7-48.8) and 10.1 (IQR 9.6-11.3) years, respectively. Of these, 22 (88.0%) patients were diagnosed with aHUS and 3 (12.0%) with C3 glomerulopathy. A total of 111 eculizumab concentrations were determined. Mean pre- and post-dose concentration values detected during the maintenance phase were 243.8 (SD 240.6) μg/mL and 747.4 (standard deviation (SD) 444.3) μg/mL, respectively. Increased complement blockade was observed at higher pre-dose concentrations (P = .002) and decreased serum creatinine at both higher pre- and post-dose concentrations (P = .001 and P = .017, respectively). Using ROC curves, it was determined that a pre-dose concentration >149.0 μg/mL was optimal to achieve complement blockade, with an AUC of 0.87 (0.78-0.95). Finally, high inter-individual (48.9% variation coefficient (CV)) with low intra-individual variabilities (11.9% CV) in eculizumab clearance were observed.

CONCLUSIONS

The present study reports supratherapeutic concentrations of eculizumab in patients with aHUS, and defines higher concentrations than those described in the data sheet to achieve blockade, thus encouraging the personalization of treatment with eculizumab.

Pharmacokinetics of eculizumab in adult and pediatric patients with atypical hemolytic uremic syndrome and C3 glomerulopathy

OBJECTIVE

The objective of the study was to analyze and describe the concentrations of eculizumab and the complement blockade in patients with atypical hemolytic uremic syndrome (aHUS) and C3 glomerulopathy, and to define a therapeutic margin where there is a high probability of achieving therapeutic efficacy.

METHODS

Observational, ambispective and multicenter study that included adult and pediatric patients diagnosed with aHUS and C3 glomerulopathy from September 2020 to October 2022 in five hospitals in Spain. Eculizumab was administered at the doses recommended by the data sheet according to the European Medicines Agency (EMA). Pre-dose and post-dose concentrations of eculizumab were determined, as well as blockade of the classical complement pathway (CH50). Sociodemographic and clinical data were collected, and pharmacokinetic parameters were calculated. To establish the cut-off point for eculizumab concentrations that predicted complement blockade, Receiver Operating Characteristic (ROC) curve analysis was performed. Lastly, the Kruskal-Wallis test was used to contrast the differences in different parameters according to eculizumab concentrations.

RESULTS

Twenty-five patients were included, 19 adults (76.0%) and 6 pediatrics (24.0%), with median ages of 43.4 (IQR 35.7-48.8) and 10.1 (IQR 9.6-11.3) years, respectively. Of these, 22 (88.0%) patients were diagnosed with aHUS and 3 (12.0%) with C3 glomerulopathy. A total of 111 eculizumab concentrations were determined. Mean pre-dose and post-dose concentration values detected during the maintenance phase were 243.8 (SD 240.6) μg/mL and 747.4 (SD 444.3) μg/mL, respectively. Increased complement blockade was observed at higher pre-dose concentrations (p=0.002) and decreased serum creatinine at both higher pre- and post-dose concentrations (p=0.001 and p=0.017, respectively). Using ROC curves, it was determined that a pre-dose concentration >149.0 μg/mL was optimal to achieve complement blockade, with an AUC of 0.87 (0.78-0.95). Finally, high inter-individual (48.9% CV) with low intra-individual variabilities (11.9% CV) in eculizumab clearance were observed.

CONCLUSIONS

The present study reports supratherapeutic concentrations of eculizumab in patients with aHUS, and defines higher concentrations than those described in the data sheet to achieve blockade, thus encouraging the personalization of treatment with eculizumab.

Proteinuria and Exposure to Eculizumab in Atypical Hemolytic Uremic Syndrome

BACKGROUND

Eculizumab is a monoclonal antibody for the treatment of atypical hemolytic uremic syndrome (aHUS). Kidney damage, a common condition in patients with aHUS, may result in proteinuria. Because proteinuria may affect the pharmacokinetics of therapeutic proteins such as eculizumab, the aim of our study was to investigate the effect of proteinuria on eculizumab pharmacokinetics.

METHODS

This study was an ancillary study of a previously performed pharmacokinetic-pharmacodynamic study of eculizumab in aHUS. Proteinuria, measured as urinary protein-creatinine ratios (UPCR), was investigated as covariate for eculizumab clearance. Thereafter, we evaluated the effect of proteinuria on the exposure to eculizumab in a simulation study for the initial phase and for a 2-weekly and 3-weekly interval in the maintenance phase.

RESULTS

The addition of UPCR as a linear covariate on clearance to our base model resulted in a statistically improved fit ( P < 0.001) and reduction of unexplained variability in clearance. From our data, we predicted that in the initial phase, 16% of the adult patients with severe proteinuria (UPCR >3.1 g/g) will have inadequate complement inhibition (classical pathway activity >10%) on day 7 of treatment, compared with 3% of the adult patients without proteinuria. None of the pediatric patients will have inadequate complement inhibition at day 7 of treatment. For the 2- and 3-weekly dosing intervals, we predicted that, respectively, 18% and 49% of the adult patients and, respectively, 19% and 57% of the pediatric patients with persistent severe proteinuria will have inadequate complement inhibition, compared with, respectively, 2% and 13% of the adult patients and, respectively, 4% and 22% of the pediatric patients without proteinuria.

CONCLUSIONS

Severe proteinuria is associated with a higher risk of underexposure to eculizumab.

CLINICAL TRIAL REGISTRY NAME AND REGISTRATION NUMBER

CUREiHUS, Dutch Trial Register, NTR5988/NL5833.

Proposal for individualized dosing of eculizumab in atypical haemolytic uraemic syndrome: patient friendly and cost-effective

BACKGROUND

Eculizumab is a lifesaving yet expensive drug for atypical haemolytic uraemic syndrome (aHUS). Current guidelines advise a fixed-dosing schedule, which can be suboptimal and inflexible in the individual patient.

METHODS

We evaluated the pharmacokinetics (PK) and pharmacodynamics (PD) [classical pathway (CP) activity levels] of eculizumab in 48 patients, consisting of 849 time-concentration data and 569 CP activity levels. PK-PD modelling was performed with non-linear mixed-effects modelling. The final model was used to develop improved dosing strategies.

RESULTS

A PK model with parallel linear and non-linear elimination rates best described the data with the parameter estimates clearance 0.163 L/day, volume of distribution 6.42 L, maximal rate 29.6 mg/day and concentration for 50% of maximum rate 37.9 mg/L. The PK-PD relation between eculizumab concentration and CP activity was described using an inhibitory Emax model with the parameter estimates baseline 101%, maximal inhibitory effect 95.9%, concentration for 50% inhibition 22.0 mg/L and  Hill coefficient 5.42. A weight-based loading dose, followed by PK-guided dosing was found to improve treatment. On day 7, we predict 99.95% of the patients to reach the efficacy target (CP activity <10%), compared with 94.75% with standard dosing. Comparable efficacy was predicted during the maintenance phase, while the dosing interval could be prolonged in ∼33% of the population by means of individualized dosing. With a fixed-dose 4-week dosing interval to allow for holidays, treatment costs will increase by 7.1% and we predict 91% of the patients will reach the efficacy target.

CONCLUSIONS

A patient-friendly individualized dosing strategy of eculizumab has the potential to improve treatment response at reduced costs.

Clinical Utility and Potential Cost Savings of Pharmacologic Monitoring of Eculizumab for Complement-Mediated Thrombotic Microangiopathy

One of the treatment options for complement-mediated thrombotic microangiopathy (CM-TMA), also known as atypical hemolytic uremic syndrome, is the administration of the C5 complement inhibitor eculizumab. In vivo studies have reported a complete complement blockade with eculizumab serum concentrations above 50 μg/mL in the case of atypical hemolytic uremic syndrome. The eculizumab trough levels and C5 functional activity were monitored in patients with CM-TMA being treated with eculizumab. For those with eculizumab trough concentrations of more than 100 μg/mL, the frequency of eculizumab 1200-mg doses was decreased. In this article, we describe the pharmacologic monitoring data with the use of C5 functional activity and mass spectrometric assessments of eculizumab to allow for a tailored eculizumab schedule for 10 patients with CM-TMA. In 9 out of 10 (90%) patients with a standard administration schedule, eculizumab trough concentrations were more than 100 μg/mL. At the time of the last eculizumab follow-up (median, 250 days; range, 85-898 days), the interval between eculizumab infusions was extended to every 3-6 weeks for 8 patients; no disease relapse was found with the modified dosing interval. Altering the administration of maintenance eculizumab from every 2-3 weeks to 3-6 weeks yields a savings of $78,185 per patient for a 6-month eculizumab treatment course. Although larger standardized cohorts are necessary to confirm these findings, our data suggest that monitoring eculizumab levels in conjunction with C5 assessment allows for safe modification of eculizumab dosing and results in considerable cost savings.

Eculizumab treatment in atypical hemolytic uremic syndrome: correlation between functional complement tests and drug levels

BACKGROUND

Atypical hemolytic uremic syndrome (aHUS) is characterized by platelet consumption, hemolysis, and renal injury. Eculizumab, a humanized antibody that blocks complement activity, has been successfully used in aHUS, but the best treatment schedule has not yet been clearly defined.

METHODS

Herein we report our experience with eculizumab maintenance treatment, in which the interval between subsequent doses was adjusted based on classical complement pathway (CCP) activity, targeted to < 30% for the prevention of relapses. Trough circulating levels of free eculizumab were determined by an immunoenzymatic method. Genetic and serologic characteristics of the patients were also assessed.

RESULTS

We report on 38 patients with aHUS with a median age of 25.0 years (range 0.5-60.0 years) treated with eculizumab. Once stable disease remission was obtained, the interval between eculizumab doses was extended based on target CCP activity. With this approach, presently, 22 patients regularly receive eculizumab infusion every 28 days and 16 receive it every 21. During a median observation period of 32.3 months (range 4.0-92.4 months) and a cumulative period of 1295 months, no patient relapsed. An inverse correlation between CCP activity and eculizumab circulating levels was present (r = - 0.690, p = 0.0001), with CCP activity being inhibited as long as free eculizumab was measurable in serum.

CONCLUSIONS

In patients with aHUS on eculizumab maintenance treatment, complement activity measurement can be used as a proxy for circulating levels of the drug. Monitoring complement activity allows for safe tailoring of the frequency of eculizumab administration, thus avoiding excessive drug exposure while keeping the disease in remission.

Ravulizumab: Characterization and quantitation of a new C5 inhibitor using isotype specific affinity purification and high-resolution mass spectrometry

Introduction

Ravulizumab (RAVUL) is a new complement inhibitor, with a difference of 4 amino acids in the heavy chain from a predecessor compound, eculizumab (ECUL).

Objectives

First, to utilize mass spectrometry (MS) to characterize RAVUL and verify differences from its predecessor and, second, to validate and implement a lab developed test (LDT) for RAVUL that will allow for quantitative therapeutic monitoring.

Methods

A time-of-flight mass spectrometer (TOF-MS) was used to characterize and differentiate the molecular weight differences between RAVUL and ECUL by both digest and reduction experiments. In parallel, an LDT for RAVUL was validated and implemented utilizing IgG4 enrichment with light chain detection and quantitation on a high throughput orbitrap MS platform.

Results

The TOF-MS platform allowed for the mass difference between RAVUL and ECUL to be verified along with providing a proof of concept for a new intact protein quantitation software. An LDT on an orbitrap MS was validated and implemented using intact light chain quantitation, with the limitation that it cannot differentiate between ECUL and RAVUL. The LDT has an analytical measuring range from 5 to 600 mcg/mL, inter-assay imprecision of ≤13% CV (n = 13) and accuracy with <4% error from expected values (n = 20).

Conclusion

The TOF-MS is a versatile development platform that can be used to characterize and verify the molecular weight differences between the ECUL and RAVUL heavy chains. Routine laboratory testing for RAVUL was viable using an orbitrap-MS to quantitate using the mass of the intact light chain. These two platforms, combined, provide incomparable value in development of LDTs for the clinical laboratory.