2.1 Protein Characterization
Filgrastim was expressed using a recombinant Escherichia coli strain. Inclusion bodies were solubilized, and refolding was performed using a glutathione redox system. Protein purification was achieved via the application of multiple orthogonal modes of chromatography.
An array of analytical methods was used to compare EP2006 (480 µg/0.8 mL and 300 µg/0.5 mL solutions for injection) and the originator drug product obtained from the US market (480 µg/0.8 mL and 300 µg/0.5 mL) and the EU market (480 µg/0.5 mL and 300 µg/0.5 mL). The procedures were designed to identify any differences in the protein structure, mass, size, charge, hydrophobicity, receptor binding, and bioactivity of the test substances. The analyses included N-terminal Edman sequencing, peptide mapping with ultraviolet/mass detection, circular dichroism spectroscopy, 1D-{1H}-nuclear magnetic resonance (NMR) spectroscopy, matrix-assisted laser desorption/ionization–time of flight mass spectrometry (MALDI-TOF-MS), size exclusion chromatography (SEC), sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE), cation exchange chromatography (CEX), reversed-phase high-performance liquid chromatography (RP-HPLC), surface plasmon resonance (SPR) spectroscopy, and an in vitro bioassay, all of which have been described in detail previously [
1]. Mass spectrometric detection of intact filgrastim and GluC-digested filgrastim, respectively, was performed by coupling RP-HPLC to an Orbitrap instrument (Thermo Fisher Scientific, Waltham, MA, USA).
In addition to these previously described methods, sub-visible protein particle determination was performed using micro-flow imaging (MFI) performed on a ProteinSimple MFI system (ProteinSimple, Santa Clara, CA, USA). Samples were evaporated before use for 20 min, and 1 mL sample volumes were analyzed. ProteinSimple MFI View Analysis Suite software was used for data evaluation. Clarity analysis was investigated by nephelometry, using a Hach Lange system (Hach Company, Loveland, CO, USA). Samples were injected as they were, and the procedure described in European Pharmacopoeia item 2.2.1 was used. Isoelectric focusing was conducted to evaluate charge.
Process-related impurities were assayed using established analytical technology. Host cell proteins (HCPs) were determined using an enzyme immunological method with lower limits of quantification (LLOQs) of 25 ppm (drug substance) and 50 ppm (drug product), respectively. Residual DNA was assayed using the Threshold™ System (Molecular Devices Corp., Menlo Park, CA, USA). Bacterial endotoxins were quantified using a suitable preparation of limulus amebocyte lysate (LAL). Product-related variants were characterized and monitored using state-of-the-art analytical technology.
2.2 Pharmacodynamics and Pharmacokinetics
2.2.1 Study Design and Population
A single-center, randomized, double-blind, two-way crossover, phase I study with two treatment periods was conducted to determine the pharmacodynamics, pharmacokinetics, and safety of EP2006 and US-approved originator filgrastim (Neupogen®) following a single subcutaneous injection in healthy subjects. The study was conducted at PharmaNet Canada Inc. (Montréal, QC, Canada) and was in compliance with Good Clinical Practice, Good Laboratory Practice, local regulatory requirements, and the Declaration of Helsinki. The study protocol was reviewed and approved by the Institutional Review Board. All participants gave written informed consent before the initial assessment.
The subjects were healthy adult non-smokers or ex-smokers (defined as not having smoked for at least 6 months before study drug administration), aged between 18 and 49 years, with body weight between 50 and 109.9 kg and a body mass index (BMI) between 19 and 29.9 kg/m2. The subjects had no prior exposure to recombinant human G-CSF products.
Subjects attended a screening visit less than 28 days before the first dosing of the study drug in period 1. Upon arrival at the unit in period 1, subjects were randomized 1:1 (using a computer-generated list) to receive a single subcutaneous injection of 10 μg/kg body weight of EP2006 or originator filgrastim. The study drug was administered in the morning on day 1 during each period. There was a wash-out period of at least 28 days between the two study drug periods. In both periods, eligible subjects resided in the clinical unit for at least 12 h prior to dosing through 36 h following dosing. Thereafter, the subjects returned to the clinical unit on an out-patient basis for scheduled pharmacodynamic, pharmacokinetic, and safety assessments on days 3 through 8, 11, and 15 of each period. A follow-up examination was performed on day 28 after dosing in period 2.
The subjects, investigator staff, persons performing the assessments, laboratory personnel, and data analysts remained blinded from the time of randomization through database lock. Unblinding was permitted only in the possible event of subject emergencies and at the conclusion of the study.
2.2.2 Objectives
The primary objective was to compare the neutrophil response in terms of the pharmacodynamic parameters: the area under the effect on the absolute neutrophil count (ANC)–time curve from time zero to 120 h (AUEC0–120h) and the maximum observed effect (E
max) following single subcutaneous injections of EP2006 and originator filgrastim. A second primary objective was to evaluate the following pharmacokinetic parameters: the area under the curve from time zero to the time of the last measurable concentration (AUC0–last) and the maximum observed serum concentration (C
max). Pharmacokinetic equivalence was assessed as a secondary test after pharmacodynamic equivalence was shown. Secondary objectives included CD34+ cell counts, safety, immunogenicity, and local tolerance of both products.
2.2.3 Evaluation of Pharmacodynamics
For ANC assessment, blood samples (17 in total) were taken from each subject in both periods at 0.5 h before the study drug injection and at 0.5, 1, 2, 4, 6, 8, 10, 12, 16, 20, 24, 32, 48, 72, 96, and 120 h post-injection. For the evaluation of CD34 + cell counts, a total of ten blood samples were taken at 0.5 h before the injection and at 24, 48, 72, 96, 120, 144, 168, 240, and 336 h post-dose. The primary pharmacodynamic parameters measured for the ANC were AUEC0–120h and E
max. The time to reach the maximum observed ANC effect (t
max,E) was also determined. The ANC was measured using a commercial flow cytometer (Advia 2120; Siemens AG, Munich, Germany). The CD34+ cell count was determined using a validated method with a commercial flow cytometer (BD LSRII; BD Biosciences, Franklin Lakes, NJ, USA) and an optimized CD34+ enumeration assay from the National Immune Monitoring Laboratory (University of Montreal, Montreal, QC, Canada). The CD34+ parameters measured were AUEC0–last, E
max, and t
max,E.
2.2.4 Evaluation of Pharmacokinetics
Blood samples (16 in total) were taken for the pharmacokinetic assessment from each subject in both periods at 0.5 h before the injection and at 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, 6, 8, 12, 16, 24, 36, and 48 h post-injection. As well as the primary pharmacokinetic parameters of AUC0–last and C
max, the area under the curve from time zero extrapolated to infinity (AUC0–∞), time to reach C
max (t
max), elimination rate constant (K
el), and apparent terminal elimination half-life (t
½) were measured as secondary parameters. Pharmacokinetic analysis was performed using a validated enzyme-linked immunosorbent assay (Quantikine® Human G-CSF; R&D Systems GmbH, Wiesbaden-Nordenstadt, Germany). The LLOQ was 0.039 ng/mL. The inter-day precision of the calibration standards of filgrastim ranged between 1.6 and 7.2 %, with accuracy between 99.0 and 101.0 %. The intra-day precision of the control samples ranged from 5.3 to 6.8 %. All control samples were within the predefined limits. The mean precision of the analyses of 20 incurred samples was 7.3 %. No sample value beyond ±20 % was observed. Thus, the incurred sample reanalysis showed the reliability of the assay.
2.2.5 Evaluation of Safety
Adverse events (AEs) were recorded at each visit during the study. Laboratory tests, vital signs, an electrocardiogram, and local tolerance assessments were also performed during the study. To assess immunogenicity, blood samples taken before drug administration (0.5 h before the injection in periods 1 and 2) and afterward (at the follow-up visit) were analyzed for anti-filgrastim antibodies.
2.2.6 Statistical Analysis
This study was powered at 90 % for a sample size of 28 subjects for both pharmacokinetic and pharmacodynamic objectives. The safety population was defined as the group of subjects who received at least one dose of the study medication. The per-protocol (PP) analysis population included all subjects who received the study drug, provided evaluable pharmacodynamic profiles (for the ANC) and pharmacokinetic profiles, and completed the study without a major protocol violation. The primary pharmacodynamic/pharmacokinetic analyses were based on this PP population.
Descriptive statistics of the concentrations versus time, as well as all pharmacodynamic and pharmacokinetic parameters, were provided for each filgrastim product. An analysis of covariance (ANCOVA) was performed on the log-transformed ANC AUEC0–120h, E
max, AUC0–last, and C
max. The ANCOVA model included sequence, treatment, and period as fixed effects, and subject nested within sequence as a random effect. The log-transformed baseline value in each period (the ANC pre-dose value [or the check-in value if the pre-dose value was missing] for the ANC parameters and the pharmacokinetic parameters, and the CD34+ pre-dose value [or the check-in value if the pre-dose value was missing] for the CD34+ parameters) served as covariates in the model. The analysis was performed using SAS statistical analysis software (SAS Institute Inc., Cary, NC, USA).
Each ANCOVA included calculation of least-squares means (LSMs) for the treatments. The ratios of the LSMs were determined using exponentiation of the differences in the LSMs from the analyses of the corresponding log-transformed parameters. Consistent with Schuirmann’s two one-sided tests for bioequivalence, 95 % (pharmacodynamic) and 90 % (pharmacokinetic) confidence intervals (CIs) for these ratios were calculated for the ANC AUEC0–120h, E
max, AUC0–last, and C
max. Equivalence of biosimilar and originator filgrastim was to be concluded if the corresponding 95 % (pharmacodynamic) and 90 % (pharmacokinetic) CIs of the ratios of the LSMs of the parameters fell entirely within the predefined boundaries of 80–125 %.
Pharmacodynamics were further compared with respect to t
max,E for the ANC, as well as AUEC0–last, E
max, and t
max,E for CD34+ cell counts. However, no formal hypothesis testing was applied to these parameters. All remaining pharmacokinetic parameters were analyzed descriptively. Therefore, all CIs reported for these secondary variables were interpreted only in an exploratory sense.