Safety and Pharmacokinetics of 120 mg/kg versus 60 mg/kg Weekly Intravenous Infusions of Alpha-1 Proteinase Inhibitor in Alpha-1 Antitrypsin Deficiency: A Multicenter, Randomized, Double-Blind, Crossover Study (SPARK)

Abstract

Augmentation therapy with the approved dose of 60 mg/kg weekly intravenous (IV) alpha-1 proteinase inhibitor (alpha₁-PI), achieves a trough serum level of 11 μM in individuals with alpha-1 antitrypsin deficiency (AATD), yet this is still below the level observed in healthy individuals. This study assessed the safety and pharmacokinetic profile of weekly infusions of a 120 mg/kg dose of alpha₁-PI in 30 adults with AATD. Subjects with symptomatic, genetically determined (genotypes PI*ZZ, PI*Z(null), PI*(null)(null) or PI*(Z)Mmalton) AATD were randomly assigned to weekly infusions of 60 or 120 mg/kg alpha₁-PI (Prolastin-C®) for 8 weeks before crossing over to the alternate dose for 8 weeks. Adverse events (AEs) (including exacerbations), vital signs, pulmonary function tests, and laboratory assessments were recorded. Pharmacokinetic measurements included AUC_0-7days, C_max, trough, t_max, and t_1/2, based on serum alpha₁-PI concentrations. In total for both treatments, 112 AEs were reported, with exacerbation of COPD being the most frequent, consistent with the subjects’ diagnoses. Mean steady-state serum alpha₁-PI concentrations following 120 mg/kg weekly IV alpha₁-PI were higher than with the 60 mg/kg dose and mean trough concentrations were 27.7 versus 17.3 μM, respectively. Dose proportionality was demonstrated for AUC_0-7days and C_max, with low inter-subject variability. The 120 mg/kg alpha₁-PI weekly dose was considered to be safe and well tolerated, and provided more favorable physiologic alpha₁-PI serum levels than the currently recommended 60 mg/kg dose. The effect of this dosing regimen on slowing and/or preventing emphysema progression in subjects with AATD warrants further investigation.

Keywords :

• alpha-1 proteinase Inhibitor
• alpha-1 antitrypsin deficiency
• chronic obstructive pulmonary disease

Introduction

A decrease in the anti-protease activity of lung tissue has been considered to be the most important pathophysiologic mechanism for the development of emphysema in subjects with genetic alpha-1 antitrypsin deficiency (AATD). In this disorder, individuals have low serum levels of alpha-1 antitrypsin (AAT), also known as alpha-1 proteinase inhibitor or alpha₁-PI. For this condition, augmentation therapy with purified preparations of alpha₁-PI derived from human plasma has been developed as a specific therapeutic option to correct the deficient state and help stabilize AATD (1).

In healthy individuals, who have the normal PI*MM genotype, alpha₁-PI circulates in serum at a concentration of >20 μM (1), however, the goal of augmentation therapy has been to maintain serum AAT above a level of 11 μM. The reasons for this lower threshold are based on epidemiological studies that show an increased risk of emphysema when serum AAT drops below this level (2, 3). In these studies, weekly intravenous infusions of 60 mg/kg of purified human alpha₁-PI were sufficient to keep trough AAT levels above 11 μM and were effective to increase the neutrophil elastase inhibitory capacity of serum and epithelial lining fluid (3). The calculations for weekly dosing were based on the serum half-life of AAT, its estimated volume of distribution and the investigators’ prior experience (4). Currently, the 60 mg/kg/week intravenously-delivered alpha₁-PI is the recommended dosing regimen for the treatment of individuals with AATD who develop COPD (1, 5), although observations from clinical practice suggest that alternate dosing is frequently used (6).

The current evidence supporting the benefits of 60 mg/kg weekly augmentation therapy is limited, and for this reason there has been controversy in recommending this treatment (7). Observational trials suggest that it can slow lung function decline in subjects with moderate lung function impairment (8–10) and a recent placebo-controlled pilot trial suggested a trend towards a reduction in the progression of emphysema (11). One possible explanation for the uncertain clinical benefit is that the current recommended dose of 60 mg/kg/week aims at increasing AAT levels to values that are still significantly below the alpha₁-PI level that is observed in healthy subjects (20–53 μM) (12). In fact, this dose does not significantly decrease urinary markers of elastin degradation (13, 14) and clinically treated individuals still experience ongoing chronic bronchitis and numerous and prolonged acute exacerbations (15).

The effect of the recommended dose of alpha₁-PI on lung function decline also appears to be suboptimal as AAT deficient individuals who are treated with augmentation therapy have an annual lung function decline that is still greater than that observed in normal individuals (34–53 ml/year, versus 17.6–19.6 ml/year in normal individuals) (10, 16). Not surprisingly, experts frequently treat the more severely affected patients with higher off-label weekly doses.

New trials with a higher weekly dose of alpha₁-PI are necessary to evaluate whether the potential for this therapy to slow the progression of or prevent emphysema in patients with AATD can be optimized. As a first step, we report the safety profile and pharmacokinetics (PK) of alpha₁-PI at twice the currently recommended dose.

Methods

Study design

This was a multicenter, randomized, double-blind crossover study to assess the safety and PK of weekly infusions of 120 mg/kg of human alpha₁-PI (Prolastin®-C, Grifols Therapeutics Inc, Research Triangle Park, NC) compared with the current recommended dose of 60 mg/kg in subjects with AATD. The study was conducted at five centers in the United States and was approved by each institution's Institutional Review Board Committee. All subjects provided written informed consent prior to any study procedure.

Subjects were randomly assigned to one of two ­treatment sequences, each consisting of two doses of alpha₁-PI and two treatment periods. Subjects received either 60 mg/kg or 120 mg/kg weekly infusions of alpha₁-PI for 8 weeks and then crossed over to the alternate dose for 8 weeks for a total of 16 weeks of treatment. After completing treatment period 1, subjects underwent a 2-week washout period prior to starting treatment period 2. At the end of treatment period 2, subjects entered a 4-week follow-up period with no treatment to allow further PK measurements. To maintain treatment blinding, 2 sequential bags of 60 mg/kg each of alpha₁-PI were administered for the 120 mg/kg phase and a bag of normal saline followed by a 60 mg/kg bag of alpha₁-PI was administered for the 60 mg/kg phase (Figure 1).

Figure 1.  Study design. Following an initial screening phase, subjects were enrolled into this crossover study, which involved two treatment periods (1 and 2), each consisting of two treatments (60 or 120 mg/kg weekly IV alpha₁-PI (Prolastin-C®), separated by a washout period. Time points for serial samples for pharmacokinetic (PK) analysis are indicated.

Subjects

Subjects eligible to take part in the study were adults (aged 18–70 years) with a documented diagnosis of AATD, defined as having a genotype associated with severe AAT deficiency (PI*ZZ, PI*Z(null), PI(null)(null), PI*SZ, or other “at-risk” allele) and having serum AAT levels <11 μM at the time of diagnosis. Eligible subjects were also required to have a positive diagnosis of COPD, with a post-bronchodilator forced expiratory volume in 1 second (FEV₁) of ≥30% and <80% of predicted and FEV₁/forced vital capacity (FVC) <0.70 (Global Initiative for Chronic Obstructive Lung Disease [GOLD] stage II or III (17)). Subjects were required to discontinue any ongoing alpha₁-PI augmentation therapy at screening and for the duration of the study.

Subjects who had a moderate or severe pulmonary exacerbation within 4 weeks before study initiation or significant liver disease (cirrhosis or elevated liver enzymes ≥ 2.5 times the upper limit of normal) were not included in the study. Additional exclusion criteria included a history of lung or liver transplant; any lung surgery during the past 2 years (excluding lung biopsy), clinically significant pulmonary fibrosis, malignant disease or history of hypersensitivity pneumonitis. Female subjects, if of child-bearing potential, had to be willing to use an effective form of contraceptive to participate. To ensure adequate assessment of the safety profile for potential viral transmission related to treatment, subjects currently infected with hepatitis A, B, or C virus, human immunodeficiency virus (HIV), or parvovirus B19 (B19V), and those with a history of previous infection with HBV, HCV, or HIV, were excluded. Other exclusion criteria included a history of active smoking during the past 6 months; history of IgA deficiency; participation in another drug study within 1 month prior to baseline; history of severe systemic response to any plasma-derived blood product; use of systemic steroids above a stable dose; and use of systemic or aerosolized antibiotics.

Safety evaluation

Safety was assessed through the recording of adverse events (AEs). Investigators were requested to assess all AEs in terms of seriousness, severity, and relationship to investigational product. Treatment-emergent AEs (TEAEs) were defined as any AE during the study that began on or after the date or time of first dose of investigational product. For the purpose of this study, all COPD exacerbations were included as AEs and were defined as an increase in dyspnea, cough, and/or production of sputum over baseline requiring medical intervention.

Clinical laboratory test samples (hematology, chemistry including high sensitivity C-reactive protein [hs-CRP] and urinalysis including urine cotinine, and urine pregnancy [females of child-bearing potential]) were collected and tested at screening and weeks 1, 11, 19, and 22. Samples for viral nucleic acid testing and serology were collected at screening and at weeks 1, 11, 19, and 22, and tested only if there were clinical signs and symptoms of viral infection. Measurement of vital signs (heart rate, blood pressure, respiratory rate, and temperature) and pulmonary function tests (pre- and post-bronchodilator FEV₁ and FVC) were performed at screening and at weeks 11 and 19.

Immunogenicity testing

Blood samples for immunogenicity testing were drawn at weeks 1, 11, and 22. In addition, blood samples were collected at weeks 9 and 19, but only tested if there was an unexpected PK profile. Samples to detect anti-alpha₁-PI IgA, IgG, or IgM were assayed by ELISA.

Pharmacokinetic evaluation

Blood samples for PK assessments were taken throughout the study. Pre-infusion samples were obtained at the first, sixth, seventh, and eighth weeks of each treatment period (study weeks 1, 6, 7, 8 and 11, 16, 17, 18, respectively) for the evaluation of steady-state trough alpha₁-PI levels. Serial post-infusion samples were collected to evaluate the steady-state PK profiles of alpha₁-PI at the end of each treatment period (study weeks 8 and 18, respectively) as follows: following the first infusion bag, following flushing the second infusion bag, and at 0.25, 0.5, 1, 2, 4, and 8 hours, and then 24 hours (±4 hours), 48 hours (±4 hours), 120 hours (5 days, +1 day window), 168 hours (7 days, +1 day window), 336 hours (14 days, +1 day window), and 504 hours (21 days, +1 day window) after flushing the second infusion bag.

Serum alpha₁-PI levels (total antigenic content) were determined by nephelometry at a central laboratory (Covance Central Laboratory Services Inc.), using a validated method. Serum alpha₁-PI concentrations from the assay are reported in mg/mL units and determined from the reference standard curve. For reporting or comparing the steady-state trough alpha-1 PI concentrations these values were also converted to micromolar (μM) units, where 1 mg/mL is equivalent to 22.6 μM (for the 44300 g/mol mass protein).

The PK profiles of alpha₁-PI following weekly 120 mg/kg or 60 mg/kg administration of alpha₁-PI included the area under the concentration-time curve from day 0 to day 7 at steady state (AUC_0-7days), the maximum alpha₁-PI concentration (C_max) following drug infusion, minimum (trough) alpha₁-PI concentration (C_min), terminal half-life (t_1/2), and the observed time to reach C_max (t_max). PK parameters were calculated using non-compartmental methods: C_max, C_min, and t_max were all directly observed values; AUC_0-7days was determined by log-linear trapezoidal rule and t_1/2 was estimated by log-linear regression with at least three time points.

For the 60 mg/kg dose t_max was adjusted by subtracting the actual time interval from the start of the first infusion bag (saline) to the start of the second (study drug). Mean trough concentrations at steady state were determined as the mean value of four trough serum concentration measurements obtained at ­pre-infusion weeks 6, 7, 8 and then at 7 days (168 hours) after the last (week 8) infusion of treatment period 1, and at pre-infusion weeks 16, 17, 18 and then at 7 days (168 hours) after the last (week 18) infusion of treatment period 2.

Statistical analyses

No formal sample size calculations were performed for this study. Approximately 30 subjects were planned to be randomized into two treatment sequences (15 subjects per treatment sequence). This sample size was considered to be adequate to achieve the study objectives and would provide at least 95% power to demonstrate comparability in dose-normalized AUC and C_max between doses, with 15% coefficient of variation in intra-subject variability for a crossover study. Power analysis for subjective or objective safety parameters was not possible due to the nature of these events. Descriptive statistics are therefore presented for safety parameters throughout. All analyses were conducted using SAS version 9.2 or higher.

All PK parameters were summarized descriptively by treatment using arithmetic as well as geometric means and standard deviation (SD), percentage coefficient of variation (CV), median, and minimum/maximum, as appropriate. The number and percent of subjects with mean trough ≥ 11 μM at each dose level was also summarized. To compare steady-state serum exposure to alpha₁-PI between administration of the 120 mg/kg/week dose (test treatment) and the 60 mg/kg/week dose (reference treatment), AUC_0-7days and C_max values of alpha₁-PI associated with each dose were analyzed using an analysis of covariance (ANCOVA) model with treatment, period, and sequence as fixed effects and subject within sequence as a random effect. The PK parameter values in individual subjects were dose-normalized to 60 mg/kg based on the actual dose administered at week 8 or week 18, respectively, and were then natural log transformed before performing ANCOVA.

Results

Subject demographics

Of the 46 subjects screened for participation in the study, 13 were excluded because of failure to meet inclusion criteria, 1 previously received gene therapy in a research study for AATD, and 2 experienced serious AEs prior to randomization (1 subject developed ­pneumonia requiring hospitalization and another ­subject developed sepsis from a leg cellulitis, both before receiving study drug). Therefore, 30 subjects were randomized to one of the two treatment sequences (15 subjects each in the 60 mg/kg–120 mg/kg and 120 mg/kg–60 mg/kg treatment sequences), as shown in Figure 2. Demographic and baseline characteristics were generally similar for subjects assigned to each of the two treatment sequences (Table 1). The majority of subjects (26/30 [86.7%]) had received prior alpha₁-PI augmentation therapy.

Figure 2.  Subject flow. ^aSubject had previously received gene therapy for alpha₁-PI in a research study.

Table 1.  Demographics and disease characteristics of the study population

	Alpha1-PI treatment sequence
Characteristic	60 mg/kg–120 mg/kg	120 mg/kg–60 mg/kg	Total
	n = 15	n = 15	n = 30
Male gender, n (%)	7 (46.7)	7 (46.7)	14 (46.7)
Female gender, n (%)	8 (53.3)	8 (53.3)	16 (53.3)
Mean age, years (SD)	59.7 (6.89)	57.4 (6.34)	58.6 (6.62)
Ethnicity, n (%)
Hispanic/Latino	1 (6.7)	1 (6.7)	2 (6.7)
Not Hispanic/Latino	14 (93.3)	14 (93.3)	28 (93.3)
Mean height, cm (SD)^a	171.9 (10.66)	171.4 (10.93)	171.6 (10.61)
Mean weight, kg (SD)^a	80.1 (16.96)	90.6 (17.97)	85.4 (17.97)
Median time since diagnosis, years (range)	7.0 (3.0–25.0)	7.5 (1.0–22.0)^b	7.0 (1.0–25.0)
Genotype, n (%)
PI*ZZ	13 (86.7)	15 (100.0)	28 (93.3)
PI*Z(null)	1 (6.7)	0	1 (3.3)
PI*ZMmalton	1 (6.7)	0	1 (3.3)
Mean alpha1-PI level at time of diagnosis (μM)	5.24 (1.50)	4.61 (0.94)^b	4.93 (1.28)
Mean baseline alpha1-PI concentration (μM),^c naïve subjects
n	2	2	4
Mean (SD)	5.65 (2.08)	7.46 (0.16)	6.55 (1.58)
Mean baseline alpha1-PI concentration (μM),^c non-naïve subjects
n	13	13	26
Mean (SD)	7.68 (3.07)	7.46 (2.26)	7.68 (2.64)
Mean% predicted FEV1 (SD)	54 (14.5)	49 (12.4)	52 (13.5)

^aBaseline values are taken from screening visit.

^bFor time since diagnosis and AAT level at time of diagnosis n = 14; verification was not provided for one subject and therefore this information for the subject was not included in the database.

^cBaseline AAT concentration is trough concentration at week 1 prior to the start of the first alpha₁-PI infusion. AAT concentration was converted from mg/mL to μM using the conversion factor of 22.6 based on the protein-only molecular weight of 44.3 KDa for AAT.

AAT, alpha-1 antitrypsin; FEV₁, forced expiratory volume in 1 second; SD, standard deviation.

Safety evaluation

Analyses of AEs were performed on all study subjects, and are summarized in Table 2. Overall, 23 subjects (76.7%) experienced a total of 69 TEAEs in the 60 mg/kg alpha₁-PI dose group, and 18 subjects (60.0%) experienced 43 TEAEs in the 120 mg/kg alpha₁-PI dose group. In the 60 mg/kg alpha₁-PI dose group five AEs with a possible relationship to the study drug were recorded in three subjects: one report of subcutaneous nodules in one subject; two reports of difficulty in focusing in another subject, and two instances of rosacea in another subject. In the 120 mg/kg alpha₁-PI dose group, one AE with a possible relationship to study drug consisted of difficulty in focusing by the same subject who experienced the same event in the 60 mg/kg treatment period.

Table 2.  Adverse events

	Dose
	60 mg/kg alpha1-PI	120 mg/kg alpha1-PI
	n = 30	n = 30
Subjects with TEAE(s), n (%)	23 (76.7)	18 (60.0)
Total number of TEAEs	69	43
Subjects with drug-related TEAE(s), n (%)	3 (10.0)	1 (3.3)
Total number of drug-related TEAEs	5	1
Subjects with exacerbations, n (%)	7 (23.3)	5 (16.7)
Total number of exacerbations	9	6
Subjects with SAE(s), n (%)	0	0
Subjects withdrawn due to an AE(s)	0	0
TEAEs occurring in ≥5% of subjects, n (%)
COPD exacerbation	7 (23.3)	5 (16.7)
Urinary tract infection	3 (10.0)	0
Contusion	1 (3.3)	2 (6.7)
Thrombocytopenia	2 (6.7)	0
Proteinuria	2 (6.7)	1 (3.3)
Blood creatinine increased^a	0	2 (6.7)
Blood glucose increased^a	0	2 (6.7)

AE, adverse event; SAE, serious adverse event; TEAE, treatment-emergent adverse event.

^aAbove the upper limit of the normal range.

All events were considered to be mild in intensity. No subject experienced a severe AE, or had to be withdrawn from the study due to an AE, and no deaths occurred during the study. COPD exacerbation was the most frequent AE recorded during the study (Table 2). Seven subjects (23.3%) experienced a total of nine COPD exacerbations in the 60 mg/kg alpha₁-PI dose group, and five subjects (16.7%) experienced six COPD exacerbations in the 120 mg/kg alpha₁-PI dose group.

During the biochemical monitoring, no clinically meaningful mean changes from baseline for any hematology, clinical chemistry (including hs-CRP), or urinalysis parameter were noted at any time point. Furthermore, no mean changes from baseline in any of these parameters were of meaningful clinical concern. Virus safety samples were collected but not tested because no subjects exhibited clinical signs or symptoms of a viral infection. There were no changes in vital signs or on physical examination over time of clinical concern for either dose. Mean baseline pre-bronchodilator, post-bronchodilator, and change from pre-bronchodilator values for FEV1 and FVC were similar between treatment sequences (see supplementary Table).

Immunogenicity analysis

A total of 30 subjects, including four treatment-naïve subjects, were tested for immunogenicity to alpha₁-PI at baseline and at weeks 11 and 22. Testing for antibodies was undertaken on 89 samples from 30 subjects. All clinical samples were negative for specific antibodies against the administered alpha₁-PI preparation.

Pharmacokinetic evaluation

Mean serum alpha₁-PI concentration over time following the eighth weekly dose of 60 mg/kg (n = 29) or 120 mg/kg (n = 30) alpha₁-PI is shown in Figure 3. Steady-state serum alpha₁-PI concentrations following the weekly dose of 120 mg/kg alpha₁-PI were higher than those following the 60 mg/kg dose (Figure 3, panel A). The semi-logarithmic plots showed that mean serum alpha₁-PI concentrations versus time curves at the two dose levels exhibited parallel multi-exponential decay (Figure 3, panel B).

Figure 3.  Mean steady-state serum alpha₁-PI concentration versus time curves. Serum concentrations of alpha₁-PI following the eighth weekly IV dose of 60 mg/kg and 120 mg/kg of alpha₁-PI were measured in blood samples. Linear scale (A); semi-logarithmic scale (B). ^aAt week 8, after receiving the 60 mg/kg dose, serum alpha₁-PI concentration hardly increased from the pre-dose level throughout the entire PK blood sampling period in one subject. This subject was excluded from PK data analysis.

Descriptive statistics of steady-state PK parameters of alpha₁-PI following the two dose levels are presented in Table 3. The inter-subject variability in C_max, ­AUC_0-7days, and t_1/2 of alpha₁-PI in serum was relatively small with a CV of ≤16.1% at each dose level. The mean C_max and AUC_0-7days values after the 120 mg/kg dose were ∼1.8 and 1.7 times the respective values after the 60 mg/kg dose. Similarly, the mean trough level measured over a 4-week period after the 120 mg/kg dose was about 1.6 times the value after the 60 mg/kg dose (27.7 and 17.3 μM, respectively).

Table 3.  Summary of steady-state PK parameters of serum alpha₁-PI following weekly intravenous infusion dose of 60 mg/kg and 120 mg/kg of alpha₁-PI

Parameter	Alpha1-PI 60 mg/kg	Alpha1-PI 120 mg/kg
	(n = 29^a)	(n = 30)
Mean AUC0-7days, mg*h/mL (%CV)	203.6 (10.1%)	344.8 (13.5%)
Mean Cmax, mg/mL (%CV)	2.47 (12.2%)	4.38 (16.1%)
Mean Cmax, μM (%CV)	55.8 (12.2%)	99.0 (16.1%)
Median adjusted tmax, hours range)	0.7 (0.3–2.4)	1.2 (0.3–8.8)
Mean t1/2, hours (%CV)	212.7 (13.4%)	184.3 (15.9%)
	Alpha1-PI 60 mg/kg	Alpha1-PI 120 mg/kg
	(n = 30)	(n = 30)
Mean trough, mg/mL (%CV)	0.77 (13.6%)	1.23 (13.5%)
Mean trough, μM (%CV)	17.3 (13.6%)	27.7 (13.5%)
Subjects with mean trough ≥11 μM, (%)	30 (100%)	30 (100%)

AUC_0-7days, area under the concentration versus time curve at steady state over the weekly dosing interval; C_max maximum serum alpha₁-PI concentration following drug infusion; CV, coefficient of variation; t_max, observed time to reach C_max; PK, pharmacokinetic; t_1/2, terminal half-life as determined for sampling period up to 504 hours’ post-infusion.

^a At week 8, after receiving the 60 mg/kg dose, serum alpha₁-PI concentration hardly increased from the pre-dose level throughout the entire PK blood sampling period in one subject. This subject was excluded from AUC_0-7days, C_max, t_max and t_1/2 analysis.

The dose-normalized (to 60 mg/kg) values of ­AUC_0-7days and C_max of alpha₁-PI were subjected to statistical analysis using ANCOVA for dose proportionality (Table 4). Although the point estimate of the geometric least-squares mean (GLSM) ratio for the 120 mg/kg versus the 60 mg/kg dose was 11–15% lower than 1.0, the 90% confidence interval (CI) of the GLSM ratio for each dose-normalized parameter was within the limit of 0.80–1.25. This indicates that the small difference (≤15%) in the dose-normalized PK parameters of ­alpha₁-PI between the two dose levels was not significant from a PK perspective. Thus, the increase in serum levels after administration of exogenous alpha₁-PI, as determined by AUC_0-7days and C_max values, increased dose proportionally between the 60 and 120 mg/kg weekly doses.

Table 4.  Statistical analysis of dose-normalized PK parameters of serum alpha₁-PI at steady-state following weekly intravenous infusion dose of 60 mg/kg and 120 mg/kg of alpha₁-PI

			Dose-normalized value(to 60 mg/kg dose)			GLSM ratio of dose normalized parameter (120 mg/kg versus 60 mg/kg)
PK parameter	Dose	N	Mean (%CV)	% diff^a	GLSM	Estimate	90% CI
AUC0-7days (hr*mg/mL)	120 mg/kg	30	172.4 (13.5%)	–15.33	170.9	0.85	(0.83, 0.88)
	60 mg/kg	29	203.6 (10.1%)		201.0
Cmax (mg/mL)	120 mg/kg	30	2.19 (16.1%)	–11.49	2.16	0.89	(0.85, 0.92)
	60 mg/kg	29	2.47 (12.2%)		2.43

^aDifference in the means of the dose-normalized PK parameters of alpha₁-PI (120 mg/kg –60 mg/kg).AUC_0-7days, area under the concentration versus time curve at steady state over the weekly dosing interval; CI, confidence interval; C_max maximum serum alpha₁-PI concentration following drug infusion; CV, coefficient of variation; GLSM, geometric least-squares mean; PK, pharmacokinetic.

Discussion

Anecdotal evidence for off-label use of higher doses of alpha₁-PI among AATD patients (18, 19), and the theoretical advantage of achieving more physiologic AAT levels, indicates an urgent need to establish the safety of this approach in the clinical setting. Our results show that alpha₁-PI dose of 120 mg/kg/week is safe and well tolerated when administered by IV infusion for 8 weeks and suitable to be further evaluated in clinical trials. In addition, consistency in the distribution and elimination of serum alpha₁-PI between 60 and 120 mg/kg/week dose levels has been demonstrated.

The AEs observed in this study were as expected, based on the Prolastin-C® US package insert (5) and consistent with the disease profile of the participants. Reassuringly, no evidence of viral infection, antibody formation, or clinically meaningful changes in hematology, clinical chemistry, or urinalysis parameters was found, and there were no serious AEs reported throughout the study.

The most common AE (occurring in ≥5% of subjects in either dose group) recorded during study treatment was COPD exacerbation, as expected in this group of patients, who had moderate to severe COPD. Although the study was not designed or statistically powered to discern between-group differences in the number of COPD exacerbations, the trend observed for fewer COPD exacerbations in the 120 mg/kg dose group compared to the 60 mg/kg dose group (6 versus 9) should be evaluated further in future trials. It is possible that AAT replacement therapy may have a clinically significant impact at the 120 mg/kg/week dose as opposed to the 60 mg/kg/week dose.

Consideration of the PK profile of alpha₁-PI from administration of the higher dose is necessary to place our findings in context, and to assess the potential safety issues surrounding clearance of alpha₁-PI at 120 mg/kg/week. The mean serum alpha₁-PI concentration versus time curves for the two dose levels showed parallel decay patterns, with similar estimates of t_1/2. The serum alpha₁-PI concentration versus time curves following intravenous infusion of 60 mg/kg or 120 mg/kg dose exhibited multi-exponential decay characteristics. Molecules exhibiting such a pattern may well relocate from the peripheral (or deep) compartment back into the central compartment during the later phase of disposition; in this scenario, the terminal half-life may reflect a re-distribution rather than an elimination (or “effective”) half-life, and a hybrid of both types of half-life is possible.

This hypothesis would explain the longer mean t_1/2 value at the 60 mg/kg dose level in this study (212.7 hours), compared with a previously reported duration of 149.2 hours from the “ChAMP” study (20). Given a hybrid profile of re-distribution and elimination half-life for alpha₁-PI at the later phase, the most likely explanation for the difference in t_1/2 estimates between this study and “ChAMP” is the sampling duration: our study utilized a longer blood sampling time, up to 504 hours after the start of infusion compared with the 168 hours used by the ChAMP research group. Evaluating data in this study using the same sampling duration (up to 168 hours), we calculated a mean t_1/2 estimate for the 60 mg/kg dose of 159 hours, consistent with the former study.

The serum trough concentrations determined over a 4-week period in each phase of the study (i.e., from weeks 6–9, or from weeks 16–19) indicate that an approximate steady-state condition was achieved after five weekly intravenous doses of 60 mg/kg or 120 mg/kg of alpha₁-PI. The time it takes to achieve a steady-state condition is consistent with the mean half-life estimate of approximately 149–159 hours using the shorter sampling period.

The mean steady-state trough concentrations of alpha₁-PI in serum observed with the 60 mg/kg/week dose (17.3 μM), although numerically higher than the previously reported level (21) (16.9 μM), is within the variability of the assays and above the theoretical protective threshold of 11 μM. The weekly dose of 120 mg/kg alpha₁-PI provided a mean steady-state trough of alpha₁-PI (27.7 μM) that falls within the reported range of alpha₁-PI serum levels (20 to 53 μM) in normal, non-AATD individuals (12). The ratio of the mean trough, 120 versus 60 mg/kg, was 1.6, which was similar to the AUC_0-7days ratio of 1.7. These ratios are slightly lower than the theoretical value of 2.0 for dose-proportional increases in serum concentrations of alpha₁-PI, which is an artifact resulting from the low-level endogenous alpha₁-PI in serum prior to alpha₁-PI administration.

Support for weekly dosing is provided by the PK properties of alpha₁-PI in serum, which has an estimated elimination half-life of 150–160 hours; a weekly dosing schedule would equate to one dose per half-life interval. Previous reports of higher alpha₁-PI dosing regimens included less frequent regimens such as 120 mg/kg every 2 weeks (18, 19), 180 mg/kg every 3 weeks (18), and 250 mg/kg every month (22, 23). These studies evaluated more convenient infusion schedules to maintain trough AAT levels at or above the 11 μM threshold and showed that less frequent infusions resulted in serum trough AAT levels that are below this threshold value for several days preceding the next infusion. Given the evidence from previous trials and PK principle, our study evaluated weekly higher dosing instead, placing more importance in raising AAT levels closer to the normal physiologic range over keeping levels above the arbitrary threshold level.

Our study clearly shows that the 120 mg/kg weekly dose maintains mean trough alpha₁-PI values greater than the lower limit of the normal range seen in healthy individuals (20 μM) and can be tested safely in clinical trials evaluating its added clinical benefits. We want to emphasize that this dose is not an approved regimen for the treatment of lung disease due to AATD and that the information presented here should not be interpreted as sufficient evidence to recommend this dose. Our trial was not designed to study the clinical efficacy of the higher dose or powered to establish statistically significant between-treatment differences in safety parameters; therefore, we are only able to report numerical trends both in terms of reduced COPD exacerbation, AEs, or any other potential benefits of a higher trough serum level. However, we believe our findings provide a strong rationale for exploration of these two endpoints, and would hope that future research might address these issues.

Augmentation therapy at its currently recommended dose of 60 mg/kg/week is associated with significant costs, and its proven efficacy is based on low-evidence studies (large observational or small randomized studies). This has led to reviews suggesting that this therapy should not be widely recommended until better evidence and cost-effective studies are available (7). Doubling the dose of alpha₁-PI would certainly increase costs, however, if raising serum AAT levels to a physiologic range is associated with more effective outcomes, such as slowing emphysema progression or reducing exacerbation costs, it may prove to be cost-effective. Furthermore, wider usage of this therapy would likely reduce production costs from a commercial point of view.

In conclusion, we have shown that 120 mg/kg ­alpha₁-PI administered weekly is as safe and well tolerated as the widely used weekly 60 mg/kg standard and provides a mean trough serum concentration of alpha₁‑PI (27.7 μM) that falls within the reported range of alpha₁-PI serum levels in normal, non-AATD individuals. The observations reported here will hopefully support the further investigation of the clinical impact of this higher dose in slowing emphysema progression and/or reducing COPD exacerbations.

Declaration of Interest Statement

This work was funded by Grifols Inc. MB was a recipient of a University of Florida Clinical Research Center Grant (#UL1 TR000064). Scientific writing revision and editorial support for this manuscript was provided by Kate Bradford, PhD, of PAREXEL and funded by Grifols Inc. The authors are responsible for the writing and content of this paper.

Acknowledgments

The authors wish to acknowledge the Study Coordinators: Jan Hoeft, RN; Sylvia Johnson, RN; Amie Finley, RN; Patricia Rebolledo, RRT; Eliana Mendes, MD; Pamela Schreck, and also the patients who made the study possible; Cristina Cruz (Grifols Inc.), who developed and validated the in-house immunogenicity assays and Susan Sorrells (Grifols Inc.) for her critical review of the manuscript.