Clinical Pharmacology for Glassia
Mechanism Of Action
GLASSIA administration is intended to inhibit serine proteases such as neutrophil elastase (NE), which is capable of degrading protein components of the alveolar walls and which is chronically present in the lung.
Alpha1-PI deficiency is a chronic, autosomal, co-dominant hereditary disorder characterized by reduced levels of Alpha1-PI in the blood and lungs1, 2. Smoking is an important risk factor for the development of emphysema in patients with Alpha1-PI deficiency3. Because emphysema affects many, but not all individuals with the more severe genetic variants of Alpha1-PI deficiency (AAT deficiency), augmentation therapy with Alpha1-Proteinase Inhibitor (Human) is indicated only in patients with severe Alpha1-PI deficiency who have clinically evident emphysema.
A large number of phenotypic variants of Alpha1-PI deficiency exist, not all of which are associated with the clinical disease. Approximately 95% of identified Alpha1-PI deficient individuals have the PiZZ variant, typically characterized by Alpha1-PI serum levels < 35% of normal. Individuals with the Pi(null)(null) variant have no Alpha1-PI protein in their serum2, 3. Individuals with the lack of, or low, endogenous serum levels of Alpha1-PI, i.e., below 11 μM, manifest a significantly increased risk for development of emphysema above the general population background risk4, 5. In addition, PiSZ individuals, whose serum Alpha1-PI levels range from approximately 9 to 23 μM are considered to have moderately increased risk for developing emphysema, regardless of whether their serum Alpha1-PI levels are above or below 11 μM6.
Augmenting the levels of functional protease inhibitor by intravenous infusion is an approach to therapy for patients with Alpha1-PI deficiency. However, the efficacy of augmentation therapy in affecting the progression of emphysema has not been demonstrated in randomized, controlled clinical trials. The intended theoretical goal is to provide protection to the lower respiratory tract by correcting the imbalance between neutrophil elastase and protease inhibitors. Whether augmentation therapy with GLASSIA or any Alpha1-PI product actually protects the lower respiratory tract from progressive emphysematous changes has not been conclusively demonstrated in adequately powered, randomized controlled clinical trials. Although the maintenance of blood serum levels of Alpha1-PI (antigenically measured) above 11 μM has been historically postulated to provide therapeutically relevant anti-neutrophil elastase protection, this has not been proven. Individuals with severe Alpha1-PI deficiency have been shown to have increased neutrophil and neutrophil elastase concentrations in lung epithelial lining fluid compared to normal PiMM individuals, and some PiSZ individuals with Alpha1-PI above 11 μM have emphysema attributed to Alpha1-PI deficiency. These observations underscore the uncertainty regarding the appropriate therapeutic target serum level of Alpha1-PI during augmentation therapy.
Pharmacodynamics
Administration of GLASSIA to patients with Alpha1-PI deficiency augments the level of the deficient protein. Normal individuals have levels of Alpha1-PI greater than 22 μM. The clinical benefit of the increased blood levels of Alpha1-PI at the recommended dose has not been established.
The clinical efficacy of GLASSIA in influencing the course of pulmonary emphysema or the frequency, duration, or severity of pulmonary exacerbations has not been demonstrated in randomized, controlled clinical trials.
GLASSIA increases antigenic and functional (anti-neutrophil elastase capacity, ANEC) levels of Alpha1-PI in both the serum and the lung epithelial lining fluid (ELF) [see Clinical Studies].
Pharmacokinetics
A prospective, open-label, uncontrolled multicenter pharmacokinetic trial was conducted in 7 females and 11 males with congenital Alpha1-PI deficiency, ranging in age from 40 to 69 years. Subjects received a single dose of GLASSIA either 30 mg/kg, 60 mg/kg or 120 mg/kg. Blood samples for pharmacokinetic study were taken prior to and within 5 minutes of completion of the infusion, and then at 1 hour, 6 hours, 12 hours, 24 hours, 3 days and 7 days.
The mean results for pharmacokinetic parameters in the 60 mg/kg dosage group are shown in Table 5. The pharmacokinetics of GLASSIA were linear over the dose range of 30-120 mg/kg.
Table 5: Pharmacokinetic Parameters for Functional Alpha1-PI (Dosage 60 mg/kg; n=6)
| Pharmacokinetic Parameter |
60 mg/kg Dose Group |
| Terminal Half-Life (h) * |
111 ± 33 |
| Area under the curve(0-168 h) (mgh/mL) |
89 ± 10 |
| Clearance (mL/h/kg) |
0.68 ± 0.1 |
| Volume of Distribution (L) |
3.2 ± 0.3 |
| *Any assessment of the clinical relevance of half-life in this trial should be viewed with caution, due to the short duration of blood sampling. |
Clinical Studies
A randomized, double-blind trial with a partial cross-over was conducted to compare GLASSIA to a commercially available preparation of Alpha1-PI (Prolastin) in 50 Alpha1-PI-deficient subjects. The trial objectives were to demonstrate that the pharmacokinetics of antigenic and/or functional Alpha1-PI in GLASSIA were not inferior to those of the control product, to determine whether GLASSIA maintained antigenic and/or functional plasma levels of at least 11 microM (57 mg/dL) and to compare Alpha1-PI trough levels (antigenic and functional) over 6 infusions.
For inclusion in the trial, subjects were required to have lung disease related to Alpha1-PI deficiency and ‘at-risk’ alleles associated with Alpha1-PI plasma levels < 11 microM. Subjects already receiving Alpha1-PI therapy were required to undergo a 5-week wash-out period of exogenous Alpha1-PI prior to dosing.
Fifty subjects received either GLASSIA (33 subjects) or the comparator product (17 subjects) at a dose of 60 mg/kg intravenously per week for 12 consecutive weeks. From Week 13 to Week 24 all subjects received open-label weekly infusions of GLASSIA at a dose of 60 mg/kg.
Trough levels of functional and antigenic Alpha1-PI were measured prior to treatment, at baseline and throughout the trial until Week 24. The median trough Alpha1-PI values for Weeks 7-12 for subjects receiving GLASSIA were 14.5 microM (range: 11.6 to 18.5 microM) for antigenic and 11.8 microM (range: 8.2 to 16.9 microM) for functional Alpha1-PI. Eleven of 33 subjects (33.3%) receiving GLASSIA had mean steady-state functional Alpha1-PI levels below 11 microM. GLASSIA was shown to be non-inferior to the comparator product.
Serum Alpha1-PI trough levels rose substantially in all subjects by Week 2 and were comparatively stable during Weeks 7 to 12. All subjects receiving GLASSIA had mean serum trough antigenic Alpha1-PI levels greater than 11 microM during Weeks 7-12.
A subset of subjects in both treatment groups (n = 7 for subjects receiving GLASSIA) underwent broncho-alveolar lavage (BAL) and were shown to have increased levels of antigenic Alpha1-PI and Alpha1-PI - neutrophil elastase complexes in the epithelial lining fluid at Week 10-12 over levels found at baseline, demonstrating the ability of the product to reach the lung.
The clinical efficacy of GLASSIA in influencing the course of pulmonary emphysema or the frequency, duration, or severity of pulmonary exacerbations has not been demonstrated in randomized, controlled clinical trials.
A prospective, randomized, double-blind, active-controlled, crossover trial was conducted in thirty healthy adult subjects (23 [77%] male and 7 [23%] female; median age of 24 years [range: 19 to 61 years]), each receiving 2 infusions of GLASSIA at a dosage of 60 mg/kg. The objective of the trial was to assess the safety and tolerability of GLASSIA at an intravenous infusion rate of 0.2 mL/kg/min. On Day 1, 15 subjects received GLASSIA at 0.04 mL/kg/min with a simultaneous administration of placebo (2.5% human albumin in normal saline, for the purpose of masking infusion) at 0.2 mL/kg/min (Cohort 1), and 15 subjects received GLASSIA at 0.2 mL/kg/min with a simultaneous administration of placebo at 0.04 mL/kg/min (Cohort 2). Two weeks later (Day 15), the 15 subjects in Cohort 1 received the second infusion of GLASSIA at 0.2 mL/kg/min with a simultaneous administration of placebo at 0.04 mL/kg/min, and the 15 subjects in Cohort 2 received GLASSIA at 0.04 mL/kg/min with a simultaneous administration of placebo at 0.2 mL/kg/min. Neither efficacy nor exposure (antigenic or functional AAT) was measured in this trial.
The safety, immunogenicity, and effects on the Alpha1-PI levels in epithelial lining fluid (ELF) following GLASSIA therapy were evaluated in a multicenter study (post-licensure) of 34 subjects with emphysema due to congenital A1PI deficiency. Subjects received GLASSIA at a dosage of 60 mg/kg for 25 weeks. Sixteen subjects underwent bronchoalveolar lavage (BAL) at baseline and at Weeks 12-14. GLASSIA augmentation therapy resulted in a statistically significant increase in antigenic Alpha1-PI levels in ELF (median change=0.5 μM; geometric mean ratio=5.4, p<0.001; Table 6). Functional Alpha1-PI levels in ELF also showed a statistically significant increase in response to GLASSIA (median change=0.3 μM, geometric mean ratio=2.3, p<0.001; Table 6).
Table 6: Summary and Analysis of Change from Baseline in Antigenic and Functional Alpha1-PI Levels in the Epithelial Lining Fluid
Alpha1-PI Levels
(n = 16) |
Geometric Meana Baseline BAL (mM) |
Geometric Meana On-Treatment BAL (mM) (Weeks 12-14) |
Geometric Mean Ratioa (p-value) |
| Antigenic Alpha1-PI Levels |
0.1 |
0.6 |
5.4 (<0.001) |
| Functional Alpha1-PI Levels |
0.2 |
0.5 |
2.3 (<0.001) |
| a From a mixed-effects model with visit as fixed effect and subject as random effect; a 1-sided paired t-test for H0: Diff (On-Treatment BAL – Baseline BAL) ≤ 0 and H1: Diff (On-Treatment BAL – Baseline BAL) > 0. |
REFERENCES
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2 Stoller JK, et al. Augmentation therapy with α1-antitrypsin: patterns of use and adverse events. Chest 2003; 123:1425-34.
3 Cox DW. α1-Antitrypsin Deficiency. In: Scriver C, Sly W, eds. The Metabolic and Molecular Bases of Inherited Disease. New York: McGraw Hill; 2002:5559-78.
4 Crystal RG, et al. The alpha1-antitrypsin gene and its mutations. Clinical consequences and strategies for therapy. Chest 1989;95:196-208.
5 Crystal RG. α1-Antitrypsin deficiency: pathogenesis and treatment. Hosp Pract (Off Ed) 1991;26:81-4, 8-9, 93-4.
6 Turino GM, et al. Clinical features of individuals with PI*SZ phenotype of α1-antitrypsin deficiency. Am J Respir Crit Care Med 1996;154:1718-25.