Pharmacotherapeutic group: Other alimentary tract and metabolism products, enzymes.
ATC code: A16AB24
Mechanism of action
ARG1‑D is an inherited metabolic disease characterised by deficiency of the arginase 1 enzyme and associated with the persistent elevation of plasma arginine leading to disease manifestations and progression of clinical symptoms.
Pegzilarginase is a cobalt substituted recombinant human arginase 1 enzyme conjugated with 5 kDa mPEG carriers at a degree of substitution of 6‑12 moles of mPEG per mole of protein. The molecular mass of the conjugated protein is approximately 224‑344 kdA. The mPEG carrier reduces clearance of pegzilarginase resulting in an extended half-life while maintaining the functions of the enzyme. Pegzilarginase is intended to substitute for the deficient human arginase 1 enzyme activity in patients with ARG1‑D. Pegzilarginase has been shown to rapidly and sustainably reduce plasma arginine and convert it to urea and ornithine.
Pharmacodynamic effects
The PD effects of pegzilarginase have been evaluated in adults and paediatric subjects with ARG1‑D across a range of doses administered both intravenously and subcutaneously.
Intravenous administration of pegzilarginase resulted in early reductions in plasma arginine levels with median time to nadir (lowest arginine level) of 2‑5 hours. It is expected that plasma arginine will reach its steady-state on or before Week 8 (see Figure 1). It is not expected for the time to reach these levels to be influenced by the baseline plasma arginine value or the route of administration.
Plasma arginine levels remained controlled after switching from intravenous to subcutaneous administration at the same dose, and subcutaneous administration led to fewer and shorter episodes of pegzilarginase-induced hypoargininaemia.
Corresponding significant increases in plasma ornithine levels and decreases in plasma guanidino compound levels were demonstrated with pegzilarginase treatment.
Treatment with pegzilarginase does not directly target elevated plasma ammonia levels.
Clinical efficacy and safety
The safety and efficacy of pegzilarginase were assessed in a multicentre, double-blind, placebo-controlled trial (CAEB1102‑300A, 'Study 300A') which included 32 paediatric and adult subjects aged 2 to 29 years at enrolment with ARG1‑D. Subjects were randomised 2:1 to receive pegzilarginase or placebo intravenously once weekly at an initial dose of 0.1 mg/kg and titrated within a range of 0.05 mg to 0.2 mg/kg. All subjects were to continue on any previously prescribed dietary regimen and ammonia scavengers throughout the trial period.
The primary endpoint assessed the reduction from baseline in plasma arginine in subjects treated with pegzilarginase compared to placebo at Week 24. The key secondary endpoints assessing functional mobility were Gross Motor Function Measure Part E (GMFM-E, walking, running, jumping) and the 2‑minute walk test (2MWT). Additionally, the proportion of subjects achieving plasma arginine levels below target per treatment guidelines (< 200 µM) and within the normal range as well as the effect on GMFM Part D (GMFM-D, standing) were evaluated as secondary endpoints.
Treatment with pegzilarginase resulted in a statistically significant reduction in plasma arginine compared to placebo (p< 0.0001) after 24 weeks of treatment (Table 2 and Figure 1). Plasma arginine levels below guideline recommended target and within normal range were achieved in 90.5% of pegzilarginase-treated subjects compared to 0% of the subjects in the placebo arm (Table 2 and Figure 1).
Table 2: Analysis of plasma arginine endpoints during Study 300A double-blind period
| | Pegzilarginase (n=21) | Placebo (n=11) |
| Primary endpoint: Change from Baseline to week 24 (Log-Transformed) |
| | Baseline | Week 24 | Baseline | Week 24 |
| n | 21 | 21 | 11 | 11 |
| Geometric mean (μM) (CV) | 354.0 (0.27) | 86.4 (0.50) | 464.7 (0.19) | 426.5 (0.27) |
| Week 24 estimated reduction compared to Baseline (95% CI) | 76.7% (-146.7%, 300.1%) | 0.0% (-234.4%, 232.4%) |
| Pegzilarginase Week 24 estimated reduction relative to placebo (95% CI)a | 76.7% (67.1%, 83.5%) |
| p-valuea | < 0.0001 |
| Proportion of subjects achieving target levels in plasma arginine at week 24 |
| Proportion of subjects who achieved guideline recommended target arginine levels (< 200 µM) | 19 (90.5%) | 0 (0%) |
| Proportion of subjects who achieved normal arginine target levels (defined as < 115 µM) | 19 (90.5%) | 0 (0%) |
a Based on an MMRM with visit, randomised trial treatment, and interaction between visit and randomised trial treatment as effects and logged Baseline value included as a covariate. Default covariance structure type=unstructured. Week 24 estimated % reduction was based on geometric mean ratio and accompanying 95% CI;
Abbreviations: CI=confidence interval; CV=coefficient of variation.
Figure 1 Summary of least square mean (95% CI) 168‑hour post dose arginine levels (µM) over time in Study 300A double-blind period
Notes: Medical guideline recommendation for plasma arginine: <200 μM; Normal range defined as 40–115 μM in the clinical trial. Last observation carried forward (LOCF) was used for missing values at Week 24.
Treatment with pegzilarginase also resulted in numerical trends of improvement in mobility relative to placebo after 24 weeks as assessed by GMFM-E, 2MWT and GMFM-D performance (Table 3).
At Week 24, more subjects treated with pegzilarginase met the defined response criteria for arginine and across multiple mobility domains. Eight out of 17 evaluable subjects treated with pegzilarginase met the criteria for response in ≥ 2 neuromotor function assessments in conjunction with normalisation of plasma arginine levels, with 6 of the responders having no worsening in any assessments. Without treatment with pegzilarginase, no subjects met clinical response criteria on 2 or more clinical outcomes.
Table 3: Analysis of secondary mobility endpoints from Study 300A double-blind period
| | Pegzilarginase (n=21) | Placebo (n=11) |
| GMFM Item E (Change from baseline to week 24) |
| n | 20 | 11 |
| Mean (SD) | 4.2 (7.69) | -0.4 (6.2) |
| LS Mean | 4.2 | -0.4 |
| 95% CI for LS Mean | 0.8, 7.6 | -4.9, 4.2 |
| LS Mean Difference (Pegzilarginase – Placebo) (95% CI) | 4.6 (-1.1, 10.2) |
| 2MWT (Change from baseline to week 24) |
| n | 19 | 10 |
| Mean (SD) | 7.3 (30.64) meters | 2.7 (19.66) meters |
| LS Mean | 7.4 | 1.9 |
| 95% CI for LS Mean | -5.0, 19.8 | -15.2, 19.1 |
| LS Mean Difference (Pegzilarginase – Placebo) (95% CI) | 5.5 (-15.6, 26.7) |
| GMFM Item D (Change from baseline to week 24) |
| n | 20 | 10 |
| Mean (SD) | 2.7 (3.88) | 0.4 (0.97) |
| LS Mean | 2.7 | 0.4 |
| LS Mean Difference (Pegzilarginase – Placebo) (95% CI) | 2.3 (-0.4, 4.9) |
Abbreviations: 2MWT=2-minute walk test; CI=confidence interval; GMFM=Gross Motor Function Measure; LS=least squares, MMRM=mixed model repeated measures; SD=standard deviation; SE=standard error.
Note: Unless noted otherwise, model-based estimates (LS means, differences, 95 % CIs, and p-values) are based on an MMRM analysis with visit, randomised trial treatment, and interaction between visit and randomised trial treatment and baseline value as covariates. Default covariance structure type=unstructured.
Long‑term treatment in ARG1‑D
Paediatric and adult subjects who participated in the double-blind period of Study 300A were eligible to continue treatment in an open‑label extension period with once weekly pegzilarginase treatment. Thirty-one (n=20 pegzilarginase and n=11 placebo) of the 32 subjects entered the extension period. Subjects previously receiving pegzilarginase were transitioned to subcutaneous administration at the earliest after 8 weeks of intravenous treatment. The median duration of pegzilarginase exposure in the long-term extension period, excluding the double-blind period of 24 weeks was 94 weeks (range: 62 to 152 weeks).
During the open‑label extension, subjects who previously received pegzilarginase demonstrated sustained improvements in plasma arginine levels, GMFM-E and GMFM-D scores and 2MWT. Subjects randomised initially to placebo and treated with pegzilarginase in the open‑label extension period also showed similar reductions from baseline in mean plasma arginine levels (Figure 2).
Figure 2 Summary of mean 168‑hour post dose arginine levels (µM) over time in Study 300A double-blind and long‑term extension period
Notes: 95% confidence interval of mean is displayed; Medical guideline recommendation for plasma arginine: <200 μM; Normal range defined as 40–115 μM in the clinical trial. Last observation carried forward (LOCF) was used for missing values at Week 24 (DB24).
Abbreviations: DB = Double-blind period, LTE = Long Term Extension Period.
Paediatric population
The Medicines and Healthcare products Regulatory Agency has deferred the obligation to submit the results of studies with Loargys in one or more subsets of the paediatric population in treatment of hyperargininaemia (see section 4.2 for information on paediatric use).
Exceptional circumstances
This medicinal product has been authorised under 'exceptional circumstances'. This means that due to the rarity of the disease it has not been possible to obtain complete information on this medicinal product. The Medicines and Healthcare products Regulatory Agency will review any new information which may become available every year and this SmPC will be updated as necessary.