1 Introduction
Fabry disease is a rare, X-linked glycosphingolipid storage disorder caused by the deficiency of the enzyme alpha-galactosidase A (α-gal) due to mutations in a single gene,
GLA, located on the X chromosome Xq22.1 (OMIM 300644) [
1]. Reduced or absent α-gal activity leads to the accumulation of globotriaosylceramide and other glycosphingolipids, within the lysosomes of various cell types throughout the body, resulting in renal, cardiovascular, and cerebrovascular complications [
1]. A severe reduction (under 5%) in α-gal function causes the classical phenotype of Fabry disease and triggers the early onset of symptoms including clustered angiokeratoma, cornea verticillata, acroparesthesia, and hypohidrosis or hyperhidrosis [
1]. Additionally, patients with the classic variant may have cardiac involvement, e.g., left ventricular hypertrophy, cardiomyopathy, or arrhythmia, stroke or transient ischemic attack, and renal involvement, with albuminuria at a young age and progressive nephropathy in adulthood [
2,
3]. Higher residual α-gal activity is typically seen in female heterozygotes; male patients with higher residual α-gal activity usually have the non-classical (late-onset) form of the disease with major involvement of a only single organ system (heart or kidney) and a more variable disease course [
4]. Although there is no ethnic predisposition associated with the disease, there are geographic areas with higher prevalence. For example, in Canada, a large kindred of patients with Fabry disease has arisen in Nova Scotia dating to a common ancestor [
5,
6].
Fabry disease is a lifelong disorder with a variable but progressive course [
7] that impairs patients’ quality of life [
8,
9] and may culminate in premature death [
10] due to renal failure, cardiovascular disease, or stroke. Prior to developments in supportive care for renal function, such as the use of angiotensin-converting enzyme inhibitors and angiotensin II receptor blockers, deaths among patients with Fabry disease were mainly attributed to complications of renal failure (31% of cases) [
11]. After such significant improvements were made in renal care, the leading cause of death in patients with Fabry disease became cardiac disease (38% of cases) [
11]. Enzyme replacement therapy (ERT) with agalsidase alfa and others may attenuate renal, cardiovascular, and neuropathic disease progression characteristics of Fabry disease [
12‐
15].
In Canada [
16,
17], there are currently two approved forms of recombinant α-gal: agalsidase alfa (produced in human cell lines) [
18] and agalsidase beta (produced in Chinese hamster ovary cells) [
19]. The approved agalsidase alfa product was initially produced using a roller bottle (RB) process, which involved using bovine serum and animal-derived proteins [
20]. Following a switch to an animal component-free (AF) bioreactor process aimed at improving operational efficiency and enhancing the robustness of the manufacturing approach [
20], supplies of agalsidase alfa produced using the RB process became depleted. There were no changes to the agalsidase alfa drug product formulation, manufacturing site, or container closure; however, the new production protocol enabled a continuous supply of bioreactor-produced agalsidase alfa AF until its safety could be confirmed and it became commercially available. The primary objective of this study was to observe the safety of agalsidase alfa produced using an adapted cell line in suspension and an AF bioreactor process in Canadian patients with Fabry disease.
2 Patients and Methods
2.1 Study Design
This open-label, single-arm, multicenter safety study was performed between August 2011 and September 2017 in Canada as a regulatory requirement and was conducted according to the International Conference on Harmonization of Good Clinical Practice guidelines and the principles of the Declaration of Helsinki (ClinicalTrials.gov identifier NCT01298141). All patients (or their legal guardians/parents) provided written informed content before enrolling in the study.
2.2 Patients
Eligible patients had a documented diagnosis of Fabry disease with evidence of cardiac, neurologic, and renal complications, or uncontrolled neuropathic pain or gastrointestinal symptoms from the disease thereby satisfying current Canadian guidelines for receiving ERT for Fabry disease [
21]. The study population consisted of patients who had participated in the Canadian Fabry Disease Initiative (CFDI) study (ClinicalTrials.gov identifier NCT 00455104) and were receiving agalsidase alfa AF. Patients were maintained on the dose they were receiving at the time of enrollment in the CFDI study. The standard agalsidase alfa AF dose was defined as 0.2 mg/kg, administered by intravenous (IV) infusion over 40 (± 10) min every other week (± 5 days). As part of the regulatory approval conditions for agalsidase alfa in Canada, patients who had shown kidney or cardiac disease progression while receiving the standard every-other-week dose of agalsidase alfa were administered a higher once-weekly dose of 0.2 mg/kg, administered by IV infusion over ≥ 40 (± 10) min once weekly (± 2 days). Patients were enrolled over the course of the CFDI study, and there was wide variation in the duration of the follow-up period, which reflected the date of diagnosis of Fabry disease, the time taken to meet criteria for ERT, and the date at which consent was given for treatment. Patients who completed the present study continued to receive agalsidase alfa AF until it was approved for commercial use.
2.3 Safety Assessments
Safety was assessed by monitoring adverse events (AEs), serious AEs (SAEs), treatment-emergent AEs (TEAEs), vital signs, blood tests, and anti-agalsidase alfa antibodies. Adverse events were reported for the duration of the study period. Adverse events were coded using Medical Dictionary for Regulatory Activities (Version 13.1). The total number of TEAEs, defined as those occurring within 30 days of the last dose, were reported by system organ class. Adverse event monitoring and assessment of vital signs were assessed at each dosing visit.
Anti-drug antibodies (ADAs) to agalsidase alfa were detected by immunoglobulin G (IgG) enzyme-linked immunosorbent assay or electrochemiluminescence [
22,
23], and in vitro neutralizing anti-drug antibodies (NAbs) were measured by an enzyme inhibition assay [
22,
23]. Centralized laboratories were employed for antibody testing and laboratory tests at annual or biannual visits. Samples confirmed positive for ADAs were further characterized for NAbs. Patients with persisting NAbs were defined as those with a positive antibody titer at the time of testing and at a previous sampling. Patients with transient NAbs were defined as those with a negative antibody titer at the time of testing but a positive result at the previous sampling. Efficacy of ERT with agalsidase alfa was not assessed in this study.
Post hoc analyses of infusion-related reactions (IRRs) by antibody status were performed. A reaction was categorized as being related to an infusion if it began either during the infusion or within 12 h after the start of the infusion and was judged by the investigator as possibly or probably related to agalsidase alfa.
2.4 Statistical Analysis
Continuous data collected prior to the administration of agalsidase alfa AF and at subsequent visits were summarized using descriptive statistics. No formal statistical tests were conducted.
4 Discussion
To ensure an uninterrupted supply of agalsidase alfa for Canadian patients with Fabry disease, the upstream production process for agalsidase alfa was switched from an RB process to an AF bioreactor process. The safety of agalsidase alfa RB has been demonstrated in several clinical trials [
24‐
26] and with over 18 years of post-marketing experience [
2,
27‐
29]. This study aimed to confirm the safety profile of agalsidase alfa AF in the context of the well-characterized historical safety profile of agalsidase alfa RB.
Findings from this study revealed that the prevalence and type of TEAEs reported with agalsidase alfa AF were consistent with those reported with agalsidase alfa RB. In this study, the most commonly reported serious TEAEs were stroke, chronic renal failure, cellulitis, myocardial infarction, pneumonia, acute renal failure, ventricular tachycardia, and angina pectoris, in line with findings from previous studies using agalsidase alfa RB [
18,
25,
30‐
32]. The majority of occurrences of these TEAEs were considered to be unrelated to agalsidase alfa AF. In previous studies [
25,
31,
33], 0.0–6.6% of serious TEAEs were considered related to agalsidase alfa RB, compared with 6.4% of serious TEAEs related to agalsidase alfa AF in the present study. Similarly, 24.0% of patients reported IRRs in this study, at the higher end of the range reported in prior clinical trials of agalsidase alfa RB (12.6–25.0% of adult patients) and were mostly mild or moderate in severity [
18,
25,
33,
34].
Overall, 25.1% of patients in the present study tested positive for IgG ADAs, and IgE was transiently detected in a single female patient, who experienced one treatment-emergent serious AE of osteonecrosis and did not report any IRRs. This is higher than reported in previous studies, where anti-agalsidase alfa IgG antibodies were detected in 6.6–20.0% of patients [
25,
29,
31,
34] and no anti-agalsidase alfa IgE antibodies were reported [
29,
31]. However, the mean duration of exposure in this long-term study, at 4.4 years, was longer than in most studies (two 0.5-year studies, one 1-year study, and one long-term phase IV study with a mean follow-up of 3.5 years) [
25,
29,
31]. Furthermore, not all ADAs possess neutralizing activity [
35], and no clear pattern between ADAs and IRRs could be established, therefore conclusions relating to potential clinical impact cannot be drawn.
Although this study population consisted mainly of adults, six pediatric patients were also included. Canadian guidelines for the initiation of ERT for patients with Fabry disease are applicable to all patients with the condition, regardless of age [
21]. The safety profile for pediatric patients who received agalsidase alfa has been shown previously to be similar to that observed for adults [
36]. Moreover, an earlier 55-week phase II study of agalsidase alfa AF in 14 children aged ≥ 7 years with Fabry disease showed that this treatment was well tolerated [
37]. In the present study, definitive conclusions relating to the induction of ERT in children could not be made owing to the small number of patients.
There were a number of limitations to this study, for example, the inclusion of patients receiving agalsidase alfa AF either once weekly or every other week. Patients receiving the once-weekly regimen were included in the study to reflect real-world variations in dose as well as continued evaluation of patients included in earlier studies with agalsidase alfa; however, the low number of patients receiving once-weekly agalsidase alfa AF precluded separate analysis. Although this study confirms that agalsidase alfa AF administered every other week is well tolerated in patients with Fabry disease, it was not possible to confirm if the weekly 0.2-mg/kg regimen would change the safety profile of the drug relative to the approved 0.2-mg/kg every-other-week regimen. Previous studies have indicated comparable efficacy with once-weekly and every-other-week treatment regimens [
25], clinical outcomes data were not collected during this study thus no correlation could be explored between clinical outcomes and ERT dosing, or likewise, between clinical outcomes and ADAs, NAbs, or TEAEs. Furthermore, owing to a large amount of missing ADA and NAb data over time in the study population, trends over time in these two parameters could not be sufficiently interpreted. Last, as only two patients in the study switched from agalsidase beta to agalsidase alfa AF, it was not possible to compare patients receiving different forms of ERT.
5 Conclusions
Long-term treatment with bioreactor-produced agalsidase alfa AF was generally well tolerated and did not reveal any new safety signals in this population of Canadian adults and children with Fabry disease above the already-known safety profile of agalsidase alfa RB. The TEAE profile was consistent with the clinical manifestations of the disease, with few patients discontinuing treatment because of TEAEs. Antidrug antibody and neutralizing antibody status did not affect the proportion of patients with infusion-related reactions. Although IgE ADAs were detected in one patient, there were no associated IRRs. Overall, this study confirms that the safety profile of agalsidase alfa AF is similar to that previously reported with agalsidase alfa RB in patients with Fabry disease.
Acknowledgements
The authors thank the investigators and staff from the centers participating in the study, including Cheryl Rockman-Greenberg, MD (University of Manitoba, Winnipeg, MB, Canada); Sarah Dyack, MD (Izaak Walton Killam Health Centre, Halifax, NS, Canada); Bruno Maranda, MD (Centre Hospitalier Universitaire de Sherbrooke, Sherbrooke, QC, Canada); Jennifer MacKenzie, MD (Kingston General Hospital, Kingston, ON, Canada); Chitra Prasad, MD (London Health Sciences Centre, Victoria Hospital, London, ON, Canada); and Alicia Chan, MD (University of Alberta Hospital, Edmonton, AB, Canada). Under the direction of the authors, Vanessa Ducas, PhD, and Latoya M. Mitchell, PhD, CMPP, employees of Excel Medical Affairs, provided writing assistance for this manuscript. Editorial assistance in formatting, proofreading, copy editing, and fact checking also was provided by Excel Medical Affairs. Shire International GmbH, a Takeda company, provided funding to Excel Medical Affairs for support in writing and editing this manuscript. The sponsor was involved in the study design, data collection, analysis, and the decision to submit the manuscript for publication, but had no involvement in the interpretation of the data.