Advances in the treatment of relapsing–remitting multiple sclerosis: the role of pegylated interferon β-1a

Abstract

Multiple sclerosis (MS) is a progressive, neurodegenerative disease with unpredictable phases of relapse and remission. The cause of MS is unknown, but the pathology is characterized by infiltration of auto-reactive immune cells into the central nervous system (CNS) resulting in widespread neuroinflammation and neurodegeneration. Immunomodulatory-based therapies emerged in the 1990s and have been a cornerstone of disease management ever since. Interferon β (IFNβ) was the first biologic approved after demonstrating decreased relapse rates, disease activity and progression of disability in clinical trials. However, frequent dosing schedules have limited patient acceptance for long-term therapy. Pegylation, the process by which molecules of polyethylene glycol are covalently linked to a compound, has been utilized to increase the half-life of IFNβ and decrease the frequency of administration required. To date, there has been one clinical trial evaluating the efficacy of pegylated IFN. The purpose of this article is to provide an overview of the role of IFN in the treatment of MS and evaluate the available evidence for pegylated IFN therapy in MS.

Keywords:

• interferon
• pegylation
• multiple sclerosis
• relapsing–remitting
• disease-modifying therapy

Multiple sclerosis: an overview

Multiple sclerosis (MS) is a progressive, neurodegenerative disease affecting roughly 2.3 million people worldwide.¹ MS is characterized by infiltration of auto-reactive T cells, B cells and other immune mediators into the central nervous system (CNS), causing demyelinating lesions, axonal degeneration and formation of sclerotic plaques.² Neural damage may manifest symptomatically as optic neuritis, numbness or tingling in the extremities, muscle weakness, slurred speech and bowel/bladder dysfunction.^3–5 There is also an increasing appreciation of “soft” or “hidden” symptoms such as fatigue,^6–8 cognitive impairment^8–10 and comorbidity with other psychiatric disorders.¹¹ Diagnosis typically occurs between 20 and 40 years of age but may occur at any stage in life, and women are affected two to three times more often than men.¹ The etiology of MS remains unknown; however, it is likely an interplay between genetics and environmental factors.^2,3,12–15

The first episode of neurological symptoms, characteristic of an inflammatory demyelinating event in the brain or spinal cord, is classified as a clinically isolated syndrome (CIS).¹⁶ This remains so until a definite diagnosis of MS, with “dissemination of demyelinating lesions in space and time”, is made based on clinical episodes, magnetic resonance imaging (MRI) and/or analysis of cerebrospinal fluid.^17,18 There are three subtypes of MS based on the manifestation of clinical symptoms: relapsing–remitting MS (RRMS), secondary progressive MS (SPMS) and primary progressive MS (PPMS), which can be further classified as active- or non-active based on clinical or MRI criteria.¹⁶ The most common diagnosis is RRMS, which affects 80–85% of patients and is characterized by acute exacerbations followed by periods of remission.^1,5,19 Exacerbations, referred to as attacks or relapses, are defined as new symptoms in the absence of fever reflecting decreased neurological function, lasting at least 24 h and separated from other new symptoms by at least 30 days.¹⁸ Remission from relapse may be partial or complete; neurologic recovery following a relapse tends to be better in early stages of the disease but becomes less complete with repeated relapses.^3,5 Approximately 75% of patients presenting with RRMS will convert to SPMS within 35 years of the initial symptoms, which is marked by a decline in acute relapses with a steady increase in the progression of disability.⁵ PPMS is diagnosed in ~15% of cases and is characterized by a steady progression of disability from onset, which may occur with or without the presence of clinical relapses and/or MRI activity.^1,5,19

Current therapies for disease management

There are currently 11 disease-modifying therapies (DMTs) approved for MS in Canada (Table 1), with several emerging therapies in Phase II and III clinical trials. All currently approved DMTs modulate immune functions and are indicated for treatment of CIS, RRMS and/or SPMS with relapses. To date, there are no approved DMTs to mitigate neurodegenerative disease mechanisms for progressive forms of MS, although some experimental therapies are targeted toward neural repair mechanisms. First-line therapies in Canada include interferon beta-1b (IFNβ-1b; Betaseron^®, Extavia^®), IFNβ-1a (Avonex^®, Rebif^®), pegylated IFNβ-1a (PEG-IFNβ-1a; Plegridy^®), glatiramer acetate (Copaxone^®), teriflunomide (Aubagio^®) and dimethyl fumarate (Tecfidera^®). Second-line therapies available are fingolimod (Gilenya^®), natalizumab (Tysabri^®) and alemtuzumab (Lemtrada^®). Given that there is no cure for MS, the goals of current therapeutic interventions are to reduce the number and severity of relapses, minimize long-term disability and improve overall quality of life. In clinical trials, outcomes typically examined include annualized relapse rates (ARRs), MRI parameters such as disease burden (T2 lesion volume) or disease activity (number of new/newly enlarging T2 lesions or gadolinium-enhancing T1 lesions) and disability progression (Expanded Disability Status Scale [EDSS]²⁰). The efficacy and safety profiles of currently available DMTs are briefly summarized in Table 1.

Table 1 Disease Modifying Therapies approved by Health Canada for the treatment of Multiple Sclerosisa

DMT: Trademark	Indication	Dosage	Clinical Trial	Efficacyb	Safetyc,d	Mechanism of Actione
First line
					Common to all interferonβ	Common to all interferonβ
Interferonβ-1b Betaseron^® Extavia^®	CIS, RRMS, SPMS w/relapses	250 µg SC; QAD 250 µg SC; QAD	IFNβ MSSG^Citation22	34%	– injection site rxn – flu-like symptoms – decreased blood cell counts – increased LFT	– decrease in pro-inflammatory and increase anti-inflammatory cytokine profiles – inhibition of Th1 cell proliferation – downregulation of antigen presentation by B cells and glial cells in CNS – reduce entry of immune cells into the CNS, most likely through inhibition of MMPs – increase expression of neurotrophic factors
Interferonβ-1a Avonex^® Rebif^®	CIS, RRMS, SPMS w/relapses	30 µg IM; QW 22 µg SC; TIW 44 µg SC; TIW	MSCRG^Citation23 PRISMS^Citation24 PRISMS^Citation24	18% 27% 33%
PEG-Interferonβ Plegridy^®	RRMS	125 µg SC; Q2W	ADVANCE^Citation25	36%
Glatiramer acetate Copaxone^®	CIS, RRMS	20 mg SC; QD	CMSSG^Citation26 CONFIRM^Citation27	29% 29%	– injection site rxn – post-injection rxn (flushing, chest pain, dyspnea)	– shifts from pro-inflammatory Th1/Th17 to anti-inflammatory Th2 response – regulation of monocytes, dendritic & B cells – increase expression of neurotrophic factors
Teriflunomide Aubagio^®	RRMS	14 mg PO; QD	TEMSO^Citation30 TOWER^Citation29	32% 36%	– GI symptoms – decreased blood cell counts – increased LFT	– dihydroorotate dehydrogenase inhibitor; reduces synthesis of pyrimidine nucleotides – reduced proliferation of activated T cells – shifts from pro-inflammatory Th1/Th17 to anti-inflammatory Th2 response
Dimethyl fumarate Tecfidera^®	RRMS	240 mg PO; BD	DEFINE^Citation28 CONFIRM^Citation27	53% 44%	– flushing – GI symptoms – decreased blood cell counts – strong allergic rxn, including anaphylaxisd – PMLd	– shifts from pro-inflammatory Th1/Th17 to anti-inflammatory Th2 response – cytoprotective effects through Nrf2 – modulation of NF-κB activity
Second line
Fingolimod Gilenya^®	RRMS	0.5 mg PO; QD	FREEDOMS^Citation40 FREEDOMS-II^Citation39	54% 48%	– bradycardia – decreased blood cell counts – infection – skin cancerd – PMLd	– S1P receptor agonist; internalization and degradation – inhibits egress of activated lymphocytes from lymph node – modulate astrocyte function
Natalizumab Tysabri^®	RRMS	300 mg IV; Q4W	AFFIRM^Citation41	68%	– infusion rxn – PML	– humanized mAb that binds α4 integrin – blocks interaction with VCAM-1 preventing migration of activated lymphocytes into CNS
Alemtuzumab Lemtrada^®	RRMS	0.5 mg IV; 5 consecutive days in year 1, then 3 consecutive days in year 2	CARE MS-I^Citation42 CARE MS-II^Citation42	55% 49% (vs IFNβ-1a)	– infusion rxn – infection – thyroid disorders – secondary autoimmunity	– humanized mAb that binds CD52 – depletion of CD52-expressing lymphocytes through antibody-mediated cytolysis

Notes:

a an additional DMT, daclizumab (humanized mAb that binds CD25) marketed as Zinbryta^®, was approved by Health Canada for treatment of RRMS in December 2016 while manuscript was in print;

b efficacy reported as % reduction in relapse rate compared to placebo, except for alemtuzumab (compared to IFNβ-1a), in Phase III clinical trials;

c reported in Phase III clinical trials, except indicated as

d recently reported by Health Canada (http://www.hc-sc.gc.ca; accessed January 14, 2017);⁴²

e proposed mechanisms based on known pharmacology and/or current evidence from clinical trials and animal models.⁵³

Abbreviations: BD, twice daily; CIS, clinically isolated syndrome; CNS, central nervous system; DMT, disease modifying therapy; GI, gastrointestinal; IFN, interferon; IM intramuscular; IV, intravenous; LFT, liver function tests; mAb; monoclonal antibody; MMP, matrix metalloproteinase; MS, multiple sclerosis; NF-κβ, nuclear factor-kappa β; Nrf2, nuclear factor-erythroid 2-related factor 2; PEG, polyethylene glycol; PO, per oral; PML, progressive multifocal leukoencephalopathy ; QAD, once every other day; QD, once daily; QW, once weekly; Q2W, once every 2 weeks; Q4W, once every 4 weeks; RRMS, relapsing-remitting MS; rxn, reaction; S1P, sphingosine-1-phosphate; SC, subcutaneous; SPMS, secondary progressive MS; TIW, three times weekly; VCAM-1, vascular cell adhesion molecule 1.

Overall, treatment decisions are based on benefit/risk profile.²¹ First-line therapies have shown similar efficacy in placebo-controlled^22–30 and head-to-head trials,^27,31–35 which is supported by recent meta-analysis data.^36–38 Second-line therapies show greater efficacy in reducing relapse rates and MRI activity but are also associated with more adverse side effects and potential toxicities.^39–43 These second-line therapies are typically used only in patients who show disease activity while on first-line therapies, who cannot tolerate first-line therapies or who have extremely active RRMS from onset.²¹ Thus, the optimization of MS therapy ultimately depends on individual disease activity, response to treatment, tolerability and practitioner or patient preference. Proven efficacy and long-term safety information from numerous clinical trials make IFNβ an attractive first-line therapy; however, an important drawback is patient adherence due to frequent dosing schedules. Thus, the development of pegylated IFN⁴⁴ (Plegridy^®) has provided an alternative injectable agent that has similar efficacy and safety profiles as traditional IFNβ therapies but significantly reduces the frequency of administration.^44–50 In this review, we focus our discussion on placebo-controlled trials of subcutaneous IFNβ-1a and head-to-head trials against other IFNβ formulations to evaluate the role of PEG-IFNβ-1a therapy in MS (Table 2).

Table 2 Summary of PRISMS, INCOMIN, EVIDENCE and ADVANCE trials

PRISMS^Citation24 – Prevention of Relapses and Disability by Interferon beta-1a Subcutaneously in Multiple Sclerosis
Inclusion criteria	Clinically definite RRMS for ≥1 year; ≥2 relapses in preceding 2 years, and baseline EDSS scores of 0–5
Exclusion criteria	Previous systemic treatment with IFNs, lymphoid irradiation or cyclophosphamide or with other immunomodulatory or immunosuppressive therapy in previous 12 months
Intervention	IFNβ-1a (Rebif^®) 22 or 44 µg SC TIW or placebo
Primary outcome	Relapse rate over the course of 2-year study
Summary of results	Relapse rates were reduced by 27% in the 22 µg IFNβ-1a intervention and 33% in the 44 µg IFNβ-1a intervention group compared to placebo group. IFNβ-1a interventions were also associated with an increased proportion of patients remaining relapse free, decreased change in EDSS scores and decreased time to first progression. MRI end points showed a decrease in total burden of disease (ΔT2 lesion volume), number of new/newly enlarging T2 lesions and number of T1 Gd-enhancing lesions with IFNβ-1a treatment compared to placebo. High-dose treatment (44 µg) showed more favorable outcomes compared to low-dose treatment (22 µg)
INCOMIN^Citation31 – Independent Comparison of Interferon
Inclusion criteria	Clinically definite RRMS; ≥2 clinically documented relapses during the preceding 2 years with no relapse (and no corticosteroid treatment) for at least 30 days before study entry and baseline EDSS score of 1–3.5
Exclusion criteria	Previous systemic treatment with IFNβ or treatment with other immunosuppressive or immunomodulatory drugs (except corticosteroids)
Intervention	IFNβ-1b (Betaseron^®) 250 µg SC QAD or IFNβ-1a (Avonex^®) 30 µg IM QW
Primary outcome	Proportion of patients who remained relapse free over the course of 2-year study
Summary of results	In the IFNβ-1b SC intervention group, 49% of patients remained relapse free compared to 33% in the IFNβ-1a IM intervention group. IFNβ-1b treatment was also associated with a decrease in ARR and 6-month sustained progression in EDSS. MRI end points showed an increase in the proportion of patients remaining free from new T2 lesions, remaining free from T1 Gd-enhancing lesions and showing no MRI activity with IFNβ-1b SC compared to IFNβ-1a IM treatment
EVIDENCE^Citation32 – Evidence of Interferon Dose-response-European North American Comparative Efficacy
Inclusion criteria	Clinically confirmed RRMS; ≥2 relapses in previous 2 years and baseline EDSS score of 0–5.5
Exclusion criteria	Previous treatment with IFNβ
Intervention	IFNβ-1a (Rebif^®) 44 µg SC TIW or IFNβ-1a (Avonex^®) 30 µg IM QW
Primary outcome	Proportion of patients who remained relapse free at ≥48 weeks
Summary of results	In the IFNβ-1a SC TIW intervention group, 56% of patients remained relapse free compared to 48% in the IFNβ-1a IM QW intervention group. IFNβ-1a SC TIW was also associated with a decrease in ARR and time to first relapse, but no difference was observed in EDSS progression. MRI end points showed a decrease in the number of new or enlarging T2 lesions in the IFNβ-1a SC TIW compared to the IFNβ-1a IM QW treatment
ADVANCE^Citation25 – Pegylated Interferon beta-1a for Relapsing–Remitting Multiple Sclerosis
Inclusion criteria	RRMS; ≥2 relapses in previous 3 years with at least one relapse in previous 12 months and baseline EDSS score of 0–5
Exclusion criteria	Progressive MS, previous treatment with IFNβ for >4 weeks or discontinuation <6 months before baseline
Intervention	PEG-IFNβ-1a Plegridy^® 125 µg SC Q2W or Q4W or placebo
Primary outcome	ARR at 48 weeks
Summary of results	ARR were reduced by 36% in the PEG-IFN Q2W and 28% in the PEG-IFN Q4W intervention groups compared to the placebo group. PEG-IFNβ interventions were also associated with an increased proportion of patients remaining relapse free and a decreased proportion of patients showing 12-week sustained EDSS progression. MRI end points showed a decrease in total burden of disease (ΔT2 lesion volume), number of new/newly enlarging T2 lesions and number of T1 Gd-enhancing lesions with PEG-IFNβ treatment compared to placebo. More frequent injections (Q2W) showed more favorable outcomes compared to low-frequency injections (Q4W)

Abbreviations: ARR, annualized relapse rate; EDSS, expanded disability status scale; IFNβ, interferon beta; IM, intramuscular; MS, multiple sclerosis; PEG, polyethylene glycol; QAD, once every other day; QW, once weekly; Q2W, once every 2 weeks; Q4W, once every 4 weeks; RRMS, relapsing–remitting MS; MRI, magnetic resonance imaging; SC, subcutaneous; TIW, three times weekly.

Interferon β

IFNβ was the first biologic approved for MS therapy. IFNs are a family of cytokines involved in the regulation of innate and adapted immunity^12,51–53 and are thus ideal candidates for immunomodulatory therapies in MS. Early attempts at IFN therapy in MS included the use of IFNγ, IFNα and IFNβ.⁵⁴ Unexpectedly, administration of IFNγ resulted in activation of the immune system and increased the occurrence of relapses. Several different formulations of IFNα and IFNβ were explored with promising results, but IFNβ had a more acceptable patient safety profile. Both recombinant IFNβ-1b produced in Escherichia coli and recombinant IFNβ-1a produced in mammalian cells are approved for the treatment of MS (Table 1). Differences in post-translational modifications confer reduced biological activity of non-glycosylated IFNβ-1b compared to glycosylated IFNβ-1a,⁵⁵ which is reflected in their dosages. Clinical trials with IFNβ have demonstrated a reduction in relapse rates and MRI activity.^22–24 Delays in disease progression, as measured with EDSS, have also been reported over the 1- to 2-year clinical trial periods,^23,24 and long-term benefits have been associated with continued IFNβ treatment in follow-up studies.^56,57 However, a large retrospective study by Shirani et al⁵⁸ reported no link between IFNβ treatment and the long-term disability progression, which has renewed debate around this issue.^59–61

Dosage and administration

IFN treatment is currently indicated for the treatment of CIS, RRMS and SPMS with relapses. Commercially available formulations of IFNβ-1b include Betaseron^® and Extavia^®, which are administered subcutaneously (SC) every other day (QAD) at a dose of 250 µg. IFNβ-1a is marketed as Avonex^® administered intramuscularly (IM) once weekly (QW) at a dose of 30 µg or Rebif ^® administered SC three times weekly (TIW) at a dose of 22 or 44 µg.

Mechanisms of action

The precise mechanisms of action of IFNβ in MS therapy are unknown but have been attributed to its antiproliferative, antiviral and immunomodulatory abilities.⁵² Systemic administration of IFNβ is believed to primarily modulate immune cell function in the periphery.⁶² In general, IFNβ appears to oppose the pathogenic processes associated with MS disease progression by shifting from a pro-inflammatory to an anti-inflammatory immune profile (Figure 1). A key player in MS pathology are auto-reactive T cells that migrate across the blood–brain barrier (BBB), initiating inflammatory cascades in the CNS inflicting damage on axons, neurons and myelin sheaths.^2,63 IFNβ therapy is associated with a decrease in the expansion of pro-inflammatory Th1 and Th17 subtypes and promotes the expansion of anti-inflammatory Th2 subtype.^64–68 IFNβ has also been shown to modulate the function of regulatory T cells,⁶⁹ B cells,^70,71 natural killer cells⁷² and dendritic cells.⁷³ The complexity of immune cell signaling networks makes it difficult to delineate the direct and indirect effects of IFNβ on each cell type.⁵² Effects of IFNβ on T cell function are mostly likely mediated indirectly through up-regulation of anti-inflammatory mediators, such as interleukin (IL)-10,^66,74–78 and down-regulation of pro-inflammatory cytokines, such as IL-17, osteopontin and tumor necrosis factor α (TNFα),^{64,73,74,78,79} secreted from other types of immune cells.

Figure 1 Schematic depicting the role of PEG-IFNβ therapy in MS.

Notes: (A) In MS, pro-inflammatory cytokines stimulate CD4+ cells to proliferate and differentiate into Th1 and Th17 effector cells. Activated T cells express VLA-4, which interacts with VCAM-1 on endothelial cells, to facilitate crossing the BBB. In the CNS, auto-reactive T cells and macrophages result in damage to the myelin sheath, axons and neurons. Inflammatory demyelinating lesions result in the clinical presentation of MS. (B) IFNβ is conjugated to PEG to increase the molecule’s serum concentration and half-life. Proposed actions of IFNβ include modulating cytokine milieu to favor anti-inflammatory pathways, which inhibits expansion of Th1/Th17 and promotes expansion of Th2 cells. Down-regulation of VLA-4 and inhibition of MMP-9 reduce migration of activated T cells into CNS. (C) Linking of anti-VCAM-1 antibodies to the PEG tail may enhance IFNβ anti-inflammatory actions by 1) blocking interaction of leukocytes expressing VLA-4 with VCAM-1 and 2) increasing local concentration of PEG-IFNβ at BBB.
Abbreviations: BBB, blood–brain barrier; CNS, central nervous system; IFNβ, interferon beta; M, macrophage; MMP, matrix metalloproteinase; MS, multiple sclerosis; PEG, polyethylene glycol; PEG-IFNβ, pegylated interferon β; TIMP-1, tissue inhibitor of metalloproteinase-1; VCAM-1, vacular cell adhesion molecule 1; VLA-4, very late activation antigen-4.

IFNβ has also been implicated in acting at the BBB, impeding migration of leukocytes into the CNS. Matrix metalloproteinases (MMPs), more specifically MMP-9 and tissue inhibitor of metalloproteinase-1 (TIMP-1), are involved in the degradation and remodeling of the extracellular matrix.⁸⁰ IFNβ has been shown to decrease serum levels associated with a decrease in the number of new and/or active MRI lesions.^81,82 To facilitate crossing the BBB, activated T cells up-regulate adhesion molecules, such as very late activation antigen-4 (VLA-4), which interact with vascular cell adhesion molecule 1 (VCAM-1) receptor expressed by endothelial cells (Figure 1). Evidence suggests that administration of IFNβ down-regulates expression of VLA-4/α-4 integrin, thereby inhibiting lymphocyte migration into the CNS.^83–85 Together, these mechanisms reduce the number of pro-inflammatory immune cells in circulation and suppress the ability of activated leukocytes to enter the CNS. In addition to immunomodulatory effects, IFNβ treatment has been associated with increased expression of neurotrophic factors,^86–88 which may convey cytoprotective effects.

Clinical trials

The Prevention of Relapses and Disability by Interferon beta-1a Subcutaneously in Multiple Sclerosis (PRISMS) study^23,89,90 was pivotal multi-centered, randomized, double-blind, placebo-controlled clinical trial investigating the benefit of SC IFNβ-1a administration TIW for RRMS (Table 2). Participants were randomized to either 22 or 44 µg or placebo groups with a primary outcome of number of relapses during the 2-year study period.²³ The number of relapses was lower in both intervention groups compared to placebo: 27% (95% confidence interval [95% CI] 14–39) reduction for the 22 µg dose (1.82 vs 2.56) and 33% (95% CI 21–44) reduction for the 44 µg dose (1.73 vs 2.56) (Table 3). This included a delay in the time to relapse and a decreased number of severe relapses, steroid courses and hospitalizations with IFNβ-1a treatment. Monitoring of disease activity with MRI⁸⁹ showed a corresponding decrease in the number of Gd-enhancing T1 lesions, number of active T2 lesions and reduction in burden of disease (T2-weighted). Participants receiving placebo showed a 10.9% increase in total lesion volume compared to a 1.2% decrease for the 22 µg intervention and 3.8% decrease for the 44 µg intervention. After 4 years, IFNβ-1a treatment continued to reduce ARR (0.90 in year 1 vs 0.44 in year 4 for high-dose group) and improve MRI outcomes.⁹⁰ Furthermore, both 4-year treatment groups showed favorable outcomes compared to the delay-treatment, crossover groups. Follow-up analyses at both 8⁹¹ and 15 years⁵⁶ are indicative of long-term benefit of IFNβ-1a therapy on disease course, favoring early treatment intervention, higher dosages and longer exposure times.

Table 3 Comparison of currently available data on interferon β-1a and pegylated interferon β-1a

	IFNβ-1a aPRISMS: 2-year study^Citation24			PEG-IFNβ-1a aADVANCE: 1-year study ^Citation5
Administration	Placebo SC; TIW	22 µg SC; TIW	44 µg SC; TIW	Placebo SC; Q2W	125 µg SC; Q2W	125 µg SC; Q2W
Number of patients enrolled	187 (170)	189 (167)	184 (165)	500 (456)	512 (438)	500 (438)
% Completed treatment	91	88	90	91	86	88
Clinical outcomes
Relapse rateb	2.56	1.82	1.73	0.40	0.26	0.29
% reduction of relapse rate vs placebo	–	27	33	–	36	28
% relapse free (1 year)	22	37	45	71	81	78
Disability progressionc	0.48	0.23	0.24	0.105	0.068	0.068
MRI outcomes
Burden of diseased	10.9%	−1.2%	−3.8%	0.77 cm^3	−0.26 cm^3	0.06 cm^3
T2 new/enlarging lesions	4.5	1.3	0	10.9	3.6	7.9
T1 Gd-enhancing lesions	8.0	1.4	1.3	1.4	0.2	0.9
New active lesionse	10.6	2.1	1.3	11.2	3.7	7.3
NAbs	–	Anti-IFN: 23.8%	Anti-IFN: 12.5%	–	Anti-IFN: <1%f anti-PEG: 6%f	Anti-IFN: <1%f anti-PEG: 8%f
Adverse events (%)g
Injection-site reactions	22	61	62	7	62	56
Influenza-like illness	24	25	27	13	47	47
Headache	44	47	45	33	44	41
Fatigue	16	14	19	10	10	11
Myalgia	8	13	14	6	19	19
Fever	6	13	12	15	45	44
Abnormal blood cell counts
Leukopenia	2	4	8	1	7	4
Lymphopenia	4	5	13	3	5	4
Elevated liver enzymes
Alanine aminotransferase	1	5	7	1	2	2
Aspartate aminotransferase	1	2	3	1	1	1
Adverse events resulting in discontinuation	1	3	5	1	5	5
Pharmacokinetics^Citation62
AUCh	–	12 IU⋅h/mL	71.6 IU⋅h/mL	–	24.5 ng⋅h/mL	23.5 ng⋅h/mL
Cmax	–	1.3 IU/mL	12.8 IU/mL	–	221 pg/mL	202 pg/mL
Tmax (h)	–	1–2	0.25	–	35.9	35.1
half-life (h)	–	n.a.	12.8	–	62.8	56.8

Notes:

a Comparison of placebo-controlled studies; no head-to-head trials have directly compared IFNβ-1a to PEG-IFNβ-1a.

b Defined as number of relapses over 2-year study period (PRISMS) or ARR at 48 weeks (ADVANCE).

c Defined as change in EDSS over duration of study (PRISMS) or proportion of patients with 12-week sustained progression in EDSS ≥1.0 (ADVANCE).

d Defined as change in total in T2 lesion volume from baseline (PRISMS, mm²; ADVANCE, cm³).

e Defined as the sum of T1 Gd-enhancing and new or newly enlarging T2 lesions (PRISMS, clinically unique; ADVANCE new active).

f Reported at 2 years.¹²²

g PRISMS reported adverse events in first 3 months of therapy and ADVANCE reported adverse events over the full 48 weeks.

h Measured over 8 h for 22 µg IFNβ-1a and measured over 168 h for 44 µg IFNβ-1a and 125 µg PEG-IFNβ-1a. C_max, maximum serum concentration; T_max, time to reach C_max.

Abbreviations: ARR, annualized relapse rate; AUC, area under curve; EDSS, Expanded Disability Status Scale; IFN, interferon; Q2W, once every 2 weeks; MRI, magnetic resonance imaging; n.a., not available; NAbs, neutralizing antibodies; PEG, polyethylene glycol; SC, subcutaneous; TIW, three times weekly.

Following the PRISMS study, head-to-head trials further investigated the efficacy of different IFNβ formulations and dosage in the Independent Comparison of Interferon (INCOMIN) study³¹ and Evidence of Interferon Dose-response-European North American Comparative Efficacy (EVIDENCE) study.³² The INCOMIN trial³¹ compared 250 µg IFNβ-1b SC injections QAD with 30 µg IFNβ-1a IM injections QW over 2 years (Table 2). The primary outcome of the proportion of patients remaining relapse free favored IFNβ-1b therapy (49%) over IFNβ-1a therapy (33%); this was also reflected by a 29% reduction in the ARR (0.5 for IFNβ-1b vs 0.7 for IFNβ-1a). For MRI outcomes, IFNβ-1b SC therapy increased the proportion of patients who remained free from Gd-enhancing T1 lesions or new T2 lesions compared to IFNβ-1a. The burden of disease for participants receiving IFNβ-1b decreased 2.8% whereas IFNβ-1a increased 11.7%. However, due to multiple variables in treatment regimen, it is difficult to ascertain whether improved outcome relates to difference in formulation, dosage, frequency or route of administration.

The EVIDENCE trial³² compared IFNβ-1a treatment at a dosage of 44 µg administered by SC injections TIW (TIW) with a dosage of 30 µg administered by IM injections QW over 1 year (Table 2). The primary outcome was the proportion of patients remaining relapse free, which favored 44 µg SC TIW therapy (56%) over 30 µg IM QW therapy (48%). There was a 17% reduction in ARR in the 44 µg SC TIW group (0.54) compared to the 30 µg IM QW group (0.65), and the mean number of active T2 lesions was also reduced by 36%. Thus, both the IFNβ-1b SC (cumulative dose 28 MIU/week) in the INCOMIN study and the IFNβ-1a SC (cumulative dose 36 MIU/week) in the EVIDENCE trial showed greater efficacy than IFNβ-1a IM (cumulative dose 6 MIU/week). Pharmacokinetic studies indicate that the bioavailability of IFNβ does not appear to differ substantially between SC and IM administration.⁶² Taken together, data from the PRISMS, INCOMIN and EVIDENCE trials demonstrated that higher, more frequent dosing of IFNβ improve patient outcomes.

Therapeutic considerations

Safety profile

IFNs are naturally occurring cytokines and generally well tolerated. The PRISMS study²³ reported common adverse events of IFNβ-1a treatment to include injection-site reactions (redness, swelling), flu-like symptoms, fever, headache and myalgia. However, flu-like symptoms were also commonly reported in placebo group (24% vs 25% and 27% in 22 and 44 µg treatment groups, respectively). Most injection-site reactions were mild, with only eight incidences of skin necrosis (>150,000 injections). Less common, but serious, adverse events include decreased numbers of white blood cells and platelets and elevated liver enzymes. Similar safety profiles were reported in 4-year follow-up studies. Over 4 years, there were three deaths reported none of which were related to the treatment.^90,92

There were initially reports of IFNβ therapy causing an increase in the incidence of depression. Given the neurologic pathology of MS and its chronic progressive nature, the estimated lifetime prevalence of major depression in MS is as high as 50%.^93,94 With such a high comorbidity rate of depression among MS patients,¹¹ it is difficult to definitively link IFNβ therapy with an increased risk of depression. There was no significant difference among treatment groups in the PRISMS trial; depression was reported by 28% of patients receiving placebo, 21% of patients receiving 22 µg of IFNβ and 24% of patients receiving 44 µg of IFNβ.²³ During the study, one patient in the placebo group committed suicide and three patients in each group reported attempting suicide or suicidal ideation. Furthermore, no difference in the incidence of depression has been found between patients receiving IFNβ and glatiramer acetate therapy.⁹⁵

Neutralizing antibodies

Another concern associated with IFNβ-1a therapy is the production of neutralizing antibodies (NAbs). In the PRISMS study, 23.8% of participants receiving the 22 µg dose and 12.5% of participants receiving the 44 µg dose were positive for NAbs but concluded that NAbs had no impact on the mean relapse count in either intervention.²³ The INCOMIN study reported more frequent production of NAbs with IFNβ-1b (30%) than with IFNβ-1a (7%) therapy, but again this did not appear to negatively impact treatment efficacy.³¹ In contrast, the EVIDENCE study with IFNβ-1a reported a higher prevalence of NAbs within the 44 µg SC TIW (26%) compared to the 30 µg IM QW (3%) intervention and noted that NAbs developed earlier among the high-dose intervention.³² Disease activity was significantly greater in participants receiving 44 µg SC TIW who were positive for NAbs compared to those who were negative for NAbs; however, NAb^+ve and NAb^−ve participants had less MRI activity than their 30 µg IM QW counterparts.

The clinical implications of NAbs in IFNβ therapy remain unclear. High titers of NAbs appear to be related to the formulation, dosing regimen and route of administration.^{31,32,96–98} NAb levels often peak within 6–12 months of starting therapy and then decline, with ~10% of patients developing persistent NAbs.⁹⁸ At persistently high titers, NAbs can reduce biological activity^99,100 and negatively impact long-term drug therapy.^{97,99,101–103} The most recent treatment recommendations provide little consensus on how to approach this issue:²¹ current practices include periodic testing of NAb levels, testing for NAbs only when considering switching therapies or opting to base treatment decisions solely on clinical outcomes.

Adherence

Frequent IFNβ administration has been shown more effective for managing RRMS;^31,32 however, given that the disease is chronic and progressive, this dosing regimen may not be amenable for many patients. Overall, adherence rates of injectable DMTs requiring frequent administration (i.e., ≥QW) have been estimated at 27–76%,^104–110 with decreased adherence associated with an increased risk of relapse.^105,106 The most commonly reported reasons for discontinuation were lack of efficacy, tolerability (i.e., adverse effects such as flu-like symptoms and injection-site reactions) and patients’ decision (i.e., both practical issues and mental exhaustion).^111–115 Discontinuation due to adverse effects typically occurs within the first year of treatment,^114,115 but this can be mitigated by dose titration, prophylactic treatment of flu-like symptoms and injection-site reactions, increased patient education and the use of autoinjectors.^116,117 Another viable approach has been drug modification to increase pharmacokinetic profile and prolong bioavailability to reduce frequency of administration, such as the pegylation of IFNβ-1a.⁴⁴

Pegylated interferon β

Pegylation is the process by which molecules of polyethylene glycol (PEG) are chemically conjugated to a biological product. The addition of PEG increases the size of a macromolecule, generally increasing its solubility, stability and mobility in solution.^118,119 Pegylation decreases the rate of renal clearance and may also reduce receptor- or antibody-mediated clearance and proteolytic degradation.^44,118 This results in increased exposure, half-life and serum concentrations of the therapeutic agent. Other potential benefits of pegylation are reduced antigenicity and immunogenicity, as PEG could potentially mask recognition of epitopes.^44,118 Addition of large PEG molecules can often decrease binding to target through steric hindrance,¹¹⁹ yet the overall goal is to balance pharmacodynamic and pharmacokinetic properties to improve treatment efficacy.¹¹⁸ These attributes are ideal for a biomolecule such as IFNs, which are rapidly cleared without any modifications.⁶² For example, pegylated forms of IFNα-2a (Pegasys^®; Hoffman La Roche) and IFNα-2b (PegIntron^®; Schering-Plough) have been used in the management of chronic hepatitis C for over a decade.^119,120 The development of PEG-IFNβ-1a, a 20 kDa linear methoxy PEG molecule conjugated to the alpha amino group of the N terminal amino acid residue of IFNβ, demonstrated a desirable pharmacokinetic and pharmacodynamic profile to decrease the frequency of administration for the management of MS.⁴⁴

Dosage and administration

PEG-IFNβ-1a is marketed as Plegridy^® and currently indicated for the treatment of RRMS. PEG-IFNβ-1a is administered SC every 2 weeks (Q2W) at a dose of 125 µg.

Mechanisms of action

The mechanisms of action of PEG-IFNβ-1a are presumably similar to its parent compound. The N-terminus of IFNβ, which is known not to be critical for its activity, was chosen for the site of attachment.⁴⁴ Although predicted not to affect ligand-binding interactions, a size-dependent decrease in antiviral activity was observed with increasing size of PEG molecules. As smaller PEG molecules did not convey the desired pharmacokinetic properties, 20 kDa was chosen for the pegylation of IFNβ-1a.⁴⁴ In healthy controls, PEG-IFNβ-1a and IFNβ-1a administration resulted in similar changes in cytokine gene expression favoring an anti-inflammatory profile.¹²¹ To our knowledge, the anti-inflammatory properties of PEG-IFNβ-1a have not yet been directly investigated or reported in clinical trials or animal models of MS.

Clinical trials

To date, there has been one randomized, double-blind, placebo-controlled clinical trial investigating PEG-IFNβ-1a in RRMS. The ADVANCE trial^25,122,123 was a 2-year study, consisting of a 48-week placebo-controlled phase and 48-week crossover phase, comparing the efficacy of 125 µg PEG-IFNβ-1a administered by SC injection Q2W or every 4 weeks (Q4W; Table 2). At 48 weeks, the primary outcome of ARRs showed a benefit for both PEG-IFNβ therapy regimens compared to placebo.²⁵ The ARRs were 0.256 (95% CI 0.206–0.318) for the Q2W intervention and 0.288 (95% CI 0.234–0.355) for the Q4W intervention compared to 0.397 for placebo (95% CI 0.328–0.481), corresponding to a 36% and 28% reduction in the Q2W and Q4W, respectively. MRI outcomes^25,123 showed a decrease in the number of new or newly enlarging T2 lesions in both PEG-IFNβ treatment groups but only a significant decrease in the number of Gd-enhancing and T1 hypointense lesions in the Q2W group compared to placebo. Total T2 lesion volume increased in the placebo group by 0.77 cm³ and Q4W treatment group by 0.06 cm³ and decreased in the Q2W treatment group by 0.26 cm³. The proportion of patients achieving “no evidence of disease activity” (NEDA), defined as absence of both clinical and MRI disease activity, was 33.9% in the PEG-IFNβ Q2W, 21.5% in the PEG-IFNβ Q4W and 15.1% in the placebo group.¹²³ These data demonstrate a benefit of both PEG-IFNβ treatments but suggest an advantage of a more frequent dosing regimen to minimize disease activity.

Upon completion of the first year, participants receiving placebo were re-randomized to one of the treatment interventions and participants already receiving drug intervention remained on the same dosing regimen.¹²² Both continuous intervention groups showed a reduction in the ARR compared to the corresponding delayed-treatment groups, 37% reduction and 17% reduction in the Q2W and Q4W dosing, respectively. The ARR decreased among participants receiving continuous PEG-IFNβ Q2W from 0.230 (95% CI 0.183–0.291) to 0.178 (95% CI 0.136–0.233), while the ARR was roughly maintained among participants receiving continuous PEG-IFNβ Q4W (0.286 [95% CI 0.231–0.355] and 0.291 [95% CI 0.231–0.368]). Also, the number of new or newly enlarging T2 lesions continued to decline for both the continuous Q2W and Q4W groups. When directly comparing the two dosing regimens, there was a 24% reduction in ARR and 60% reduction in the number of new or newly enhancing T2 lesions in the Q2W compared to the Q4W. Subgroup analysis indicated that the efficacy of PEG-IFNβ was similar across different populations of RRMS patients.¹²⁴ A recent preliminary report from the ATTAIN study, an extension of the ADVANCE trial, indicates that the efficacy of each treatment was maintained over 3 years.⁴⁵ This suggests, similar to other IFNβ formulations, that early intervention, higher cumulative dosage and increased exposure time are advantageous.

Therapeutic considerations

Safety profile

Reported side effects of PEG-IFNβ were similar to those previously reported for both SC and IM injections of IFNβ. These included mild-to-moderate adverse events such as injection-site reactions, influenza-like illness, fever, chills, headache and myalgia. In year 1, the incidence of discontinuation of the study due to adverse events was 6% in both treatment groups and 1% in the placebo group, the most commonly reported reason being influenza-like illness. The rate of severe adverse events was similar among the three study groups: 11% in the placebo, 18% for the every 2-week intervention and 16% for the every 4-week intervention.²⁵ Participants in both intervention groups had decreased number of blood cells and elevated liver enzymes, but neither was determined to be clinically significant and the majority returned to normal ranges within 2 years. The incidence of abnormal white blood cell counts remained low (≤10% of participants) across both intervention groups.^25,122 Over the 2-year study, nine deaths occurred; however, an independent safety-monitoring board reported that these events were not likely related to the study drug and did not change the risk–benefit profile of PEG-IFN.¹²² A 3-year follow-up from the ATTAIN study indicates that PEG-IFN continues to show a similar safety profile.¹²⁵ As with other pegylated pharmaceuticals, adverse side effects are associated primarily with the active drug not the PEG moiety.¹¹⁹

Neutralizing antibodies

As stated previously, traditional SC IFNβ-1a therapy can result in persistently high levels of NAbs (~10% of patients), which may negatively impact the treatment efficacy. Development of IFNβ antibodies was <1% in both interventions, whereas development of antibodies against PEG was reported at 6% in Q2W and 8% in Q4W interventions.¹²² The appearance of NAbs was determined not to impact efficacy or safety of treatment, but due to low rate of incidence in this study, data should be interpreted with caution.¹²⁶

Adherence

The use of PEG-IFNβ-1a has been estimated to reduce the number of injections by >90% compared to other first-line therapies.³⁷ In the ADVANCE study, 88% of the participants completed the first year²⁵ and 90% of continuing patients completed the second year.¹²² Tolerability and adverse events, such as flu-like symptoms and injection-site reactions, were still major factors leading to discontinuation; however, management strategies similar to standard IFN therapies can be used to mitigate impact.¹²⁷ Adherence to treatment, defined by the number of doses received divided by the number of doses expected to receive, was >99% in each group.²⁵ It should be noted though that adherence in controlled trials is usually greater than in a clinical setting.¹¹⁶ While reduced frequency of administration is expected to increase adherence,^44,45,47,49 this will need to be further evaluated as PEG-IFN therapy is integrated into clinical practice.

Interferon β versus pegylated interferon β

A comparison of the efficacy, safety profile and pharmacokinetics data for PEG-IFNβ-1a and its parent compound IFNβ-1a is reported in Table 3. A considerable amount of data are available regarding the pharmacokinetic properties of different IFNβ formulations, dosages and routes of administration; the only factor that substantially alters the pharmacokinetic profile is pegylation.⁶² PEG-IFNβ-1a administration by IM injection showed a fourfold increase in drug exposure, assessed by the area under the curve (AUC), compared to an equal dosage of IFNβ-1a.¹²¹ PEG-IFNβ and IFNβ administration both resulted in altered cytokine expression profiles, but the pharmacological response with PEG-IFNβ had a more rapid onset and was sustained for a longer period.¹²¹ Only one study has done a direct comparison between standard therapeutic doses of IFNβ-1a and PEG-IFNβ-1a administered by SC injection over the course of 2 weeks.¹²⁸ When healthy participants were evaluated for accumulative drug exposure with six doses of 44 µg IFNβ-1a SC compared to a single dose of 125 µg PEG-IFNβ-1a, the AUC was found to be 60% higher for the PEG-IFNβ dosage regime. This corresponds to approximately fourfold increase in C_max, approximately sixfold increase in T_max and approximately twofold increase in half-life. Thus, pegylation of the IFNβ-1a molecule results in an increased serum concentration and greater drug exposure compared to the traditional IFNβ-1a therapy. The tolerability of PEG-IFNβ was favorable with a lower incidence of adverse events compared to the IFNβ dosing regimen.¹²⁸ This was presumably due to the need for less frequent injections with PEG-IFNβ.

To date, there are no published head-to-head clinical trials comparing PEG-IFNβ to the alternative formulations of IFNβ or any other DMT. In the PRISMS study²³ and the ADVANCE study,²⁵ similar efficacy was observed between IFNβ-1a and PEG-IFNβ-1a interventions when comparing % relative reduction in relapse rate. Both studies also reported favorable MRI outcomes, including a decrease in disease activity (T1- and/or T2-weighted) and burden of disease (total lesion volume) with treatment. However, due to different methodology and reporting measures, direct comparisons of study outcomes are difficult. Although meta-analysis of efficacy and safety profiles³⁷ and cost-effectiveness analysis¹²⁹ tend to favor PEG-IFNβ-1a, these are relatively premature. Full results from the ATTAIN study will provide further data on the long-term efficacy on safety of PEG-IFNβ therapy. In addition to clinical trial data, longitudinal studies with IFNβ-1a treatment also suggest positive effects on cognitive function^130–132 and long-term benefits of disease progression,^55,90 but these types of data sets are not yet available for PEG-IFNβ-1a. Ultimately, head-to-head clinical trials and observational studies from clinical practice will continue to inform us about the role of PEG-IFNβ in MS disease management.

What are future therapeutic possibilities for PEG-IFN?

The conjugation of PEG to IFNβ-1a has expanded the therapeutic options for the management of MS. By prolonging the half-life of IFNβ-1a, increasing its exposure and decreasing its elimination,^44,62 this novel formulation provides a safe and effective first-line therapy with a decreased frequency of administration. This new PEG-IFNβ formulation has also created a platform upon which other immunomodulatory molecules may be added (Figure 1). This may serve to enhance the efficacy of IFNβ by 1) providing opportunity to develop combination therapies and 2) targeting the IFNβ to specific locations within the body. For example, by specifically targeting VCAM-1, expressed on activated endothelial cells, the anti-VCAM-PEG-IFN molecule could more effectively block activated T cells from crossing the BBB. Theoretically, this would also increase the local concentration of IFNβ to the BBB possibly directing its immunomodulatory effects to this compartment and reduce non-specific systemic effects. Whether these hypothetical modifications would enhance IFN activity has yet to be determined. However, if successful it may lead to targeted delivery of IFNβ with potentially greater efficacy and a reduction in frequency of side effects.

Conclusion

IFNβ, a naturally occurring cytokine, was the first DMT approved for MS therapy. Clinical evidence has consistently demonstrated a decrease in relapse rates and MRI activity; however, the inherent physical properties require it to be frequently administered in order to maintain therapeutic concentrations. The conjugation of PEG molecules to IFNβ alters the pharmacokinetic properties of the parent drug, thereby decreasing the frequency of administration. This also provides a novel platform for combination therapy approach.

ADVANCE is currently the only clinical trial with published results on the efficacy of PEG-IFNβ-1a compared to placebo in the treatment of RRMS; to date, there are no head-to-head trials comparing PEG-IFNβ-1a to other approved DMTs. Furthermore, there are no treatment guidelines for practitioners that include initiating or switching to PEG-IFNβ therapy. Here, we have made an effort to compile currently available information regarding IFNβ therapy options with respect to various formulations. All available data suggest that the efficacy and safety profile of PEG-IFNβ-1a is comparable to other IFNβ therapies, with the added benefit of a decreased dosing schedule. This provides patients and practitioners with a viable alternate first-line therapy in the treatment of MS.

Acknowledgments

Funding from Canadian Institutes of Health Research, Saskatchewan Health Research Foundation and Natural Sciences and Engineering Research Council of Canada is gratefully acknowledged. KLF is supported by the endMS Postdoctoral Fellowship from the Multiple Sclerosis Society of Canada. We thank Dr. Katherine Knox for review of an earlier draft of the manuscript. This manuscript is dedicated to our colleague Dr. J. Ronald Doucette who passed away last year.

Disclosure

The authors report no conflicts of interest in this work.