Introduction

While treatment with immunomodulatory therapy is effective for most patients with multiple sclerosis (MS), a number of patients lack a robust and prolonged response to these immunomodulatory agents. Presentations at the 55th Annual Meeting of the American Academy of Neurology (AAN) provided additional insight into the lack of response with these agents, including the unexpected finding that antibodies produced by glatiramer acetate (Copaxone) may block the biologic response resulting in diminished clinical benefit of this agent. Additionally, a number of studies evaluated combination therapy strategies that might enhance treatment efficacy in patients with progressing MS disease activity.

Investigators from Baylor College of Medicine, Houston, Texas, conducted what is considered to be the first study to show that serum antibodies produced in response to treatment with Copaxone diminish the in vitro biological activity of the agent.¹ While long-term Copaxone treatment is known to induce an antibody response, the biological effect and therapeutic implications of these antibodies had not been previously established, according to Principal Investigator Ying C. Q. Zang, MD, PhD.

The study tested serum specimens from 42 patients with MS, taken prior to and following treatment (1 to 5 years) with Copaxone, for antibody reactivity to Copaxone. Samples from 6 of the patients who had high antibody titers (antibody binding index (ABI) of ≥16 to 64) were further evaluated for their ability to block Copaxone-stimulated immunoregulatory effects in vitro. Specifically, the proliferation of peripheral blood mononuclear cells (PBMC) and Copaxone-specific T cells was determined using ³H thymidine assays. Levels of interleukin (IL)-10, IL-4, IL-12, and tumor necrosis factor (TNF)-α were measured by enzyme-linked immunosorbent assay (ELISA). A preliminary assessment of the clinical relevance of these antibodies was made by measuring serum cytokine levels in the 42 patient specimens.

High Titers Block Immunomodulatory Effects of Copaxone

Copaxone-induced antibodies were demonstrated in samples from 48% of the patients; high antibody titers [ABI ≥16 to 64] occurred in 33% and low antibody titers (ABI ≤4) in 14% of these patients. The high antibody titers induced by Copaxone not only blocked the agent's normal stimulatory effects on the proliferation of PBMC and Copaxone-specific T cells in vitro but may have reduced clinical efficacy as well, Dr. Zang reported.

The increase in IL-10 and IL-4 levels and the decrease in IL-12 and TNF-α levels, which normally result from Copaxone stimulation, were reversed in the presence of the Copaxone antibodies. Patients with low antibody titers, however, had a post-treatment increase in IL-10 and a reduction in TNF-α and IL-12.

"These results suggest that the in vivo effects of glatiramer acetate on serum cytokine levels are blocked by high titers of glatiramer acetate molecules," Dr. Zang noted.

Immunoblot analysis of the serum specimens from the 6 high-antibody patients confirmed the specific reactivity of serum antibodies to Copaxone.

Diminished Clinical Efficacy Associated with High Antibody Titers Induced by Copaxone

The link to diminished therapeutic efficacy for patients with high antibody titers was demonstrated by comparing the Expanded Disability Scale Scores (EDSS) pre- and post-treatment. "Patients with high antibody titers showed more deterioration in EDSS scores and more relapses than patients with low antibody titers," Dr. Zang commented.

With Copaxone treatment, mean EDSS generally improved from pre-treatment levels in patients with low antibody titers (Table 1). But for the 14 patients with high antibody titers, mean EDSS worsened in all categories during the duration of treatment (1 to 5 years). For example, in the 3 patients with high antibody titers treated for 4 years with Copaxone, EDSS worsened from 4.3 to 4.8 post-treatment; for the 8 patients treated for 5 years with Copaxone, EDSS worsened from 3.9 to 4.1. Relapse rates, however, were generally reduced with continued treatment, though more so in patients with low antibody titers.

In an interview with Jeffrey Greenstein, MD, founder of the Multiple Sclerosis Institute of Philadelphia, Pennsylvania, Dr. Greenstein noted, "Apparently 15% of the patients treated with glatiramer acetate in this study had antibodies that one could categorize as neutralizing. This was shown by preparing glatiramer acetate-specific T-cell lines and then determining whether the sera inhibited the proliferation of those T-cell lines. For patients with high antibody titers, there was indeed inhibition of proliferation. The investigators then extended the study to see if there was inhibition of cytokine production across a broad range of cytokines, and they found a decrease in cytokine production in both Th1 and Th2 cytokines."

"This is an important study that gives new insights into why glatiramer acetate may not be that different from the interferons in the potential to develop antibodies. It is a synthetic biological protein therapy that with the right assays can be shown to produce neutralizing antibodies and/or other forms of inhibition," Dr. Greenstein continued. "This leaves us with the suggestion that we should re-examine glatiramer acetate to see if we have the same problem of neutralization of effect that we see with the interferons."

Combination Therapy for Breakthrough MS Disease

Although the currently available immunomodulatory agents are relatively effective in reducing relapse rates, and in some cases slowing disability progression, many patients still progress with their disease. Switching between immunomodulatory agents has been an approach used to try to manage these patients--with little or no benefit. Emerging data suggest that the use of adjunctive agents, along with initial immunomodulatory platform therapy, may be a beneficial strategy in patients with treatment-resistant MS disease, which is of growing concern to clinicians.

In a multicenter study presented by Derek R. Smith, MD, Assistant Professor of Neurology, Harvard Medical School, Boston, Massachusetts the addition of 6 monthly intravenous infusions of cyclophosphamide plus methylprednisolone to a regimen of interferon beta-1a (Avonex) was effective in reducing the signs of MS disease activity and preventing treatment failure.²

The study included 58 patients who were considered to have active MS despite therapy with Avonex. After receiving a 3-day course of methylprednisolone, patients were randomized to either 6 monthly infusions of cyclophosphamide (800 mg/m²) plus methylprednisolone (1000 mg) or methylprednisolone alone. Patients continued Avonex therapy (30 mcg intramuscularly once weekly) during the 6-month infusion phase and the 18-month follow-up phase. The primary outcome measure was change in number of gadolinium enhancing lesions with a secondary outcome measure of time to treatment failure (defined as the occurrence of two or more confirmed relapses in a 9-month period).

One month after the initial 3-day course of methylprednisolone, the baseline mean number of gadolinium enhancing lesions was 0.87, with no differences observed between the two treatment arms (P = 0.71). Treatment with cyclophosphamide plus methylprednisolone successfully reduced the number of gadolinium enhancing lesions and resulted in fewer treatment failures, reported Dr. Smith.

Six months after completion of the infusion phase (at Month 12), patients receiving methylprednisolone plus Avonex had an increase of +0.58 gadolinium enhancing lesions compared to a decrease of -0.53 in patients treated with the combination of Avonex and cyclophosphamide plus methylprednisolone (P = 0.02).

The addition of cyclophosphamide to methylprednisolone also resulted in fewer total scans that contained at least one gadolinium enhancing lesion during the infusion phase, and a much lower mean number of gadolinium enhancing lesions: 0.2 for cyclophosphamide plus methylprednisolone-treated patients compared to 1.18 in patients receiving methylprednisolone (P = 0.001).

Protocol-defined treatment failures were also twice as great in the methylprednisolone treatment arm as the cyclophosphamide plus methylprednisolone treatment arm: 25% versus 50% (P = 0.03). The time to treatment failure was also significantly shorter in the methylprednisolone treatment arm (13 months versus 16 months; P = 0.04), noted Dr. Smith.

"The analysis of treatment failures favored the cyclophosphamide plus methylprednisolone treatment arm, both in patients with gadolinium-positive and gadolinium-negative scans. Overall, however, patients with gadolinium-positive scans had much more disease activity, compared to those with negative scans at the time of baseline MRI," advised Dr. Smith. Continuing, Dr. Smith added, "To my surprise, the number of eosinophils was lower in the gadolinium-positive versus negative patients. Eosinophils are associated with shifts in Th2, and we believe they may be a marker of cyclophosphamide efficacy."

Rescue Therapy with High-Dose Intravenous Methotrexate

High doses of intravenous methotrexate combined with Avonex therapy appears to stop the progression of disease activity in patients who are worsening on Avonex treatment,³ according to Vernon D. Rowe, MD, and colleagues from the MidAmerica Neuroscience Institute, Kansas City, Missouri.

This open-label study enrolled 15 patients with relapsing MS worsening while on Avonex therapy. Patients were eligible if they experienced a decrease in the MS Functional Composite (MSFC) score over a minimum of 3 months while being treated with Avonex for at least 6 months. The MSFC is comprised of 3 tests: the Paced Auditory Serial Addition Test (PASAT), 9-Hole Peg Test, and the 25-foot Timed Walk. Remaining on Avonex, patients received high dose intravenous methotrexate (2 g/m²) followed by leucovorin rescue, every 2 months for a total of 6 treatments.

In the first 8 patients to complete the treatment, there was a significant improvement in the composite MSFC of 0.39 points (mean MSFC score at baseline 0.137, range,
-2.03 to 1.23; P = 0.016). Significant improvements were also noted for the subsets of the PASAT (P = 0.031) and 9-Hole Peg Test (P = 0.008).

"The statistically significant improvement in the MSFC composite represents a clinically important improvement in patient functioning," advised Dr. Rowe. "No patient significantly worsened during treatment and each improved in one or more subsets during the 1-year treatment period. All the patients were worsening prior to the first infusion," reported Dr. Rowe.

In addition, magnetic resonance imaging (MRI) evaluations before and after leucovorin rescue therapy showed no increase in enhancement for 7 of the 8 patients; one patient missed multiple Avonex treatments and had minimal enhancement at the end of the study.

Changes occurred and persisted in several immunological parameters, in particular, chemokine receptors and cytokine secretion. These, in addition to the clinical improvement, may reflect lasting decreases in MS inflammatory responses in the central nervous system brought about by this combination therapy, Dr. Rowe suggested.

"When you give an intravenous dose of methotrexate that is high enough to cross the blood-brain barrier, you may affect the primary biology of this disease. Furthermore, this is a very safe drug when given with leucovorin rescue," advised Dr. Rowe.

In Dr. Rowe's opinion, "The real promise of [this therapy] is in the early modification of the biology of multiple sclerosis, because it addresses multiple sclerosis as what it is--a disease of the central nervous system. Combination therapy is the direction in which multiple sclerosis therapy is going in managing breakthrough disease."

References

1. Zang YCQ, Salama HH, El-Mongui A. Blocking effects of serum-reactive antibodies induced by glatiramer acetate treatment in patients with multiple sclerosis. Neurology. 2003;60(Suppl 1):A396. P05.132.
2. Smith DR, Weinstock-Guttman B, Cohen JA, et al. Blinded, randomized trial of pulse cyclophosphamide in IFN B resistant active MS. Neurology. 2003;60(Suppl 1):A84. S11.005.
3. Rowe VD, Wang D, John HA, Dressman LA, Rowe ES, Moreng GR. Rescue therapy with high dose intravenous methotrexate in MS patients worsening despite Avonex therapy. Neurology. 2003;60(Suppl 1):A149. P02.135.