Hematological effects of intermittent 2-hour infusions of cladribine in multiple sclerosis patients: a comparison of 2 dosage patterns

Potential mechanisms of action related to the efficacy and safety of cladribine

Oral cladribine is a novel treatment for relapsing multiple sclerosis (MS). This appears to be a semi-selective immune-reconstitution therapy that induces long-term therapy from short treatment cycles. It has a relatively good safety profile that currently does not require extensive monitoring associated with some continuous immunosuppressive and relatively non-selective immune reconstitution therapies. The efficacy and safety of cladribine relates to its particular physicochemical properties, the function of the lymphocyte subsets that are selectively targeted by the drug and the repopulation kinetics of these subsets. As such, there is marked and long-term depletion of memory B cell subsets, which probably relates to the therapeutic efficacy. This is also coupled with a more limited, but likewise long-term, depletion of CD4 T subsets. There is limited depletion of cells of the innate immune system and modest effects on CD8 and probably plasma cells, which provide immediate and durable protection from infection. Targeting of CD4 T regulatory cells, CD8 T suppressor cells and regulatory B cell subsets appears more limited as these populations recover rapidly and so repopulating pathogenic cells re-emerge into a regulatory environment. This appears to lead to re-establishment of immune-tolerance that produces long-term control of MS. Although this hypothesis contains a number of unknown details, it is based on knowledge about the biology of cladribine, basic immunology and the effects of other high-efficacy B and T cell depleting agents that exhibit stereotyped repopulation behaviours. These concepts are relatively simple to interrogate, and can be modified as new knowledge about the durability of disease control and safety with cladribine emerges.

Optimizing the benefit of multiple sclerosis therapy: the importance of treatment adherence

Poor treatment adherence is problematic in many therapy areas, including multiple sclerosis (MS). Several immunomodulatory drugs are available for the treatment of MS, all of which require frequent parenteral administration. Current first-line therapies are two formulations of interferon (IFN) beta-1a, one of IFN beta-1b, and one of glatiramer acetate. Discontinuation of treatment is common, particularly in the first few months after initiation. Although the true effect of poor adherence to MS therapy is not known, it is likely to lead to a fall in treatment efficacy. Many factors influence a patient's adherence to treatment, including the patient's MS subtype and disability level, cognitive impairment resulting from MS, perceived lack of efficacy of the prescribed medication, and adverse events associated with MS therapy. This article summarizes the barriers to adherence to MS therapies, and discusses patient management strategies that can be employed to encourage adherence. Future advances in the field of MS treatment will be explored, including the development of orally administered drugs, which may enhance adherence.

The potential role for cladribine in the treatment of multiple sclerosis: clinical experience and development of an oral tablet formulation

BACKGROUND

Disease-modifying drugs available for multiple sclerosis (MS) require chronic, regular, parenteral administration. Effective oral MS therapies may improve long-term adherence. A number of oral therapies are in development, including cladribine--a preferential lymphocyte-depleting therapy with a well-established safety profile across other indications.

OBJECTIVE

To review information available on the safety and efficacy of cladribine in the treatment of MS, in the context of the ongoing development of an oral tablet formulation.

METHODS

An electronic search was performed to identify publications in which 'cladribine' was listed as a major index term. Results of the literature search were supplemented by other relevant secondary references and publications.

FINDINGS

The majority of published data on cladribine describe its use in diseases other than MS. However, three major, industry-sponsored, double-blind, placebo-controlled trials of parenteral cladribine were identified, involving 262 patients with relapsing or progressive forms of MS. Patients received cumulative doses of 0.7-2.8 mg/kg of cladribine over 4-6 months and were followed-up for at least 6-12 months thereafter. Individual results of these studies of parenteral cladribine indicate that it can reduce: (i) the number and volume of T1 gadolinium-enhancing lesions; (ii) the accumulation of T2 lesion volume; (iii) relapse rate; and (iv) disability progression. A dose-dependent increase in adverse events was observed, leading to selection of low doses for use in an ongoing clinical development program of an oral tablet formulation. Efficacy and safety data from four independent studies/case reports have also supported the potential benefits of cladribine in MS. While parenteral cladribine (at doses of 0.7-2.1 mg/kg) is associated with a good short-term safety and tolerability profile, additional long-term data are required--and the safety profile of the oral tablet formulation is yet to be established. To this end, the efficacy and safety of oral cladribine tablets are now being assessed as monotherapy and add-on therapy to interferon-beta-1a in two, 96-week, double-blind clinical trials of relapsing forms of MS. These ongoing studies will utilize newer diagnostic criteria and more sensitive evaluation techniques than were available at the time of the parenteral studies of cladribine.

CONCLUSION

Preliminary data indicate that cladribine is effective for the treatment of MS and has a promising safety and tolerability profile. The sustained immunologic effects of cladribine make it suitable for intermittent oral dosing, which is expected to offer benefits for patient satisfaction and therapeutic adherence.