In contrast, the CdATP:5-NT ratio is relatively low in other cell types, thus sparing numerous non-hematologic cells.In multiple sclerosis, cladribines effectiveness may be due to depletion of B cells, in particular memory B cells. In the pivotal phase 3 clinical trial of oral cladribine in multiple sclerosis, CLARITY, cladribine selectively depleted 80% of peripheral B cells, compared to only 40–45% of CD4+ T cells and 15‒30% CD8+ T cells. More recently, cladribine has been shown to induce long term, selective suppression of certain subtypes of B cells, especially memory B cells.Although cladribine is selective for B cells, the long-term suppression of memory B cells, which may contribute to its effect in multiple sclerosis, is not explained by gene or protein expression. Instead, cladribine appears to deplete the entire B cell department, but while naïve B cells rapidly move from lymphoid organs, the memory B cell pool repopulates slowly from the bone marrow. Both hairy cell leukemia and B-cell chronic lymphocytic leukaemia are types of B cell blood cancers. History in hairy cell leukemia
Ernest Beutler and Dennis A. Carson had studied adenosine deaminase deficiency and recognised that because the lack of adenosine deaminase led to the destruction of B cell lymphocytes, a drug designed to inhibit adenosine deaminase might be useful in lymphomas. Carson then synthesised cladribine, and through clinical research at Scripps starting in the 1980s, Beutler tested it as intravenous infusion and found it was especially useful to treat hairy cell leukemia.
Efficacy of cladribine tablets in multiple sclerosis
Clinical trial results have shown that cladribine tablets can be an effective treatment for highly active, relapsing forms of multiple sclerosis, with significant clinical benefits in relapse rate, disability progression, and radiological measures. Compared with placebo, patients who received cladribine tablets (3.5 mg/kg) in the CLARITY study had a 58% reduction in annualized relapse rate and 47% of patients showed no evidence of disease activity at 2 years. Clinical improvements can be observed at Week 24 of treatment, and benefits may be sustained up to 4 years, beyond the 2-year dosing period and recovery of total lymphocytes. Post-hoc analyses of clinical trial data showed that 89% of patients remained free from disability progression two years after treatment.Further analyses of a subgroup of patients in the CLARITY study who had very active multiple sclerosis showed a 67% reduction in relapse rates and an 82% reduction in disability progression in those treated with cladribine tablets. Similarly, clinical improvements were seen in lesion burden on MRI scans in this population.Studies evaluating the treatment effects of cladribine tablets across a spectrum of baseline demographics and disease characteristics showed that the relative risk of relapse was significantly reduced compared with placebo, irrespective of previous treatment experience.Furthermore, treatment with cladribine tablets has been shown to significantly reduce the rate of brain atrophy in patients with highly active relapsing-remitting multiple sclerosis.