Cladribine is a synthetic purine nucleoside analogue with immunosuppressive functions that has demonstrated beneficial effects in patients with relapsing-remitting multiple sclerosis (MS) and that may also regulate the immune function as an analogue of adenosine receptors. Although the effect of cladribine is well studied on immune cells, it remains unveiled how it affects the immune function of glial populations of the central nervous system.
In the context of MS, we aimed to test the effect of cladribine on proliferation, survival and cytokine release of human astrocytes.
To assess the effect of cladribine on cell survival and proliferation, primary human astrocytes were cultured with cladribine at high concentrations (2µM, 0.2µM), at the mean estimated brain exposure of the drug (0.02µM) and at a low concentration (0.002µM) for 72h. The percentages of dead and proliferating cells were determined by flow cytometry. To assess the effect of cladribine on cytokine release, human astrocytes were stimulated for 6h with 20ng/ml IL1-β and TNF-α. The stimulus was withdrawn and cells were cultured for additional 18h. Cladribine was added for the whole 24h of culture. Supernatants were harvested to quantify IL1-β, IL6, TNF-α and GM-CSF release by Luminex. To assess the effect of cladribine independently of deoxycytidine kinase (DCK), deoxycytidine was also added to human astrocytes.
Only high concentrations of cladribine induced death on human astrocytes (2µM: 35.89%±7.62 or 0.2µM: 7.27%±3.12 vs control: 3.17%1.84±; p<0.0001 and p=0.156, respectively) and inhibited their proliferative capacity (2µM: 0.96%±1.14 or 0.2µM: 14.06%±5.44 vs control: 33.06%±1.42; both p-values<0.0001). Additionally, the percentage of proliferating cells in the 2µM and 0.2µM conditions presented a limited capacity of proliferation (measured as the Relative Intensity of Proliferation Staining respect to basal; 2µM: 0.24±0.04 and 0.2µM: 0.55±0.22, both p-values<0.0001). When DCK activity was blocked by deoxycytidine, cell death and proliferation were reversed to control condition values. We are currently determining the effect of cladribine on pro-inflammatory cytokine release by human astrocytes.
The mean estimated brain exposure to cladribine does not influence cell survival or proliferation of human astrocytes neither in a DCK-dependent nor in a DCK-independent manner, suggesting that cladribine does not affect the normal astrocyte function in MS patients.