Thalidomide enhances cyclophosphamide and dexamethasone-mediated cytotoxicity towards cultured chronic lymphocytic leukaemia cells

Numerous chemotherapeutic regimens exist for the treatment of symptomatic or progressive chronic lymphocytic leukaemia (CLL). However, once the disease becomes refractory to nucleoside-based therapy the prognosis is poor. In this study we investigated the cytotoxicity of thalidomide in combination with dexamethasone, fludarabine and cyclophosphamide. Cells from a cohort of 25 CLL patients were incubated for 72 h with each of these three agents, at 3 concentrations, both with and without thalidomide. Cell viability was assessed using the Annexin V:FITC assay. Fludarabine was highly toxic to the cells, producing very high levels of cell death; however, thalidomide did not increase this effect. Cyclophosphamide combined with thalidomide showed a small, non-significant improvement in toxicity compared with monotherapy. Median cell death for 5 µM dexamethasone monotherapy and for combination with thalidomide was 15% [interquartile range (IQR) 0-38%] and 17% (IQR 0-54%), respectively (Wilcoxon Signed Rank analysis, p=0.034). Cell death for 10 µM dexamethasone monotherapy was 15% (IQR 0-45%) and 16% (IQR 0-62%) in combination with thalidomide (Wilcoxon Signed Rank analysis, p=0.035). At the highest doses tested 11 of 25 cases displayed an enhancement of cyclophosphamide-mediated cytotoxicity, and 14 of 25 cases showed enhanced dexamethasone-mediated cytotoxicity in the presence of thalidomide. Some CLL cells in which dexamethasone-mediated killing was enhanced were derived from patients with poor prognostic markers, including p53 mutations and unmutated IgVH genes. In summary, thalidomide enhances cyclophosphamide- and dexamethasone-mediated cytotoxicity of CLL cells in vitro in a proportion of cases.