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

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.