Role of Nocodazole on the survival of chronic lymphocytic leukemia B cells

B-cell Chronic Lymphocytic Leukemia (B-CLL) is the most common leukemia in adults and is characterized by the accumulation of clonal CD19+/CD5+/CD23+ B lymphocytes, due to uncontrolled growth and resistance to apoptosis. Leukemic cells from B-CLL show reduced crosslink with specific molecules and high susceptibility to microtubule disrupting drugs, which suggest cytoskeletal alterations. Microtubules play a crucial role in the vital functions of neoplastic cells, including mitosis, motility and cell-cell contact, and for this reason they became an important target in cancer therapies. In particular, tubulin, a cytoskeletal member, is the target of specific drugs, named microtubule inhibitors. Among these inhibitors, nocodazole induces tubulin depolimerization, mitotic process blocking and shows an apoptotic effect in B leukemic cells. The aim of this study was to define the effects of nocodazole on B-CLL cells. First of all, we verified nocodazole capability to favour the depolymerization of tubulin cytoskeleton in different cell types. In addition, we tested nocodazole-induced apoptosis in normal and leukemic B cells, in cell lines (Jurkat, Raji, and K562), in mesenchymal stromal cells (MSCs), and in T lymphocytes of B-CLL patients. Our data pointed out the high specificity of nocodazole for B-CLL cell apoptosis (leukemic cells: 57±25% vs normal B cells: 98±6%, p<0.0001; data are expressed as mean±standard deviation (SD) of percentage of viable cells after treatment with nocodazole) and the absence of toxicity to others cell types. Growing evidence suggests that the marrow microenvironment, where MSCs are present, protects B-CLL cells from conventional anti-neoplastic drugs. The cultures of neoplastic B cells with MSCs and nocodazole demonstrated that nocodazole is able to overcome MSC protective effect, even after survival signal supplemental, such as CD40L or plasma from the same patients. The action mechanism of nocodazole in B-CLL cells is still under investigation. However, we observed that nocodazole is able to turn off the increased basal tyrosine phosphorylation of leukemic cells mediated by Src-kinase Lyn through the down-modulation of Lyn active site. Since the specific inhibition of Lyn induces B-CLL cells apoptosis, this linking will be further investigated. The results obtained in this study suggest a future role of nocodazole as a possible agent for treatment of B-CLL, for its extreme selectivity, the absence of toxicity and its ability to counteract the protective effect provided by marrow microenvironment.