Fludarabine-Induced Apoptosis in Chronic Lymphocytic Leukemia Cells Is Not Affected by Inhibitor of Apoptosis Proteins (IAPS).

B-cell chronic lymphocytic leukemia (B-CLL) is characterized by the accumulation of mature lymphocytes due to defective apoptosis. Inhibition of apoptosis also contributes to chemoresistance, mainly in patients in advanced clinical stages. Fludarabine is a potent chemotherapeutic drug used for patients with B-CLL. Despite good initial clinical responses, some patients acquire resistance to this drug. One of the mechanisms through which malignant cells are believed to acquire resistance to apoptosis is by overexpression of inhibitor of apoptosis proteins (IAPs). IAPs are a family of proteins able to block apoptosis either by binding and inhibiting caspases or through caspases-independent mechanisms. To date, overexpression of IAPs has been detected in many types of malignant diseases, including B-CLL. As fludarabine can induce apoptosis trough caspases activation and this proteases could be inhibited by IAPs, we evaluated in this current study, the expression of three members of IAP family (c-IAP1, c-IAP2 and XIAP) by immunocitochemistry in 30 peripheral blood B-CLL specimens and correlated it to fludarabine-induced apoptosis. In parallel, we also evaluated the expression of these IAPs before and after in vitro fludarabine treatment. B-CLL cells were incubated with fludarabine25 m M for 12 hours and the induction of apoptosis were measured by annexin-V assay. The apoptosis index by fludarabine was extremely significant (p < 0.001). Different levels of c-IAP1, c-IAP2 and XIAP expression were commonly found in circulating B-CLL cells. High levels of c-IAP1, c-IAP2 and XIAP expression were observed in 20%, 60,7% and 60% of samples, respectively. However, the overexpression of these IAPs was not correlated with an in vitro fludarabine apoptosis-resistance. Besides, fludarabine was not able to change the levels of IAPs expression as described for other drugs in literature. These results suggest that fludarabine might cause apoptosis by a caspase-independent manner.