Valproic Acid Induces Apoptosis in CLL

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[4949] Valproic Acid Induces Apoptosis in Chronic Lymphocytic

Leukemia Cells through Activation of the Death Receptor Pathway and

Potentiates TRAIL Response. Session Type: Publication Only

ce Lagneaux, Nicolas Gillet, Alain Delforge, Marielle

Dejeneffe, Basile Stamatopoulos, e Massy, Nathalie Meuleman,

Alain Kentos, Luc Willems, Dominique Bron Experimental Hematology,

Bordet Institute, Brussels, Belgium; Molecular and Cellular Biology,

FUSAG, Gembloux, Belgium; Hematology, Erasme University Hospital,

Brussels, Belgium

Background: The anti-leukemic in vitro activity of valproic acid

(VPA), a commonly used antiepileptic agent, was tested on lymphocytes

derived from 40 patients with chronic lymphocytic leukemia (CLL)

(Binet stage A=34, B=3, C=3). These patients had not been previously

treated or remained untreated for the previous 6 months. Combined

analysis of ZAP-70, CD38 and IgVH mutational status was performed for

each patient.

Methods: Mononuclear cells were incubated with VPA at 1, 5 and 10 mM

for 24 hours. Cell viability was assessed by trypan blue exclusion

assay, apoptosis by annexin V/propidium iodide(PI) labelling and PI

staining after cell permeabilisation. Caspase activation was studied

by flow cytometry analysis after cell treatment with selective

caspase inhibitors.

Results: Exposure of CLL cells to VPA resulted in dose-dependent

cytotoxicity and apoptosis in all CLL patients tested. VPA-treatment

induced apoptotic changes in CLL cells including phosphatidylserine

(PS) externalisation and DNA fragmentation. The mean apoptotic rate

was similar between IgVH mutated and unmutated patients or ZAP-

70+/ZAP-70- cases. VPA induced apoptosis by the extrinsic pathway

involving engagement of the caspase-8 dependent cascade. Although CLL

cells are commonly resistant to death receptor-induced apoptosis, VPA

increased significantly the sensitivity of leukemic cells to TRAIL

(tumor necrosis factor -related apoptosis-inducing ligand). In

addition, VPA overcomed the prosurvival effects of bone marrow

stromal cells.

Conclusions: These data indicate that VPA, at the pharmacological

concentration of 1 mM, is a potent inducer of apoptosis in CLL and

should be further explored as a single agent. Also the combination of

VPA and TRAIL may be a promising approach in the treatment of CLL.