Valproate synergizes with purine nucleoside analogues to induce apoptosis of B‐chronic lymphocytic leukaemia cells

Abstract

Summary Resistance to chemotherapy and drug toxicity are two major concerns of chronic lymphocytic leukaemia (B‐CLL) treatment by purine nucleoside analogues (PNA, i.e. fludarabine and cladribine). We hypothesized that targeting epigenetic changes might address these issues and evaluated the effect of the histone deacetylase inhibitor valproate (VPA) at a clinically relevant concentration. VPA acted in a highly synergistic/additive manner with fludarabine and cladribine to induce apoptosis of B‐CLL cells. Importantly, VPA also restored sensitivity to fludarabine in B cells from poor prognosis CLL patients who became resistant to chemotherapy. Mechanism of apoptosis induced by VPA alone or combined with fludarabine or to cladribine was caspase‐dependent and involved the extrinsic pathway. VPA, but neither fludarabine nor cladribine, enhanced the production of reactive oxygen species (ROS) and inhibition of ROS with N‐acetylcysteine decreases apoptosis of CLL cells. VPA stimulates hyperphosphorylation of p42/p44 ERK, cytochrome c release and overexpression of Bax and Fas. Together, our data indicate that VPA may ameliorate the outcome of PNA‐based therapeutic protocols and provide a potential alternative treatment in both the relapsed and front‐line resistant patients and in patients with high risk features.

Antileukemic activity of valproic acid in chronic lymphocytic leukemia B cells defined by microarray analysis

“…These results validated earlier reports on cancer cells, 35 leukemia cells 18 and fresh CLL B cells. [20][21][22] Interestingly, we also observe that VPA induces apoptosis in cells from patients with unfavorable cytogenetic abnormalities such as 6q deletion, 17p deletion or showing a complex karyotype (Supplementary data 6). This indicates that the VPA effect would be independent of cytogenetic features, as well as effective in P53-deficient cells that are chemotherapy resistant and associated with a poor outcome.…”

“…The increased apoptosis observed when VPA was associated with various drugs seems to be an additive effect after 24 h: indeed, the sum of VPA-induced and drug-induced cell death is very close to the cell death induced by their association (except for bortezomib, for which a clear synergistic effect is observed). Bouzar et al 22 also observed that VPA acted in an additive/synergistic manner with fludarabine and cladribine to induce apoptosis. In this study, we did not observe a high synergistic effect for fludarabine, probably because of the different experimental conditions used (technique, viability vs apoptosis; time of treatment, 24 vs 48 h; concentration, 7 vs 1 mM).…”

“…[17][18][19] Recently, our group showed that VPA at low pharmacological concentration could induce apoptosis of CLL B cells in vitro. 20 Bokelmann and Mahlknecht 21 showed decrease in the BCL-2/Bax ratio in CLL B cells treated with VPA in vitro and Bouzar et al 22 reported that valproate synergizes with purine nucleoside analogues to induce apoptosis of CLL B cells. Moreover, VPA has already been used in phase I/II clinical trials in combination with other classical chemotherapies such as purine analogues, 23,24 anthracyclin 25 and chemoimmunotherapy.…”

Analysis of apoptosis regulatory genes altered by histone deacetylase inhibitors in chronic lymphocytic leukemia cells

“…However, there is still controversy on which would be the initiating pathway. It has been reported that valproate-mediated apoptosis in CLL cells involved the extrinsic pathway through caspase 8 activation, 28 which is required for mitochondrial amplification loop through BID cleavage and caspase 9 activation. 29 However, the specific mechanism underlying the activation of the extrinsic apoptotic pathway remains unclear.…”

Cytotoxic Activity of Valproic Acid on Primary Chronic Lymphocytic Leukemia Cells

“…In the present study, we found that VPA induces apoptosis at a concentration of 10 mM independent of the disease stage according to the Rai system, ZAP-70 and CD38 expression, IGHV status and cytogenetics, but it depends on LDH serum levels. This indicates that It has already been shown that VPA increases acetylation of histones H3 and H4 [19]. Kawagoe et al [17] demonstrated that in a B-myeloid cell line, VPA activates two different apoptotic pathways -a caspase-dependent pathway causing nuclear apoptotic changes and a caspase-independent pathway [17].…”