Free radical stress in chronic lymphocytic leukemia cells and its role in cellular sensitivity to ROS-generating anticancer agents

Abstract

2-Methoxyestradiol (2-ME), a new anticancer agent currently in clinical trials, has been demonstrated to inhibit superoxide dismutase (SOD) and to induce apoptosis in leukemia cells through a free radicalmediated mechanism. Because the accumulation of superoxide (O 2 ؊ ) by inhibition of SOD depends on the cellular generation of O 2 ؊ , we hypothesized that the endogenous production of superoxide may be a critical factor that affects the antileukemia activity of 2-ME. In the present study, we investigated the relationship between cellular O 2 ؊ contents and the cytotoxic activity of 2-ME in primary leukemia cells from 50 patients with chronic lymphocytic leukemia (CLL). Quantitation of O 2؊ revealed that the basal cellular O 2 ؊ contents are heterogeneous among patients with CLL. The O 2 ؊ levels were significantly higher in CLL cells from patients with prior chemotherapy. CLL cells with higher basal O 2 ؊ contents were more sensitive to 2-ME in vitro than those with lower O 2 ؊ contents. There was a significant correlation between the 2-ME-induced O 2 ؊ increase and the loss of cell viability. Importantly, addition of arsenic trioxide, a compound capable of causing reactive oxygen species (ROS) generation, significantly enhanced the activity of 2-ME, even in the CLL cells that were resistant to 2-ME alone. These results suggest that the cellular generation of O 2 ؊ plays an important role in the cytotoxic action of 2-ME and that it is possible to use exogenous ROS-producing agents such as arsenic trioxide in combination with 2-ME to enhance the antileukemia activity and to overcome drug resistance. Introduction 2-Methoxyestradiol (2-ME) is an endogenous metabolite of 17␤-estradiol that is present in human urine and blood. 2-ME is produced by sequential 2-hydroxylation and O-methylation. 1 This metabolic modification causes a loss of its ability to bind the estrogen receptor. 2-ME has been shown to have potent tumorinhibiting effects in a number of cancer cell lines in vitro and in tumor xenograft models in vivo. [2][3][4][5][6][7][8][9] This compound is currently in clinical trials, as a single agent or in combination with other anticancer agents, for treatment of several types of human cancer, including breast cancer, prostate cancer, and multiple myeloma. 2-ME also shows antileukemia activity in vitro with therapeutic selectivity. 10

Emodin-Provoked Oxidative Stress Induces Apoptosis in Human Colon Cancer HCT116 Cells through a p53-Mitochondrial Apoptotic Pathway

“…So cancer cells are more sensitive to ROS-generating anticancer agents (Zhou et al, 2003). Our study demonstrated emodin could provoke oxidative stress in HCT116 cells.…”

CD40 stimulation sensitizes CLL cells to rituximab-induced cell death

“…By bypassing the anti-apoptotic machinery, 6,7,17 RXL is able to induce caspase-independent cell death in CD40-stimulated CLL cells that are resistant to various drugs as result of upregulation of Bcl-2 family members. 5,6 Moreover, our findings suggest that it might be very relevant to combine rituximab with other ROS-inducing drugs like arsenic trioxide 56 or cisplatin. 59 …”

“…55 Rituximab-induced ROS production was impaired in the presence of EGTA, supporting our hypothesis that Ca 2 þ is important for rituximab-induced ROS. Zhou et al 56 showed that CLL cells with higher basal ROS are more sensitive to 2-Methoxyestradiol, a compound that induces apoptosis via a free radical-mediated mechanism. On the basis of our data, we propose that CD40 stimulation sensitizes CLL cells to rituximab-mediated death by increasing basal ROS production, which is further increased by rituximab.…”

Mitochondria in hematopoiesis and hematological diseases

“…For example, adenine deoxynucleoside analogs commonly used for treating some lymphoid malignancies such as cladribine and 2-chlororo-2 0 -ara-fluorodeoxyadenosine (Genini et al, 2000) and arsenic trioxide, an old cytotoxic agents that proved efficient in treating acute promyelocytic leukemia (Kroemer and de The, 1999;Larochette et al, 1999;Sordet et al, 2001). In acute promyelocytic leukemia cells, cellular toxicity of arsenic trioxide appears to mainly result from increased production of ROS, leading to the opening of the permeability transition pore complex, a decrease in mitochondrial membrane potential, cytochrome c release and caspase activation (Zhou et al, 2003;Chou et al, 2004). Ascorbic acid can enhance the efficacy of arsenic trioxide by reducing intracellular glutathione concentrations and this combination is currently tested in elderly patients with acute myeloid leukemia when these patients are not able to withstand intensive chemotherapy.…”