Apoptotic cell death induced by taxol is inhibited by nitric oxide in human leukemia HL-60 cells

Resistance to paclitaxel is proportional to cellular total antioxidant capacity

Paclitaxel, one of the most commonly prescribed chemotherapeutic agents, is active against a wide spectrum of human cancer. The mechanism of its cytotoxicity, however, remains controversial. Our results indicate that paclitaxel treatment increases levels of superoxide, hydrogen peroxide, nitric oxide (NO), oxidative DNA adducts, G2-M arrest, and cells with fragmented nuclei. Antioxidants pyruvate and selenium, the NO synthase inhibitor N(omega)-nitro-L-arginine methyl ester, and the NO scavenger manganese (III) 2-(4-carboxyphenyl)-4,4,5,5-tetramethyl-imidazoline-1-oxyl-3-oxide all decreased paclitaxel-mediated DNA damage and sub-G1 cells. In contrast, the glutamylcysteine synthase inhibitor buthionine sulfoximine (BSO) and the superoxide dismutase (SOD) inhibitor 2-methoxyestradiol (2-ME) increased the sub-G1 fraction in paclitaxel-treated cells. These results suggest that reactive oxygen and nitrogen species are involved in paclitaxel cytotoxicity. This notion is further supported with the observation that concentrations of paclitaxel required to inhibit cell growth by 50% correlate with total antioxidant capacity. Moreover, agents such as arsenic trioxide (As2O3), BSO, 2-ME, PD98059, U0126 [mitogen-activated protein/extracellular signal-regulated kinase inhibitors], and LY294002 (phosphatidylinositol 3-kinase/Akt inhibitor), all of which decrease clonogenic survival, also decrease the total antioxidant capacity of paclitaxel-treated cells, regardless whether they are paclitaxel sensitive or paclitaxel resistant. These results suggest that paclitaxel chemosensitivity may be predicted by taking total antioxidant capacity measurements from clinical tumor samples. This, in turn, may then improve treatment outcomes by selecting out potentially responsive patients.

Arginine deiminase enhances dexamethasone-induced cytotoxicity in human T-lymphoblastic leukemia CCRF-CEM cells

Since arginine deiminase (ADI; EC 3.5.3.6) inhibits cell proliferation by arresting cells in the G1 phase, we tested its synergistic effect on cell death induced by dexamethasone (DEX), which also induces apoptosis by G1 cell cycle arrest. ADI inhibited cell proliferation and induced apoptosis in human leukemic CEM cells in a dose-dependent manner. Simultaneous treatment with ADI and DEX showed synergistic effects on DNA fragmentation and LDH release. In addition, ADI exerted its anti-proliferative activity against DEX-resistant CEM cells. ADI suppressed expression of c-myc, a potential key regulator of cell proliferation and apoptosis, and increased expression of p27Kip1 cyclin-dependent kinase inhibitor. These results suggest that ADI efficiently increases the anti-cancer effect of DEX on human leukemic CEM cells through G1 cell cycle arrest involving downregulation of c-myc and upregulation of p27Kip1.

In Vitro Cytotoxicity of Mokko Lactone in Human Leukemia HL‐60 Cells: Induction of Apoptotic Cell Death by Mitochondrial Membrane Potential Collapse

We studied the effect of mokko lactone (ML) isolated from the roots of Saussurea lappa (Compositae), a plant that is used for medicinal purposes in Korea, on the induction of apoptosis in human leukemia HL-60 cells. ML was cytotoxic to HL-60 cells, and this cytotoxic effect of ML appears to be attributable to its induction of apoptotic cell death, as ML induced nuclear morphologic changes and internucleosomal DNA fragmentation and increased the proportion of Annexin V-positive cells and the activity of caspase-3. Further studies revealed that the induction of apoptosis by ML was associated with the loss of mitochondrial membrane potential. Collectively, our results suggest that apoptosis induced by ML in HL-60 cells was executed by a collapse of mitochondrial membrane potential followed by the activation of caspase-3. This is the first report on the mechanism of apoptosis-inducing effect of ML.

Anti-proliferative and differentiation-inducing activities of the green tea catechin epigallocatechin-3-gallate (EGCG) on the human eosinophilic leukemia EoL-1 cell line

A novel approach for the treatment of leukemia is the differentiation therapy in which immature leukemia cells are induced to attain a mature phenotype when exposed to differentiation inducers, either alone or in combinations with other chemotherapeutic or chemopreventive drugs. Over the past decade, numerous studies indicated that green tea catechins (GTC) could suppress the growth and induce apoptosis on a number of human cancer cell lines. However, the differentiation-inducing activity of GTC on human tumors remains poorly understood. In the present study, the effect of the major GTC epigallocatechin-3-gallate (EGCG) on the proliferation and differentiation of a human eosinophilc leukemic cell line, EoL-1, was examined. Our results showed that EGCG suppressed the proliferation of the EoL-1 cells in a dose-dependent manner, with an estimated IC(50) value of 31.5 microM. On the other hand, EGCG at a concentration of 40 microM could trigger the EoL-1 cells to undergo morphological differentiation into mature eosinophil-like cells. Using RT-PCR and flow cytometry, it was found that EGCG upregulated the gene and protein expression of two eosinophil-specific granule proteins, the major basic protein (MBP) and eosinophil peroxidase (EPO), in EoL-1 cells. Taken together, our findings suggest that EGCG can exhibit anti-leukemic activity on a human eosinophilic cell line EoL-1 by suppressing the proliferation and by inducing the differentiation of the leukemia cells.

Killing of lymphoblastic leukemia cells by nitric oxide and taxol: involvement of NF-kappaB activity

Nitric oxide (NO) and taxol are cytotoxic towards leukemia and tumor cells and interfere with the transcription factor NF-kappaB activity. NO and taxol inhibited NF-kappaB activity and were cytotoxic to human and murine leukemia cells, but at a different magnitude (30% cell killing and 80% inhibition of NF-kappaB). Sub-effective concentrations of SNAP and taxol synergized in killing L-1210 cells but either alone or in combination completely inhibited NF-kappaB. Pyrrolidine dithiocarbamate (PDTC) was cytotoxic on its own and inhibited NF-kappaB activity. It potentiated NO and taxol killing but again there was no direct relationship between inhibition of NF-kappaB and cell killing. Neither NO nor taxol cytotoxicity was related to the cytoskeleton. Our results show that NO, taxol and PDTC induced apoptosis and NF-kappaB inhibition in leukemic cells but their cytotoxicity either alone or in combination, does not seem to be dependent on the inhibition of NF-KB activity.

The regulatory role of nitric oxide in apoptosis

Nitric oxide (NO) is a multi-faceted molecule with dichotomous regulatory roles in many areas of biology. The complexity of its biological effects is a consequence of its numerous potential interactions with other molecules such as reactive oxygen species (ROS), metal ions, and proteins. The effects of NO are modulated by both direct and indirect interactions that can be dose-dependent and cell-type specific. For example, in some cell types NO can promote apoptosis, whereas in other cells NO inhibits apoptosis. In hepatocytes, NO can inhibit the main mediators of cell death-caspase proteases. Moreover, low physiological concentrations of NO can inhibit apoptosis, but higher concentrations of NO may be toxic. High NO concentrations lead to the formation of toxic reaction products like dinitrogen trioxide or peroxynitrite that induce cell death, if not by apoptosis, then by necrosis. Long-term exposure to nitric oxide in certain conditions like chronic inflammatory states may predispose cells to tumorigenesis through DNA damage, inhibition of DNA repair, alteration in programmed cell death, or activation of proliferative signaling pathways. Understanding the regulatory mechanisms of NO in apoptosis and carcinogenesis will provide important clues to the diagnosis and treatment of tissue damage and cancer. In this article we have reviewed recent discoveries in the regulatory role of NO in specific cell types, mechanisms of pro-apoptotic and anti-apoptotic induction by NO, and insights into the effects of NO on tumor biology.

Potentiation of tumor necrosis factor-alpha-induced apoptosis by mistletoe lectin

Mistletoe lectins (MLs) constitute the active principle in extract preparations from mistletoe, commonly used as immunomodulator in adjuvant tumor therapy. MLs, classified as type II ribosome inactivating proteins, inhibit protein synthesis. Inhibitors of protein synthesis may modify cancer cell response to tumor necrosis factor-alpha (TNF). In the present study, we have hypothesized that the anticancer efficacy of TNF may be potentiated by MLs. In deed, simultaneous treatment of human cervix carcinoma HeLa or breast carcinoma MCF-7 cells with MLs isolated from European or Korean mistletoe rendered them more sensitive to induction of apoptosis by TNF. The mechanism by which MLs amplify the effect of TNF may involve suppression of the survival protein synthesis.

Heat shock treatment protects human HL-60 cells from apoptosis induced by lectin II isolated from Korean mistletoe, Visum album var. Coloratum

Mistletoe lectin II (ML II) isolated from Korean mistletoe (Viscum album var. Coloratum), an effective therapeutic agent for cancers, is known to induce cell death via apoptosis. In the present study, we found the protective effect of heat shock treatment of human leukemia HL-60 cells against ML II-induced apoptosis. Exposure of HL-60 cells to ML II for 4 h resulted in apoptosis of the cells, which was evaluated by examining "DNA ladder" formation and DNA fragmentation assay. The DNA fragmentation was significantly reduced in the cells subjected to heat shock treatment by incubation at 42 degrees C for 1 h and subsequently allowed to recover for 2-16 h at 37 degrees C, prior to exposure to ML II. HL-60 cells transfected with heat shock protein (hsp) 70 gene exhibited resistance to ML II-induced apoptosis very similar to that seen when untransfected cells were heat-shocked. These results indicate that ML II-induced apoptosis in HL-60 cells is inhibited by heat shock treatment, at least in part, via a hsp 70-mediated mechanism.