Increased cytosol Ca(2+) and type 1 programmed cell death in Bcl-2-positive U937 but not in Bcl-2-negative PC-3 and Panc-1 cells induced by the 5-lipoxygenase inhibitor MK 886

Augmentation of the cytotoxic effects of zinc oxide nanoparticles by MTCP conjugation: Non-canonical apoptosis and autophagy induction in human adenocarcinoma breast cancer cell lines

Zinc oxide nanoparticles are very toxic, but their agglomeration reduces their lethal cytotoxic effects. Here we tested the hypothesis that conjugation of ZnO nanoparticles via Meso-Tetra (4-Carboxyphenyl) Porphyrin (MTCP) could provide electrostatic or steric stabilization of ZnO nanoparticles and increase their cytotoxic effects. The cytotoxicity and cell death induction were assessed using two human breast adenocarcinoma cell lines (MCF-7 and MDA-MB-468). The MTT results indicated that the toxicity of ZnO nanoparticles was significantly increased upon MTCP conjugation. Annexin/PI and real time RT-PCR results demonstrated that the ZnO-MTCP nanoparticles induced cell death via different non-canonical pathways that are under ca2+ control. Calcium signaling could regulate lysosomal dependent apoptosis and death autophagy, and killing of the two selected types of breast cancer cells.

Pre-treatment of HT-29 cells with 5-LOX inhibitor (MK-886) induces changes in cell cycle and increases apoptosis after photodynamic therapy with hypericin

It may be hypothesized that the lipoxygenase (LOX) metabolic pathway plays an important role in photodynamic therapy (PDT) of malignant tumours, and modification of this pathway may result in administration of lower doses of photodynamic active agents accompanied by reduced side effects. In this study, we examine in more detail the cytokinetic parameters of human colon adenocarcinoma HT-29 cells pre-treated for 48 or 24h with LOX inhibitor MK-886, followed by PDT induced by hypericin. Based on MTT assay the concentrations of both agents (MK-886 and hypericin) with relatively slight (non-significant) cytotoxic effects were selected. These concentrations were used for combined treatment, where MTT response, total cell number, floating cells quantification, viability, cell cycle progression and DNA synthesis were detected. Hoechst/PI staining, PARP fragmentation and mitochondrial membrane potential (MMP) were evaluated to determine the extent of apoptosis. While MK-886 alone caused mainly necrosis, 48h pre-treatment of cells with MK-886 followed by PDT with hypericin clearly shifted the type of cell death to apoptosis. PDT with hypericin alone caused apoptosis in 19% of the cell population. Some combined modalities significantly potentiated the apoptotic effect (31% of apoptotic cells; 2.5microM MK-886/0.1microM hypericin), i.e., by 60% more than after single treatment with hypericin. Increased apoptosis was confirmed by PARP (116kDa) cleavage to characteristic 89kDa fragments and changes in MMP. Increasing concentration of MK-886 was accompanied by massive changes in the cell cycle progression. Combined treatment with lower concentrations of MK-886 and hypericin increased accumulation of cells in the S phase, accompanied by inhibition of DNA synthesis. Increasing concentration of MK-886 in this combination caused the opposite effect, manifesting significant accumulation of cells in the G0/G1 phase. More pronounced effects were observed after the 48h pre-treatment schedule. This anti-proliferative effect was confirmed by BrdU incorporation. These results indicate that combined treatment involving PDT and LOX inhibitor MK-886 may improve the therapeutic effectiveness of PDT.

Attenuation of breast tumor cell growth by conjugated linoleic acid via inhibition of 5-lipoxygenase activating protein

Conjugated linoleic acid (CLA) consists of a group of linoleic acid geometric isomers that have been shown to reduce tumor growth and metastasis in animal models of breast, prostate and colon cancer. To delineate a possible mechanism of action for CLA, we have recently shown that the 5-lipoxygenase product, 5-hydroxyeicosatetraenoic acid (5-HETE), could play a role in CLA alteration of mammary tumorigenesis. In this study, we determined how CLA could modulate 5-lipoxygenase activity. The t10, c12-CLA isomer reduced production of 5-HETE but not 12- and 15-HETE in MDA-MB-231 human breast tumor cells. That isomer and the c9, t11-CLA isomer decreased 5-HETE production by competition with the lipoxygenase substrate, arachidonic acid (AA). Interestingly, t10, c12-CLA reduced the expression of five-lipoxygenase activating protein (FLAP) but not the 5-lipoxygenase enzyme. Over-expression of FLAP abrogated t10, c12-CLA-reduced viability of MDA-MB-231 cells. These data suggest that the reduction of 5-HETE by t10, c12-CLA was due to competition with AA and the reduction of FLAP expression.

Disparate forms of MK 886-induced programmed death in BCL-2 (+) blood and BCL-2 (–) solid cancer cells and a putative “nuclear” Ca2+ channel: “soil” trumps “seed”?

The five-lipoxygenase inhibitor, MK 886, in micromolar concentration induces a "type 1" form of programmed cell death in U937 human monoblastoid cells and a "type 2" form in Panc-1 pancreatic and PC3 prostate cell lines. The latter two lines originate from epithelial-derived solid human cancers. An acute rise in Ca(2+) occurs in U937 and HL 60 myeloid cells, in U937 cells located in their nuclei (HL 60 not tested), both of which are Bcl-2 positive. The two solid cancer cell lines express neither of these features. Solid tumor-derived Bcl-2-positive HeLa cervical cancer cells exhibit an acute increase in Ca(2+) after challenge with MK 886. In U937, PC3 and Panc-1 cells tested, the agent acutely increases oxidative stress and decreases mitochondrial membrane potential, indicating that neither event is directly determinative for the form of PCD. The role of mitochondria and the mechanism by which increased oxidative stress initiates the acute rise in U937 "nuclear" Ca(2+), the contribution, if any, of Bcl-2 in initiating the Ca(2+) signal and the latter in mandating the type of PCD, presumably through differential modulation of transcription, remain to be determined. Lastly, these results demonstrate that "soil" trumps "seed".

HYPOTHESIS

Despite similarities in response, including those of the mitochondria to micromolar concentrations of MK 886, hematopoietic and epithelial-derived non-hematopoietic solid cancer cell lines exhibit dissimilar forms of programmed cell death. These differences may depend upon the presence of Bcl-2 or a related protein participating in a juxta-nuclear/nuclear Ca(2+) ion-channel. Evidence for this supposition is discussed.