Bcl-2 mediated inhibition of erucylphosphocholine-induced apoptosis depends on its subcellular localisation

Saponin B, a novel cytostatic compound purified from Anemone taipaiensis, induces apoptosis in a human glioblastoma cell line

Glioblastoma multiforme (GBM) is one of the most common malignant brain tumors. Saponin B, a novel compound isolated from the medicinal plant, Anemone taipaiensis, has been found to have a strong time- and dose-dependent cytostatic effect on human glioma cells and to suppress the growth of U87MG GBM cells. In this study, we investigated whether saponin B induces the apoptosis of glioblastoma cells and examined the underlying mechanism(s) of action of saponin B. Saponin B significantly suppressed U87MG cell proliferation. Flow cytometric analysis of DNA in the U87MG cells confirmed that saponin B blocked the cell cycle at the S phase. Furthermore, treatment of the U87MG cells with saponin B induced chromatin condensation and led to the formation of apoptotic bodies, as observed under a fluorescence microscope, and Annexin V/PI assay further suggested that phosphatidylserine (PS) externalization was apparent at higher drug concentrations. Treatment with saponin B activated the receptor-mediated pathway of apoptosis, as western blot analysis revealed the activation of Fas-l. Saponin B increased the Bax and caspase-3 ratio and decreased the protein expression of Bcl-2. The results from the present study demonstrate that the novel compound, saponin B, effectively induces the apoptosis of GBM cells and inhibits glioma cell growth and survival. Therefore, saponin B may be a potential candidate for the development of novel cancer therapeutics with antitumor activity against gliomas.

Erucylphosphocholine induces growth inhibition, cell cycle arrest, and apoptosis in human choriocarcinoma cells

A membrane-targeted, lipophilic ether lipid of synthetic phospholipid analog, erucylphosphocholine (ErPC), induces apoptosis in some lines of human tumor cells. We investigated the effect of ErPC in the choriocarcinoma cell line, BeWo. BeWo cells were treated with various concentrations of ErPC, and changes in cell growth, the cell cycle, apoptosis, and related parameters were examined. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay showed that BeWo cells were sensitive to the growth inhibitory effect of ErPC. Cell cycle analysis indicated that exposure to ErPC decreased the proportion of cells in the S phase and increased the proportion in the G0/G1 phases of the cell cycle. Induction of apoptosis was confirmed by Annexin V staining of externalized phosphatidylserine and by the loss of mitochondrial transmembrane potential. This induction occurred in conjunction with the altered expression of genes related to cell growth, malignant phenotype, and apoptosis. These results suggest that ErPC may serve as a therapeutic agent for the treatment of choriocarcinoma.

Differential protection by wildtype vs. organelle-specific Bcl-2 suggests a combined requirement of both the ER and mitochondria in ceramide-mediated caspase-independent programmed cell death

Background

Programmed cell death (PCD) is essential for development and homeostasis of multicellular organisms and can occur by caspase-dependent apoptosis or alternatively, by caspase-independent PCD (ciPCD). Bcl-2, a central regulator of apoptosis, localizes to both mitochondria and the endoplasmic reticulum (ER). Whereas a function of mitochondrial and ER-specific Bcl-2 in apoptosis has been established in multiple studies, corresponding data for ciPCD do not exist.

Methods

We utilized Bcl-2 constructs specifically localizing to mitochondria (Bcl-2 ActA), the ER (Bcl-2 cb5), both (Bcl-2 WT) or the cytosol/nucleus (Bcl-2 ΔTM) and determined their protective effect on ceramide-mediated ciPCD in transiently and stably transfected Jurkat cells. Expression of the constructs was verified by immunoblots. Ceramide-mediated ciPCD was induced by treatment with human recombinant tumor necrosis factor and determined by flow cytometric measurement of propidium iodide uptake as well as by optical analysis of cell morphology.

Results

Only wildtype Bcl-2 had the ability to efficiently protect from ceramide-mediated ciPCD, whereas expression of Bcl-2 solely at mitochondria, the ER, or the cytosol/nucleus did not prevent ceramide-mediated ciPCD.

Conclusion

Our data suggest a combined requirement for both mitochondria and the ER in the induction and the signaling pathways of ciPCD mediated by ceramide.

Erucylphospho-N,N,N-trimethylpropylammonium shows substantial cytotoxicity in multiple myeloma cells

Multiple myeloma (MM) is a frequent hematological malignancy that is incurable despite recent developments, such as proteasome and angiogenic inhibitors. Erucylphospho-N,N,N-trimethylpropylammonium (erufosine) is an i.v. injectable alkylphosphocholine with antineoplastic activity based on an unusual mode of action and is currently undergoing clinical trials in leukemia patients. The aim of this investigation was to evaluate the efficacy of erufosine in MM cells and to study the modulation of cell-death pathways. The cytotoxicity of erufosine against three MM cell lines (RPMI-8226, U-266, and OPM-2) was determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide-dye reduction assay. All MM cell lines responded to erufosine, RPMI-8226 cells being most and U-266 being least sensitive. The respective IC(50) values were 3.2 and 16.2 micromol/L. Various cell-death characteristics were studied in response to erufosine, such as morphological changes, oligonucleosomal DNA fragmentation, caspase activation, and poly (ADP)-ribose polymerase cleavage. Erufosine was found to cause cell shrinkage, chromatin condensation, and caspase-8 and -3 activation. Taken together, our data indicate that erufosine is a potential antimyeloma drug eliciting specific features of apoptotic cell death in vitro.

BNIP3 mediates cell death by different pathways following localization to endoplasmic reticulum and mitochondrion

BNIP3 (Bcl-2/adenovirus E1B 19-kDa interacting protein 3) is a BH3-only proapoptotic member of the Bcl-2 family. Because the interaction of Bcl-2 proteins with intracellular Ca(2+) stores has been linked to apoptosis, the role of Ca(2+) transfer between endoplasmic reticulum (ER) and mitochondria in BNIP3-mediated cell death was determined in a rat dopaminergic neuronal cell line, Mes 23.5. BNIP3 mutants were constructed to target either ER or mitochondria. Localization of BNIP3 to the ER membrane facilitated release of Ca(2+) and subsequently increased uptake of Ca(2+) into mitochondria. Excessive accumulation of mitochondrial Ca(2+) decreased mitochondrial membrane potential (DeltaPsi(m)), resulting in execution of a caspase-independent cell death. Reduction of ER Ca(2+) induced by ER-targeted BNIP3 and the subsequent cell death was blocked by the antiapoptotic protein, Bcl-2. On the other hand, mitochondria-targeted BNIP3 initiated apoptosis by a Ca(2+)-independent mechanism by inducing mitochondrial pore transition and dissipation of DeltaPsi(m). The disruption of DeltaPsi(m) and cell death was not blocked by Bcl-2 overexpression. These findings show that BNIP3 undergoes a dual subcellular localization and initiates different cell death signaling events in the ER and mitochondria. Bcl-2 counters the BNIP3-initiated mobilization of ER Ca(2+) depletion to reduce the level of apoptosis.

Combined action of celecoxib and ionizing radiation in prostate cancer cells is independent of pro-apoptotic Bax

BACKGROUND AND PURPOSE

The cyclooxygenase-2-inhibitor celecoxib has been shown to inhibit cell growth and to reduce prostatic intraepithelial neoplasia in mice. The drug was suggested to increase efficacy of ionizing radiation. However, extent and mechanisms of the suggested benefit of celecoxib on the radiation response are still unclear. The aim of the present study was to analyze cytotoxic efficacy of celecoxib in combination with irradiation on human prostate cancer cell lines and to define the importance of pro-apoptotic Bax in this process.

MATERIALS AND METHODS

Induction of apoptosis and global and clonogenic cell survival upon irradation- (2-10Gy), celecoxib- (10-75microM) or combined treatment were evaluated in prostate cancer cells by fluorescence microscopy, WST-1 assay and standard colony formation assays.

RESULTS

Celecoxib <25microM caused morphological changes and growth inhibition without substantial apoptosis or radiosensitization in terms of decreased clonogenic cell survival. In contrast, celecoxib 25microM increased radiation-induced cell death and clonogenic kill. While radiation-induced clonogenic death was increased in the presence of Bax, effects of celecoxib or combined treatment were Bax independent.

CONCLUSIONS

Our findings reveal Bax-independent beneficial effects of celecoxib on radiation-induced apoptosis and eradication of clonogenic prostate cancer cells in vitro providing a rationale for clinical evaluation of high-dose celecoxib in combination with irradiation in prostate cancer patients.

Erucylphosphocholine shows a strong anti-growth activity in human endometrial and ovarian cancer cells

OBJECTIVES

A membrane-targeted, lipophilic ether lipid of synthetic phospholipid analog, erucylphosphocholine (ErPC) induces apoptosis in some lines of human tumor cells. We investigated the effect of ErPC on three endometrial cancer cell lines, two ovarian cancer cell lines, and normal human endometrial epithelial cells.

METHODS

Endometrial and ovarian cancer cells were treated with various concentrations of ErPC, and its effect on cell growth, cell cycle, apoptosis, and related measurements was investigated.

RESULTS

The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay showed that all endometrial and ovarian cancer cell lines were sensitive to the growth-inhibitory effect of ErPC, although normal endometrial epithelial cells were viable after treatment with the same doses of ErPC that induced growth inhibition in endometrial and ovarian cancer cells. Cell cycle analysis indicated that their exposure to ErPC decreased the proportion of cells in the S-phase and increased the proportion in the G2/M phases of the cell cycle. Induction of apoptosis was confirmed by annexin V staining of externalized phosphatidylserine and loss of the transmembrane potential of mitochondria. This induction occurred in concert with altered expression of genes related to cell growth, malignant phenotype, and apoptosis.

CONCLUSIONS

These results suggest that the anticancer activity of ErPC may occur with higher sensitivity of cancer cells compared with normal healthy cells, when using low concentration, rising hopes that ErPC may become a useful adjuvant therapy for endometrial and ovarian cancers.

Lysosomal and mitochondrial pathways in miltefosine-induced apoptosis in U937 cells

Hexadecylphosphocholine (HePC) is an anticancer agent whose effect has been shown to involve apoptosis induction but the signaling pathways leading to apoptosis remain to be elucidated. We show here that HePC induces activation of caspase-9, -3, and -8 via the intrinsic pathway, release of cytochrome c, activation and relocation of Bax to the mitochondria as well as the cleavage of Bid. Moreover, a lysosomal pathway characterized by partial lysosomal rupture, cathepsin B activation and relocation from lysosomes to the cytosol, is involved in HePC-induced apoptosis. A cathepsin B/L inhibitor partially suppresses caspase activation and apoptosis induction, indicating signaling between lysosomes and mitochondria. Conversely, the pancaspase inhibitor Q-VD-OPH inhibits lysosomal rupture, but only at early time points, suggesting that immediate lysosomal rupture involves caspases. Overexpression of Bcl-2, an anti-apoptotic protein known to prevent mitochondrial dysfunction, totally abrogates lysosomal destabilization and cell death.

Asterosaponin 1, a cytostatic compound from the starfish Culcita novaeguineae, functions by inducing apoptosis in human glioblastoma U87MG cells

Malignant glioblastoma is one of the most common malignant tumors in the neurological system. Asterosaponin 1, a new cytostatic agent from the starfish Culcita novaeguineae appear to exhibit various biological activities, including antitumor effect, but the function and mechanism of this new agent on glioblastoma cells has not previously been determined. In the present study, we investigated the proliferation change of human glioblastoma U87MG cells exposed to different concentrations (2.5-20.0 microg/ml) of asterosaponin 1 for a certain time. The results showed that asterosaponin 1 significantly suppressed U87MG cell proliferation in a time- and dose-dependent manner (IC50 =4.3 microg/ml). Flow cytometric analysis of DNA in U87MG cells showed that asterosaponin 1 induces the prominent appearance of a sub-G1 peak in the cell cycle suggestive of apoptosis identical with the result of annexin V/PI assay. Furthermore, U87MG cells treatment with asterosaponin 1 resulted in nuclear condensation with apoptotic bodies observed by both fluorescence and electron microscopy. Agarose gel electrophoresis of DNA from asterosaponin 1-treated cells revealed a typical "ladder" consistent with apoptotic DNA fragmentation. Western-blot staining showed asterosaponin 1 decreased the expression of Bcl-2 protein and increased the expression of Bax protein. The novel findings suggest that the cytostatic actions of asterosaponin 1 toward U87MG cells result from the induction of cell apoptosis. Overall, our data demonstrate that asterosaponin 1 is fully equipped for an efficient apoptotic killing of glioblastoma cells and suggest that this mechanism may play a critical role in anti-tumor chemotherapy.