Simultaneous modulation of the intrinsic and extrinsic pathways by simvastatin in mediating prostate cancer cell apoptosis

ABSTRACT: BACKGROUND: Recent studies suggest the potential benefits of statins as anti-cancer agents. Mechanisms by which statins induce apoptosis in cancer cells are not clear. We previously showed that simvastatin inhibit prostate cancer cell functions and tumor growth. Molecular mechanisms by which simvastatin induce apoptosis in prostate cancer cells is not completely understood. METHODS: Effect of simvastatin on PC3 cell apoptosis was compared with docetaxel using apoptosis, TUNEL and trypan blue viability assays. Protein expression of major candidates of the intrinsic pathway downstream of simvastatin-mediated Akt inactivation was analyzed. Gene arrays and western analysis of PC3 cells and tumor lysates were performed to identify the candidate genes mediating extrinsic apoptosis pathway by simvastatin. RESULTS: Data indicated that simvastatin inhibited intrinsic cell survival pathway in PC3 cells by enhancing phosphorylation of Bad, reducing the protein expression of Bcl-2, Bcl-xL and cleaved caspases 9/3. Over-expression of PC3 cells with Bcl-2 or DN-caspase 9 did not rescue the simvastatin-induced apoptosis. Simvastatin treatment resulted in increased mRNA and protein expression of molecules such as TNF, Fas-L, Traf1 and cleaved caspase 8, major mediators of intrinsic apoptosis pathway and reduced protein levels of pro-survival genes Lhx4 and Nme5. CONCLUSIONS: Our study provides the first report that simvastatin simultaneously modulates intrinsic and extrinsic pathways in the regulation of prostate cancer cell apoptosis in vitro and in vivo, and render reasonable optimism that statins could become an attractive anti-cancer agent.     

Involvement of both intrinsic and extrinsic pathways in IFN-gamma-induced apoptosis that are enhanced with cisplatin

IFN-gamma has direct anti-proliferative effects on ovarian cancer cell lines and tumour cells isolated from ovarian cancer ascites. The aim of this study was to further elucidate the mechanisms involved. An IFN-gamma-mediated cell cycle blockade was detectable in synchronised cell populations. Apoptosis, which was caspase dependent, was also induced. When caspase activity was blocked, the anti-proliferative effect of IFN-gamma was only partially reduced indicating independent roles for both growth inhibition and apoptosis in its actions. We have demonstrated involvement of the intrinsic apoptotic pathway; IFN-gamma treatment resulted in mitochondrial membrane depolarisation, cytochrome c release into the cytosol and activation of caspase 9. Cytochrome c release was blocked by the presence of a general caspase inhibitor, suggesting a role for caspases upstream of the mitochondria. One candidate is caspase 8, which was also activated in cells treated with IFN-gamma. Levels of Bid, a pro-apoptotic molecule that can mediate mitochondrial membrane permeabilisation when cleaved by caspase 8, were also decreased and indicated a potential link between these two pathways in IFN-gamma-induced apoptosis. Furthermore, together with cisplatin, IFN-gamma exerted a more powerful anti-proliferative effect.     

Bufalin induces apoptosis through activation of both the intrinsic and extrinsic pathways in human bladder cancer cells

Bufalin, a major digoxin-like immunoreactive component of the Chinese medicine Chansu, is prepared from toad venom. This compound has been shown to exert a potential for anticancer activity against various human cancer cell lines in?vitro. However, the detailed molecular mechanisms of its induction of apoptosis are still unclear. In this study, we investigated the apoptosis-inducing effect of bufalin in T24 human bladder cancer cells. Our data revealed that bufalin treatment resulted in a concentration-response growth inhibition of T24 cells by inducing cell cycle arrest at the G2/M phase and apoptosis, as evidenced by formation of apoptotic bodies, chromatin condensation and accumulation of cells in the sub-G1 phase. Apoptosis induction of T24 cells by bufalin showed correlation with proteolytic activation of caspase-3, -8 and -9, and concomitant degradation of poly (ADP-ribose) polymerases, and collapse of the mitochondria membrane potential. In addition, bufalin treatment resulted in an increase of the Bax/Bcl-2 (or Bcl-xL) ratio and caused down-regulation of inhibitor of apoptosis protein (IAP) family members. The increase in apoptosis by bufalin treatment was also associated with up-regulation of death receptor-related factors. Our data indicate that the growth inhibitory effects of bufalin occur through blockade of the G2/M phase, and that these cancer cells do not enter cell cycle progression and die through apoptosis via both intrinsic and extrinsic pathways.     

Allicin induces apoptosis in gastric cancer cells through activation of both extrinsic and intrinsic pathways

Allicin is an active compound derived from garlic that has been shown to have antitumor properties in vitro. The current study was designed to explore the effects and the underlying mechanism of allicin on gastric cancer cells. The MTT assay was used to detect cell viability. Transmission electron microscopy, Rh123 and propidium iodide staining, annexin V/FITC assay and the mitochondrial membrane potential were used to assess for the presence of apoptosis. Immunocytochemistry, western blot analysis, and Q-RT-PCR were used to detect gene expression. We found that allicin reduced cell viability in a dose- and time-dependent manner, partly through induction of apoptosis in gastric cancer cells. At the molecular level, allicin induced cytochrome c release from the mitochondria and increased caspase-3, -8, and -9 activation, with concomitant upregulation of bax and fas expression in the tumor cells. Allicin treatment inhibited proliferation and induced apoptosis in SGC-7901 cancer cells. Both intrinsic mitochondrial and extrinsic Fas/FasL-mediated pathways of apoptosis occur simultaneously in SGC-7901 cells following allicin treatment. Data from the current study demonstrated that allicin should be further investigated as a novel cancer preventive or therapeutic agent in control of gastric cancer, with potential uses in other tumor types.     

Vitamin E succinate induced apoptosis and enhanced chemosensitivity to paclitaxel in human bladder cancer cells in vitro and in vivo

There have been several studies on the antitumor activities of vitamin E succinate (α-TOS) as complementary and alternative medicine. In the present study, we investigated the cytotoxic effect of α-TOS and the enhancement of chemosensitivity to paclitaxel by α-TOS in bladder cancer. KU-19-19 and 5637 bladder cancer cell lines were cultured in α-TOS and/or paclitaxel in vitro . Cell viability, flow cytometric analysis, and nuclear factor-kappa B (NF-κB) activity were analyzed. For in vivo therapeutic experiments, pre-established KU-19-19 tumors were treated with α-TOS and/or paclitaxel. In KU-19-19 and 5637 cells, the combination treatment resulted in a significantly higher level of growth inhibition, and apoptosis was significantly induced by the combination treatment. NF-κB was activated by paclitaxel; however, the activation of NF-κB was inhibited by α-TOS. Also, the combination treatment significantly inhibited tumor growth in mice. In the immunostaining of the tumors, apoptosis was induced and proliferation was inhibited by the combination treatment. Combination treatment of α-TOS and paclitaxel showed promising anticancer effects in terms of inhibiting bladder cancer cell growth and viability in vitro and in vivo . One of the potential mechanisms by which the combination therapy has synergistic cytotoxic effects against bladder cancer may be that α-TOS inhibits NF-κB induced by chemotherapeutic agents. ( Cancer Sci 2009;)     

Inhibition of EGFR signaling augments oridonin-induced apoptosis in human laryngeal cancer cells via enhancing oxidative stress coincident with activation of both the intrinsic and extrinsic apoptotic pathways

Oridonin, a bioactive diterpenoid isolated from Rabdosia rubescens, has been reported to have anti-tumor effects, while the epidermal growth factor receptor (EGFR) signal pathway has been reported to play a vital role in the biological progression of several tumors and to be a target for therapeutic intervention. In this work, we show that inhibition of EGFR with tyrphostin AG1478 enhances oridonin-induced cell death in human laryngeal cancer cells HEp-2, a cell line characterized by EGFR gene amplification. The enhanced apoptotic effect correlates with high expression and activation of Bax, FADD, caspase-8 as well as caspase-3 and decreased protein levels of Bcl₂ and SIRT1, suggesting that both the extrinsic and intrinsic apoptosis pathways are involved in the apoptotic processes. However, treatment with oridonin and AG1478 greatly enhances nuclear translocation of apoptosis inducing factor (AIF) without caspase-9 activation, indicating that the apoptosis occurs via a caspase-9-independent mitochondrial pathway. Here, it is the active form of caspase-8 but not caspase-9 that activates downstream effector caspase-3, resulting in the cleavage of critical cellular proteins and apoptosis. Furthermore, the combined use of AG1478 and oridonin augments the production of reactive oxygen species (ROS). Incubation of cells with N-Acetylcysteine (NAC) attenuates the apoptosis and the mitochondrial membrane potential (Δψm) disruption induced by the combination of oridonin and AG1478, which indicates that ROS plays a pivotal role in cell death. In conclusion, targeting EGFR combined with other conventional pro-apoptotic drugs should be a potentially very effective anti-neoplastic therapy for laryngeal cancer.     

Arsenic trioxide mediates intrinsic and extrinsic pathways of apoptosis and cell cycle arrest in acute megakaryocytic leukemia

Arsenic trioxide (ATO) induces apoptosis in a range of solid tumors and leukemia cells, and has been clinically applied for the treatment of acute promyelocytic leukemia with confirmed efficacy. Acute megakaryocytic leukemia (AMKL) is an aggressive malignancy with poor prognosis, if bone marrow transplantation is not possible. In this study, we applied flow cytometry, Western blot analysis and microarray techniques to investigate the effects of ATO on apoptosis and the cell division cycle of AMKL cell lines CHRF-288-11 and MEG-01. Our data demonstrated that ATO is a potent agent against AMKL as indicated by apoptotic markers, Annexin V and caspase-3. ATO activated the intrinsic (mitochondrial) pathway of apoptosis, which involved disrupting mitochondrial membrane potential, increased Bax/Bcl-2 ratio and caspase-9 activation, as well as the extrinsic (death receptor) pathway mediated by Fas and caspase-8 activation. We provided the first evidence that ATO stimulated expressions of CD137 mRNA and protein, which might be relevant to the extrinsic mechanism. ATO induced delays of cell cycle progression at S phase and arrest at G2/M phase of AMKL cells, but caspase-3 expression appeared not to be phase-specific. The multiple-signaling mechanism of ATO warrants it a potential agent to incorporate in the treatment regimen of AMKL.     

Differential effects of bexarotene on intrinsic and extrinsic pathways in TRAIL-induced apoptosis in two myeloid leukemia cell lines

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces programmed cell death (apoptosis) preferentially in tumor cells. However, not all cancer cells are sensitive to TRAIL. We determined whether ligation of the retinoid receptor, RXR, would sensitize cells to TRAIL-mediated apoptosis. The leukemic cell lines KG1a (apoptosis-resistant) and ML-1 (apoptosis-sensitive) were treated with the RXR-specific retinoid bexarotene, TRAIL, or both, and apoptosis was determined. In KG1a cells, bexarotene downregulated FLIP(Long) and activated caspase-8, thereby allowing for TRAIL-triggered apoptosis. Overexpression of FLIP(Long) in ML-1 cells abrogated apoptosis. In unmodified ML-1 cells bexarotene enhanced programmed cell death via truncation of Bid and release of cytochrome C. Blockade of caspase-8 prevented enhancement in both cell lines; blockade of caspase-9 had a significant effect only in ML-1 cells. Thus, the effect of bexarotene on TRAIL-mediated programmed cell death involved proximal events of the extrinsic pathway; however, downstream signals involved the intrinsic pathway in ML-1 but not in KG1a cells. These studies add further information to the regulation of programmed cell death in leukemic cells that have to be considered when designing therapeutic strategies.     

Differential-effects of fibroblast coculture on mcf-7 and mda-231 breast-carcinoma cell invasion through matrigel

The stimulative effect of conditioned media collected from fibroblasts or breast epithelial cells on breast carcinoma cell invasion through Matrigel was studied. Fibroblast conditioned medium was more efficient than media collected from breast epithelial cells in stimulating chemoinvasion of highly invasive MDA-MB-231 and MDA-MB-436 cells. In contrast, fibroblast conditioned medium was found to be less effective than breast epithelial cell conditioned medium in stimulating invasion of weakly metastatic MCF-7 cells. These data suggest that fibroblasts preferentially enhance the invasive capacity of highly malignant breast carcinoma cells.     

Radiation-induced immunogenic modulation of tumor enhances antigen processing and calreticulin exposure,resulting in enhanced T-cell killing

Radiation therapy (RT) is used for local tumor control through direct killing of tumor cells. Radiation-induced cell death can trigger tumor antigen-specific immune responses, but these are often noncurative. Radiation has been demonstrated to induce immunogenic modulation (IM) in various tumor types by altering the biology of surviving cells to render them more susceptible to T cell-mediated killing. Little is known about the mechanism(s) underlying IM elicited by sub-lethal radiation dosing. We have examined the molecular and immunogenic consequences of radiation exposure in breast, lung, and prostate human carcinoma cells. Radiation induced secretion of ATP and HMGB1 in both dying and surviving tumor cells. In vitro and in vivo tumor irradiation induced significant upregulation of multiple components of the antigen-processing machinery and calreticulin cell-surface expression. Augmented CTL lysis specific for several tumor-associated antigens was largely dictated by the presence of calreticulin on the surface of tumor cells and constituted an adaptive response to endoplasmic reticulum stress, mediated by activation of the unfolded protein response.This study provides evidence that radiation induces a continuum of immunogenic alterations in tumor biology, from immunogenic modulation to immunogenic cell death. We also expand the concept of immunogenic modulation, where surviving tumor cells recovering from radiation-induced endoplasmic reticulum stress become more sensitive to CTL killing. These observations offer a rationale for the combined use of radiation with immunotherapy, including for patients failing RT alone.     

Cisplatin and a potent platinum(IV) complex-mediated enhancement of TRAIL-induced cancer cells killing is associated with modulation of upstream events in the extrinsic apoptotic pathway

TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) can selectively trigger apoptosis in various cancer cell types. However, many cancer cells are resistant to death receptor-mediated apoptosis. Combination therapy with platinum complexes may affect TRAIL-induced signaling via modulation of various steps in apoptotic pathways. Here, we show that cisplatin or a more potent platinum(IV) complex LA-12 used in 20-fold lower concentration enhanced killing effects of TRAIL in human colon and prostate cancer cell lines via stimulation of caspase activity and overall apoptosis. Both platinum complexes increased DR5 surface expression in colon cancer cells. Small interfering RNA-mediated DR5 silencing rescued cells from sensitizing effects of platinum drugs on TRAIL-induced caspase-8 activation and apoptosis, showing the functional importance of DR5 in the effects observed. In addition, both cisplatin and LA-12 triggered the relocalization of DR4 and DR5 receptors to lipid rafts and accelerated internalization of TRAIL, which may also affect TRAIL signaling. Collectively, modulations of the initial steps of the extrinsic apoptotic pathway at the level of DR5 and plasma membrane are important for sensitization of colon and prostate cancer cells to TRAIL-induced apoptosis mediated by LA-12 and cisplatin.     

Nitric oxide-mediated tumor cell killing of cisplatin-based interferon-gamma gene therapy in murine ovarian carcinoma

We have determined the role of nitric oxide (NO)-mediated tumor cell killing in the treatment of an animal model of murine ovarian carcinoma grown in the peritoneum with a combination of cisplatin and cationic liposomes containing an expression vector for interferon-gamma (IFN-gamma). The approach was to determine whether the therapy was effective in mice homozygous for a disrupted inducible NO synthase (iNOS) allele; these mice were unable to produce NO in response to IFN-gamma. iNOS (-/-) mice treated with both cisplatin and liposomal IFN-gamma gene did not produce a significant amount of NO in ascites (12.1+/-4.5 microM), although they expressed a high level of IFN-gamma (9002+/-723 U/mL of ascitic fluid). As a result, mice died of tumors within 11-62 days. However, wild-type mice treated with both cisplatin and liposomal IFN-gamma gene produced a significant amount of NO in ascites (113.7+/-17.9 microM) with a high level of IFN-gamma gene expression (9350+/-1254 U/mL of ascitic fluid) and were free of tumors for at least 80 days. This result confirmed that NO was a direct mediator of IFN-gamma cytotoxicity.     

Aggravated DNA damage as a basis for enhanced glioma cell killing by MJ-66 in combination with minocycline

Despite recent advances in the treatment of malignant glomas, the prognosis of patients remains very poor and more efficient therapeutic approaches are urgently needed. In the present study, we investigated whether 2-(naphthalene-1-yl)-6-pyrrolidinyl-4-quinazolinone (MJ-66), a synthetic quinazolinone analog, induces glioma cell death through DNA damage. Treatment of C6 glioma cells with MJ-66 resulted in a time-dependent increase in γ-H2AX and increased the appearance of nuclear γ-H2AX foci. MJ-66 interfered with G2/M DNA damage checkpoint through increasing phosphorylated levels of Chk1 and Cdc25C. UCN-01, a Chk1 inhibitor, reversed MJ-66-induced activation of Cdc25C and caspase 3. MJ-66 inhibited tumor growth and prolonged survival time in intracranial glioma xenograft model. The combination of MJ-66 and Mino enhanced DNA damage and synergistically inhibited tumor growth and prolonged survival time in intracranial glioma xenograft model. These results suggest that the combination of MJ-66 and Mino may be developed as a new therapeutic strategy against malignant gliomas.     

Photodynamic therapy-generated tumor cell lysates with CpG-oligodeoxynucleotide enhance immunotherapy efficacy in human papillomavirus 16 (E6/E7) immortalized tumor cells

Immunotherapy with photodynamic therapy (PDT) offers great promise as a new alternative for cancer treatment; however, its use remains experimental. In this study, we examined the immunotherapeutic significance of human papillomavirus (HPV)-immortalized tumor cell lysates induced by PDT with CpG-oligodeoxynucleotide (ODN). PDT-cell lysates were generated by irradiating Radachlorin (5 microg/mL) preloaded TC-1 cells carrying HPV 16 E7. PDT-cell lysates plus ODN coinjection for protection against E7-expressing tumors as well as specific immune responses were evaluated with the following tests: heat shock protein 70 (HSP70) enzyme-linked immunosorbent assay, in vitro and in vivo tumor growth inhibition, interferon-gamma (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha) assay, cytotoxic T-lymphocyte assay, and fluorescence activated cell sorting (FACS) analysis. PDT-cell lysates plus ODN coinjection showed a significant suppression of tumor growth at both prophylactic and therapeutic levels, compared to PDT (or F/T)-cell lysates or ODN alone. In addition, we evaluated the level of the immune response with the coinjection. HSP70, an important regulator of inflammatory and immune response, was observed in abundance in the PDT-cell lysates. IFN-gamma production and cytotoxic T lymphocytes (CTL) responses were induced by PDT-cell lysates plus ODN injection. The coinjection resulted in PDT-cell lysate-specific antibodies (IgG1, IgG2a, IgG2b, and IgG3) and T-helper cell responses significantly higher than PDT-cell lysates alone. Moreover, IFN-gamma production and CTL responses were significantly induced in the PDT-cell lysate plus ODN immunized groups. These enhanced immune responses appeared to be mediated by CD8+ T cells only. These data suggest that PDT-cell lysates plus ODN injection may be an effective approach to induce CTL immune responses as a possible immunotherapeutic strategy for cancer therapy.