TAM-induced Cell Death Research Articles

Concanavalin-A shows synergistic cytotoxicity with tamoxifen via inducing apoptosis in estrogen receptor-positive breast cancer: In vitro and molecular docking studies

Background: Tamoxifen (TAM) is the main treatment of estrogen receptor (ER)-positive breast cancer, however; its adverse effects and development of resistance hinder its use. Concanavalin A (Con A) is a mannose/glucose-binding lectin that has been reported to induce apoptosis in a variety of cell lines. Methods: Therefore, we aimed to elucidate the effects of Con A on TAM-induced cell death in ERα positive cell line (MCF-7) and to identify the potential underlying molecular mechanisms using in silico and in vitro techniques. Results: Our results demonstrated that combined treatment with Con A and TAM reduced the expression of ERα, which showed clear synergistic effects on inhibiting the cell viability of MCF-7 cells. Interestingly, the combined treatment induces G1 phase arrest and reduces cyclin D1 activity while increasing apoptosis and autophagy as indicated by decreasing the expression level of anti-apoptosis gene BCl-2 and increased apoptosis/autophagic gene BNIP3. Molecular docking was conducted to evaluate the binding affinity of Con A towards ERα, and it revealed its potential activity as an ERα antagonist. Our data further indicated that Con A administration increased the drug reduction index of TAM. Conclusion: Overall, our findings suggested that Con A could be used as an adjuvant agent with TAM to improve its effectiveness as an anticancer agent while minimizing its side effects.

1981P RelB silencing reversed tamoxifen resistance by regulating GPx4 and ferroptosis in breast cancer

Tamoxifen (Tam) resistance poses a significant challenge for successfully treating breast cancer (BCa). It has been shown to increase oxidative stress and induce cell death by regulation of reactive oxygen species (ROS) which accumulation leaded to the production of lipid hydroperoxides. Ferroptosis, a cell death process riven by the accumulation of iron-dependent lipid hydroperoxides, has been induced by inactivation/depletion of glutathione peroxidases (GPxs). The RelB level were examined by IHC and western blot in BCa tumor tissues and cell lines. The cell viability were determined by colony survival and MTT. The ROS and oxygen consumption rates were measured using ROS detection probes and a Seahorse XF96 Analyzer. The lipid peroxidation level was analyzed by immunofluorescence assay. The morphological changes of mitochondria were observed by TEM. RelB binding to the NF-κB intronic enhancer region of the human GPx4 gene was determined using a ChIP assay. The effect of RelB on BCa Tam resistance was further validated using BCa mice xenograft models. RelB was uniquely expressed at the high level in Tam resistance BCa tissues and cell lines, and correlated to BCa progression and patient survival. Down-regulation of RelB remarkably sensitized resistance cells to Tam. The high level of ROS and declination of mitochondrial respiration which induced by Tam were inhibited in resistant cells. Tam enhanced lipid peroxidation with concomitant non-apoptotic cell death, which are negatively regulated by GPx4 activity. In addition to GPx4 knockdown, deferoxamine was able to rescue Tam-induced cell death at certain extent in breast cancer cells. Importantly, RelB upregulates GPx4 expression through binding to an NF-κB enhancer element located at the 5’-flanking region. Consistently, in vivo functional validation confirmed that RelB inhibition not only impairs tumor growth, but also inhibits Tam resistance in nude mice. It's demonstrated that the RelB-based noncanonical NF-κB pathway plays a predominant role in mediating the sensitivity of Tam in BCa. RelB could inhibit ferroptosis which induced by hydroxyl radicals accumulation through upregulating GPx4 in BCa.

RelB silencing to reverse tamoxifen resistance by regulating GPx4 and ferroptosis in breast cancer.

e12513 Background: Tamoxifen(Tam), as an essential therapeutic treatment of estrogen receptor(ER)-positive breast cancer(BCa), has been available for the past three decades. However, the induction of Tam resistance during therapy has indicated a significant challenge with regards to this agent. Tam could increase oxidative stress and induce cell death by regulating reactive oxygen species(ROS). Ferroptosis, a cell death process driven by the accumulation of iron-dependent lipid peroxides, has been induced by inactivation/depletion of glutathione peroxidases(GPxs). Our previous studies found that the expression level of RelB gene, a member of NF-κB family, is negatively correlated with ER targeted by Tam in BCa. Methods: The RelB level of BCa tumor tissues and the corresponding cell lines were examined by immunoblotting and western blot. The effects of Tam on cell viability were determined using colony survival and MTT assay. The ROS and oxygen consumption rates(OCR) were measured using specific ROS detection probes and a Seahorse XF96 Analyzer, respectively. The lipid peroxidation level of cells was analyzed by immunofluorescence assay. The morphological changes of mitochondria were observed by transmission electron microscope. RelB binding to the NF-κB intronic enhancer region of the human GPx4 gene was determined using a ChIP assay. Accordingly, the effect of RelB on BCa Tam resistance was further validated using BCa mice xenograft models. Results: RelB was uniquely expressed at the high level in Tam resistance BCa tissues and cell lines. Down-regulation of RelB based on a CRISPR/Cas9 system remarkably sensitized resistance BCa cells to Tam. Treatment with SN52, a RelB inhibitor, illuminated the role of RelB in Tam-treated BCa cells. The high level of ROS and declination of mitochondrial respiration which induced by Tam were inhibited in resistance cells. Tam enhanced lipid peroxidation with concomitant non-apoptotic cell death, which are negatively regulated by GPx4 activity. In addition to GPx4 knockdown, deferoxamine was able to rescue Tam-induced cell death in BCa cells, verifying that Tam induces cell death partially through ferroptosis. Importantly, RelB upregulates GPx4 expression through binding to an NF-κB enhancer element located at the 5’-flanking region. Consistently, in vivo functional validation confirmed that RelB inhibition not only impairs tumor growth, but also inhibits Tam resistance in nude mice. Conclusions: RelB could inhibit ferroptosis which induced by hydroxyl radicals accumulation through upregulating GPx4 in BCa.

Tamoxifen-induced cytotoxicity in breast cancer cells is mediated by glucose-regulated protein 78 (GRP78) via AKT (Thr308) regulation

Glucose regulated protein 78 (GRP78) has recently been suggested to be associated with drug resistance in breast cancer patients. However, the precise role of GRP78 in drug resistance and the involved signaling pathways are not clearly understood. In the present study, we show that among a panel of drugs, namely Paclitaxel (TAX), Doxorubicin (DOX), 5-fluorouracil (5-FU), UCN-01 and Tamoxifen (TAM) used, TAM alone up-regulated the expression of GRP78 significantly and induced apoptosis in MCF-7 and MDA-MB-231 cells. Interestingly, inhibition of GRP78 by a specific pharmacological inhibitor, VER-155008 augmented TAM-induced apoptosis, and overexpression of GRP78 rendered the cells resistant to TAM-induced cell death suggesting a role for GRP78 in TAM-induced cytotoxicity. Mechanistically, the expression of phosphorylated AKT as determined by Western blot analyses revealed that TAM selectively upregulated phosphorylation of AKT at Thr308 but not at Ser473, and siRNA silencing of GRP78 resulted in inhibition of AKT phosphorylation at Thr308 but not at Ser473. Further, a GRP78 inhibitor, VER155008 inhibited TAM-induced phosphorylation of GSK3β, a downstream substrate of AKT. These results, thus suggests a role for GRP78 in TAM-induced AKT activation. Additionally, co-localization studies by immunofluorescence, and immunoprecipitation experiments demonstrated a complex formation of AKT and GRP78. Furthermore, in glucose-free medium, the cells were sensitized to TAM-induced cell death that was associated with reduced AKT phosphorylation at Thr308, thus strengthening the association of AKT regulation with drug response. Collectively, our findings identify a role of GRP78 in AKT regulation in response to TAM in breast cancer cells.

Cytoplasmic PELP1 and ERRgamma protect human mammary epithelial cells from Tam-induced cell death.

Tamoxifen (Tam) is the only FDA-approved chemoprevention agent for pre-menopausal women at high risk for developing breast cancer. While Tam reduces a woman's risk of developing estrogen receptor positive (ER+) breast cancer, the molecular mechanisms associated with risk reduction are poorly understood. Prior studies have shown that cytoplasmic proline, glutamic acid and leucine rich protein 1 (PELP1) promotes Tam resistance in breast cancer cell lines. Herein, we tested for PELP1 localization in breast epithelial cells from women at high risk for developing breast cancer and found that PELP1 was localized to the cytoplasm in 36% of samples. In vitro, immortalized HMECs expressing a nuclear localization signal (NLS) mutant of PELP1 (PELP1-cyto) were resistant to Tam-induced death. Furthermore, PELP1-cyto signaling through estrogen-related receptor gamma (ERRγ) promoted cell survival in the presence of Tam. Overexpression of ERRγ in immortalized HMECs protected cells from Tam-induced death, while knockdown of ERRγ sensitized PELP1-cyto expressing HMECs to Tam. Moreover, Tam-induced HMEC cell death was independent of apoptosis and involved accumulation of the autophagy marker LC3-II. Expression of PELP1-cyto and ERRγ reduced Tam-induced LC3-II accumulation, and knockdown of ERRγ increased LC3-II levels in response to Tam. Additionally, PELP1-cyto expression led to the upregulation of MMP-3 and MAOB, known PELP1 and ERRγ target genes, respectively. Our data indicate that cytoplasmic PELP1 induces signaling pathways that converge on ERRγ to promote cell survival in the presence of Tam. These data suggest that PELP1 localization and/or ERRγ activation could be developed as tissue biomarkers for Tam responsiveness.

Secretory prostate apoptosis response (Par)-4 sensitizes multicellular spheroids (MCS) of glioblastoma multiforme cells to tamoxifen-induced cell death

Glioblastoma multiforme (GBM) is the most malignant form of brain tumor and is associated with resistance to conventional therapy and poor patient survival. Prostate apoptosis response (Par)-4, a tumor suppressor, is expressed as both an intracellular and secretory/extracellular protein. Though secretory Par-4 induces apoptosis in cancer cells, its potential in drug-resistant tumors remains to be fully explored. Multicellular spheroids (MCS) of cancer cells often acquire multi-drug resistance and serve as ideal experimental models. We investigated the role of Par-4 in Tamoxifen (TAM)-induced cell death in MCS of human cell lines and primary cultures of GBM tumors. TCGA and REMBRANT data analysis revealed that low levels of Par-4 correlated with low survival period (21.85±19.30days) in GBM but not in astrocytomas (59.13±47.26days) and oligodendrogliomas (58.04±59.80days) suggesting low PAWR expression as a predictive risk factor in GBM. Consistently, MCS of human cell lines and primary cultures displayed low Par-4 expression, high level of chemo-resistance genes and were resistant to TAM-induced cytotoxicity. In monolayer cells, TAM-induced cytotoxicity was associated with enhanced expression of Par-4 and was alleviated by silencing of Par-4 using specific siRNA. TAM effectively induced secretory Par-4 in conditioned medium (CM) of cells cultured as monolayer but not in MCS. Moreover, MCS were rendered sensitive to TAM-induced cell death by exposure to conditioned medium (CM)-containing Par-4 (derived from TAM-treated monolayer cells). Also TAM reduced the expression of Akt and PKCζ in GBM cells cultured as monolayer but not in MCS. Importantly, combination of TAM with inhibitors to PI3K inhibitor (LY294002) or PKCζ resulted in secretion of Par-4 and cell death in MCS. Since membrane GRP78 is overexpressed in most cancer cells but not normal cells, and secretory Par-4 induces apoptosis by binding to membrane GRP78, secretory Par-4 is an attractive candidate for potentially overcoming therapy-resistance not only in malignant glioma but in broad spectrum of cancers.

Sensitivity Evaluation of Two Human Breast Cancer Cell Lines to Tamoxifen through Apoptosis Induction

Tamoxifen citrate (TAM) has been used to treat breast cancer in women for many years. The com-parative effects of TAM in inducing apoptosis were evaluated in estrogen receptor-positive (ER- positive MCF-7) and estrogen receptor-negative (ER-negative MDA-MB-231) human breast cancer cell lines in vitro in order to determine if these two cell lines differ in their sensitivity to TAM. Mi-tochondrial membrane permeability potential disruption was assessed in both cell lines by a lip-ophilic cationic dye (DePsipher assay, Trevigen, Inc.) utilizing fluorescence microscopy. Using this specific fluorochrome, we were able to associate mitochondrial membrane disruption to early, mid-, and late apoptotic cells. TAM induced cell death via apoptosis in both ER-positive and ER- negative cells, however, apoptosis induction was more pronounced in ER-positive MCF-7 compared to ER-negative MDA-MB-231 breast cancer cells. These findings may have some therapeutic use in the treatment of estrogen dependent and estrogen independent breast cancer.

Induction of Autophagy and Cell Death by Tamoxifen in Cultured Retinal Pigment Epithelial and Photoreceptor Cells

We investigated the mechanism of tamoxifen (TAM) retinotoxicity using human retinal pigment epithelial (RPE)-derived (ARPE-19) and photoreceptor-derived (661W) cells. Cultured ARPE-19 and 661W cells were treated with 5 to 10 μM TAM, and the resultant cell death was quantified using lactate dehydrogenase (LDH) release assay. Cellular oxidative stress was determined by measuring 5-(and-6)-carboxy-2',7'-dichlorohydrofluorescein diacetate (H(2)-DCFDA) fluorescence. Changes in intracellular free zinc levels were monitored using the zinc-specific fluorescent dye, FluoZin-3 AM. Autophagic vacuole formation was assessed morphologically in ARPE-19 and 661W cells transfected with the fluorescent protein-conjugated markers, RFP-LC3 or GFP-LC3. Following exposure to TAM, both ARPE-19 and 661W cells had cytosolic vacuoles within 1 hour and underwent cell death within 18 hours. In both cell types, TAM-induced cell death was accompanied by increased oxidative stress and elevated zinc levels, and was attenuated by the antioxidant N-acetyl-L-cysteine (NAC) or the zinc chelator N,N,N'N'-tetrakis(-)(2-pyridylmethyl)-ethylenediamine (TPEN). The levels of LC3-II as well as the number of autophagic vacuoles (AVs) increased after TAM treatment. Double staining for lysosomes and AVs showed that autolysosome formation proceeded normally. Consistent with this, autophagy flux was increased. Finally, as shown in other cases of autophagic cell death, lysosomal membrane permeabilization (LMP) as well as caspase-dependent apoptosis contributed to TAM-induced cell death. ARPE-19 and 661W cells were vulnerable similarly to TAM-induced cytotoxicity. Increases in zinc levels and oxidative stress, excessive activation of autophagy flux, and ultimately the occurrence of LMP and consequent caspase activation may contribute to the well-established retinal cytotoxicity of TAM.

LMTK3 is implicated in endocrine resistance via multiple signaling pathways

Resistance to endocrine therapy in breast cancer is common. With the aim of discovering new molecular targets for breast cancer therapy, we have recently identified LMTK3 as a regulator of the estrogen receptor-alpha (ERα) and wished to understand its role in endocrine resistance. We find that inhibition of LMTK3 in a xenograft tamoxifen (Tam)-resistant (BT474) breast cancer mouse model results in re-sensitization to Tam as demonstrated by a reduction in tumor volume. A whole genome microarray analysis, using a BT474 cell line, reveals genes significantly modulated (positively or negatively) after LMTK3 silencing, including some that are known to be implicated in Tam resistance, notably c-MYC, HSPB8 and SIAH2. We show that LMTK3 is able to increase the levels of HSPB8 at a transcriptional and translational level thereby protecting MCF7 cells from Tam-induced cell death, by reducing autophagy. Finally, high LMTK3 levels at baseline in tumors are predictive for endocrine resistance; therapy does not lead to alteration in levels, whereas in patient's plasma samples, acquired LMTK3 gene amplification (copy number variation) was associated with relapse while receiving Tam. In aggregate, these data support a role for LMTK3 in both innate (intrinsic) and acquired (adaptive) endocrine resistance in breast cancer.

Abstract 5747: Elucidating the mechanisms by which Snail transcription factor promotes resistance to chemotherapy in breast carcinomas

Abstract Snail (Snail1) is a zinc finger transcription factor that can induce EMT and is expressed at high levels in tumors. Maspin is a potential tumor suppressor, whose expression is lost as breast and prostate tumors progress during EMT. Maspin can be transcriptionally repressed by androgen receptor (AR) in prostate cancer cells. We hypothesized that overexpression of Snail will inhibit maspin expression and confer resistance to chemotherapy. Initially, we examined the expression of Snail and maspin in a panel of breast epithelial and breast cancer cells by RT-PCR and Western blot analysis. Preliminary results suggest that breast cancer cells express variable levels of Snail that is higher in breast cancer cells than in the normal MCF10A cells. We then utilized MCF-7 cells transfected stably with an empty Neo vector (MCF-7 Neo) or constitutively active Snail cDNA (MCF-7 Snail) that have been shown previously to represent an EMT model, and examined maspin, estrogen receptor alpha (ER-α) and AR levels by western blot analysis. MCF-7 Snail cells had upregulated levels of Snail and lower levels of maspin, ER-α and AR, as compared to MCF-7 Neo. MCF-7 Neo and MCF-7 Snail cells were also xenografted into nude mice and tissue sections stained immunohistochemically for Snail, maspin, and ER-α. Tumor volumes of MCF-7 Snail tumor xenografts were significantly larger than the MCF-7 Neo xenografts. MCF-7 Snail tissue sections expressed higher levels of Snail and lower levels of maspin and ER-α as compared to MCF-7 Neo sections. MCF-7 Neo and MCF-7 Snail cells were also treated with estradiol (E2, 0.01uM), tamoxifen (TAM, 10uM), and docetaxel (DOX, 1uM) individually; and in combination with E2 plus TAM and TAM plus DOX for periods of 24h and 72h to analyze changes in cell morphology and EMT marker expression. No effect on cell morphology or cell death was observed in MCF-7 Snail cells after TAM treatments, whereas TAM induced cell death in MCF-7 Neo. Expression of Snail was increased with E2 treatments and decreased with TAM, DOX, and combination treatments in MCF-7 Neo and MCF-7 Snail. AR expression decreased further in MCF-7 Snail cells and MCF-7 Neo following treatments with TAM and DOX. Overall, the Snail overexpression appears to promote resistance to TAM and DOX chemotherapeutic agents. The mechanism of Snail-regulated EMT needs to be investigated further to determine changes in breast cancer progression. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5747. doi:1538-7445.AM2012-5747

Role of mitochondria in tamoxifen-induced rapid death of MCF-7 breast cancer cells

Tamoxifen (Tam) is widely used in chemotherapy of estrogen receptor-positive breast cancer. It inhibits proliferation and induces apoptosis of breast cancer cells by estrogen receptor-dependent modulation of gene expression, but recent reports have shown that Tam (especially at pharmacological concentrations) has also rapid nongenomic effects. Here we studied the mechanisms by which Tam exerts rapid effects on breast cancer cell viability. In serum-free medium 5-7 microM Tam induced death of MCF-7 and MDA-MB-231 cells in a time-dependent manner in less than 60 min. This was associated with release of mitochondrial cytochrome c, a decrease of mitochondrial membrane potential and an increase in production of reactive oxygen species (ROS). This suggests that disruption of mitochondrial function has a primary role in the acute death response of the cells. Accordingly, bongkrekic acid, an inhibitor of mitochondrial permeability transition, was able to protect MCF-7 cells against Tam. Rapid cell death induction by Tam was not associated with immediate activation of caspase-9 or cleavage of poly (ADP-ribose) polymerase. It was not blocked by the caspase inhibitor z-Val-Ala-Asp-fluoromethylketone either. Diphenylene ionodium (DPI), an inhibitor of NADPH oxidase, was able to prevent Tam-induced cell death but not cytochrome c release, which suggests that ROS act distal to cytochrome c. The pure antiestrogen ICI 182780 (1 microM) could partly oppose the effect of Tam in estrogen receptor positive MCF-7 cells, but not in estrogen receptor negative MDA-MB-231 cells. Pre-culturing MCF-7 cells in the absence of 17beta-estradiol (E(2)) or in the presence of a low Tam concentration (1 microM) made the cells even more susceptible to rapid death induction by 5 or 7 microM Tam. This effect was associated with decreased levels of the anti-apoptotic proteins Bcl-X(L) and Bcl-2. In conclusion, our results demonstrate induction of a rapid mitochondrial cell death program in breast cancer cells at pharmacological concentrations of Tam, which are achievable in tumor tissue of Tam-treated breast cancer patients. These mechanisms may contribute to the ability of Tam therapy to induce death of breast cancer cells.

Effects of Polyamines on TNFalpha- or Tamoxifen-induced Apoptosis in Human Breast Cancer Cells.

To investigate the effects of polyamines on tumor necrosis factor alpha (TNFalpha)-or tamoxifen (TAM)-induced apoptosis in estrogen receptor (ER)-positive MCF- 7 and ER-negative MDA-MB-231 human breast cancer cells. Cell viability was assessed by using MTT assay. Reactive oxygen species (ROS) generation was measured using 2', 7'-dichlorofluorescin diacetste (DCFDA) by fluorescence plate reader. DNA fragmentation was assessed by 1.5% agarose gel electrophoresis. TNFalpah and TAM showed significant dose- and time- dependent inhibitory effects on the growth of MCF-7 human cells. However, the growth of MDA-MB-231 cells were not inhibited by TNFalpha or TAM treatment. The generation of ROS was increased in dose-and time-dependent manner by TNFalpha treatment in MCF-7 cells. Polyamines, especially spermine suppressed TNFalpha-induced ROS generation in MCF-7 cells. Antioxidant effects of polyamines were also demonstrated by DNA fragmentation, cell morphology as well as ROS generation assay. Polyamines also blocked TAM-induced cell death in MCF-7 cell. However, MDA-MB-231 cells showed resistance to the cytotoxic effects of TNFalpha or TAM. These results suggest that polyamines may prevent TNFalpha or TAM-induced apoptosis in MCF-7 human breast cancer cells.

Involvement of fas in tamoxifen-induced apoptosis of cholangiocarcinoma

Cholangiocarcinoma continues to have a dismal prognosis with a less than 10% survival. Thus, new modalities of treatment are needed. Tamoxifen (TAM) is an antiestrogen compound which has been shown to provide antimitogenic effects through numerous mechanisms. We have demonstrated that TAM inhibits human cholangiocarcinoma growth in vitro and in vivo (Canc Res 57:1997). Consequently, TAM may provide an effective treatment alternative. The purpose of this study is to evaluate the role of Fas receptor in TAM-induced cell death in cholangiocarcinomas. METHOD: Human cholangiocarcinoma cells, SK-ChA-1, were evaluated for Fas receptor expression using fluorescence-activated cell sorting (FACS). Distinct cell populations were isolated and cloned. Fas receptor expression was assessed using immunohistochemical staining (IHC), Western blot (WB) and RT-PCR. SK-ChA-1 cells were treated for 72 hours with 10PM TAM with and without inhibitory anti-Fas mab, which binds Fas receptor but does not induce apoptosis. Cell viability and apoptotic index were evaluated by trypan blue and TUNEL assay respectively. TAM treatment of these cells was evaluated in BALB/c nude mice (2.5 x 106 cells per subcutaneous injection, TAM IP injections of 0.ling 3x/week). After four weeks, tumors were harvested and evaluated by IHC, WB and RT-PCR. RESULTS: Populations of Fas+ and Fascells were identified and confirmed by FACS, IHC, WB and RT-PCR. Treatment with TAM produced a 74% reduction in cell viability at 72 hours in Fas+ cells versus no decrease in viability in Fascells by trypan blue cell count. TUNEL staining showed an apoptotic index of 75% for Fas+ cells incubated in TAM, but no significant evidence of apoptosis in the Fascells. TAM-induced reduction in cell viability in Fas+ cells was blocked by inhibitory anti-Fas mab indicating involvement of the Fas pathway. No effect was seen in Fascells. In vivo, Fascells formed tumor nodules with and without TAM treatment. Fas+ cells failed to form subcutaneous nodules with and without TAM treatment. CONCLUSION: TAM induced apoptosis in vitro in Fas+ ceils, and Fas receptor expression appears to be a critical determinant for cholangiocarcinoma in vivo tumor growth.