Lack of correlation between caspase activation and caspase activity assays in paclitaxel-treated MCF-7 breast cancer cells

Recent advances in caspase-3, breast cancer, and traditional Chinese medicine: a review

Caspases (cysteinyl aspartate-specific proteinases) are a group of structurally similar proteases in the cytoplasm that can be involved in cell differentiation, programmed death, proliferation, and inflammatory generation. Experts have found that caspase-3 can serve as a terminal splicing enzyme in apoptosis and participate in the mechanism by which cytotoxic drugs kill cancer cells. Breast cancer (BC) has become the most common cancer among women worldwide, posing a severe threat to their lives. Finding new therapeutic targets for BC is the primary task of contemporary physicians. Numerous studies have revealed the close association between caspase-3 expression and BC. Caspase-3 is essential in BC's occurrence, invasion, and metastasis. In addition, Caspase-3 exerts anticancer effects by regulating cell death mechanisms. Traditional Chinese medicine acting through caspase-3 expression is increasingly used in clinical treatment. This review summarizes the biological mechanism of caspase-3 and research progress on BC. It introduces a variety of traditional Chinese medicine related to caspase-3 to provide new ideas for the clinical treatment of BC.

Integrated Acoustic Chip for Culturing 3D Cell Arrays

Three-dimensional (3D) cell arrays provide an in vitro platform for clinical drug screening, but the bulky culture devices limit their application scenarios. Here, we demonstrate an integrated portable device that can realize contact-free construction of 3D cell spheroids. The interaction between the ultrasound generated by the portable device and the capillary results in periodic pressure nodes or anti-nodes, which lead to form a 3D cell array for cell culture. Such a 3D cell array pattern can be constructed in seconds and requires only 1 μL of cell samples. We further assessed the spheroids formed by the portable device and the impact of the acoustic field on spheroids and demonstrated the drug screening with assembled spheroids. More importantly, the integrated acoustic device can be further integrated with other components for more complex cell culture and all-round analysis. This portable and effective integrated device provides a new avenue for clinical biomedicine.

Amlodipine inhibits proliferation, invasion, and colony formation of breast cancer cells

Calcium channel upregulation has been implicated in cancer cell proliferation and progression including in breast cancer. Fortunately, the function of calcium channels can be manipulated pharmacologically using calcium channel blockers (CCBs). Amlodipine, a dihydropyridine CCB, has been demonstrated to exert cytotoxic effects in several types of cancers. The present study evaluated the effects of amlodipine on proliferation, caspase activation, colony formation, and invasion of human breast cancer cells. Cell viability was assessed using a colorimetric MTT assay. An Apo-ONE® caspase-3/7 assay was used to measure caspase-3/7 levels. Cell invasion was evaluated using Matrigel invasion chambers. The expression of phospho-(p-)ERK1/2, Bcl-2, and integrin β1 proteins were analyzed using western blotting. A one-way ANOVA with a post-hoc Tukey's multiple comparison tests was used for statistical analysis. Amlodipine significantly inhibited the growth of both MDA-MB-231 and MCF-7 human breast cancer cells in a dose-dependent manner and inhibited colony formation of MCF-7 cells, and this was accompanied by the downregulation of p-ERK1/2 in MDA-MB-231 cells. In addition, treatment with amlodipine resulted in increased caspase-3/7 levels in MDA-MB-231 cells, which was accompanied by the downregulation of the anti-apoptotic protein, Bcl-2. Moreover, amlodipine impaired the invasive abilities of MDA-MB-231 cells, and integrin β1 expression was concurrently downregulated. The present study illustrates the anticancer effects of amlodipine on breast cancer proliferation, colony formation, and invasion in vitro and highlights the potential value of amlodipine as an anticancer agent.

Intracellular leucine-rich alpha-2-glycoprotein-1 competes with Apaf-1 for binding cytochrome c in protecting MCF-7 breast cancer cells from apoptosis

Leucine-rich alpha-2-glycoprotein-1 (LRG1) has been shown to compete with apoptosis activating factor-1 (Apaf-1) for binding cytochrome c (Cyt c) and could play a role in inhibition of apoptosis. Employing MCF-7 breast cancer cells, we report that intracellular LRG1 does protect against apoptosis. Thus, cells transfected with the lrg1 gene and expressing higher levels of LRG1 were more resistant to hydrogen peroxide-induced apoptosis than parental cells, while cells in which LRG mRNA was knocked down by short hairpin (sh) RNA-induced degradation were more sensitive. The amount of Cyt c co-immunoprecipitated with Apaf-1 from the cytosol of apoptotic cells was inversely related to the level of LRG1 expression. In lrg1-transfected cells partially-glycosylated LRG1 was found in the cytosol and there was an increase in cytosolic Cyt c in live lrg1-transfected cells relative to parental cells. However, apoptosis was not spontaneously induced because Cyt c was bound to LRG1 and not to Apaf-1. Cyt c was the only detectable protein co-immunoprecipitated with LRG1. Following hydrogen peroxide treatment degradation of LRG1 allowed for induction of apoptosis. We propose that intracellular LRG1 raises the threshold of cytoplasmic Cyt c required to induce apoptosis and, thus, prevents onset of the intrinsic pathway in cells where Cyt c release from mitochondria does not result from committed apoptotic signaling. This mechanism of survival afforded by LRG1 is likely to be distinct from its extracellular survival function that has been reported by several research groups.

Synthesis and biological evaluation of amino acid derivatives containing chrysin that induce apoptosis

A series of chrysin amino acid derivatives were synthesized to evaluate for their antiproliferative activities against several cancer cell lines. Among the compounds tested, N-(2-((5-hydroxy-4-oxo-2-phenyl-4H-chromen-7-yl)oxy)octanoyl)-L-leucine methyl ester(5d) presented a good anti-proliferative activity in MDA-MB-231 and MCF-7 cells. Flow cytometry analysis showed that 5d induced apoptosis and prolonged cell cycle progression in MDA-MB-231 and MCF-7 cells. Western blot analysis showed that 5d significantly inhibited Akt phosphorylation (Ser473) in MDA-MB-231 and MCF-7 cells. In addition, 5d treatment markedly downregulated Bcl-2 and upregulated Bax in a dose-dependent manner. In vitro caspase activation assay showed that 5d induced apoptosis of MDA-MB-231 cells by enhancing caspase 3/7 activity. The regulatory effect of 5d on apoptosis of MDA-MB-231 and MCF-7 cells may be induced by mitochondrial apoptosis pathway. This study is of great significance for designing and developing more effective chrysin amino acid derivatives.

A review on the effects of current chemotherapy drugs and natural agents in treating non-small cell lung cancer

Lung cancer is the leading cause of cancer deaths worldwide, and this makes it an attractive disease to review and possibly improve therapeutic treatment options. Surgery, radiation, chemotherapy, targeted treatments, and immunotherapy separate or in combination are commonly used to treat lung cancer. However, these treatment types may cause different side effects, and chemotherapy-based regimens appear to have reached a therapeutic plateau. Hence, effective, better-tolerated treatments are needed to address and hopefully overcome this conundrum. Recent advances have enabled biologists to better investigate the potential use of natural compounds for the treatment or control of various cancerous diseases. For the past 30 years, natural compounds have been the pillar of chemotherapy. However, only a few compounds have been tested in cancerous patients and only partial evidence is available regarding their clinical effectiveness. Herein, we review the research on using current chemotherapy drugs and natural compounds (Wortmannin and Roscovitine, Cordyceps militaris, Resveratrol, OSU03013, Myricetin, Berberine, Antroquinonol) and the beneficial effects they have on various types of cancers including non-small cell lung cancer. Based on this literature review, we propose the use of these compounds along with chemotherapy drugs in patients with advanced and/or refractory solid tumours.

Induction of accelerated senescence by the microtubule-stabilizing agent peloruside A

Chemotherapeutic agents can induce accelerated senescence in tumor cells, an irreversible state of cell cycle arrest. Paclitaxel, a microtubule-stabilizing agent used to treat solid tumors of the breast, ovary, and lung and discodermolide, another stabilizing agent from a marine sponge, induce senescence in cultured cancer cells. The aim of this study was to determine if the microtubule-stabilizing agent peloruside A, a polyketide natural product from a marine sponge, can induce accelerated senescence in a breast cancer cell line MCF7. Doxorubicin, a DNA-damaging agent, paclitaxel, and discodermolide were used as positive controls. Senescence-associated-β-galactosidase activity was increased by peloruside A, similar to paclitaxel, discodermolde, and doxorubicin, with a potency heirarchy of doxorubicin > paclitaxel > discodermolide > peloruside, based on IC₂₅ concentrations that inhibit proliferation. Clonogenic survival was significantly decreased by peloruside A, similar to doxorubicin and the two other microtubule-stabilizing agents. The tumor suppressor protein p53 increased after treatment, whereas pRb decreased in response to all four compounds. It was concluded that in addition to apoptosis, peloruside A causes accelerated senescence in a subpopulation of MCF7 cells that contributes to its potential anticancer activity in a breast cancer cell line.

Anticancer activity and toxicity profiles of 2-benzylidene indanone lead molecule

3-(3',4',5'-Trimethoxyphenyl)-4,5,6-trimethoxy,2-(3″,4″-methylenedioxybenzylidene)-indan-1-one (1) is an optimized anti-cancer lead molecule obtained on modification of gallic acid, a plant phenolic acid. It exhibited potent cytotoxicities (IC50=0.010-14.76μM) against various human carcinoma cells. In cell cycle analysis, benzylidene indanone 1 induced G2/M phase arrest in both MCF-7 and MDA-MB-231 cells. It also induced apoptosis in DU145 cells which was evident by cleavage of PARP. In Ehrlich ascites carcinoma, benzylidene indanone 1 showed 45.48% inhibition of tumour growth at 20mg/kg dose in Swiss albino mice. Further, in sub-acute toxicity experiment in Swiss-albino mice, it was found to be non-toxic up to 100mg/kg dose for 28days. The lead compound benzylidene indanone 1 can further be optimized for better anti-cancer activity.

A novel bisindole-PBD conjugate causes DNA damage induced apoptosis via inhibition of DNA repair pathway

DNA damage response (DDR) that includes cell cycle check points, DNA repair, apoptosis, and senescence is intimately linked with cancer. It shields an organism against cancer development when genomic integrity fails. DNA repair pathways protect the cells from tumor progression caused as a result of DNA damage induced by irradiation or due to chemotherapeutic treatment. Many promising anticancer agents have been identified that target specific DNA repair pathways in response to DNA damage thereby leading to apoptosis. Here we identified a novel bisindole-PBD conjugate that possess potent anticancer activity in breast cancer cells. Further studies aimed at understanding the mechanism of action of the molecule showed its role in DNA damage induced apoptosis via inhibition of DNA repair pathway. Trypan blue and BrdU assay exhibited a dose-dependent effect. Single-stranded DNA damage was observed by COMET assay. In addition DNA damage induced ROS generation with simultaneous activation of ATM and ATR upon compound treatment was observed. Further downregulation of Bcl-XL and activation of Bax showed DNA damage induced apoptosis in MCF-7 and MDAMB-231 cells. In conclusion, it can be summarized that bisindole-PBD conjugate induces DNA damage in a dose dependent (2, 4, and 8 μM) manner by inhibiting the DNA repair genes.

Induction of apoptosis in human breast cancer cells via caspase pathway by vernodalin isolated from Centratherum anthelminticum (L.) seeds

BACKGROUND

Centratherum anthelminticum (L.) seeds (CA) is a well known medicinal herb in Indian sub-continent. We recently reported anti-oxidant property of chloroform fraction of Centratherum anthelminticum (L.) seeds (CACF) by inhibiting tumor necrosis factor-α (TNF-α)-induced growth of human breast cancer cells. However, the active compounds in CACF have not been investigated previously.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we showed that CACF inhibited growth of MCF-7 human breast cancer cells. CACF induced apoptosis in MCF-7 cells as marked by cell size shrinkage, deformed cytoskeletal structure and DNA fragmentation. To identify the cytotoxic compound, CACF was subjected to bioassay-guided fractionation which yielded 6 fractions. CACF fraction A and B (CACF-A, -B) demonstrated highest activity among all the fractions. Further HPLC isolation, NMR and LC-MS analysis of CACF-A led to identification of vernodalin as the cytotoxic agent in CACF-A, and -B. 12,13-dihydroxyoleic acid, another major compound in CACF-C fraction was isolated for the first time from Centratherum anthelminticum (L.) seeds but showed no cytotoxic effect against MCF-7 cells. Vernodalin inhibited cell growth of human breast cancer cells MCF-7 and MDA-MB-231 by induction of cell cycle arrest and apoptosis. Increased of reactive oxygen species (ROS) production, coupled with downregulation of anti-apoptotic molecules (Bcl-2, Bcl-xL) led to reduction of mitochondrial membrane potential (MMP) and release of cytochrome c in both human breast cancer cells treated with vernodalin. Release of cytochrome c from mitochondria to cytosol triggered activation of caspase cascade, PARP cleavage, DNA damage and eventually cell death.

CONCLUSIONS/SIGNIFICANCE

To the best of our knowledge, this is the first comprehensive study on cytotoxic and apoptotic mechanism of vernodalin isolated from the Centratherum anthelminticum (L.) seeds in human breast cancer cells. Overall, our data suggest a potential therapeutic value of vernodalin to be further developed as new anti-cancer drug.

Short-term hyperthermia promotes the sensitivity of MCF-7 human breast cancer cells to paclitaxel

As a physical adjuvant approach in the treatment of solid tumors, regional hyperthermia plays a synergistic role in enhancing the efficacy of simultaneous chemotherapy. Paclitaxel (PTX) is an anti-mitotic taxane drug that is widely used in chemotherapy for the treatment of various human malignancies such as lung, ovarian, breast, and head and neck cancers. Since the possibility that hyperthermia can enhance the anti-tumor effects of PTX has not yet been investigated, the present study was designed to evaluate the effects of short-term hyperthermia on PTX-induced antitumor activity in the human breast cancer line MCF-7. It was found that short-term hyperthermia promoted PTX-induced suppression of cell proliferation. The IC for PTX was reduced from 18.2±1.0 to 15.0±0.45 nM (p<0.05). The level of PTX-induced cell apoptosis was increased from 8.5±1.2 to 16.4±2.4% (p<0.05) and from 15.2±1.4 to 34.9±2.8% (p<0.05), at the end of the first and second hyperthermia cycles, respectively; both the activity and expression of caspase-7 were enhanced. In addition, PTX-induced cell cycle arrest in the G2/M phase was further promoted by short-term hyperthermia, from 9.3±0.7 to 12.5±0.9% (p<0.05). In contrast, short-term hyperthermia affected neither tumor cell migration nor invasion in the presence or absence of PTX. The presented data thus suggest that short-term hyperthermia may serve as a feasible approach in the promotion of breast cancer cell sensitivity to PTX.

MicroRNA-9 inhibition of cell proliferation and identification of novel miR-9 targets by transcriptome profiling in breast cancer cells

Although underexpression of miR-9 in cancer cells is reported in many cancer types, it is currently difficult to classify miR-9 as a tumor suppressor or an oncomir. We demonstrate that miR-9 expression is down-regulated in MCF-7 and MDA-MB-231 breast cancer cells compared with MCF-10-2A normal breast cell line. Increasing miR-9 expression levels in breast cancer cells induced anti-proliferative, anti-invasive, and pro-apoptotic activity. In addition, microarray profiling of the transcriptome of MCF-7 cells overexpressing miR-9 identified six novel direct miR-9 targets (AP3B1, CCNG1, LARP1, MTHFD1L, MTHFD2, and SRPK1). Among these, MTHFD2 was identified as a miR-9 target gene that affects cell proliferation. Knockdown of MTHFD2 mimicked the effect observed when miR-9 was overexpressed by decreasing cell viability and increasing apoptotic activity. Despite variable effects on different cell lines, proliferative and anti-apoptotic activity of MTHFD2 was demonstrated whereby it could escape from miR-9-directed suppression (by overexpression of MTHFD2 with mutated miR-9 binding sites). Furthermore, endogenous expression levels of miR-9 and MTHFD2 displayed inverse expression profiles in primary breast tumor samples compared with normal breast samples; miR-9 was down-regulated, and MTHFD2 was up-regulated. These results indicate anti-proliferative and pro-apoptotic activity of miR-9 and that direct targeting of MTHFD2 can contribute to tumor suppressor-like activity of miR-9 in breast cancer cells.

Acetonic extract of Buxus sempervirens induces cell cycle arrest, apoptosis and autophagy in breast cancer cells

Plants are an invaluable source of potential new anti-cancer drugs. Here, we investigated the cytotoxic activity of the acetonic extract of Buxus sempervirens on five breast cancer cell lines, MCF7, MCF10CA1a and T47D, three aggressive triple positive breast cancer cell lines, and BT-20 and MDA-MB-435, which are triple negative breast cancer cell lines. As a control, MCF10A, a spontaneously immortalized but non-tumoral cell line has been used. The acetonic extract of Buxus sempervirens showed cytotoxic activity towards all the five studied breast cancer cell lines with an IC(50) ranging from 7.74 µg/ml to 12.5 µg/ml. Most importantly, the plant extract was less toxic towards MCF10A with an IC(50) of 19.24 µg/ml. Fluorescence-activated cell sorting (FACS) analysis showed that the plant extract induced cell death and cell cycle arrest in G0/G1 phase in MCF7, T47D, MCF10CA1a and BT-20 cell lines, concomitant to cyclin D1 downregulation. Application of MCF7 and MCF10CA1a respective IC(50) did not show such effects on the control cell line MCF10A. Propidium iodide/Annexin V double staining revealed a pre-apoptotic cell population with extract-treated MCF10CA1a, T47D and BT-20 cells. Transmission electron microscopy analyses indicated the occurrence of autophagy in MCF7 and MCF10CA1a cell lines. Immunofluorescence and Western blot assays confirmed the processing of microtubule-associated protein LC3 in the treated cancer cells. Moreover, we have demonstrated the upregulation of Beclin-1 in these cell lines and downregulation of Survivin and p21. Also, Caspase-3 detection in treated BT-20 and T47D confirmed the occurrence of apoptosis in these cells. Our findings indicate that Buxus sempervirens extract exhibit promising anti-cancer activity by triggering both autophagic cell death and apoptosis, suggesting that this plant may contain potential anti-cancer agents for single or combinatory cancer therapy against breast cancer.

Micronucleus assay and labeling of centromeres with FISH technique

The cytokinesis-block micronucleus (CBMN) assay has since many years been applied for in vitro genotoxicity testing and biomonitoring of human populations. The standard in vitro/ex vivo micronucleus test is usually performed on human lymphocytes and has become a comprehensive method to assess genetic damage, cytostasis, and cytotoxicity. The predictive association between the frequency of micronuclei (MN) in cytokinesis-blocked lymphocytes and cancer risk has recently been demonstrated. MN frequencies can be influenced by inherited (or acquired) genetic polymorphisms (or mutations) in genes responsible for the metabolic activation, detoxification of clastogens, and for the fidelity of DNA replication. An important advantage of the CBMN assay is its ability to detect both clastogenic and aneugenic events by centromere and kinetochore identification and contributes to the high sensitivity of the method. The objective of the present chapter is to review the mechanisms of induction of micronuclei, the method of the micronucleus assay and its combination with centromeric labeling in the FISH technique. Furthermore, an overview is given of recent results obtained by our laboratory by the application of the micronucleus assay.

Recombinant analogs of a novel milk pro-apoptotic peptide, lactaptin, and their effect on cultured human cells

We recently isolated and characterized a human milk peptide, lactaptin, which induced apoptosis of cultured human MCF-7 cells. Lactaptin was identified as a proteolytic fragment of human kappa-casein. Here, we generated two recombinant analogs of the peptide, RL1 and RL2, containing truncated and complete amino acid sequences of lactaptin, respectively. Analogs were produced in E.coli, purified and assayed for biological activity on cultured human MCF-7 cells. RL1 was shown to induce only a small decrease in cell viability, whereas RL2 lowered the viability of MCF-7 cells by 60%. This reduction in MCF-7 cell viability was associated with apoptosis, which was indicated by phosphatidilserine externalization and caspase-7 activation. The viability of A549 and Hep-2 cells was also reduced by RL2, albeit to a lesser degree than seen with MCF-7 cells; this reduced viability was not accompanied by apoptosis. Non-malignant human mesenchymal stem cells (MSC) were completely resistant to RL2 action.

Expression of insulin receptor isoform A and insulin-like growth factor-1 receptor in human acute myelogenous leukemia: effect of the dual-receptor inhibitor BMS-536924 in vitro

The insulin receptor (IR) and insulin-like growth factor-1 receptor (IGF1R) are receptor tyrosine kinases that participate in mitogenic and antiapoptotic signaling in normal and neoplastic epithelia. In the present study, immunoblotting and reverse transcription-PCR demonstrated expression of IGF1R and IR isoform A in acute myelogenous leukemia (AML) cell lines as well as in >80% of clinical AML isolates. Treatment with insulin enhanced signaling through the Akt and MEK1/2 pathways as well as survival of serum-starved AML cell lines. Conversely, treatment with BMS-536924, a dual IGF1R/IR kinase inhibitor that is undergoing preclinical testing, inhibited constitutive receptor phosphorylation as well as downstream signaling through MEK1/2 and Akt. These changes inhibited proliferation and, in some AML cell lines, induced apoptosis at submicromolar concentrations. Likewise, BMS-536924 inhibited leukemic colony formation in CD34+ clinical AML samples in vitro. Collectively, these results not only indicate that expression of IGF1R and IR isoform A is common in AML but also show that interruption of signaling from these receptors inhibits proliferation in clinical AML isolates. Accordingly, further investigation of IGF1R/IR axis as a potential therapeutic target in AML appears warranted.

In vitro and in vivo anti-angiogenic activities and inhibition of hormone-dependent and -independent breast cancer cells by ceramide methylaminoethylphosphonate

Ceramide methylaminoethylphosphonate (CMAEPn) was isolated from eastern oyster ( Crassostrea virginica ) and screened against in vitro and in vivo angiogenesis and against MCF-7 and MDA-MB-435s breast cancer cell lines. In vitro angiogenesis was evaluated by the vascular endothelial growth factor (VEGF)-induced human umbilical vein endothelial cell (HUVEC) tube formation assay. MCF-7 and MDA-MB-435s cell viability was evaluated by the CellTiter 96 AQ(ueous) One Solution Cell Proliferation assay. Apoptosis was evaluated by the caspase-9 assay, autophagy by acridine orange staining and beclin-1 level. Our study indicates that CMAEPn at 50 microM inhibited VEGF-induced tube formation by HUVEC. The viability of MCF-7 and MDA-MB-435s breast cancer cells exposed to 125 microM CMAEPn for 48 h was reduced to 76 and 85%, respectively. The viability of MCF-7 and MDA-MB-435s cells exposed to 250 microM CMAEPn for 48 h under the same conditions was reduced to 38 and 45%, respectively. CMAEPn at 125 microM inhibited VEGF-induced MDA-MB-435s cell migration and invasion. CMAEPn at 125 microM also decreased VEGF, EGF levels in the conditioned media, PI3K, IkappaB phosphorylation and degradation in the cytoplasmic extracts, and NFkappaB nuclear translocation. Both acridine orange staining and beclin-1 indicated autophagic cell death in MCF-7 and MDA-MB-435s cells, respectively. In vivo, CMAEPn at 30 mg/kg body weight inhibited bFGF-induced angiogenesis and caused a 57% reduction in hemoglobin levels in the matrigel plug assay within 7 days. This is the first report on CMAEPn-inhibited angiogenesis both in vitro and in vivo.

Assessment of apoptosis by immunohistochemistry to active caspase-3, active caspase-7, or cleaved PARP in monolayer cells and spheroid and subcutaneous xenografts of human carcinoma

Immunohistochemistry to active caspase-3, recently recommended for apoptosis detection, is inappropriate to detect apoptosis involving caspase-7. Cleavage of poly-ADP-ribose polymerase 1 (PARP-1), a major substrate of both caspases, is a valuable marker of apoptosis. Apoptosis evaluation induced in vitro either by paclitaxel or by photodynamic treatment (PDT) with Foscan in HT29 or KB monolayer cells and HT29 spheroids yielded a close percentage of labeled cells whatever the antibody used, whereas in control specimens, cleaved PARP (c-PARP) immunostaining failed to detect apoptosis as efficiently as active caspase-3 or -7 immunostaining. Studies in MDA-MB231 monolayer cells and HT29 xenografts either subjected or not subjected to Foscan-PDT resulted in a significant higher number of active caspase-3-labeled cells, although immunofluorescence analysis showed c-PARP and active caspase-3 perfectly colocalized in tumors. A restricted expression of c-PARP was obvious in the greater part of caspase-3 expressing cells from control tumor, whereas photosensitized tumors showed a higher number of cells expressing large fluorescent spots from both active caspase-3 and c-PARP. These results support the assumption that c-PARP expression was dependent on treatment-induced apoptosis. The absence of caspase-7 activation in some caspase-3-expressing cells undergoing Foscan-PDT shows the relevance of using antibodies that can discriminate caspase-dependent apoptotic pathways.

Apoptosis-associated caspase activation assays

Caspases are aspartate-directed cysteine proteases that cleave a diverse group of intracellular substrates to contribute to various manifestations of apoptosis. These proteases are synthesized as inactive precursors and are activated as a consequence of signaling induced by a wide range of physiological and pathological stimuli. Caspase activation can be detected by measurement of catalytic activity, immunoblotting for cleavage of their substrates, immunolabeling using conformation-sensitive antibodies or affinity labeling followed by flow cytometry or ligand blotting. Here we describe methods for each of these assays, identify recent improvements in these assays and outline the strengths and limitations of each approach.

Survival of aneuploid, micronucleated and/or polyploid cells: crosstalk between ploidy control and apoptosis

Microtubule inhibitors are known to block the cell cycle at M-phase, by damaging the mitotic spindle. However, under certain circumstances, cells can escape these effects and become aneuploid, polyploid and/or micronucleated. It is well known that aneuploidy can have adverse effects on human health such as pregnancy wastage, birth defects and the development of human tumours. The present paper aims at reviewing the data our laboratory has accumulated during the last years about the relation between aneuploidy/polyploidy/presence of micronuclei and the induction of apoptosis in human cells after in vitro exposure to the microtubule inhibitor nocodazole. Exposure to high doses of nocodazole results in polyploidy due to mitotic slippage in the absence of a functional spindle. Depending on their p53-status polyploid cells may eventually arrest, die or continue cycling. In these experimental conditions, our data showed that polyploidy does not constitute a strong apoptotic signal. In case of exposure to low concentrations of nocodazole, microtubule depolymerization is disturbed resulting in a spindle with damaged microtubules. This can give rise to chromosome loss and non-disjunction. Our data showed that in particular micronucleated cells, originating from chromosome loss can be eliminated by apoptosis. In addition, nocodazole-induced apoptosis involves the apical caspase-8 and -9 and the effector caspase-3. We show evidence that caspase-3, in addition to its function in apoptosis, plays a role in the formation of micronuclei.

5-FdUrd-araC heterodinucleoside re-establishes sensitivity in 5-FdUrd- and AraC-resistant MCF-7 breast cancer cells overexpressing ErbB2

ErbB2 overexpressing breast tumors have a poor prognosis and a high risk to develop chemoresistance to therapeutic treatment. "Chemoresistance" is a response of cells to toxic stress, and, although it is a common phenomenon, it is still poorly defined. However, a detailed understanding is required to target desensitized pathways and mechanisms for successful reactivation as part of a tailored therapy. To gain insight, which malfunctions contribute to chemoresistance, two mechanisms relevant for tissue homeostasis, the regulation of the cell cycle and of apoptosis, were investigated. Maternal MCF-7- and ErbB2-overexpressing MCF-7(erbB2) breast cancer cells were long term pretreated with 2'-deoxy-5-fluorodeoxyuridine (5-FdUrd) or 1-beta-d-arabinofuranosylcytosine (AraC) and the acquisition of drug-insensitivity was analyzed. A phosphate-conjugated heterodinucleoside consisting of one 5-FdUrd- and one AraC-moiety (5-fluoro-2'-desoxyuridylyl-(3'-->5')-Arabinocytidine) was utilized as a tool to assess the type of acquired resistances. ErbB2-overexpression disrupted proper cell cycle regulation and furthermore facilitated the development of an apoptosis-refractory phenotype upon exposure to 5-FdUrd. Experiments with dimer 5-FdUrd-araC in ErbB2-overexpressing MCF-7(erbB2) cells, and also with nucleoside 5-FdUrd in maternal MCF-7 cells, evidenced that the phenotypes of resistance to cell cycle inhibition and to apoptosis induction were differently affected. The expression profile of cyclin D1 (but not that of p53, p21, or p27) correlated with the proliferative phenotypes and nuclear accumulation of apoptosis inducing factor (but not activation of caspase 7) with apoptotic phenotypes. Dimer 5-FdUrd-araC overrode acquired chemoresistances, whereas combined application of 5-FdUrd and AraC exhibited significantly less activity. Dimer 5-FdUrd-araC remained active in MCF-7 clones most likely by circumventing the prerequisite of first-step phosphorylation. The acquisition of chemoresistance encompassed the affection of apoptosis- and cell-cycle regulation to, respectively, different extents. Thus, drug-induced cell cycle arrest and apoptosis induction are independent of each other.

Cytotoxic effects of intra and extracellular zinc chelation on human breast cancer cells

Zinc is an essential trace element with cofactor functions in a large number of proteins of intermediary metabolism, hormone secretion pathways, immune defence mechanisms, and as a cofactor of transcription factors it is also involved in the control of gene expression. Our study demonstrates that the modulation of intra and extracellular zinc alone is sufficient to induce metabolic changes or even apoptosis in two model human breast cancer cell lines MCF-7 and MDA-MB468. Treatment of breast cancer cells with different concentrations of a cell membrane permeable zinc chelator, N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine (TPEN) and the membrane impermeable zinc chelator, diethylenetriaminepentacetic acid, (DTPA) resulted in a significant increase of cell death. Features of apoptosis, such as chromatin condensation and nuclear fragmentation accompanied the DTPA and TPEN-induced cell death. A significant increase in the activity of caspase-9 was observed in both cell lines; whereas, caspase-3 activity was only increased in MDA-MB468 cells since caspase-3 is not expressed in MCF-7 cells. Caspase-8 activation was negligible in both cell lines. Addition of Zn(2+) or Cu(2+) prevented DTPA and TPEN-induced cytotoxicity, indicating that both bivalent cations can be replaced functionally to a certain extent in our experimental system. Interestingly, addition of Ca(2+), or Mg(2+) had no effect. The antioxidant N-Acetyl-L-Cysteine inhibited the cytotoxic effect of DTPA and TPEN, indicating that oxidative stress is the likely mediator of Zn-deficiency-related cell death.

Involvement of caspase activation and mitochondrial stress in taxol-induced apoptosis of Epstein–Barr virus-infected Akata cells

Taxol (paclitaxel) is one of the most potent antimicrotubule agents currently used in cancer chemoprevention and treatment. However, the effects of taxol on the induction of apoptosis in Epstein-Barr virus (EBV)-infected cells are unknown. This study investigated the mechanisms of taxol on cell cycle arrest and apoptosis induction using the EBV-infected cell line, Akata. Taxol treatment sensitively and dose-independently induced growth inhibition, cytotoxicity, and apoptosis in the cells, which was demonstrated by the decreased level of tritium incorporation and cell viability, the increased number of positively stained cells in the trypan blue staining and TUNEL assay, the increased population of cells in the sub-G(0)/G(1) phase in flow cytometric analysis, and ladder formation of the genomic DNA. Treatment with z-VAD-fmk almost completely protected the cells from taxol-induced apoptosis indicating that the taxol-induced apoptosis of Akata cells is caspase-dependent. In addition, taxol-induced apoptosis is proposed to be associated with a lower mitochondrial membrane potential and G(2)/M arrest. However, the tubulin expression level doses not appear to be a direct mediator of taxol-induced apoptosis in cells. The presence of EBV in these cells was not related to the sensitivity of the cells to the induction of apoptosis by taxol. Overall, these results demonstrate that taxol induces apoptosis in EBV-infected Akata cells in a dose-independent manner, and that caspase activation and mitochondrial stress are involved in the induction.

Autophagy delays apoptotic death in breast cancer cells following DNA damage

Early signaling in camptothecin-treated MCF-7 cells followed an intrinsic pathway, but death was delayed and late events exhibited few hallmarks of apoptosis. BH3-only proteins, such as Noxa, Puma and BimEL, were activated and localized to mitochondrial sites within 24 h following drug exposure. However, caspase activity was low and death was unaffected by caspase inhibition. Transmission electron micrographs showed the presence of large vacuoles in drug-treated cells. An autophagic survival response has been attributed to MCF-7 cells following nutrient starvation or exposure to tamoxifen. Here, we show that autophagy also plays an important role in the delayed DNA damage response. Confocal microscopy revealed colocalization of mitochondria with large autophagic vacuoles and inhibitors of autophagy increased mitochondrial depolarization and caspase-9 activity, and accelerated cell death. Furthermore, downregulation of autophagy proteins, Beclin 1 and Atg7, unmasked a caspase-dependent, apoptotic response to DNA damage. We propose that a post-mitochondrial caspase cascade is delayed as a result of early disposal of damaged mitochondria within autophagosomes. Our data also suggest that the use of autophagy as a means of delaying apoptosis or prolonging survival may be characteristic of noninvasive breast tumor cells. These studies underscore a potential role for autophagy inhibitors in combination with conventional chemotherapeutic drugs in early breast cancer therapy.

Presence of mesenchymal stem cells in human bone marrow after exposure to chemotherapy: evidence of resistance to apoptosis induction

For various potential clinical applications, the use of autologous human MSCs (hMSCs) would be favorable. In vitro observations suggested that hMSCs are resistant for chemotherapeutic substances; however, no data exist on the characteristics of hMSCs from bone marrow (BM) of chemotherapeutically treated patients. Here, we analyzed the character of hMSCs derived from chemotherapy-exposed BM and the in vitro response of hMSCs to chemotherapeutic substances. Colony-forming units-fibroblast (CFU-Fs) were isolated from BM aspirates of patients after high-dose or standard chemotherapy and of donors with unaffected BM. CFU-Fs from chemotherapy-exposed and unaffected BM contained hMSCs with similar phenotype, proliferation capacity, and differentiation potential. No obvious influence of age, sex, or time since chemotherapy exposure on the presence and characteristics of hMSCs was observed. In vitro, hMSCs showed a significant resistance for cisplatin, vincristine, and etoposide compared with sensitive tumor cell lines, particularly at apoptosis-inducing doses. The phenotype and differentiation potential of hMSCs was not altered by genotoxic treatment under clinically relevant conditions in vitro. hMSCs showed an elevated threshold for cisplatin-induced apoptosis, which was characterized by a lack of caspase-9 activity in apoptotic cells. In vitro exposure of hMSCs to cisplatin, vincristine, and etoposide resulted in an increased p53 expression, independent of apoptosis induction. We conclude that hMSCs can be isolated from chemotherapy-exposed BM in sufficient number and quality for potential clinical applications in chemotherapeutically treated patients. Our data suggest that an elevated apoptotic threshold contributes not only to the persistence of hMSCs in the BM after chemotherapy but also to their lifelong presence in the adult BM.

In vitro and In vivo Antitumor Effects of the Dual Insulin-Like Growth Factor-I/Insulin Receptor Inhibitor, BMS-554417

The insulin-like growth factor receptor (IGF-IR) and insulin receptor are either overactivated and/or overexpressed in a wide range of tumor types and contribute to tumorigenicity, proliferation, metastasis, and drug resistance. Here, we show that BMS-554417, a novel small molecule developed as an inhibitor of IGF-IR, inhibits IGF-IR and insulin receptor kinase activity and proliferation in vitro, and reduces tumor xenograft size in vivo. In a series of carcinoma cell lines, the IC50 for proliferation ranged from 120 nmol/L (Colo205) to >8.5 micromol/L (OV202). The addition of stimulatory ligands was unnecessary for the antiproliferative effect in MCF-7 and OV202 cells. BMS-554417 treatment inhibited IGF-IR and insulin receptor signaling through extracellular signal-related kinase as well as the phosphoinositide 3-kinase/Akt pathway, as evidenced by decreased Akt phosphorylation at Ser473. At doses that inhibited proliferation, the compound also caused a G0-G1 arrest and prevented nuclear accumulation of cyclin D1 in response to LR3 IGF-I. In Jurkat T-cell leukemia cells, this agent triggered apoptotic cell death via the mitochondrial pathway. BMS-554417 was orally bioavailable and significantly inhibited the growth of IGF1R-Sal tumor xenografts in vivo. BMS-554417 is a member of a novel class of IGF-IR/insulin receptor inhibitors that have potential clinical applications because of their antiproliferative and proapoptotic activity in vitro and in vivo.

The role of caspases in cell death and differentiation

The complexity, redundancy and interdependence of the biological systems involved in tumour response to different treatments hamper progress towards developing specific and effective therapies. In addition, the many and even contradictory roles played by certain key proteins can significantly amend our view on tumourigenesis. The role of caspases in the modulation of cell death and differentiation is a prominent example of such a complexity. Here we focus on the role of caspases in apoptotic cell death, mainly in haematological malignancies, tumourigenesis, sepsis, T-cell proliferation and cell differentiation.

Caspase-1 activation of caspase-6 in human apoptotic neurons

Active caspase-6 (Csp-6) induces cell death in primary cultures of human neurons and is abundant in the neuropathological lesions of Alzheimer's disease. However, the mode of Csp-6 activation is not known. Here, we show that the Csp-1 inhibitor, Z-YVAD-fmk specifically prevents activation of Csp-6 and cell death in human neurons. A transient increase in Csp-1-like activity and an increase in the p23Csp-1 subunit occur early after serum deprivation. Recombinant active Csp-1 (R-Csp-1) cleaves recombinant and neuronal pro-Csp-6 in vitro resulting in Csp-6 activity. However, R-Csp-1 does not induce cell death when microinjected in human neurons despite the inhibition of serum-deprivation induced cell death with a Csp-1 dominant negative construct. These results show that Csp-1 is an upstream positive regulator of Csp-6-mediated cell death in primary human neurons. Furthermore, these results suggest that the activation of Csp-1 must be accompanied by an apoptotic insult to induce Csp-6-mediated cell death.

Ribonucleic acids of human milk

The milk feeding is the most essential process laying the foundation of human health at the postnatal development. However little is known about nucleic acids secreted into mother's milk during lactation. In order to investigate the composition and abundance of human milk NA we adapted the conventional isolation method to achieve high yield of total nucleic acids from milk samples. Concentration of total NA in milk samples of different donors varies from 20 to 68 mkg/ml at early stages of lactation. The average concentration tends to fall down to the end of lactation. The chain length of the major forms of NA varies from mononucleotides up to approximately 100 bases. Compositions of milk oligonucleotides are similar in samples of different donors. Major milk oligonucleotides are formed of RNA. Human milk contains the set of long-chain oligonucleotides with a developed secondary structure. Sequences of some oligo-RNAs correspond to the 3'-part of 5.8 S human ribosomal RNA and to the 3'-parts of tRNAVal and tRNATyr Primary structures of some others oligo-RNAs were related to fragments of human 18S and 28S rRNAs.

Oligonucleosome DNA fragmentation of caspase 3 deficient MCF-7 cells in palmitate-induced apoptosis

Oligonucleosomal fragmentation of nuclear DNA is the late stage hallmark of the apoptotic process. In mammalian apoptotic cells fragmentation is catalyzed by DFF40/ CAD DNase. DFF40/CAD primary activated through site-specific proteolytic cleavage by caspase 3. The absence of caspase 3 in MCF-7 leads to lack of oligonucleosomal DNA fragmentation under numerous apoptotic stimuli. In this study it was shown that palmitate induces apoptotic changes of nuclei and oligonucleosomal DNA fragmentation in casp3 deficient MCF-7. Activation and accumulation of 40-50 kDa DFF40 like DNases in nuclei and cytoplasm of palmitate-treated MCF-7 were detected by SDS-DNA-PAGE assay. Microsomes of apoptotic MCF-7 activate 40-50 kDa nucleases when incubated with human placental chromatin and induce oligonucleosomal fragmentation of chromatin in cell free system. Both DNases activation and chromatin fragmentation are suppressed in presence of caspase 3/7 inhibitor Ac-DEVD-CHO. Microsome associated caspase 7 is suggested to play the principal role in induction of oligonucleosomal DNA fragmentation of casp3 defitient MCF-7.

Influence of caspase activity on micronuclei detection: a possible role for caspase-3 in micronucleation

Aneugenic and clastogenic agents are good inducers of both micronuclei and apoptosis. In its turn, apoptosis may modify the threshold values for the induction of micronuclei. This is of major concern for accurate assessment of hazard related to exposure to mutagens. In the present work we studied the influence of caspases, the key regulators of the apoptotic process, on the induction of micronuclei in the cytokinesis block micronucleus assay. For this, we applied a combined approach in which both human peripheral blood mononucleated cells (PBMC) and the paired human breast carcinoma cell lines MCF-7, which is caspase-3 deficient, and the caspase-3 transfected MCF-7 (MCF-7casp-3) were used to study the influence of caspase activity on micronuclei. When nocodazole induced apoptosis was inhibited by the use of inhibitors of the two main apical caspases-8 and -9 in PBMC, the frequencies of micronucleated binucleates (MNCB) increased with inhibition of these caspases confirming that apoptosis can eliminate micronucleated cells. On the contrary when caspase-3 was inhibited, the frequencies of MNCB was lower, suggesting a role of caspase-3, also in micronuclei formation. To verify this hypothesis, we compared the induction of apoptosis and micronuclei by the aneugen nocodazole, the clastogen methyl methane sulfonate (MMS) and the non-mutagenic apoptogen staurosporin in MCF-7 and MCF-7casp-3 cells. The results showed that when caspase-3 activity was impaired, in the parental MCF-7 cell line or in the MCF-7casp-3 cells in the presence of the caspase-3 inhibitor, the frequencies of nocodazole or MMS induced micronuclei decreased. These results suggest that caspase-3, besides its function as an effector caspase in the apoptotic pathway, is also involved in the formation of micronuclei.

Components of the cell death machine and drug sensitivity of the National Cancer Institute Cell Line Panel

PURPOSE

According to some studies, susceptibility of cells to anticancer drug-induced apoptosis is markedly inhibited by targeted deletion of genes encoding apoptotic protease activating factor 1 (Apaf-1) or certain caspases. Information about levels of these polypeptides in common cancer cell types and any possible correlation with drug sensitivity in the absence of gene deletion is currently fragmentary.

EXPERIMENTAL DESIGN

Immunoblotting was used to estimate levels of Apaf-1 as well as procaspase-2, -3, -6, -7, -8, and -9 in the 60-cell-line panel used for drug screening by the National Cancer Institute. Sensitivity of the same lines to >80,000 compounds was determined with 48-hour sulforhodamine B binding assays. Additional 6-day assays were performed for selected agents.

RESULTS

Levels of Apaf-1 and procaspases varied widely. Apaf-1 and procaspase-9, which are implicated in caspase activation after treatment of cells with various anticancer drugs, were detectable in all of the cell lines, with levels of Apaf-1 ranging from approximately 1 x 10(5) to 2 x 10(6) molecules per cell and procaspase-9 from approximately 5 x 10(3) to approximately 1.6 x 10(5) molecules per cell. Procaspase-8 levels ranged from 1.7 x 10(5) to 8 x 10(6) molecules per cell. Procaspase-3, a major effector caspase, varied from undetectable to approximately 1.6 x 10(6) molecules per cell. Correlations between levels of these polypeptides and sensitivity to any of a variety of experimental or conventional antineoplastic agents in either 2-day or 6-day cytotoxicity assays were weak at best.

CONCLUSIONS

With the exception of caspase-3, all of the components of the core cell-death machinery are expressed in all of the cell lines examined. Despite variations in expression, levels of any one component are not a major determinant of drug sensitivity in these cells in vitro.

Apoptotic Pathways and Therapy Resistance in Human Malignancies

Apoptosis and necrosis are two morphologically distinct forms of cell death that are important for maintaining of cellular homeostasis. Almost all agents can provoke either response when applied to cells; however, the duration of treatment and the dose of the used agents determine which type of death (apoptosis or necrosis) is initiated. The response of tumors to chemo-, radio-, and hormone therapy or to treatment with biologically active agents may depend at least in part on the propensity of these tumors to undergo cell death. Some tumors, e.g., leukemias, small cell lung cancer, and seminomas, respond quickly to first-line therapy; this fast response is thought to result from induction of apoptosis. Solid tumors, on the other hand, usually respond slowly and less effectively, with cell death characterized not only by apoptosis but also by necrosis, or mitotic catastrophe. It is likely that resistance of tumors to treatment might be associated with defects in, or dysregulation of, different steps of the apoptotic pathways. Several attempts were undertaken to use the knowledge of these defects to design new drugs, which might either activate or re-activate the apoptotic machinery of tumor cells. Here we discuss the apoptotic pathways and their role in therapy resistance of human malignancies. Although such studies are still in progress, they offer great promise for future cancer therapy. We hope that some of these agents will turn out to be valuable additions to the future therapeutic arsenal, which will most probably include a combination of conventional cytotoxic drugs and molecular target-based pro-apoptotic drugs.

Streptococcus pneumoniae-induced caspase 6-dependent apoptosis in lung epithelium

Streptococcus pneumoniae is the major pathogen of community-acquired pneumonia and one of the most common causes of death due to infectious diseases in industrialized countries. Lung epithelium lines the airways and constitutes the first line of innate defense against respiratory pathogens. Little is known about the molecular interaction of pneumococci with lung epithelial cells. Apoptosis of lung epithelium is involved in some bacterial lung infections. In this study different pneumococcal strains specifically induced either apoptotic or necrotic death of human alveolar and bronchial epithelial cells. Pneumococcus-induced apoptosis did not depend on the virulence factors pneumolysin and H(2)O(2). Apoptotic cells showed increased activity of caspases 6, 8, and 9 but not increased activity of caspase 3. Moreover, programmed cell death could be strongly reduced by a caspase 6 inhibitor and a pan-caspase inhibitor. Inhibitors of calpain and chymotrypsin- and trypsin-like proteases also reduced pneumococcus-induced apoptosis. Furthermore, pneumococcus-infected human alveolar epithelial cells showed Bid cleavage and reduced levels of Bcl2 and Bax. Overexpression of Bcl2 in these cells reduced apoptosis significantly. Thus, pneumococci induced apoptosis of human alveolar and bronchial epithelial cells. Programmed cell death was executed by caspase 6 and noncaspase proteases, but not by caspase 3, and could be blocked by overexpression of Bcl2.

Apoptosis: an optimization approach

The present study examined the levels of procaspases (zymogens of the main apoptosis enzymes, caspases) that are predicted based on application of the optimization principle. Optimization models have previously been successfully developed for many other physiological systems (e.g., circulation, oxygen transport system, fibrinolysis, and blood coagulation) but have not previously been applied to apoptotic biochemical pathways. Our model assumed that apoptotic pathways are designed to minimize protein consumption. Procaspase concentrations were predicted based on this assumption, along with known schemes of apoptosis reactions and kinetic constants for procaspase activation and target cleavage. Good agreement between the model predictions and actual procaspase levels was observed.

Intermediate filaments control the intracellular distribution of caspases during apoptosis

Caspases are responsible for a cascade of events controlling the disassembly of apoptotic cells. We now demonstrate that caspase-9 is activated at an early stage of apoptosis in epithelial cells and all its detectable, catalytically active large subunits (both the p35 and p37) are concentrated on cytokeratin fibrils. Immunolabeling of distinctive neoepitopes, exposed by cleavage of procaspase-9 at either Asp315 or Asp330, was co-localized on these fibrils with active caspase-3, caspase-cleaved cytokeratin-18, death-effector-domain containing DNA-binding protein and ubiquitin. Cytokeratin filaments may thus provide a scaffold whereby active subunits of caspase-9 can activate caspase-3 which, in turn, can activate more caspase-9 so forming an amplification loop to facilitate cleavage of cytokeratin-18, disruption of the cytoskeleton and the ensuing formation of cytoplasmic inclusions. These inclusions, formed from the collapse of fibrils, together with their associated components, also contain ubiquitinated proteins, vimentin, heat-shock protein 72, and tumor necrosis factor receptor type-1-associated death domain protein. Many of their constituents, including active caspases, remain sequestered within these inclusions, even after detergent treatment and isolation. Thus, such inclusions do not merely accumulate disrupted cytokeratins but also sequestrate potentially noxious proteins that could injure healthy neighboring cells.

A new class of peroxisome proliferator-activated receptor γ (PPARγ) agonists that inhibit growth of breast cancer cells: 1,1-Bis(3′-indolyl)-1-(p-substituted phenyl)methanes

1,1-Bis(3′-indolyl)-1-(p-trifluoromethylphenyl)methane (DIM-C-pPhCF3) and several p-substituted phenyl analogues have been investigated as a new class of peroxisome proliferator-activated receptor γ (PPARγ) agonists. Structure-activity studies in PPARγ-dependent transactivation assays in MCF-7 breast cancer cells show that 5–20 μm concentrations of compounds containing p-trifluoromethyl, t-butyl, cyano, dimethylamino, and phenyl groups were active, whereas p-methyl, hydrogen, methoxy, hydroxyl, or halogen groups were inactive as PPARγ agonists. Induction of PPARγ-dependent transactivation by 15-deoxy-Δ12,14-prostaglandin J2 (PGJ2) and DIM-C-pPhCF3 was inhibited in MCF-7 cells cotreated with the PPARγ-specific antagonist N-(4′-aminopyridyl)-2-chloro-5-nitrobenzamide. In mammalian two-hybrid assays, DIM-C-pPhCF3 and PGJ2 (5–20 μm) induced interactions of PPARγ with steroid receptor coactivator (SRC) 1, SRC2 (TIFII), and thyroid hormone receptor-associated protein 220 but not with SRC3 (AIB1). In contrast, DIM-C-pPhCF3, but not PGJ2, induced interactions of PPARγ with PPARγ coactivator-1. C-substituted diindolylmethanes inhibit carcinogen-induced rat mammary tumor growth, induce differentiation in 3T3-L1 preadipocytes, inhibit MCF-7 cell growth and G0/G1-S phase progression, induce apoptosis, and down-regulate cyclin D1 protein and estrogen receptor α in breast cancer cells. These compounds are a novel class of synthetic PPARγ agonists that induce responses in MCF-7 cells similar to those observed for PGJ2.

Rad9 protects cells from topoisomerase poison-induced cell death

Previous studies have suggested two possible roles for Rad9 in mammalian cells subjected to replication stress or DNA damage. One model suggests that a Rad9-containing clamp is loaded onto damaged DNA, where it participates in Chk1 activation and subsequent events that contribute to cell survival. The other model suggests that Rad9 translocates to mitochondria, where it triggers apoptosis by binding to and inhibiting Bcl-2 and Bcl-x(L). To further study the role of Rad9, parental and Rad9(-/-) murine embryonic stem (ES) cells were treated with camptothecin, etoposide, or cytarabine, all prototypic examples of three classes of widely used anticancer agents. All three agents induced Rad9 chromatin binding. Each of these agents also triggered S-phase checkpoint activation in parental ES cells, as indicated by a caffeine-inhibitable decrease in [3H]thymidine incorporation into DNA and Cdc25A down-regulation. Interestingly, the ability of cytarabine to activate the S-phase checkpoint was severely compromised in Rad9(-/-) cells, whereas activation of this checkpoint by camptothecin and etoposide was unaltered, suggesting that the action of cytarabine is readily distinguished from that of classical topoisomerase poisons. Nonetheless, Rad9 deletion sensitized ES cells to the cytotoxic effects of all three agents, as evidenced by enhanced apoptosis and diminished colony formation. Collectively, these results suggest that the predominant role of Rad9 in ES cells is to promote survival after replicative stress and topoisomerase-mediated DNA damage.

Correlation between nucleocytoplasmic transport and caspase-3-dependent dismantling of nuclear pores during apoptosis

During apoptosis (also called programmed cell death), the chromatin condenses and the DNA is cleaved into oligonucleosomal fragments. Caspases are believed to play a major role in nuclear apoptosis. However, the relation between dismantling of nuclear pores, disruption of the nucleocytoplasmic barrier, and nuclear entry of caspases is unclear. We have analyzed nuclear import of the green fluorescent protein fused to a nuclear localization signal (GFP-NLS) in tissue culture cells undergoing apoptosis. Decreased nuclear accumulation of GFP-NLS could be detected at the onset of nuclear apoptosis manifested as dramatic condensation and redistribution of chromatin toward the nuclear periphery. At this step, dismantling of nuclear pores was already evident as indicated by proteolysis of the nuclear pore membrane protein POM121. Thus, disruption of nuclear compartmentalization correlated with early signs of nuclear pore damage. Both these events clearly preceded massive DNA fragmentation, detected by TUNEL assay. Furthermore, we show that in apoptotic cells, POM121 is specifically cleaved at aspartate-531 in its large C-terminal portion by a caspase-3-dependent mechanism. Cleavage of the C-terminal portion of POM121, which is adjoining the nuclear pore complex, is likely to disrupt interactions with other nuclear pore proteins affecting the stability of the pore complex. A temporal correlation of apoptotic events supports a model where caspase-dependent disassembly of nuclear pores and disruption of the nucleocytoplasmic barrier paves the way for nuclear entry of caspases and subsequent activation of CAD-mediated DNA fragmentation.

Heterogeneous role of caspase-8 in fenretinide-induced apoptosis in epithelial ovarian carcinoma cell lines

The mechanism of action of fenretinide, a synthetic retinoid currently undergoing testing as a chemopreventive and chemotherapeutic agent, is incompletely understood. In the present study, fenretinide caused apoptotic changes, including DNA fragmentation and cleavage of caspase substrates, in six low-passage ovarian cancer cell lines. However, the caspase activation pathway used by this agent varied. Transient transfection of cDNA-encoding cytokine response modifier A (CrmA), a caspase-8 inhibitor, diminished fenretinide-induced death in OV177 cells. Likewise, IETD(OMe)-fluoromethylketone (fmk) inhibited fenretinide-induced apoptosis by >80% in OV177 or OV266 cells and by approximately 50% in OV17, OV167, or OV207 cells. Further analysis demonstrated that inhibition of Fas ligand, tumor necrosis factor-alpha, or TRAIL signaling with blocking reagents did not affect fenretinide-induced apoptosis, raising the possibility that fenretinide activates caspase-8 in a death receptor-independent manner. In contrast, CrmA transfection or IETD(OMe)-fmk treatment did not inhibit fenretinide-induced apoptosis in OV202 cells. These divergent behaviors did not correlate with increased levels of procaspase-10, which is relatively resistant to CrmA and IETD(OMe)-fmk, nor with the expression of procaspase-8 and -9, apoptotic protease activating factor-1, or cellular FLICE-like inhibitory protein. Similarly, fenretinide treatment increased ceramide levels equally in cells that do (OV177) and do not (OV202) rely on caspase-8 to initiate apoptosis. These results indicate that synthetic retinoids can use caspase-8 as an initiating caspase, but they also indicate unexpected heterogeneity in caspase activation pathways among closely related cell lines.

Induction of survivin expression by taxol (paclitaxel) is an early event, which is independent of taxol-mediated G2/M arrest

Survivin is a novel anti-apoptotic protein that is highly expressed in cancer but is undetectable in most normal adult tissues. It was reported that taxol-mediated mitotic arrest of cancer cells is associated with survivin induction, which preserves a survival pathway and results in resistance to taxol. In this study, we provide new evidence that induction of survivin by taxol is an early event and is independent of taxol-mediated G(2)/M arrest. Taxol treatment of MCF-7 cells rapidly up-regulated survivin expression (3.5-15-fold) within 4 h without G(2)/M arrest. Lengthening the treatment of cells (48 h) with taxol resulted in decreased survivin expression in comparison with early times following taxol treatment, although G(2)/M cells were significantly increased at later times. Interestingly, 3 nm taxol induces survivin as effectively as 300 nm and more effectively than 3000 nm. As a result, 3 nm taxol is ineffective at inducing cell death. However, inhibition of taxol-mediated survivin induction by small interfering RNA significantly increased taxol-mediated cell death. Taxol rapidly activated the phosphatidylinositol 3-kinase/Akt and MAPK pathways. Inhibition of these pathways diminished survivin induction and sensitized cells to taxol-mediated cell death. A cis-acting DNA element upstream of -1430 in the survivin pLuc-2840 construct is at least partially responsible for taxol-mediated survivin induction. Together, these data show, for the first time, that taxol-mediated induction of survivin is an early event and independent of taxol-mediated G(2)/M arrest. This appears to be a new mechanism for cancer cells to evade taxol-induced apoptosis. Targeting this survival pathway may result in novel approaches for cancer therapeutics.

Caspase-7 gene disruption reveals an involvement of the enzyme during the early stages of apoptosis

Caspases play a key role during apoptotic execution. In an attempt to elucidate the specific role of caspase-7 we generated a chicken DT40 cell line in which both alleles of the gene were disrupted. Viability assays showed that caspase-7-/- clones are more resistant to the common apoptosis-inducing drugs etoposide and staurosporine. Caspase-7-/- cells show a delay in phosphatidylserine externalization and DNA fragmentation as well as cleavage of the caspase substrates poly(ADP-ribose) polymerase 1 and lamins B1 and B2. Caspase affinity labeling and activity assays indicated that deficient cells exhibit a delay in caspase activation compared with wild type DT40 cells, providing an explanation for the differences in apoptotic execution between caspase-7 null and wild type DT40 cells. These results strongly suggest that caspase-7 is involved earlier than other effector caspases in the apoptotic execution process in DT40 B lymphocytes.

Avian encephalomyelitis virus nonstructural protein 2C induces apoptosis by activating cytochrome c /caspase-9 pathway

The nonstructural protein 2C is highly conserved among picornaviruses and plays an important role in the assembly of mature virions, membrane association, and viral RNA synthesis. The investigation of other potential functions of nonstructural protein 2C from avian encephalomyelitis virus (AEV) resulted in identifying for the first time that the protein 2C is involved in apoptosis. Expression of the protein 2C on chick embryo brain (CEB) and Cos-7 cells produced TUNEL-positive cells characterized by a cleavage of cellular DNA and the formation of membrane-enclosed apoptotic bodies. Analysis of the protein 2C showed that the N-terminal domain containing 35 amino acid (aa) residues (between 46 and 80 aa) is associated with apoptotic function. Transfection of the deletion mutant lacking this 35 aa's into CEB and Cos-7 cells failed to induce apoptosis. Furthermore, the protein 2C induced apoptosis in the transfected CEB and Cos-7 cells through activation of caspase-9 rather than caspase-8 followed by activation of caspase-3 pathway. Analysis of the Western blots of caspase-3 and caspase-9 showed the characteristics of active caspase-3 and -9 in the 2C-transfected CEB and Cos-7 cells as seen in the AEV-infected CEB cells while they were in the form of procaspase-3 and procaspase-9 in the 2C mutant-transfected cells. To further elucidate the mechanism of the 2C-induced apoptosis, the 2C-transfected CEB and Cos-7 cells were fractionated into mitochondria and cytosol and subjected for Western blotting, located cytochrome c in the mitochondria as well as the cytosol fractions, while it was only sequestered in the mitochondrial fraction in the mutant 2C-transfected cells. The protein 2C was located in the mitochondria and cytosol of the transfected/infected CEB and transfected Cos-7 cells, but the mutant lost its ability to localize to the mitochondria. Altogether, the results demonstrate that the protein 2C localized to the mitochondria of the transfected cells triggered the efflux of cytochrome c into the cytosol in turn activating the upstream caspase-9 and then the downstream caspase-3, thus leading to apoptosis in the cells.

Caspase-3 inhibits the growth of breast cancer cells independent of protease activity

In this study, the MCF-7 breast cancer cells that lack caspase-3 were transfected with a wild type (WT) or mutant caspase-3 cDNA. Expression of the WT, but not of the mutant, caspase-3 was associated with increased caspase activity and susceptibility to staurosporine (STS)-induced apoptosis. Both derivatives displayed inhibition of cell growth compared with vector control cells. Growth inhibition was associated with increased expression of the cyclin dependent kinase (CDK) inhibitor p27Kip1 in the WT, but not in the mutant caspase-3 expressing cells. Cyclin D1 expression level was not affected by caspase-3 expression. Phosphorylation of the Akt protein was decreased in both WT and mutant caspase transfected cells, although Akt expression level remained unchanged. These results suggest that caspase-3 might have biological functions independent of its protease activity and that its loss might contribute to tumor development by increasing the growth potential of cancer cells.

Alterations in the apoptotic machinery and their potential role in anticancer drug resistance

Anticancer drugs can potentially kill cells in two fundamentally different ways, by interfering with cellular processes that are essential for maintenance of viability or by triggering an endogenous physiological cell death mechanism. Apoptosis is a form of physiological cell death mediated by caspases, a unique family of intracellular cysteine proteases. Zymogen forms of these proteases are found in virtually all somatic cells, but remain latent until their activation is induced by ligation of specific cell surface receptors (the so-called "death receptors"), by mitochondrial alterations that allow release of cytochrome c and other intermembrane components, or possibly by other mechanisms. Most anticancer drugs activate the mitochondrial pathway. This apoptotic pathway is regulated by pro- and antiapoptotic members of the Bcl-2 family of proteins. Once activated, certain caspases might also be controlled by the inhibitor of apoptosis (IAP) proteins. Alterations in apoptotic pathway components or their regulators have been detected in a variety of cancers, suggesting that loss of the ability of cells to undergo apoptosis might contribute to carcinogenesis. Because cancer therapies such as radiation, glucocorticoids, and chemotherapeutic drugs exert their beneficial effects, at least in part, by inducing apoptosis of cancer cells, the same alterations in apoptotic pathways would be predicted to contribute to resistance. A key issue is whether the direct toxic activity of these treatments is of benefit when neoplastic cells contain changes that diminish their ability to undergo apoptosis.

Central role of Fas-associated death domain protein in apoptosis induction by the mitogen-activated protein kinase kinase inhibitor CI-1040 (PD184352) in acute lymphocytic leukemia cells in vitro

Because the MAPK pathway plays important roles in cell proliferation and inhibition of apoptosis, this pathway has emerged as a potential therapeutic target for solid tumors and leukemia. At the present time there is little information about activation of this pathway and the consequences of its inhibition in acute lymphocytic leukemia cells (ALL). In the present study, constitutive MAPK pathway activation, as evidenced by phosphorylation of ERK1 and ERK2, was observed in 8 of 8 human lymphoid cell lines and 33% (8:24) of pretreatment ALL bone marrows. Inhibition of this pathway by the MEK inhibitors CI-1040 and PD098059 induced apoptosis through a unique pathway involving dephosphorylation and aggregation of Fas-associated death domain protein followed by death receptor-independent caspase-8 activation. Jurkat cell variants lacking Fas-associated death domain protein or procaspase-8 were resistant to CI-1040-induced apoptosis, as were Jurkat or Molt3 cells treated with the O-methyl ester of the caspase-8 inhibitor N-(Nalpha-benzyloxycarbonylisoleucylglutamyl) aspartate fluoromethyl ketone. In contrast, CI-1040-induced apoptosis was unaffected by blocking anti-Fas antibody, soluble tumor necrosis factor-alpha-related apoptosis-inducing ligand decoy receptor, or transfection with cDNA encoding the anti-apoptotic Bcl-2 family member Mcl-1 or dominant negative caspase-9. Collectively, these results identify the MAPK pathway as a potential therapeutic target in ALL and delineate a mechanism by which MEK inhibition triggers apoptosis in ALL cells.

Multiple effects of paclitaxel are modulated by a high c-myc amplification level

Paclitaxel affects microtubule stability by binding to beta-tubulin, thus leading to cell accumulation in the G(2)/M phase, polyploidization, and apoptosis. Because both cell proliferation and apoptosis could be somehow regulated by the protooncogene c-myc, in this work we have investigated whether the c-myc amplification level could modulate the multiple effects of paclitaxel. To this aim, paclitaxel was administered to SW613-12A1 and -B3 human colon carcinoma cell lines (which are characterized by a high and low c-myc endogenous amplification level, respectively), and to the B3mycC5 cell line, with an enforced exogenous expression of c-myc copies. In this experimental system, we previously demonstrated that a high endogenous/exogenous level of amplification of c-myc enhances serum deprivation- and DNA damage-induced apoptosis. Accordingly, the present results indicate that a high c-myc amplification level potentiates paclitaxel cytotoxicity, confers a multinucleated phenotype, and promotes apoptosis to a great extent, thus suggesting that c-myc expression level is relevant in modulating the cellular responses to paclitaxel. We have recently shown in HeLa cells that the phosphorylated form of c-Myc accumulates in the nucleus, as distinct nucleolar and extranucleolar spots; here, we demonstrated that, after the treatment with paclitaxel, phosphorylated c-Myc undergoes redistribution, becoming diffused in the nucleoplasm.

Styrylpyrone Derivative (SPD) induces apoptosis in a caspase-7-dependent manner in the human breast cancer cell line MCF-7

BACKGROUND: Styrylpyrone derivative (SPD) is a plant-derived pharmacologically active compound extracted from Goniothalamus sp. Previously, we have reported that SPD inhibited the proliferation of MCF-7 human breast cancer cells by inducing apoptotic cell death, while having minimal effects on non-malignant cells. Here, we attempt to further elucidate the mode of action of SPD. RESULTS: We found that the intrinsic apoptotic pathway was invoked, with the accumulation of cytosolic cytochrome c and processing of the initiator caspase-9. Cleaved products of procaspase-8 were not detected. Next, the executioner caspase-7 was cleaved and activated in response to SPD treatment. To confirm that apoptosis was induced following caspase-7 activation, the caspase inhibitor Ac-DEVD-CHO was used. Pre-incubation of cells with this inhibitor reversed apoptosis levels and caspase-7 activity in SPD-treated cells to untreated levels. CONCLUSIONS: Taken together, these results suggest SPD as a potent antiproliferative agent on MCF-7 cells by inducing apoptosis in a caspase-7-dependent manner.