Mammary Carcinoma Cell Line MCF-7 Research Articles

Antioxidant and Antitumor Potential of Micropropagated Balkan Endemic Sideritis scardica Griseb

Sideritis scardica Griseb. is a critically endangered Balkan endemic species, known for its antioxidant, neuroprotective and anti-inflammatory properties. The aim of the present study was to detail an efficient protocol for the micropropagation of S. scardica. In vitro cultures were initiated from the shoot tips of 40 days-old in vivo seedlings and the effects of different plant growth regulator treatments were examined. A Murashige and Skoog nutrient medium (MS) containing 1 mg/L zeatin and 0.1 mg/L indole-3-acetic acid (IAA) proved to be the most efficient for shoot multiplication as it produced quality, vigorous shoots with a mean number of six shoots per explant. For the first time, the antioxidant and antitumor activities of extracts from in vitro-obtained plants were evaluated. In vitro cultivated plants grown in the field revealed a higher total polyphenol content (3929.1 ± 112.2 mg GAE/100 g vs. 3563.5 ± 52.8 mg GAE/100 g) and higher ORAC antioxidant activity (1211.6 ± 27.3 µmol TE/g vs. 939.9 ± 52.4 µmol TE/g) than in situ cultivated plants. A comparison of the antitumor activities of extracts from in vitro propagated shoots, field-grown in vitro-obtained plants and in situ plants on HeLa (cervical adenocarcinoma), HT-29 (colorectal adenocarcinoma) and MCF-7 (breast cancer) human cancer cell lines showed that in vitro propagated shoots had a significant concentration-dependent cytotoxic effect on the cervical adenocarcinoma cell line HeLa, while the field-grown in vitro-obtained and in situ-collected samples induced the highest reduction in the viability of the mammary carcinoma cell line MCF-7. In both cases, the cells of the control non-tumor cell line, BALB/3T3, were significantly less affected. The results showed that the in vitro multiplication protocol ensured the obtainment of numerous plants with antioxidant and antitumor potential.

β-Apo-13-carotenone Regulates Retinoid X Receptor Transcriptional Activity through Tetramerization of the Receptor

Retinoid X receptor (RXRα) is activated by 9-cis-retinoic acid (9cRA) and regulates transcription as a homodimer or as a heterodimer with other nuclear receptors. We have previously demonstrated that β-apo-13-carotenone, an eccentric cleavage product of β-carotene, antagonizes the activation of RXRα by 9cRA in mammalian cells overexpressing this receptor. However, the molecular mechanism of β-apo-13-carotenone's modulation on the transcriptional activity of RXRα is not understood and is the subject of this report. We performed transactivation assays using full-length RXRα and reporter gene constructs (RXRE-Luc) transfected into COS-7 cells, and luciferase activity was examined. β-Apo-13-carotenone was compared with the RXRα antagonist UVI3003. The results showed that both β-apo-13-carotenone and UVI3003 shifted the dose-dependent RXRα activation by 9cRA. In contrast, the results of assays using a hybrid Gal4-DBD:RXRαLBD receptor reporter cell assay that detects 9cRA-induced coactivator binding to the ligand binding domain demonstrated that UVI3003 significantly inhibited 9cRA-induced coactivator binding to RXRαLBD, but β-apo-13-carotenone did not. However, both β-apo-13-carotenone and UVI3003 inhibited 9-cRA induction of caspase 9 gene expression in the mammary carcinoma cell line MCF-7. To resolve this apparent contradiction, we investigated the effect of β-apo-13-carotenone on the oligomeric state of purified recombinant RXRαLBD. β-Apo-13-carotenone induces tetramerization of the RXRαLBD, although UVI3003 had no effect on the oligomeric state. These observations suggest that β-apo-13-carotenone regulates RXRα transcriptional activity by inducing the formation of the "transcriptionally silent" RXRα tetramer.

Cytotoxic polyacetylenes from the Red Sea sponge Siphonochalina siphonella.

Two new polyacetylenes, callyspongenol-D (1) and callyspongendiol (2), the known polyacetylene dehydrosiphonochalynol (3), and the known triterpenoid sipholenol-A (4) were isolated from the Red Sea sponge Siphonochalina siphonella. Their chemical structures were elucidated on the basis of spectroscopic analyses. The cytotoxicity of the isolated compounds towards the human mammary carcinoma cell line MCF-7 was determined by the lactate dehydrogenase (LDH) assay, and compounds 4 and 1 were found to be the most toxic of the four, with IC50 values of 8.8 and 11.7 microM, respectively.

Diosgenin exhibits beneficial efficiency on human mammary carcinoma cell line MCF-7 and against N-nitroso-N-methylurea (NMU) induced experimental mammary carcinoma

The purpose of the present study was to investigate the impact of diosgenin on the human mammary carcinoma cell line (MCF-7) and to investigate its therapeutic potential against NMU-induced experimental breast cancer. Mammary carcinoma cells were treated with different concentrations of diosgenin and its cytotoxicity effect was measured by MTT method, lactate dehydrogenase leakage and by estimating GSH assays. N-nitroso-N-methylurea (NMU) is a highly reliable carcinogen, mutagen and teratogen used in the present study to promote breast carcinogenesis in experimental rats. In in vitro studies, diosgenin significantly inhibited the proliferation of MCF-7 cells in a dose-dependent manner and the depletion of GSH and an increase of LDH activity were observed in MCF-7 cells due to cytotoxic nature of the drug. Elevated lipid peroxidation in NMU-induced breast cancer-bearing animals were drim down (P<0.05) due to management with steroidal diosgenin. The altered lysosomal enzymes were neutralised by diosgenin and also, it protects macromolecular damage from oxidative stress and free fadicals production due to its antioxidant activity. From the results of our present analysis, it gives an idea about that diosgenin may be used as a chemoprotective agent against human mammary carcinoma.

ChemInform Abstract: Highly Enantioselective Synthesis of Biologically Important 2,5‐Dihydropyrroles via Phosphoric Acid Catalyzed Three‐Component Reactions and Evaluation of Their Cytotoxicity.

AbstractSeveral of the synthesized dihydropyrroles exhibit moderate cytotoxicity towards the mammary carcinoma cell line MCF7.

Live-Cell Imaging Visualizes Frequent Mitotic Skipping During Senescence-Like Growth Arrest in Mammary Carcinoma Cells Exposed to Ionizing Radiation

Senescence-like growth arrest in human solid carcinomas is now recognized as the major outcome of radiotherapy. This study was designed to analyze cell cycle during the process of senescence-like growth arrest in mammary carcinoma cells exposed to X-rays. Fluorescent ubiquitination-based cell cycle indicators were introduced into the human mammary carcinoma cell line MCF-7. Cell cycle was sequentially monitored by live-cell imaging for up to 5 days after exposure to 10 Gy of X-rays. Live-cell imaging revealed that cell cycle transition from G2 to G1 phase without mitosis, so-called mitotic skipping, was observed in 17.1% and 69.8% of G1- and G2-irradiated cells, respectively. Entry to G1 phase was confirmed by the nuclear accumulation of mKO(2)-hCdt1 as well as cyclin E, which was inversely correlated to the accumulation of G2-specific markers such as mAG-hGeminin and CENP-F. More than 90% of cells skipping mitosis were persistently arrested in G1 phase and showed positive staining for the senescent biochemical marker, which is senescence-associated ß-galactosidase, indicating induction of senescence-like growth arrest accompanied by mitotic skipping. While G2 irradiation with higher doses of X-rays induced mitotic skipping in approximately 80% of cells, transduction of short hairpin RNA (shRNA) for p53 significantly suppressed mitotic skipping, suggesting that ionizing radiation-induced mitotic skipping is associated with p53 function. The present study found the pathway of senescence-like growth arrest in G1 phase without mitotic entry following G2-irradiation.

Effect of flavonone hesperidin on the apoptosis of human mammary carcinoma cell line MCF-7

The aim of the present study was to investigate the impact of a natural citrus flavonoglycoside hesperidin on the human mammary carcinoma cell line (MCF-7) and its possible role in the induction of apoptosis. Human breast cancer cells were treated with different concentrations of hesperidin and its cytotoxicity effect was measured by MTT method and lactate dehydrogenase leakage assays. Apoptosis was analyzed by light microscopic studies and DNA fragmentation. The mechanism of apoptosis was studied with the expression of p53 and caspase-3 proteins. Glutathione content was also measured in MCF-7 cells after hesperidin treatment. The results revealed that hesperidin significantly inhibited the proliferation of MCF-7 cells in a concentration-dependent manner. Apoptotic morphology was observed in MCF-7 cells treated with hesperidin at the concentration of 60 and 80 μM. DNA fragmentation, accumulation of p53 and expression of caspase-3 proteins were observed in MCF-7 cells after the treatment with hesperidin. The depletion of GSH and an elevation of LDH were observed in MCF-7 cells treated with hesperidin. Therefore in conclusion, hesperidin induced cytotoxicity in MCF-7 cells in vitro. Apoptosis of MCF-7 cells may be due to the DNA damage and expression of apoptotic proteins. Depletion of GSH may be involved in the induction of apoptosis of Michigan cancer foundation-7 cells.

A microarray based expression profiling of paclitaxel and vincristine resistant MCF-7 cells

Resistance to the broad spectrum of chemotherapeutic agents in cancer cell lines and tumors has been called multiple drug resistance (MDR). In this study, the molecular mechanisms of resistance to two anticancer agents (paclitaxel and vincristine) in mammary carcinoma cell line MCF-7 were investigated. Drug resistant sublines to paclitaxel (MCF-7/Pac) and vincristine (MCF-7/Vinc) that were developed from sensitive MCF-7 cells (MCF-7/S) were used. cDNA microarray analysis was performed for the RNA samples of sensitive and resistant cells in duplicate experiments. GeneSpring GX 7.3.1 Software was used in data analysis. The results indicated that the upregulation of MDR1 gene is the dominating mechanism of the paclitaxel and vincristine drug resistance. Additionally the upregulation of the genes encoding the detoxifying enzymes (i.e. GSTP1) was observed. Significant downregulation of apoptotic genes (i.e. PDCD2/4/6/8) and upregulation of some cell cycle regulatory genes ( CDKN2A, CCNA2 etc.) was seen which may be in close relation to MDR in breast cancer. Drug resistant cancer cells exhibit different gene expression patterns depending on drug treatment, and each drug resistance phenotype is probably genetically different. Further functional studies are needed to demonstrate the complete set of genes contributing to the drug resistance phenotype in breast cancer cells.

Calpain small-1 modulates Akt/FoxO3A signaling and apoptosis through PP2A

Here, we show that FoxO3A transcription factor is upregulated upon calpain small-1 (CAPNS1) depletion both in mouse embryonic fibroblasts (MEFs) and in the human mammary carcinoma cell line MCF-7. On starvation, CAPNS1 depletion is associated with a higher rate of FoxO3A dephosphorylation and translocation to the nucleus and to a sharper increase in the levels of p27Kip1 and Bim, the products of two FoxO target genes. Notably, FoxO3A depletion in CAPNS1-/- MEFs reduces both the induction of Bim and apoptosis. Both okadaic acid treatment and silencing of the protein phosphatase 2A (PP2A) catalytic subunit can partially reduce starvation-induced FoxO3A activation and apoptosis in CAPNS1-/- fibroblasts. PP2A associates more tightly with Akt in CAPNS1 knockout cells, indicating that PP2A is involved in calpain-mediated FoxO regulation. Finally, we show that PP2A regulatory subunits B56 alpha and gamma are in vitro substrates of calpain, and calpain regulates B56 alpha stability in vivo, suggesting a direct role of calpain in the regulation of PP2A function. In conclusion, for the first time we report that CAPNS1 interferes with PP2A-Akt interaction consequently affecting FoxO3A-dependent cell death. Calpain inhibition might therefore be exploited as a tool to induce apoptosis in tumors sensitive to FoxO activation.

Autocrine Human Growth Hormone Promotes Tumor Angiogenesis in Mammary Carcinoma

Accumulating literature implicates pathological angiogenesis and lymphangiogenesis as playing key roles in tumor progression. Autocrine human growth hormone (hGH) is a wild-type orthotopically expressed oncogene for the human mammary epithelial cell. Herein we demonstrate that autocrine hGH expression in the human mammary carcinoma cell line MCF-7 stimulated the survival, proliferation, migration, and invasion of a human microvascular endothelial cell line (HMEC-1). Autocrine/paracrine hGH secreted from mammary carcinoma cells also promoted HMEC-1 in vitro tube formation as a consequence of increased vascular endothelial growth factor-A (VEGF-A) expression. Semiquantitative RT-PCR analysis demonstrated that HMEC-1 cells express both hGH and the hGH receptor (hGHR). Functional antagonism of HMEC-1-derived hGH reduced HMEC-1 survival, proliferation, migration/invasion, and tube formation in vitro. Autocrine/paracrine hGH secreted by mammary carcinoma cells increased tumor blood and lymphatic microvessel density in a xenograft model of human mammary carcinoma. Autocrine hGH is therefore a potential master regulator of tumor neovascularization, coordinating two critical processes in mammary neoplastic progression, angiogenesis and lymphangiogenesis. Consideration of hGH antagonism to inhibit angiogenic processes in mammary carcinoma is therefore warranted.

Gene trapping identifies a putative tumor suppressor and a new inducer of cell migration

Tumor necrosis factor alpha (TNFα) is a pleiotropic cytokine involved in apoptotic cell death, cellular proliferation, differentiation, inflammation, and tumorigenesis. In tumors it is secreted by tumor associated macrophages and can have both pro- and anti-tumorigenic effects. To identify genes regulated by TNFα, we performed a gene trap screen in the mammary carcinoma cell line MCF-7 and recovered 64 unique, TNFα-induced gene trap integration sites. Among these were the genes coding for the zinc finger protein ZC3H10 and for the transcription factor grainyhead-like 3 (GRHL3). In line with the dual effects of TNFα on tumorigenesis, we found that ZC3H10 inhibits anchorage independent growth in soft agar suggesting a tumor suppressor function, whereas GRHL3 strongly stimulated the migration of endothelial cells which is consistent with an angiogenic, pro-tumorigenic function.

Pharmacological separation of hEAG and hERG K+ channel function in the human mammary carcinoma cell line MCF-7

Pharmacological inhibitors of the human ether-a-go-go (hEAG) potassium channel, astemizole and imipramine, have been used to demonstrate that hEAG plays a role in cancer cell proliferation. Astemizole and imipramine are, however, relatively non-specific ion channel blockers, as astemizole can also block the related potassium channel, human ether-a-go-go-related (hERG). Therefore, we aimed to determine the molecular target of astemizole, in the human mammary carcinoma cell line MCF-7. We initially confirmed the expression of KCNH1 and KCNH2 mRNA and hEAG and hERG channel protein in MCF-7 cells. Using a [3H]-thymidine incorporation assay we determined that astemizole inhibited MCF-7 cell proliferation, whereas the hERG-specific channel blocker E-4031 had no effect. We then determined that E-4031 inhibited the regulatory volume decrease (RVD) observed in these cells following exposure to hypotonic solutions, confirming that functional hERG channels are present and may be important for cell volume regulation in MCF-7 cells. Our results suggest, for the first time, that hERG is involved in cell volume regulation. In addition, the function of hEAG and hERG in MCF-7 cell proliferation can be separated pharmacologically by utilizing the channel inhibitors astemizole and E-4031. The hEAG channel function in MCF-7 cells appears to be involved in the regulation of cell proliferation, whereas hERG is involved in cell volume regulation.

Phosphorylation-Dependent Sumoylation of Estrogen-Related Receptor α1

We previously showed that estrogen-related receptor alpha1 (ERRalpha1) can compete with estrogen receptor alpha (ERalpha) for binding to estrogen response elements (EREs), repressing transcription in the mammary carcinoma cell line MCF-7. Given that ERRalpha1 can function in the absence of ligands and exists as a phosphoprotein in vivo, we wished to determine sites of phosphorylation involved in regulating its transcriptional activity. Using a combination of electrophoretic mobility shift analysis, phospho-specific fluorescent dye staining, and site-directed mutagenesis, we identified two novel in vivo sites of phosphorylation in the A/B ligand-independent activation domain of ERRalpha1 at Ser19 and Ser22. Inhibition of phosphorylation at amino acid residue 22 did not have a significant effect on ERRalpha1's transcriptional activity. However, mutation of amino acid residue 19 from serine to alanine enhanced two-fold ERRalpha1's response to the coactivator GRIP-1. We also identified two sites of sumoylation at Lys14 and Lys403. We found that inhibition of sumoylation at Lys14 could enhance five-fold ERRalpha1's response to coactivator GRIP-1. Furthermore, phosphorylation of Ser19 enhanced the sumoylation at Lys14. Taken together, we conclude that phosphorylation at Ser19 and sumoylation at Lys14 within the A/B domain play roles in regulating ERRalpha1's transcriptional activities via affecting its response to coactivators.

The epidermal growth factor stimulates sphingosine kinase-1 expression and activity in the human mammary carcinoma cell line MCF7

Sphingosine 1-phosphate (S1P) the product of sphingosine kinase (SK) action plays an important role in various pathological conditions like inflammation and cancer. In this study, we show that in the human breast cancer cell line MCF7, epidermal growth factor (EGF) stimulates SK-1 activity in a biphasic manner with a first peak after 15 min and a second delayed activation occurring after 1 h up to 18 h and thereafter declining again. This delayed activation is accompanied by increased mRNA and protein expression of SK-1, but not SK-2. Mechanistically, the transcriptional upregulation is dependent on the classical mitogen-activated protein kinase, protein kinase C (PKC) and the phosphoinositide 3-kinase, since specific inhibitors of these enzymes all abolish the EGF-induced mRNA upregulation and activity of SK-1. Moreover, dexamethasone also suppressed EGF-induced SK-1 mRNA expression and activity which is reversed by the glucocorticoid receptor antagonist RU486. To see whether EGF-induced upregulation of SK-1 is of relevance for tumor progression, we investigated two hallmarks of carcinogenesis, i.e., cell proliferation and migration. Stimulation of cells with EGF leads to enhanced [ 3H]thymidine incorporation into DNA and also to stimulated migration in a modified Boyden chamber assay. When cells are depleted of SK-1, but not SK-2, by siRNA transfection or by dexamethasone treatment, EGF-induced proliferation and migration are drastically reduced. In summary, these data show that EGF causes an acute stimulation of SK-1 activity and, moreover, triggers a delayed SK activation which is due to increased gene transcription and de novo synthesis of SK-1, which in turn directs cells towards growth and increased motility. Thus, the sphingosine kinase-1 may represent a novel attractive target for cancer therapy.

Cytotoxic and proapoptotic activity of ent-16β-17α-dihydroxykaurane on human mammary carcinoma cell line MCF-7

Here we describe the cytotoxic and proapoptotic effect of an ent-kaurane (ent-16β-17α-dihydroxykaurane), compound isolated from Croton malambo barks, on malignant cell growth. When MCF-7 mammary carcinoma cells were treated with increasing concentrations of the ent-kauranoid, its cytotoxic activity showed an IC 50 of 12.5 μg/ml, dose that is 2.66-fold lower than the corresponding value for non-malignant cells. At this growth inhibitory dose, both mRNA and protein levels for Bcl-2 as well as mRNA for hTERT were significantly reduced. The observed preapoptotic activity seemed to be triggered by a mechanism that is not directly affecting NF-κB binding ability. The potential use of this plant-derived compound as a cancer chemotherapy agent is discussed.

The pesticide malathion induces alterations in actin cytoskeleton and in cell adhesion of cultured breast carcinoma cells.

We have studied the effects of the organophosphorous pesticide malathion on cell viability, actin cytoskeleton, cell adhesion complex E-cadherin/beta-catenin, and Rho and Rac1 GTPases from the human mammary carcinoma cell line MCF-7. Malathion induced cell lethality, determined by the MTT assay, depending on the treatment conditions. Cells incubated with low concentrations of malathion, 16-32 microg/ml, showed high survival rates (>95%) at any evaluated time (1-5 days), whereas complete cell lethality was found using 512 microg/ml and 5 days of treatment. Deep morphological changes were induced with high doses of 64 and 128 microg/ml, and long incubation time (5 days); cells showed perinuclear vacuoles, rounding, shrinkage, and a gradual loss of adhesion. These changes were related to a decrease in the expression of the adhesion molecules, E-cadherin and beta-catenin, and to the distribution and reactivity of actin microfilaments to TRITC-phalloidin. Disruption of microfilaments, accompanied by the collapse of actin to perinuclear region, were characteristic of cells with loss of adhesion. At lower concentrations, some cells presented deformations on the plasma membrane as lamellipodia-like structures, which were particularly evident from 32 to 128 microg/ml. Conversely, we observed an increase in the expression of Rho and Rac1 GTPases, modulators of actin cytoskeleton and cell adhesion.

Alternative splicing of the human estrogen receptor α primary transcript: Mechanisms of exon skipping

The 1785 nucleotides of the coding region of the estrogen receptor alpha (ER-alpha) are dispersed over a region of more than 300,000 nucleotides in the primary transcript. Splicing of this precursor RNA frequently leads to variants lacking one or more exons that have been associated to breast cancer progression. The most frequent splice variant lacks exon 4 and is expressed in the human mammary carcinoma cell line MCF-7 at a level similar to that of the full-length messenger. The in silico analysis of ER-alpha splice sites by Hamming clustering, a self learning method trained on more than 28,000 experimentally proved splice sites, reveals high relevance for the 5' and 3' splice sites of exon 4. The splicing analysis of transfected mini-gene constructs containing drastically shortened introns excludes that weak splice sites, intron or exon lengths or splice enhancers are responsible for exon skipping. Exon 6 is never skipped in MCF-7 cells but is spliced out from mini-gene derived primary transcripts if inserted between exons 3 and 5 instead of exon 4. As a consequence, it appears that a particular splice site affinity of exon 3 donor (5' splice site) and exon 5 acceptor sites (3' splice site) is responsible for skipping of the exon in between.

Studies on the inhibition of tumor cell growth and microtubule assembly by 3-hydroxy-4-[( E)-(2-furyl)methylidene]methyl-3-cyclopentene-1,2-dione, an intensively coloured Maillard reaction product

Very recently, 3-hydroxy-4-[( E)-(2-furyl)methylidene]methyl-3-cyclopentene-1,2-dione (1) has been successfully identified as an intensively coloured Maillard product formed from glucose and l-proline upon thermal food processing. Using a biomimetic synthetic strategy, reference material of compound 1 was prepared and purified, and then used to study its effect on the growth of human tumor cells. Compound 1 was found to potently inhibit the growth of human tumor cells in vitro. Using a reporter gene assay we could show that in growth inhibitory concentrations compound 1 effectively inhibits the phosphorylation of the transcription factor Elk-1. In addition, 1 was found to affect the microtubule skeleton. The human mammary carcinoma cell line MCF-7 exhibits a decrease of the microtubule organisation when treated for 24 h with 1 (⩾20 μ m). At concentrations of 30 μ m and above a loss of microtubule integrity is observed after 1 h incubation. In vitro studies demonstrated that the polymerisation and, to a minor extent, also the depolymerisation of tubulin, isolated and purified from bovine brain, is inhibited in a dose-dependent manner at concentrations of 30 μ m and above. This is the first time that a non-enzymatically formed browning compound of known structure was reported to effectively inhibit tumor cell growth and microtubule assembly.

Dexamethasone inhibits TNF-alpha-induced apoptosis and IAP protein downregulation in MCF-7 cells.

Exposure of human mammary carcinoma cell line MCF-7 to TNF-alpha leads to apoptotic cell death within 24 h. In search for apoptosis-preventing signals, we identified glucocorticoids as potent death-preventing compounds. Ten nM dexamethasone provided a significant protective effect whereas 100 nM dexamethasone roughly blocked 80 - 90% of TNF-alpha-induced apoptosis. Surprisingly, dexamethasone exerted a protective effect even when supplied several hours after TNF-alpha. This points to a powerful inhibition of even advanced apoptotic processes by dexamethasone. To further pinpoint the anti-apoptotic glucocorticoid action, we investigated the expression levels of several members of the inhibitors of apoptosis (IAPs) family of proteins in response to TNF-alpha and dexamethasone. IAP proteins directly block caspase protease activities including caspase-3, caspase-7, and caspase-9. Exposure of MCF-7 cells to TNF caused an extensive downregulation of cIAP1, cIAP2, and XIAP protein levels. The decline of the IAP protein levels temporally paralleled the appearance of apoptotic DNA fragments which started 12 - 14 h following TNF-alpha addition and maximal effects were seen within 24 h. Coincubation of cells with TNF-alpha and dexamethasone potently blocked cIAP1, cIAP2, and XIAP downregulation. TNF-alpha-mediated IAP protein downregulation was not affected by proteasome inhibitors like lactacystin, ALLN or ALLM, whereas it was blocked by the broad-spectrum caspase inhibitor Z-VAD-fmk which also prevented TNF-alpha-induced apoptotic cell death. These data suggest that inhibition of IAP downregulation mediated by a caspase proteolytic activity constitutes the anti-apoptotic action of glucocorticoids in MCF-7 carcinoma cells.

Inhibition of cyclin-dependent kinase 1 (CDK1) by indirubin derivatives in human tumour cells.

The bisindole indirubin has been described, more than 30 years ago, as being clinically active in the treatment of human chronic myelocytic leukaemia. However, the underlying mechanism of action has remained unclear. We have reported previously that indirubin and its analogues are potent and selective inhibitors of cyclin-dependent kinases (CDK). In this study, we investigated the influence of indirubin and derivatives on CDK1/cyclin B kinase in human tumour cells at concentrations known to induce growth inhibition. Cells of the mammary carcinoma cell line MCF-7, synchronized by serum deprivation, after serum repletion stay arrested in the G1/G0 phase of the cell cycle in the presence of 2 μM indirubin-3′-monoxime. At higher drug concentrations (≥ 5 μM) an increase of the cell population in the G2/M phase is additionally observed. Cells synchronized in G2/M phase by nocodazole remain arrested in the G2/M phase after release, in the presence of indirubin-3′-monoxime (≥5 μM). After 24 h treatment with 10 μM indirubin-3′-monoxime a sub-G2 peak appears, indicative for the onset of apoptotic cell death. Treatment of MCF-7 cells with growth inhibitory concentrations of indirubin-3′-monoxime induces dose-dependent inhibition of the CDK1 activity in the cell. After 24 h treatment, a strong decrease of the CDK1 protein level along with a reduction of cyclin B in complex with CDK1 is observed. Taken together, the results of this study strongly suggest that inhibition of CDK activity in human tumour cells is a major mechanism by which indirubin derivatives exert their potent antitumour efficacy. © 2001 Cancer Research Campaign http://www.bjcancer.com