Phorbol ester and bryostatin effects on growth and the expression of oestrogen responsive and TGF-beta 1 genes in breast tumour cells

Effect of TPA and HTLV-1 Tax on BRCA1 and ERE controlled genes expression

Interference with the expression and/or functions of the multifunctional tumor suppressor BRCA1 leads to a high risk of breast and ovarian cancers. BRCA1 expression is usually activated by the estrogen (E2) liganded ERα receptor. Activated ERα is considered as a potent transcription factor which activates various genes expression by 2 pathways. A classical pathway, ERα binds directly to E2-responsive elements (EREs) in the promoters of the responsive genes and a non-classical pathway where ERα indirectly binds with the appropriate gene promoter. In our previous study, HTLV-1Tax was found to strongly inhibit ERα induced BRCA1 expression while stimulating ERα induced ERE dependent genes. TPA is a strong PKC activator which found to induce the expression of HTLV-1. Here we examined the effect of TPA on the expression of BRCA1 and genes controlled by ERE region in MCF-7 cells and on Tax activity on these genes. Our results showed strong stimulatory effect of TPA on both BRCA1 and ERE expression without treatment with E2. Tax did not show any significant effect on these TPA activities. It seems that TPA activation of BRCA1 and ERE expression is dependent on PKC activity but not through the NFκB pathway. However, 53BP1 may be involved in this TPA activity because its overexpression significantly reduced the TPA stimulatory effect on BRCA1 and ERE expression. Additionally, our Chip assay results probably exclude possible involvement of ERα pathway in this TPA activity because TPA did not interfere with the binding of ERα to both BRCA1 promoter and ERE region.

hEGR1 is induced by EGF, inhibited by gefitinib in bladder cell lines and related to EGF receptor levels in bladder tumours

The effect of EGF and gefitinib on two EGFR-positive human bladder cancer cell lines has been investigated using array-based gene expression profiling. The most prominent transcript, increased up to 6.7-fold by EGF compared with controls in RT112 cells, was human early growth response protein 1 (hEGR1). This induction was prevented by gefitinib. The hEGR1 mRNA in EGF-treated samples was reduced in the presence of gefitinib, as was hEGR1 protein in cell lysates. In the RT4 cells, hEGR1 expression was halved in the presence of EGF and gefitinib in combination. In bladder tumour samples, there was a significant correlation between hEGR1 mRNA detected by RT-PCR and EGFR detected by ligand binding, (P=0.042). The induction by EGF of the hEGR1 gene, mRNA and protein in RT112 cells, and its inhibition by gefitinib, together with the detection of hEGR1 mRNA in bladder tumours, suggests that hEGR1 may be important in the EGFR growth-signalling pathway in bladder cancer and should be further investigated for its prognostic significance and as a potential therapeutic target.

A role for protein kinase C delta in the differential sensitivity of MCF-7 and MDA-MB 231 human breast cancer cells to phorbol ester-induced growth arrest and p21(WAFI/CIP1) induction

The goal of this study was to investigate the differential sensitivity of estrogen receptor (ER) positive MCF-7 and ER negative MDA-MB 231 breast cancer cells to phorbol myristate acetate (PMA)-dependent growth arrest. MCF-7 cells were growth arrested by 80% while MDA-MB 231 cells were arrested by 20% in response to seven days of treatment with 10 nM PMA. Coincident with the increased sensitivity of MCF-7 cells to be growth arrested by the protein kinase C (PKC) activator PMA, PMA induced 9-fold higher levels of the cyclin dependent kinase (Cdk) inhibitor p21(WAF1/GIP1) in MCF-7 compared to MDA-MB 231 cells. A comparison of the PKC isoforms expressed in MCF-7 versus MDA-MB 231 cells showed that only the PMA-sensitive PKC delta and eta isoforms were expressed at markedly (> or =10-fold) elevated levels in MCF7 versus MDA-MB 231 cells. These results suggested that the differential sensitivity to growth arrest and induction of p2l(WAFl/CIPl) could reflect, at least in part, increased expression of PMA-dependent PKC isoforms delta and/or eta. Direct evidence to support this hypothesis was provided by the ability of transient transfections into MCF-7 cells of constitutively active PKC delta but not of PKC's eta or alpha or epsilon to enhance p21(WAFl/CIP1) promoter activity. These results suggest that PKC delta plays a fundamental role in the regulation of growth in estrogen receptor positive breast cancer cells.

New methods for detection of potential endocrine disruptors

It has been hypothesized that recent adverse trends in humans are linked to an increased exposure to potential endocrine disrupting agents. These include widely used compounds that mimic the action of sex hormones, including bisphenol A, phthalates and parabens. Since the chemical structure is not sufficient to determine whether a chemical will act as an oestrogen, there is a need for assays that can determine whether a compound interferes with the endocrine systems. The Environmental Protection Agency has recently suggested a testing scheme, composed of an initial screening followed by a more comprehensive investigation of chemicals that are positive in the screening. The screening will use several short-term assays to screen many thousands of compounds for potential endocrine disrupting properties. However, none of these tests determines compound-induced effects on the expression of endogenous genes, which is the cause of the adverse effects. We propose to use a precise quantification of the expression levels of endogenous oestrogen-regulated genes to test whether a chemical has oestrogenic properties, and describe how an endogenous gene expression assay can be established and conducted. Furthermore, different applications of such an assay are discussed: in cell cultures; in experimental animals; or, optimally, directly in blood samples from exposed humans.

Matrix metalloproteinase-1 is induced by epidermal growth factor in human bladder tumour cell lines and is detectable in urine of patients with bladder tumours

The matrix metalloproteinases are a family of enzymes that degrade the extracellular matrix and are considered to be important in tumour invasion and metastasis. The effect of epidermal growth factor (EGF) on matrix metalloproteinase-1 (MMP1) production in two human bladder tumour cell lines, RT112 and RT4, has been investigated. In the RT112 cell line, an increase in MMP1 mRNA levels was found after a 6-h incubation with EGF, and this further increased to 20-fold that of control levels at 24- and 48-h treatment with 50 ng ml(-1) of EGF. MMP2 mRNA levels remained constant over this time period, whereas in the RT4 cells no MMP2 transcripts were detectable, but MMP1 transcripts again increased with 24- and 48-h treatment with 50 ng ml(-1) of EGF. MMP1 protein concentration in the conditioned medium from both cell lines increased with 24- and 48-h treatment of the cells and the total MMP1 was higher in the medium than the cells, demonstrating that the bladder tumour cell lines synthesize and secrete MMP1 protein after continuous stimulation with EGF. MMP1 protein was detected in urine from patients with bladder tumours, with a significant increase in concentration with increased stage and grade of tumour. MMP1 urine concentrations may therefore be a useful prognostic indicator for bladder tumour progression.

Differential effects of protein kinase C agonists on prostaglandin production and growth in human breast cancer cells

A regulatory role for protein kinase C (PKC) and eicosanoids has been implicated in the control of breast cancer cell growth and function. Here we report on the effects of the two PKC agonists 12-O-tetradecanoyl-phorbol-13-acetate (TPA) and bryostatin 1 on arachidonic acid metabolism, prostaglandin E2 (PGE2) production, and growth in MDA MB 231 human breast cancer cells. TPA caused a dose-dependent increase in PGE2 production which was maximal at 100 nM and which was blocked in the presence of an equimolar concentration of bryostatin 1. Bryostatin 1 alone had no effect on PGE2 synthesis. Both TPA and bryostatin 1 stimulated arachidonic acid release and reduced fatty acid incorporation into phosphatidylinositol, their combined effect being less than additive in co-incubation. Interleukin-1beta (IL-1beta) induced a tenfold and twofold synergistic increase in PGE2 production in the presence of TPA (10 nM) and bryostatin 1 (10 nM) respectively. Bryostatin 1 caused a dose-dependent inhibition of the phorbol ester-potentiated IL-1beta response. Treatment of MDA MB 231 cells for 4 days with TPA (10 nM) or bryostatin 1 (10 nM) inhibited cell growth by 74% and 20% respectively. Co-treatment with both PKC agonists reversed the anti-proliferative effect of TPA to that seen with bryostatin 1 alone. In contrast the anti-proliferative action of ceramide, another PKC modulator, was unaffected in the presence of bryostatin 1. TPA also induced morphological changes in MDA MB 231 cells which were prevented by co-treatment with bryostatin 1. This study further supports a regulatory role for PKC in the control of eicosanoid synthesis and growth in human breast cancer cells. Although the findings are consistent with bryostatin 1 acting as an antagonist/weak agonist in relation to TPA action, the mechanistic basis for this differential action of TPA and bryostatin 1 is uncertain.

Induction of metalloproteinase (MMP1) expression by epidermal growth factor (EGF) receptor stimulation and serum deprivation in human breast tumour cells

The levels of the matrix metalloproteinase MMP1 mRNA in three breast tumour cell lines with varying numbers of epidermal growth factor (EGF) receptors, MDA-MB-231, T47D and MCF7, were investigated following treatment with EGF or TGF alpha in serum-free medium for up to 24 h. A higher level of MMP1 mRNA was found in both control and treated MDA-MB-231 cells compared with the other two cell lines. A 2-fold increase in MMP1 transcripts was observed in MDA-MB-231 cells following a 30 min treatment with EGF and 2 h with TGF alpha. An increase in MMP1 transcripts following serum deprivation in the absence of growth factor stimulation was also seen. This effect was not evident with the other cell lines. In MDA-MB-231 cells, low concentrations of MMP1 protein were detected in medium from treated cells and was only significantly increased after 24 h but it was inhibited by cycloheximide. The early effect of EGF on MMP1 expression was not inhibited by cycloheximide. Treatment with cycloheximide for longer periods produced increased transcripts of MMP1, TGF alpha and EGF-receptor, suggesting the activation of processes for tissue breakdown and subsequent repair may occur on prolonged inhibition of protein synthesis. These results confirm a relationship between EGF-receptor stimulation and MMP1 expression in some EGF-receptor positive tumour cells, which, in part, occurs at the transcriptional level, and have implications for the invasive progression of EGF-receptor positive tumours particularly in areas of nutritional deprivation.

Relationship between tamoxifen-induced transforming growth factor beta 1 expression, cytostasis and apoptosis in human breast cancer cells

Previously we have shown that tamoxifen (TAM) induces morphological and biochemical changes typical of apoptosis in oestrogen receptor (ER)-positive MCF-7 or ER-negative MDA-231 human breast cancer cells. In this study the effects of TAM on expression of transforming growth factor beta 1 (TGF-beta 1) were correlated with the effects on cell cycle kinetics and apoptosis. TAM had similar biphasic effects on both cell lines. Short-term (< 6 h) TAM incubation resulted in a slight decrease in TGF-beta 1 protein despite an increase in TGF-beta 1 mRNA and was associated with an increase in cells in S-phase. No apoptotic effects were noted. Longer (> or = 12 h) TAM incubation induced TGF-beta 1 protein (about 3-fold) and mRNA expression (about 2-fold) in both cell lines, and was associated with G1/G0 blockade and induction of apoptosis. The accumulation of TAM-induced TGF-beta 1 mRNA was increased by cycloheximide, but was not affected by 17 beta-oestradiol. Long-term incubation with TAM had no significant effect on TGF-beta 1 gene copy number. TAM-induced internucleosomal DNA cleavage was inhibited in both cell lines by the addition of an anti-TGF-beta 1 antibody. TAM has dose- and time-dependent effects on TGF-beta 1 expression associated with changes in cell cycle kinetics. These effects are independent of ER status and may be the result of a direct regulatory effect of TAM on TGF-beta 1 transcription. It also appears that induction of TGF-beta 1 plays an important role in TAM-induced apoptosis in breast cancer cells.

A phase I trial of bryostatin 1 in patients with advanced malignancy using a 24 hour intravenous infusion

Bryostatin 1 is a macrocyclic lactone derived from the marine invertebrate Bugula neritina. In vitro, bryostatin 1 activates protein kinase C (PKC), induces the differentiation of a number of cancer cell lineages, exhibits anti-tumour activity and augments the response of haemopoietic cells to certain growth factors. In vivo, bryostatin 1 is also immunomodulatory, but the range of tumours which respond to bryostatin 1 in xenograft tumour models is mostly the same as the in vitro tumour types, suggesting a direct mode of action. Nineteen patients with advanced malignancy were entered into a phase I study in which bryostatin 1 was given as a 24 h intravenous infusion, weekly, for 8 weeks. Myalgia was the dose-limiting toxicity and the maximum tolerated dose was 25 micrograms m-2 per week. The myalgia was cumulative and dose related, and chiefly affected the thighs, calves and muscles of extraocular movement. The mechanism of the myalgia is unknown. CTC grade 1 phlebitis affected every patient for at least one cycle and was caused by the diluent, PET, which contains polyethylene glycol, ethanol and Tween 80. Most patients experienced a 1 g dl-1 decrease in haemoglobin within 1 h of commencing the infusion which was associated with a decrease in haematocrit. Radiolabelled red cell studies were performed in one patient to investigate the anaemia. The survival of radiolabelled red cells during the week following treatment was the same as that seen in the week before treatment. However, there was a temporary accumulation of radiolabelled red cells in the liver during the first hour of treatment, suggesting that pooling of erythrocytes in the liver might account for the decrease in haematocrit. Total or activated PKC concentrations were measured in the peripheral blood mononuclear cells (PBMCs) of three patients for the first 4 h of treatment and during the last hour of the infusion. This showed that PKC activity was significantly modulated during the infusion. Bryostatin 1 is immunomodulatory in vitro, and we have confirmed this activity in vivo. An investigation of the first three cycles of treatment in seven patients showed an increased IL-2-induced proliferative response in peripheral blood lymphocytes and enhanced lymphokine-activated killer (LAK) activity. A previously reported rise in serum levels of interleukin 6 (IL-6) and tumour necrosis factor alpha (TNF 1) was not confirmed in our study; of nine patients in this study, including patients at all dose levels, none showed an increase in these cytokines.(ABSTRACT TRUNCATED AT 400 WORDS)

Review of survival analyses published in cancer journals

Survival analysis has found widespread applications in medicine in the last 10-15 years. However, there has been no published review of the use and presentation of survival analyses. We have carried out a systematic review of the research papers published between October and December 1991 in five clinical oncology journals. A total of 132 papers were reviewed. We looked at several aspects of study design, data handling, analysis and presentation of the results. We found that almost half of the papers did not give any summary of length of follow-up; that in 62% of papers at least one end point was not clearly defined; and that both logrank and multivariate analyses were frequently reported at most only as P-values [63/84 (75%) and 22/47 (47%) respectively]. Furthermore, although many studies were small, uncertainty of the estimates was rarely indicated [in 13/84 (15%) logrank and 16/47 (34%) multivariate results]. The procedure for categorisation of continuous variables in logrank analyses was explained in only 8/49 (16%) papers. The quality of graphs was felt to be poor in 43/117 (37%) papers which included at least one survival curve. To address some of the presentational inadequacies found in this review we include new suggested guidelines for the presentation of survival analyses in medical journals. These would complement the statistical guidelines recommended by several clinical oncology journals.

Cultured human melanocytes respond to MSH peptides and ACTH

Although the administration of melanocyte-stimulating hormone (MSH) peptides results in skin darkening in man, cultured human melanocytes have been reported to be unresponsive to these peptides. This may be a consequence of the conditions under which the cells were maintained in vitro, particularly the use of phorbol esters and cholera toxin as melanocyte mitogens. By culturing the cells in the absence of these additives, we demonstrate that alpha-MSH and its synthetic analogue Nle4DPhe7 alpha-MSH (NDP-MSH) induce dose-related increases in melanin content and tyrosinase activity and affect cell morphology in the majority of human melanocyte cultures. In addition, NDP-MSH induces increases in tyrosinase mRNA and tyrosinase-related protein-1 (TRP-1) mRNA. The dose-response curves for the MSH peptides are sigmoidal and the two peptides are equipotent in their effects on human melanocytes. Adrenocorticotropic hormone (ACTH) also affects morphology and stimulates melanogenesis and tyrosinase activity in human melanocytes. However, the dose-response curves for ACTH are biphasic, and the melanocytes respond to lower concentrations of ACTH than MSH peptides, similar to those normally present in human plasma. These findings may be important in understanding the role of these pro-opiomelanocortin peptides in human skin pigmentation.

Gene therapy through signal transduction pathways and angiogenic growth factors as therapeutic targets in breast cancer

Angiogenesis is a major new prognostic factor in breast cancer. Small vessels quantitatively assessed by staining with anti-CD31 antibodies correlate with lymph node involvement and are a better independent predictor of survival. There are many vascular growth factors, but predominant in primary tumors assessed by nuclease protection assays are vascular endothelial growth factor and platelet-derived endothelial cell growth factor. Acidic and basic fibroblast growth factor are also detectable. A common feature of these angiogenic factors is heparin binding, so novel analogues of suramin that can compete for heparin binding have been developed. These are more potent in vitro against endothelial cells and are less toxic in vivo, thereby giving a much better therapeutic ratio. Protein kinase C is also important in endothelial growth, as it is in carcinoma growth. Thus, a novel agent inhibiting this pathway, and inducing transforming growth factor-beta production has been assessed in a Phase I trial; this agent is bryostatin. It does not cause marrow suppression and has stimulatory effects of tumor necrosis factor-alpha and interleukin (IL)-6 production. High expression of epidermal growth factor (EGF) receptors and erbB-2 has been related to poor prognosis. EGF receptors are mainly regulated by transcription, as are some cases of high erbB-2 expression. Thus, a novel approach to gene therapy is being developed using direct tumor injection of cDNA, with a tumor specific promoter ligated to the IL-2 gene. This avoids many problems associated with targeting. Because IL-2 stimulation of cytotoxic T-cells will depend on appropriate antigen presentation, human lymphocyte antigen Class I expression was studied, as was the peptide transporter system RING4 (TAP1). Losses were found in 50% of cases, and in some cases only in lymph nodes but not primary cancers, thereby providing evidence for a role in suppressing metastasis. Thus, many new approaches to therapy are possible as a result of understanding growth factors and intracellular signaling pathways.

The role of protein kinase C isoenzymes in the growth inhibition caused by bryostatin 1 in human A549 lung and MCF-7 breast carcinoma cells

Bryostatin I is a natural product currently under clinical evaluation as an antitumor agent. Like the tumor-promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) it activates protein kinase C (PKC). Bryostatin I inhibits the growth of the human-derived A549 lung and MCF-7 adenocarcinoma cell lines, but much more weakly than TPA. The hypotheses were tested that differences between cell lines in their response to bryostatin I are related to cellular PKC isotype content, and that differences between TPA and bryostatin I in their effects on cell growth are associated with differential abilities to modulate specific PKC isoenzymes. PKC isozyme profiles were studied by Western-blot analysis in the cytosol, particulate and nuclear fractions of A549 and MCF-7 cells. PKCs-alpha, -epsilon and -zeta were detected in both cell types with predominant location in the cytosol. Separation of cytosolic PKC isoenzymes in A549 cells by hydroxylapatite column chromatography and determination of PKC activity in fractions yielded a major peak which contained PKC-alpha. Exposure of cells to bryostatin I or TPA for 30 min caused the redistribution of PKCs-alpha and -epsilon from the cytosol to the particulate and nuclear fractions in a concentration-dependent fashion. PKC-epsilon was completely down-regulated by exposure to 10 nM bryostatin I for 18 hr or to TPA for 24 hr. Down-regulation of PKC-alpha was partial at 10 nM and complete at 1 microM of either agent. Bryostatin I inhibited incorporation of [3H]-labelled thymidine into cells only transiently, whereas TPA arrested growth for several days in A549 cells and irreversibly in MCF-7 cells. A549 cells, in which PKC was depleted by exposure to phorbol ester for 9 weeks, were resistant towards bryostatin-induced inhibition of DNA synthesis. The results suggest that the susceptibility of adenocarcinoma cells towards bryostatin-induced growth delay are determined by cellular levels of PKCs-alpha and/or -epsilon. However, differences between bryostatin I and TPA in their abilities to inhibit cell growth do not seem to be intrinsically related to differences in redistribution or down-regulation of specific PKC isoenzymes.

Phorbol 12-myristate 13-acetate stimulates proliferation and ductal morphogenesis and inhibits functional differentiation of normal rat mammary epithelial cells in primary culture

The effect of the tumor promoter phorbol 12-myristate 13-acetate (PMA) on proliferation and differentiation of normal mammary epithelial cells from 50-day-old virgin rats was investigated using a model system that allows for full morphological and functional development of the cells. In this model, mammary epithelial cells are grown within a reconstituted basement membrane in a defined serum-free medium. PMA at a concentration of 10(-6) M effected translocation of protein kinase C from cytosol to membrane. At the same concentration, it stimulated cell proliferation both in the presence and absence of EGF, and this stimulation was observed even when PMA exposure was limited to 15 min at the time of each media change. In contrast to the effect on proliferation, PMA at concentrations of 10(-7) and 10(-6) M inhibited functional differentiation as assessed by casein accumulation. Phorbol 12,13-dibutyrate at 10(-6) M also stimulated proliferation and inhibited casein accumulation and was more effective than PMA in both cases. In contrast, the nonactive tumor promoter 4-alpha PMA had no effect on either proliferation or differentiation. One of the most striking effects of PMA was its ability to stimulate an atypical ductal morphogenesis, as manifested by the formation of intricate web-like colonies, and to inhibit the development of the well-differentiated alveolar-like multilobular colonies. PMA was also shown to completely suppress the growth of the squamous-like colonies that develop when EGF is absent or deficient. These effects of phorbol esters in mammary epithelial cells to stimulate proliferation, inhibit functional differentiation, and stimulate the development of ductal colonies are consistent with the suggestion that the signal transduction pathways evoked by PMA could act to stimulate the growth of initiated cells or render normal cells more sensitive to carcinogen.

Cytostatic and cytotoxic properties of the marine product bistratene A and analysis of the role of protein kinase C in its mode of action

Bistratene A is a polyether which was isolated from the marine ascidian Lissoclinum bistratum Sluiter. The hypothesis has been tested that the cytostatic effect of bistratene A is mediated by modulation of protein kinase C (PKC). Human-derived A549 lung and MCF-7 breast adenocarcinoma cells are extremely sensitive to growth inhibition induced by activators of PKC. Therefore, the effect of bistratene A on these cell lines was compared with that of the known PKC activator 12-O-tetradecanoylphorbol-13-acetate (TPA). The ability of bistratene A to modulate PKC activity in cellular cytosol was assessed to determine the involvement of PKC in the induction of cytostasis. Bistratene A inhibited the growth of both cell lines and initial seeding density determined its cytostatic potency. IC50 values were between 1.0 and 2.9 nM. Bistratene A also had a profound effect on the colony forming ability of A549 cells, preventing clonal growth at 5 nM. Using the incorporation of [3H]thymidine into cells to assess DNA synthetic activity and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide assay to define cytotoxicity, the compound was found to have both cytostatic and cytotoxic properties. Bistratene A decomposed by 50% after only 2.8 hr in cell culture medium. TPA induced rapid motility and the formation of a network of branched colonies in both cell lines grown on Matrigel, whereas bistratene A did not cause the same effect. Cell cytosol was analysed for phorbol ester binding sites after treatment with bistratene A or TPA. Incubation with TPA (10 nM) caused a reduction in binding sites to 57% of binding in control cells after 30 min and to 35% after 24 hr. Bistratene A did not cause a significant change in binding sites. Assays of PKC activity in cellular cytosol revealed that bistratene A was unable to activate or inhibit the enzyme at concentrations of up to 10 microM. The results suggest that bistratene A is an exquisitely potent cytostatic agent in the two cell lines studied, but modulation of PKC is not involved in the mode of action by which it elicits this effect.

Interaction of 2,3,7,8-tetrachlorodibenzo-p-dioxin, 12-O-tetradecanoylphorbol-13-acetate (TPA) and 17 beta-estradiol in MCF-7 human breast cancer cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) and 12-O-tetradecanoylphorbol-13-acetate (TPA) are both tumor promoters which act through different mechanisms. In MCF-7 human breast cancer cells, both TCDD and TPA inhibited constitutive and 17 beta-estradiol-induced cell proliferation but showed no apparent interactive effects. TCDD also inhibited the 17 beta-estradiol-induced secretion of the 52-kDa protein (procathepsin D) and induced CYP1A1 gene expression whereas TPA alone was inactive for these responses. Moreover, TPA did not modulate the TCDD-mediated antiestrogenic or induction responses and did not decrease levels of the nuclear Ah receptor complex as determined in a gel mobility shift assay using a 32P-dioxin responsive element (DRE). The interactions of TPA and TCDD on the metabolism of [13C]glucose to [13C]lactate was also investigated using 13C-nuclear magnetic resonance spectroscopy. The rate of formation of [13C]lactate from [13C]glucose in MCF-7 cells treated with DMSO (control), 1 nM 17 beta-estradiol, 1 nM TCDD, 1 nM TCDD plus 1 nM 17 beta-estradiol, and 0.1 ng/ml TPA plus 1 nM 17 beta-estradiol was 28, 48, 20, 22 and 50 fmol lactate formed/cell/h, respectively. Thus, TCDD, but not TPA, inhibited this estrogen-induced response. However, a comparison of the rate of lactate formation in cells treated with TCDD plus 17 beta-estradiol (22 fmol/cell/h) or TCDD plus 17 beta-estradiol plus TPA (61 fmol/cell/h) showed that TPA significantly inhibited the TCDD-mediated antiestrogenic response. The results of these studies in MCF-7 cells demonstrate that the interactions of TCDD and TPA are highly response-specific and do not involve TPA-mediated downregulation of the nuclear Ah receptor complex.

RRR-alpha-tocopheryl succinate inhibits proliferation and enhances secretion of transforming growth factor-beta (TGF-beta) by human breast cancer cells

The RRR-alpha-tocopheryl succinate form of vitamin E inhibits the proliferation of estrogen receptor-positive and estrogen receptor-negative human breast cancer cell lines in a dose-dependent manner in vitro. Analyses of cell-conditioned medium from RRR-alpha-tocopheryl succinate growth-inhibited cells revealed the presence of a potent antiproliferative activity. Characterization of the antiproliferative activity as transforming growth factor-beta (TGF-beta) was established by 1) growth inhibition of the TGF-beta-responsive Mv1Lu-CCL-64 mink lung and murine CTLL-2 cell lines, 2) combination of physical characteristics including heat stability, acid stability, and Bio-Gel P-60 column chromatography elution profile, and 3) neutralization of the antiproliferative activity in the conditioned media by antibodies specific for TGF-beta.