Inhibition of growth-factor-activated proliferation by anti-estrogens and effects on early gene expression of MCF-7 cells

Regulation of autophagic activity by 14-3-3ζ proteins associated with class III phosphatidylinositol-3-kinase

14-3-3s are binding proteins with survival functions in cells by interaction with proteins involved in the regulation of cell fate. The role of 14-3-3 during autophagy was investigated, thus, a forced expression of 14-3-3ζ reduces C2-ceramide-induced autophagy, whereas depletion of 14-3-3ζ promotes autophagy. The 14-3-3 role in autophagyc-related proteins was also investigated. The human vacuolar protein sorting 34 (hVps34), the class III phosphatidylinositol-3-kinase mediates multiple vesicle-trafficking processes such as endocytosis and autophagy, its activation being a requirement for autophagy initiation. Using chromatography techniques, hVps34 were eluted from a 14-3-3 affinity column, showing also a direct interaction with 14-3-3 proteins under physiological condition. Further analysis suggests that hVps34/14-3-3 association is a phorbol-12-myristate-13-acetate-dependent phosphorylated mechanism promoting a strong inhibition of the hVps34 lipid kinase activity, proteins kinase C being the likely kinase involved in phosphorylation and 14-3-3 binding of hVps34 under physiological conditions. Meanwhile, stimulation of autophagy leads to the dissociation of the 14-3-3/hVps34 complex enhancing hVps34 lipid kinase activity. Forced expression of 14-3-3ζ reduces hVps34 kinase activity and depletion of 14-3-3ζ promotes upregulation of this activity. In this study, 14-3-3ζ proteins are shown as a negative regulator of autophagy through regulation of a key component of early stages of the autophagy pathway, such as hVps34.

ApoG2 induces cell cycle arrest of nasopharyngeal carcinoma cells by suppressing the c-Myc signaling pathway

BACKGROUND

apogossypolone (ApoG2) is a novel derivate of gossypol. We previously have reported that ApoG2 is a promising compound that kills nasopharyngeal carcinoma (NPC) cells by inhibiting the antiapoptotic function of Bcl-2 proteins. However, some researchers demonstrate that the antiproliferative effect of gossypol on breast cancer cells is mediated by induction of cell cycle arrest. So this study was aimed to investigate the effect of ApoG2 on cell cycle proliferation in NPC cells.

RESULTS

We found that ApoG2 significantly suppressed the expression of c-Myc in NPC cells and induced arrest at the DNA synthesis (S) phase in a large percentage of NPC cells. Immunoblot analysis showed that expression of c-Myc protein was significantly downregulated by ApoG2 and that the expression of c-Myc's downstream molecules cyclin D1 and cyclin E were inhibited whereas p21 was induced. To further identify the cause-effect relationship between the suppression of c-Myc signaling pathway and induction of cell cycle arrest, the expression of c-Myc was interfered by siRNA. The results of cell cycle analysis showed that the downregulation of c-Myc signaling pathway by siRNA interference could cause a significant arrest of NPC cell at S phase of the cell cycle. In CNE-2 xenografts, ApoG2 significantly downregulated the expression of c-Myc and suppressed tumor growth in vivo.

CONCLUSION

Our findings indicated that ApoG2 could potently disturb the proliferation of NPC cells by suppressing c-Myc signaling pathway. This data suggested that the inhibitory effect of ApoG2 on NPC cell cycle proliferation might contribute to its use in anticancer therapy.

C1q, the recognition subcomponent of the classical pathway of complement, drives microglial activation

Microglia, central nervous system (CNS) resident phagocytic cells, persistently police the integrity of CNS tissue and respond to any kind of damage or pathophysiological changes. These cells sense and rapidly respond to danger and inflammatory signals by changing their cell morphology; by release of cytokines, chemokines, or nitric oxide; and by changing their MHC expression profile. We have shown previously that microglial biosynthesis of the complement subcomponent C1q may serve as a reliable marker of microglial activation ranging from undetectable levels of C1q biosynthesis in resting microglia to abundant C1q expression in activated, nonramified microglia. In this study, we demonstrate that cultured microglial cells respond to extrinsic C1q with a marked intracellular Ca(2+) increase. A shift toward proinflammatory microglial activation is indicated by the release of interleukin-6, tumor necrosis factor-alpha, and nitric oxide and the oxidative burst in rat primary microglial cells, an activation and differentiation process similar to the proinflammatory response of microglia to exposure to lipopolysaccharide. Our findings indicate 1) that extrinsic plasma C1q is involved in the initiation of microglial activation in the course of CNS diseases with blood-brain barrier impairment and 2) that C1q synthesized and released by activated microglia is likely to contribute in an autocrine/paracrine way to maintain and balance microglial activation in the diseased CNS tissue.

Acute neuroprotection by pioglitazone after mild brain ischemia without effect on long-term outcome

Peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists (thiazolidinediones) have anti-inflammatory effects and improve endothelium function. Here, we analyzed the effects of pioglitazone on short- and longer-term outcome after mild transient brain ischemia. 129/SV mice were subjected to 30 min filamentous middle cerebral artery occlusion (MCAo), followed by reperfusion. Post event, animals were treated with daily intraperitoneal (i.p.) pioglitazone (20 mg/kg body weight) or vehicle. Pioglitazone given acutely after transient brain ischemia/reperfusion reduced lesion size and the number of Iba1-expressing microglia in the ischemic striatum at three days. In vitro, pioglitazone attenuated migration and proliferation of primary mouse microglia. However, analysis at 6 weeks after MCAo/reperfusion no longer yielded an effect of pioglitazone on either lesion size or Iba1+ cell counts. Regarding functional longer-term outcome, we also did not detect a beneficial effect of pioglitazone on motor function measured either on the pole test or the wire hanging test or on learning and memory in the Morris water maze. Our study thus underscores the importance of extending experimental stroke studies to an analysis of longer-term outcome.

Pivotal role of glutathione depletion in plasma-induced endothelial oxidative stress during sepsis

OBJECTIVE

Plasma from septic shock patients can induce production of reactive oxygen species (ROS) by human umbilical vein endothelial cells (HUVEC) in vitro. How endothelial cells defend themselves against ROS under increased oxidative stress has not yet been examined. This study investigates the antioxidant defenses of HUVEC exposed to plasma obtained from either septic shock patients or healthy volunteers.

DESIGN

Prospective, observational study.

SETTING

Medical intensive care unit in a university hospital.

PATIENTS

Twenty-five patients with septic shock and 10 healthy volunteers.

INTERVENTIONS

Blood samples were collected within the first 24 hrs of septic shock. In vitro HUVEC production of ROS was studied by spectrofluorimetry using 2',7'-dichlorodihydrofluorescein diacetate fluorescent dye. Reactive nitrogen species were also assessed. Intracellular reduced glutathione (GSH) levels were measured using monochlorobimane fluorescent dye. Activity of catalase and superoxide dismutase in HUVEC were also measured. Cell death was assessed using YOPRO fluorescent dye and the MTT assay.

MEASUREMENTS AND RESULTS

On admission, the septic shock population's mean age was 55 yrs old, the mean Sequential Organ Failure Assessment score was 12, mean simplified acute physiology score was 50, and intensive care unit mortality rate was 45%. Evaluation of HUVEC antioxidant defenses showed a significantly decreased GSH level, increased catalase activity, and unchanged superoxide dismutase activity. ROS levels and cell death were significantly reduced when cells were pretreated with N-acetylcysteine or GSH, but no changes in reactive nitrogen species were observed.

CONCLUSION

This study demonstrates that plasma-induced ROS production by HUVEC is associated with an intracellular decrease in reduced GSH. Both ROS levels and cell death decreased when N-acetylcysteine or GSH were added before exposing the cells to plasma. These data suggest a pivotal role of alterations in GSH in damage caused by sepsis-generated ROS in endothelial cell.

Retinoic acid decreases ATF-2 phosphorylation and sensitizes melanoma cells to taxol-mediated growth inhibition

Cutaneous melanoma is often resistant to chemo- and radiotherapy. This resistance has recently been demonstrated to be due, at least in part, to high activating transcription factor 2 (ATF-2) activity in these tumors. In concordance with these reports, we found that B16 mouse melanoma cells had higher levels of ATF-2 than immortalized, but non-malignant mouse melanocytes. In addition, the melanoma cells had a much higher amount of phosphorylated (active) ATF-2 than the immortalized melanocytes. In the course of determining how retinoic acid (RA) stimulates activating protein-1 (AP-1) activity in B16 melanoma, we discovered that this retinoid decreased the phosphorylation of ATF-2. It appears that this effect is mediated through p38 MAPK, because RA decreased p38 phosphorylation, and a selective inhibitor of p38 MAPK (SB203580) also inhibited the phosphorylation of ATF-2. Since ATF-2 activity appears to be involved in resistance of melanoma to chemotherapy, we tested the hypothesis that treatment of the melanoma cells with RA would sensitize them to the growth-inhibitory effect of taxol. We found that pretreatment of B16 cells with RA decreased the IC50 from 50 nM to 1 nM taxol. On the basis of these findings and our previous work on AP-1, we propose a model in which treatment of B16 cells with RA decreases the phosphorylation of ATF-2, which results in less dimer formation with Jun. The "freed-up" Jun can then form a heterodimer with Fos, resulting in the increased AP-1 activity observed in RA-treated B16 cells. Shifting the balance from predominantly ATF-2:Jun dimers to a higher amount of Jun:Fos dimers could lead a change in target gene expression that reduces resistance to chemotherapeutic drugs and contributes to the pathway by which RA arrests proliferation and induces differentiation.

Autophagic cell death, polyploidy and senescence induced in breast tumor cells by the substituted pyrrole JG-03-14, a novel microtubule poison

JG-03-14, a substituted pyrrole that inhibits microtubule polymerization, was screened against MCF-7 (p53 wild type), MDA-MB231 (p53 mutant), MCF-7/caspase 3 and MCF-7/ADR (multidrug resistant) breast tumor cell lines. Cell viability and growth inhibition were assessed by the crystal violet dye assay. Apoptosis was evaluated by the TUNEL assay, cell cycle distribution by flow cytometry, autophagy by acridine orange staining of vesicle formation, and senescence based on beta-galactosidase staining and cell morphology. Our studies indicate that exposure to JG-03-14, at a concentration of 500 nM, induces time-dependent cell death in the MCF-7 and MDA-MB231 cell lines. In MCF-7 cells, a residual surviving cell population was found to be senescent; in contrast, there was no surviving senescent population in treated MDA-MB231 cells. No proliferative recovery was detected over a period of 15 days post-treatment in either cell line. Both the TUNEL assay and FLOW cytometry indicated a relatively limited degree of apoptosis (<10%) in response to drug treatment in MCF-7 cells with more extensive apoptosis (but <20%) in MDA-MB231 cells; acidic vacuole formation indicative of autophagic cell death was relatively extensive in both MCF-7 and MDA-MB231 cells. In addition, JG-03-14 induced the formation of a large hyperdiploid cell population in MDA-MB231 cells. JG-03-14 also demonstrated pronounced anti-proliferative activity in MCF-7/caspase 3 cells and in the MCF-7/ADR cell line. The observation that JG-03-14 promotes autophagic cell death and also retains activity in tumor cells expressing the multidrug resistance pump indicates that novel microtubule poisons of the substituted pyrroles class may hold promise in the treatment of breast cancer.

Effect of ethanol on human osteosarcoma cell proliferatation, differentiation and mineralization

The habitual consumption of even moderate quantities of alcoholic beverages is clearly associated with reduced bone mass, increased prevalence of skeletal fracture and also it is the major risk factor for the development of secondary osteoporosis. The present in vitro study was designed to determine the dose response effects of ethanol on osteoblast-like human osteosarcoma cells (SaOS-2) proliferation, differentiation, mineralization and cyto-toxicity. SaOS-2 cells were plated in 48 and 6 well culture plates and exposed to different concentrations of ethanol (1, 10, 100, 200 and 300 mM) for 24, 48 and 72 h. At the end of incubation, proliferation of cells was studied using crystal violet Bioassay. The cell lysate was utilized to determine ALP activity and conditioned media were used to measure LDH activity. Histochemical localization of ALP and mineralized nodules were studied from cells treated with ethanol (10 and 100 mM) for 21 days. At higher doses, there was a significant reduction in cell number, whereas at lower doses there were variable effects. In 24 h treatment, the higher doses showed a significant increase in ALP activity, whereas 48 and 72 h treatments showed an opposite trend. Ethanol treatment caused a dose- and time-dependent increase in LDH activity. Ethanol treatment altered the quality of mineralization at 10 mM dose whereas completely inhibited mineralization at 100 mM dose, despite the presence of serum. In conclusion, the toxic effect of ethanol is reflected on cell proliferation, differentiation and mineralization even at low doses and at extended treatment duration.

Antiproliferative effect of diallyl disulfide (DADS) on prostate cancer cell line LNCaP

Garlic has been used throughout the world to treat coughs, toothache, earache, dandruff, hypertension, hysteria, diarrhoea, dysentery, diptheria, vaginitis and many other conditions. Garlic contains a complex mixture of oil and water-soluble organosulfur compounds. Diallyl disulfide (DADS), an oil-soluble constituent of garlic seems to be effective in reducing tumour cells originating from colon, lung and skin. Hence our present study focuses on the dose-dependent effect of DADS on an androgen-dependent prostate cancer cell line. Various concentrations of DADS ranging from 25 to 100 microM were given to LNCaP cells and the activity of lactate dehydrogenase (LDH) prostatic acid phosphatase (PAcP) and the level of prostate specific antigen were studied. DADS reduced the secretory activity of LNCaP cells with the gradual increase in dosage. DADS was found to act as a good antiproliferative agent, which was confirmed by proliferation assay. DADS also induced apoptosis and nuclear segmentation in the higher doses.

Antiepileptic drugs inhibit cell growth in the human breast cancer cell line MCF7

Several antiepileptic drugs (AEDs) are associated with anti-cancer activity. At the same time, many AEDs alter endocrine function with phenytoin (PHT) and phenobarbital (PB) causing-reduced free fractions of sex-steroid hormones, while VPA induces hyperandrogenism. Changes in sex-steroid hormone levels are known to affect apoptosis in endocrine tissue. The aim of the study was to investigate the influence of the antiepileptic drugs PHT, PB, VPA and lamotrigine (LTG) on estrogen-stimulated cell growth of human breast cancer cells (MCF-7), and to evaluate whether this effect could be related to a direct estrogen receptor (ER) binding. VPA reduced cell growth at therapeutically relevant concentrations; half-maximum effect of VPA on cell growth was 230 microM. PHT (100 microM) and PB (10 microM) reduced cell growth by 47 and 21%, respectively. None of the drugs had affinity to isolated estrogen receptors, and excess of estrogen was not able to abolish the growth inhibition provoked by VPA. However, sub-therapeutic concentrations of VPA (100 microM) mimicked estrogen by inducing cell growth (11%) in an estrogen-depleted medium, an effect that was abolished by adding an estrogen receptor antagonist. In conclusion; the estrogen receptor appear to be indirectly activated by sub-therapeutic concentrations of VPA, but therapeutic concentrations of VPA inhibits cell growth by mechanisms that do not seem to involve the estrogen receptor or estrogen stimulation.

Resveratrol is a potent inducer of apoptosis in human melanoma cells

Resveratrol is a plant polyphenol found in grapes and red wine. It has been found to have beneficial effects on the cardiovascular system. Resveratrol also inhibits the growth of various tumor cell lines in vitro and inhibits carcinogenesis in vivo. In this study we examined the effect of resveratrol on growth of two human melanoma cell lines. We found that this plant polyphenol inhibited growth and induced apoptosis in both cell lines, with the amelanotic cell line A375 being more sensitive. The potential involvement of different MAP kinases in the action of resveratrol was also examined. Although resveratrol did not alter the phosphorylation of p38 or JNK MAP kinases in either cell line, it induced phosphorylation of ERK1/2 in A375, but not in SK-mel28 cells. These results suggest that in vivo studies of the effect of resveratrol on melanoma are warranted and that this plant polyphenol might have effectiveness as either a therapeutic or chemopreventive agent against melanoma.

Evaluation of potential implication of membrane estrogen binding sites on ERE-dependent transcriptional activity and intracellular estrogen receptor-alpha regulation in MCF-7 breast cancer cells

The potential involvement of membrane estrogen binding sites in the induction of ERE-dependent transcriptional activity as well as in the regulation of intracellular estrogen receptor alpha (ER-alpha) level under estradiol (E2) stimulation was investigated. Our approach relied upon the use of two DCC-treated E2-BSA (bovine serum albumin) solutions (E2-6-BSA and E2-17-BSA). The absence of detectable free E2 in these solutions was established. Both E2-BSA conjugates led to a transient dose-dependent stimulation of the expression of ERE-luciferase (LUC) reporter gene in MVLN cells (MCF-7 cells stably transfected with a pVit-tk-LUC reporter plasmid), a property not recorded with free E2, which maintained enhanced transcriptional activity during the whole experiment. A very low concentration of E2 (10 pM) synergistically acted with E2-BSA conjugates. Hence, ERE-dependent transcriptional activity induced by these conjugates appeared to result from their known interactions with membrane estrogen binding sites. Anti-estrogens (AEs: 4-OH-TAM and RU 58,668), which antagonize genomic ER responses, abrogated the luciferase activity induced by E2-BSA conjugates, confirming a potential relationship between membrane-related signals and intracellular ER. Moreover, induction of luciferase was recorded when the cells were exposed to IBMX (3-isobutyl-1-methylxanthine) and cyclic nucleotides (cAMP/cGMP), suggesting the implication of the latter in the signal transduction pathway leading to the expression of the reporter gene. Growth factors (IGF-I, EGF and TGF-alpha) also slightly stimulated luciferase and synergistically acted with 10 pM E2, or 1 microM E2-BSA conjugates, in agreement with the concept of a cross-talk between steroids and peptides acting on the cell membrane. Remarkably, E2-BSA conjugates, IBMX and all investigated growth factors failed to down-regulate intracellular ER in MCF-7 cells, indicating the need for a direct intracellular interaction of the ligand with the receptor to regulate its level. ER elimination was, however, found in the presence of conditioned media (CMs) prepared from cells pre-exposed to E2-BSA conjugates, suggesting that they may produce (a) modulator(s) that may enhance receptor down-regulation when released within the medium.

Bisphosphonates induce apoptosis in human breast cancer cell lines

Breast cancer has a prodigious capacity to metastasize to bone. In women with advanced breast cancer and bone metastases, bisphosphonates reduce the incidence of hypercalcaemia and skeletal morbidity. Recent clinical findings suggest that some bisphosphonates reduce the tumour burden in bone with a consequent increase in survival, raising the possibility that bisphosphonates may have a direct effect on breast cancer cells. We have investigated the in vitro effects of bisphosphonates zoledronate, pamidronate, clodronate and EB 1053 on growth, viability and induction of apoptosis in three human breast cancer cell lines (MDA-MB-231, Hs 578T and MCF-7). Cell growth was monitored by crystal violet dye assay, and cell viability was quantitated by MTS dye reduction. Induction of apoptosis was determined by identification of morphological features of apoptosis using time-lapse videomicroscopy, identifying morphological changes in nucleis using Hoechst staining, quantitation of DNA fragmentation, level of expression of bcl-2 and bax proteins and identification of the proteolytic cleavage of Poly (ADP)-ribose polymerase (PARP). All four bisphosphonates significantly reduced cell viability in all three cell lines. Zoledronate was the most potent bisphosphonate with IC50 values of 15, 20 and 3 microM respectively in MDA-MB-231, MCF-7 and Hs 578T cells. Corresponding values for pamidronate were 40, 35 and 25 microM, whereas clodronate and EB 1053 were more than two orders of magnitude less potent. An increase in the proportion of cells having morphological features characteristic of apoptosis, characteristic apoptotic changes in the nucleus, time-dependent increase in the percentage of fragmented chromosomal DNA, down-regulation in bcl-2 protein and proteolytic cleavage of PARP, all indicate that bisphosphonates have direct anti-tumour effects on human breast cancer cells.

EGF activates highly selective estrogen-responsive reporter plasmids by an ER-independent pathway

Epidermal growth factor (EGF) mimics the effects of estrogen on some cells, suggesting that it may activate the estrogen receptor (ER). We examined the ability of EGF to increase expression of several different estrogen-responsive luciferase reporters in MCF-7 breast cancer cells. Although EGF increased reporter activity, this effect was not inhibited by estrogen antagonists and was not dependent on estrogen response elements in the reporter plasmid. Similar results were obtained in BG-1 (ovarian) and Ishikawa (uterine) cells. In ER-negative JEG-3 cells, EGF, but not estradiol, increased reporter activity in the absence of transfected ER. The estrogen antagonist ICI 182780 blocked the ability of estradiol, but not EGF, to stimulate proliferation of T47D breast cancer cells, suggesting that the mitogenic effects of EGF are not mediated by ER. EGF does not appear to activate ER-mediated transcription in these experimental systems, although crosstalk between the estrogen and EGF signaling pathways may occur by other mechanisms.

Characterization of insulin-like growth factor binding protein-3 (IGFBP-3) binding to human breast cancer cells: kinetics of IGFBP-3 binding and identification of receptor binding domain on the IGFBP-3 molecule

Insulin-like growth factor binding protein-3 (IGFBP-3) binds to specific membrane proteins located on human breast cancer cells, which may be responsible for mediating the IGF-independent growth inhibitory effects of IGFBP-3. In this study, we evaluated IGFBP-3 binding sites on breast cancer cell membranes by competitive binding studies with IGFBP-1 through -6 and various forms of IGFBP-3, including synthetic IGFBP-3 fragments. Scatchard analysis revealed the existence of high-affinity sites for IGFBP-3 in estrogen receptor-negative Hs578T human breast cancer cells (dissociation constant (Kd) = 8.19 +/- 0.97 x 10(-9) M and 4.92 +/- 1.51 x 10(5) binding sites/cell) and 30-fold fewer receptors in estrogen receptor-positive MCF-7 cells (Kd = 8.49 +/- 0.78 x 10(-9) M and 1.72 +/- 0.31 x 10(4) binding sites/cell), using a one-site model. These data demonstrate binding characteristics of typical receptor-ligand interactions, strongly suggesting an IGFBP-3:IGFBP-3 receptor interaction. Among IGFBPs, only IGFBP-5 showed weak competition, indicating that IGFBP-3 binding to breast cancer cell surfaces is specific and cannot be attributed to nonspecific interaction with glycosaminoglycans. This was confirmed by showing that synthetic IGFBP-3 peptides containing IGFBP-3 glycosaminoglycan-binding domains competed only weakly for IGFBP-3 binding to the cell surface. Rat IGFBP-3 was 20-fold less potent in its ability to compete with human IGFBP-3(Echerichia coli), as well as 10- to 20-fold less potent for cell growth inhibition than human IGFBP-3, suggesting the existence of species specificity in the interaction between IGFBP-3 and the IGFBP-3 receptor. When various IGFBP-3 fragments were evaluated for affinity for the IGFBP-3 receptor, only those fragments that contain the midregion of the IGFBP-3 molecule were able to inhibit 125I-IGFBP-3(Escherichia coli) binding, indicating that the midregion of the IGFBP-3 molecule is responsible for binding to its receptor. These observations demonstrate that specific, high-affinity IGFBP-3 receptors are located on breast cancer cell membranes. These receptors have properties that support the notion that they may mediate the IGF-independent inhibitory actions of IGFBP-3 in breast cancer cells.

Endocrine response and resistance in breast cancer: a role for the transcription factor Fos

We have previously demonstrated that elevated Fos expression may be important in de novo endocrine resistance in breast cancer. However, changes in Fos expression during endocrine response and subsequently on acquisition of resistance are unknown. This study immunocytochemically monitors Fos protein within sequential biopsies from primary human breast cancer patients obtained pre-treatment (T1), during tamoxifen therapy (T2, T3) and on disease progression (T5), examining in parallel proliferation [i.e., MIBI (Ki67) immunostaining, mitotic activity], cellularity and endocrine response. Significantly diminished Fos, proliferation and cellularity were observed after 6 weeks of therapy in patients exhibiting a better quality and/or duration of response, while modest Fos increases and a maintained proliferation and cellularity were seen in poorer responders. Decreases in Fos, proliferation and cellularity at 6 months similarly hallmarked better responders. We confirmed a significant association between de novo resistance and elevated Fos and proliferation. Additionally, however, these parameters increased at the time of disease relapse over pre-treatment and "on therapy" values. Our data indicate that tamoxifen response involves a reduction in both tumor cell proliferation and cell survival, potentially entailing diminished Fos protein expression in better-responding patients. Our data are also supportive of elevated Fos expression being involved in the departure from endocrine control inherent in both primary and acquired resistance.

Role of astroglia and insulin-like growth factor-I in gonadal hormone-dependent synaptic plasticity

Gonadal hormones exert a critical influence over the architecture of specific brain areas affecting the formation of neuronal contacts. Cellular mechanisms mediating gonadal hormone actions on synapses have been studied extensively in the rat arcuate nucleus, a hypothalamic center involved in the feed-back regulation of gonadotropins. Gonadal steroids exert organizational and activational effects on arcuate nucleus synaptic connectivity. Perinatal testosterone induces a sexual dimorphic pattern of synaptic contacts. Furthermore, during the preovulatory and ovulatory phases of the estrous cycle there is a transient disconnection of inhibitory synaptic inputs to the somas of arcuate neurons. This synaptic remodeling is induced by estradiol, blocked by progesterone, and begins with the onset of puberty in females. Astroglia appear to play a significant role in the organizational and the activational hormone effects on neuronal connectivity by regulating the amount of neuronal membrane available for the formation of synaptic contacts and by releasing soluble factors, such as insulin-like growth factor I (IGF-I), which promote the differentiation of neural processes. Recent evidence indicates that gonadal steroids and IGF-I may interact in their trophic effects on the neuroendocrine hypothalamus. Estradiol and IGF-I promote the survival and morphological differentiation of rat hypothalamic neurons in primary cultures. The effect of estradiol depends on IGF-I, while the effects of both estradiol and IGF-I depend on estrogen receptors. Furthermore, estrogen activation of astroglia in hypothalamic tissue fragments depends on IGF-I receptors. These findings indicate that IGF-I may mediate some of the developmental and activational effects of gonadal steroids on the brain and suggest that IGF-I may activate the estrogen receptor to induce its neurotrophic effects on hypothalamic cells. In addition, IGF-I levels in the neuroendocrine hypothalamus are regulated by gonadal steroids. IGF-I levels in tanycytes, a specific astroglia cell type present in the arcuate nucleus and median eminence, increase at puberty, are affected by neonatal androgen levels, show sex differences, and fluctuate in accordance to the natural variations in plasma levels of ovarian steroids that are associated with the estrous cycle. These changes appear to be mediated by hormonal regulation of IGF-I uptake from blood or cerebrospinal fluid by tanycytes. These results suggest that tanycytes may be involved in the regulation of neuroendocrine events in adult rats by regulating the availability of IGF-I to hypothalamic neurons. In summary, IGF-I and different forms of neuron-astroglia communication are involved in the effects of estradiol on synaptic plasticity in the hypothalamic arcuate nucleus.

Defining a role for c-Myc in breast tumorigenesis

The proto-oncogene c-myc is commonly amplified and overexpressed in human breast tumors, and the tumorigenic potential of c-myc overexpression in mammary tissue has been confirmed by both in vitro and in vivo models of breast cancer. However, the mechanisms by which Myc promotes tumorigenesis are not well understood. Recent evidence indicates that Myc can promote cell proliferation as well as cell death via apoptosis. These studies provide new insight and impetus in defining a role for c-Myc in breast tumorigenesis and may point toward novel targets for breast cancer therapy.

Vitamin D receptors and anti-proliferative effects of vitamin D derivatives in human pancreatic carcinoma cells in vivo and in vitro

The GER human pancreatic carcinoma cell line possesses receptors for 1,25-dihydroxyvitamin D3. We report that the vitamin D analogue EB 1089 inhibits the growth of these cells in vitro and when grown as tumour xenografts in immunodeficient mice. Tumour-bearing mice were given EB 1089 at a dose of 5 microg kg(-1) body weight i.p. thrice weekly for 4-6 weeks. Tumour growth was significantly inhibited in treated animals compared with controls in the absence of hypercalcaemia. These findings may have therapeutic implications in pancreatic cancer.

Interaction of insulin-like growth factor-I and estradiol signaling pathways on hypothalamic neuronal differentiation

Neurotrophic effects of estradiol and insulin-like growth factor-I were assessed in primary cultures from fetal rat hypothalamus. Cultured neurons were immunostained with an antibody for the microtubule-associated protein-2. While both estradiol and insulin-like growth factor-I increased the number of microtubule-associated protein-2-immunoreactive neurons and the extension of immunoreactive processes, the effect of these two factors was not additive. The estradiol-induced increases in neuronal numbers and extension of neuronal processes were blocked by either the estrogen receptor antagonist ICI 182,780 or by an anti-sense oligonucleotide to the estrogen receptor. Furthermore, incubation of the cultures with an anti-sense oligonucleotide directed against the insulin-like growth factor-I messenger RNA also blocked the effect of estradiol. In turn, the effects of insulin-like growth factor-I were blocked by the estrogen receptor antagonist ICI 182,780 and by the anti-sense oligonucleotide to the estrogen receptor. These findings suggest that estradiol-induced activation of the estrogen receptor in developing hypothalamic cells requires the presence of insulin-like growth factor-I, and that both estradiol and insulin-like growth factor-I use the estrogen receptor as a mediator of their trophic effects on hypothalamic neurons.

A flow cytometric study of c-erbB-3 expression in breast cancer

In order to assess the specificity of biotinylated anti-c-erbB-3 antibody, screening was performed on a series of tumour cell lines and lymphocytes. Staining was found to be consistent, with good reproducibility. Twenty-nine consecutive breast cancer samples were obtained from women treated with tamoxifen and undergoing elective mastectomy. Twenty-eight invasive ductal carcinomas and 1 DCIS were stained for c-erbB-3 expression: 2 were grade I (Bloom and Richardson), 15 grade II, and 11 grade III tumours, 1 being unclassified; 16 were axillary node positive and 10 node negative; in 2 cases no nodes were sampled. Tumours examined by flow cytometry were stained with cytokeratin FITC antibody and the cytokeratin-positive population gated. Using Mann-Whitney analysis no association was seen between c-erbB-3 expression and Bloom and Richardson grade or axillary node status. In the tumour samples c-erbB-3 expression was found to show as association with EGF-R (P = 0.021 r2 = 0.16), PgR (P = 0.02, r2 = 0.16), c-myc (P < 0.0001, r2 = 0.5), c-jun (P = 0.001, r2 = 0.4) and c-fos (P = 0.001, r2 = 0.5) but not with c-erbB-2 (P = 0.2, r2 = 0.06), ER (P = 0.4, r2 = 0.02) or p53 1801 (P = 0.05, r2 = 0.2). Expression of c-erbB-3 may not be an independent marker of prognosis, but it is associated with other markers of poor prognosis and early cellular events linked with aberrant growth and differentiation.

Mechanisms of action of endocrine treatment in breast cancer

Endocrine treatment plays an important role in the therapy of breast cancer. While the basic mechanisms are understood, additional mechanisms may be of importance to their action and they may also contribute to the mechanism(s) of acquired resistance. Currently, several novel drugs are entering into clinical trials. Observations of the absence or presence of cross resistance to novel 'pure' steroidal antiestrogens and the non-steroidal tamoxifen may add important information to our understanding of the mechanisms of action of both classes of drugs. Similarly, exploration of different aromatase inhibitors in sequence or concert, as well as the combining of different endocrine treatment options may be warranted. Additionally, alterations in different biochemical parameters such as growth factors should not only be carefully explored in relation to treatment options but should also be followed during the course of treatment to asess alterations over time and in relation to the development of drug resistance.

Intracellular levels and secretion of insulin-like-growth-factor-binding proteins in MCF-7/6, MCF-7/AZ and MDA-MB-231 breast cancer cells. Differential modulation by estrogens in serum-free medium

The synthesis and secretion of insulin-like growth factor binding proteins (IGFBPs) were studied in MDA-MB-231 (estrogen-receptor-negative), MCF-7/6 (estrogen-receptor-positive, invasive) and in MCF-7/AZ (estrogen-receptor-positive, non-invasive) human breast carcinoma cell lines. Cells were grown or maintained in a chemically defined medium. Under these conditions, we found different patterns of IGFBPs in the three cell types. MDA-MB-231 cells secrete most of the IGFBPs they produce whereas MCF-7/6 and MCF-7/AZ cells maintain a high intracellular level. In MDA-MB-231 cells, the major IGFBP is IGFBP-4 which is the minor form in MCF-7/6 and MCF-7/AZ cells. IGFBP-2 and IGFBP-5 are predominant in MCF-7/6 cells while MCF-7/AZ cells produce far less IGFBPs and do not contain detectable amounts of 29-32-kDa forms (IGFBP-5). In MCF-7/6 cells, estradiol-17 beta specifically decreases both the intracellular content and secretion of IGFBP-2 and IGFBP-5. Estrogen regulation of IGFBPs cell content and secretion was found to be tamoxifen-resistant, and only slightly antagonized by ICI 182,780, a pure antiestrogen. The function of these regulations relative to the invasive phenotype and proliferation has now to be determined.

Studies on heterocycle-based pure estrogen antagonists

2-Phenylindoles and isosteric structures such as benzo[b]furans and benzo[b]thiophenes were used as estrogen receptor binding moiety for the syntheses of new nonsteroidal antiestrogens. The antiestrogenic potency was considerably enhanced following the introduction of polar functional groups into the side chain in position 1 (indole) or 3 (benzofuran, benzothiophene). The amino compounds could be characterized as mixed agonist/antagonists. Among the derivatives with an amide group compounds without any agonistic activity both in vitro and in vivo were identified. The amide function can be replaced by alkylthio or alkylsulfonyl groups without changing the endocrine profile very much. In this study, the estrogenic activity was determined in a new transcription assay with luciferase as the reporter. The results obtained in this assay were in very good agreement with those from the conventional mouse uterine weight test. Antitumor activity was determined in hormone-sensitive MCF-7 breast cancer cells. There was no difference in activity between partial and pure estrogen antagonists. However, the derivatives with sulfur containing side chains were much more active than the corresponding heterocycles with amino or carbamoyl functions. They reached IC50-values of about 1 nM. 2-Phenylindoles and 2-phenylbenzothiophenes were rather similar in their potencies whereas the benzofuran derivatives were less active probably due to their lower binding affinities for the ER.

Transforming growth factor-beta-induced cell growth inhibition in human breast cancer cells is mediated through insulin-like growth factor-binding protein-3 action

Most estrogen receptor-negative breast cancer cells, including Hs578T cells, express mRNAs encoding insulin-like growth factor-binding protein (IGFBP)-3, as well as transforming growth factor (TGF)-beta receptors. Our previous studies (Oh, Y., Muller, H. L., Lamson, G., and Rosenfeld, R. G. (1993) J. Biol. Chem. 268, 14964-14971; Oh, Y., Muller, H. L., Pham, H. M., and Rosenfeld, R. G. (1993) J. Biol. Chem. 268, 26045-26048) have demonstrated a significant inhibitory effect of exogenous IGFBP-3 on Hs578T cell growth and existence of IGFBP-3-specific receptors that may mediate those direct inhibitory effect of IGFBP-3. TGF-beta is also a potent growth inhibitor in human breast cancer cells in vitro and regulates IGFBP-3 production in different cell systems, suggesting that IGFBP-3 is a major anti-proliferative factor and a key element for TGF-beta-induced growth inhibition in human breast cancer cells. In support of this hypothesis, we have demonstrated using Hs578T cells that: 1) TGF-beta stimulates IGFBP-3 gene expression and production prior to its inhibition of cell growth, 2) treatment with an IGFBP-3 antisense oligodeoxynucleotide selectively inhibits TGF-beta-induced IGFBP-3 synthesis and cell growth inhibition, and 3) treatment with IGF-II and IGF-II analogs diminish TGF-beta effects by blocking TGF-beta-induced binding of IGFBP-3 to the cell surface. These findings suggest that IGFBP-3 is a major anti-proliferative factor and a key element in TGF-beta-induced growth inhibition in human breast cancer cells.

Insulin-like growth factors and breast cancer

Several years of research have indicated that the insulin-like growth factor (IGF) family of ligands, receptors and binding proteins are expressed in human breast cancer. The ligands are potent mitogens for breast cancer cell lines, and blockade of IGF signaling inhibits tumor growth. The IGFs can be regulated in normal and neoplastic tissue, indicating their important role in proliferation. For example, estrogen, a hormone important in the growth and progression of breast cancer is able to alter expression of IGF ligands, receptors and binding proteins. In addition, recent data now indicate that IGF ligands can also activate estrogen receptor (ER) in a ligand-independent manner. The apparent cross-talk between IGF and ER signaling is especially important to consider since anti-estrogens, such as tamoxifen, are a major modality for the treatment of breast cancer. Recent data suggest that IGFs may also be involved in tamoxifen resistance, through upregulation of the IGF-I receptor. Thus blockade of IGF signaling in combination with tamoxifen may prove to be a beneficial treatment for breast cancer patients.

Preclinical data for Droloxifene

The new antiestrogen Droloxifene has a 10-60-fold higher binding affinity to the estrogen receptor (ER) compared to the related compound Tamoxifen. A similar relationship was found in growth inhibition studies which showed that Droloxifene inhibited the different ER positive human breast cancer cells more effectively than Tamoxifen, predominantly in drug concentrations which are found in humans during therapy. As another consequence of the high stability of the complex formed by Droloxifene binding to the ER, intermittent exposures with clinically relevant concentrations of Droloxifene brought about effective growth inhibition of human ER positive tumor cells even after short-term application. Droloxifene was found, like Tamoxifen, to block human breast cancer cells in G1-phase of the cell cycle. Moreover, cell-cycle data confirmed the superior growth-inhibiting potency of Droloxifene compared to Tamoxifen. Droloxifene was also found to effectively induce expression of the negative growth factor TGF-beta, to inhibit IGF-I stimulated cell growth and to prevent estrogen-stimulated proto-oncogene c-myc expression. Unlike Tamoxifen, Droloxifene is a potent inhibitor of protein biosynthesis in ER-positive breast cancer cells at physiologically relevant concentrations. Lower estrogenic and higher antiestrogenic effects on immature rat uterus indicate a higher therapeutic index for Droloxifene compared to Tamoxifen. In vivo, Droloxifene displayed increased growth inhibition of different tumors of animal (R3230AC and 13762) and human origin (T61). Furthermore, it was found that the two structurally similar drugs differ in their toxicologic characteristics in the following important respects: Droloxifene is devoid of any in vivo or in vitro carcinogenic or mutagenic effects, whereas Tamoxifen causes liver tumors in rats, induces DNA adduct formation in rats and hamsters and shows transforming activity in SHE-cells (Syrian hamster embryo fibroblasts). Considerably less toxicity and a lower level of intrinsic estrogenicity was observed even after maximum long-term exposure of different animal species to Droloxifene, in comparison with Tamoxifen. Therefore, it can be assumed that Droloxifene may represent an important step forward in the treatment of mammary carcinomas in women through its better tolerability and increased efficacy compared with Tamoxifen. For long-term adjuvant or preventive treatment of breast cancer, Droloxifene may well be the safer choice.

Effects of 4-hydroxytamoxifen and a novel pure antioestrogen (ICI 182780) on the clonogenic growth of human breast cancer cells in vitro

We have investigated the effects on breast cancer cell growth of 4-hydroxytamoxifen (4OHT), a conventional antioestrogen with agonist activity, and 7 alpha-[9-(4,4,5,5,5-pentafluoropentylsulphinyl)nonyl]oestra- 1,3,5,(10)- triene-3,17 beta-diol (ICI 182780), a novel, pure antioestrogen, using established human breast cancer cell lines and cancer cells obtained directly from breast cancer patients with malignant pleural effusions who had relapsed on tamoxifen. The effects of the two agents were assessed using the Courtenay-Mills clonogenic assay, which measures the growth of single cancer cells as colonies suspended in soft agar. The standard assay was modified by the use of defined serum- and phenol red-free growth medium. The growth of oestrogen receptor (ER)-positive MCF-7 cells in the assay was oestrogen responsive. Both antioestrogens inhibited the stimulatory effects of 1 nM oestradiol, but ICI 182780 caused significantly greater inhibition than 4OHT at 0.1-1.0 microM concentrations. In the absence of oestradiol, 4OHT but not ICI 182780 caused significant stimulation of colony formation at low (0.01-1.00 nM) concentrations. Neither antioestrogen had any effects on colony formation by the ER-negative Hs578T cell line. Successful colony formation was obtained in primary cultures from six out of eight malignant effusions. Colony formation was significantly stimulated by 0.1 nM oestradiol in four cases and by 10 nM 40HT in two cases. In contrast, ICI 182780 exhibited no intrinsic stimulatory activity and significantly inhibited both oestradiol- and 4OHT-stimulated cell growth. We conclude that the agonist activity of 4OHT and other conventional antioestrogens may cause treatment failure in some patients by stimulating breast cancer cell growth. The new, pure antioestrogen ICI 182780 is a more potent oestrogen antagonist than 4OHT and exhibits no growth-stimulatory activity. This agent may therefore offer therapeutic advantages over conventional antioestrogens in patients with advanced breast cancer and may be effective after conventional agents have failed.

Association of insulin-like growth-factor-I-induced DNA synthesis with phosphorylation and nuclear exclusion of p53 in human breast cancer MCF-7 cells

Human breast cancer MCF-7 cells, growth-arrested by serum starvation, were stimulated with recombinant human insulin-like growth factor-I (IGF-I). An increase in DNA synthesis was induced 20 hr later, which was as effective as that induced by serum. The increase in DNA synthesis was significantly inhibited either by antibody to the IGF-I receptor or by the tyrosine kinase inhibitor, methyl-2,5-dihydroxycinnamate (2,5-MeC). The IGF-I-induced DNA synthesis coincided with an elevated level of phosphorylation of p53 on tyrosine and an alteration in the subcellular distribution of the protein from the nucleus to the cytoplasm. Whereas the increases in DNA synthesis and p53 phosphorylation were inhibited by antibody to the IGF-I receptor and by 2,5-Mec, the nuclear exclusion of p53 was prevented by the antibody and also, although not significantly, by 2,5-Mec. The results suggest that growth stimulation of MCF-7 cells by IGF-I is accompanied by tyrosine phosphorylation and nuclear exclusion of p53.

Contrasting action of antiestrogen (ICI-182780) for preventing initiation of embryo implantation by estradiol or epidermal growth factor (EGF)

The pure estrogen antagonist ICI-182780, at doses above 50 micrograms/kg, effectively inhibited the initiation of embryo implantation in rats when administered on day 4 of pregnancy (day 1 = sperm positive). The same dose inhibited the implantation initiating effect of intravenous 25 ng of estradiol-17 beta in delayed implanting progesterone-primed hypophysectomized rats. In contrast, the anti-estrogen at a dose of 1 mg/kg was ineffective at inhibiting the initiation of implantation induced by intrauterine plus intravenous administration of murine epidermal growth factor to delayed implanting rats. The growth factor also initiated implantation of blastocysts transferred from donor animals injected with the anti-estrogen to progesterone-primed hypophysectomized recipients. The results clearly demonstrate that the implantation initiating effect of the growth factor is not inhibited by a pure estrogen antagonist, and therefore this estrogenic function does not appear to require action initiated by the classical estrogen receptor.