Relationship of growth stimulated by lithium, estradiol, and EGF to phospholipase C activity in MCF-7 human breast cancer cells

Drugs and Chemicals that Affect the Endocrine System

The mammalian endocrine system is very dynamic, and undergoes frequent physiological fluctions due to diurnal variations and cyclical hormonal feedback systems. Both hormonal modulations and chemicall drug perturbations can affect the reproductive systems in males and females. An endocrine disrup-tor, a contemporary term that has been used to define an agent that disrupts the endocrine system, is a hormone or antihormone mimic that can modulate endocrine signaling pathways. Unfortunately, this terminology is confusing and ambiguous and fails to account for the ever-changing endogenous hormonal milieu. The endocrine system can be disrupted or modulated by many physiologic events (e.g., exercise, menstruation, pregnancy), by pharm acologic intervention (e.g., oral contraceptives, antithyroidal medication), and by nutritional states (e.g., iodine deficiencies, vitamin deficiencies and malnutrition). Seasonal changes (e.g., light and temperature) can also modulate endocrine events. Phytoestrogens and xenoestrogens (e.g., chlorinated pesticides) can also affect the dynamics of the endocrine system. Heavy metals and certain anti-cancer agents can interfere with testicular and ovarian function and may cause sterility. Several sites of action can be involved between a drug/chemical and the endocrine system, including the central nervous system, specific target organs or subpopulation of cells, hormone-transporting proteins, and xenobi-otic-m etabolizing enzymes in the liver. At the endocrine target organ level, mechanism(s) of action may involve competition for a cell receptor or affect non-receptor-mediated actions. Some drug!chemicals may act as hormone agonists (i.e., mimic) or conversely act as hormone antagonists (i.e., an antihormone); other agents may act as partial agonists or partial antagonists. Clearly, there are many internal and external factors that can modulate the endocrine system, yet the paracrine and autocrine regulation of specific target organs is finely regulated, and, importantly, is very resilient to drugl chemical perturbation.

Optimization of an MCF7-E3 Cell Proliferation Assay and Effects of Environmental Pollutants and Industrial Chemicals

Environmental contaminants might adversely affect human health by acting as endocrine disruptors and thus need to be identified. Our objective was to optimize the MCF7 cell proliferation assay to screen industrial chemicals for potential oestrogenic effects. Growth conditions, performance of the clone E3 and WT-MCF7 cells and five methods to derive proliferation indices were compared. The E3 cells were further characterized by testing the effects of transforming growth factorbeta (TGFbeta), epidermal growth factor (EGF), insulin, testosterone, the anti-oestrogen ICI 164,384 (ICI) and environmental contaminants with known oestrogenic potential. Industrial chemicals with unknown oestrogenic effects were then tested. As expected, induction of proliferation by estradiol-17beta (E2) was greater and less variable using the clone E3. To generate proliferation indices, the alamarBlue assay had a sensitivity comparable to that of [(3)H]thymidine incorporation ((3)H-TI). The E3 cells were not responsive to EGF (0-100 ng/ml) or insulin (0-313 ng/ml) but their proliferation was decreased (P<0.05) by TGFbeta (45 ng/ml) and testosterone (10(-8)m), which might be typical of highly oestrogen-responsive MCF7 cells. ICI (5x10(-7)m) inhibited the proliferative effects of 10(-10)m E2 and that of 10(-6)m 4-tert-octylphenol (Op) but not the proliferative effect of 10(-5)m Op, suggesting displacement of ICI by Op or induction of oestrogen-receptor independent proliferation. N-oxydiethylene-2-benzothiazole sulfenamide (OBTS) altered (3)H-TI in the MCF7 cells, although not in a dose related manner. OBTS did not induce uterotrophic effects in immature female rats, or any response in a human oestrogen chimeric receptor/reporter gene assay, suggesting that its effects were not mediated through the binding of the oestrogen-receptor. Seven other industrial chemicals were tested and had no effects. In conclusion, the MCF7 cell proliferation assay is one screening tool that permits identification of chemicals with oestrogenic potential which thus require further testing.

Inositol 1,4,5-trisphosphate-induced Ca2+ signalling is involved in estradiol-induced breast cancer epithelial cell growth

Background

Ca²⁺ is a ubiquitous messenger that has been shown to be responsible for controlling numerous cellular processes including cell growth and cell death. Whereas the involvement of IP₃-induced Ca²⁺ signalling (IICS) in the physiological activity of numerous cell types is well documented, the role of IICS in cancer cells is still largely unknown. Our purpose was to characterize the role of IICS in the control of growth of the estrogen-dependent human breast cancer epithelial cell line MCF-7 and its potential regulation by 17β-estradiol (E₂).

Results

Our results show that the IP₃ receptor (IP₃R) inhibitors caffeine, 2-APB and xestospongin C (XeC) inhibited the growth of MCF-7 stimulated by 5% foetal calf serum or 10 nM E₂. Furthermore, Ca²⁺ imaging experiments showed that serum and E₂ were able to trigger, in a Ca²⁺-free medium, an elevation of internal Ca²⁺ in a 2-APB and XeC-sensitive manner. Moreover, the phospholipase C (PLC) inhibitor U-73122 was able to prevent intracellular Ca²⁺ elevation in response to serum, whereas the inactive analogue U-73343 was ineffective. Western-blotting experiments revealed that the 3 types of IP₃Rs are expressed in MCF-7 cells and that a 48 hours treatment with 10 nM E₂ elevated IP₃R3 protein expression level in an ICI-182,780 (a specific estrogen receptor antagonist)-dependent manner. Furthermore, IP₃R3 silencing by the use of specific small interfering RNA was responsible for a drastic modification of the temporal feature of IICS, independently of a modification of the sensitivity of the Ca²⁺ release process and acted to counteract the proliferative effect of 10 nM E₂.

Conclusions

Altogether, our results are in favour of a role of IICS in MCF-7 cell growth, and we hypothesize that the regulation of IP₃R3 expression by E₂ is involved in this effect.

Lithium treatment enhances estradiol-induced proliferation and hyperplasia formation in the uterus of mice

OBJECTIVES

It is suggested that the Wnt/beta-catenin pathway plays a role in the regulation of estrogen action in the uterus. However, this suggestion has not been proved. Lithium can mimic increased activity of the Wnt/beta-catenin pathway by blocking the activity of glycogen synthase kinase-3beta. There are no data on the effects of lithium on estrogen-dependent processes in the uterus. This work was therefore aimed to examine the action of lithium on proliferative and morphogenetic reactions in the uterus under short- and long-term estrogen treatments.

STUDY DESIGN

Ovariectomized mice received estradiol dipropionate (2 microg per 100g; s.c.) once a week or vehicle and drank tap water with 0.05% lithium chloride or plain tap water for 2 or 30 days.

RESULTS

In animals treated with estradiol and lithium for a month, the incidence of atypical endometrial hyperplasia was significantly higher. In animals treated with estradiol and lithium for 2 days or for a month, uterine mass, the number of mitotic cells and BrdU-labelled cells in luminal epithelium, glandular epithelium, stromal and myometrial cells was markedly greater, whereas the levels of estrogen receptors-alpha, beta-catenin and glycogen synthase kinase-3beta were markedly lower in all uterine compartments, than in those in mice received estradiol with no lithium to drink.

CONCLUSIONS

Lithium treatment results in an increase in estradiol-induced proliferative and morphogenetic changes in the uterus. This action of lithium is associated with decreased expression of estrogen receptors-alpha, beta-catenin and glycogen synthase kinase-3beta in the uterus.

Evaluation of estrogenicity of major heavy metals

We have employed an estrogen receptor dependent transcriptional expression assay and E-Screen assay systems to evaluate the estrogenicity of various heavy metals and their species. Using the former, the following estrogenicity ranking was measured: bis(tri-n-butyltin)>cadmium chloride>antimony chloride>barium chloride=chromium chloride>lithium hydroxide>sodium selenate=lead acetate>stannous chloride. Using the latter, the following estrogenicity ranking was measured: bis(tri-n-butyltin)>cadmium chloride>antimony chloride>lithium hydroxide>barium chloride>sodium selenate>chromium chloride. Especially, bis(tri-n-butyltin), cadmium chloride, antimony chloride, lithium hydroxide, barium chloride, and chromium chloride showed estrogenicity in both assay systems. Recent studies suggesting that bis(tri-n-butyltin), cadmium chloride, and lithium hydroxide have estrogenicities are compatible with the present findings. Furthermore, our studies are the first to suggest that antimony, barium, chromium may be estrogenic. A range of estrogenicity was observed for different species of the same heavy metal. The results demonstrate that an estrogen receptor dependent transcriptional expression assay and the E-Screen assay systems could serve as a useful method to assess the estrogenicity of heavy metals.

Altered prostate growth and daily sperm production in male mice exposed prenatally to subclinical doses of 17alpha-ethinyl oestradiol

Approximately 2 million women in the USA and Europe continue taking oral contraceptives each year during undetected pregnancy due primarily to non-compliance and also to individual variation in sensitivity to hormones in the contraceptives. Prenatal exposure to oral contraceptives containing 17alpha-ethinyl oestradiol (EE) has generally not been associated with an increased incidence of externally observable malformations at birth. The purpose of this study was to assess effects on reproductive organs in adult male mice that had been exposed during gestation day 0 through 17 (equivalent to gestation week 16 in humans) to clinically relevant (approximately 0.5 microg/kg/day) and lower doses of EE. Doses used in this study ranged from 0.002 to 2 microg/kg/day. By 5 months of age, prostate weight was significantly (P < 0.05) higher than controls in most treatment groups of EE (0.02-2 microg/kg). Prostatic androgen receptor populations were significantly elevated only in the 0.02 microg/kg group, suggesting different mechanisms for the increase in prostate weight at different doses. Daily sperm production (DSP) and DSP per gramme of testis were reduced in all treatment groups during adolescence, but not later in adulthood. These findings are consistent with prior studies showing that prenatal exposure of mice to very low doses of a number of oestrogenic chemicals can alter the adult male reproductive system without causing gross external malformations.

Effects of psychotropic drugs on cell proliferation and differentiation

Some of the psychotropic agents widely used for the amelioration of anxiety, depression, and psychosis also show an effect at the cellular proliferation level. Surprisingly little research, however, has been directed to the antitumoral potential of these drugs, alone or in combination with established cancer treatments. Our review of the literature to date has yielded some promising early findings. Ligands active at the benzodiazepine (BZ) receptors have been studied the most extensively and were found to have differential, concentration-dependent effects on the growth and proliferation of both normal and cancer cells. Of the phenothiazines tested, chlorpromazine (CPZ) and perphenazine (PPZ) had the most potent cytotoxic action on fibroblasts and glioma cells. Antiproliferative effects also were noted by these and other agents in leukemic and breast cancer cell lines. Additional psychotropic drugs studied include the atypical antipsychotics, antidepressants, and mood stabilizers, especially lithium. Most of the reported activities were observed in in vitro studies and were achieved at high pharmacological concentrations. Further in vivo studies in well-designed animal models are warranted to determine whether these well-tolerated, relatively inexpensive, and widely available drugs or their derivatives may be added in the future to the armamentarium of cancer pharmacotherapy.

Comparative anti-mitotic effects of lithium gamma-linolenate, gamma-linolenic acid and arachidonic acid, on transformed and embryonic cells

The effects of gamma-linolenic acid (GLA), the lithium salt of gamma-linolenic acid (LiGLA) and arachidonic acid (AA) were compared at doses of 50 microg/ml for periods of 6 and 24 h on cell cycle progression and apoptosis induction in transformed and in normal cells. In WHCO3 (oesophageal cancer) cells and on primary embryonic equine lung cells, we found LiGLA to be the most effective in apoptosis induction. After 24 h, 94% of the WHCO3 cancer cells and 44% of the primary embryonic equine lung cells exposed to LiGLA were apoptotic. The WHCO3 cancer cells were also very susceptible to the apoptosis-inducing effects of AA (56%) and GLA (44%), whereas the embryonic equine lung cells were much less affected by these two fatty acids. After 6 h exposure to all three compounds, most of the cycling WHCO3 cancer cells were blocked in S-phase. After 24 h treatment, some of the S-phase cells exposed to AA and GLA were apparently able to move into the G2/M phase, the LiGLA exposed cells were mostly apoptotic and no cycling cells were present. The primary embryonic equine lung cells were fairly resistant to the cytotoxic effects of GLA and AA. From our studies we conclude that, although LiGLA was the most toxic to the cancer cells, it is apparently less selective, compared to AA and GLA, in the killing of cancer and normal cells. It would also appear that the lithium might have added to the cytotoxic effects of LiGLA. The mechanism needs to be clarified.

Lithium-stimulated proliferation and alteration of phosphoinositide metabolites in MCF-7 human breast cancer cells

Lithium, which is used to treat bipolar psychiatric disorders, can stimulate proliferation of a number of cells in tissue culture. Proliferation of MCF-7 human breast cancer cells, which also respond to EGF and estrogens, was stimulated by LiCl (1-5 mM) within the concentration range that is encountered during human therapy with lithium. Stimulation of growth was specific for lithium; rubidium, potassium, and sodium showed no such effect. In the presence of antiestrogen, lithium stimulated the growth of hormone-dependent breast cancer cells MCF-7, ZR-75-1, and T47D but not hormone-independent MDA-MB-231 cells or an estrogen-independent clone of MCF-7 cells. Lithium-stimulated proliferation was limited by cytotoxicity which could be moderated by added potassium chloride (5-20 mM) in the medium. Each of the mitogens lithium, 17 beta-estradiol, and EGF increased the rate of uptake of myo-inositol into MCF-7 cells. Whether normalized to inositol lipids, to protein, or to DNA, steady-state levels of inositol phosphates were elevated by each of the mitogens including lithium, which inhibits the breakdown of inositol phosphates in the phosphoinositide signaling pathway. These data indicate that therapeutic concentrations of lithium can stimulate the proliferation of human breast cancer cells by a mechanism that may involve the phosphoinositide pathway.