Melatonin suppression of aerobic glycolysis (Warburg effect), survival signalling and metastasis in human leiomyosarcoma.

Leiomyosarcoma (LMS) represents a highly malignant, rare soft tissue sarcoma with high rates of morbidity and mortality. Previously, we demonstrated that tissue-isolated human LMS xenografts perfused in situ are highly sensitive to the direct anticancer effects of physiological nocturnal blood levels of melatonin which inhibited tumour cell proliferative activity, linoleic acid (LA) uptake and metabolism to 13-hydroxyoctadecadienoic acid (13-HODE). Here, we show the effects of low pharmacological blood concentrations of melatonin following oral ingestion of a melatonin supplement by healthy adult human female subjects on tumour proliferative activity, aerobic glycolysis (Warburg effect) and LA metabolic signalling in tissue-isolated LMS xenografts perfused in situ with this blood. Melatonin markedly suppressed aerobic glycolysis and induced a complete inhibition of tumour LA uptake, 13-HODE release, as well as significant reductions in tumour cAMP levels, DNA content and [(3) H]-thymidine incorporation into DNA. Furthermore, melatonin completely suppressed the phospho-activation of ERK 1/2, AKT, GSK3ß and NF-kB (p65). The addition of S20928, a nonselective melatonin antagonist, reversed these melatonin inhibitory effects. Moreover, in in vitro cell culture studies, physiological concentrations of melatonin repressed cell proliferation and cell invasion. These results demonstrate that nocturnal melatonin directly inhibited tumour growth and invasion of human LMS via suppression of the Warburg effect, LA uptake and other related signalling mechanisms. An understanding of these novel signalling pathway(s) and their association with aerobic glycolysis and LA metabolism in human LMS may lead to new circadian-based therapies for the prevention and treatment of LMS and potentially other mesenchymally derived solid tumours.

Doxorubicin resistance in breast cancer is driven by light at night-induced disruption of the circadian melatonin signal.

Chemotherapeutic resistance, particularly to doxorubicin (Dox), represents a major impediment to successfully treating breast cancer and is linked to elevated tumor metabolism and tumor over-expression and/or activation of various families of receptor- and non-receptor-associated tyrosine kinases. Disruption of circadian time structure and suppression of nocturnal melatonin production by dim light exposure at night (dLEN), as occurs with shift work, and/or disturbed sleep-wake cycles, is associated with a significantly increased risk of an array of diseases, including breast cancer. Melatonin inhibits human breast cancer growth via mechanisms that include the suppression of tumor metabolism and inhibition of expression or phospho-activation of the receptor kinases AKT and ERK1/2 and various other kinases and transcription factors. We demonstrate in tissue-isolated estrogen receptor alpha-positive (ERα+) MCF-7 human breast cancer xenografts, grown in nude rats maintained on a light/dark cycle of LD 12:12 in which dLEN is present during the dark phase (suppressed endogenous nocturnal melatonin), a significant shortening of tumor latency-to-onset, increased tumor metabolism and growth, and complete intrinsic resistance to Dox therapy. Conversely, a LD 12:12 dLEN environment incorporating nocturnal melatonin replacement resulted in significantly lengthened tumor latency-to-onset, tumor regression, suppression of nighttime tumor metabolism, and kinase and transcription factor phosphorylation, while Dox sensitivity was completely restored. Melatonin acts as both a tumor metabolic inhibitor and circadian-regulated kinase inhibitor to reestablish the sensitivity of breast tumors to Dox and drive tumor regression, indicating that dLEN-induced circadian disruption of nocturnal melatonin production contributes to a complete loss of tumor sensitivity to Dox chemotherapy.

Molecular deficiency (ies) in MT1 melatonin signaling pathway underlies the melatonin-unresponsive phenotype in MDA-MB-231 human breast cancer cells.

Melatonin has been shown repeatedly to inhibit the growth of human breast tumor cells in vitro and in vivo. Its antiproliferative effects have been well studied in MCF-7 human breast cancer cells and several other estrogen receptor α (ERα)-positive human breast cancer cell lines. However, the MDA-MB-231 breast cancer cell line, an ERα-negative cell line widely used in breast cancer research, has been shown to be unresponsive to melatonin's growth-suppressive effect in vitro. Here, we examined the effect of melatonin on the cell proliferation of several ERα-negative breast cancer cell lines including MDA-MB-231, BT-20, and SK-BR-3 cells. Although the MT1 G-protein-coupled receptor is expressed in all three cell lines, melatonin significantly suppressed the proliferation of SK-BR-3 cells without having any significant effect on the growth of MDA-MB-231 and BT-20 cells. We confirmed that the MT1-associated Gα proteins are expressed in MDA-MB-231 cells. Further studies demonstrated that the melatonin unresponsiveness in MDA-MB-231 cells may be caused by aberrant signaling downstream of the Gαi proteins, resulting in differential regulation of ERK1/2 activity.

Study on the Psychological Effects of Intangible Cultural Heritage Advertising with Different Degrees of Situational Involvement.

This review addresses the issues of low consumer engagement and market development difficulties in intangible cultural heritage (ICH) products. Dietary ICH products are selected as research materials to discover contemporary commercial survival paths for ICH through the psychological effects of advertising. Firstly, this study examines the respective advantages of rational and emotional ICH advertisement in terms of emotional responses, cognitive responses, attitudes, recall, and recognition. Then, it explores the effects of different ICH advertisement types (rational advertisement, emotional advertisement) and different degrees of situational involvement (purchasing for oneself, purchasing gifts for others) on the advertising effectiveness, aiming to identify factors influencing the psychological effects of ICH advertisement. Through statistical analysis, the main conclusions are as follows: (1) Rational ICH advertisement prompts consumers to consider the actual attributes of ICH products, leading to a more positive purchasing attitude. (2) Emotional ICH advertisement is more effective in eliciting positive emotions from consumers and enhancing brand memory. (3) Under the scenario of purchasing a gift for others, emotional ICH advertisement has a more positive impact on consumers' attitudes towards advertising. (4) Under different degrees of situational involvement, rational ICH advertisement has a more positive impact on consumers' purchasing attitudes. This study not only provides guidance for optimizing ICH advertising strategies but also offers new directions for market expansion, contributing valuable insights into cultural heritage preservation, as well as the development and protection of ICH.

Mechanochemical degradation performance of lindane in different types of soils: The effects of soil properties and elemental components.

Although mechanochemical remediation of organic-contaminated soil has received substantial attention in recent years, the effects of soil properties on soil remediation performance are not clear. In this work, the properties and elemental components of 16 soils were tested, and the mechanochemical degradation performance of lindane in these soils was investigated through experiments. Most importantly, the relationships between soil variables and the mechanochemical degradation rates of lindane in the additive-free and CaO systems were elucidated. The results showed that the mechanochemical degradation efficiencies of lindane in the 16 soils were significantly different without additives, with a range of 31.0 %-97.2 % after 4 h. The mechanochemical degradation rates of lindane in the 16 soils varied from 0.7 h-1 to 15 h-1 after the addition of 9 % CaO. Correlation analysis, redundancy analysis and the partial least squares path modeling results clearly showed that the main factors affecting the reaction rate (k1) without additives were organic matter (-) > clay (+) > bound water (-) > Si (+). After the addition of 9 % CaO, the order in which the main factors affected the reaction rate (k2) was organic matter (-) > bound water (-) > Ti/Fe/Al (-) > pH (+) > clay (+). The established and corrected multiple nonlinear regression equations can be used to accurately predict the mechanochemical degradation performance of hexachlorocyclohexanes in actual soils with and without additives.

Comprehensive insight into mercury contamination in atmospheric, terrestrial and aquatic ecosystems surrounding a typical antimony-coal mining district.

This study comprehensively investigated mercury (Hg) contents of various environmental compartments in a typical antimony-coal mining area with intensive industrial activities over the past 120 years to analyze Hg environmental behaviors and evaluate Hg risks. The total mercury (THg) contents in river water, sediments, soils, PM10, dust falls, vegetables and corns were 1.16 ± 0.63 µg/L, 2.01 ± 1.64 mg/kg, 1.87 ± 3.88 mg/kg, 7.87 ± 18.68 ng/m3, 13.01 ± 14.53 mg/kg, 0.30 ± 0.34 mg/kg and 3.11 ± 0.51 µg/kg, respectively. The δ202Hg values in soils and dust falls were - 1.58 ∼ 0.12‰ and 0.25 ∼ 0.30‰, respectively. Environmental samples affected by industrial activities in the Xikuangshan (XKS) presented higher THg and δ202Hg values. Binary mixing model proved that atmospheric deposition with considerable Hg deposition flux (0.44 ∼ 6.40, 3.12 ± 2.20 mg/m2/y) in the XKS significantly contributed to Hg accumulations on surface soils. Compared with soils, sediments with more frequent paths and higher burst probabilities presented higher dynamic Hg risks. Children were faced higher health risk of multiple Hg exposure than adults. Furthermore, the health risk of THg by consuming leaf vegetables deserved more attention. These findings provided scientific basis for managing Hg contamination.

Insulin and IGF1 enhance IL-17-induced chemokine expression through a GSK3B-dependent mechanism: a new target for melatonin's anti-inflammatory action.

Obesity is a chronic inflammation with increased serum levels of insulin, insulin-like growth factor 1 (IGF1), and interleukin-17 (IL-17). The objective of this study was to test a hypothesis that insulin and IGF1 enhance IL-17-induced expression of inflammatory chemokines/cytokines through a glycogen synthase kinase 3ß (GSK3B)-dependent mechanism, which can be inhibited by melatonin. We found that insulin/IGF1 and lithium chloride enhanced IL-17-induced expression of C-X-C motif ligand 1 (Cxcl1) and C-C motif ligand 20 (Ccl20) in the Gsk3b(+/+) , but not in Gsk3b(-/-) mouse embryonic fibroblast (MEF) cells. IL-17 induced higher levels of Cxcl1 and Ccl20 in the Gsk3b(-/-) MEF cells, compared with the Gsk3b(+/+) MEF cells. Insulin and IGF1 activated Akt to phosphorylate GSK3B at serine 9, thus inhibiting GSK3B activity. Melatonin inhibited Akt activation, thus decreasing P-GSK3B at serine 9 (i.e., increasing GSK3B activity) and subsequently inhibiting expression of Cxcl1 and Ccl20 that was induced either by IL-17 alone or by a combination of insulin and IL-17. Melatonin's inhibitory effects were only observed in the Gsk3b(+/+) , but in not Gsk3b(-/-) MEF cells. Melatonin also inhibited expression of Cxcl1, Ccl20, and Il-6 that was induced by a combination of insulin and IL-17 in the mouse prostatic tissues. Further, nighttime human blood, which contained high physiologic levels of melatonin, decreased expression of Cxcl1, Ccl20, and Il-6 in the PC3 human prostate cancer xenograft tumors. Our data support our hypothesis and suggest that melatonin may be used to dampen IL-17-mediated inflammation that is enhanced by the increased levels of insulin and IGF1 in obesity.

Mercury contamination in the water and sediments of a typical inland river - Lake basin in China: Occurrence, sources, migration and risk assessment.

In the area affected by non-ferrous metal mining activities, mercury (Hg) contamination in the water and sediments posed potential risks to ecology and human health. In this study, river water and sediment samples were collected in the Zijiang river - South Dongting Lake basin to analyze Hg residues, identify potential Hg sources and evaluate the ecological and health risks posed by Hg contamination. In this study, the average concentrations of THg, PHg, DHg and DMeHg in river water were 38.05 ± 27.13 ng/L, 25.18 ± 26.83 ng/L, 12.88 ± 9.64 ng/L and 0.29 ± 0.07 ng/L, respectively. The THg and MeHg contents in sediments were 234.24 ± 152.93 µg/kg and 0.48 ± 0.16 µg/kg, respectively. The more enrichment of Hg in sediments was observed in the Zijiang River than in the South Dongting Lake, especially in the upstream and midstream regions. Two potential Hg sources in the basin were identified by correlation matrix, principal component analysis (PCA) and positive matrix factorization (PMF) model. The comparable Hg flux with other rivers worldwide was found in the Zijiang River (0.53 Mg/y). Furthermore, it was found by the delayed geochemical hazard (DGH) model that the ecological risk of Hg was more significant in the Zijiang River with more frequent transformation pathways. For different populations, the health risk values caused by Hg were all lower than the USEPA's guideline value. This study provided sound evidence for further control of Hg contamination.

Tracking the multiple Hg sources in sediments in a typical river-lake basin by isotope compositions and mixing models.

In this study, total mercury (THg) contents and Hg isotope compositions in sediments were investigated in the Lianxi River, Zijiang River and South Dongting Lake to identify and quantify multiple Hg sources and evaluate the Hg environmental processes. The THg contents, δ202Hg and Δ199Hg values in sediments were 48.22 ∼ 4284.32 µg/kg, - 1.33 ∼ 0.04‰ and - 0.25 ∼ 0.03‰, respectively. Relatively distinct Hg isotope characteristics of sediments were presented in the Lianxi River, Zijiang River and South Dongting Lake, indicating the dominant Hg sources considerably varied in these regions. Source apportionment based on MixSIAR proved that Hg in sediments mainly originated from industrial activities, and the ternary mixing model concluded non-ferrous metal smelting was the dominant industrial Hg contributor in the Lianxi River. Compared with the Lianxi River, the relative contribution of Hg in sediments from industrial activities significantly decreased, while the relative contributions of Hg from background releases significantly increased in the Zijiang River and South Dongting Lake. Nonetheless, the contribution of industrial Hg in this study area deserves more attention. These results are conducive to further manage Hg pollution.

Impaired mouse mammary gland growth and development is mediated by melatonin and its MT1G protein-coupled receptor via repression of ERα, Akt1, and Stat5.

To determine whether melatonin, via its MT(1) G protein-coupled receptor, impacts mouse mammary gland development, we generated a mouse mammary tumor virus (MMTV)-MT1-Flag-mammary gland over-expressing (MT1-mOE) transgenic mouse. Increased expression of the MT(1) -Flag transgene was observed in the mammary glands of pubescent MT1-mOE transgenic female mice, with further significant increases during pregnancy and lactation. Mammary gland whole mounts from MT1-mOE mice showed significant reductions in ductal growth, ductal branching, and terminal end bud formation. Elevated MT(1) receptor expression in pregnant and lactating female MT1-mOE mice was associated with reduced lobulo-alveolar development, inhibition of mammary epithelial cell proliferation, and significant reductions in body weights of suckling pups. Elevated MT(1) expression in pregnant and lactating MT1-mOE mice correlated with reduced mammary gland expression of Akt1, phospho-Stat5, Wnt4, estrogen receptor alpha, progesterone receptors A and B, and milk proteins ß-casein and whey acidic protein. Estrogen- and progesterone-stimulated mammary gland development was repressed by elevated MT(1) receptor expression and exogenous melatonin administration. These studies demonstrate that the MT(1) melatonin receptor and its ligand melatonin play an important regulatory role in mammary gland development and lactation in mice through both growth suppression and alteration of developmental paradigms.

Melatonin and associated signaling pathways that control normal breast epithelium and breast cancer.

This review article discusses recent work on the melatonin-mediated circadian regulation and integration of molecular and metabolic signaling mechanisms involved in human breast cancer growth and the associated consequences of circadian disruption by exposure to light-at-night (LAN). The anti-proliferative effects of the circadian melatonin signal are, in general, mediated through mechanisms involving the activation of MT(1) melatonin receptors expressed in human breast cancer cell lines and xenografts. In estrogen receptor-positive (ERα+) human breast cancer cells, melatonin suppresses both ERα mRNA expression and estrogen-induced transcriptional activity of the ERα via MT(1)-induced activation of G(αi2) signaling and reduction of cAMP levels. Melatonin also regulates the transcriptional activity of additional members of the nuclear receptor super-family, enzymes involved in estrogen metabolism, and the expression of core clock and clock-related genes. The anti-invasive/anti-metastatic actions of melatonin involve the blockade of p38 phosphorylation and matrix metalloproteinase expression. Melatonin also inhibits the growth of human breast cancer xenografts via MT(1)-mediated suppression of cAMP leading to a blockade of linoleic acid (LA) uptake and its metabolism to the mitogenic signaling molecule 13-hydroxyoctadecadienoic acid (13-HODE). Down-regulation of 13-HODE reduces the activation of growth factor pathways supporting cell proliferation and survival. Finally, studies in both rats and humans indicate that light-at-night (LAN) induced circadian disruption of the nocturnal melatonin signal activates human breast cancer growth, metabolism, and signaling, providing the strongest mechanistic support, thus far, for epidemiological studies demonstrating the elevated breast cancer risk in night shift workers and other individuals increasingly exposed to LAN.

Occurrence, allocation and geochemical controls for mercury in a typical estuarine ecosystem: Implications for the predictability of mercury species.

In this study, surface seawater, bottom seawater and surface sediments were collected from the Yellow River Estuary Area (YREA) and the Laizhou Bay (LB) to investigate the occurrence, spatial distribution and geochemical control factors for total mercury (THg) and methylmercury (MeHg) in different phases. The geochemical characteristics of seawater and sediments suggested significant variances in the YREA and the LB. The high contamination of Hg in the YREA showed the discharge of the Yellow River (YR) contributed significantly to the Hg contamination in the LB. The partial least squares regression (PLSR) model was utilized to explore the complicated interactions between geochemical controls and methylation potentials in different phases. Although the ecological risk (ER) of Hg was not significant in this study area, the higher values of ER in the YREA suggested that the YR was the primary Hg contributor to LB. Therefore, the potential Hg risk should not be ignored.

Declining melatonin levels and MT1 receptor expression in aging rats is associated with enhanced mammary tumor growth and decreased sensitivity to melatonin.

Serum melatonin (MLT) levels have been reported to diminish significantly by the 5th and 6th decades of life as the incidence of breast cancer increases. Given MLT's anti-cancer activity, we hypothesize that age-related decline in pineal MLT production leads to enhanced breast cancer development and growth as women age. In this study, we sought to determine whether the growth of tissue-isolated mammary tumors in young, adult, and old female Buffalo rats relates to the age-related changes in MLT and its MT1 receptor. Significant decreases in the peak nighttime serum MLT levels were observed in old as compared to adult and young rats. Significantly diminished nighttime and early morning levels of MT1-melatonin receptors were observed in uteri from old rats compared to adult and young rats. Growth rates in transplanted, tissue-isolated, carcinogen-induced mammary tumors are significantly increased in old rats as compared to adult or young rats. The growth-suppressive actions of exogenous MLT are diminished in old rats compared to adult and young rats. This decrease in tumor response correlates with reduced expression of the MT1 receptor in old as compared to young and adult rats. Thus, enhanced mammary tumor growth is associated with old age and diminished levels of MLT and MT1 receptor during old age, resulting in reduced sensitivity to exogenous MLT. Finally, our studies demonstrate that the tissue-isolated tumor model is viable model system in which to study the role of aging on breast cancer growth.

Circadian regulation of molecular, dietary, and metabolic signaling mechanisms of human breast cancer growth by the nocturnal melatonin signal and the consequences of its disruption by light at night.

This review article discusses recent work on the melatonin-mediated circadian regulation and integration of molecular, dietary, and metabolic signaling mechanisms involved in human breast cancer growth and the consequences of circadian disruption by exposure to light at night (LAN). The antiproliferative effects of the circadian melatonin signal are mediated through a major mechanism involving the activation of MT(1) melatonin receptors expressed in human breast cancer cell lines and xenografts. In estrogen receptor (ERα+) human breast cancer cells, melatonin suppresses both ERα mRNA expression and estrogen-induced transcriptional activity of the ERα via MT(1) -induced activation of G(αi2) signaling and reduction of 3',5'-cyclic adenosine monophosphate (cAMP) levels. Melatonin also regulates the transactivation of additional members of the steroid hormone/nuclear receptor super-family, enzymes involved in estrogen metabolism, expression/activation of telomerase, and the expression of core clock and clock-related genes. The anti-invasive/anti-metastatic actions of melatonin involve the blockade of p38 phosphorylation and the expression of matrix metalloproteinases. Melatonin also inhibits the growth of human breast cancer xenografts via another critical pathway involving MT(1) -mediated suppression of cAMP leading to blockade of linoleic acid uptake and its metabolism to the mitogenic signaling molecule 13-hydroxyoctadecadienoic acid (13-HODE). Down-regulation of 13-HODE reduces the activation of growth factor pathways supporting cell proliferation and survival. Experimental evidence in rats and humans indicating that LAN-induced circadian disruption of the nocturnal melatonin signal activates human breast cancer growth, metabolism, and signaling provides the strongest mechanistic support, thus far, for population and ecological studies demonstrating elevated breast cancer risk in night shift workers and other individuals increasingly exposed to LAN.

Seasonal occurrence, allocation and ecological risk of organophosphate esters in a typical urbanized semi-closed bay.

In this study, water and sediment samples from the Jiaozhou Bay and surrounding rivers were collected to analyze the seasonal occurrence and allocation of 12 organophosphate esters (OPEs) and the associated ecological risk. The higher contamination of OPEs in the adjacent rivers indicated the impact of terrestrial input. Tris(1-chloropropan-2-yl) phosphate (TCIPP) was the predominant OPE in the four environmental sample groups investigated. The spatial distribution of OPEs in seawater varied greatly seasonally and was mainly affected by terrestrial input, with OPEs being redistributed under the influence of tidal currents. The partition coefficients (log Koc) of the OPEs were calculated, and their strong correlation with the log Kow (octanol-water) values suggested that the water-sediment allocation was significantly affected by hydrophobicity. The homologous relationships among the 7 OPEs with detection frequencies greater than 40% were identified by principal component analysis (PCA). The partial least squares regression (PLSR) model explicated that ∑OPEs cycling dynamics and principal controlling factors were dissimilar in the bay versus surrounding rivers. The risk quotient (RQ) faced by typical organisms in seawater and river water indicated that short-term OPEs exposure was safe for green algae, daphnia and fish. The organisms in rivers faced the higher ecological risk of OPEs in spring than in summer and winter. Therefore, the terrestrial transport of OPEs in spring should be controlled.

Trophic transfer and dietary exposure risk of mercury in aquatic organisms from urbanized coastal ecosystems.

In this study, 26 surface seawater samples, 26 surface sediment samples and 114 organisms were collected to study the trophic transfer and dietary exposure risk of mercury (Hg) in organisms from the Jiaozhou Bay, which is a typical semi-enclosed urbanized bay. The total mercury (THg) and methylmercury (MeHg) concentrations did not exceed the threshold limits and performed as: fish > crustaceans > mollusks. The trophic level values (TLs) were less than 3 in all the groups, indicating simple structure of food chain. With the increasing δ15N value, THg and MeHg were significantly biomagnified in the mollusks and fish but not in the crustaceans. In addition, the bioaccumulation and biomagnification of MeHg were higher than inorganic mercury (IHg) in the aquatic food chain. Target hazard quotient (THQ) and provisional tolerable weekly intake (PTWI) indicated that Hg exposure via consumption of seafood from the Jiaozhou Bay did not pose significant health risks for general population. Consuming fish will face the higher health risk than crustaceans and mollusks, especially in urban regions. Moreover, the risk of MeHg caused by intaking seafood deserved more attention. Trophic transfer function (TTF) explicated the transfer of Hg in the ecosystem and higher trophic transfer efficiency of MeHg than IHg. TTF interpreted the terrestrial input of Hg should be controlled to ensure the safety of consuming seafood from the Jiaozhou Bay.

Inhibition of breast cancer cell invasion by melatonin is mediated through regulation of the p38 mitogen-activated protein kinase signaling pathway.

INTRODUCTION: The pineal gland hormone, melatonin, has been shown by numerous studies to inhibit the proliferation of estrogen receptor α (ERα)-positive breast cancer cell lines. Here, we investigated the role of melatonin in the regulation of breast cancer cell invasion. METHODS: Three invasive MCF-7 breast cancer cell clones - MCF-7/6, MCF-7/Her2.1, and MCF-7/CXCR4 cells - were employed in these studies. All three cell lines exhibited elevated phosphorylation of the ERK1/2 and p38 mitogen-activated protein kinase (MAPK) as determined by Western blot analysis. The effect of melatonin on the invasive potential of these human breast cancer cells was examined by matrigel invasion chamber assays. The expression and proteinase activity of two matrix metalloproteinases (MMPs), MMP-2 and MMP-9, were analyzed by Western blot analysis and gelatin zymography, respectively. RESULTS: Melatonin (10-9 M) significantly suppressed the invasive potential of MCF-7/6 and MCF-7/Her2.1 cells as measured by matrigel invasion chamber assays, and significantly repressed the proteinase activity of MMP-2 and MMP-9. In MCF-7/CXCR4 cells, melatonin significantly inhibited stromal-derived factor-1 (SDF-1/CXCL12) induced cell invasion and activity of MMP-9. Elevated expression of the MT1 melatonin receptor further enhanced, while luzindole, an MT1/MT2 antagonist, abrogated melatonin's anti-invasive effect, suggesting that melatonin's effect on invasion is mediated, principally, through the MT1 receptor. Furthermore, melatonin repressed the phosphorylation of p38 MAPK in MCF-7/Her2.1 cells and blocked stromal-derived factor-1 (SDF-1) induced p38 phosphorylation in MCF-7/CXCR4 cells. SB230580, a p38 inhibitor, was able to mimic, while transfection of the cells with a constitutively-active MKK6b construct blocked melatonin's effect on cell invasion, suggesting that the anti-invasive action of melatonin is mediated through the p38 pathway. CONCLUSIONS: Melatonin exerts an inhibitory effect on breast cancer cell invasion through down-regulation of the p38 pathway, and inhibition of MMP-2 and MMP-9 expression and activity.

In vitro and in vivo antitumor activity of melatonin receptor agonists.

Melatonin has been shown to inhibit the proliferation of estrogen receptor α (ERα)-positive human breast cancer cells in vitro and suppress the growth of carcinogen-induced mammary tumors in rats. Melatonin's antiproliferative effect is mediated, at least in part, through the MT1 melatonin receptor and mechanisms involving modulation of the estrogen-signaling pathway. To develop melatonin analogs with greater therapeutic effects, we have examined the in vitro and in vivo antimitotic activity of two MT1/MT2 melatonin receptor agonists, S23219-1 and S23478-1. In our studies, both agonists are quite effective at suppressing the growth of MCF-7 human breast cancer cells. At a concentration of 10⁻6 m, S23219-1 and S23478-1 inhibited the growth of MCF-7 cells by 60% and 73%, respectively. However, S23478-1 is more effective than melatonin and S23219-1 at repressing the expression and transactivation of the ERα, and modulating the expression of pancreatic spasmolytic polypeptide (pS2), an estrogen-regulated gene. The melatonin agonist S23478-1 exhibited enhanced antitumor potency in the subsequent studies in our animal model. At a dosage of 25 mg/kg/day, S23478-1 is more efficacious than melatonin at inducing regression of the established N-nitroso-N-methyl-urea-induced rat mammary tumors. This dose of S23478-1 (25 mg/kg/day) generated a significant (P < 0.05) overall regression response of 52%. Furthermore, at this dosage, S23478-1 is more effective than melatonin at suppressing the estrogen-signaling pathway and promoting tumor cell apoptosis, significantly increasing the expression of the pro-apoptotic protein Bax, while decreasing the expression of ERα and the anti-apoptotic protein Bcl-2.