Studies on the effects of the pineal hormone melatonin on an androgen-insensitive rat prostatic adenocarcinoma, the Dunning R 3327 HIF tumor

Anti-Cancer Effect of Melatonin via Downregulation of Delta-like Ligand 4 in Estrogen-Responsive Breast Cancer Cells

BACKGROUND

The Notch signaling pathway has a key role in angiogenesis and Delta - Like Ligand 4 (DLL4) is one of the main ligands of Notch involved in cell proliferation in sprouting vessels.

OBJECTIVE

In this study, we aimed to evaluate the expression of DLL4 in primary breast tumors and to examine the effect of melatonin on DLL4 expression in vitro.

METHODS

Eighty-five breast tumor and paired adjacent non-tumor tissue samples were collected. Apoptosis assay was performed on breast cancer cells to evaluate melatonin effects. Western blot and quantitative RT-PCR were used to measure DLL4 expression. Then, we investigated the effect of melatonin on the expression of DLL4 in four breast cancer cell lines at RNA and protein levels. We also performed a probabilistic neural network analysis to study genes closely associated with DLL4 expression.

RESULTS

Our results showed a significantly higher expression of DLL4 in tumor tissues compared to non-tumor tissues (P = 0.027). Melatonin treatment substantially attenuated DLL4 expression in BT474 and MCF-7 cells, but not in SK-BR-3 and MDA-MB-231 cells. Also, melatonin induced apoptosis in all four cell lines. Network analysis revealed a set of 15 genes that had close association and interaction with DLL4. DLL4 was overexpressed in breast cancer tissues as compared to the non-tumor tissues.

CONCLUSION

It can be concluded that melatonin treatment attenuated DLL4 expression only in estrogen- responsive breast cancer cells and is able to induce apoptosis in breast cancer cells.

Melatonin and urological cancers: a new therapeutic approach

Urological cancers are responsible for thousands of cancer-related deaths around the world. Despite all developments in therapeutic approaches for cancer therapy, the absence of efficient treatments is a critical and vital problematic issue for physicians and researchers. Furthermore, routine medical therapies contribute to several undesirable adverse events for patients, reducing life quality and survival time. Therefore, many attempts are needed to explore potent alternative or complementary treatments for great outcomes. Melatonin has multiple beneficial potential effects, including anticancer properties. Melatonin in combination with chemoradiation therapy or even alone could suppress urological cancers through affecting essential cellular pathways. This review discusses current evidence reporting the beneficial effect of melatonin in urological malignancies, including prostate cancer, bladder cancer, and renal cancer.

WOMEN IN CANCER THEMATIC REVIEW: Circadian rhythmicity and the influence of 'clock' genes on prostate cancer

The androgen receptor (AR) plays a key role in the development and progression of prostate cancer (CaP). Since the mid-1990s, reports in the literature pointed out higher incidences of CaP in some select groups, such as airline pilots and night shift workers in comparison with those working regular hours. The common finding in these 'high-risk' groups was that they all experienced a deregulation of the body's internal circadian rhythm. Here, we discuss how the circadian rhythm affects androgen levels and modulates CaP development and progression. Circadian rhythmicity of androgen production is lost in CaP patients, with the clock genes Per1 and Per2 decreasing, and Bmal1 increasing, in these individuals. Periodic expression of the clock genes was restored upon administration of the neurohormone melatonin, thereby suppressing CaP progression. Activation of the melatonin receptors and the AR antagonized each other, and therefore the tumour-suppressive effects of melatonin and the clock genes were most clearly observed in the absence of androgens, that is, in conjunction with androgen deprivation therapy (ADT). In addition, a large-scale study found that high-dose radiation was more effective in CaP patients when it was delivered before 17:00 h, compared with those delivered after 17:00 h, suggesting that the therapy was more effective when delivered in synchrony with the patient's circadian clock. As CaP patients are shown to become easily resistant to new therapies, perhaps circadian delivery of these therapeutic agents or delivery in conjunction with melatonin and its novel analogs should be tested to see if they prevent this resistance.

Therapeutic Actions of Melatonin in Cancer: Possible Mechanisms

Melatonin is a phylogenetically well-preserved molecule with diverse physiological functions. In addition to its well-known regulatory control of the sleep/wake cycle, as well as circadian rhythms generally, melatonin is involved in immunomodulation, hematopoiesis, and antioxidative processes. Recent human and animal studies have now shown that melatonin also has important oncostatic properties. Both at physiological and pharmacological doses melatonin exerts growth inhibitory effects on breast cancer cell lines. In hepatomas, through its activation of MT 1 and MT2 receptors, melatonin inhibits linoleic acid uptake, thereby preventing the formation of the mitogenic metabolite 1,3-hydroxyoctadecadienoic acid. In animal model studies, melatonin has been shown to have preventative action against nitrosodiethylamine (NDEA)-induced liver cancer. Melatonin also inhibits the growth of prostate tumors via activation of MT1 receptors thereby inducing translocation of the androgen receptor to the cytoplasm and inhibition of the effect of endogenous androgens. There is abundant evidence indicating that melatonin is involved in preventing tumor initiation, promotion, and progression. The anticarcinogenic effect of melatonin on neoplastic cells relies on its antioxidant, immunostimulating, and apoptotic properties. Melatonin's oncostatic actions include the direct augmentation of natural killer (NK) cell activity, which increases immunosurveillance, as well as the stimulation of cytokine production, for example, of interleukin (IL)-2, IL-6, IL-12, and interferon (IFN)-γ. In addition to its direct oncostatic action, melatonin protects hematopoietic precursors from the toxic effect of anticancer chemotherapeutic drugs. Melatonin secretion is impaired in patients suffering from breast cancer, endometrial cancer, or colorectal cancer. The increased incidence of breast cancer and colorectal cancer seen in nurses and other night shift workers suggests a possible link between diminished secretion of melatonin and increased exposure to light during nighttime. The physiological surge of melatonin at night is thus considered a “natural restraint” on tumor initiation, promotion, and progression.

Differential regulation of estrogen receptor alpha, glucocorticoid receptor and retinoic acid receptor alpha transcriptional activity by melatonin is mediated via different G proteins

Melatonin has been shown to bind to the MT1 G protein-coupled receptor (GPCR) in MCF-7 breast cancer cells to modulate the estrogen response pathway suppressing estrogen-induced estrogen receptor alpha (ERalpha) transcriptional activity, blunting ER/DNA binding activity and suppressing cell proliferation. In these studies we have examined the effect of melatonin on the transcriptional activity of the ERalpha and other members of the steroid/thyroid hormone receptor superfamily, namely, the glucocorticoid receptor (GR) and the retinoic acid receptor alpha (RARalpha). As with the ERalpha, melatonin represses ligand (dexamethasone)-induced activation of the GR. This effect of melatonin on ERalpha and GR is blocked by pertussis toxin (PTX) suggesting that melatonin's actions may be mediated via a PTX-sensitive G(alphai) protein. In contrast, melatonin potentiates the action of all-trans-retinoic acid on RARalpha transcriptional activation and enhances RARalpha/DNA binding activity, an action which is not PTX-sensitive. Expression of a dominant-positive G(alphai2) protein, with which the MT1 receptor has been shown to couple, is able to mimic the effect of melatonin on ERalpha but not RARalpha transcriptional activation in breast cancer cells. This demonstrates that GPCRs can modulate the transcriptional activity of various steroid receptors in response to their ligand through activation of different G protein signaling pathways.

Melatonin: from basic research to cancer treatment clinics

Melatonin, the chief secretory product of the pineal gland, is a direct free radical scavenger, an indirect antioxidant, as well as an important immunomodulatory agent. In both in vitro and in vivo investigations, melatonin protected healthy cells from radiation-induced and chemotherapeutic drug-induced toxicity. Furthermore, several clinical studies have demonstrated the potential of melatonin, either alone or in combination with traditional therapy, to yield a favorable efficacy to toxicity ratio in the treatment of human cancers. This study reviews the literature from laboratory investigations that document the antioxidant and oncostatic actions of melatonin and summarizes the evidence regarding the potential use of melatonin in cancer treatment. This study also provides rationale for the design of larger translational research-based clinical trials.

Growth-inhibitory activity of melatonin on human androgen-independent DU 145 prostate cancer cells

BACKGROUND

The pineal hormone melatonin has been shown to exert a direct oncostatic activity on neoplastic cells, particularly from breast cancer. In the present study, we evaluated the effects of melatonin on the proliferation and on the cell cycle distribution of human androgen-independent DU 145 prostate cancer cells. Experiments were also performed to gain insights into the possible mechanism of action of the hormone.

METHODS

The effects of melatonin on DU 145 cell proliferation was analyzed by counting the cells by hemocytometer at the end of treatment. The effects of the pineal hormone on cell cycle distribution were evaluated by FACS analysis. RT-PCR studies were performed to detect Mel(1a) and Mel(1b) expression in DU 145 cells. The cellular localization of (125)I-melatonin binding sites was investigated by radioreceptor assay. A commercially available binding-protein assay kit was utilized to evaluate intracellular cAMP levels.

RESULTS

Melatonin, in physiological doses, significantly inhibited DU 145 cell proliferation and induced cell cycle withdrawal by accumulating cells in G0/G1 phase. The mRNA for Mel(1a) receptors was found to be expressed in DU 145 cells; however, by radioreceptor assay, no binding sites for (125)I-melatonin could be detected in membrane preparations, suggesting that, in these cells, the level of translation of this mRNA is too low to possibly mediate the antiproliferative action of the hormone. In agreement with this hypothesis, melatonin did not affect forskolin-induced intracellular cAMP accumulation. Binding sites for (125)I-melatonin were found in nuclear extracts of DU 145 cells.

CONCLUSIONS

Melatonin exerts a direct oncostatic activity on human androgen-independent prostate cancer cells, by affecting cell cycle progression. This activity seems to be mediated by nuclear, but not by membrane, receptors.

Melatonin receptors in PC3 human prostate tumor cells

Melatonin, secreted nocturnally by the pineal gland, can bind to human benign prostate epithelial cells and attenuate their growth and viability. In the present study, melatonin binding and responses were explored in the human steroid-independent PC3 prostatic tumor cells. PC3 cells bound 125I-melatonin with low affinity (Kd ca. 0.9 nM) at high as well as low cell density. Melatonin enhanced cGMP and 3H-thymidine incorporation at low, but attenuated them at high cell density. In addition, melatonin inhibited cAMP at low, but augmented it at high cell density. These effects were associated with an increase in cell count at low- but not high-density cultures. Pertussis toxin treatment suppressed 125I-melatonin binding and ablated all the effects of melatonin on 3H-thymidine incorporation, cAMP, and cGMP at both cell densities. Cholera toxin treatment failed to block the effects of melatonin on 3H-thymidine incorporation, but prevented the modulation by melatonin of cAMP at low and cGMP at high cell density. The cGMP analog 8-Br-cGMP, inhibited melatonin's effects on 3H-thymidine incorporation at both cell densities. H89, a protein kinase A inhibitor, prevented melatonin's effects on 3H-thymidine incorporation at low but not high cell density. These results provide the first demonstration of direct interaction of melatonin with hormone-insensitive prostate tumor cells. The melatonin receptors in the PC3 cells are coupled to pertussis toxin-sensitive G proteins to induce cell density-dependent changes in cGMP, cAMP, and cell growth.

Hormonal interactions in human prostate tumor LNCaP cells

Melatonin, the hormone secreted by the pineal gland at night, has recently been found to attenuate growth and viability of benign human prostate epithelial cells. Estradiol suppressed these responses by efflecting a protein kinase C mediated inactivation of melatonin receptors. In the present study, the effects of melatonin on growth and viability of the human androgen-sensitive prostatic tumor cell line-LNCaP and the influence of estradiol on these responses were explored. Melatonin inhibited 3H-thymidine incorporation into LNCaP cells at physiological concentrations. This response decayed within 24 h. The inactivation of the response slowed down in the presence of the protein kinase C inhibitor GF-109203X. Estradiol also inhibited 3H-thymidine incorporation and its effects were additive to those of melatonin. Suppression of DNA content was observed in cells treated for 2 days with melatonin (0.1 nM); this suppression was maintained for longer periods in the presence than in the absence of estradiol. In addition, estradiol and melatonin slightly and additively decreased cell viability. These results demonstrate for the first time a direct interaction of melatonin with androgen-sensitive prostate tumor cells leading to attenuation of cell growth. They also show that unlike in benign prostate epithelial cells, estrogen attenuates LNCaP cell growth and supports rather than inactivates melatonin's action.

Meditation, melatonin and breast/prostate cancer: hypothesis and preliminary data

The objective of this study was to test the hypothesis that the regular practice of mindfulness meditation is associated with increased physiological levels of melatonin. Melatonin may be related to a variety of biologic functions important in maintaining health and preventing disease, including breast and prostate cancer. Previous studies have shown melatonin production is photosensitive and we suggest here that it also may be psychosensitive. A cross-sectional study of 12-hour (20:00-08:00) urinary 6-sulphatoxymelatonin was conducted from which we analyzed data from 8 women who regularly meditate (RM) and 8 women who do not meditate (NM). All samples were collected in the homes of study participants. Volunteers were recruited to provide 12-hour overnight samples of urine. All subjects collected the samples on one night during the same 1-week period. There was no explicit intervention. However, all RM were either graduates of, or teachers in, the University of Massachusetts Stress Reduction and Relaxation Program. The main outcome measure was the total excretion of urinary 6-sulphatoxymelatonin. Multiple linear regression (Proc GLM in SAS) was performed to test the effect of meditation (RM vs NM) on 6-sulphatoxymelatonin. The results of the study were that after controlling for the non-significant effect of menstrual period interval, we found an effect of meditation group (RM vs NM: b = 1.983; F = 6.78; p = 0.02) and age (for each integer year: b = 0.169; F = 8.41; p = 0.01). The conclusion is that study results are consistent with our hypothesis and indicate that melatonin might be a useful parameter in testing similar psycho-social interventions.(ABSTRACT TRUNCATED AT 250 WORDS)

Circadian analysis of mononuclear cells in the rat following pinealectomy and superior cervical ganglionectomy

The role of the pineal gland and adrenocorticosteroids in circadian rhythmicity of immune function was investigated in Sprague-Dawley rats that either had been pinealectomized (PX) or had undergone superior cervical ganglionectomy (SCGX), which functionally denervates the pineal. For both experiments, conducted between August and October, rats were entrained to a 10-h light:14-h dark cycle and fed ad libitum. The circadian rhythm in monocytes (ANOVA, p less than .01 for Control + Sham + PX samples) tended to parallel that of plasma corticosteroid levels (ANOVA, p less than .01) with the peak during early dark and the nadir at early light. In comparison, suppressor/cytotoxic T cells and B cells tended to be more frequent during early light with minimum levels during early dark (ANOVA, p less than .05 and .01, respectively, for Control + Sham + PX samples). Natural killer (NK) activity in control animals varied significantly (ANOVA, p less than .05) over the light:dark cycle with peak activity during early dark in the SCGX experiment, but was only slightly elevated during late dark in the PX experiment. PX animals exhibited increased frequency of NK cells, but only in samples collected during the day (t test, p less than .05). This effect was not observed in sham-operated PX controls and in SCGX animals. Neither PX nor SCGX had a significant (ANOVA) effect on plasma corticosterone levels. These observations in the rat are consistent with findings in mice and humans that corticosteroids play an important general role in circadian rhythmicity of immune functions. In contrast, the present study suggests that pineal gland influence of immune function(s) is more specific and that pineal gland interaction with NK cells has a circadian component.