Inhibition of malignant trophoblastic cell proliferation in vitro and in vivo by melatonin

Our previous work showed that melatonin (N-acetyl-5-methoxytryptamine) inhibits proliferation of the human endometrial cancer cell line, Ishikawa, which is estrogen receptor-positive. The aim of the present study was to determine whether Ishikawa cells possess membrane melatonin receptors. Binding of the radioligand 2-[125I]-iodomelatonin to membrane preparations obtained from Ishikawa cells was detectable, saturable and stable. Scatchard analysis revealed that the dissociation constant (Kd) of the binding sites was 179.0 pm (similar to that of the MT2 [Mel1b] melatonin receptor subtype), and that the concentration (Bmax) of the binding sites was 12.9 fmol/mg protein. Luzindole, a selective MT2 melatonin receptor antagonist, significantly suppressed binding of 2-[125I]-iodomelatonin at all concentrations tested (10(-8) to 10(-4) m). These results suggest that the MT2 melatonin receptor subtype is present in the membranes of Ishikawa cells, and that the antiproliferative effect of melatonin on Ishikawa cells is mediated via the MT2 receptor. This may have implications for the use of melatonin in endometrial cancer therapy.

Section: Discussionsupporting

confidence: 85%

Melatonin binding sites in estrogen receptor‐positive cells derived from human endometrial cancer

Kobayashi¹,

Itoh

Kondo³

et al. 2003

“…The expression plasmids pcDNA3‐MT 1 [8] or pcDNA3‐MT 2 were transfected into 3A‐Sub‐E cells, which do not express MT 1 and MT 2 receptors [16], or PC‐3 cells, which do not express MT 1 receptor [8], using SuperFect TM Transfection Reagent according to the protocol recommended by the manufacturer (Qiagen GmbH, Hilden, Germany). Clonal lines of 3A‐Sub‐E and PC‐3 cells stably transfected with pcDNA3‐MT 1 or pcDNA3‐MT 2 plasmids were isolated in the presence of 0.4 mg/mL geneticin G‐418 (Gibco) in the growth medium [8, 16], harvested in ice‐cold 0.05 m Tris–HCl buffer with proteinase inhibitors [1 m m DTT, 1 m m ethylenediaminetetraacetic acid (EDTA), 1 mg/L aprotinin, 1 m m benzamidine–HCl, 0.1 m m phenylmethylsulfony fluoride (PMSF), pH 7.4], frozen in liquid nitrogen and stored at –70°C until saturation and competition 2‐[ 125 I]iodomelatonin binding studies were conducted as described above. Briefly, membranes were incubated with 2‐[ 125 I]iodomelatonin ranging in concentrations from 9 to 442 p m , with or without melatonin or other melatonergic ligands [6‐hydroxymelatonin, N‐acetylserotonin and 4‐P‐PDOT] for 2 hr at 25 ° C. A single concentration of 2‐[ 125 I]iodomelatonin in the range of 77–85 p m was used for competition studies.…”

Section: Saturation and Competition 2‐[125i]iodomelatonin Binding Stumentioning

confidence: 99%

Melatonin slowed the early biochemical progression of hormone‐refractory prostate cancer in a patient whose prostate tumor tissue expressed MT₁ receptor subtype

Shiu

Law

Lau

et al. 2003

Melatonin inhibited the proliferation of hormone-independent LNCaP prostate cancer cells partly via MT1 receptor activation both in vitro and in nude mice xenograft model. In this study, the melatonin receptor expression in the prostate cancer tissue of a patient with bone metastases and the effect of melatonin on the biochemical progression of hormone-refractory prostate tumor which later developed in the same patient were reported. Saturation and competition 2-[125I]iodomelatonin binding assays were conducted on prostate tumor tissue obtained by transurethral resection of the prostate from the index patient. The receptor subtype identity of melatonin receptor expressed in the cancer tissue was determined by comparison of the rank order of inhibition constants (Ki) of various melatonergic ligands and the affinity of 4-phenyl-2-propionamidotetraline relative to melatonin in inhibiting 2-[125I]iodomelatonin binding to the tumor sample and to human cell lines stably transfected with MT1 or MT2 melatonin receptor subtype. MT1 receptor expression in the cancer tissue was also examined by immunohistochemistry. The surgically castrated patient later developed biochemical relapse of his disease. His serum total prostate-specific antigen (PSA) level was monitored before and during treatment with 5 mg/day oral melatonin at 20:00 hr. High-affinity (Kd = 103.7 pm) MT1 melatonin receptor subtype was expressed by the patient's prostate cancer. As indicated by his PSA levels, melatonin induced stabilization of his hormone-refractory disease for 6 wk. This report validates melatonin's oncostatic action on prostate cancer and the potential involvement of MT1 receptor subtype in the attendant antiproliferative signal transduction as suggested by recent preclinical laboratory findings in a human.

“…Substantial evidence has also accumulated demonstrating that the pineal secretory product, melatonin, exerts an inhibitory influence on tumor growth in a number of experimental models, including undifferentiated neoplasms, sarcomas and carcinomas such as squamous cell cervical carcinomas, prostate cancer, endometrial cancer, colon cancer, trophoblastoma, choriocarcinoma, neuroblasteoma, hepatocarcinoma, ovarian carcinoma, melanoma, and mammary carcinoma [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Although the precise underlying mechanisms remain to be elucidated, proapoptotic effects of melatonin have been noted in a number of tumor cell lines [10][11][12][13]15].…”

Section: Introductionmentioning

confidence: 99%

Inhibitory effects of melatonin on the growth of pituitary prolactin‐secreting tumor in rats

Yang

et al. 2006

The in vivo effects of melatonin on proliferation and apoptosis of 17-beta-estradiol (E2)-induced pituitary prolactin-secreting tumor (prolactinoma) were investigated in rats kept in 12 L/12 D (lights on: 06:00-18:00 hr). As melatonin was shown to induce apoptosis of breast and liver tumor cells, we examined whether melatonin would induce apoptosis of rat pituitary prolactinoma cells. 0.125, 0.25, 0.50 or 1.0 mg melatonin/day/rat was administrated subcutaneously at 17:30-18:00 hr. The weight of prolactinomas was measured. Apoptosis was evaluated using the TdT-mediated dUTP nick-end labeling method. It was found that treatment with 0.25 and 0.50 mg melatonin for 97 days inhibited prolactinoma cell proliferation and increased prolactinoma cell apoptosis. Furthermore, melatonin induced mRNA expression of Bax and cytochrome c protein expression. Conversely, mRNA expression of Bcl-2, and mitochondrial membrane potential were inhibited by melatonin treatment. These results suggest that melatonin inhibits the proliferation and induces apoptosis of rat pituitary prolactin-secreting tumor via perturbation of mitochondria physiology.