Co-administering Melatonin With an Estradiol-Progesterone Menopausal Hormone Therapy Represses Mammary Cancer Development in a Mouse Model of HER2-Positive Breast Cancer

Abstract

Melatonin has numerous anti-cancer properties reported to influence cancer initiation, promotion, and metastasis. With the need for effective hormone therapies (HT) to treat menopausal symptoms without increasing breast cancer risk, co-administration of nocturnal melatonin with a natural, low-dose HT was evaluated in mice that develop primary and metastatic mammary cancer. Individually, melatonin (MEL) and estradiol-progesterone therapy (EPT) did not significantly affect mammary cancer development through age 14 months, but, when combined, the melatonin-estradiol-progesterone therapy (MEPT) significantly repressed tumor formation. This repression was due to effects on tumor incidence, but not latency. These results demonstrate that melatonin and the HT cooperate to decrease the mammary cancer risk. Melatonin and EPT also cooperate to alter the balance of the progesterone receptor (PR) isoforms by significantly increasing PRA protein expression only in MEPT mammary glands. Melatonin significantly suppressed amphiregulin transcripts in MEL and MEPT mammary glands, suggesting that amphiregulin together with the higher PRA:PRB balance and other factors may contribute to reducing cancer development in MEPT mice. Melatonin supplementation influenced mammary morphology by increasing tertiary branching in the mouse mammary glands and differentiation in human mammary epithelial cell cultures. Uterine weight in the luteal phase was elevated after long-term exposure to EPT, but not to MEPT, indicating that melatonin supplementation may reduce estrogen-induced uterine stimulation. Melatonin supplementation significantly decreased the incidence of grossly-detected lung metastases in MEL mice, suggesting that melatonin delays the formation of metastatic lesions and/or decreases aggressiveness in this model of HER2 + breast cancer. Mammary tumor development was similar in EPT and MEPT mice until age 8.6 months, but after 8.6 months, only MEPT continued to suppress cancer development. These data suggest that melatonin supplementation has a negligible effect in young MEPT mice, but is required in older mice to inhibit tumor formation. Since melatonin binding was significantly decreased in older mammary glands, irrespective of treatment, melatonin supplementation may overcome reduced melatonin responsiveness in the aged MEPT mice. Since melatonin levels are known to decline near menopause, nocturnal melatonin supplementation may also be needed in aging women to cooperate with HT to decrease breast cancer risk.

Novel Melatonin, Estrogen, and Progesterone Hormone Therapy Demonstrates Anti-Cancer Actions in MCF-7 and MDA-MB-231 Breast Cancer Cells

“…These effects of MEMP HT in neu female mice were dependent upon age (young, 3 months vs old, 1 year) and tissue (non-tumor mammary vs tumor). 3,10 Although MEMP HT demonstrated anti-cancer actions against HER2 BC, the effect of and mechanisms underlying MEMP HT actions on ER+ and TNBC are not known and formed the basis for the present study.…”

“…The in vitro concentrations of E2, P4, and melatonin used in this study were based on serum levels of MEMP HT achieved in neu mice following consumption of 0.5 mg E2 and 50 mg P4 in the diet and 15 mg/L melatonin in water at night. 3,21 These doses of melatonin, E2, and P4 demonstrated anti-cancer actions in neu female mice. 3…”

“…1,2 The MEMP HT, which contains 5 mg melatonin (M), 0.5 mg estradiol (E/E2), and half the recommended dose of progesterone (50 vs 100 mg; P/P4), decreased tumor incidence, delayed tumor onset, and protected the uterus in HER2/neu mice. 3 The MEMP's anti-cancer actions against ER+ and triple negative breast cancer (TNBC) are not known but highly relevant based on the fact that PremPro increased myriad BCs that included ER+, HER2, and TNBC. 1 Melatonin has been incorporated in MEMP HT due to its multiple effects in organisms, including immunomodulatory, metabolic, geno-protective, anti-estrogenic, or direct antineoplastic activities.…”

“…The mechanisms underlying MEMP's anti-cancer actions in neu mice demonstrate actions on the mitogen activated protein kinases (MAPKs), Mek1/2, and Mek5 in mammary (young and old) and tumor tissue; however, these actions are tissue-dependent (non-tumor mammary vs tumor) and time-dependent (young, 3 months vs old, 1 year). 3,10 Mek1/2/5 and proteins that lay downstream from them (i.e., Runx2, NF-κB, Rankl, Elf-5, and β1-integrin) have been shown in past studies to be involved in BC by regulating proliferative and/or metastatic properties. [11][12][13][14][15][16][17][18][19][20] Although MEMP HT's anti-cancer actions in neu female mouse mammary were associated with Mek1/2-and Mek5-dependent pathways, 10 definitive studies regarding their involvement can only be achieved by knocking out, knocking down, or inhibiting Mek1/2 and 5.…”

“…[11][12][13][14][15][16][17][18][19][20] Although MEMP HT's anti-cancer actions in neu female mouse mammary were associated with Mek1/2-and Mek5-dependent pathways, 10 definitive studies regarding their involvement can only be achieved by knocking out, knocking down, or inhibiting Mek1/2 and 5. The involvement of MEK1/2 and 5 (and downstream proteins) in MEMP-mediated anti-cancer actions in MCF-7 and MDA-MB-231 cells was addressed by use of small molecule inhibitors selective for MEK1/2 or MEK5 and by using therapeutically relevant and equivalent concentrations of melatonin, 17β-estradiol (E2), and progesterone (P4) 3,21 to determine whether and how MEMP HT affects ER+ and TNBC.…”