Abstract A91: Over-the-counter melatonin supplementation in human subjects: A potentially novel chronotherapeutic approach targeting the Warburg effect and fatty acid metabolism in breast cancer therapy/prevention

Melatonin, a circadian anti-cancer hormone produced by the pineal gland during darkness at night suppresses the Warburg effect, linoleic acid (LA) uptake/metabolism and tumor cell proliferation in both estrogen receptor (ERα+) and ERα- in tissue-isolated human breast cancer xenografts. The nighttime circadian melatonin signal regulates circadian rhythms in tumor glucose and fatty acid metabolism as well as related signaling pathways that are important in controlling cell proliferative and survival mechanisms. Over-the-counter (OTC) melatonin supplements are used by millions of individuals to treat insomnia and/or jet-lag. The present study addressed the hypothesis that oral ingestion of OTC melatonin supplements by normal adult human female volunteers results in blood levels of melatonin that suppress LA uptake/metabolism, aerobic glycolysis and cell proliferative activity in human breast cancer xenografts, growing in nude female rats, directly perfused in situ with human subject donor whole-blood following melatonin intake. Twelve young, healthy premenopausal women were recruited to ingest an OTC melatonin supplement at a single dose of either 75μg, 150μg, 300μg or 1 mg during midday (low endogenous melatonin levels) resulting in low to high pharmacological blood concentrations of melatonin. A pre-supplement venous blood sample was collected from the antecubital vein of the forearm. Each subject then ingested a randomly selected oral dose of melatonin followed approximately 1 hour later by the withdrawal of a post-supplement venous blood sample. On the following day, the pre- and post-supplement whole-blood samples collected from a given subject were separately placed into a tumor perfusion reservoir. Tissue-isolated ERα- MCF-7 human breast cancer xenografts grown in female nude rats were then directly perfused in situ for 1 hour with either pre- or post-supplement oxygenated blood (37°C). Irrespective of the dose tested, melatonin induced a 50% decrease in both tumor glucose uptake and lactate release, 22% and 44% deceases in O2 uptake and CO2 production, respectively, 50% decrease in cAMP concentrations, and a 100% decrease in linoleic acid (LA) uptake and 13-hydroxyoctadecadienoic acid (13-HODE) formation. Melatonin also caused a marked decrease in the expression of phospho-AKT, GSK3β and ERK1/2, and an 85% decrease in the incorporation of [3H]thymidine into DNA. Similar results were obtained at the lowest dose of melatonin (e.g., 75μg) in ERα+ human breast cancer xenografts. The melatonin-induced suppression tumor proliferative and metabolic activity in both ERα- and ERα+ breast cancer xenografts was completely prevented by the co-perfusion with the non-selective MT1/MT22 melatonin receptor blocker S20928 consistent with the involvement of a melatonin receptor-mediated mechanism. These results indicate that oral administration of an OTC melatonin supplement at a variety of low to high doses were equally effective in suppressing the Warburg effect and key tumor proliferative and survival signaling pathways, cAMP-dependent LA uptake and metabolism to mitogenically active 13-HODE and ultimately cell proliferation in tissue-isolated human breast xenografts irrespective of ERα status via a melatonin receptor-mediated mechanism. These findings suggest that even low doses of OTC melatonin preparations may play a potentially important role as a new chronotherapeutic agent in human breast cancer treatment and/or prevention by targeting aerobic glycolysis and fatty acid signaling and metabolism. Supported by NIH Grants R21CA129875 (DEB) and R01CA54152 (SMH). Citation Format: David E. Blask, Robert T. Dauchy, Erin M. Dauchy, Steven M. Hill, Lulu Mao, Melissa M. Wren, Mary M.C. Meyaski-Schluter, Lin Yuan. Over-the-counter melatonin supplementation in human subjects: A potentially novel chronotherapeutic approach targeting the Warburg effect and fatty acid metabolism in breast cancer therapy/prevention. [abstract]. In: Proceedings of the AACR Special Conference: Metabolism and Cancer; Jun 7-10, 2015; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(1_Suppl):Abstract nr A91.