Abstract PR13: Circadian/melatonin disruption by dim light at night drive chemotherapy resistance in breast cancer
Authors: Hill Steven M. , Xiang Shulin , Dauchy Robert T. , Mao Lulu , Hauch Adam , Brimmer Samantha , Belancio Victoria P. , Wren Melissa , Mondal Debasis , Blask David E. 
Published: October 2015

Abstract
Introduction: The purpose of this study was to test the hypothesis that dim light exposure at night (dLEN)-induced melatonin suppression promotes chemotherapeutic resistance to doxorubicin (Dox) by inducing a circadian-disrupted, hyper-metabolic state relative to linoleic acid (LA) metabolism and the Warburg effect together with constitutive activation of key proliferative and survival signaling pathways. Breast cancer patients often present with de novo (intrinsic) resistance to chemotherapy and many that initially respond will eventually develop acquired resistance. Tumors with chemotherapeutic resistance often exhibit elevated expression/activation of key proliferative and survival signaling pathways and frequently show alterations in tumor metabolism, particularly the biochemical pathways involved in stimulating aerobic glycolysis (Warburg effect).
The pineal hormone melatonin inhibits breast cancer proliferation in vitro and the endogenous nocturnal circadian melatonin signal modulates circadian rhythms in tissue-isolated human breast cancer xenografts including LA uptake and metabolism to 13-hydroxyoctadecadeinoic acid (13-HODE), 13-HODE-stimulated Warburg effect, and proliferative and survival signaling. As we have previously reported, these circadian rhythms are induced during the light phase in breast tumor xenografts but inhibited in the dark phase by melatonin. dLEN-induced melatonin suppression drives the constitutive activation of these pathways resulting in tumor hyper-metabolism, increased proliferative and survival signaling activity, and resistance to endocrine therapy with tamoxifen; these effects are repressed by melatonin supplementation.
Experimental Procedures: Female nude rats with tissue-isolated ERα+ MCF-7 breast cancer xenografts were housed in environmentally controlled light boxes under photoperiodic conditions of LD, 12L:12D, 12:12dLEN (0.2 lux), or 12:12dLEN with melatonin supplementation during dLEN in the drinking water (lights on at 0600 hrs and off or dLEN on at 1800 hrs). When estimated tumor weights reached ~2.5 g, animals in both dLEN groups were treated daily with either diluent or Dox (6 mg/kg BW) administered by intraperitoneal injection 2 h prior to onset of dLEN.
Data Summary: Blood samples collected during the mid-dark phase (2400 hrs) showed elevated nocturnal melatonin levels (118.4 pg/ml) in the LD,12L:12D group, but significantly suppressed melatonin (10.0 pg/ml) in the dLEN group. Rats housed in 12L:12dLEN showed a 3-fold decrease in latency-to-onset of tumor development and a 2.8-fold increase in tumor growth rates vs. those on the 12L:12dLEN photoperiod receiving nighttime melatonin supplementation. Under dLEN circadian-disrupted conditions, tumor metabolism was characterized by a hyper-metabolic state with tumor cAMP-dependent LA-uptake/metabolism to 13-HODE, glucose uptake and lactate release (Warburg effect), O2 uptake and CO2 production, and [3H] thymidine incorporation into DNA all markedly elevated. Furthermore, numerous proliferative and survival signaling pathways including many down stream of the human epidermal growth factor receptors (HER2, HER3) including extracellular signal-related kinase (ERK1/2), protein kinase B (AKT), protein kinase C (PKCα and γ), signal transducer and activator of transcription 3 (STAT3) etc. were highly elevated at 2400 hrs in response to dLEN, but repressed in dLEN melatonin supplemented tumors. Tumor Xenografts from dLEN rats showed complete intrinsic resistance to Dox, whereas tumors from rats on dLEN and supplemented with melatonin exhibited marked sensitivity to Dox and regressed.
Conclusions: When circadian-regulated and integrated metabolic and signal transduction mechanisms underlying human breast cancer growth are disrupted by dLEN-induced melatonin suppression, this results in rapid tumor progression and the development of resistance to chemotherapy. Thus, melatonin acts as both a tumor metabolic inhibitor and a circadian-regulated kinase inhibitor (CRKI) to reestablish the sensitivity of breast tumors to Dox and drive tumor regression.
Citation Format: Steven M. Hill, Shulin Xiang, Robert T. Dauchy, Lulu Mao, Adam Hauch, Samantha Brimmer, Victoria P. Belancio, Melissa Wren, Debasis Mondal, David E. Blask. Circadian/melatonin disruption by dim light at night drive chemotherapy resistance in breast cancer. [abstract]. In: Proceedings of the Thirteenth Annual AACR International Conference on Frontiers in Cancer Prevention Research; 2014 Sep 27-Oct 1; New Orleans, LA. Philadelphia (PA): AACR; Can Prev Res 2015;8(10 Suppl): Abstract nr PR13.