Night Light May Drive Breast Cancer Growth

MSteven M. Hill, Ph.D. Professor, Structural & Cellular Biology Edmond & Lily Safra Chair for Breast Cancer Research Co-Director, Molecular Signaling Program, Louisiana Cancer Research Consortium Director, Tulane Circadian Biology CenteredicalResearch.com Interview with
Steven M. Hill, Ph.D.
Professor, Structural & Cellular Biology
Edmond & Lily Safra Chair for Breast Cancer Research
Co-Director, Molecular Signaling Program, Louisiana Cancer Research Consortium
Director, Tulane Circadian Biology Center

Medical Research: What are the main findings of the study?

Dr. Hill: The main findings of our study are that exposure to even dim light at night can drive human breast tumors to a hyper metabolic state, activating key tumor cell signaling pathways involved in tumor cell survival and proliferation, leading to increased tumor growth, all resulting in a tumor which is completely resistant to tamoxifen therapy. Our work shows that this effect is due to the repression of nighttime melatonin by dim light at night. When nighttime melatonin is replace the tumors become sensitive to tamoxifen resulting in cell death and tumor regression.

Medical Research: Were any of the findings unexpected?

Dr. Hill: Yes, we hypothesized that exposure to dim light at night would eventually make the tumors resistant to tamoxifen, but we believed that this would take months before they developed acquired resistance. Instead, after just a few weeks of light at night, the tumors were intrinsically resistant to tamoxifen. In addition, the degree of synergy between melatonin and tamoxifen was much greater than we expected.

Medical Research: What should clinicians and patients take away from your report?

Dr. Hill: Our study suggests that if a patient were to take their tamoxifen at night and sleep in a dark room (keeping melatonin levels high) they could receive added benefit and tumor cell killing. Furthermore, our data suggest that taking tamoxifen at a time of day when ones melatonin is elevated (just before going to sleep in a dark room) will be more effective than taking it in the morning when the sun is up and melatonin levels are depressed.

Medical Research: What recommendations do you have for future research as a result of this study?

Dr. Hill: For future research in cancer biology, particularly using animal models, we believe investigators need to take into account the animals circadian cycle and how this impacts the specific area and molecules they are investigating. We also believe that investigators need to use circadian competent animal models and they need to ensure there is no light contamination in the rooms where the animals are housed to avoid unwanted light at night- induced activity in the tumor.

Citation:

Circadian and Melatonin Disruption by Exposure to Light at Night Drives Intrinsic Resistance to Tamoxifen Therapy in Breast Cancer

Robert T. Dauchy, Shulin Xiang, Lulu Mao, Samantha Brimer, Melissa A. Wren, Lin Yuan, Muralidharan Anbalagan, Adam Hauch, Tripp Frasch, Brian G. Rowan, David E. Blask, and Steven M. Hill

Cancer Res; Published OnlineFirst July 25, 2014; doi:10.1158/0008-5472.CAN-13-3156