Nighttime Light Exposure May Spur Tamoxifen Resistance
Thursday, July 31, 2014 (Last Updated: 08/01/2014)
THURSDAY, July 31, 2014 (HealthDay News) -- An animal study suggests that exposure to light at night, which disrupts circadian rhythm and melatonin production, may drive intrinsic resistance to tamoxifen therapy in breast cancer. The study was published online July 25 in Cancer Research.
Robert T. Dauchy, of Tulane University in New Orleans, and colleagues used a rat model to examine the effects of light/dark cycles with dim light exposure at night (dLEN) on estrogen receptor (ERα+) MCF-7 tumor xenografts.
The researchers found that dLEN sped the development of the breast tumors in the rats by increasing their metabolism and growth and conferring an intrinsic resistance to tamoxifen. These findings were not observed in rats without disruption of the circadian melatonin rhythm or in rats subjected to dLEN which received nocturnal melatonin replacement. Melatonin acted both as a tumor metabolic inhibitor and as a circadian-regulated kinase inhibitor to restore the sensitivity of breast tumors to tamoxifen and promote tumor regression.
"Together, our findings show how dLEN-mediated disturbances in nocturnal melatonin production can render tumors insensitive to tamoxifen," the authors write.
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