Nighttime dim light exposure may increase breast cancer resistance to doxorubicin

the ONA take:

According to new findings presented at the 13th Annual American Association for Cancer Research (AACR) International Conference on Frontiers in Cancer Prevention Research in New Orleans, Louisiana, exposure to dim light at night may make breast tumors resistant to chemotherapy. Researchers at Tulane University School of Medicine in New Orleans, Louisiana, exposed rats with human breast tumors to 12 hours of normal light followed by 12 hours of dim light. Half of the rats received melatonin supplementation during the 12 hours of dim light. All rats were treated with doxorubicin for their human breast tumors.

The researchers found that the rats who did not have melatonin supplementation had a 2.8-fold faster tumor growth rate compared with the rats not receiving melatonin supplementation. Furthermore, rats not receiving melatonin supplementation were completely resistant to doxorubicin, while the rats who received melatonin supplementation were susceptible to doxorubicin and their tumors regressed rapidly.

The researchers believe that melatonin helps to keep high levels of doxorubicin in the tumor cells because rats given melatonin supplementation had lower levels of enzymes and transporters that break down and transport doxorubicin out of cells compared with the rats that did not receive melatonin supplementation.

Nighttime dim light exposure may increase breast cancer resistance to doxorubicin
Exposure to dim light at night may make breast tumors resistant to chemotherapy

For rats bearing human breast tumors, exposure to dim light at night made the tumors resistant to the standard breast cancer chemotherapy doxorubicin, but giving the rats a melatonin supplement during the dim-light exposure at night prevented resistance development and promoted tumor regression, according to data presented at the 13th Annual AACR International Conference on Frontiers in Cancer Prevention Research, held Sept. 28–Oct. 1.

"Using our rat model of breast cancer, we recently reported [see July 25, 2014, news release] that exposure to dim light at night made human breast tumors resistant to the antihormone breast cancer drug tamoxifen," said Steven M. Hill, PhD, professor of structural and cellular biology and the Edmond and Lily Safra chair for breast cancer research at Tulane University School of Medicine in New Orleans.

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