Recently, we reported that exposure to light at night caused tamoxifen resistance in an animal model of breast cancer. Now this work has been expanded to include the effects of exposure to light at night on treatment with the chemotherapy drug Adriamycin (doxorubicin).

Melatonin protects against serious Adriamycin-induced side effects

Heart damage (cardiomyopathy) is perhaps the most serious potential side effect of Adriamycin since it can lead to short-term or long-term heart failure. One study using a rat model of breast cancer reported that melatonin reduced Adriamycin-induced oxidative damage in heart cells. Another study reported that melatonin helped prevent the low blood platelet count, neurotoxicity, and fatigue that can be associated with Adriamycin treatment, while at the same time improving survival.

Latest research finds melatonin counteracts Adriamycin resistance caused by light

Data recently presented at the 13th Annual AACR International Conference on Frontiers in Cancer Prevention Research in New Orleans demonstrated that supplemental melatonin reduced the negative effects of exposure to light at night in rats bearing human breast tumors. Exposure to even low levels of light at night made the tumors resistant to Adriamycin. In fact, melatonin not only prevented the development of Adriamycin resistance but also promoted tumor regression.

To conduct the study, rats were exposed to 12 hours of normal light followed by 12 hours of dim light (during normal nighttime hours). Half of the rats were given melatonin supplements during the dim-light period. Rats that did not receive melatonin experienced tumor growth that was 2.8 times faster than that of rats receiving nighttime melatonin. Furthermore, dim light at night caused complete resistance to Adriamycin in the tumors of rats that did not receive melatonin, whereas tumors of rats in the melatonin group remained sensitive to doxorubicin and shrank rapidly. The authors found that tumors from rats that did not receive melatonin had significantly elevated levels of (1) two enzymes that break down Adriamycin to a less active form; and (2) membrane proteins that transport Adriamycin out of cells. The authors conclude that melatonin helps maintain active Adriamycin in tumor cells, whereas exposure to light at night, which suppresses melatonin production, has the reverse effect.

According to professor Steven M. Hill, breast cancer and circadian clock researcher at Tulane University School of Medicine in New Orleans, "although our research is very promising, it is not at a point where we can make recommendations to breast cancer patients taking either tamoxifen or doxorubicin about melatonin supplementation." He also noted that "taking melatonin supplements at the wrong time of day would potentially disrupt the natural melatonin cycle, which may, in itself, impair breast cancer responsiveness to tamoxifen and doxorubicin." However Hill was willing to make the recommendation that breast cancer patients "follow a natural light/dark cycle as much as possible, try to sleep or stay in a completely dark room during the night, and/or use a sleep mask."

Please see our article on breast cancer diet during Adriamycin chemotherapy for more information on how to optimize treatment and reduce side effects.