Tuesday, February 08, 2005

Clock News 25: Clocks and Cancer

Chemo On The Clock
Genes that regulate cycles of sleep and wakefulness
may also determine how well cancer patients respond to chemotherapy, according
to researchers at Northwestern University.Oncologists have long argued that the
benefits of chemotherapy vary depending upon the time of day it is administered.
According to research published in the online edition of Proceedings of the
National Academy of Sciences, mice given the cyclophosphamide in the late
afternoon had better survival rates than mice given the chemotherapeutic agent
in the morning.The researchers then tested mice bred to have mutations of two
genes known to dampen the effect of the body's circadian rhythms, or the 24-hour
cycle that influences functions such as body temperature, oxygen consumption,
rest and activity.The mice with mutations in the two "clock" genes gene showed
high sensitivity to chemotherapy, no matter when it was administered. By
contrast, mice with a defect in another clock, which stops the body's internal
clock at the body's most active point in the cycle, did not respond to the
chemotherapy agent, no matter when it was administered.The researchers said the
genes seem to influence survival of immune system cells and affect their
sensitivity to chemotherapy.The findings could one day be used to help
oncologists determine the best time of day to administer therapies and
potentially lower doses of the toxic agents.


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