Timing of cancer radiation therapy may minimise hair loss

Hair loss in humans from toxic cancer radiotherapy and chemotherapy might be minimised if these treatments are given late in the day, scientists, including an Indian-origin researcher, have found.
Researchers found that mouse hair has a circadian clock - a 24-hour cycle of growth followed by restorative repair.
In the study, mice lost 85 per cent of their hair if they received radiation therapy in the morning, compared to a 17 per cent loss when treatment occurred in the evening.
The researchers, from the Salk Institute for Biological Studies, the University of Southern California (USC) and the University of California, Irvine (UCI), worked out the precise timing of the hair circadian clock, and also uncovered the biology behind the clockwork - the molecules that tells hair when to grow and when to repair damage.

They then tested the clock using radiotherapy.
"These findings are particularly exciting because they present a significant step towards developing new radiation therapy protocols that include minimising negative side effects on normal tissues, such as hair or bone marrow, while maintaining the desired effects on cancer cells," said Maksim Plikus, assistant professor of developmental and cell biology at UCI and the study's first author.

"We will now apply our findings to design novel circadian rhythm-based approaches to cancer therapy," Plikus said.
The scientists could not say whether their findings will directly translate to human cancer therapy because they haven't yet studied that possibility.

However, they said it is becoming increasingly clear that body organs and tissues have their own circadian clocks that, when understood, could be used to time drug therapy for maximum benefit.
"There are clocks everywhere in the body - clocks that have their own unique rhythm that, we found, have little to do with the central clock in our brains," said the study's co-lead investigator, Satchidananda Panda, an associate professor in Salk's Regulatory Biology Laboratory and an expert on circadian rhythm.
"This suggests that delivering a drug to an organ while it is largely inactive is not a good idea. You could do more damage to the organ than when it is awake, repairing and restoring itself," said Panda.

"If you know when an organ is mending itself, you might be able to deliver more potent doses of a drug or therapy. That might offer a better outcome while minimising side effects," Panda said.
Radiotherapy damages DNA in cells that divide rapidly, which is why it is used against growing cancer cells. That means that DNA damage to hair cells from radiotherapy delivered in the morning is not repaired until the evening, leading to hair loss.
Damage from radiotherapy at night, however, is minimised because hair cells, already in the process of repairing DNA, can quickly heal, the study found.