Timing of cancer radiation therapy may minimise hair loss

Discovering that mouse hair has a circadian clock - a 24-hour cycle of growth followed by restorative repair - researchers suspect that hair loss in humans from toxic cancer radiotherapy and chemotherapy might be minimised if these treatments are given late in the day.

The study found that mice lost 85 percent of their hair if they received radiation therapy in the morning, compared to a 17 percent loss when treatment occurred in the evening.

The researchers, from 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,' says 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.'

The scientists can't say their findings will directly translate to human cancer therapy because they haven't yet studied that possibility. But they say 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,' says 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,' says 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.'

Salk Institute for Biological Studies