The drug selectively kills cancer stem cells which help tumours grow and spread the disease through the body.
Unlike other cancer cells, stem ‘mother’ cells are resistant to radiotherapy and chemotherapy, allowing cancer to return after treatment.
In laboratory tests, the new drug, salinomycin, was 100 times more effective at destroying stem cells than the powerful chemo treatment Taxol.
Injected into mice with breast cancer, it also slowed the growth of tumours.
Stem cells treated with the new drug were less able to start tumours in the animals than cells treated with Taxol, the journal Cell reports.
The U.S. researchers believe dozens of drugs with similar properties could be developed over the next few years. The treatment is around a decade away from the market.
The new drugs could be used in combination with standard therapies to mop up cancer stem cells left behind by traditional treatment.
This would cut the odds of the cancer coming back.
They could also be used to halt the spread of the disease through the body. This is the most common cause of death in the 155,000 cancer patients who die each year.
Piyush Gupta, of the , said: ‘It wasn’t clear it would be possible to find compounds that selectively kill cancer stem cells. We’ve shown it can be done.
‘Our work reveals the biological effects of targeting cancer stem cells.
‘Moreover, it suggests a general approach to finding novel anti-cancer therapies that can be applied to any solid tumour maintained by cancer stem cells.’
Initially, the researchers identified a way of creating large quantities of cancer stem cells in the lab.
Then they tested 16,000 different chemicals on the cells to see which, if any, would prove toxic.
Salinomycin, an antibiotic given to farm animals, was the clear winner, also zapping breast tumours in mice.
Much more work is now needed to pin down how it works and to establish whether it will be effective against human tumours.
If it is deemed safe for use, many years of large-scale and rigorous testing will be needed before it is put on the market. Even then, it is unlikely to work on all tumours. The breakthrough has however caused excitement among experts.
John Stingl, of Cancer Research UK’s Cambridge institute, likened the killing of cancer stem cells to gardening.
‘It is kind of like mowing your lawn – you cut the dandelions and they keep coming back,’ he said.
‘The roots are like the stem cells, they are the main things.
‘If you have one treatment that works a little bit here and another that works a little bit there, alone they may not be curative but together they could have a big effect.’
Professor Colin Goding, a stem cell expert at Oxford University, warned there was a danger of the drug killing the wrong type of cells.