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Targeting cancer stem cells could be a powerful way to beat cancer in the future (Image from the Cancer Research UK LRI EM Unit)

What did they do?
It’s very difficult to work with ‘real life’ cancer stem cells, as they only make up a tiny fraction of cells in a given tumour, so are tricky to extract from tumour samples.

So the researchers developed a technique for growing immortal – but non-cancerous – human breast cells in the lab, and then used genetic engineering to give them the properties of cancer stem cells. This meant that they could grow stem cell-like cancer cells in thousands of tiny plastic dishes.

The next step was to expose these cells to thousands of different chemical compounds, to find ones that killed them.  To start with, the scientists studied around 16,000 compounds, including those from commercial chemical ‘libraries’ as well as extracts from natural sources. Just 32 of these killed the stem cell-like cells. And, of these, only four worked consistently.

Narrowing it down further, the researchers found that one chemical – an agricultural antibiotic called salinomycin – was particularly selective and effective at killing off the stem cells.  Further tests in the lab showed that salinomycin was over a hundred-fold more effective at killing cancer stem cells than paclitaxel – a commonly-used breast cancer drug.

Tests with mice transplanted with human breast cancer cells revealed that salinomycin was effective at reducing the levels of stem cells in the tumours, and reduced the chances of the cancer spreading around the body.

Is salinomycin the ‘cure for cancer’?
We need to stress that these were laboratory experiments, and there is no evidence yet that salinomycin can treat cancer in humans.  Salinomycin is currently used as an antibiotic for chickens and cows, and it can be toxic or even fatal to humans, causing serious muscle and heart problems.

There’s still a long way to go before salinomycin is tested in cancer patients, and we would not recommend anybody to take salinomycin as a treatment for cancer.  More research needs to be done to find out if it works on human tumours in the body, and if a safe dose can be given.

It may even be the case that salinomycin itself never makes it to the clinic. Quite often researchers need to tweak the chemical formula of a promising compound to make it safe or effective, and this can take time. Or there are serious side effects that mean that it’s unsafe for general use.