A DRUG being trialled by Australian researchers could control leukaemia without the harrowing side-effects that plague conventional treatments. Clinical trials of the antibody, known as KB004, have produced no side-effects even at high doses. And while the trials are designed to test the drug's safety, some patients - most of whom have acute myeloid leukaemia, one of the most untreatable forms - have already responded positively. The drug targets a protein called EphA3 which clings to cancer stem cells but is undetectable on normal cells. Conventional chemotherapy does not target stem cells, according to molecular biologist Martin Lackmann, who has researched the protein for 15 years. "Tumour stem cells give rise to tumour cells again and again," said Dr Lackmann, of Monash University's School of Biomedical Sciences. The hope with this drug is that the response may be more lasting. While chemotherapy kills tumours it also targets other rapidly proliferating cells, leading to hair loss and gastrointestinal problems including nausea, loss of appetite, constipation and diarrhoea. "The side effects are what normally limit the dose of a conventional therapy," Dr Lackmann said. He said the absence of side effects from the new drug, combined with its targeting of stem cells, increased the likelihood of eradicating the tumours. The second phase of clinical trials, to assess the drug's efficacy, will begin in the next few months. If these and large scale phase three trials prove successful, the drug could be on the market in five years. Dr Lackmann said other drugs targeting cancer stem cells were being tested, but none so far had worked. Often clinical trials stop at this point, especially in the current climate, because side effects and limited positive effects make the financial risk of continuing too high. Separate trials are planned next year to test the drug on other forms of cancer. The leukaemia trials have been underway for two years at four hospitals in Australia and the US. They also involve researchers from the Queensland Institute of Medical Research, the international Ludwig Cancer Research network and US-based KaloBios Pharmaceuticals.