A drug which functions in a unique fashion is being used to cure small-cell lung cancer in the UK. Researchers are looking for further uses of this drug
cancer patients at a hospital in Edinburgh, uk, are being treated with a drug that gums up the molecular 'accelerator pedals' on the surface of tumour cells. Blocking these sites could halt the growth of tumour cells, so that they wither and die. The drug is designed to treat small-cell lung cancer, which often effects smokers and accounts for one in four lung cancer cases, killing 10,000 people each year in Britain. The new Imperial Cancer Research Fund (icrf) drug works in a novel way. It does not destroy fast-growing cells but blocks the molecular messages that tell the cells to proliferate, breaking a vicious circle that makes small-cell lung tumours grow explosively ( New Scientist , Vol 150, No 2026).
Cells in these cancers secrete abnormally high amounts of growth factor hormones called neuropeptides. When these hormones lock onto surface receptors on the same or the neighboring cancer cells, they tell the cells to grow and divide faster, churning out yet more growth factors. The icrf's drug occupies the sites on the surface of the cancer cells and breaks the vicious circle. What makes the drug very special is that it blocks receptors for several different growth factors.
"I think the approach we are taking is unique," says Enrique Rozengurt, head of the team at the icrf that has spent the past 15 years developing a new approach. Rozengurt found that the tumour cells in small-cell lung cancer secrete and respond to a variety of growth factors, includ-ing vasopressin (an anti diuretic hormone) and gastrin-releasing peptide (a hormone that regulates digestion). They all accelerate growth, so only by gumming up the receptor sites for all of them can the tumour cell be tamed.
The drug is a synthetic peptide that is similar in structure to the naturally occurring neurotransmitter called substance p, which transmits pain signals. It was initially developed to block substance p receptors. Rozengurt and his colleagues found that it blocks several others as well.
Although normal cells produce and respond to growth factors, Rozengurt expects the cancer cells to be uniquely sensitive to the drug because their survival depends on them. If the drug works, he expects it will be used after orthodox chemotherapy has neutralised most tumour cells.
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