DNA of tobacco damage laid bare

THE damage that cigarettes and sunlight wreak on human DNA has been laid bare for the first time, along with the valiant, if eventually futile, effort of cells to repair the harm done.
Scientists have worked out the entire genetic code of two of the most deadly types of cancers - lung and melanoma - revealing the tens of thousands of mutations present in these tumours.
The research, regarded as a pivotal point in the search for new treatments for cancer, reveals a typical smoker would acquire one mutation, on average, for every 15 cigarettes smoked. More than 23,000 mutations were found in the lung cancer cells of a 55-year-old man, most of them caused by the cocktail of chemicals in cigarettes, the British-led team said.
Melanoma cells from a 43-year-old man were found to be ravaged by more than 33,000 mutations.
Mike Stratton, of the Cancer Genome Project at the Wellcome Trust Sanger Institute in Cambridge, said that the research provided an unprecedented view of the genetic impact of smoking and exposure to ultraviolet light.
''We have been able to explore deep into the past of each tumour, uncovering with remarkable clarity the imprints of these environmental mutagens on DNA, which occurred years before the tumour became apparent.''
The ''desperate'' attempts by the genome to defend itself against these attacks were also obvious, Professor Stratton said. ''Our cells fight back furiously to repair the damage, but frequently lose that fight.''
The mutations identified in the studies, which were published in the journal Nature, ranged from changes in single letters in the DNA code to missing sequences or rearrangement of hundreds of thousands of letters.
Tracking down mutations responsible for driving the cancer's development was the next challenge, the researchers said, as it enabled the development of drugs to target the cancer.