Robots one-thousandth the width of a human hair are now able to fight cancer by destroying tumours in the body.
Scientists have built nano-robots from DNA sheets shaped into tubes and injected into the bloodstream.
The tubes carry a blood-clotting enzyme, thrombin, and are painted with proteins which home in on a separate protein found only in tumour cells.
When the robots reach their target and bind to its surface they spring open and deliver the enzyme which clots the blood supply to the tumour and causes it to have a mini heart attack and die. The nanorobots work fast, congregating in large numbers to surround a tumour just hours after injection.
They were found to be safe in tests on mice and pigs, with no evidence of spreading to the brain where they could cause a stroke. The treatment blocked tumour blood supply and generated tumour tissue damage within 24 hours, while having no effect on healthy tissue.
Three out of eight mice with skin cancer saw their tumours shrink, with their survival time from cancer more than doubling on average from 20.5 to 45 days.
The research comes after a team of scientists, involving Durham University, last year created nanorobots able to drill into and destroy cancer cells.
Nanorobots are so-called because of their tiny size and because they contain parts capable of movement within the body. In this case, the mechanical action is the springing open of the DNA sheet to reveal the blood-clotting drug.
Baroness Delyth Morgan, chief executive of Breast Cancer Now, said: 'The development of nanorobots that can deliver drugs to a specific target within a tumour is an exciting glimpse into the future of cancer medicine.
'This is the first time that DNA molecules have been manipulated to deliver drugs in this way – a fascinating advance that, if refined and proven effective in humans, could have far-reaching implications for treating cancer and other diseases.'
Professor Peter Dobson, from the University of Oxford, said: 'It is a neat idea and there is a lot of evidence in the paper to show that this is a promising approach.'
Professor Hao Yan, a co-author of the study from Arizona State University, said: 'We have developed the first fully autonomous, DNA robotic system for a very precise drug design and targeted cancer therapy.
'Moreover, this technology is a strategy that can be used for many types of cancer, since all solid tumour-feeding blood vessels are essentially the same.' Nanotechnology, which is smaller than most of us can imagine, is seen as the way forward to tackle cancer through a simple injection.
One sheet of newspaper is around 100,000 nanometres thick. The nanorobots used to fight cancer are made from sheets of DNA measuring just 90 nanometres by 60.
Dr James Tour of Rice University in the US, who was involved in last year's breakthrough with Durham University, said the 'spring-loaded' nanorobot was 'exciting', adding: 'It is a nano-Trojan horse!'
The research, which was led by the National Centre for Nanoscience and Technology in China, is published in the journal Nature Biotechnology.
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