24 April 2017
ByAppeared in BioNews 897
A new highly sensitive diagnostic system for diseases has been adapted from CRISPR.
Named SHERLOCK (Specific High-sensitivity Enzymatic Reporter UnLOCKing), the diagnostic system could detect miniscule amounts of RNA or DNA from samples and offer rapid, accurate results without the need for sophisticated lab equipment.
'This tool offers the sensitivity that could detect an extremely small amount of cancer DNA in a patient's blood sample, for example, which would help researchers understand how cancer mutates over time,' said Professor James Collins at MIT and Harvard University, who co-led the team behind the system. 'For public health, it could help researchers monitor the frequency of antibiotic-resistant bacteria in a population. The scientific possibilities get very exciting very quickly.'
The team led by Professor Collins and Professor Feng Zhang at MIT and Harvard University combined novel methods with established techniques to amplify genetic material in a sample, find a target sequence and then create a visible result.
The system uses an enzyme called Cas13a which targets RNA, and which was discovered by Professor Zhang of MIT and colleagues last year. By attaching a sequence tag, Cas13a can be guided to find and cut a specific RNA target. Once it has done this it will randomly cut any nearby pieces of 'collateral' RNA, regardless of their sequence.
The system adds so-called fluorescent reporter RNA to the samples, which emits a fluorescent signal only when cut. So if Cas13a finds its target sequence, its subsequent cutting of the reporter RNA produces a fluorescence which can be easily detected without the use of sophisticated equipment.
The precision of the enzyme is such that even a difference of one base-pair - such as between the genetic codes of the African and American strains of Zika - will affect whether or not activation occurs. It is also able to detect concentrations as low as two molecules in a quintillion.
The system can be run in a standard test tube or on glass fibre paper, and requires no high-tech lab equipment or temperatures higher than body heat. The authors say the molecules for the test can be designed and made for as little as US $0.61.
'One thing that's especially powerful about SHERLOCK is its ability to start testing without a lot of complicated and time-consuming upstream experimental work,' said Professor Pardis Sabeti of Harvard University, a co-author of the paper. 'This ability to take raw samples and immediately start processing could transform the diagnosis of Zika and a boundless number of other infectious diseases.'
Dr Alexander McAdam, a medical microbiologist at Boston Children's Hospital who was not involved in the project, said to STAT: 'They've developed a promising method of detecting extremely low concentrations of [genetic material], but the key word is "promising". It's going to be a long walk from hopeful to clinically useful, and there is a lot to do to demonstrate practicality.'
The study was published in Science.