Scientists have successfully used gene-editing to reduce tumor growth in mice, according to a study published September 5th, in the journal Nature Methods. The gene-editing tool, called Crispr-Cas9, replaces faulty DNA with code that kills cancerous cells. Cell-signaling pathways which would otherwise accelerate tumor growth in mice were reprogrammed. The reprogrammed code was led to mice developing much smaller tumors than the control mice who did not receive treatment. The research was conducted by Dr Weiren Huang, and other colleagues, from the First Affiliated Hospital of Shenzhen University, in China.

Crispr-Cas9 is a system for “cutting and pasting” DNA, used in nature by bacteria to fend off dangerous viral DNA. Scientists have been working on using the system to target and remove harmful DNA which cause illness in humans. The process can, however, carry risks – even when effective. In particular, it can cut out too much DNA, possibly altering important genes. In the process it could actually trigger cancer.

First, a “guide RNA” searches the DNA to target the gene in question. The Cas9 enzyme then cuts through both strands of DNA. At this point, the harmful gene can either be inactivated, or replaced with healthy DNA. If these edits miss their targets, they can potentially do more harm than good.

According to Dr. Chris Lord, who is a gene expert at the Institute of Cancer Research, “The key to translating this technique into the clinic will be to see how specific to the tumor cell the crispr activation will be and how specific, in terms of genes, the crispr-mediated gene cutting will be. These are essentially the same two issues you have with all cancer treatments – how specific for the tumor cell and how specific for the target.”

The technology was published four years ago in 2012, developed by a team led by UC Berkeley Professor Jennifer Doudna and French microbiologist Emmanuelle Charpentier. Since then, the gene editing method has been applied to a wide variety of practical uses in a wide range of living organisms. In humans, it has already been used to reverse mutations that cause blindness, to protect cells from the virus that causes AIDS, and to limit the growth of cancer cells. In agriculture, it has been used to protect wheat from harmful fungi.

The name is an acronym for “clustered regularly interspaced short palindromic repeats”, which essentially describes the genetic basis for the method, while Cas9 names the protein that used to make the ‘crispr’ method function.

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