The technique has already been used to identify such a domain on the BRD4 protein and inhibitors that bind to this domain had significant antitumor activity in leukemia, Dr. Vakoc reported. A screen targeting 192 chromatin regulatory domains expressed in mouse acute myeloid leukemia cells was subsequently performed and identified 25 domains that impacted survival, 6 that are already being therapeutically targeted, and 19 novel potential targets.
Another development in CRISPR-Cas9 technology creates an inactive version of the Cas9 enzyme, one that has lost the ability to cut DNA. Though it seems counterintuitive, this has opened up a wealth of new possible uses. Jonathan S. Weissman, Ph.D., professor of cellular and molecular pharmacology, University of California, San Francisco, part of the group to develop this ‘dead’ Cas9 (dCas9), published a description of the use of two new tools dubbed CRISPR interference and CRISPR activation (Cell 2013;152[5]:1173-83).
Essentially, by fusing dCas9 with different proteins, such as epigenetic modifiers or transcriptional activators or repressors, it can be used as a delivery system to fine-tune gene expression, instead of editing the gene sequence.
Treating cancer?
Ultimately, CRISPR-Cas9 could be used to treat cancers by cutting out defective genes and replacing them with a wild-type version, or by repairing mutations, though for the time being this is theoretical. Studies have suggested it is possible with other types of diseases, however.
“It is not clear exactly how the CRISPR system would be used to directly treat cancer, but the discoveries that come from its use will likely lead to new ways to treat cancer,” said Dr Armstrong.
Dr Jacks highlighted the technical challenges that will need to be overcome first. “In principle, CRISPR-based genome editing could be used to correct cancer-causing mutations in tumors in vivo or to inactivate activated cancer genes,” he said. “At this point, however, we lack the technology necessary to deliver the CRISPR system to all cancer cells in the body. Improvements in this so-called ‘delivery problem’ may allow CRISPR to become a powerful anticancer therapy strategy.”