A new way to model cancer

August 06, 2014

CAMBRIDGE, MA -- Sequencing the genomes of tumor cells has revealed thousands of mutations associated with cancer. One way to discover the role of these mutations is to breed a strain of mice that carry the genetic flaw -- but breeding such mice is an expensive, time-consuming process.

Now, MIT researchers have found an alternative: They have shown that a gene-editing system called CRISPR can introduce cancer-causing mutations into the livers of adult mice, enabling scientists to screen these mutations much more quickly.

In a study appearing in the August 6th issue of Nature, the researchers generated liver tumors in adult mice by disrupting the tumor suppressor genes p53 and pten. They are now working on ways to deliver the necessary CRISPR components to other organs, allowing them to investigate mutations found in other types of cancer.

"The sequencing of human tumors has revealed hundreds of oncogenes and tumor suppressor genes in different combinations. The flexibility of this technology, as delivery gets better in the future, will give you a way to pretty rapidly test those combinations," says Phillip Sharp, the David H. Koch Institute Professor at MIT and an author of the paper.

Tyler Jacks, director of MIT's Koch Institute for Integrative Cancer Research and the David H. Koch Professor of Biology, is the paper's senior author. The lead authors are Koch Institute postdocs Wen Xue, Sidi Chen, and Hao Yin.

Gene disruption

CRISPR relies on cellular machinery that bacteria use to defend themselves from viral infection. Researchers have copied this bacterial system to create gene-editing complexes that include a DNA-cutting enzyme called Cas9 bound to a short RNA guide strand that is programmed to bind to a specific genome sequence, telling Cas9 where to make its cut.

In some cases, the researchers simply snip out part of a gene to disrupt its function; in others, they also introduce a DNA template strand that encodes a new sequence to replace the deleted DNA.

To investigate the potential usefulness of CRISPR for creating mouse models of cancer, the researchers first used it to knock out p53 and pten, which protect cells from becoming cancerous by regulating cell growth. Previous studies have shown that genetically engineered mice with mutations in both of those genes will develop cancer within a few months.

Studies of such genetically engineered mice have yielded many important discoveries, but the process, which requires introducing mutations into embryonic stem cells, can take more than a year and costs hundreds of thousands of dollars. "It's a very long process, and the more genes you're working with, the longer and more complicated it becomes," Jacks says.

Using Cas enzymes targeted to cut snippets of p53 and pten, the researchers were able to disrupt those two genes in about 3 percent of liver cells, enough to produce liver tumors within three months.

Many models possible

The researchers also used CRISPR to create a mouse model with an oncogene called beta catenin, which makes cells more likely to become cancerous if additional mutations occur later on. To create this model, the researchers had to cut out the normal version of the gene and replace it with an overactive form, which was successful in about 0.5 percent of hepatocytes (the cells that make up most of the liver).

The ability to not only delete genes, but also to replace them with altered versions "really opens up all sorts of new possibilities when you think about the kinds of genes that you would want to mutate in the future," Jacks says. "Both loss of function and gain of function are possible."

Using CRISPR to generate tumors should allow scientists to more rapidly study how different genetic mutations interact to produce cancers, as well as the effects of potential drugs on tumors with a specific genetic profile.

In this study, the researchers delivered the genes necessary for CRISPR through injections into veins in the tails of the mice. While this is an effective way to get genetic material to the liver, it would not work for other organs of interest. However, nanoparticles and other delivery methods now being developed for DNA and RNA could prove more effective in targeting other organs, Sharp says.
-end-
The research was funded by the National Institutes of Health and the National Cancer Institute.

Massachusetts Institute of Technology

Related Cancer Articles from Brightsurf:

New blood cancer treatment works by selectively interfering with cancer cell signalling
University of Alberta scientists have identified the mechanism of action behind a new type of precision cancer drug for blood cancers that is set for human trials, according to research published in Nature Communications.

UCI researchers uncover cancer cell vulnerabilities; may lead to better cancer therapies
A new University of California, Irvine-led study reveals a protein responsible for genetic changes resulting in a variety of cancers, may also be the key to more effective, targeted cancer therapy.

Breast cancer treatment costs highest among young women with metastic cancer
In a fight for their lives, young women, age 18-44, spend double the amount of older women to survive metastatic breast cancer, according to a large statewide study by the University of North Carolina at Chapel Hill.

Cancer mortality continues steady decline, driven by progress against lung cancer
The cancer death rate declined by 29% from 1991 to 2017, including a 2.2% drop from 2016 to 2017, the largest single-year drop in cancer mortality ever reported.

Stress in cervical cancer patients associated with higher risk of cancer-specific mortality
Psychological stress was associated with a higher risk of cancer-specific mortality in women diagnosed with cervical cancer.

Cancer-sniffing dogs 97% accurate in identifying lung cancer, according to study in JAOA
The next step will be to further fractionate the samples based on chemical and physical properties, presenting them back to the dogs until the specific biomarkers for each cancer are identified.

Moffitt Cancer Center researchers identify one way T cell function may fail in cancer
Moffitt Cancer Center researchers have discovered a mechanism by which one type of immune cell, CD8+ T cells, can become dysfunctional, impeding its ability to seek and kill cancer cells.

More cancer survivors, fewer cancer specialists point to challenge in meeting care needs
An aging population, a growing number of cancer survivors, and a projected shortage of cancer care providers will result in a challenge in delivering the care for cancer survivors in the United States if systemic changes are not made.

New cancer vaccine platform a potential tool for efficacious targeted cancer therapy
Researchers at the University of Helsinki have discovered a solution in the form of a cancer vaccine platform for improving the efficacy of oncolytic viruses used in cancer treatment.

American Cancer Society outlines blueprint for cancer control in the 21st century
The American Cancer Society is outlining its vision for cancer control in the decades ahead in a series of articles that forms the basis of a national cancer control plan.

Read More: Cancer News and Cancer Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.