MIT researchers using the CRISPR-Cas9 genome editing and organoid technology have developed a new mouse model with a cancer that closely resembles colon cancer in humans. This new model may help scientists understand the mechanism underlying the disease, and ultimately develop better, more efficient therapies against it.
The study, “In vivo genome editing and organoid transplantation models of colorectal cancer and metastasis,” appeared in the journal Nature Biotechnology.
One of the challenges in creating appropriate, reliable mice models is capturing all aspects of human disease. In colorectal cancer, the disease often metastasizes, or spreads, to the liver.
“That’s been a missing piece in the study of colon cancer,” assistant biology professor Omer Yilmaz, a member of MIT’s Koch Institute for Integrative Cancer Research, said in a press release. “There is really no reliable method for recapitulating the metastatic progression from a primary tumor in the colon to the liver.”
A previous study by Tyler Jacks, director of the Koch Institute, also used CRISPR to generate lung and liver tumors in mice.
“CRISPR-based technologies have begun to revolutionize many aspects of cancer research, including building mouse models of the disease with greater speed and greater precision,” said Jacks. “This study is a good example of both.”
Cancer research has long relied on two models. In the first, researchers grow human cancer cells in vitro in a lab and maintain them indefinitely. The second method requires generating mice carrying mutations in genes that predispose them to cancer. However, these mice can take years to breed, depending on how many mutations are required.
The introduction of CRISPR genome editing technology allows scientists to introduce mutations in specific regions within a mouse genome. Yilmaz and his team generated tumors in colon organoids, or small versions of a colon, grown in a dish in the lab.
In their study, researchers used CRISPR to insert cancer-causing mutations into the colon organoids, which were then surgically placed into the colons of mice. The gene-edited organoids attached to the colon and formed tumors. “We were able to transplant these 3-D mini-intestinal tumors into the colon of recipient mice and recapitulate many aspects of human disease,” Yilmaz said.
Colon tumors in humans have been shown to acquire mutations in a certain order, but reproducing these events in mice has been difficult until now.
“In human patients, mutations never occur all at once,” said Tuomas Tammela, a Koch Institute research scientist and study author. “Mutations are acquired over time as the tumor progresses and becomes more aggressive, more invasive, and more metastatic. Now we can model this in mice.”
The mutated APC gene initiates tumors in 80 percent of colon cancer patients. Researchers delivered organoids with a mutated form of this gene to mice. After the tumors established themselves, researchers introduced a second mutation, now in another important gene, called KRAS, which is often mutated in colon and many other cancers. They also targeted mutations to another key gene in many cancers, the P53 gene.
“These new approaches reduce the time frame to develop genetically engineered mice from two years to just a few months, and involve very basic gene engineering with CRISPR,” said Jatin Roper, a Koch Institute research affiliate and a gastroenterologist at Tufts Medical Center. “We used P53 and KRAS to demonstrate the principle that the CRISPR editing approach and the organoid transplantation approach can be used to very quickly model any possible cancer-associated gene.”
This study shows that researchers can grow organoids from patients’ tumor cells, which may then be transplanted into mice. This represents a potential personalized form of treatment, in which drugs could be tested in a patient’s cells before being given to patients. In fact, the research team is now using its mice model and CRISPR to test investigative drugs for colon cancer.
Fernando Camargo, a professor of stem cell and regenerative biology at Harvard University who was not involved in the study, said the research is important. “It allows investigators to have a very flexible model to look at multiple aspects of colorectal cancer, from basic biology of the genes involved in progression and metastasis, to testing potential drugs,” Camargo said.
