By Daniel Dunaief
In the battle against cancer, human bodies have built-in defenses. Cancers, however, can hijack those systems, turning them against us, not only allowing them to avoid these protective systems, but converting them into participants in a process that can often become fatal.
Such is the case for the p53 gene. One of the most closely studied genes among researchers and clinicians, this gene eliminates cells with damaged DNA, which could turn into cancer. Mutations in this genetic watchdog, however, can turn this genetic hero into a villainous cancer collaborator. Indeed, changes in the genetic code for p53 can allow it to produce a protein that protects cancer from degradation.
Ute Moll, professor and the vice chair for research in the Department of Pathology at the Stony Brook University School of Medicine, has made important strides in studying the effect of mutations in this gene over the last five years, demonstrating how the altered gene and the protein it creates are an important ally for cancer.
Moll published her most recent finding in this arena in the journal Cancer Cell. The Stony Brook scientist, working with an international team of researchers that included collaborators from her satellite lab at the University of Göttingen, advanced the work on previous results.
This research, which is done on mice that develop tumors through a process that more closely resembles human cancer growth, is a “very good mimic in the molecular and clinical features of human colon cancer,” Moll said.
The main research was done on a faithful mouse model of human colorectal cancer that produces mutant p53, Moll explained. She then confirmed key findings in human colon cancer cells and in survival analysis of patients.
This model allowed Moll to “study tumors in their natural environment in the intact organism with its tumor surrounding connective tissue and immune system,” Ken Shroyer, the chairman of the Department of Pathology at SBU School of Medicine, explained in an email.
The tumors that develop in these mice are driven by mutant p53 and are dependent on it for their continued growth. “These tumors overexpress mutant p53 at high levels,” which makes them a “formidable drug target for their removal,” Moll said.
By deleting the mutant p53 gene, she was able to slow and even stop the progression of the cancer. “We can show that when we remove mutant p53 either genetically or pharmacologically, we are cutting down invasiveness.” Mice with deleted mutants had fewer and smaller tumors and showed over a 50 percent reduction in invasive tumor numbers, she explained.
Finding ways to mitigate the effect of mutant p53 is important for a wide range of cancers. The mutated version Moll studied is the single most common p53 mutation in human cancer, which has a mutation that switches an amino acid for an incorrect one. This amino acid change destroys the normal function of the p53 gene.
The mutation she studies represents about 4.5 percent of all cancers. That amounts to 66,000 cancer patients in the United States each year.
More broadly, mutations in p53 in general, including those Moll didn’t study, are involved in half of all human cancers, Shroyer explained, which makes it the “single most common cancer mutation.”
Yusuf Hannun, director of the Stony Brook University Cancer Center, suggested that the work Moll did could have important clinical implications.“The deciphering of this mechanism clearly indicates new cancer therapy possibilities,” Hannun wrote in an email. The models she worked with are “quite promising.”
In addition to finding ways to stop the progression of cancer in mice with this damaged gene, Moll and her colleagues also used an Hsp90 inhibitor, which blocks a protein that protects the mutant protein from being degraded.
Inhibiting this protein has other positive effects, as the inhibitor eliminates other co-mutant proteins that could also drive tumors. “We are hitting multiple birds with one stone,” Moll said.
Hsp90 inhibitors are a “complicated story” in part because they have strong side effects in the liver and the retina. Researchers are working on the next generation of inhibitors.
A class of anti-cholesterol drugs called statins, which Moll called “one of the blockbuster drugs of medicine,” also has mutant p53 degrading effects, which work against some mutants, but not in others. The benefits are inconsistent and involve confounding variables, which makes interpreting their usefulness difficult, she added.
Moll said her recent article in Cancer Cell has triggered a number of email exchanges with a range of people, including with a patient whose cancer involved a different type of mutation. She has also had discussions with researchers on several other possible collaborations and has started one after she published her recent work.
The scientist is hopeful that her studies will continue to contribute to an understanding of the development and potential treatment of cancer.
Degrading mutant p53 has shown positive results for mice, which indicates “in principle” that such an approach could work down the road in humans, she suggested.