Tumors are like smoothtalking scam artists. Through the messages they send out, they convince other cells to do their bidding. Vascular endothelial cells, in particular, are duped into providing tumors with the blood supply they need to grow. Decades ago, cancer pioneer Judah Folkman realized that without sufficient vascularization tumors would starve. His insight spurred the development of several angiogenesis inhibitors now in clinical use.
In a study published in the Nov. 4 issue of Cancer Cell, Breakefield and her colleagues identify a new anti-angiogenesis target, the microRNA miR-296, which they found regulates glioma-induced angiogenesis.
Thomas Würdinger, a postdoctoral fellow in Breakefield’s lab, discovered that by secreting well-known growth factors like vascular endothelial growth factor (VEGF), glioma cells not only induce endothelial cells to form blood vessels, they also enhance endothelial expression of the receptors that respond to these angiogenic signals. Würdinger, who is also a member of the neuro-oncology research group at the VU University Medical Center in the Netherlands, determined that both of these angiogenic effects are stimulated by miR-296 in endothelial cells.
“Other miRNAs are known to be involved in angiogenesis,” said Anna Krichevsky, HMS assistant professor of neurology at Brigham and Women’s Hospital and senior author of the study. “But what makes this miRNA different is that it is upregulated within endothelial cells in response to soluble signals from the glioma.”
Like most miRNAs, miR-296 has hundreds of bioinformatically predicted mRNA targets. The researchers focused their validation efforts on a target with a known role in growth factor signaling.
“Hepatocyte growth factor–regulated tyrosine kinase substrate [HGS] facilitates the degradation of internalized growth factor receptors,” said Krichevsky. “We found that when it is silenced by miR-296, more receptors return to the cell surface and amplify the angiogenic signal.”
To determine how miR-296 affects tumor-induced angiogenesis in vivo, the researchers developed an antisense inhibitor of miR-296, which they injected into a mouse model of glioma. Mice injected with this antagomir showed a marked decrease in angiogenesis at the tumor site.
“It is too early to say whether inhibiting miR-296 would ultimately limit tumor size or enhance survival,” said Breakefield, who is also a geneticist at MGH. “Further studies are needed to address that question.”
“We would like to test antagomirs in combination with standard cancer therapies, such as chemotherapy,” said Würdinger by e-mail, suggesting that antagonizing the activity of an angiogenic factor, like miR-296, might restrain a tumor while genotoxic drugs do their work.
“In gliomas new targets are badly needed,” said Krichevsky. “I don’t believe that inhibiting a single miRNA will stop gliomas, but combinational therapy could be very promising.”
Breakefield, Krichevsky, and their colleagues have published a related paper, which appeared online Nov. 16 in Nature Cell Biology, describing another way that glioma cells manipulate their environment. The researchers, including first author Johan Skog, an instructor in neurology in Breakefield’s lab, found that glioma cells shed vesicles, called exosomes, that contain mRNA, miRNA, and proteins. These exosomes are taken up by vascular endothelial cells and alter their physiology, causing them to form new blood vessels, for example, which benefits the blood-thirsty glioma.
These vesicles could be harnessed to benefit patients, too. The researchers found that because the vesicles enter the bloodstream, they provide accessible information about the glioma that could help physicians design tailored therapies and monitor progress without invasive brain surgery.
Conflict Disclosure: The authors declare no conflicts of interest.
Funding Sources: The American Brain Tumor Association, Brain Tumor Society, National Institutes of Health, National Cancer Institute (NIH), National Institute of Neurological Disorders and Stroke (NIH), Wenner-Gren Foundation, and Stiftelsen Olle Engkvist Byggmästare
A few years back, as Catherine DeAngelis was going about her job as editor in chief of The Journal of the American Medical Association, she got word that a major pharmaceutical company wanted to run an expensive ad, but only if it would appear in a particular issue—one with articles relating to the company’s product. Under pressure by her sales department, DeAngelis agreed to let the ad run.
“And I moved the articles ahead two months,” she told a packed auditorium attending the 26th Fae Golden Kass Lecture, which was established in 1970 by Edward Kass to honor outstanding women in medical science. At her talk, titled “Conflict of Interest—Facts and Friction,” DeAngelis was humorous, lively, and passionate as she folded this and other personal anecdotes into a larger narrative about how the noble profession of medicine is being threatened by big business greed and corruption.
It is an epic tale with many actors—investigators, authors, reviewers, and editors may all fall prey to a conflict between private interest and official responsibility. The desire for career advancement, recognition, and funding can cause scientists to compromise their standards of accuracy and fairness. But the really questionable players, according to DeAngelis, are the pharmaceutical and biotech companies, and especially their marketing departments, who use their big budgets to lure scientists into compromising positions.
“Financial interests can bias what authors publish and also when, where, how, and if research is published,” said DeAngelis.
She spent much of her talk reviewing a litany of such transgressions, including nonreporting and hiding of negative results; delaying publication for proprietary reasons; suppressing and withholding data; and outright lying and fabrication. Nor did she shy away from naming names, implicating the makers of such industry giants as Synthroid, Celebrex, and Vioxx. Some pharmaceutical companies are soliciting and paying for articles by researchers, and in some cases even ghostwriting them. “The total result arouses public concern and threatens the credibility of biomedical research,” she said.
She and editorial colleagues have taken corrective measures like demanding that companies who publish in their journals register all of their clinical trials. New disclosure practices require that authors reveal funding sources and financial interests, but more needs to be done to monitor conflicts of interest, especially by medical schools, she said.
“My bottom line for this talk is, we’ve got to take back our profession,” she said. And getting more personal, “Harvard is the number one medical school, maybe in the world. Who better to set the example?”
Few family dramas have fascinated biologists like the one playing out among the BCL-2 group of proteins. Some family members, such as BAX, promote apoptosis while others prevent it, and they do so by trapping their destructive cousins in a groove located on their surface. Some researchers have assumed that it is only when BAX is released from this groove that it can be activated. Indeed, efforts to harness BAX for the purpose of killing cancer cells have focused on keeping or pulling it out of the anti-apoptotic proteins’ pocket.
Loren Walensky, Evripidis Gavathiotis, and colleagues have discovered a new binding site on BAX, one that can trigger its killer activity directly. The finding, reported in the Oct. 23 Nature, supports an expanded view about how BAX is activated.
The view was first put forth several years ago by the late Stanley Korsmeyer, who suggested that another set of BCL-2 family members might be activating BAX directly. These proteins, which include BIM and BID, are known to respond to various stresses on the cell by promoting apoptosis. Korsmeyer thought they might be doing so by touching and activating BAX, but it was not clear if proteins like BIM could actually bind BAX.
Part of the problem is that BIM’s key binding subunit, an alpha-helical peptide, loses its normal shape once separated from the rest of the protein. Employing a method developed by Harvard University’s Gregory Verdine, Walensky, HMS assistant professor of pediatrics at Dana–Farber Cancer Institute, and colleagues stapled the peptide into its natural helical shape and, in 2006, reported that some of the stapled peptides bound BAX. But it was not clear where the peptides were binding.
Gavathiotis, research fellow in pediatrics at DFCI, Walensky, and colleagues, working with researchers at the National Institutes of Health, conducted nuclear magnetic resonance (NMR) studies and were able to identify the binding site. They went on to solve the structure of the bound complex, using a specialized method, paramagnetic relaxation enhancement (PRE) NMR. To see if the binding was linked to BAX activation, they mutated the binding site at various spots, both in vitro and in intact cells. Under both conditions, they found BAX’s ability to carry out its death-inducing activities was greatly impaired.
“We’ve now determined how BAX is directly triggered,” said Walensky, adding that the trigger might be manipulated to combat a variety of diseases. “In the case of premature cell death that occurs in stroke, heart attack, or neurodegeneration, where you want to turn the death process off in a cell, you would want to prevent access to the trigger site. To kill unwanted cells as in cancer, you would want to mobilize BAX by deploying a compound that directly binds and activates the trigger site.”
For Students: Contact Loren Walensky at Loren_Walensky@dfci.harvard.edu for further information about this and other lab projects.
Conflicts of interest: L.D.W. is a scientific advisory board member and consultant for Aileron Therapeutics, Inc.
Funding Sources: The National Cancer Institute, the Burroughs Wellcome Fund, the Goldman Philanthropic Partnerships, the American Society of Hematology the William Lawrence Children's Foundation, the National Heart, Lung, and Blood Institute, and the Searle Scholars Program