Manipulating the decision-makers of cell fate

By Matthew Pariselli

Some scientists opt to pore over the intricacies and complexities of cell proliferation. It’s the cell’s ability to survive adversity and reproduce that such researchers find fascinating. For Dr. David Andrews, director of Biological Sciences at Sunnybrook Research Institute (SRI), however, it’s the contrary that piques his interest.

One of Andrews’ areas of research is apoptosis, or programmed cell death. It is a process that rids the body of potentially harmful or unneeded cells, and irregularity in its function can have severe repercussions. A dramatic rise in cell death is associated with some human immunodeficiency disorders, and Alzheimer’s and Parkinson’s diseases, for example, while a decrease is linked to cancer, among other concerns. The ability to control apoptosis, therefore, is coveted as it could lead to new and effective treatments for diseases. One molecule with this power is venetoclax, which was recently granted breakthrough status by the Food and Drug Administration, and features heavily in Andrews’ work. Scientists worldwide have been spurred to extensive research with the aim of increasing apoptosis to treat cancer, and Andrews, who is also a professor in the department of biochemistry at the University of Toronto, is among a smaller group that additionally focuses on preventing cell death.

Along with an international team of scientists, Andrews has found a way to forbid Bax and Bak—two proteins known as the ultimate decision-makers in apoptosis—from oligomerizing, an activity critical to the execution of cell death. By oligomerizing, Bax and Bak make holes in the mitochondria that provide energy to the cell. Andrews and his team have proven that cell death can be stopped by introducing to the mitochondria a small molecule—MSN-50, MSN-125 and DAN004 were all successful in tests. This was a welcome result as the researchers initially set out to study only Bax.

The team’s work also marks a milestone on the path toward understanding the Bax/Bak mechanism better. Up until now, only a general sense of the proteins’ behaviour and interactions had been grasped.

The findings, which Andrews unpacks via a paper published in Cell Chemical Biology, could lead to substantial clinical applications down the road. Andrews and his team have already made use of what they learned from MSN-50, MSN-125 and DAN004 to identify molecules with better drug-like properties that inhibit Bax in next-step tests. They are now testing Bak. “If [the molecules] don’t inhibit both, it doesn’t matter. It’s not good enough to inhibit one or the other; you have to be able to inhibit both if you want to keep the cell alive,” Andrews says.

If Andrews and his team can show that these new molecules inhibit Bak as they do Bax, then they can proceed with moving on to preclinical experiments. The goal, as distant as it may be at this point, is to improve the treatment of many human illnesses. “This is important for any cell-based therapy, and will be useful for other acute interventions,” Andrews says.

One area this work could affect is stroke treatment. Andrews explains: “When administering a clot-busting drug, for example, you could prevent damage to surrounding tissue that has been depleted of oxygen by the stroke. When oxygen returns after blood flow is restored, you get a lot of cell kill; this could keep these highly stressed but otherwise healthy cells from dying.” The goal would be to turn off Bax and Bak temporarily, but not permanently. “Bax and Bak are proteins that prevent you from getting cancer. The idea of shutting them off for a long period of time is worrisome,” he warns.

Another potential avenue to pursue is cell-based therapies. Andrews expresses his interest in exploring what he calls “zombie stem cells”: “If you want to take stem cells or any cells you’ve made in a lab and put them in a patient, you’ll need to shut off apoptosis in them temporarily. As a safety mechanism, cells are programmed to die when they are in the wrong place; when we make normal cells in the lab, they are by definition in the wrong place. As a result, you need the system to be shut off while you take the cells from the dish and put them in the patient. That’s why we wanted to try to make these molecules.” Small molecule-inhibitors of Bax and Bak would prevent apoptosis and therefore ensure the cells remain alive while they’re transferred from lab to patient.

Further discussion of stem cell therapy leads Andrews to mention Dr. Marc Jeschke, senior scientist in Biological Sciences and principal investigator of the burn research and skin regeneration lab at SRI. “We’ve talked about using [small molecule-inhibitors] in Marc’s work, where they’re pulling out stem cells from burned skin. Keeping stem cells alive while you’re manipulating or purifying them out of burned tissue from a person, this is the kind of thing you want to do. Any place where you want to keep cells alive temporarily, this work applies,” he says.

To enable preclinical studies, more drug molecules that inhibit Bax and Bak need to be identified. For this, Andrews recently received funding through a collaboration with Charité, a research institute at a hospital in Berlin, Germany that is affiliated with Humboldt Universität and Freie Universität. If he is successful in finding these elusive molecules, then Andrews can begin pitching the project to a pharmaceutical company, which could then take the work and develop a drug. On the flip side, he recognizes the value in discovering that such molecules allow one to create zombie cells that are of no value to patients—for example, neurons that stay alive but cannot send signals. The latter outcome would save scientists time, and potentially interested drug companies—as well as taxpayers—money.

Peering into the rear-view mirror and recalling his feeling when he learned his paper would be published, Andrews sighs before he says, “It was such a long slog, and so hard. We had seven reviewers because the project was so interdisciplinary; I was very relieved when it was done.” He underscores the international effort it took to get the work published with contributions from colleagues in Canada, China, Germany, India and the U.S.

As Andrews considers the promise of the future, though, his tone sharply turns from fatigued to enthusiastic. He says, “I was very nervous about whether or not we could take the next step; now, it looks like we might, and I’m very excited. If the new molecules inhibit both Bax and Bak, then we’ve taken the next big intellectual leap forward.”

This research was funded by the Canadian Institutes of Health Research and Ontario Institute for Cancer Research, with infrastructure support from the Canada Foundation for Innovation, and Ministry of Research, Innovation and Science.

Original article: Niu X, Brahmbhatt H, Mergenthaler P, Zhang Z, Sang J, Daude M, Ehlert FGR, Diederich WE, Wong E, Zhu W, Pogmore J, Nandy JP, Satyanarayana M, Jimmidi RK, Arya P, Leber B, Lin J, Culmsee C, Yi J, Andrews DW. A small-molecule inhibitor of Bax and Bak oligomerization prevents genotoxic cell death and promotes neuroprotection. Cell Chem Biol. 2017 Apr 20;24(4):493–506.