Identifying New Targets in Cancer Metabolism and Treatment

Progress in cancer research over the past ten years has helped scientists gain a greater understanding of cancer cell metabolism and how cancer cells interact – metabolically speaking – with neighboring cells in the tumor microenvironment in order to secure the nutrients they need to proliferate.

“Learning which conversations between cancer cells and their neighbors to interrupt could potentially point us to new targets for treatments that are more effective than those in use today,” said Deepak Nagrath, associate professor, who joined the BME faculty in January 2017.

In ongoing work begun at Rice University, Nagrath takes a systems biology approach, combining a metabolic isotope tracing technique with a computational framework, together known as 13C-based metabolic flux analysis. He has conducted a number of studies to more fully understand the metabolism of cancer cells as well as their interactions with their immediate environment.

In work published in November 2016 in Cell Metabolism, Nagrath focused on glutamine, an amino acid for which many types of cancer cells have been shown to have a voracious appetite. He also focused on the related enzyme glutamine synthetase in the stroma, or the connective tissue that makes up the tumor microenvironment.

In ovarian cancer cells, Nagrath’s team found greater expression of genes that control glutamine production than in normal cells and that, when the cancer cells were put into a glutamine-deprived environment, surrounding cells known as cancer-associated fibroblasts (CAFs) began producing higher than normal levels of the amino acid.

Upon further investigation, the researchers observed an interesting dynamic between the cancer and stromal cells: The cancer cells appeared to barter with their neighbors. The cancer cells contributed two enzymes, lactate and glutamate, and in exchange, the neighboring CAFs used the enzymes to produce – and share – glutamine.

But when the team inhibited glutamine production by the neighboring CAFs using drugs or through depriving them of nutrients, the ovarian cancer cells stopped growing.

Precisely how ovarian and other types of cancer cells metabolically coax their neighbors to produce nutrients is still not fully known, but Nagrath’s latest work helps snap another important puzzle piece in place.

“We now know that targeting glutamine-producing enzymes in the tumor microenvironment slowed the growth of tumors,” he said. “This suggests to us that using a combination of therapies, rather than just one, to simultaneously target glutamine production and metabolism within cancer cells as well as in their surrounding environment may help us improve treatment.”

The work was funded by a St. Louis Ovarian Cancer Research Awareness grant.

Yang, L. Targeting stromal glutamine synthetase in tumors disrupts tumor microenvironment-regulated cancer cell growth. Cell Metabolism, 24 (2016), 685-700; dx.doi.org/10.1016/j.cmet.2016.10.011

One Lab, Three Approaches to Restoring Ovarian Function Ariella Shikanov

By Aimee Balfe

BME Assistant Professor Ariella Shikanov has just received an NSF CAREER award to help fund one of the three approaches her lab is taking to help restore ovarian function in women and girls undergoing treatment for cancer and autoimmune disease that is toxic to the ovaries.

While physicians can freeze a woman’s eggs, allowing her to later have a biologically related child, the process isn’t suitable for some patients, including young girls. It also doesn’t address the issue of ovaries’ endocrine function. “Ovaries are not only about making babies,” says Shikanov, “they also produce estrogen, progesterone, and other hormones that are very important for the health of a woman’s bones, cardiovascular system, and skin.”

“Ovaries are not only about making babies…they also produce estrogen, progesterone, and other hormones that are very important for the health of a woman’s bones, cardiovascular system, and skin.” Shikanov

They’re also essential for enabling girls to go through puberty. Girls who’ve lost ovarian function require synthetic hormones, whose long-term use carries a health risk. In addition, the dosage has to be just right. Too little and the girls won’t grow sufficiently. Too much and the bones’ growth plates close prematurely. Without optimal dosing, the girls are at increased risk for various bone, cardiovascular, and metabolic problems like diabetes and obesity.

The Path to U-M

shikanovShikanov would become captivated by this issue and begin down a road that would lead her from the Hebrew University in Jerusalem to U-M via a postdoctoral fellowship in the lab of Lonnie Shea. Then at Northwestern, and now U-M’s William and Valerie Hall Chair and Professor of BME, Shea had been working on ovarian tissue engineering and needed a postdoc with expertise in polymer synthesis and hydrogel development. Shikanov, a medicinal chemist by training, had the right skill set.

“He told me, ‘Don’t worry; you’ll learn about reproduction,’” she says. Over the next four years, she found herself doing surgeries in mice, looking for ways to make ovarian tissue transplantation more successful, and developing synthetic culture environments for ovarian follicles – the structures that contain immature eggs and are essential to endocrine function.

The latter offered an intriguing engineering challenge. “We had to design a hydrogel that would be soft enough not to kill an ovarian follicle, but rigid enough to support its 3D structure as it matures and expands 100 times in volume,” she says. “It also had to be physiologic, allowing the diffusion of nutrients and oxygen.”

“We had to design a hydrogel that would be soft enough not to kill an ovarian follicle, but rigid enough to support its 3D structure as it matures and expands 100 times in volume” Shikanov

She was deep in this work when U-M announced a cluster-hire position in reproductive biomaterials that precisely matched her expertise. She was hired in 2012, launching a lab that would address ovarian function through three distinct but mutually reinforcing projects.

The Projects

Restoring endocrine function in girls

Shikanov’s first project aims to restore endocrine function in girls with damaged ovaries, allowing them to undergo physiologic puberty. She is developing an implant that encapsulates donor ovarian tissue in an immunoisolating hydrogel. Injected under the skin, it won’t restore fertility but would stimulate the production of estrogen at this critical time.

“Puberty starts in the brain,” says Shikanov. “The hypothalamus secretes a hormone, which stimulates the pituitary gland to secrete follicular stimulating hormone, which tells the ovarian tissue to secrete estrogen. Then the estrogen goes back to the brain, controlling things through a finely tuned loop. This is what allows us to go through puberty, and this why it is so important to have a healthy and functioning ovarian tissue that we aim to engineer.”

With a grant from The Hartwell Foundation, her lab has already demonstrated in mice that the process works and that its longevity is determined by the number of follicles implanted. She plans to move to larger animal models before testing the product in humans.

Understanding how ovarian follicles develop

Shikanov’s second project, for which she won her CAREER award, aims to understand the cell signaling involved in the development of ovarian follicles so she can design better culture systems for harvested tissue.

Harvesting of immature ovarian follicles holds promise for restoring fertility when a woman can’t freeze her eggs – either because she doesn’t have time to undergo ovarian stimulation prior to starting treatment or because she has a hormone-driven cancer where stimulation would be inappropriate. The problem has been getting follicles to survive and mature in culture.

The reason for this, says Shikanov, is that follicles’ essential signaling networks are poorly understood. “Right now, we know that follicles grow best when they’re co-cultured with other follicles and stem cells, but we don’t know why.”

She hopes to remedy this through mechanistic studies of folliculogenesis. Using transcription factor reporters, metabolomics, and systems biology, she aims to reveal the identity, timing and activity pattern of secreted growth factors and transcription factors that allow follicles to grow.

During the project, she plans to continue collaborating with Lonnie Shea, as well as with BME computational modeling expert David Sept, new faculty member Kelly Arnold, and U-M’s metabolomics core, MRC2.

She will start the experimental work in mice, but hopes to move to human tissue in a matter of years. “I want to get to the point where I can take one follicle and say, if I add this list of factors at these concentrations in this timing sequence, I will be able to grow the follicle without adding other follicles or cells,” she says.

Designing an artificial ovary
engineering-ovary
Her final project is the design of an artificial ovary. This involves encapsulating the smallest, primordial follicles in a synthetic polymer that mimics the ovaries’ natural environment with the goal of restoring both fertility and endocrine function. She expects that her mechanistic studies will offer substantial insights to this work.

Shikanov says her research is extremely gratifying, and she enjoys introducing it to young people, especially women, through camps and programs for middle and high schoolers. In addition, her lab is always seeking talented postdocs interested in learning more about biomaterials in reproductive sciences. She can be contacted at shikanov@umich.edu.

2016 NSF Fellowships

Three BME students won prestigious National Science Foundation (NSF) Graduate Research Fellowships in 2016. They include PhD students Chrono Nu from Cindy Chestek’s Cortical Neural Prosthetics Lab and Peter Washabaugh from Chandramouli Krishnan’s Neuromuscular and Rehabilitation Robotics Laboratory, as well as master’s student Makeda Stephenson from Scott Hollister’s Scaffold Tissue Engineering Group.

 

Nu, who has also been awarded a Department of Defense (DoD) National Defense Science and Engineering Graduate (NDSEG) Fellowship, is using data from cortical recording systems to conduct computational analyses of brain activity in primates, such as decoding motor-related neurological signals. Washabaugh is working to design robotic devices for use in physical therapy and to explore the neuromuscular changes associated with these therapies. Stephenson is developing functional architectures for tissue engineering scaffolds.