Cancer connection

Some say that the origins of the keto diet can be traced to celebrated bodybuilder and publishing entrepreneur Bernarr Macfadden, who in 1905 purchased a 2,000-acre tract of farmland about 15 miles east of Princeton to set up Physical Culture City, a place where men and women could escape the dissipation of modern life and enjoy, according to one of his books, “the vitality of a young lion.”

A self-educated fitness guru, Macfadden believed in the power of fasting to cure disease, a practice also espoused in ancient Greece. And although Macfadden’s legacy is little remembered — his Physical Culture City lasted only a few years, a casualty of legal battles — his impact on diet remains with us today through the work of one of his protégés, a physician named Hugh Conklin.

Conklin observed that fasting reduces epileptic seizures in children, a finding that was something of a medical miracle at a time when few drugs were available. Other researchers traced the mechanism to the body’s response to starvation. Deprived of fuel, the liver converts fat to ketone bodies, which serve as an alternate energy source for the brain and body. This state of ketosis, physician Russell Wilder at the Mayo Clinic found in 1921, could be achieved without starvation by eating a diet high in fat and low in carbohydrates. And a few years later, the ketogenic — or keto for short — diet was born.

One hundred years later, the keto diet has attained widespread popularity for weight loss, although it is still used to treat epilepsy. Now scientists at Princeton and other universities are hoping that the keto diet can treat another disease: cancer. In combination with traditional chemotherapies, this diet might boost the success rate and lead to longer remission for one of the most intractable forms of the disease, pancreatic cancer.

The teaming of chemotherapy and diet is an example of a growing strategy in the fight against cancer: exploiting cancer’s links to metabolism. Princeton’s Joshua Rabinowitz is one of the leaders in the field. Rabinowitz’s interest in cancer treatment grew out of a deeper fascination with how the body processes, or metabolizes, nutrients. A more comprehensive understanding of metabolism, Rabinowitz believes, could help treat a number of diseases. In spring 2021, Rabinowitz teamed with Eileen White of nearby Rutgers University and Princeton colleague Yibin Kang to lead a major new cancer initiative, a new Branch of the Ludwig Institute for Cancer Research, to be located at Princeton and dedicated wholly to the study of cancer metabolism and the translation of its findings into cancer prevention and treatment.

“We’re entering a time where people recognize that diet can be used in a much more targeted way to tackle diseases,” said Rabinowitz, director of the Ludwig Princeton Branch and a professor of chemistry and the Lewis-Sigler Institute for Integrative Genomics. “Diet is a primary biochemical input to our beings, and there is a relationship that connects our genes, diets and disease states. Unlocking this code — this is one of the greatest opportunities to improve medical care.”

Keto comes to the clinic

The approach will be put to the test as part of a randomized clinical trial that will examine whether the keto diet paired with chemotherapy can extend the life of pancreatic cancer patients. Previous trials have already determined that the keto diet alone cannot cure cancer, but Rabinowitz’s collaborators hope that forcing the body into starvation mode, combined with cancer-killing drugs, can slow the progress of the disease.

“If we can give multiple years of survival — good quality-of-life survival — to people in that disease state, that would be a wonderful achievement,” Rabinowitz said.

One of the first inklings that the keto diet could make inroads against cancer came from Lewis Cantley, a professor of cancer biology at the Weill Cornell Medical College in New York. In 2018, Cantley and colleagues found that mice treated with a targeted cancer therapy that tamps down an enzyme called PI3K lived longer if they were fed a keto diet instead of a normal diet.

Exactly how the keto-treatment combination helps fight cancer is still unclear. The most popular theory has to do with insulin, the hormone that promotes glucose uptake into the cells. Insulin can fuel cancer growth, and it can cancel out the effects of drugs that aim at PI3K. With carbohydrate-rich and sugary foods on the forbidden list, the body takes in less sugar, so the body makes less insulin.

Rabinowitz and his team are also exploring other possibilities. For example, ketone bodies may induce a state of metabolic imbalance in which tumor cells become overloaded with high-energy electrons, leading to a state called redox stress. Another possible explanation is that the low-sugar content of the keto diet starves tumors of the energy molecules needed for growth.

He cautions that there may also be types of cancer for which the ketogenic diet may be ill-advised, such as certain types of lung cancer. “The world of cancer is complicated, and no one should think of this as a cure-all,” he said. “It’s also premature to think of this as guidance that if you want to avoid cancer, you should eat a ketogenic diet.”

His team is exploring the intersection of nutrition and disease with tools that track nutrients as they travel through the body. In his lab at Princeton on the second floor of Frick Chemistry Lab stand some of the most sensitive devices on the planet for measuring the players in metabolism — sugars, proteins, fats and other molecules — in minute amounts.

These are high-powered versions of the machines that a lab technician would use to determine the levels of certain components in a standard blood test. Each one is essentially an elaborate postal scale — but instead of weighing packages, it weighs molecules. By finding the weight of a molecule and knowing its electric charge, researchers can identify a molecule’s signature ratio of mass to charge. Although the basic technique has been around for a long time, in the past decade researchers in the Rabinowitz lab have pushed it to a new level of accuracy.

Tapping regional expertise

Rabinowitz’s interest in cancer metabolism blossomed in 2009 when he joined a collaboration aimed at developing therapies that cut the fuel supply to pancreatic cancer. The team included researchers at the University of Pennsylvania and Memorial Sloan Kettering Cancer Center in New York City. He also began collaborating with Professor Eileen White, associate director of the Ludwig Princeton Branch and deputy director and chief scientific officer of the Rutgers Cancer Institute of New Jersey, a National Cancer Institute-designated comprehensive cancer center, which Princeton joined in 2011.

Princeton is a global leader in genomics, biology and the computational and physical sciences. The strong collaboration between Rabinowitz and White was one of the factors that led the Ludwig Institute for Cancer to select Princeton as the site of a new Branch, enabling Princeton to rapidly grow its portfolio in cancer research.

“Cancer is a metabolic disease,” White said. “For one cancer cell to make more cancer cells requires a massive change in the metabolic activity of the cell.”

The cancer cell needs to transform from a passive existence into full-blown replication mode, White said. Most normal tissues — in the heart, the brain, the muscles or the organs — don’t go through this transformation. Cancer cells stand out for their voracious need for nutrients to fuel growth and their eventual, deadly spread to other places in the body.

As these cells take up more nutrients, they also need to activate specific pathways for channeling those nutrients into growth. White wondered, might these metabolic supply chains be attacked — thus weakening the enemy?

Her team quickly found that this was easier said than done. Cancer cells, it turns out, are very difficult to starve to death. “We had some cancer cells in a plastic dish,” White said, “and normally if you take all the nutrients away from a cell, that would be a lethal event. But in many cancer cells, it was not.”

Through a series of experiments, White’s team discovered the reason why: Cancer cells can cannibalize their own innards to survive a spell of starvation. The cells break down their internal organelles into basic nutrients and use them as energy sources.

This process, known as autophagy, Latin for “self-eating,” had been known for decades but was likened more to a garbage-removal service. The discovery of the genetic mechanism for autophagy in the 1990s earned Japanese researcher Yoshinori Ohsumi the 2016 Nobel Prize in physiology or medicine.

Cancer’s weak link

White’s team discovered that autophagy was behind cancer’s ability to survive starvation. The team grew cancer cells in a nutrient-rich broth and then switched to a broth depleted of nutrients. Over the next few days, the cancer cells shriveled in place — apparently dying. But after several days, the researchers added back the food-laden liquid, and watched via time-lapse video as the cells came back to life. “We called that the cancer horror movie,” White said. “The cells just sat there until the food came back, and then they sprung back to life.”

To show that autophagy was responsible, the researchers grew identical cancer cells in which an essential gene that enables autophagy had been deleted. When starved, those cells simply shriveled away and died.

“When we made our discovery, every student in my lab wanted to work on it,” White said. “They thought this concept that cancer cells could eat themselves, and, in this process would keep themselves alive, was fascinating.”

In subsequent experiments, in collaboration with Rabinowitz, the researchers unraveled the role of this self-cannibalization at the chemical level in cancer metabolism. White has since co-founded a company to explore autophagy targets for cancer treatment.

From this and other researchers’ work, several drugs that inhibit the autophagy pathway in different ways have entered clinical trials.

The Ludwig Princeton Branch will focus on three main areas of cancer metabolism: how the body supports tumor growth and spread; how diet can be a strategy for the prevention and treatment of cancer; and the interplay of human metabolism, the gut microbiome and the anti-cancer immune response.

Branching out

One of the new directions that the Ludwig Princeton team will take is the role of metabolism in metastasis, the spread of cancer cells from the original tumor to other parts of the body. Cancer cells break away from the primary tumor and travel through the bloodstream or lymph system and into other organs such as the liver, the lungs and the brain. One question is what makes the new environment capable of supporting tumor growth.

Yibin Kang, Princeton’s Warner-Lambert/Parke-Davis Professor of Molecular Biology, is exploring how cancer cells utilize metabolic pathways to suppress the body’s immune system in ways that make the cancer difficult to treat. Over the past two decades, it became apparent that tumors can employ strategies to suppress the body’s immune response. Several new anti-cancer drugs that reactivate the immune system have proved capable of curing cancers that previously were death sentences.

But those cures worked in only a subset of patients, and one of the goals for the Ludwig group is to find out how metabolism may play a role. This is an area that Kang is especially interested in exploring. Much of his work is on breast cancer, which has not responded well to immunotherapy. Also, studies show that tumors that have already metastasized respond less well to strategies that boost the immune system.

Recently, Kang’s team discovered enzymes that tumors use to build an immunosuppressive safe zone in which they can escape immune system attack. Mark Esposito, a former graduate student in Kang’s lab, founded a company called KayoThera, supported with funding from the New Jersey Health Foundation, to develop small molecule drugs that block those enzymes. “We make a cold tumor become hot again, so that it becomes recognizable by the immune system,” Kang said.

Kang is excited about the influx of energy and support for cancer research via the Ludwig Princeton Branch. The formation of the Ludwig Branch will allow researchers in distinct disciplines — from microbiology and engineering to computer science — to contribute to studies on cancer metabolism and the tumor microenvironment.

Another project that is just taking off focuses on how the body’s metabolism of nutrients is affected by the gut microbiome, and how this interaction alters the anti-cancer immune response.

The gut microbiome — the teeming trillions of bacteria that peacefully inhabit our intestines — appear to have an outsized effect on how well nutrients and other ingested items, such as drugs, are able to pass through the intestinal walls and into the bloodstream. Ludwig Princeton researchers hope to uncover the impact that the microbiome has on cancer metabolism as well.

Like the famed New Jerseyan Bernarr Macfadden from a century ago, researchers based at Princeton and its collaborating institutions think that diet for the treatment of disease has untapped promise. Rabinowitz in particular sees metabolism research as a major area for growth. With about 20% of our genes having some function relating to metabolism, he says it is surprising that scientists don’t devote more resources to studying the relationship between what we eat and how we feel.

Certainly our state of health is influenced by many factors. Genetics play a role. Fitness and exercise matter. Love and social support are essential. But when it comes to diet, Rabinowitz admits to a bit of frustration. “Despite all this progress,” he said, “if you come to me and say, my back is killing me, or I’m really down with depression, or I have cancer, we still have no reliable guidance on what you should eat to help with your particular disease.

“Diet is one of the foundational pieces of good health,” he said, “so it would be really important to be able to tell people, in a more targeted way, what’s right for them.”