Research Area: Cancer Biology

Why cancer cells waste so much energy

MIT study sheds light on the longstanding question of why cancer cells get their energy from fermentation.

Anne Trafton | MIT News Office
January 19, 2021

In the 1920s, German chemist Otto Warburg discovered that cancer cells don’t metabolize sugar the same way that healthy cells usually do. Since then, scientists have tried to figure out why cancer cells use this alternative pathway, which is much less efficient.

MIT biologists have now found a possible answer to this longstanding question. In a study appearing in Molecular Cell, they showed that this metabolic pathway, known as fermentation, helps cells to regenerate large quantities of a molecule called NAD+, which they need to synthesize DNA and other important molecules. Their findings also account for why other types of rapidly proliferating cells, such as immune cells, switch over to fermentation.

“This has really been a hundred-year-old paradox that many people have tried to explain in different ways,” says Matthew Vander Heiden, an associate professor of biology at MIT and associate director of MIT’s Koch Institute for Integrative Cancer Research. “What we found is that under certain circumstances, cells need to do more of these electron transfer reactions, which require NAD+, in order to make molecules such as DNA.”

Vander Heiden is the senior author of the new study, and the lead authors are former MIT graduate student and postdoc Alba Luengo PhD ’18 and graduate student Zhaoqi Li.

Inefficient metabolism

Fermentation is one way that cells can convert the energy found in sugar to ATP, a chemical that cells use to store energy for all of their needs. However, mammalian cells usually break down sugar using a process called aerobic respiration, which yields much more ATP. Cells typically switch over to fermentation only when they don’t have enough oxygen available to perform aerobic respiration.

Since Warburg’s discovery, scientists have put forth many theories for why cancer cells switch to the inefficient fermentation pathway. Warburg originally proposed that cancer cells’ mitochondria, where aerobic respiration occurs, might be damaged, but this turned out not to be the case. Other explanations have focused on the possible benefits of producing ATP in a different way, but none of these theories have gained widespread support.

In this study, the MIT team decided to try to come up with a solution by asking what would happen if they suppressed cancer cells’ ability to perform fermentation. To do that, they treated the cells with a drug that forces them to divert a molecule called pyruvate from the fermentation pathway into the aerobic respiration pathway.

They saw, as others have previously shown, that blocking fermentation slows down cancer cells’ growth. Then, they tried to figure out how to restore the cells’ ability to proliferate, while still blocking fermentation. One approach they tried was to stimulate the cells to produce NAD+, a molecule that helps cells to dispose of the extra electrons that are stripped out when cells make molecules such as DNA and proteins.

When the researchers treated the cells with a drug that stimulates NAD+ production, they found that the cells started rapidly proliferating again, even though they still couldn’t perform fermentation. This led the researchers to theorize that when cells are growing rapidly, they need NAD+ more than they need ATP. During aerobic respiration, cells produce a great deal of ATP and some NAD+. If cells accumulate more ATP than they can use, respiration slows and production of NAD+ also slows.

“We hypothesized that when you make both NAD+ and ATP together, if you can’t get rid of ATP, it’s going to back up the whole system such that you also cannot make NAD+,” Li says.

Therefore, switching to a less efficient method of producing ATP, which allows the cells to generate more NAD+, actually helps them to grow faster. “If you step back and look at the pathways, what you realize is that fermentation allows you to generate NAD+ in an uncoupled way,” Luengo says.

Solving the paradox

The researchers tested this idea in other types of rapidly proliferating cells, including immune cells, and found that blocking fermentation but allowing alternative methods of NAD+ production enabled cells to continue rapidly dividing. They also observed the same phenomenon in nonmammalian cells such as yeast, which perform a different type of fermentation that produces ethanol.

“Not all proliferating cells have to do this,” Vander Heiden says. “It’s really only cells that are growing very fast. If cells are growing so fast that their demand to make stuff outstrips how much ATP they’re burning, that’s when they flip over into this type of metabolism. So, it solves, in my mind, many of the paradoxes that have existed.”

The findings suggest that drugs that force cancer cells to switch back to aerobic respiration instead of fermentation could offer a possible way to treat tumors. Drugs that inhibit NAD+ production could also have a beneficial effect, the researchers say.

The research was funded by the Ludwig Center for Molecular Oncology, the National Science Foundation, the National Institutes of Health, the Howard Hughes Medical Institute, the Medical Research Council, NHS Blood and Transplant, the Novo Nordisk Foundation, the Knut and Alice Wallenberg Foundation, Stand Up 2 Cancer, the Lustgarten Foundation, and the MIT Center for Precision Cancer Medicine.

Disarming cancer
Greta Friar | Whitehead Institute
December 21, 2020

Cancer is at its most deadly when two things occur: the cancer cells metastasize, spreading to new sites in the body, and the cells become resistant to treatment. The epithelial-mesenchymal transition (EMT) is a process that cancer cells may undergo that enables them to do both of these things. Cells that undergo this process are called “quasi-mesenchymal” cancer cells, and they are mobile, aggressive, and harder to kill. They can resist attacks launched both by the body’s own immune system as well as immune checkpoint blockade therapy (ICB), an increasingly employed clinical treatment that works by liberating cells of the immune system from certain constraints, thereby allowing them to attack cancer cells. Anushka Dongre, a postdoctoral researcher in the lab of Whitehead Institute Founding Member Robert Weinberg, had previously found that even a small population of quasi-mesenchymal cells within a mouse breast cancer tumor—as little as 10% amongst a majority of cells that had not gone through the EMT—could protect the entire tumor from a version of ICB called anti-CTLA4 therapy. Most breast cancers in humans contain some minority populations of quasi-mesenchymal cells, as do many other types of human tumors, likely contributing to ICB therapy’s mixed success rates in the clinic.

Because cells that have been through the EMT process play such a large role in making cancers more deadly and less responsive to treatment, Dongre set out to understand how to defang them. Her first step was to figure out how minority populations of quasi-mesenchymal cells within a breast tumor make the tumors as a whole resistant to immune therapy. Then she studied how to disable those mechanisms. The work, described in a paper published in Cancer Discovery on December 16, includes studies in mice showing that disabling those resistance mechanisms can sensitize otherwise-resistant tumors to anti-CTLA4 checkpoint blockade immunotherapy and reduce the severity of metastasis.

Dongre had previously studied how quasi-mesenchymal cells alter the area in and around a tumor to render it more favorable for the outgrowth of a cancer. They keep out of the core of the tumor the type of immune cells that can destroy cancers, and instead let in other types of immune cells that the tumor is able to co-opt to its benefit, thereby protecting it from immune attack. 

In her latest research, Dongre identified six molecules that quasi-mesenchymal cells produce and release that help them perturb the tumor’s surroundings, protecting cells throughout the tumor from immune attack and elimination. She then tested what happened when the release of each of the protective molecules was suppressed. She discovered that eliminating release of either of two molecules, CSF1 and SPP1, made the tumors significantly more susceptible to the immune attack and thus elimination by ICB therapy. However, the strongest therapeutic benefit came when she prevented production of CD73, an enzyme usually made by the quasi-mesenchymal cells that produces the immunosuppressive molecule adenosine. In mice, anti-CTLA4 therapy was very effective against tumors in which CD73 and thus adenosine had been eliminated from the quasi-mesenchymal cells, in some cases, succeeding in eliminating the tumors entirely. These findings are consistent with previous research that identified CD73 as a good complementary target for immunotherapy. Furthermore, the experiments demonstrated the utility of combining anti-CD73 therapy with anti-CTLA4 immunotherapy in order to successfully treat tumors that would usually not respond to treatment by ICB therapy alone. Dongre was particularly excited to see the combination of anti-CD73 and anti-CTLA4 reduce the number and size of metastatic tumors.

Dongre hopes that these insights will prove useful for patients.

“There is this minority population of mesenchymal cells present in many patient tumors, creating a big barrier to therapy. I’m hopeful that by identifying the drivers that can sensitize this population to treatment, our work can one day help patients suffering from cancers that are resistant to current therapies,” Dongre says.

Two treatment methods enhance chemotherapy by the same means: cellular senescence
Raleigh McElvery
November 10, 2020

In 2019, cancer researchers from MIT found a drug that targeted an elusive molecular interaction previously considered “undruggable.” In so doing, they opened up a new realm of chemotherapy. This drug, called JH-RE-06, sensitized tumors to treatment, but the scientists didn’t fully understand how it exerted its effects. Now, in a pair of studies published in PNAS, the same team is closer to determining which cellular processes this drug alters to enhance cancer therapy.

Many widely-used chemotherapies, like cisplatin, kill tumors by damaging their DNA and inducing programmed cell death. But cells are resilient, and many can continue to function with the help of repair enzymes that simply bypass the damage and continue to replicate the DNA. As a result, some tumors not only defy death, but gain mutations that render them more resistant to treatment or spur new malignancies elsewhere.

“If you’re not making a patient better, it’s very likely you’re making them worse,” says Michael Hemann, associate professor of biology and co-author on both studies. Rather than fully replacing conventional DNA-damaging treatments — which could take decades — Hemann suggests an effective “medium-term” solution: augmenting low doses of cisplatin with safer agents that strengthen the chemotherapy’s tumor-killing capacity.

The team had tested this approach back in 2019, when they first identified JH-RE-06 and saw it enhanced chemotherapy treatment. These experiments revealed that JH-RE-06 bound to an especially shallow (and infamously undruggable) pocket of one DNA repair enzyme called REV1. This barred REV1 from interacting with another key enzyme, and prevented the cancer cells from recovering after cisplatin treatment. But what happened next to cause the tumors to shrink was unclear.

As they began their next round of experiments, the researchers expected to find that the drug would simply enhance the way cisplatin kills tumors via programmed cell death.

Nimrat Chatterjee, Walker’s former postdoc and lead author of the first study, treated mice and individual cells with a combination of cisplatin and JH-RE-06. She expected to see signs of programmed cell death, but for months, she saw no such markers.“We thought that if we blocked the DNA repair process with the JH compound, we’d see more programmed cell death,” says co-author Graham Walker, American Cancer Society Professor and Howard Hughes Medical Institute Professor. “As it turns out, we did see more cell death — just not the kind we were expecting.”

One evening, just as she was about to head home for the day, she peeked through her microscope at the cancer cells treated with JH-RE-06 and cisplatin. She noticed they were fluorescing a strange green color.

“At first, I didn’t know what I was seeing,” she recalls. But after some follow-up, it became clear that the mysterious green color was coming from lipid-containing residues that usually appear as cells age and stop dividing. The cells appeared to be in a permanently dormant state known as senescence — not yet dead but unable to proliferate. JH-RE-06 was altering cisplatin function by triggering a second molecular pathway independent of programmed cell death.

“That was one of the best ‘aha’ moments of my scientific career so far,” Chatterjee says. “REV1, the DNA repair enzyme that JH-RE-06 binds, may have other novel biological functions and a larger role in cancer cell etiology than we originally thought. We’re now grappling with more questions about REV1 than ever before.”

Around the same time, Faye-Marie Vassel PhD ’20, Walker and Hemann’s former joint graduate student and lead author of the second study, witnessed a similar phenomenon in her own experiments. She was investigating a different way of inhibiting the two key DNA repair enzymes that enable cancer cells to survive chemotherapy. Instead of probing JH-RE-06, which latches onto REV1, she tried deleting REV1’s binding partner, called REV7. This protein is particularly influential because it serves an important role in fixing double-stranded breaks in addition to interacting with REV1.

When Vassel deleted REV7 from mice with non-small cell lung cancer, the tumors became more sensitive to cisplatin, as expected. But, like Chatterjee, she saw signs of senescence rather than programmed cell death. The two studies had converged on a common biology: adding JH-RE-06 or deleting REV7 strengthened the effects of cisplatin by inducing this dormant state.

Cancer detection and treatment methods have improved dramatically in the last two decades, but drug-resistant cancers like non-small cell lung cancer remain difficult to combat, Vassel says. “Our experiments are the first to show that senescence induction is likely a consequence of REV7 inhibition,” she adds. “Inhibiting REV7 in tandem with cisplatin therapy may prove to be an effective strategy for enhancing a chemotherapeutic response.”

Chemotherapies that trigger programmed cell death have been the mainstay of cancer treatment for decades. But studies like these show that triggering senescence may be a promising complementary strategy. Most senescent cells are eventually cleared by the immune system, and the researchers suspect this is how cancer cells treated with JH-RE-06 or REV7 inhibitors would be eliminated from the body.

Walker and Hemann agree that, at the moment, their sister studies raise more questions than answers. As Walker explained, “We’ve pried open a new discovery, and hopefully set the stage for many exciting experiments to come.”

Top image: Genetically-engineered mouse model for lung cancer. Credit: Credit: National Cancer Institute, National Institutes of Health. NIH Image Gallery/Flickr (CC BY-NC)
The REV7 image was originally published in: “Structural basis of Rev1-mediated assembly of a quaternary vertebrate translesion polymerase complex consisting of Rev1, heterodimeric polymerase (Pol) ζ, and Pol κ.”
Journal of Biological Chemistry, online August 2, 2012, DOI: 10.1074/jbc.M112.394841
Jessica Wojtaszek, Chul-Jin Lee, Sanjay D’Souza, Brenda Minesinger, Hyungjin Kim, Alan D. D’Andrea, Graham C. Walker, and Pei Zhou.

Citations:
“REV1 inhibitor JH-RE-06 enhances tumor cell response to chemotherapy by triggering senescence hallmarks”
Proceedings of the National Academy of Sciences, online November 9, 2020, DOI: 10.1073/pnas.2016064117
Nimrat Chatterjee , Matthew A Whitman, A Harris , Sophia M Min , Oliver Jonas , Evan C Lien , Alba Luengo , Matthew G Vander Heiden , Jiyong Hong , Pei Zhou , Michael T Hemann , and Graham C Walker 

“Rev7 loss alters cisplatin response and increases drug efficacy in chemotherapy-resistant lung cancer”
Proceedings of the National Academy of Sciences, online November 3, 2020, DOI: 10.1073/pnas.2016067117
Faye-Marie Vassel, Ke Bian, Graham C. Walker, and Michael T. Hemann

A computational approach to cancer

Toni-Ann Nelson transformed remote summer research into an opportunity to learn a new set of tools for analyzing tumors.

Raleigh McElvery
August 20, 2020

Toni-Ann Nelson has wanted to find a cure for cancer ever since she was nine years old and lost her grandfather to the disease. “I remember thinking there must be something that the doctors and scientists were missing,” she recalls. “It just couldn’t be that complicated.” Now one semester away from earning her degree in molecular biology, Nelson is realizing cancer is just that — complicated. After conducting cancer research during MIT’s Summer Research Program in Biology (MSRP-Bio), she understands much more about the intricacies of tumors and metastasis. But she’s also glimpsed just how many cellular puzzles remain to be solved.

Growing up in Jamaica, Nelson enjoyed all her science classes, but preferred biology because she knew it would provide the foundation to probe cancer. She graduated as the valedictorian of her high school class, and earned a scholarship to Alcorn State University in Mississippi, where she began in the spring of 2017.

Alcorn doesn’t have any cancer research facilities, so Nelson secured a position as an undergraduate researcher in Yan Meng’s plant tissue culture lab. For three years, Nelson aimed to improve viral disease resistance in sweet potatoes. Even though she wasn’t conducting clinical research, she mastered key molecular biology techniques like PCR, gel electrophoresis, and tissue culture.

“Fundamental research is important because many times finding a cure requires starting with the basics, and understanding what’s going on inside the cell,” she says.

When Nelson was accepted into MSRP-Bio as a Gould Fellow and assigned to work in Tyler Jacks’ lab, she was elated to get her first hands-on cancer research experience. But in April 2020 — two months before the program was slated to begin — MIT’s campus temporarily shut down due to the COVID-19 pandemic, and MSRP-Bio 2020 became a remote learning experience.

As a result, Nelson and her MSRP-Bio cohort conducted their research from home. She took on a computationally-intensive project that was conducive to remote work and required taking an online quantitative methods class. In a manner of weeks, she learned an entirely new set of skills, including programming languages like Python.

“I always thought that I wouldn’t need those types of computational tools as part of my cancer research,” she explains. “But working at MIT was enlightening, because it showed me that they are key to understanding disease. I can definitely see myself using them on my own projects in the future.”

Pink and purple histology image
Light micrograph of a lung adenocarcinoma. Credit: Vasilena Gocheva/Jacks Lab, Koch Institute

The Jacks lab studies the genetic events that contribute to cancer, and Nelson’s project centered on lung adenocarcinoma. The predominant form of non-small cell lung cancer, it begins in alveolar type II (AT2) cells. Past studies showed that, as the tumor progresses, AT2 cells change state and lose their original identity. Nelson wanted to determine which genes and proteins underlie this evolution. Her analyses showed that genetic markers characteristic of AT2 cells tend to decrease over time, while markers denoting faster-growing “high grade” tumors become more prevalent.

“The kinetics of these gene expression changes that are happening early on are still poorly understood,” she explains. “It just goes to show how complicated this pathology is, which I find even more fascinating.”

Once researchers can pinpoint the genes and proteins that drive changes in cancer cell state, they’ll be better equipped to design drugs that target and prevent metastatic processes.

Although Nelson couldn’t visit the lab in person, as on-campus research slowly began ramping up again, her graduate student mentor Amanda Cruz would show her around during their video conference calls. Cruz also helped Nelson explore the scientific literature, choose studies for the lab’s journal club, and perform computational analyses.

Given the unprecedented circumstances, Nelson says having a solid support system was key to her success. Nelson and her MSRP cohort also relied on one another for encouragement, and were each assigned a graduate student “pal” for guidance outside of lab.

“The program catered to our every need, and it’s structured to ensure that someone will always check up on you if you’re feeling alone,” Nelson says. “I never expected to get so much from this experience, especially because I’m not physically on campus. But what I learned this summer was so much more than I could ever have anticipated.”

Her time in the Jacks lab has solidified her fervor for cancer research, and she intends to apply to cancer biology PhD programs in order to continue this line of inquiry. “I’ve realized there’s still so much more to learn,” she says, “but we’re getting there.”

Top image courtesy of Toni-Ann Nelson
Posted: 8.19.20
Gene-controlling mechanisms play key role in cancer progression

Study finds “epigenomic” alterations evolve as lung tumors become more aggressive and metastasize.

Anne Trafton | MIT News Office
July 22, 2020

As cancer cells evolve, many of their genes become overactive while others are turned down. These genetic changes can help tumors grow out of control and become more aggressive, adapt to changing conditions, and eventually lead the tumor to metastasize and spread elsewhere in the body.

MIT and Harvard University researchers have now mapped out an additional layer of control that guides this evolution — an array of structural changes to “chromatin,” the mix of proteins, DNA, and RNA that makes up cells’ chromosomes. In a study of mouse lung tumors, the researchers identified 11 chromatin states, also called epigenomic states, that cancer cells can pass through as they become more aggressive.

“This work provides one of the first examples of using single-cell epigenomic data to comprehensively characterize genes that regulate tumor evolution in cancer,” says Lindsay LaFave, an MIT postdoc and the lead author of the study.

In addition, the researchers showed that a key molecule they found in the more aggressive tumor cell states is also linked to more advanced forms of lung cancer in humans, and could be used as a biomarker to predict patient outcomes.

Tyler Jacks, director of MIT’s Koch Institute for Integrative Cancer Research, and Jason Buenrostro, an assistant professor of stem cell and regenerative biology at Harvard University, are the senior authors of the study, which appears today in Cancer Cell.

Epigenomic control

While a cell’s genome contains all of its genetic material, the epigenome plays a critical role in determining which of these genes will be expressed. Every cell’s genome has epigenomic modifications — proteins and chemical compounds that attach to DNA but do not alter its sequence. These modifications, which vary by cell type, influence the accessibility of genes and help to make a lung cell different from a neuron, for example.

Epigenomic changes are also believed to influence cancer progression. In this study, the MIT/Harvard team set out to analyze the epigenomic changes that occur as lung tumors develop in mice. They studied a mouse model of lung adenocarcinoma, which results from two specific genetic mutations and closely recapitulates the development of human lung tumors.

Using a new technology for single-cell epigenome analysis that Buenrostro had previously developed, the researchers analyzed the epigenomic changes that occur as tumor cells evolve from early stages to later, more aggressive stages. They also examined tumor cells that had metastasized beyond the lungs.

This analysis revealed 11 different chromatin states, based on the locations of epigenomic alterations and density of the chromatin. Within a single tumor, there could be cells from all 11 of the states, suggesting that cancer cells can follow different evolutionary pathways.

For each state, the researchers also identified corresponding changes in where gene regulators called transcription factors bind to chromosomes. When transcription factors bind to the promoter region of a gene, they initiate the copying of that gene into messenger RNA, essentially controlling which genes are active. Chromatin modifications can make gene promoters more or less accessible to transcription factors.

“If the chromatin is open, a transcription factor can bind and activate a specific gene program,” LaFave says. “We were trying to understand those transcription factor networks and then what their downstream targets were.”

As the structure of tumor cells’ chromatin changed, transcription factors tended to target genes that would help the cells to lose their original identity as lung cells and become less differentiated. Eventually many of the cells also gained the ability to leave their original locations and seed new tumors.

Much of this process was controlled by a transcription factor called RUNX2. In more aggressive cancer cells, RUNX2 promotes the transcription of genes for proteins that are secreted by cells. These proteins help remodel the environment surrounding the tumor to make it easier for cancer cells to escape.

The researchers also found that these aggressive, premetastatic tumor cells were very similar to tumor cells that had already metastasized.

“That suggests that when these cells were in the primary tumor, they actually changed their chromatin state to look like a metastatic cell before they migrated out into the environment,” LaFave says. “We believe they undergo an epigenetic change in the primary tumor that allows them to become migratory and then seed in a distal location like the lymph nodes or the liver.”

A new biomarker

The researchers also compared the chromatin states they identified in mouse tumor cells to chromatin states seen in human lung tumors. They found that RUNX2 was also elevated in more aggressive human tumors, suggesting that it could serve as a biomarker for predicting patient outcomes.

“The RUNX positive state was very highly predictive of poor survival in human lung cancer patients,” LaFave says. “We’ve also shown the inverse, where we have signatures of early states, and they predict better prognosis for patients. This suggests that you can use these single-cell gene regulatory networks as predictive modules in patients.”

RUNX could also be a potential drug target, although it traditionally has been difficult to design drugs that target transcription factors because they usually lack well-defined structures that could act as drug docking sites. The researchers are also seeking other potential targets among the epigenomic changes that they identified in more aggressive tumor cell states. These targets could include proteins known as chromatin regulators, which are responsible for controlling the chemical modifications of chromatin.

“Chromatin regulators are more easily targeted because they tend to be enzymes,” LaFave says. “We’re using this framework to try to understand what are the important targets that are driving these state transitions, and then which ones are therapeutically targetable.”

The research was funded by a Damon Runyon Cancer Foundation postdoctoral fellowship, the Paul G. Allen Frontiers Group, the National Institutes of Health, and the Koch Institute Support (core) Grant from the National Cancer Institute.

Lindsay Case

Education

  • PhD, 2014, University of North Carolina at Chapel Hill
  • BA, 2008, Biology, Franklin and Marshall College

Research Summary

We study how cells regulate the spatial organization of signaling molecules at the plasma membrane to control downstream signaling. For example, receptor clustering and higher-order assembly with cytoplasmic proteins can create compartments with unique biochemical and biophysical properties. We use quantitative experimental approaches from biochemistry, molecular biophysics, and cell biology to study transmembrane signaling pathways and how they are misregulated in diseases like cancer.

Awards

  • NSF Career Award, 2025
  • Searle Scholar, 2022
  • NIH Director’s New Innovator Award, 2022
  • AFOSR Young Investigator Award, 2021
  • Brown-Goldstein Award, 2020
  • Damon Runyon-Dale F. Frey Breakthrough Scientist, 2020
Discovery of how cancer drugs find their targets could lead to a new toolset for drug development
Whitehead Institute
June 17, 2020

In the watery inside of a cell, complex processes take place in tiny functional compartments called organelles. Energy-producing mitochondria are organelles, as is the frilly golgi apparatus, which helps to transport cellular materials. Both of these compartments are bound by thin membranes.

But in the past few years, research at Whitehead Institute and elsewhere has shown that there are other cellular organelles held together without a membrane. These organelles, called condensates, are tiny droplets which keep certain proteins close together amidst the chaos of the cell, allowing complex functions to take place within. “We know of about 20 types of condensate in the cell so far,” says Isaac Klein, a postdoc in Richard Young’s lab at Whitehead Institute and oncologist at the Dana-Farber Cancer Institute.

Now, in a paper published in Science on June 19, Klein and Ann Boija, another postdoc in Young’s lab, show the mechanism by which small molecules, including cancer drugs, are concentrated in these cellular droplets — a finding that could have implications for the development of new cancer therapeutics. If researchers could tailor a chemical to seek out and concentrate in one kind of droplet in particular, it might have a positive effect on the delivery efficiency of the drug. “We thought, maybe that’s an avenue by which we can improve cancer treatments and discover new ones,” says Klein.

“This [research] is part of a revolutionary new way of looking at the organization within cells,” says Phillip Sharp, a professor at the Massachusetts Institute of Technology’s Koch Institute for Integrative Cancer Research and a co-author on the study. “Cells are not little pools of soup, all mixed together. They are actually highly organized, compartmentalized units, and that organization is important in their function and in their diseases. We’ve just started to understand that, and this new paper is a really important step, using that insight, to understand how to potentially treat diseases differently.”

CONDENSATES AND DRUG DELIVERY

To explore how different properties of condensates inside the cell’s nucleus affected the delivery of cancer drugs, Boija and Klein selected a few example condensates to study. These included splicing speckles, which store cellular materials needed for RNA splicing, nucleoli, where ribosomes are formed, and a new kind of droplet Young’s lab discovered in 2018 called a transcriptional condensate. These new condensates bring together all the different proteins needed to successfully transcribe a gene.

The researchers created their own suite of four different fluorescently-labeled condensates by adding glowing tags to marker proteins specific to each kind of droplet. For example, transcriptional condensates are marked by the droplet-forming protein MED1, splicing speckles by a protein called SRSF2, and nucleoli by FIB1 and NPM1.

Now that they could tell individual droplets apart by their cellular purpose, the team, along with the help of Nathanael Gray, a chemical biologist at Harvard University and the Dana-Farber Cancer Institute, created fluorescent versions of clinically important drugs. The tested drugs included cisplatin and mitoxantrone, two anti-tumor medicines commonly used in chemotherapy. These therapeutics were the perfect test subjects, because they both target proteins that lie within nuclear condensates.

The researchers added the cancer drugs to a mixture containing various droplets (and only droplets, none of the actual drug targets), and found that the drugs sorted themselves into specific condensates. Mitoxantrone concentrated in condensates marked by MED1, FIB1 and NPM1, selectively avoiding the others. Cisplatin, too, showed a particular affinity for droplets held together by MED1.

“The big discovery with these in vitro studies is that a drug can concentrate within transcriptional condensate independent of its target,” Boija says. “We used to think that drugs come to the right place because their targets are there, but in our in vitro system, the target is not there. That’s really informative — it shows the drug is actually being concentrated in a different way than we thought.”

To understand why some drugs were drawn into transcriptional condensates, they screened a panel of chemically-modified dyes and found that the important part of many drugs — the part that led them to concentrate in transcriptional condensates  —  is the molecules’ aromatic ring structure. Aromatic rings are stable, ring-shaped groupings of carbon atoms. The aromatic ring in some drugs are thought to stack with rings in MED1’s amino acids, leading the drug to concentrate in transcriptional condensates.

Being able to tailor a drug to enter a certain condensate is a powerful tool for drug developers. “We found that if we add an aromatic group to a molecule, it becomes concentrated within the transcriptional condensate,” Boija says. “It’s that type of interaction that is important when we design new drugs to enter transcriptional condensates — and maybe we can improve existing drugs by modifying their structure. This will be very exciting to look into.”

WHERE DRUGS CONCENTRATE AFFECTS HOW WELL THEY FIGHT CANCER

In order for this tool to be practically useful in drug development, the researchers had to make sure that concentration in specific droplets would actually impact the drugs’ performance. Boija and Klein decided to test this using cisplatin, which is drawn to transcriptional condensates by MED1 and works to fight cancer by adding clunky platinum molecules to DNA strands. This damages tumor cells’ genetic material. When the researchers administered cisplatin to a mixture of different condensates, both in the test tube and in cells, the drug preferentially altered DNA that lay within transcriptional condensates.

This could explain why cisplatin and other platinum drugs are effective against so many diverse cancers, says Young, who is also a professor of biology at MIT; cancer-causing genes often carry regions of DNA called super enhancers, which are extremely active in transcription, leading to very large transcriptional condensates. “We now think the reason that drugs like cisplatin can work well in patients with diverse cancers is because they’re becoming selectively concentrated at the cancer-causing genes, where these large transcriptional condensates occur,” he said. “The effect is to have the drug home in on the gene that’s causing each cancer to be so deadly.”

A DRUG RESISTANCE MYSTERY, SOLVED

The new insights in condensate behavior also provided some answers to another question in cancer research: why people become immune to the breast cancer drug tamoxifen.Tamoxifen works by attaching itself to estrogen receptors in the cancer cells, preventing them from getting the hormones they need to grow and eventually slowing or stopping the formation of new cancer cells altogether. The drug is one of the most effective treatments for the disease, reducing recurrence rates for ER+ breast cancers by around 50%.

Unfortunately, many patients quickly develop a resistance to tamoxifen — sometimes as soon as a few months after they start taking it. This happens in a variety of ways — for example, sometimes the cancer cells will mutate to be able to kick the tamoxifen out of the cells, or simply produce fewer estrogen receptors for the drug to bind. One form of resistance was associated with an overproduction of the protein MED1, but scientists didn’t know why.

With their newfound knowledge of how a drug’s activity is affected by where it concentrates, Boija and Klein had a hypothesis: the extra MED1 might increase the size of the droplets, effectively diluting the concentration of tamoxifen and making it more difficult for the drug to bind its targets. When they tested this in the laboratory, the team found that more MED1 did indeed cause larger droplets, leading to lower concentrations of tamoxifen.

A NEW TOOLSET FOR DRUG DESIGNERS

The ability to better understand the behavior of drugs in cancer cells — how they concentrate, and why the cancer could become resistant to them — may provide drug developers with a new arsenal of tools to craft efficient therapeutics. “This study suggests that we should be exploring whether we can design or isolate drugs that are concentrated in a given condensate, and to understand how existing drugs are concentrated in the cell,” says Phil Sharp. “I think this is really important for drug development — and I think [figuring it out] is going to be fun.”

Chimeras offer a new way to study childhood cancer in mice
Eva Frederick | Whitehead Institute
March 5, 2020

In a new paper published March 5 in the journal Cell Stem Cell, researchers in Whitehead Institute Member Rudolf Jaenisch’s lab introduce a new way to model human neuroblastoma tumors in mice using chimeras — in this case, mice that have been modified to have human cells in parts of their nervous systems. “This may serve as a unique model that you can use to study the dynamic of immune cells within human tumors,” says Malkiel Cohen, a postdoc in Jaenisch’s lab and the first author of the paper.

Neuroblastoma is a rare and unpredictable form of childhood cancer that affects around 800 young children in the US each year. Neuroblastoma tumors often occur in parts of the sympathetic nervous system, which includes the nerves that run parallel to the spinal cord and the adrenal medulla, part of the glands that produce hormones such as adrenaline. Neuroblastoma is notoriously hard to study primarily because of its disparate behavior: the tumors often shrink spontaneously in infants, while in toddlers they are highly aggressive and often fatal. “The seeds for the cancer are sown during fetal life,” says Rani George, MD, PhD, an associate professor of pediatrics at Harvard Medical School and a neuroblastoma researcher and physician at Dana-Farber Cancer Institute and Boston Children’s Hospital, and a co-senior author on the paper. “For obvious reasons, you can’t really study the development of these tumors in humans.”

Until now, researchers didn’t have many realistic ways to study these tumors in animal models, either. They could create transgenic mice with cancer-causing genes, but the resulting tumors were mouse tumors, not human ones, and had some key differences. Another method involved taking human tumor cells and implanting them in a mouse — a process called xenotransplantation — but that only worked in mice with compromised immune systems, and didn’t allow researchers to study how the tumors formed in the first place or how they interacted with a fully functioning immune system. “This is where we think the new model is a perfect fit,” said Stefani Spranger, PhD, an assistant professor of Biology at the Massachusetts Institute of Technology (MIT) and the Koch Institute for Integrative Cancer Research at MIT and a co-senior author on the paper.

Human-mouse chimeras have been used in the past to study Alzheimer’s disease and brain development. Jaenisch, who is also a professor of biology at MIT, and his lab had been working for years to create chimeric mice with human cells in the neural crest — the group of developing cells that go on to form parts of the sympathetic nervous system — and published their findings in 2016. “In this study, we hoped to use these mice with human neural crest cells to study how neuroblastoma tumors form and respond to immune system attacks,” Jaenisch says.

To create these chimeric mice, Cohen and coauthors at MIT’s Koch Institute and the Dana-Farber Cancer Institute first engineered human pluripotent stem cells to express two genes known to be abnormal in neuroblastoma, MYCN and mutated ALK, and modified them so they became neural crest cells, from which human neuroblastomas are derived. The genes could be turned on and off with the addition of doxycycline, an antibiotic. They also inserted the gene for eGFP, a brightly glowing fluorescent protein originally isolated from jellyfish. This would allow the team to tell whether the cells were spreading correctly through the bodies of the mice, and would cause any tumors originating from these human cells to be luminous under fluorescent light.

The researchers injected mouse embryos with these cells, and watched over the course of embryonic development as the cells proliferated and human tissues crept into the developing peripheral nervous systems of the tiny mice. To activate the two cancer-causing genes, researchers spiked the pregnant mice’ water with doxycycline, and over the next few days in utero — and in the weeks and months after the pups were born — the researchers inspected the chimeras to see whether tumors would appear.

Over the course of the next 15 months, 14% of the mice developed tumors — 29 mice out of 198 total. The tumors mostly appeared in the space behind the abdominal cavity close to the nerves along the spinal cord, although one mouse developed a tumor in its adrenal gland. Both locations are common places for human children to develop neuroblastoma. The researchers took samples of the tumors and found that they contained the glowing protein eGFP, which confirmed that they were of human origin.

When the team examined the growth patterns of the cancerous cells, they found that the tumors were remarkably similar to human neuroblastomas: they contained cell markers typical of human tumors, and some grew in characteristic rosette shapes — features that did not often appear in tumors implanted in immunocompromised mice through xenotransplantation.

Having successfully induced neuroblastoma tumors in the chimeric mice, the researchers took the opportunity to examine the communication between immune cells and tumors — and specifically, how the tumors evaded destruction by anti-cancer immune cells called T cells. One factor that makes human neuroblastomas and many other cancers dangerous is their sophisticated strategy for avoiding being destroyed by T cells. “The cancer tricks the immune system,” Cohen says.  By activating chemical signals that exhaust the T cells, the tumors effectively weaken their attack. The tumors in the chimeric mice, Cohen found, use a similar method to human neuroblastomas to evade immune responses.

Cohen and others plan to test the new system’s potential for modeling other cancers such as melanoma, and to use it to investigate potential treatments for neuroblastoma patients. “The obvious next step is to study how treatment of these tumors will allow these chimeric mice to be cured,” he says. “This is a model that will allow us to approach not only how to get rid of the tumor, but also to fix the immune system and recover those exhausted T cells, allowing them to fight back and deplete the tumor.”

This research was funded by the National Institutes of Health, as well as grants from the Emerald Foundation, the LEO Foundation, the Melanoma Research Foundation, and the St. Baldrick’s Foundation.

Citation: Cohen, M., et al. Formation of Human Neuroblastoma in Mouse-Human Neural Crest Chimeras. Cell Stem Cell. March 5, 2020. DOI: https://doi.org/10.1016/j.stem.2020.02.001

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Written by Eva Frederick

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Singing for joy and service

After surgery to correct childhood hearing loss, Swarna Jeewajee discovered a a desire to be a physician-scientist, and a love of a cappella music.

Shafaq Patel | MIT News correspondent
February 3, 2020

Swarna Jeewajee grew up loving music — she sings in the shower and blasts music that transports her to a happy state. But until this past year, she never felt confident singing outside her bedroom.

Now, the senior chemistry and biology major spends her Saturdays singing around the greater Boston area, at hospitals, homes for the elderly, and rehabilitation centers, with the a cappella group she co-founded, Singing For Service.

Jeewajee says she would not have been able to sing in front of people without the newfound confidence that came after she had transformative ear surgery in the spring of 2018.

Jeewajee grew up in Mauritius, a small island off the east coast of Madagascar, where she loved the water and going swimming. When she was around 8 years old, she developed chronic ear infections as a result of a cholesteatoma, which caused abnormal skin growth in her middle ear.

It took five years and three surgeries for the doctors in Mauritius to diagnose what had happened to Jeewajee’s ear. She spent some of her formative years at the hospital instead of leading a normal childhood and swimming at the beach.

By the time Jeewajee was properly diagnosed and treated, she was told her hearing could not be salvaged, and she had to wear a hearing aid.

“I sort of just accepted that this was my reality,” she says. “People used to ask me what the hearing aid was like — it was like hearing from headphones. It felt unnatural. But it wasn’t super hard to get used to it. I had to adapt to it.”

Eventually, the hearing aid became a part of Jeewajee, and she thought everything was fine. During her first year at MIT, she joined Concourse, a first-year learning community which offers smaller classes to fulfill MIT’s General Institute Requirements, but during her sophomore year, she enrolled in larger lecture classes. She found that she wasn’t able to hear as well, and it was a problem.

“When I was in high school, I didn’t look at my hearing disability as a disadvantage. But coming here and being in bigger lectures, I had to acknowledge that I was missing out on information,” Jeewajee says.

Over the winter break of her sophomore year, her mother, who had been living in the U.S. while Jeewajee was raised by her grandmother in Mauritius, convinced Jeewajee to see a specialist at Massachusetts Eye and Ear Hospital. That’s when Jeewajee encountered her role model, Felipe Santos, a surgeon who specializes in her hearing disorder.

Jeewajee had sought Santos’ help to find a higher-performing hearing aid, but instead he recommended a titanium implant to restore her hearing via a minimally invasive surgery. Now, Jeewajee does not require a hearing aid at all, and she can hear equally well from both ears.

“The surgery helped me with everything. I used to not be able to balance, and now I am better at that. I had no idea that my hearing affected that,” she says.

These changes, she says, are little things. But it’s the little things that made a large impact.

“I gained a lot more confidence after the surgery. In class, I was more comfortable raising my hand. Overall, I felt like I was living better,” she says.

This feeling is what brought Jeewajee to audition for the a cappella group. She never had any formal training in singing, but in January, during MIT’s Independent Activities Period, her friend mentioned that she wanted to start an a cappella group and convinced Jeewajee to help her launch Singing For Service.

Jeewajee describes Singing For Service as her “fun activity” at MIT, where she can just let loose. She is a soprano singer, and the group of nine to 12 students practices for about three hours a week before their weekly performances. They prepare three songs for each show; a typical lineup is a Disney melody, Josh Groban’s “You Raise Me Up,” and a mashup from the movie “The Greatest Showman.”

Her favorite part is when they take song requests from the audience. For example, Singing For Service recently went to a home for patients with multiple sclerosis, who requested songs from the Beatles and “Bohemian Rhapsody.” After the performance, the group mingles with the audience, which is one of Jeewajee’s favorite parts of the day.

She loves talking with patients and the elderly. Because Jeewajee was a patient for so many years growing up, she now wants to help people who are going through that type of experience. That is why she is going into the medical field and strives to earn an MD-PhD.

“When I was younger, I kind of always was at the doctor’s office. Doctors want to help you and give you a treatment and make you feel better. This aspect of medicine has always fascinated me, how someone is literally dedicating their time to helping you. They don’t know you, they’re not family, but they’re here for you. And I want to be there for someone as well,” she says.

Jeewajee says that because she grew up with a medical condition that was poorly understood, she wants to devote her career to search for answers to tough medical problems. Perhaps not surprisingly, she has gravitated toward cancer research.

She discovered her passion for this field after her first year at MIT, when she spent the summer conducting research in a cancer hospital in Lyon, through MISTI-France. There, she experienced an “epiphany” as she watched scientists and physicians come together to fight cancer, and was inspired to do the same.

She cites the hospital’s motto, “Chercher et soigner jusqu’à la guérison,” which means “Research and treat until the cure,” as an expression of what she will aspire to as a physician-scientist.

Last summer, while working at The Rockefeller University investigating mechanisms of resistance to cancer therapy, she developed a deeper appreciation for how individual patients can respond differently to a particular treatment, which is part of what makes cancer so hard to treat. Upon her return at MIT, she joined the Hemann lab at the Koch Institute for Integrative Cancer Research, where she conducts research on near-haploid leukemia, a subtype of blood cancer. Her ultimate goal is to find a vulnerability that may be exploited to develop new treatments for these patients.

The Koch Institute has become her second home on MIT’s campus. She enjoys the company of her labmates, who she says are good mentors and equally passionate about science. The walls of the lab are adorned with science-related memes and cartoons, and amusing photos of the team’s scientific adventures.

Jeewajee says her work at the Koch Institute has reaffirmed her motivation to pursue a career combining science and medicine.

“I want to be working on something that is challenging so that I can truly make a difference. Even if I am working with patients for whom we may or may not have the right treatment, I want to have the capacity to be there for them and help them understand and navigate the situation, like doctors did for me growing up,” Jeewajee says.

New pathway for lung cancer treatment

MIT researchers identify pyrimidine biosynthesis as a target for the treatment of small cell lung cancer.

Bendta Schroeder | Koch Institute
November 11, 2019

MIT cancer biologists have identified a new therapeutic target for small cell lung cancer, an especially aggressive form of lung cancer with limited options for treatment.

Lung cancer is the leading cause of cancer-associated mortality in the United States and worldwide, with a five-year survival rate of less than 20 percent. But of the two major sub-types of lung cancer, small cell and non-small cell, small cell is more aggressive and has a much poorer prognosis. Small cell lung cancer tumors grow quickly and metastasize early, resulting in a five-year survival rate of about 6 percent.

“Unfortunately, we haven’t seen the same kinds of new treatments for small cell lung cancer as we have for other lung tumors,” says Tyler Jacks, director of the Koch Institute for Integrative Cancer Research at MIT. “In fact, patients are treated today more or less the same way they were treated 40 or 50 years ago, so clearly there is a great need for the development of new treatments.”

A study appearing in the Nov. 6 issue of Science Translational Medicine shows that small cell lung cancer cells are especially reliant on the pyrimidine biosynthesis pathway and that an enzyme inhibitor called brequinar is effective against the disease in cell lines and mouse models.

Jacks is the senior author of this study. Other MIT researchers include Associate Professor of Biology and Koch Institute member Matthew Vander Heiden, and co-lead authors postdoc researcher Leanne Li and graduate student Sheng Rong Ng.

Roadblock for cell replication

Researchers in the Jacks lab used CRISPR to screen small cell lung cancer cell lines for genes that already have drugs targeting them, or that are likely to be druggable, in order to find therapeutic targets that can be tested more quickly and easily in a clinical setting.

The group found that small cell lung cancer tumors are particularly sensitive to the loss of a gene encoding dihydroorotate dehydrogenase (DHODH), a key enzyme in the de novo pyrimidine biosynthesis pathway. Upon discovering that the sensitivity involved a metabolic pathway, the researchers sought the collaboration of the Vander Heiden lab, experts in normal and cancer cell metabolism who were already conducting studies on the role of pyrimidine metabolism and DHODH inhibitors in other cancers.

Pyrimidine is one of the major building blocks of DNA and RNA. Unlike healthy cells, cancer cells are constantly dividing and need to synthesize new DNA and RNA to support the production of new cells. The investigators found that small cell lung cancer cells have an unexpected vulnerability: Despite their dependence on the availability of pyrimidine, this synthesis pathway is much less active in small cell lung cancer cells than in other types of cancer cells examined in the study. Through inhibiting DHODH, they found that small cell lung cancer cells were not able to produce enough pyrimidine to keep up with demand.

When researchers treated a genetically engineered mouse model of small cell lung cancer tumors with the DHODH inhibitor brequinar, tumor progression slowed down and the mice survived longer than untreated mice. Similar results were observed for small cell lung cancer tumors in the liver, a frequent site of metastasis in patients.

In addition to mouse model studies, the researchers tested four patient-derived small cell lung cancer tumor models and found that brequinar worked well for two of these models — one of which does not respond to the standard platinum-etoposide regimen for this disease.

“These findings are noteworthy because second-line treatment options are very limited for patients whose cancers no longer respond to the initial treatment, and we think that this could potentially represent a new option for these patients,” says Ng.

Shorter pathway to the clinic

Brequinar has already been approved for use in patients as an immunosuppressant, and there has been some preclinical research showing that brequinar and other DHODH inhibitors may be effective for other types of cancers.

“We’re excited because our findings could provide a new way to help small cell lung cancer patients in the future,” says Li. “While we still have a lot of work to do before brequinar can be tested in the clinic as a therapy for small cell lung cancer, we’re hopeful that this might happen more quickly now that we’re starting with a drug that is known to be safe in humans.”

Next steps for the researchers include optimizing the therapeutic efficacy of DHODH inhibitors and combining them with other currently available treatment options for small cell lung cancer, such as chemotherapy and immunotherapy. To help clinicians tailor treatments to individual patients, researchers will also work to identify biomarkers for tumors that are susceptible to this therapy, and investigate resistance mechanisms in tumors that do not respond to this treatment.

The research was funded, in part, by the MIT Center for Precision Cancer Medicine and the Ludwig Center for Molecular Oncology at MIT.