Scripps Florida Scientists Identify Critical New Protein Complex Involved in Learning and Memory.


Scientists from the Florida campus of The Scripps Research Institute (TSRI) have identified a protein complex that plays a critical but previously unknown role in learning and memory formation.

The study, which showed a novel role for a protein known as RGS7, was published April 22, 2014 in the journal eLife, a publisher supported by the Howard Hughes Medical Institute, the Max Planck Society and the Wellcome Trust.

“This is a critical building block that regulates a fundamental process—memory,” said Kirill Martemyanov, a TSRI associate professor who led the study. “Now that we know about this important new player, it offers a unique therapeutic window if we can find a way to enhance its function.”

The team looked at RGS7 in the hippocampus, a small part of the brain that helps turn short-term memory in long-term memory.

The scientists found the RGS7 protein works in concert with another protein, R7BP, to regulate a key signaling cascade that is increasingly seen as a critical to cognitive development. The cascade involves the neurotransmitter GABA, which binds to the GABAb receptor and opens inhibitory channels known as GIRKs in the cell membrane. This process ultimately makes it more difficult for a nerve cell to fire.

This process turned out to be critical to normal functioning, as the research showed mice lacking RGS7 exhibited deficits in learning and memory.

Martemyanov believes the findings could ultimately have broad therapeutic application. “GIRK channels are implicated in a range of neuropsychiatric conditions, including drug addiction and Down’s syndrome, that result from a disproportionate increase in neuronal inhibition as a result of greater mobilization of these channels,” he said. “Now that we know the identity of the critical modulator of GIRK channels we can try to find a way to increase its power with the hopes of reducing the inhibitory overdrive, and that might potentially alleviate some of the disruptions seen in Down’s syndrome. It is possible that similar strategies might apply for dealing with addiction, where adaptations in the GABAb-GIRK pathway play a significant role.”

Targeting the RGS7 protein could allow for better therapeutic outcomes with fewer side effects because it allows for fine tuning of the signaling, according to Olga Ostrovskaya, the first author of the study and a member of Martemyanov’s lab, who sees many ways to follow up on the findings.

“We’re looking into how RGS7 is involved in neural circuitry and functions tied to the striatum, another part of the brain responsible for procedural memory, mood disorders, motivation and addiction,” Ostrovskaya said. “We may uncover the RGS7 regulation of other signaling complexes that may be very different from those in hippocampus.”

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Gene responsible for hereditary cancer syndrome found to disrupt critical growth-regulating pathway.


 Whitehead Institute scientists report that the gene mutated in the rare hereditary disorder known as Birt-Hogg-Dubé cancer syndrome also prevents activation of mTORC1, a critical nutrient-sensing and growth-regulating cellular pathway.

This is an unexpected finding, as some cancers keep this pathway turned on to fuel their unchecked growth and expansion. In the case of Birt-Hogg-Dubé syndrome, the mutated gene prevents mTORC1 pathway activation early in the formation of tumors. Reconciling these opposing roles may give scientists a new perspective on how cancer cells can distort normal cellular functions to maintain their own harmful ways.

Cells use the mTORC1 (for “mechanistic target of rapamycin complex 1”) pathway to regulate growth in response to the availability of certain nutrients, including amino acids. Whitehead Member David Sabatini and other researchers have teased apart many components of this pathway, but the precise mechanism by which nutrient levels are actually sensed has remained elusive. Recently, Sabatini and his lab determined that a family of proteins known as Rag GTPases act as a switch for the pathway—when nutrients are present, the Rag proteins turn on the mTORC1 pathway.

Now, several members of the Sabatini lab, including graduate student Zhi-Yang Tsun, have determined that the FLCN protein acts as a trigger to activate the Rag protein switch. Their work is described in the November 7 issue of the journal Molecular Cell.

“Zhi has ascribed a molecular function to this protein, and that’s a major contribution,” says Sabatini, who is also a Howard Hughes Medical Institute investigator and a professor of biology at MIT. “For the first time, we have a biochemical function that’s associated with it. And in my view, that’s an important first step to understanding how it might be involved in cancer.”

Before Tsun’s work, very little was known about FLCN’s role in the cell. In the early 2000s, scientists determined that mutations in the gene coding for FLCN caused the rare cancer Birt-Hogg-Dubé syndrome, but the syndrome’s symptoms offered little insight into FLCN’s molecular function.

Birt-Hogg-Dubé syndrome causes unsightly but benign hair follicle tumors on the face, benign tumors in the lungs that can lead to collapsed lungs, and kidney cancer. The syndrome is an autosomal dominant disorder, which means that a child inheriting one mutated copy of the FLCN gene will eventually develop the syndrome. Currently, the disease is managed by treating symptoms, but no cure exists.

FLCN’s dual roles—as a cause of a rare cancer in its mutated form and as a trigger for a growth pathway that is often hijacked in cancer cells—has prompted Tsun and Sabatini to rethink how a mutation can push cells to become cancerous.

“Basically, the mTORC1 pathway is essential for life,” explains Tsun. “So when you lose this nutrient switch or if it can’t be turned on, then the cell seems to freak out and cause all other growth promoting pathways to be turned on to somehow overcompensate for this loss. And this is actually what we see in patient tumors.”

For Birt-Hogg-Dubé syndrome patients and their families, better understanding of FCLN’s function moves the field one step closer to developing a therapy.

“Usually diseases are first described, then the responsible gene or genes are identified, and then that gene’s molecular function is figured out,” says Tsun. “And you need to know the gene’s function before you can start working on drugs or therapy. We’ve done that third step, which is a very important discovery for these patients.”

NOBEL PRIZE IN PHYSIOLOGY AND MEDICINE 2013.


The Nobel Assembly at Karolinska Institutet has today decided to award

The 2013 Nobel Prize in Physiology or Medicine

jointly to

James E. Rothman, Randy W. Schekman
and Thomas C. Südhof

for their discoveries of machinery regulating vesicle traffic,
a major transport system in our cells

Summary

The 2013 Nobel Prize honours three scientists who have solved the mystery of how the cell organizes its transport system. Each cell is a factory that produces and exports molecules. For instance, insulin is manufactured and released into the blood and chemical signals called neurotransmitters are sent from one nerve cell to another. These molecules are transported around the cell in small packages called vesicles. The three Nobel Laureates have discovered the molecular principles that govern how this cargo is delivered to the right place at the right time in the cell.

Randy Schekman discovered a set of genes that were required for vesicle traffic. James Rothman  unravelled protein machinery that allows vesicles to fuse with their targets to permit transfer of cargo. Thomas Südhof revealed how signals instruct vesicles to release their cargo with precision.

Through their discoveries, Rothman, Schekman and Südhof have revealed the exquisitely precise control system for the transport and delivery of cellular cargo. Disturbances in this system have deleterious effects and contribute to conditions such as neurological diseases, diabetes, and immunological disorders.

How cargo is transported in the cell

In a large and busy port, systems are required to ensure that the correct cargo is shipped to the correct destination at the right time. The cell, with its different compartments called organelles, faces a similar problem: cells produce molecules such as hormones, neurotransmitters, cytokines and enzymes that have to be delivered to other places inside the cell, or exported out of the cell, at exactly the right moment. Timing and location are everything. Miniature bubble-like vesicles, surrounded by membranes, shuttle the cargo between organelles or fuse with the outer membrane of the cell and release their cargo to the outside. This is of major importance, as it triggers nerve activation in the case of transmitter substances, or controls metabolism in the case of hormones. How do these vesicles know where and when to deliver their cargo?

Traffic congestion reveals genetic controllers

Randy Schekman was fascinated by how the cell organizes its transport system and in the 1970s decided to study its genetic basis by using yeast as a model system. In a genetic screen, he identified yeast cells with defective transport machinery, giving rise to a situation resembling a poorly planned public transport system. Vesicles piled up in certain parts of the cell. He found that the cause of this congestion was genetic and went on to identify the mutated genes. Schekman identified three classes of genes that control different facets of the cell´s transport system, thereby providing new insights into the tightly regulated machinery that mediates vesicle transport in the cell.

Docking with precision

James Rothman was also intrigued by the nature of the cell´s transport system. When studying vesicle transport in mammalian cells in the 1980s and 1990s, Rothman discovered that a protein complex enables vesicles to dock and fuse with their target membranes. In the fusion process, proteins on the vesicles and target membranes bind to each other like the two sides of a zipper. The fact that there are many such proteins and that they bind only in specific combinations ensures that cargo is delivered to a precise location. The same principle operates inside the cell and when a vesicle binds to the cell´s outer membrane to release its contents.

It turned out that some of the genes Schekman had discovered in yeast coded for proteins corresponding to those Rothman identified in mammals, revealing an ancient evolutionary origin of the transport system. Collectively, they mapped critical components of the cell´s transport machinery.

Timing is everything

Thomas Südhof was interested in how nerve cells communicate with one another in the brain. The signalling molecules, neurotransmitters, are released from vesicles that fuse with the outer membrane of nerve cells by using the machinery discovered by Rothman and Schekman. But these vesicles are only allowed to release their contents when the nerve cell signals to its neighbours. How is this release controlled in such a precise manner? Calcium ions were known to be involved in this process and in the 1990s, Südhof searched for calcium sensitive proteins in nerve cells. He identified molecular machinery that responds to an influx of calcium ions and directs neighbour proteins rapidly to bind vesicles to the outer membrane of the nerve cell. The zipper opens up and signal substances are released. Südhof´s discovery explained how temporal precision is achieved and how vesicles´ contents can be released on command.

Vesicle transport gives insight into disease processes

The three Nobel Laureates have discovered a fundamental process in cell physiology. These discoveries have had a major impact on our understanding of how cargo is delivered with timing and precision within and outside the cell.  Vesicle transport and fusion operate, with the same general principles, in organisms as different as yeast and man. The system is critical for a variety of physiological processes in which vesicle fusion must be controlled, ranging from signalling in the brain to release of hormones and immune cytokines. Defective vesicle transport occurs in a variety of diseases including a number of neurological and immunological disorders, as well as in diabetes. Without this wonderfully precise organization, the cell would lapse into chaos.

 

James E. Rothman was born 1950 in Haverhill, Massachusetts, USA. He received his PhD from Harvard Medical School in 1976, was a postdoctoral fellow at Massachusetts Institute of Technology, and moved in 1978 to Stanford University in California, where he started his research on the vesicles of the cell. Rothman has also worked at Princeton University, Memorial Sloan-Kettering Cancer Institute and Columbia University. In 2008, he joined the faculty of Yale University in New Haven, Connecticut, USA, where he is currently Professor and Chairman in the Department of Cell Biology.

Randy W. Schekman was born 1948 in St Paul, Minnesota, USA, studied at the University of California in Los Angeles and at Stanford University, where he obtained his PhD in 1974 under the supervision of Arthur Kornberg (Nobel Prize 1959) and in the same department that Rothman joined a few years later. In 1976, Schekman joined the faculty of the University of California at Berkeley, where he is currently Professor in the Department of Molecular and Cell biology. Schekman is also an investigator of Howard Hughes Medical Institute.

Thomas C. Südhof was born in 1955 in Göttingen, Germany. He studied at the Georg-August-Universität in Göttingen, where he received an MD in 1982 and a Doctorate in neurochemistry the same year. In 1983, he moved to the University of Texas Southwestern Medical Center in Dallas, Texas, USA, as a postdoctoral fellow with Michael Brown and Joseph Goldstein (who shared the 1985 Nobel Prize in Physiology or Medicine). Südhof became an investigator of Howard Hughes Medical Institute in 1991 and was appointed Professor of Molecular and Cellular Physiology at Stanford University in 2008.

 

Key publications:

Novick P, Schekman R: Secretion and cell-surface growth are blocked in a temperature-sensitive mutant of Saccharomyces cerevisiae. Proc Natl Acad Sci USA 1979; 76:1858-1862.
Balch WE, Dunphy WG, Braell WA, Rothman JE: Reconstitution of the transport of protein between successive compartments of the Golgi measured by the coupled incorporation of N-acetylglucosamine. Cell 1984; 39:405-416.
Kaiser CA, Schekman R: Distinct sets of SEC genes govern transport vesicle formation and fusion early in the secretory pathway. Cell 1990; 61:723-733.
Perin MS, Fried VA, Mignery GA, Jahn R, Südhof TC: Phospholipid binding by a synaptic vesicle protein homologous to the regulatory region of protein kinase C. Nature 1990; 345:260-263.
Sollner T, Whiteheart W, Brunner M, Erdjument-Bromage H, Geromanos S, Tempst P, Rothman JE: SNAP receptor implicated in vesicle targeting and fusion. Nature 1993;
362:318-324.
Hata Y, Slaughter CA, Südhof TC: Synaptic vesicle fusion complex contains unc-18 homologue bound to syntaxin. Nature 1993; 366:347-351.

Rate of Chronic Disease Increasing Exponentially.


 

A growing global epidemic of chronic disease, such as heart disease, stroke, cancer and diabetes, will cause at least 35 million deaths this year, costing the world economy billions of dollars, even though medical science has identified the principal causes and knows ways to prevent it, experts said at a AAAS seminar in Washington, D.C.

 Speakers at the first Philip Hauge Abelson Advancing Science Seminar said that twice as many premature deaths are caused worldwide by chronic diseases as by all infectious diseases, maternal and perinatal conditions and nutritional deficiencies combined. And while the toll from infectious diseases is declining globally, deaths from chronic disease are expected to increase by 17 percent in the next 10 years.

The 8 December seminar included speakers from the World Health Organization (WHO), from pharmaceutical and medical device manufacturers and from university research labs. It was the inaugural event in a series named for Abelson, a researcher in physics, biology and other sciences, and the editor for 22 years of Science, which is published by AAAS. Abelson died last year at the age of 91.

Alan I. Leshner, AAAS chief executive officer and executive publisher of Science, said the seminar series would address major societal challenges and focus on the frontiers of science and technology.
Robert Beaglehole, WHO’s director of Chronic Diseases and Health Promotion, said in the keynote address that the toll of premature death from chronic disease is increasing worldwide principally because of unhealthy diets, physical inactivity and the use of tobacco and the aging of populations in almost all countries.

Diet and the lack of physical activity is contributing to a growing pattern of obesity, a key risk factor for diabetes and early heart disease. And it’s not just happening in the rich countries, such as the United States and South Africa, where recent reports show that 75 percent of women aged 30 and over are overweight. A “very frightening statistic,” said Beaglehole, is that in countries both rich and poor, about 22 million children worldwide under the age of five are already obese.

“We’ve done a lot to observe the emergence of this problem,” he said. “We have done practically nothing to solve it.”

Beaglehole said that common misunderstandings about chronic disease have affected policy decisions and slowed the worldwide response to the emerging epidemic.

For instance, he said it’s widely believed that premature heart disease, stroke, diabetes and other chronic diseases are mostly a plague among the elderly and among the rich in high-income countries.
Actually, said Beaglehole, 80 percent of deaths from chronic diseases are in low- and middle-income countries. A WHO report found that poor people, in all but the least developed countries, are more likely than the rich to develop chronic diseases and are more likely to die early. And it is not just the elderly who are victims. The WHO report found that almost half of the deaths from chronic diseases occur in people under 70 years old.

“A very dangerous misunderstanding is that chronic disease is the result of unhealthy lifestyles under the control of individuals,” Beaglehole said. “The reality is that poor people and children have very limited choices, and it is unfair to blame them for the environmental conditions in which they suffer.”
There’s also the belief by many that chronic diseases and premature deaths cannot be prevented.
“The reality is that approximately 80 percent of premature heart disease, stroke and type 2 diabetes is preventable, as are 40 percent of all cancers — many of which result from tobacco consumption,” said Beaglehole. “A few known risk factors explain the vast majority of premature chronic disease deaths.”

A global effort to attack the causes of chronic disease could reduce death rates by 2 percent a year and save 36 million lives within a decade, he said. Ninety percent of the lives saved, said Beaglehole, would be in low- and middle-income countries. Slowing the epidemic of premature death from chronic diseases will have to involve policy issues beyond the health field, he said. For instance, farm subsidies often affect the type of food available in some countries. An example: The consumption of full fat milk is encouraged in schools in some European countries because of subsidies, said Beaglehole. Excessive fat, sugar and salt in the diet lead to obesity, type 2 diabetes, heart disease and stroke.

Other specialists at the Abelson seminar reported recent findings that offer new hope for treatment and management of heart disease, high blood pressure, obesity, diabetes and cancer.
Eric J. Topol, provost of the Cleveland Clinic Lerner College of Medicine, said studies of families with heart attack have demonstrated specific genes that are causative or induce susceptibility. This will allow strategies of lifestyle and individualized therapy early in life to prevent heart attacks decades later.

The battle against the growing epidemic of obesity will require fundamental changes in attitudes toward food and exercise, said Holly Wyatt, the program director at the Centers for Obesity Research and Education at the University of Colorado Health Sciences Center. In American society, she said, “we’ve had a lot of pressures to not expend more energy than we have to and we had a lot of pressure to eat more than we need.”

To change the behaviors that lead to obesity will require encouragement from virtually every element in society — employers, schools, churches, community centers and retail stores, she said. Such programs have worked in the past to discourage tobacco use and encourage using seat belts in cars. Without such an effort, Wyatt said that by 2008 about 75 percent of Americans will be at a body weight that negatively affects health.

Basic research on how the kidneys regulate salt in the body has given medical science a new understanding of the causes of high blood pressure, a major risk factor for heart attack, stroke and kidney failure, said Rick Lifton, Sterling Professor and chairman of Genetics atYale University School of Medicine. He said there are biological pathways and gene mutations that cause the kidneys to sequester sodium, leading to increases in blood pressure. Drugs to counter these effects could lead to dramatically improved treatments for hypertension, a disorder that affects a billion people world wide and is linked to about 5 million deaths annually.

Dr. Gerald I. Shulman, an investigator of the Howard Hughes Medical Institute and professor of internal medicine and cellular & molecular physiology at Yale University, said that new, non-invasive studies using magnetic resonance spectroscopy have demonstrated that the development of insulin resistance in type 2 diabetes is directly related to the build-up of fat inside muscle and liver cells where it disrupts normal insulin signaling and action in these organs. Studies in transgenic and knockout mice as well as in humans have shown that removing this excess intracellular fat can restore insulin sensitivity and cure type 2 diabetes. The results from these studies provide new targets for novel therapies that might be developed to reduce intracellular fat levels and reverse insulin resistance in patients with type 2 diabetes, said Shulman.

Copyright 2005. American Association for the Advancement of Science

Source: oasisadvancedwellness.com

Using Precisely-Targeted Lasers, Researchers Manipulate Neurons in Worms’ Brains and Take Control of Their Behavior.


In the quest to understand how the brain turns sensory input into behavior, Harvard scientists have crossed a major threshold. Using precisely-targeted lasers, researchers have been able to take over an animal’s brain, instruct it to turn in any direction they choose, and even to implant false sensory information, fooling the animal into thinking food was nearby.

As described in a September 23 paper published in Nature, a team made up of Sharad Ramanathan, an Assistant Professor of Molecular and Cellular Biology, and of Applied Physics, Askin Kocabas, a Post-Doctoral Fellow in Molecular and Cellular Biology, Ching-Han Shen, a Research Assistant in Molecular and Cellular Biology, and Zengcai V. Guo, from the Howard Hughes Medical Institute were able to take control of Caenorhabditis elegans — tiny, transparent worms — by manipulating neurons in the worms’ “brain.”

The work, Ramanathan said, is important because, by taking control of complex behaviors in a relatively simple animal — C. elegans have just 302 neurons -we can understand how its nervous system functions..

“If we can understand simple nervous systems to the point of completely controlling them, then it may be a possibility that we can gain a comprehensive understanding of more complex systems,” Ramanathan said. “This gives us a framework to think about neural circuits, how to manipulate them, which circuit to manipulate and what activity patterns to produce in them .”

“Extremely important work in the literature has focused on ablating neurons, or studying mutants that affect neuronal function and mapping out the connectivity of the entire nervous system. ” he added. “Most of these approaches have discovered neurons necessary for specific behavior by destroying them. The question we were trying to answer was: Instead of breaking the system to understand it, can we essentially hijack the key neurons that are sufficient to control behavior and use these neurons to force the animal to do what we want?”

Before Ramanathan and his team could begin to answer that question, however, they needed to overcome a number of technical challenges.

Using genetic tools, researchers engineered worms whose neurons gave off fluorescent light, allowing them to be tracked during experiments. Researchers also altered genes in the worms which made neurons sensitive to light, meaning they could be activated with pulses of laser light.

The largest challenges, though, came in developing the hardware necessary to track the worms and target the correct neuron in a fraction of a second.

“The goal is to activate only one neuron,” he explained. “That’s challenging because the animal is moving, and the neurons are densely packed near its head, so the challenge is to acquire an image of the animal, process that image, identify the neuron, track the animal, position your laser and shoot the particularly neuron — and do it all in 20 milliseconds, or about 50 times a second. The engineering challenges involved seemed insurmountable when we started. But Askin Kocabas found ways to overcome these challenges”

The system researchers eventually developed uses a movable table to keep the crawling worm centered beneath a camera and laser. They also custom-built computer hardware and software, Ramanathan said, to ensure the system works at the split-second speeds they need.

The end result, he said, was a system capable of not only controlling the worms’ behavior, but their senses as well. In one test described in the paper, researchers were able to use the system to trick a worm’s brain into believing food was nearby, causing it to make a beeline toward the imaginary meal.

Going forward, Ramanathan and his team plan to explore what other behaviors the system can control in C. elegans. Other efforts include designing new cameras and computer hardware with the goal of speeding up the system from 20 milliseconds to one. The increased speed would allow them to test the system in more complex animals, like zebrafish.

“By manipulating the neural system of this animal, we can make it turn left, we can make it turn right, we can make it go in a loop, we can make it think there is food nearby,” Ramanathan said. “We want to understand the brain of this animal, which has only a few hundred neurons, completely and essentially turn it into a video game, where we can control all of its behaviors.”

Source: http://www.sciencedaily.com

 

Tumor microenvironment helps skin cancer cells resist drug treatment .


Neighboring non-cancer cells may contribute to drug resistance

One of cancer’s most frightening characteristics is its ability to return after treatment. In the case of many forms of cancer, including the skin cancer known as melanoma, tailored drugs can eradicate cancer cells in the lab, but often produce only partial, temporary responses in patients. One of the burning questions in the field of cancer research has been and remains: how does cancer evade drug treatment?

New research by a team from Dana-Farber Cancer Institute, the Broad Institute and Massachusetts General Hospital suggests that some of the answers to this question do not lie in cancer cells themselves. To find the answers, scientists are looking beyond tumor cells, studying the interplay between cancer cells and their healthy counterparts. The research team has found that normal cells that reside within the tumor, part of the tumor microenvironment, may supply factors that help cancer cells grow and survive despite the presence of anti-cancer drugs. These findings appear online this week in a paper published in Nature.

“Historically, researchers would go to great lengths to pluck out tumor cells from a sample and discard the rest of the tissue,” said senior author Todd Golub, MD, the Charles A. Dana Investigator in Human Cancer Genetics at Dana-Farber Cancer Institute, pediatric oncologist at Dana-Farber/Children’s Hospital Cancer Center, and director of the Broad’s Cancer Program. Golub is also a professor at Harvard Medical School and an investigator at Howard Hughes Medical Institute. “But what we’re finding now is that those non-tumor cells that make up the microenvironment may be an important source of drug resistance.”

To investigate how the tumor microenvironment may contribute to drug resistance, the researchers designed experiments in which cancer cells were grown in the same wells (miniscule test tubes no larger than a pencil eraser) along with normal cells. These co-cultured cells were then treated with anti-cancer drugs. When grown alone, such cancer cells died in the presence of many of these targeted agents, but when grown together with normal cells, cancer cells developed resistance to more than half of the 23 agents tested.

These observations reflect what clinicians often see in patients with cancers such as melanoma. In the case of melanoma, targeted therapies have been developed against a specific, common mutation in a gene known as BRAF. While some patients’ tumors show an overwhelming response to BRAF inhibitors and seem to disappear, other patients’ tumors only respond by slightly decreasing in size. The failure to shrink tumors at the outset suggests that those tumors possess some level of innate resistance — the ability to evade drugs from the beginning of treatment.

“Even though recent advanced in targeted therapy have caused tremendous excitement in melanoma, the fact remains that drug resistance eventually develops in nearly all metastatic melanomas treated with RAF inhibitors, and in some cases is present at the outset of treatment,” said Levi A. Garraway, MD, PhD, an associate professor at Dana-Farber and Harvard Medical School and a senior associate member of the Broad Institute. “There are many different types of mechanisms that tumors may hijack to circumvent the effects of therapy…no single experimental approach can capture all of these potential mechanisms. Thus, the application of complementary approaches can offer considerable synergy in terms of discovering the full spectrum of clinically relevant resistance mechanisms.”

Scientists have uncovered resistance mechanisms that cancer cells develop over time – genetic changes in specific genes that may give cancer the ability to overcome the effects of a drug with time – but these acquired resistance mechanisms do not explain the innate resistance seen in many tumors.

“We can take cancer cells out of a melanoma patient, put them on a dish, and most times they will turn out to be extremely sensitive to the targeted agents, but that’s not what we see in patients,” said Ravid Straussman, MD, PhD, a postdoctoral fellow at the Broad Institute and first author of the Nature paper. “Why do we get just a partial response in most patients? We set out to dissect this question, and the next logical step was to think beyond cancer cells.”

After completing systematic, high-throughput screens of more than 40 cancer cell lines, the researchers chose to focus on melanoma, looking at whether factors normal cells secrete help cancer cells resist treatment. They measured more than 500 secreted factors and found that the factor most closely linked to BRAF inhibitor drug resistance was hepatocyte growth factor (HGF). HGF interacts with the MET receptor, abnormal activation of which has been tied to tumor growth in previous studies but never to drug resistance in melanoma.

In addition to studying cells in the lab, the research team sought to replicate their findings in samples from cancer patients. Keith Flaherty, MD, director of developmental therapeutics at Massachusetts General Hospital Cancer Center and an associate professor at Harvard Medical School, and his lab provided 34 patient samples for study. The team measured levels of HGF in these samples and saw a relationship between how much HGF was present and the amount of tumor shrinkage patients experienced. For example, tumors in patients with high levels of HGF shrank less than those in patients with low HGF levels.

“To try to explore in patient samples what factors in the microenvironment are not only present but functionally important in drug resistance would have been largely impossible. Coming up with candidates in the lab and then exploring relevance in humans in a targeted way is the only tractable approach,” said Flaherty. “By taking this high-throughput screening, hypothesis-generating approach, we could then follow up by looking at patient samples. In a case like melanoma, where you already have a targeted therapy available, it puts you on good footing to narrow in on specific factors that may be at play in drug resistance.”

Several HGF/MET inhibitors are in clinical development or are FDA-approved for other indications, making clinical trials combining these inhibitors with BRAF inhibitors feasible in the future. In addition, researchers could follow the same approach taken by the team to screen other drugs currently in development, identifying mechanisms of resistance and ways to counter them even before treatment begins.

“Drug resistance should no longer surprise us,” said Golub. “We’re thinking about how to do this – how to systematically dissect resistance – much earlier in the drug development process so that by the time a new drug enters the clinic, we have a good sense of what the likely mechanisms of resistance will be and have a strategy to combat them.”

Source: Dana Faber cancer Institute.