HDAC1

Researchers discovered how anti-cancer drugs called HDAC inhibitors help treat pancreatic cancer by altering scar tissue (fibroblast) development. The findings suggest HDAC inhibitors could be powerful tools in fighting pancreatic cancer -- alone and in combination with other therapies. Pancreatic cancer is one of the deadliest cancers -- only about one in eight patients survives five years after diagnosis. Those dismal statistics are in part due to the thick, nearly impenetrable wall of fibrosis, or scar tissue, that surrounds most pancreatic tumors and makes it hard for drugs to access and destroy the cancer cells. Now, researchers at the Salk Institute have discovered how a class of anti-cancer drugs called HDAC inhibitors can help treat pancreatic cancer by modulating the activation of fibroblasts -- the cells that make up that wall of scar tissue. The new research was published in Nature Communications on December 6, 2023. "These drugs turn out to be hitting both the tumor itself as well as the fibrotic tissue around it. This could be a very effective way to treat pancreatic cancers, which have typically been very difficult to reach," says senior author Professor Ronald Evans, director of Salk's Gene Expression Laboratory and March of Dimes Chair in Molecular and Developmental Biology. In response to a new pancreatic tumor, the pancreas typically activates fibroblasts -- the connective cells that support the structure of most organs. When flipped from a resting state to an active state, fibroblasts build a thick layer of scar tissue around the cancer. While this normal protective mechanism can help wall off a cancer and prevent its spread, fibroblasts also produce signaling molecules that the tumor itself takes advantage of to grow. "In the context of most pancreatic cancers, fibroblasts are acting as both good players and bad players," says Michael Downes, senior staff scientist and co-corresponding author on the paper. "It's a double-edged sword." In the new research, the team probed the effect on fibroblasts of an experimental class of cancer drugs known as histone deacetylase (HDAC) inhibitors. HDACs alter the three-dimensional structure of DNA inside cells, making some stretches of DNA easier or harder for other molecules to access and read. Targeting HDACs can therefore prevent cells from making large changes to their behavior, such as the out-of-control growth of cancer cells. But how the drugs work on all cell types is not well understood. In experiments on isolated cells, the researchers discovered that HDAC inhibitors prevented fibroblasts from becoming activated and tumor supportive. "Using HDAC inhibitors actually did two things -- it both turned down the growth signals from the fibroblasts to the cancer cells and it reduced the actual activation and accumulation of the fibroblasts," says Gaoyang Liang, first author and research associate in Evans' lab. In mice, the researchers found that one experimental HDAC inhibitor, entinostat, both reduced the activation of fibroblasts around pancreatic tumors and slowed tumor growth. When the researchers analyzed data from humans with pancreatic cancer, they discovered something similar: the higher the levels of HDAC1 in the fibrotic tissue around a patient's tumor, the worse their outcome. "This is in agreement with what we saw in cells and in mice," says Downes. "If you have more HDAC activities in the fibroblasts, you have a worse outcome. On the other hand, if you inhibit the HDACs, you have a better outcome." Since HDAC inhibitors work by preventing cells from activating certain genetic programs, the researchers wanted to know which stretches of DNA impacted by the drugs were most relevant for fibroblast activation. They identified several genes that HDAC inhibitors prevent from being expressed -- suggesting that new drugs could target those genes to keep fibroblasts from becoming activated and promoting cancer growth and fibrosis. "There have been some questions in the past about whether targeting fibroblasts is a good thing or a bad thing in pancreatic cancers, because people have shown that if you get rid of fibroblasts altogether it actually makes the cancers more aggressive," says Annette Atkins, co-author of the study and senior research scientist in Evans' lab. "But what our results suggest is that we don't have to get rid of them; just limiting their activation is beneficial." More work is needed to pinpoint how to best deliver HDAC inhibitors to the dense fibrotic tissue around pancreatic tumors, as well as how they might be most effectively combined with other cancer treatments. Other authors of the paper are Tae Gyu Oh, Nasun Hah, Yu Shi, Morgan L. Truitt, Corina E. Antal, Annette R. Atkins, Yuwenbin Li, Antonio F. M. Pinto, Dylan C. Nelson, Gabriela Estepa, Senada Bashi, Ester Banayo, Yang Dai, Ruth T. Yu, Tony Hunter, and Dannielle D. Engle of Salk; Hervé Tiriac of UC San Diego; Cory Fraser of HonorHealth Scottsdale; Serina Ng, Haiyong Han, and Daniel D. Von Hoff of The Translational Genomic Research Institute; and Christopher Liddle of the University of Sydney. The work was supported by grants from the Lustgarten Foundation (including award 552873), Don and Lorraine Freeberg Foundation, Ipsen Bioscience, a Stand Up To Cancer-Cancer Research UK-Lustgarten Foundation Pancreatic Cancer Dream Team Research Grant (SU2C-AACR-DT-20-16), a Ruth L. Kirschstein National Research Service Award (F32CA217033), a Life Sciences Research Foundation Fellowship, the Damon Runyon Cancer Research Foundation (DRG-2244-16), the National Institutes of Health (CA082683, 5T32CA009370), and the William Isacoff Research Foundation.

A potential new Alzheimer's drug represses the harmful inflammatory response of the brain's immune cells, reducing disease pathology, preserving neurons and improving cognition in preclinical tests. Though drug developers have achieved some progress in treating Alzheimer's disease with medicines that reduce amyloid-beta protein, other problems of the disease including inflammation, continue unchecked. In a new study, scientists at The Picower Institute for Learning and Memory at MIT describe a candidate drug that in human cell cultures and Alzheimer's mouse models reduced inflammation and improved memory. The target of the new "A11" molecule is a genetic transcription factor called PU.1. Prior research has shown that amid Alzheimer's disease, PU.1 becomes an overzealous director of inflammatory gene expression in the brain's microglia immune cells. A11 suppresses this problematic PU.1 activity, the new research shows, by recruiting other proteins that repress the inflammatory genes PU.1 works to express. But because A11 concentrates mostly in the brain and does not reduce PU.1 levels, it does not appear to disrupt PU.1's other job, which is to ensure the production of a wide variety of blood cells. "Inflammation is a major component of Alzheimer's disease pathology that has been especially hard to treat," said study senior author Li-Huei Tsai, Picower Professor of Neuroscience at MIT and director of The Picower Institute and MIT's Aging Brain Initiative. "This preclinical study demonstrates that A11 reduces inflammation in human microglia-like cells as well as in multiple mouse models of Alzheimer's disease and significantly improves cognition in the mice. We believe A11 therefore merits further development and testing." Tsai and Elizabeta Gjoneska of the National Institutes of Health are co-corresponding authors of the study published in the Journal of Experimental Medicine. As a postdoc, Gjoneska co-led a 2015 study that implicated PU.1 as a regulator of errant microglia inflammation in a mouse model of Alzheimer's disease. That research was a collaboration between Tsai's lab and that of MIT Computer Science Professor Manolis Kellis, co-led by former postdoc Andreas Pfenning, now a faculty member at Carnegie Mellon University. Ever since then, Tsai has been seeking a safe way to restore PU.1 activity to healthier levels. The work described in the new paper, led by Picower Institute research scientist William Ralvenius, starts with experiments to further validate that PU.1 would be a therapeutically meaningful target. To do that the scientists compared gene expression in immune cells of postmortem brain samples from Alzheimer's patients and mouse models and matching non-Alzheimer's controls. The comparisons showed that Alzheimer's effects major changes in microglial gene expression and that an increase in PU.1 binding to inflammatory gene targets was a significant component of that change. Moreover, they showed that reducing PU.1 activity in a mouse model of Alzheimer's reduced inflammation and neurodegeneration, the death of neurons. Screening success Genetically knocking down PU.1 in the body is not a viable therapeutic strategy given its importance in normal healthy function. The team therefore screened more than 58,000 small molecules from libraries of FDA-approved drugs and novel chemicals to see if any could safely and significantly reduce key inflammation and Alzheimer's related genes regulated by by PU.1 in cell cultures. After several rounds of increasingly stringent screening, they narrowed the field down to six chemicals. A11 was by far the most potent among them. They tested the effects of A11 doses on the function of human microglia-like cells cultured from patient stem cells. When they exposed the microglia-like cells to immune molecules that typically trigger inflammation, cells dosed with A11 exhibited reduced expression and secretion of inflammatory cytokines and less of the cell body shape changes associated with microglia inflammatory responses. The cells also showed less accumulation of lipid molecules, another sign of inflammatory activation. Looking at gene expression patterns, the scientists observed that A11-treated cells exposed to inflammatory triggers behaved much like unperturbed microglia, suggesting that A11 helps prevent microglia from overreacting to inflammatory cues. Two more lab tests aimed at understanding how A11 exerts its effects revealed that it doesn't change PU.1 levels. Instead it counteracts PU.1 activity by recruiting several proteins including MECP2, HDAC1, SIN3A and DMNT3A, known to repress expression of its targets. Essentially amid Alzheimer's disease, A11 tamps down what PU.1 amps up. "A11 represents a first-in-class molecule that converts PU.1 from a transcriptional activator to a transcriptional repressor, resulting in a controlled state of microglial inflammation," the authors wrote. Mice in mazes Having established that A11 reduced inflammatory activity in microglia and determined how that happens, the team focused on whether it worked as a medicine in mouse models of Alzheimer's disease. Pharmacological tests indicated that A11 is readily cleared from tissues and is capable of reaching brain cells. Moreover, in healthy mice the chemical successfully crossed the blood-brain barrier and remained in brain cells much longer than anywhere else. Finally the team tested the effects of the drugs on Alzheimer's disease pathology and symptoms in three mouse strains that each model different aspects of Alzheimer's disease: CK-p25 mice (severe neurodegeneration), Tau P301S transgenic mice (tauopathy), and 5XFAD mice (amyloid pathology). Male and female CK-p25 mice dosed with A11 showed less inflammatory response among microglia and astrocyte cells and lost fewer neurons than untreated controls. TauP301S Tg mice responded similarly, also exhibiting a significant reduction of phosphorylated tau protein in the hippocampus region of the brain, which is an essential area for memory. In 5XFAD mice, amyloid was significantly reduced. The team subjected the Tau P301S Tg and CK-p25 mice to mazes designed to test their short-term working memory and longer-term learning. In both models and on both tests, A11-treated mice performed significantly better than untreated controls. For example, in the "Morris Water Maze," where mice have to learn the location of a submerged platform that allows them to rest, treated CK-p25 mice learned much faster than untreated ones. Much more testing needs to be done before A11 could become an approved medicine, Tsai said, but she noted that it could complement the new treatments that target amyloid. "Given that A11 acts via a distinct mechanism from existing AD therapeutics, A11 could be used alone or in combination with approved therapeutics to provide improved treatment options for neurodegenerative diseases," the authors concluded. In addition to Tsai, Gjoneska and Ralvenius, the paper's other authors are Alison E. Mungenast, Hannah Woolf, Margaret M. Huston, Tyler Z. Gillingham, Stephen K. Godin, Jay Penney, Hugh P. Cam, Fan Gao, Celia G. Fernandez, Barbara Czako, Yaima Lightfoot, William J. Ray, Adrian Beckmann, Alison M. Goate, Edoardo Marcora, Carmen Romero-Molina, Pinar Ayata, and Anne Schaefer. The Robert A. and Renee E. Belfer Family Foundation and the National Institutes of Health funded the research. Additional support came from The JPB Foundation and The Picower Institute for Learning and Memory, The Halis Family Foundation, Lester A. Gimpelson and Jay L. and Caroll Miller.

A new study has revealed FDA-approved trametinib and entinostat (which is currently in clinical trials) can be given in tandem to produce fewer and smaller tumors in mice with LKB1-mutated non-small cell lung cancer. Cancer treatments have long been moving toward personalization -- finding the right drugs that work for a patient's unique tumor, based on specific genetic and molecular patterns. Many of these targeted therapies are highly effective, but aren't available for all cancers, including non-small cell lung cancers (NSCLCs) that have an LKB1 genetic mutation. A new study led by Salk Institute Professor Reuben Shaw and former postdoctoral fellow Lillian Eichner, now an assistant professor at Northwestern University, revealed FDA-approved trametinib and entinostat (which is currently in clinical trials) can be given in tandem to produce fewer and smaller tumors in mice with LKB1-mutated NSCLC. The findings were published in Science Advances on March 17, 2023. "For non-small cell lung cancer cases with the LKB1 mutation, standard chemotherapy and immunotherapy treatments are not effective," says Shaw, senior and co-corresponding author of the study, and director of Salk's Cancer Center. "Our findings demonstrate there is a way to target these cases using drugs that are FDA-approved or already in clinical trials, so this work could easily be used for a clinical trial in humans." Roughly 20 percent of all NSCLCs have the LKB1 genetic mutation, which means there are no effective targeted therapies currently on the market for patients with this cancer type. To create a therapy that could target the LKB1 mutation, the researchers turned to histone deacetylases (HDACs). HDACs are proteins associated with tumor growth and cancer metastasis, with characteristic overexpression in solid tumors. Several HDAC-inhibitor drugs are already FDA-approved (safe for human use) for specific forms of lymphoma, but data on their efficacy in solid tumors or whether tumors bearing specific genetic alterations may exhibit heightened therapeutic potential has been lacking. Based on previous findings connecting the LKB1 gene to three other HDACs that all rely on HDAC3, the team started by conducting a genetic analysis of HDAC3 in mouse models of NSCLC, discovering an unexpectedly critical role for HDAC3 in multiple models. After establishing that HDAC3 was critical for the growth of the difficult-to-treat LKB1-mutant tumors, the researchers next examined whether pharmacologically blocking HDAC3 could give a similarly potent effect. The team was curious about testing two drugs, entinostat (an HDAC inhibitor in clinical trials known to target HDAC1 and HDAC3) and FDA-approved trametinib (an inhibitor for a different class of enzymes related to cancer). Tumors often become quickly resistant to trametinib, but co-treatment with a drug that inhibits a protein downstream of HDAC3 helps reduce this resistance. Because that protein relies on HDAC3, the researchers believed that a drug that targets HDAC3 -- like entinostat -- would help manage trametinib resistance, too. After treating mice with LKB1-mutated lung cancer with variable treatment regimens for 42 days, the team found that mice given both entinostat and trametinib had 79 percent less tumor volume and 63 percent fewer tumors in their lungs than the untreated mice. Additionally, the team confirmed that entinostat was a viable treatment option in cases where a tumor was resistant to trametinib. "We thought the whole HDAC enzyme class was directly linked to the cause of LKB1 mutant lung cancer. But we didn't know the specific role of HDAC3 in lung tumor growth," says first and co-corresponding author Eichner. "We've now shown that HDAC3 is essential in lung cancer, and that it is a druggable vulnerability in therapeutic resistance." The findings may lead to clinical trials to test the new regimen in humans, since entinostat is already in clinical trials and trametinib is FDA-approved. Importantly, Shaw sees this discovery as transformative for cancers beyond NSCLC, with potential applications in lymphoma, melanoma, and pancreatic cancer. "Our lab has committed years to this project, taking small and meaningful steps toward these findings," says Shaw, holder of the William R. Brody Chair. "This is truly a success story for how basic discovery science can lead to therapeutic solutions in the not-so-distant future." "My independent laboratory is fortunate to be part of the Lurie Cancer Center at the Feinberg School of Medicine at Northwestern University, which is very supportive of translational research. We hope that this environment will facilitate the initiation of a clinical trial based on these findings," says Eichner. Other authors include Stephanie D. Curtis, Sonja N. Brun, Joshua T. Baumgart, Elijah Trefts, Debbie S. Ross, and Tammy J. Rymoff of Salk; and Caroline K. McGuire and Irena Gushterova of Northwestern University. The work was supported by the National Institutes of Health (R35CA220538, P01CA120964, K22CA251636, 5T32CA009370, 5F32CA206400, CCSG P30CA014195, and CCSG P30CA23100), Leona M. and Harry B. Helmsley Charitable Trust (#2012-PG-MED002), American Cancer Society (PF-15-037-01-DMC), and Chapman Foundation.