SREBP-2

An image of cancer organoid cells treated with perhexiline maleate. The red in the image is a marker of cell death, indicating where the cells were destroyed by the drug. Scientists have shown that an old heart drug can inhibit growth of one of the most common and lethal forms of pancreatic cancer, at least in preclinical models.  In a study published Dec. 26 in Cell Stem Cell, researchers from Weill Cornell Medicine showed that perhexiline maleate—a calcium channel blocker used to treat angina—could stifle the growth of KRAS-G12D-mutated pancreatic ductal adenocarcinoma in human organoid models that had been transplanted into mice. Its mechanism of action could form the basis of future drugs.  Perhexiline maleate, prescribed as Pexid or Pexsig, was used as an anti-angina treatment until the 1980s, when it was sidelined in most countries due to its side effect profile, a review article by researchers at the University of Adelaide explains. While the drug was never approved for use in the U.S., it is still used by clinicians in New Zealand and Australia. It works by shifting the metabolism of fatty acids and carbohydrates in a way that helps the heart process oxygen more efficiently, thus reducing the symptoms of angina.   Scientists first demonstrated perhexiline’s anti-cancer potential in 1984, when they showed that it could sensitize leukemia cells to chemotherapy. Since then, it has shown to not only boost chemo but also to inhibit growth on its own in cell lines and mouse models of breast, lung, brain, liver and other cancers with a variety of different gene mutations.  In the new study, the researchers didn’t set out to test perhexiline maleate specifically. They started by setting up an automated drug screening system that looked at the efficacy of different drugs on organoids made from mouse pancreatic cells that had been engineered with the many different types of mutations associated with pancreatic ductal adenocarcinoma, including a mouse version of KRAS-G12D. Organoids are three-dimensional cell cultures grown from stem cells that function like the tissue of the organ they represent.  Of the 6,000 compounds tested, perhexiline maleate emerged the winner. The drug was able to not only stop all of the cancerous organoids from growing, but even destroyed some of them altogether. It also appeared to have no effect on healthy, non-mutated organoid cells.  The researchers then tested perhexiline maleate on mice transplanted with the same type of organoids, along with another group that received human-derived cancerous organoids. The drug inhibited the growth of the cells in both of those models, along with a separate set of human-derived pancreatic cancer organoids with different types of KRAS mutations.  When the researchers compared gene patterns between treated and untreated organoids, they noticed that the KRAS-G12D mutation was boosting the production of cholesterol in the mutated cells. Perhexiline maleate was counteracting that effect, thereby stopping the cancerous organoids from growing, by inhibiting a protein involved in cholesterol synthesis called SREBP2.  While this wasn’t news to the researchers, as cholesterol is well known to play a role in cancer progression and synthesis, it did mark the first time that scientists had shown that targeting it could be effective against pancreatic ductal adenocarcinoma with KRAS-G12D mutations. The fact that it worked in human organoids with other types of KRAS mutations could mean that the treatment mechanism is less vulnerable to being overcome by cancer resistance, the researchers noted in a press release.  In the same release, the scientists added perhexiline maleate itself will not be used as an anti-cancer agent, as the risk of side effects—namely liver and nerve damage—is too high. Instead, researchers will likely tinker with its chemical structure to come up with a candidate that has the same anti-cancer effects without the drawbacks.

A drug screening system that models cancers using lab-grown tissues called organoids has helped uncover a promising target for future pancreatic cancer treatments. A drug screening system that models cancers using lab-grown tissues called organoids has helped uncover a promising target for future pancreatic cancer treatments, according to a new study from researchers at Weill Cornell Medicine. In the study, published Dec. 26 in Cell Stem Cell, the scientists tested more than 6,000 compounds on their pancreatic tumor organoids, which contain a common pancreatic cancer-driving mutation. They identified one compound -- an existing heart drug called perhexiline maleate -- that powerfully suppresses the organoids' growth. The researchers discovered that the cancer-driving mutation in the organoids forces the abnormally high production of cholesterol, which the drug largely reverses. "Our findings identify hyperactive cholesterol synthesis as a vulnerability that may be targetable in most pancreatic cancers," said study co-senior author Dr. Todd Evans, vice chair for research in surgery, the Peter I. Pressman MD Professor in Surgery, and a member of the Hartman Institute for Therapeutic Organ Regeneration at Weill Cornell Medicine. "This study also highlights the value of using genetically well-defined organoids to model cancer and discover new treatment strategies," said co-senior author Dr. Shuibing Chen, director of the Center for Genomic Health, the Kilts Family Professor Surgery and a member of the Hartman Institute for Therapeutic Organ Regeneration at Weill Cornell Medicine. The other co-senior author was Dr. Fong Cheng Pan, a research assistant professor in the department of surgery at Weill Cornell Medicine during the study. The study's co-first authors were postdoctoral researcher Dr. Xiaohua Duan, instructor Dr. Tuo Zhang, and a visiting fellow, Dr. Lingling Feng, all at Weill Cornell Medicine during the study. A Tumor Organoid-Based Screening System Organoids have become popular tools for studying tissues in health and disease. They can be made from human or animal tissue, they can recreate much of an organ's complex architecture, and they can be genetically engineered for precision modeling. Organoids can also model specific tumor types with their cancer-driving gene mutations. Indeed, when these tumor organoids are derived from human tissue, they have the potential to model human cancers better than any animal model. In the study, the researchers set up an organoid-based automated drug-screening system for the most common form of pancreatic cancer, pancreatic ductal adenocarcinoma (PDAC) -- one of the most untreatable and lethal of cancers. The organoids, made from normal mouse pancreatic tissue, were engineered to contain various sets of mutations known to drive human pancreatic tumors. All the organoids contained KrasG12D, the mouse version of a cancer-driving mutant gene found in most cases of PDAC. The researchers tested a library of more than 6,000 compounds, including FDA-approved drugs, on the organoids, identifying several that could substantially disrupt their growth. The best of these was perhexiline maleate, an older drug used to treat the heart condition called angina. A modest dose of the drug blocked growth in all the KrasG12D-containing organoids, destroying some of them outright within days, while having no adverse impact on healthy organoids lacking the mutation. The drug had similar effects against mouse and human PDAC-derived tumor organoids transplanted into mice, and in human tumor organoids carrying other types of Kras mutation. By comparing gene activity patterns in treated and untreated organoids, the researchers found that cancer-associated mutant Kras greatly boosts the production of cholesterol in organoid cells, and that perhexiline maleate opposes this effect by inhibiting a key cholesterol metabolic pathway regulatory factor called SREBP2. Cholesterol as an Emerging Cancer Target The discovery of cholesterol's role was not entirely surprising, since cholesterol is an essential building-block used in making new cells, and a promoter of cell survival; it is already known to be an important sustainer of malignant growth for some other tumors, including lung tumors. Now, the results suggest that targeting it may be an effective new treatment strategy against PDAC. Perhexiline maleate's effectiveness in human organoids harboring several different Kras mutations also suggests that turbo-charged cholesterol synthesis can be a general treatment target in KRAS-mutant cancers. "We hope that our cholesterol-targeting strategy will be independent of particular KRAS mutations and will make it hard for treated tumors to evolve resistance," said Dr. Evans, who is also a member of the Sandra and Edward Meyer Cancer Center . Perhexiline maleate is unlikely to be used as-is for treating PDAC. Although it is still prescribed as an angina drug in Australia and some other countries, it can have serious side effects, including liver damage and peripheral nerve damage -- which is why it was withdrawn from several European markets in the 1980s, and was never approved in the United States. "We want a better compound for cancer treatment," said Dr. Chen. The simplicity of the drug's chemical structure suggests that it probably can be modified to improve its potency, safety, bloodstream half-life and other properties, she said. The team now plans to use perhexiline maleate as a starting point for the development of a more refined candidate PDAC drug, and as a laboratory tool for studying cholesterol synthesis in PDAC and other cancers.

Hard-to-detect colorectal pre-cancerous lesions known as serrated polyps, and the aggressive tumors that develop from them, depend heavily on the ramped-up production of cholesterol, according to a preclinical study. The finding points to the possibility of using cholesterol-lowering drugs to prevent or treat such tumors. Hard-to-detect colorectal pre-cancerous lesions known as serrated polyps, and the aggressive tumors that develop from them, depend heavily on the ramped-up production of cholesterol, according to a preclinical study from researchers at Weill Cornell Medicine. The finding points to the possibility of using cholesterol-lowering drugs to prevent or treat such tumors. In the study, published Oct. 13 in Nature Communications, the researchers analyzed mice that develop serrated polyps and tumors, detailing the chain of molecular events in these tissues that leads to increased cholesterol production. They confirmed their findings in analyses of human serrated polyps and tumors, and showed in mouse models that replicate the human cancer that blocking cholesterol production prevented the progression of these types of intestinal tumors. "Serrated-type polyps and tumors currently are not treated differently from other colorectal neoplasias, but as our work shows, they have this specific metabolic vulnerability that can be targeted," said study co-senior author Dr. Jorge Moscat, a Homer T. Hirst III Professor of Oncology in Pathology, Vice-Chair for Cell and Cancer Pathobiology in the Department of Pathology and Laboratory Medicine and a member of the Sandra and Edward Meyer Cancer Center at Weill Cornell Medicine. The other co-senior author is Dr. Maria Diaz-Meco, also a Homer T. Hirst III Professor of Oncology in Pathology and a member of the Meyer Cancer Center at Weill Cornell Medicine. The study's first author is Dr. Yu Muta, a postdoctoral associate in the Moscat/Diaz-Meco laboratories. Cholesterol is generally considered a pro-growth molecule, being a building block for cell membranes and having other growth-supporting functions. Prior studies have linked high blood cholesterol levels to various cancers, including colorectal cancers. However, it hasn't been clear that lowering cholesterol, for example with common statin drugs, can prevent colorectal cancers. "Trials of statins to prevent colorectal cancer have had conflicting results," Dr. Diaz-Meco said. "Our findings suggest that this is because targeting cholesterol has a preventive but selective effect only against polyps and tumors of this serrated type." Serrated polyps are so-called because of their sawtooth appearance under a microscope. They are flatter than ordinary colorectal polyps and can often be missed during colonoscopies. Yet the tumors into which they develop, which account for roughly 15 to 30 percent of colorectal cancers, contain many "metaplastic" cells that are particularly invasive and resistant to treatments. Several years ago, the Moscat/Diaz-Meco team linked serrated polyps and tumors to low levels of two enzymes known as aPKCs. They showed that mice engineered to lack these aPKC enzymes in their gut linings reliably form serrated polyps and then aggressive tumors. In the new study, the scientists found that in serrated-type tumors in these mice, and even in intestinal tissue poised to develop these types of cancerous lesions, cholesterol synthesis was strikingly upregulated, suggesting that cholesterol may be an early driver of tumor development. The researchers revealed how the absence of aPKC enzymes, especially in metaplastic tumor cells, unleashes the activation of a transcription factor called SREBP2, which switches on cholesterol production. Tests on colorectal polyp and tumor samples from human patients dovetailed with the mouse findings. They found, for example, that only serrated-type tumors had low aPKC levels concomitant with the accumulation of SREBP2, a driver and a marker of upregulated cholesterol biosynthesis in the serrated cancer cells. Lastly, the researchers tested a combination of two cholesterol synthesis-blocking drugs, including the widely used atorvastatin. The treatment, delivered when the low-aPKC mice were still quite young, significantly lowered the rate at which both serrated polyps and tumors later formed -- and the serrated-type tumors that did form were less aggressive than those normally arising in the untreated mice. The results indicate that targeting cholesterol could be a viable strategy for treating and preventing serrated-type colorectal tumors. The Moscat and Diaz-Meco labs are now hoping to set up an initial clinical trial of a cholesterol-lowering intervention in patients from whom serrated colorectal polyps have been removed. "Currently when these polyps are detected early with colonoscopy, they are removed and patients have to hope that they don't come back," Dr. Moscat said. "In the future, we hope to have a more active method to prevent this very aggressive form of cancer before it is fully developed and more difficult to treat."