BreakThrough Digest Medical News |
- Scripps Research scientists devise powerful new method for finding therapeutic antibodies
- Improved nanoparticles deliver drugs into brain
- Bad strep throat? It’s probably not strep, most likely viral
| Scripps Research scientists devise powerful new method for finding therapeutic antibodies Posted: 10 Sep 2012 09:00 PM PDT
Scientists at The Scripps Research Institute have found a new technique that should greatly speed the discovery of medically and scientifically useful antibodies, immune system proteins that detect and destroy invaders such as bacteria and viruses. New methods to discover antibodies are important because antibodies make up the fastest growing sector of human therapeutics; it is estimated that by 2014 the top-three selling drugs worldwide will be antibodies.
The new technique, described in an article this week published online ahead of print by the journal Proceedings of the National Academy of Sciences, enables researchers to search large libraries of antibodies and quickly select the ones with a desired biological effect. It also provides for the creation of unusual, asymmetric antibodies whose capabilities extend beyond those of natural antibodies. The Scripps Research scientists demonstrated the power of the technique by using it to find an asymmetric antibody that almost perfectly mimics the activity of erythropoietin (EPO), a medically valuable hormone. “Traditionally we’ve looked at antibodies as tools for binding to specific targets, but we should view them more generally, as tools for probing and altering functions in cells,” said Richard Lerner, the Lita Annenberg Hazen Professor of Immunochemistry and member of the Department of Molecular Biology at Scripps Research who led the new study. At the Vanguard Lab-grown antibodies already represent a major part of the ongoing biotechnology revolution. Used as scientific probes or medical therapies, they recreate the versatility of natural antibodies, which are produced by immune cells in a vast diversity to bind to highly specific shapes on viruses, bacteria, and other targets. Two decades ago, Lerner and his laboratory at Scripps Research, in parallel with the group of Sir Gregory Winter at the Laboratory of Molecular Biology in Britain, developed the first techniques for generating very large libraries of combinatorial antibodies and quickly isolating those that can bind to a desired target. Since then, such techniques have been used to find antibodies to treat cancer, arthritis, transplant rejection, and other conditions. Humira, an anti-inflammatory antibody that was discovered this way, is expected to be the world’s top-selling drug this year. Belimumab (Benlysta®) was approved by the US Food and Drug Administration in 2011 to treat lupus, becoming the first new drug to treat the chronic, life-threatening inflammatory disease in more than 50 years. Current antibody-discovery techniques have one big drawback, however. Although they can rapidly find antibodies that bind tightly to a known target, they can’t rapidly determine which of those antibodies has useful biological activity. An antibody may bind tightly to a virus without affecting the virus’s ability to infect cells, for example, or it may bind to a cellular receptor without activating that receptor. With current techniques, determining the overall biological effect of a target-binding antibody typically requires further, painstaking analysis. A More Direct Path In the new study, Lerner and his postdoctoral researcher Hongkai Zhang sought a method for rapidly finding antibodies that have a desired effect on cells, not just a desired ability to bind to a target. As a proof of principle, they aimed to discover an antibody that could mimic the activity of EPO, a hormone that stimulates red blood cell production. Drugs that mimic EPO’s effect are commonly used to treat anemia and related conditions. Zhang began by using traditional techniques to quickly sift through a large antibody library to find tens of thousands of antibodies that bind tightly to the EPO receptor. He then stepped beyond traditional techniques, by taking the genes that encoded these EPO-receptor-binding antibodies and inserting them into lentiviruses. Unlike the phage viruses used in traditional methods, lentiviruses can usefully infect mammalian cells, delivering their payloads ? antibodies, in this case ? into a more human-like cellular environment. Zhang applied this new library of antibody-coding lentiviruses to a single, large culture of mammalian test cells. The cells were of a type that express EPO receptors and proliferate when these receptors are bound by EPO proteins ? or by antibodies that effectively mimic EPO. Each of these cells could host only a few viral particles at most, so in this way Zhang was able to distribute the entire library of EPO-receptor-binding antibodies broadly within the cell culture. Zhang also cultured the cells in a special way that prevented antibodies secreted by one cell from spreading easily to nearby cells and muddying any cause-effect relationship. “This concern over the diffusion of antibodies in the culture was one of the factors that had discouraged other researchers from using such a technique,” said Zhang. After the lentiviruses had delivered the antibodies to the cultured cells, Zhang was able to note which cells were proliferating the most ? signifying the presence of antibodies that mimic EPO. To identify the antibodies responsible, Zhang had only to harvest these faster-growing cells and sequence the antibody genes inside them. This method quickly yielded an antibody that in a further test showed about 60 percent of the biological activity of natural EPO ? which was as good as any antibody EPO-mimic that had ever been described. Opening the Door to the Unknown But Zhang and Lerner also noted that many of the proliferating cells had been infected by multiple lentivirus particles, and contained sequences from more than one antibody. Puzzlingly, Zhang found that when he recreated antibodies from these sequences, and tested them individually or in combinations, they showed no significant EPO-mimicking effect. Further tests showed that the source of the EPO-mimicking effect in the test cells was an antibody that does not occur naturally. An antibody of the type used in the study has a Y-shaped structure, normally with two identical binding arms. But the presence of multiple antibody genes within some of Zhang’s test cells meant that, in a few cases, antibodies assembled themselves with two different binding arms. One of these “bispecific” antibodies turned out to bind to the EPO receptor ? which has two binding sites ? in a way that very accurately mimics the binding of a natural EPO molecule. “It turned out to be 100 percent as potent as authentic EPO in further tests,” Zhang said. The serendipitous finding represents another major innovation, for, in principle, it extends the medical and scientific antibody repertoire from the 100 billion or so known variants of same-armed antibodies to an astronomically higher number of bispecific variants. Experiments to test such variants will be limited by the maximum number of usable cells in cultures, but that number is still very high, on the order of 10 million. “That allows for a lot of unique binding events,” said Lerner. “You probably can get almost anything that way.” Lerner emphasizes that this new antibody-engineering/discovery technique can be used not just against known targets such as the EPO receptor, but also against cellular functions involving targets that have not yet been found. “The real power of this technique is its ability to help us discover the unknown,” he said. ### Another author of the study, titled “Selection of antibodies that regulate phenotype from intracellular combinatorial antibody libraries,” was Ian A. Wilson, the Hansen Professor of Structural Biology at Scripps Research and an expert on the structure of the EPO receptor. For more information on the paper, see http://www.pnas.org/content/early/2012/09/05/1214275109.abstract Contact: Mika Ono |
| Improved nanoparticles deliver drugs into brain Posted: 10 Sep 2012 09:00 PM PDT The brain is a notoriously difficult organ to treat, but Johns Hopkins researchers report they are one step closer to having a drug-delivery system flexible enough to overcome some key challenges posed by brain cancer and perhaps other maladies affecting that organ.
In a report published online on August 29 in Science Translational Medicine, the Johns Hopkins team says its bioengineers have designed nanoparticles that can safely and predictably infiltrate deep into the brain when tested in rodent and human tissue. “We are pleased to have found a way to prevent drug-embedded particles from sticking to their surroundings so that they can spread once they are in the brain,” says Justin Hanes, Ph.D., Lewis J. Ort Professor of Ophthalmology, with secondary appointments in chemical and biomolecular engineering, biomedical engineering, oncology, neurological surgery and environmental health sciences, and director of the Johns Hopkins Center for Nanomedicine. After surgery to remove a brain tumor, standard treatment protocols include the application of chemotherapy directly to the surgical site to kill any cells left behind that could not be surgically removed. To date, this method of preventing tumor recurrence is only moderately successful, in part, because it is hard to administer a dose of chemotherapy high enough to sufficiently penetrate the tissue to be effective and low enough to be safe for the patient and healthy tissue. To overcome this dosage challenge, engineers designed nanoparticles ? about one-thousandth the diameter of a human hair ? that deliver the drug in small, steady quantities over a period of time. Conventional drug-delivery nanoparticles are made by entrapping drug molecules together with microscopic, string-like molecules in a tight ball, which slowly breaks down when it comes in contact with water. According to Charles Eberhart, M.D., a Johns Hopkins pathologist and contributor to this work, these nanoparticles historically have not worked very well because they stick to cells at the application site and tend to not migrate deeper into the tissue. Elizabeth Nance, a graduate student in chemical and biomolecular engineering at Hopkins, and Hopkins neurosurgeon Graeme Woodworth, M.D., suspected that drug penetration might be improved if drug-delivery nanoparticles interacted minimally with their surroundings. Nance first coated nano-sized plastic beads of various sizes with a clinically tested molecule called PEG, or poly(ethylene glycol), that had been shown by others to protect nanoparticles from the body’s defense mechanisms. The team reasoned that a dense layer of PEG might also make the beads more slippery. The team then injected the coated beads into slices of rodent and human brain tissue. They first labeled the beads with glowing tags that enabled them to see the beads as they moved through the tissue. Compared to non-PEG-coated beads, or beads with a less dense PEG coating, they found that a dense coating of PEG allowed larger beads to penetrate the tissue, even those beads that were nearly twice the size previously thought to be the maximum possible for penetration within the brain. They then tested these beads in live rodent brains and found the same results. The researchers then took biodegradable nanoparticles carrying the chemotherapy drug paclitaxel and coated them with PEG. As expected, in rat brain tissue, nanoparticles without the PEG coating moved very little, while PEG-covered nanoparticles distributed themselves quite well. “It’s really exciting that we now have particles that can carry five times more drug, release it for three times as long and penetrate farther into the brain than before,” says Nance. “The next step is to see if we can slow tumor growth or recurrence in rodents.” Woodworth added that the team “also wants to optimize the particles and pair them with drugs to treat other brain diseases, like multiple sclerosis, stroke, traumatic brain injury, Alzheimer’s and Parkinson’s.” Another goal for the team is to be able to administer their nanoparticles intravenously, which is research they have already begun. ### Authors on the paper include Elizabeth Nance, Graeme Woodworth, Kurt Sailor, Ting-Yu Shih, Qingguo Xu, Ganesh Swaminathan, Dennis Xiang, Charles Eberhart and Justin Hanes, all from The Johns Hopkins University. This work was supported by grants from the National Cancer Institute (R01CA164789 and U54CA151838) Contact: Cathy Kolf
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| Bad strep throat? It’s probably not strep, most likely viral Posted: 09 Sep 2012 09:00 PM PDT
When it is strep, penicillin is the antibiotic of choice, say IDSA Group A Streptococcal Throat Infection GuidelinesAT A GLANCE
[September 10, 2012: ARLINGTON, Va.] ? Although people often say they have “strep” throat, most sore throats actually are caused by a virus, not streptococcus bacteria, and shouldn’t be treated with antibiotics, suggest guidelines (http://cid.oxfordjournals.org/content/early/2012/09/06/cid.cis629.full) published by the Infectious Diseases Society of America (IDSA). Antibiotics are ineffective against viruses. The IDSA’s newly revised guidelines for Group A streptococcal pharyngitis ? strep throat ? also advise that when a strep infection is confirmed by testing, it should be treated with penicillin or amoxicillin ? if the patient does not have an allergy ? and not azithromycin or a cephalosporin. Further, the guidelines recommend that children who suffer from recurrent strep throat should not have their tonsils surgically removed solely to reduce the frequency of infection. The guidelines are being published today in the journal Clinical Infectious Diseases. About 15 million people in the U.S. see the doctor for a sore throat every year and up to 70 percent receive antibiotics, although only a smaller percentage actually have strep throat: approximately 20 to 30 percent of children and just 5 to 15 percent of adults. The guidelines note that children and adults do not need to be tested for strep throat if they have a cough, runny nose, hoarseness and mouth sores, which are strong signs of a viral throat infection. A sore throat is more likely to be caused by strep if the pain comes on suddenly, swallowing hurts and the sufferer has a fever without the above listed features, but should be confirmed through testing before antibiotics are prescribed, the guidelines note. If strep is suspected, the guidelines recommend physicians use the rapid antigen detection test, which provides results in a few minutes. If that test is negative, a follow-up throat culture is recommended for children and adolescents, but not for adults. Results of the culture can take up to several days, but antibiotics should not be prescribed unless results are positive, the guidelines note. Because strep throat is uncommon in children three years old or younger, they don’t need to be tested, the guidelines recommend. “The guidelines promote accurate diagnosis and treatment, particularly in avoiding the inappropriate use of antibiotics, which contributes to drug-resistant bacteria,” said lead author Stanford T. Shulman, MD, chief of the division of infectious diseases at Ann & Robert H. Lurie Children’s Hospital of Chicago and professor of pediatrics at Northwestern University Fineberg School of Medicine. “We recommend penicillin or amoxicillin for treating strep because they are very effective and safe in those who are not allergic, and there is increasing resistance of strep to the broader-spectrum ? and more expensive ? macrolides, including azithromycin.” He notes the guidelines recommend against tonsillectomy for children with repeated throat infection except in very specific cases ? such as a child who has obstructive breathing ? because the risks of surgery are generally not worth the transient benefit. Serious complications from strep throat ? particularly rheumatic fever ? have diminished in the United States, but occasionally do occur, so accurate diagnosis is key, Dr. Shulman said. The voluntary guidelines are not intended to take the place of a doctor’s judgment, but rather to support the decision-making process, which must be individualized according to each patient’s circumstances. The eight-member Group A streptococcal pharyngitis guidelines panel comprises experts representing a variety of specialties, including adult and pediatric infectious diseases physicians, pediatricians and respiratory diseases authorities. In addition to Dr. Shulman, the panel includes: Alan L. Bisno, Herbert W. Clegg, Michael A. Gerber, Edward L. Kaplan, Grace Lee, Judith M. Martin and Chris Van Beneden. ### IDSA has published more than 50 treatment guidelines on various conditions and infections, ranging from HIV/AIDS to Clostridium difficile. As with other IDSA guidelines, the Group A strep pharyngitis guidelines will be available in a smartphone format and a pocket-sized quick-reference edition. A podcast with the lead author and the full guidelines are available free on the IDSA website at www.idsociety.org. Note: The guidelines are available online (LINK). Founded in 1979, Clinical Infectious Diseases publishes clinical articles twice monthly in a variety of areas of infectious disease, and is one of the most highly regarded journals in this specialty. The Infectious Diseases Society of America (IDSA) is an organization of physicians, scientists, and other health care professionals dedicated to promoting health through excellence in infectious diseases research, education, patient care, prevention, and public health. The Society, which has nearly 10,000 members, was founded in 1963 and is based in Arlington, Va. For more information, see www.idsociety.org. Contact: Ashley Mattys |
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