Bacterial Drug Blimp Delivery Devices

BIOMEDICINE

Making Bacteria into Drug Blimps

A new approach can make bacteria deliver medicine where it's needed.

• FRIDAY, APRIL 1, 2011
• BY KATHARINE GAMMON

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Coaxing bacteria into producing medicines for humans' benefit has been a common quest. But the goal of getting those bacteria to drop loads of medicine at a specific target inside the body is more unusual.

According to research presented Tuesday at the American Chemical Society meeting in Anaheim, California, that goal is now within sight. The researchers, led by William Bentley of the University of Maryland, say their engineered bacteria could serve as on-the-go nanofactories inside the body, both to produce illness-fighting agents and to deliver them to the correct spots.

They developed a prototype using a strain of the E. coli bacterium specially engineered with a targeting molecule attached to its outer surface. The bacterium cruises around, finds its target, attaches to it, and begins producing preprogrammed drugs. In the laboratory, in vitro, the prototype was able both to find targeted intestinal cells and to produce chemical signals that triggered nearby bacteria to produce proteins they typically don't make.

"We envision a cell that seeks out a cancer tumor and locks on to it, then starts to create its own antitumor drug and deliver it on the spot," said Bentley. He said this method could also treat conditions such as other gastrointestinal illnesses or vitamin deficiency. "One thing that is different from other treatments is that this is site-specific," he said. "Most medicines kill all the cells or tissue, while this system only delivers drugs to one spot."

The bacterial drug factories could also produce signaling molecules to communicate with natural bacteria and keep them from starting an infection. They could, Bentley said, be injected or swallowed as probiotics—beneficial live organisms—though clinical applications of the technology are years away. 

Other researchers say that transferring the process from the lab to a person can be difficult. "Getting a lab strain of E. coli to survive the stomach is going to be tricky," says J. Christopher Anderson, a bioengineering professor at the University of California, Berkeley. "There are issues to the genetic stability of the organisms, and depending on the specific goal, the ability to get enough bacteria into the intestines to do something could be tricky." Anderson says that the intestine is a good place to start for engineered bacteria therapy because E. coli last longer in the intestines than in other parts of the body.

Getting bacterial dirigibles past regulatory hurdles could also be problematic, Anderson says. "Treating chronic diseases with gastrointestinal engineered bacteria will necessarily result in environmental release. Since these bacteria produce biologically active chemicals or proteins to be functional, there are likely to be significant safety concerns and thereby barriers to getting them approved."

Lightswitch for Bacteria

BIOMEDICINE

A Light Switch for Bacterial Infections

A new contrast agent could detect bacteria on medical implants, and help doctors decide how to treat infection.

• MONDAY, JULY 25, 2011
• BY KATHERINE BOURZAC

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A new contrast agent that targets microbes can be used to illuminate bacterial infections in living animals. It could ultimately enable doctors to safely spare more of a limb during amputations.

It's usually clear when a patient has a bacterial infection and needs to be treated with antibiotics, says Jason Bowling, director of epidemiology at the University of Texas Health Science Center at San Antonio, who was not involved with developing the imaging agent. But sometimes an infection is more difficult to diagnose. For example, it can be difficult to tell when a patient who has pain at the site of a hip or knee replacement has an infection. This sometimes leads doctors to prescribe antibiotics when they aren't necessary.

An imaging scan capable of detecting bacteria would quickly answer the question, sparing uninfected patients from unnecessary antibiotics or even from surgery to remove the implant. Where there is an infection and the implant is removed, imaging could help ensure that no new hardware is implanted until the infection has been completely cleared.

It's challenging to image infections because many of the molecules used to target bacteria can accumulate in tissue that is merely inflamed rather than infected, says Niren Murthy, professor of biomedical engineering at Georgia Tech, who was involved with developing the new agent. The new imaging agent is taken up by bacteria in large quantities, but it won't stick around in other tissue. "We had to find something very specific to bacteria," he says.

Murthy's group stole a trick from a group of viruses that gets its genome inside bacteria by attaching it to a bacterial food source, a carbohydrate called maltohexaose. Bacteria have proteins on their cell walls whose job is to bring maltohexaose inside the cell, and this happens even if that maltohexaose is attached to an imaging agent. Animal cells don't have these proteins, so they don't take up the contrast agent. 

Future Diabatic Therapy (Probiotics)

BIOMEDICINE

Biotech Bacteria Could Help Diabetics

Genetically engineered gut bacteria trigger insulin production in mice.

• TUESDAY, AUGUST 25, 2009
• BY EMILY SINGER

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Friendly gut microbes that have been engineered to make a specific protein can help regulate blood sugar in diabetic mice, according to preliminary research presented last week at the American Chemical Society conference in Washington, D.C. While the research is still in the very early stages, the microbes, which could be grown in yogurt, might one day provide an alternative treatment for people with diabetes.

The research represents a new take on probiotics: age-old supplements composed of nonharmful bacteria, such as those found in yogurt, that are ingested to promote health. Thanks to a growing understanding of these microbes, a handful of scientists are attempting to engineer them to alleviate specific ailments. "The concept of using bacteria to help perform (or fix) human disorders is extremely creative and interesting," wrote Kelvin Lee, a chemical engineer at the University of Delaware, in Maryland, in an e-mail. "Even if it does not directly lead to a solution to the question of diabetes, it opens up new avenues of thought in a more general sense," says Lee, who was not involved in the research.

People with type 1 diabetes lack the ability to make insulin, a hormone that triggers muscle and liver cells to take up glucose and store it for energy. John March, a biochemical engineer at Cornell University, in Ithaca, NY, and his collaborators decided to re-create this essential circuit using the existing signaling system between the epithelial cells lining the intestine and the millions of healthy bacteria that normally reside in the gut. These epithelial cells absorb nutrients from food, protect tissue from harmful bacteria, and listen for molecular signals from helpful bacteria. "If they are already signaling to one another, why not signal something we want?" asks March.

The researchers created a strain of nonpathogenic E. coli bacteria that produce a protein called GLP-1. In healthy people, this protein triggers cells in the pancreas to make insulin. Last year, March and his collaborators showed that engineered bacterial cells secreting the protein could trigger human intestinal cells in a dish to produce insulin in response to glucose. (It's not yet clear why the protein has this effect.)

In the new research, researchers fed the bacteria to diabetic mice. "After 80 days, the mice [went] from being diabetic to having normal glucose blood levels," says March. Diabetic mice that were not fed the engineered bacteria still had high blood sugar levels. "The promise, in short, is that a diabetic could eat yogurt or drink a smoothie as glucose-responsive insulin therapy rather than relying on insulin injections," says Kristala Jones Prather, a biochemical engineer at MIT, who was not involved in the research.

Creating bacteria that produce the protein has a number of advantages over using the protein itself as the treatment. "The bacteria can secrete just the right amount of the protein in response to conditions in the host," says March. That could ultimately "minimize the need for self-monitoring and allow the patient's own cells (or the cells of the commensal E. coli) to provide the appropriate amount of insulin when needed," says Cynthia Collins, a bioengineer at Rensselaer Polytechnic Institute, in Troy, NY, who was not involved in the research.

In addition, producing the protein where it's needed overcomes some of the problems with protein-based drugs, which can be expensive to make and often degrade during digestion. "Purifying the protein and then getting past the gut is very expensive," says March. "Probiotics are cheap--less than a dollar per dose." In underprivileged settings, they could be cultured in yogurt and distributed around a village.

The researchers haven't yet studied the animals' guts, so they don't know exactly how or where the diabetic mice are producing insulin. It's also not yet clear if the treatment, which is presumably triggering intestinal cells to produce insulin, has any harmful effects, such as an overproduction of the hormone or perhaps an inhibition of the normal function of the epithelial cells. "The mice seem to have normal blood glucose levels at this point, and their weight is normal," says March. "If they stopped eating, we would be concerned."

March's microbes are one of a number of new strains being developed to treat disease, including bacteria designed to fight cavities, produce vitamins and treat lactose intolerance. March's group is also engineering a strain of E. coli designed to prevent cholera. Cholera prevention "needs to be something cheap and easy and readily passed from village to village, so why not use something that can be mixed in with food and grown for free?" says March.

However, the work is still in its early stages; using living organisms as therapies is likely to present unique challenges. More research is needed to determine how long these bacteria can persist in the gut, as well as whether altering the gut flora has harmful effects, says MIT's Prather.

In addition, recent research shows that different people have different kinds of colonies of gut bacteria, and it's unclear how these variations might affect bacterial treatments. "This may be particularly challenging when it comes to determining the appropriate dose of the therapeutic microbe," says Collins at Rensselaer. "The size of the population of therapeutic bacterial and how long it persists will likely depend on the microbes in an individual's gut."

Pro-Biotic: engineered for Crohn Disease

BIOMEDICINE

Genetically Engineered Probiotics

A twist on a traditional therapy shows promise for treating bowel disease.

• TUESDAY, FEBRUARY 1, 2011
• BY EMILY SINGER

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Public interest in probiotics  is on the upswing, if the glut of advertisements for probiotic yogurts—those with added doses of beneficial bacteria—is any evidence. Scientists are bringing this traditional therapy into the 21st century by genetically engineering the microbes to enhance their effect on the immune system. They hope the new bugs will ultimately help treat inflammatory bowel diseases such as Crohn's disease and ulcerative colitis, as well as other disorders that result from an overactive immune system.

In research published today in the Proceedings of the National Academy of Sciences, scientists deleted a gene from the bacterium Lactobacillus acidophilus, which is commonly found in yogurt. Mansour Mohamadzadeh, associate professor of medicine at Northwestern University, and collaborators had previously shown that the enzyme this gene manufactures increases inflammation, a defining characteristic of Crohn's disease and ulcerative colitis. But the unaltered form of the bacterium also triggered production of a beneficial immune molecule, IL-10m, which helps to regulate the immune system. The goal of the engineering the microbes was to deliver the beneficial effects without the harmful ones.

When fed to mice with colitis and inflammation of the colon, the engineered bacteria prevented the weight loss and bloody diarrhea that typically accompanies this condition. In addition, the treated mice had 90 percent less inflammation in their colon tissue than did their untreated counterparts.

While probiotic foods and supplements are a huge industry, it's unclear whether they actually help treat most gastrointestinal diseases. The research published today is part of a trend in microbiology to explore in rigorous detail the effects of probiotics and the mechanisms that underlie them.

"The concept [of probiotics] is wonderful, but the evidence of their [effectiveness] is fairly limited," says Balfour Sartor, co-director of the Center for Gastrointestinal Biology and Disease at the University of North Carolina, who was not involved in the new study. Because probiotics are considered a food and not a drug, they are not regulated by the U.S. Food and Drug Administration, and therefore don't require the large clinical tests that drugs do.

Inflammatory bowel disease is one of the prime areas of interest for probiotic treatment, but "there really has been little direct evidence that probiotics are effective in treatment or prevention of Crohn's disease," says Sartor. Some research suggests that two different probiotic formulations can help prevent recurrence of ulcerative colitis, he says. "But that's just two out of thousands of formulations."

Scientists still don't know exactly how probiotic bacteria influence the gastrointestinal system, but previous research suggests several possible mechanisms. Beneficial bacteria might temporarily alter the ratio of good to bad bacteria that inhabit the intestine, or they might specifically block activity of bad bacteria. And probiotics seem to influence the immune system, "stimulating protective immune cells or blocking detrimental activities of immune cells," says Sartor.

Bio-Degradable Implants

As a graduate student at MIT, Christopher Bettinger created strong, rubbery polymers that mimic natural tissue and can be tailored to break down after anywhere from two months to two years. For Bettinger, the hardest part was making sure the molecular building blocks of his polymers were interconnected enough to yield a material that held its shape but not so strongly interconnected that the result was brittle. He initially used the new polymers to make scaffolds for laboratory-grown tissue. Now, as an assistant professor at Carnegie Mellon University, Bettinger is using them to produce degradable catheters and drug-delivery systems that he's testing in animals.

As part of his postdoctoral work at Stanford in 2009, Bettinger also created a biodegradable semiconductor for electronics used in temporary medical implants. Simple electronic circuits constructed from biodegradable materials could lead to drug-delivery devices and nerve-regeneration scaffolds that a doctor would trigger with radio frequencies from outside the body. Once therapy was complete, the devices would disappear without a trace. —Prachi Patel

Cavity Preventing Bacteria (MIT) - just awesome

Plaque-busting bugs: Students from MIT are engineering the bacteriumLactobacillus bulgaricus (shown here in brown), found in yogurt, to prevent cavities.
Utah State University

BIOMEDICINE

Engineering Edible Bacteria

Synthetic biology could yield microbes that fight cavities and produce vitamins.

• TUESDAY, NOVEMBER 11, 2008
• BY EMILY SINGER

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Probiotics, a field that seeks to use edible bacteria to improve human health, may soon undergo a metamorphosis. Students at MIT and Caltech are using the techniques of synthetic biology to create bacteria that fight cavities, produce vitamins, and treat lactose intolerance, as part of the International Genetically Engineered Machines (iGEM) competition at MIT. The new research might lead to a cheaper way to produce medicines or improve diets in the developing world.

Synthetic biology is the quest to design and build novel organisms that perform useful functions. Much research in the field has concentrated on using bacteria as a factory: one of its early successes was the development of microbes that produce malaria medicine. Other research has investigated targeted delivery vehicles, such as microbes engineered to bring medicine to a specific part of the body. But the new projects are attempts to enhance the health benefits of edible bacteria.

These projects capitalize on the fact that our bodies are already colonized by billions of bacteria. "If you really want to apply a bacterium to a person, think about where they naturally exist and survive in a human while still trying to engineer new functions," says Christina Smolke, a synthetic biologist at Caltech who advises the university's team.

Our mouths, for example, are a haven to bacteria, both good and bad. Bacteria that live in the dental plaque, called Streptococcus mutans, feed off of sugar on our teeth and then excrete acids, which wear away dental enamel and cause cavities. To create cavity-fighting microbes, the MIT team started with a peptide--a short protein segment--that has been previously shown to prevent the bad bacteria from sticking to the teeth. The team built a piece of DNA containing both the gene that makes the peptide and a gene for a molecular signal that causes the bacterium to excrete it.

The next step will be to insert this piece of DNA into Lactobacillus bulgaricus, a microbe common in yogurt. The students haven't done that yet, but they have successfully introduced foreign DNA into the microbe, which primes the microbe for further genetic engineering. That in itself is an impressive feat, given that Lactobacillus bulgaricus is not commonly used in the lab and thus requires development of new experimental techniques.

If the microbe can be successfully engineered, eating yogurt would deposit it on the teeth, where it would produce the protective peptide. "This would probably be more effective than an antibacterial that kills everything," says Chia-Yung Wu, a biology graduate student at MIT who advises the team. "It just targets the harmful stuff." (A common problem with antibiotics is that they kill both harmful and helpful bacteria in the mouth and gut, leaving an open landscape for bad bacteria to colonize.)

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One central project in synthetic biology is the attempt to create a huge, publicly accessible "parts list," a catalogue of gene sequences and the functions of the resulting proteins. The MIT team doesn't intend to develop a product for commercial use, but the biological parts that it creates might one day be used in other applications--enhancing the nutritional value of yogurt, for example, with bacteria that produce a specific type of vitamin. The team, which includes undergrads Sara Mouradian and Derek Ju, has already deposited the parts that it's created in a central repository at MIT called the Registry of Standard Biological Parts. Expanding the registry is one of the most important aspects of the competition. "This year, we sent out 2,000 DNA parts to each team, and we're getting back 1,500 new parts," says Randy Rettberg, iGEM director and a principal research scientist at MIT.