Researchers discover metabolic vulnerability in TB and potential drug target

Tuberculosis (TB) has been present in humans since ancient times. The origins of the disease date back to the first domestication of cattle, and skeletal remains show prehistoric humans (4,000 B.C.) had TB. Although relatively rare in the United States, it is the single leading bacterial cause of death worldwide. Approximately 8 million people are infected each year and 2 million people die from TB.

The cause of tuberculosis is Mycobacterium tuberculosis (Mtb), a slow-growing aerobic bacterium that divides every 16 to 20 hours. Scientists know that carbon metabolism plays a significant role in the ability of Mtb to replicate and persist in the body and that fatty acids are the major source of carbon and energy during infection. However, the specific enzymes required for the metabolism of fatty acids have not been completely defined.

New research conducted at Weill Cornell Medical College and published online in the Proceedings of the National Academy of Sciences (PNAS) sheds light on a previously unrecognized aspect of fatty acid metabolism that could potentially lead to new targets for drug therapy. A team led by Dr. Sabine Ehrt, professor of microbiology and immunology at Weill Cornell Medical College, reported that Mtb relies primarily on gluconeogenic substrates for in vivo growth and persistence, and that phosphoenolpyruvate carboxykinase (PEPCK) plays a pivotal role in the growth and survival of Mtb during infections in mice, making PEPCK a potential target for drugs that fight tuberculosis.

Dr. Ehrt and her colleagues found a way to silence the gene encoding PEPCK in Mtb during mouse infections to assess the importance of gluconeogenesis for Mtb's ability to maintain a chronic infection. According to Dr. Ehrt, "Silencing a gene when the pathogen is not or only slowly replicating, after an infection has established, is an important tool for studying diseases such as TB, which can be dormant for years only to become active again years later."

Dr. Ehrt, the lead author on the paper, conducts basic research on the pathogenesis of tuberculosis. She and her team investigate the role of the macrophage in the immune response to Mtb and the molecular mechanisms used by the pathogen to establish and maintain persistent infections. A goal of Dr. Ehrt's research is to validate novel drug targets that may facilitate the development of new therapies against active and chronic TB.

"Tuberculosis is very difficult to treat," says Dr. Erht. "It is especially challenging as the infection can lay dormant in the body even though there are no symptoms. We investigated the metabolic requirements of Mtb during acute and chronic infections and found that the gluconeogenic enzyme PEPCK is critical for both."

The study used a novel mass spectrometry-based metabolic profiling tool, developed at Weill Cornell (in collaboration with Agilent Technologies) by Dr. Kyu Rhee to biochemically examine Mtb carbon metabolism. The tool has provided the first direct insights into the metabolic architecture of Mtb. Dr. Rhee is a co-author and assistant professor of medicine, microbiology & immunology, and the Hearst Clinical Scholar in Microbiology & Infectious Diseases at Weill Cornell Medical College.

Dr. Ehrt hopes that her work will eventually lead to new drug therapies to treat tuberculosis. "Although the current treatments we have to treat Mtb are effective, the treatment times are too long and the regimens too complex. This leads to treatment failures, due to poor adherence and multidrug resistance. We need new, safer drugs that work faster to eliminate tuberculosis."

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New drug-resistant TB strains could become widespread says new study

The emergence of new forms of tuberculosis could swell the proportion of drug-resistant cases globally, a new study has found. The finding raises concern that although TB incidence is falling in many regions, the emergence of antibiotic resistance could see virtually untreatable strains of the disease become widespread.

Australian researchers from the University of New South Wales and the University of Western Sydney have published the new finding in the latest issue of the Proceedings of the National Academy of Sciences.

Laboratory-based studies have suggested that antibiotic-resistant TB strains cause longer-lasting infections but with a lower transmission rate. Therefore, scientists have questioned whether drug-resistant TB strains are more likely than drug-sensitive strains to persist and spread – an important question for predicting the future impact of the disease.

One in three humans already carries the TB bacterium. Although it remains latent in most cases, the World Health Organisation (WHO) has estimated there were 9.27 million new cases of TB in 2007. There were 1.6 million TB-related deaths in 2005. Drug-resistant TB is caused by inconsistent or partial treatment, when patients do not take all their medicines regularly for the required period or because the drug supply is unreliable.

A research team led by UNSW's Dr Mark Tanaka used epidemiological and molecular data from Mycobacterium tuberculosis strains isolated from Cuba, Estonia and Venezuela to estimate the rate of evolution of drug resistance and to compare the relative "reproductive fitness" of resistant and drug-sensitive strains.

"We found that the overall fitness of drug-resistant strains is comparable to drug-sensitive strains," says Dr Tanaka of the Evolution and Ecology Research Centre. "This was especially so in Cuba and Estonia, where the there is a high prevalence of drug-resistant cases."

The finding may reflect an inconsistency in drug treatment programs in these countries. Indeed, Estonia now has one of the highest rates of multi-drug resistance in the world. The intermittent presence of drugs and the resulting transmission of resistant strains would have let drug-resistant strains collectively spend more time within untreated hosts, allowing them to evolve ways to become more infectious and out-compete the drug-sensitive strains.

The study also reveals that the contribution of transmission to the spread of drug resistance is very high – up to 99 per cent – compared with acquired resistance due to treatment failure. "Our results imply that drug resistant strains of TB are likely to become highly prevalent in the next few decades," says UNSW's Dr Fabio Luciani, the study's lead author. "They also suggest that limiting further transmission of TB might be an effective approach to reducing the impact of drug resistance."

"Mathematical and statistical methods can add a lot of value to empirical data by allowing us to account for the processes behind them," says research co-author, Dr Andrew Francis from the University of Western Sydney. "In this case, we use samples of TB genotypes, together with information about drug resistance, to make inferences and predictions that wouldn't have been possible just a few years ago."

Source : www.eurekalert.org

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Parkinson's medications may help treat extreme drug-resistant TB

Two drugs that are commonly used to treat Parkinson's disease have been found to be effective in treating extreme drug-resistant tuberculosis, say researchers at the University of California, San Diego.

They have discovered that the two commercially available drugs, entacapone and tolcapone, have the potential to treat multi-drug resistant and extensively drug resistant tuberculosis.

"We have computational, and experimental data to support this repositioning," said Dr Philip E. Bourne, professor of pharmacology at UCSD's Skaggs School of Pharmacy and Pharmaceutical Sciences and the principle investigator on the project.

"What is exciting about this finding is that the TB target, enzyme InhA, is already well known. But existing drugs are highly toxic and of completely different chemical structure than entacapone and tolcapone.

"Here we have drugs that are known to be safe and with suitable binding properties which can be further optimized to treat a completely different condition," he added.

While working with the TB bacterium itself, they found that the active component in Comtan tablets (entacapone) is effective at inhibiting M.tuberculosis in concentrations well below a level that is toxic to cells.

"Although we have demonstrated in the lab that Comtan is active against M.tuberculosis, additional studies are required in order to transform it into an anti-tubercular therapeutic," said Sarah L. Kinnings, a graduate student and lead author on the study.

"Given the continuing emergence of M.tuberculosis strains that are resistant to all existing, affordable drug treatments, the development of novel, effective and inexpensive drugs is an urgent priority," she added.

The study appears in PLoS Computional Biology.

Source : www.newkerala.com

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Carb Synthesis Sheds Light on Promising Tuberculosis Drug Target

A fundamental question about how sugar units are strung together into long carbohydrate chains has also pinpointed a promising way to target new medicines against tuberculosis.

Working with components of the tuberculosis bacterium, researchers from the University of Wisconsin-Madison identified an unusual process by which the pathogen builds an important structural carbohydrate. In addition to its implications for human health, the mechanism offers insight into a widespread but poorly understood basic biological function — controlling the length of carbohydrate polymers.

“Carbohydrate polymers are the most abundant organic molecules on the planet, and it’s amazing that we don’t know more about these are made,” says Laura Kiessling, a professor of chemistry and biochemistry at UW-Madison. “There’s not much known about how length is controlled in these carbohydrate polymers.”

Kiessling is senior author, along with graduate students John May and Rebecca Splain and postdoctoral fellow Christine Brotschi, of a new study appearing in the online Early Edition of the Proceedings of the National Academy of Sciences the week of June 22.

Most carbohydrates exist as many sugar molecules linked into long chains, or polymers. The right number of sugars in the chain is vital for them to work properly, but different types of carbohydrate polymers range from a few dozen sugars in some bacterial molecules to tens of thousands of sugar links in cellulose, a common plant material.

Despite its importance, it's not clear how carbohydrate length is determined, Kiessling says. Unlike some biological chains — such as DNA and proteins — that are built off a template that guides the length of the final product, carbohydrate-synthesizing enzymes work without templates.

“Nature has strategies to generate polymers of different lengths, but we know very little about those strategies,” she says. “If you make something too short, it’s probably not going to function in the role that you want, and if you make something too long, you’re wasting energy that you need to use elsewhere.”

The research team focused on an enzyme called GlfT2 that is responsible for building a critical carbohydrate component of the TB bacterial cell wall.

The researchers found that a small fatty component at the starting end binds to the enzyme and helps it track the length of the growing polymer. As the enzyme adds more and more sugar units to the opposite end, the chain becomes increasingly unwieldy.

“If the chain gets too long, it gets hard to hold on to both of the ends, so the chain falls off” the synthesizing enzyme, Kiessling says, forming a completed carbohydrate polymer.

The researchers believe that the enzymes responsible for building different types of carbohydrates exceed their comfort level at different points, leading to molecules of different prescribed lengths.

The current report is the first description of this “tethering” mechanism — named for the fatty lipid that tethers the start of the polymer to the enzyme — in carbohydrate synthesis, Kiessling says, though it may prove to be common among other organisms as well.

In addition to providing insight into what may be a general mechanism for designing and building carbohydrates, the work gives insight into developing new therapeutics against TB. The GlfT2 enzyme is essential for bacterial survival and growth but has never yet been targeted by potential treatment methods. Knowing that the enzyme has two binding sites — one for each end of the growing carbohydrate — makes it an especially appealing candidate.

“Our mechanism provides a blueprint for strategies to block a new anti-mycobacterial target,” Kiessling says.

New drug targets will be critical in the fight against tuberculosis, as drug-resistant strains are becoming increasingly widespread. The carbohydrate-synthesizing enzyme represents an untapped and promising resource for crippling even strains that are resistant to current drugs.

The prevalence of carbohydrate polymers in biological systems also means that understanding how their length is controlled has many possible applications, ranging from designing more potent and effective vaccines to facilitating the production of useful fuels from plant materials.

“It’s a nice illustration of how basic research can lead to applications that are very practical,” says Kiessling.

The research was funded by the National Institutes of Health, National Science Foundation, American Chemical Society and Swiss National Science Foundation.

Sourec : www.newswise.com

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Promising new drug fights TB

South African researchers have announced a massive breakthrough in the fight against tuberculosis — a new “wonder drug” that appears to cure multidrug-resistant TB patients much faster than the existing treatment.

Sputum samples from almost half (48%) of TB patients enrolled in a major South African drug trial show no trace of TB infection eight weeks after starting a new drug combination, containing TMC207 — the first drug of a completely new class of antibiotics developed in Europe, which is being tested for drug-resistant TB.

Although still in the clinical trial phase, the drug, dubbed “J”, is almost certain to be the first new drug approved to fight TB in over 40 years. It remains to be seen whether it is a complete cure, what other drugs it must be combined with and whether it is completely safe.

Trial patients who test negative for TB after eight weeks may still revert (test positive for TB again) — if they stop their medication too soon. But if further tests show no signs of TB, or concerns for safety, then the drug will be considered one of the most important medical breakthroughs in years — thanks to a major contribution by the University of Stellenbosch.

TB kills two million people a year, and affects mostly the developing world. South Africa is one of the worst affected countries, with 460000 TB cases and 16000 drug-resistant TB cases, according to the latest World Health Organisation figures.

Results of the latest clinical trial, conducted at four South African hospitals and co-ordinated by the University of Stellenbosch, were published last week in the New England Journal of Medicine.

“This is an enormous event in the world of TB drugs. The last TB drug that has really worked was introduced in 1966,” said lead researcher Professor Andreas Diacon from the department of medical physiology at the University of Stellenbosch. “This drug is so new that there is no resistance against it.”

The trial result is good news for South Africa’s public healthcare system, battling to cope with an avalanche of drug-resistant TB cases. The Western Cape is particularly hard hit, with many patients failing to complete antibiotic medication.

Drug-resistant TB is a bacterial infection that usually requires at least 18 months of treatment, but an increasing number of patients are dying despite treatment.

The trial showed that a drug cocktail containing five known anti-TB drugs, in combination with TMC207, killed the TB bacteria in 48% of patient sputum samples, a massive increase compared with a conversion rate of 9% for patients on the drug cocktail without TMC207.

Trial participants were all multidrug-resistant patients of all races aged between 18 and 65.

“The reports of this particular drug are extremely encouraging,” said Professor Keertan Dheda from the department of medicine at the University of Cape Town. “It holds promise in the future to shorten the duration of TB treatment. It also offers a prospect for treating multidrug-resistant and extensively drug-resistant TB.”

Source : www.thetimes.co.za

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New drug for MDR-TB does well in trial

TMC207 is a safe and effective drug for the treatment of multidrug-resistant tuberculosis (TB), the results of a randomised, placebo-controlled trial published in the June 4th edition of the New England Journal of Medicine have shown. Patients who received the drug were significantly more likely to have a negative culture result after eight weeks than patients who received standard second-line TB treatment.

The author of an editorial accompanying the study describes the development of the drug as “an important advance in the chemotherapy of tuberculosis.”

In 2006, there were over 9 million cases of TB diagnosed around the world and 1.7 million deaths because of the infection. Many patients with TB are also infected with HIV, and the infection is the leading cause of death amongst HIV-positive individuals around the world.

Treatment for TB consists of therapy with multiple drugs for at least six months. Multidrug-resistant strains of the infection (MDR-TB) have emerged that are resistant to the key first-line anti-TB drugs isoniazid and rifampicin. Furthermore, some strains of the infection, known as extensively drug-resistant TB (XDR-TB) have evolved with resistance to second-line drugs as well.

TMC207 is an investigational drug that belongs to a class of agents known as diarylquinolines. Test tube studies demonstrated that it had considerable activity against drug-resistant TB.

Investigators designed a Phase II, placebo-controlled trial involving patients with newly diagnosed, sputum smear-positive MDR-TB to assess TMC207’s safety, side-effects, pharmacokinetics, and antibacterial action.

The study involved 47 hospitalised patients aged between 18 and 65 years in South Africa. All the patients received a five-drug combination for the treatment of MDR-TB.

They were randomised on an equal basis to also receive either TMC207 (400mg daily for two weeks, followed by 200mg three times a week for six weeks) or a placebo.

Most of the patients (74%) were male, 55% were black and 13% were HIV-positive. Adherence was good with 97% of doses taken in both arms of the study.

An identical proportion of patients in both arms (87%) completed the study. There were no premature discontinuations due to side-effects. The profile of side-effects was similar in the two arms of the study, however the TMC207-treated patients were more likely than those taking the placebo to report nausea (26% vs. 4%, p = 0.04).

The majority of patients achieved the target steady-state plasma concentration of 600 ng/ml throughout the study.

Sputum became smear-negative significantly faster in patients treated with TMC207 in addition to their background therapy than those receiving the placebo. A negative culture was achieved by 48% of patients receiving TMC207 compared to only 9% of those taking the placebo.

Rates of negative smears for acid-fast bacilli at week four of the study were 77% for the TMC207 group and 57% for those receiving the placebo. At week eight this had increased to 84% for the patients taking TMC207 and 68% for patients taking the placebo.

“Our data present evidence that TMC207, in combination with a five-drug second-line regimen, had an acceptable side-effect profile; reduced the time to sputum-culture conversion in patients with newly-diagnosed, smear-positive, multidrug-resistant tuberculosis; and significantly increased the proportion of patients with negative sputum cultures after 8 weeks”, comment the investigators.

The authors of the accompanying editorial believes that both the drug and trial are “very encouraging.” However, he believes that the use of TMC207 is likely to be restricted to second-line TB therapy. This is because the available safety data are limited and “urgently need to be expanded.” Furthermore, the drug is metabolised using the P450 pathway, as is the important anti-TB drug rifampicin, raising the possibility of a negative interaction between the two drugs. Interactions with antiretroviral drugs such as efavirenz and nevirapine, also processed through this pathway, will be investigated by the drug's developer, Tibotec, a Johnson & Johnson company.

Source : www.aidsmap.com

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Experimental drug works in resistant tuberculosis

An experimental drug that starves the bacteria responsible for tuberculosis makes conventional therapy five times more effective against drug-resistant TB, doctors reported on Wednesday.

The company-run study found that the Johnson & Johnson drug TMC207, if added to a standard cocktail of five other TB medicines, cleared traces of the tuberculosis bacteria in the sputum of 48 percent of the volunteers after eight weeks. Only 9 percent of patients given the five older drugs alone showed that type of improvement.

TMC207 is being billed as the first new tuberculosis drug in 40 years. It works by interfering with the enzyme ATP synthase, which the bacteria need to store energy.

"It starves them. It's like cutting off your food supply," Dr. David McNeeley of Tibotec Inc., the subsidiary of Johnson & Johnson that developed the drug, said in a telephone interview. Other drugs attack TB in different ways.

The only notable side effect was nausea, experienced by 26 percent of volunteers in the TMC207 group, versus 4 percent among those getting the conventional cocktail plus a placebo, they reported in the New England Journal of Medicine.

The test involved 47 people in South Africa with newly diagnosed lung TB that was resistant to two standard drugs, isoniazid and rifampin.

About 1.8 million people die worldwide each year from tuberculosis and a third of the world's population -- 2 billion people -- are infected, according to the World Health Organization.

The WHO says that of 9 million new TB cases annually, about 490,000 are multiple-drug resistant TB or MDR-TB and about 40,000 are extensively drug resistant or XDR-TB.

HARD TO TREAT

Fewer than 3 percent of MDR-TB cases worldwide are being treated according to WHO recommendations.

The bacteria is extremely difficult to treat because it can remain dormant in the body, unresponsive to drugs. That means patients have to take medicine for a long time, and people often stop their therapy, allowing resistance to develop.

"It's like the bacteria are hibernating. They can go for 20 years and then there's a relapse," McNeeley said.

But even hibernating cells need to use some energy, he said. The new drug cuts off this lifeline. "So whether you're actively replicating or sleeping slowly, you strangle to death," he said.

The development of TMC207 represents an important advance in the chemotherapy of tuberculosis," Clifton Barry of the National Institute of Allergy and Infectious Diseases in Bethesda, Maryland, said in a commentary.

It represents "a new class of drugs that increase the therapeutic options for patients who have multidrug-resistant or extensively drug-resistant tuberculosis, for whom treatment options are often sparse, largely ineffective, and often highly toxic," Barry wrote.

McNeeley said another characteristic of the drug is that its effects show up later than conventional TB medicines, whose effectiveness may wane just as TMC207 is starting to have a real impact.

Asked if the drug, if approved, would be cheap enough for widespread use in the sometimes-poor countries where TB is the biggest problem, McNeeley said, "Johnson & Johnson is committed to bringing this out to the people who need it."

Source : www.reuters.com

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New Drug Promises to Help Curb Tuberculosis

Tuberculosis is a major public health problem. The deadly disease affects millions of people around the world annually, and no new medications have been discovered to fight TB in decades. But new research indicates that may be about to change.
Over the past four decades, the tuberculosis bacteria has evolved to be resistant to many, if not most, of the drugs used to curb the disease. So, to fight it, University of Lausanne researcher Stewart Cole says he and his team needed to come up with a new strategy to kill the TB-causing bacteria.

"We have demonstrated that there is an important enzyme which is required to build the cell wall of Mycobacterium tuberculosis," Cole says. "And our compound blocks this enzyme from acting."

When this enzyme is blocked, the cell wall gets assembled incorrectly, and the bacteria burst open, dying in the process. Cole says no other drug has exploited this enzyme in the cell wall of Mycobacterium tuberculosis.

One advantage of this strategy is that there's no similar enzyme in the walls of human cells. So there's little chance that the drug will make people sick.

Source : www.voanews.com

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