Progress towards new treatments for tuberculosis

Boosting the body's own disease-fighting immune pathway could provide answers in the desperate search for new treatments for tuberculosis.

Tuberculosis still represents an enormous global disease burden and is one of the top 10 causes of death worldwide.

Led by WEHI's Dr. Michael Stutz and Professor Marc Pellegrini and published in Immunity, the study uncovered how cells infected with tuberculosis bacteria can die, and that using new medicines to enhance particular forms of cell death decreased the severity of the disease in a preclinical model.

Fighting antibiotic resistance

Tuberculosis is caused by bacteria that infect the lungs, spreading from person to person through the air. A challenge in the fight against tuberculosis is that the bacteria that cause the disease have developed resistance to most antibiotic treatments, leading to a need for new treatment approaches.

Tuberculosis bacteria grow within immune cells in the lungs. One of the ways that cells protect against these 'intracellular' pathogens is to undergo a form of cell death called apoptosis—destroying the cell as well as the microbes within it.

Using preclinical models, researchers sequentially deleted key apoptosis effectors, to demonstrate their roles in controlling tuberculosis infections. This demonstrated that a proportion of tuberculosis-infected cells could die by apoptosis—opening up new opportunities for controlling the disease.

Using host-directed therapies to reduce disease burden

Dr. Stutz said researchers then tested new drugs that force cells to die. This revealed that a drug-like compound that inhibits cell death-regulatory proteins called IAPs could promote death of the infected cells.

"When we treated our infection models with this compound, we were able to significantly reduce the amount of tuberculosis disease," he said.

"The longer the treatment was used, the greater the reduction of disease."

The research team was able to replicate these results using various different IAP inhibitors.

"Excitingly, many of these compounds are already in clinical trials for other types of diseases and have proven to be safe and well-tolerated by patients," Dr. Stutz said.

"We predict that if these compounds were progressed for treating tuberculosis, they would be most effective if used alongside existing antibiotic treatments."

Opening the door to new treatment methods

Professor Marc Pellegrini said until now, antibiotics were the only treatment for tuberculosis, which were limited in their application due to increasing antibiotic resistance.

"Unlike antibiotics, which directly kill bacteria, IAP inhibitors kill the cells that the tuberculosis bacteria need to survive," he said.

"The beauty of using a host-directed therapy is that it doesn't directly target the microbe, it targets a host process. By targeting the host rather than the microbe, the chances of resistance developing are incredibly low."

The team hope the research will lead to better treatments for tuberculosis.

"This research increases our understanding of the types of immune responses that are beneficial to us, and this is an important step towards new treatments for tuberculosis, very few of which have been developed in the last 40 years," Dr. Stutz said.

"We have demonstrated that host-directed therapies are viable for infections such as tuberculosis, which is particularly important in the era of extensive antibiotic resistance."

https://www.sciencedirect.com/science/article/abs/pii/S1074761321002533?via%3Dihub

Scientists identify new agent to combat tuberculosis

(Griselimycin)

Above pic: The protein forms a homodimeric ring (shown as blue cartoon & surface representation). Each polypetide chain binds one molecule of griselimycin (red). The optimized compound cyclohexylgriselimycin contains an additional cyclohexane moiety (yellow, shown only for the ligand in the foreground).

According to figures of the World Health Organization, some 8.7 million people contracted tuberculosis in 2012 and this disease is fatal for approximately 1.3 million people throughout the world each year. One of the main problems is that the tuberculosis pathogens have become resistant to the antibiotics used to fight them. Scientists from the Helmholtz Institute for Pharmaceutical Research Saarland (HIPS) in Saarbrücken, the Helmholtz Centre for Infection Research (HZI) in Braunschweig and the German Center for Infection Research (DZIF) joined forces with scientists from Sanofi, a global health care company, and identified a new agent, which might potentially remedy these problems. The scientists just described this agent and its unique mechanism of action in the highly renowned scientific journal Science.

Mycobacterium tuberculosis is the main cause of tuberculosis. The treatment for drug-susceptible tuberculosis consists of the daily administration of multiple drugs for a minimum of six months. Lack of adherence to this regimen can result in treatment failure and the emergence of drug resistance. "Complexity and duration of the treatment are true issues and the main reasons for the development of resistant pathogens," says Prof Rolf Müller, who is the Executive Director and head of the Microbial Natural Substances department of the HIPS, an institution jointly sponsored by the HZI and Saarland University.

Consequently, there is an urgent need for new medications and therapeutic approaches to both fight the resistant pathogens, as well as to shorten the duration for the treatment of drug-susceptible organisms. Based on earlier reports, Müller, in collaboration with Prof Jacques Grosset from the Johns Hopkins University School of Medicine in Baltimore, and his colleagues from the HZI and Sanofi scientists, initially focused on the natural substance called griselimycin. The potential of this natural substance, was discovered in the 1960s. However, due to the success of other tuberculosis medications and its low efficacy in an infection model, the substance was not developed any further at the time.

"We resumed the work on this agent and optimised it such that it shows excellent activity in the infection model - even against multi-resistant tuberculosis pathogens," says Müller. In the course of their work, the scientists discovered that cyclohexylgriselimycin, a variant of griselimycin, is particularly effective against Mycobacterium tuberculosis, both in cells and in the animal model. Importantly, cyclohexylgriselimycin was effective when administered orally, which is key in tuberculosis treatment, non-orally available drugs are extremely burdensome to administer daily during the many months of treatment. Moreover, combining this substance with current TB antibiotics increases the efficacy compared to the antibiotic cocktail that is usually administered.

Scientists identify new agent to combat tuberculosis

New drug regimens could significantly improve treatment for tuberculosis

Researchers from UCLA and Shanghai Jiao Tong University have made an important step toward a substantially faster and more effective treatment for tuberculosis, which infects some 10 million people and causes 1.5 million deaths each year.

Combination therapy, which utilizes a series of drugs, is a clinical standard for many major diseases. However, the number of potential combinations of different drugs and dose levels can be in the billions, making the prospect of choosing the best one seem daunting.

The research was published in the Proceedings of the National Academy of Sciences.

In the study, researchers used a technique called feedback system control, which was developed at UCLA, to study cells infected with the bacteria that cause tuberculosis. They quickly narrowed combinations of 14 different tuberculosis drugs with five different doses -- resulting in 6 billion possibilities -- into several promising combination treatments that kill the bacteria that cause tuberculosis much faster than the standard regimen used to treat tuberculosis.

"Designing a drug combination with optimized drug-dose ratios has, until now, been virtually impossible," said Chih-Ming Ho, the study's principal investigator and the Ben Rich-Lockheed Martin Chair Professor at UCLA's Henry Samueli School of Engineering and Applied Science. "Feedback system control technology demonstrated it can pinpoint these best possible ratios for a wide spectrum of diseases."

"If our findings are confirmed in human studies, the new drug regimens that we have identified should dramatically shorten the time needed to treat tuberculosis," said Dr. Marcus Horwitz, a senior author on the research and a distinguished professor of medicine and microbiology, immunology and molecular genetics at the UCLA David Geffen School of Medicine. "This will increase the likelihood of successful treatment and decrease the likelihood of patients developing drug-resistant tuberculosis. A highly successful and rapid treatment may hasten the eventual eradication of tuberculosis."

New drug regimens could significantly improve treatment for tuberculosis: Researchers from UCLA and Shanghai Jiao Tong University have made an important step toward a substantially faster and more effective treatment for tuberculosis, which infects some 10 million people and causes 1.5 million deaths each year.

Beating Drug-Resistant TB.....

An antibiotic produced naturally by common soil bacteria kills Mycobacterium species that cause various human diseases, including tuberculosis (TB), according to a report published Monday (September 17) in EMBO Molecular Medicine. The antibiotic even kills drug-resistant strains that escape current TB treatments.

“I seldom get so tickled when I read a paper,” said William Jacobs, a microbiologist and immunologist at the Albert Einstein College of Medicine in New York, who did not participate in the research. The emergence of multidrug resistant strains of Mycobacterium tuberculosis “is a big problem,” he said. “This could be a godsend.”

Tuberculosis infections are commonly treated with a mixture of antibiotics, including one called isoniazid, which Jacobs described as “the cornerstone of TB therapy.”  Unfortunately, the most common drug-resistant strains of M. tuberculosis are isoniazid-resistant, he said.

Many researchers, including Stewart Cole, chair of the microbial pathogenesis department at the École Polytechnique Fédérale de Lausanne in Switzerland, have thus been searching for new M. tuberculosis-killing drugs. “In the past we’ve been working a lot on TB drug discovery using target-based approaches… [but] this has been spectacularly unsuccessful,” said Cole. So instead, he and his colleagues looked back over decades of academic literature searching for reports of natural compounds with M. tuberculosis-killing activity.

They found pyridomycin (see above structure). First described in the 1950s, the drug was reportedly produced by the bacteria Streptomyces pyridomyceticus and Dactylosporangium fulvum. Surprisingly, little was known about pyridomycin—perhaps, Cole suggested, because isoniazid was discovered around the same time and simply stole the limelight.

Cole’s team grew cultures of D. fulvum bacteria, figured out how to isolate and purify pyridomycin, and then showed that the drug was indeed capable of killing M. tuberculosis, as well as many otherMycobacterium species, in culture.

This indiscriminate Mycobacterium-killing ability is a bonus, said Cole. “One of the problems with isoniazid is that it only works against TB,” he said. “If pyridomycin makes it into the clinic, it could have applications in leprosy or Buruli ulcer or atypical mycobacterial infections that can occur in cystic fibrosis patients.”

The team went on to identify the bactericidal target of pyridomycin—a protein called inhA, which is involved in synthesis of bacterial cell wall components. As it happens, inhA is the same protein targeted by isoniazid, but there is a difference in the two drugs’ mechanisms. While isoniazid is a pro-drug that requires activation by an intracellular enzyme called KatG before it can bind to inhA, pyridomycin binds inhA directly.

This is an important distinction, explained Valerie Mizrahi, director of the Institute of Infectious Disease and Molecular Medicine at Cape Town University, South Africa, who was not involved in the study. The overwhelming majority of drug resistance mutations in M. tuberculosis occur in the KatGgene, she explained, and such mutant strains should not be resistant to pyridomycin. Indeed, the team showed that clinical isolates of isoniazid-resistant M. tuberculosis carrying KatG mutations were killed effectively by pyridomycin. “The efficacy against drug resistant forms of M. tuberculosis is particularly encouraging,” Mizrahi said.

There is, however, much to be done before pyridomycin can be used in the clinic. “We would [need to] test that it works in animal models and that it is safe and doesn’t have any side effects,” said Cole. “That will take a couple of years.”

“It’s a long journey,” agreed Mizrahi, “but the big plus is that they don’t really need to validate inhA as a drug target because inhA is already the most well validated drug target out there… [so] it has got a good head start.”

Ref : http://onlinelibrary.wiley.com/doi/10.1002/emmm.201201689/abstract

FDA Approves Sirturo to Treat Multi-Drug Resistant Tuberculosis

In continuation of my update on Sirturo

On Dec. 28, the U.S. Food and Drug Administration approved Sirturo (bedaquiline) as part of combination therapy to treat adults with multi-drug resistant pulmonary tuberculosis (TB) when other alternatives are not available.

Bedaquiline (also known as Sirturo, TMC207 or R207910 see structure) is an diarylquinoline anti-tuberculosis drug, which was discovered by Koen Andries and his team at Janssen Pharmaceutica. It was described for the first time in 2004 at the Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC) meeting Late-Breaker Session, after the drug had been in development for over 7 years, and a trial of 47 patients showed that it is effective in the treatment of M. tuberculosis.

Multi-drug resistant TB occurs when M. tuberculosis becomes resistant to isonazid and rifampin, two powerful drugs most commonly used to treat TB. Sirturo is the first drug approved to treat multi-drug resistant TB and should be used in combination with other drugs used to treat TB. Sirturo works by inhibiting an enzyme needed by M. tuberculosis to replicate and spread throughout the body.

“Multi-drug resistant tuberculosis poses a serious health threat throughout the world, and Sirturo provides much-needed treatment for patients who have don’t have other therapeutic options available,” said Edward Cox, M.D., M.P.H, director of the Office of Antimicrobial Products in the FDA’s Center for Drug Evaluation and Research. “However, because the drug also carries some significant risks, doctors should make sure they use it appropriately and only in patients who don’t have other treatment options.”

Sirturo is being approved under the FDA’s accelerated approval program, which allows the agency to approve a drug to treat a serious disease based on clinical data showing that the drug has an effect on a surrogate endpoint that is reasonably likely to predict a clinical benefit to patients. This program provides patients earlier access to promising new drugs while the company conducts additional studies to confirm the drug’s clinical benefit and safe use.

The FDA also granted Sirturo fast track designation, priority review and orphan-product designation. The drug demonstrated the potential to fill an unmet medical need, has the potential to provide safe and effective treatment where no satisfactory alternative therapy exists, and is intended to treat a rare disease, respectively.

Sirturo carries a Boxed Warning alerting patients and health care professionals that the drug can affect the heart’s electrical activity (QT prolongation), which could lead to an abnormal and potentially fatal heart rhythm. The Boxed Warning also notes deaths in patients treated with Sirturo. Nine patients who received Sirturo died compared with two patients who received placebo. Five of the deaths in the Sirturo group and all of the deaths in the placebo arm seemed to be related to tuberculosis, but no consistent reason for the deaths in the remaining Sirturo-treated patients could be identified.

FDA Approves Sirturo to Treat Multi-Drug Resistant Tuberculosis

New Drug, Bedaquiline to Tackle Resistant TB

Johnson & Johnson said that it is seeking U.S. approval for the first new type of medicine to fight deadly tuberculosis in more than four decades.

The experimental drug, called bedaquiline (discovered by Koen Andries, see structure), also would be the first medicine specifically for treating multi-drug-resistant tuberculosis. That's an increasingly common form in which at least two of the four primary TB drugs don't work.

Mode of action : Bedaquiline affects the proton pump for ATP synthase, which is unlike the quinolones, whose target is DNA gyrase

Tuberculosis, caused by bacterial infection of the lungs and other body areas, is the world's No. 2 killer of adults among infectious diseases.

J&J's Janssen Research & Development unit created the drug, which was tested in several hundred patients with multidrug-resistant tuberculosis in two mid-stage studies lasting for six months. Some patients were studied for about 1 1/2 years.

The company this fall is to begin late-stage testing that will compare bedaquiline to dummy pills over nine months in about 600 patients; each will also take six other drugs that are the standard treatments for tuberculosis. That study is aimed at seeing whether treatment for resistant tuberculosis can be reduced to nine months from the current 18 to 24 months recommended by the World Health Organization.

Roughly one-third of the world's population is estimated to be infected with the bacteria causing tuberculosis. It remains latent in most people for many years but can be activated by another infection or serious health problem.

TB is rare in the U.S. but kills about 1.4 million people a year worldwide, with about 150,000 of those succumbing to the increasingly common multidrug-resistant forms.

Janssen's head of infectious diseases, Dr. Wim Pays, said the company will also apply for approval of bedaquiline in other countries where TB is very common.

The disease is a serious problem in developing countries because it takes so long to cure and many patients stop taking their pills once they begin to feel better. That helps bacteria still alive in the patient to develop resistance to the medicines already taken, making future treatment much more difficult.

Ref : http://www.inpharm.com/news/173302/janssen-submits-tuberculosis-pill-fda

A New approach for the TB drug discovery ?

We are aware that the development of new drugs to combat tuberculosis (TB) has become urgent, as strains of TB resistant to all major anti-TB drugs have emerged worldwide. The World Health Organization estimates that one third of the world's population is asymptomatically infected with TB and that ten percent will eventually develop the disease. More over people with HIV are more prone to TB and hence the need is urgent. As it has happened in other fields of drug discoveries, its something really interesting now it’s the turn of TB drugs, thanx to Barbara Gerratana, Asst., Prof.,. of Chemistry and Biochemistry, university's College of Chemical and Life Sciences, Maryland for their achievement. The significance of the research lies in the fact that “ the NAD+ synthetase enzyme is essential for the survival of the tuberculosis bacteria and hence it can be considered as a drug target.”. So even the structure based inhibitors specific for M. tuberculosis NAD+ synthetase, can be tried and tested for the tuberculosis activity.

Even the experts are really happy over the outcome of the research and following are the lines of appreciation from Clifton E. Barry, Chief of the Tuberculosis Research Section of the Intramural Research Division of the National Institute of Allergy and Infectious Diseases “NadE [NAD+ synthetase] represents one of a small handful of TB drug targets that has iron-clad validation, the lack of a crystal structure was the only serious impediment to drug development and this study represents a hugely important step forward. Inhibiting NadE even kills non-replicating cells, so this discovery may well benefit the one-third of the human population that carries latent bacteria.".

Most interesting part of the research is the fact that “there are only two pathways involved in producing NAD+ in the tuberculosis bacterium and both depend on the activity of NAD+ synthetase to obtain NAD+ (unlike in human beings, where in several different complex pathways..). One can target these two pathways and get good drugs, those are essential and there by one can overcome the drawbacks of the present drugs (current treatment of tuberculosis targets the active tuberculosis bacterium and has little effect on the non-replicating bacterium). Once again congrats for the research group……

Tuberculosis can evade immune response !

As I have mentioned in my earlier blog, more than two million people worldwide die from tuberculosis infection every year. Due in part to inappropriate antibiotic usage, there are a rising number (0.5 million in 2007) of cases of multidrug-resistant (MDR-TB) and extensively drug-resistant (XDR-TB) tuberculosis. New therapies are needed to treat these dangerous infections. We are aware that immune responses to tuberculosis rarely result in complete eradication of the infection. Instead, TB-infected immune cells promote the generation of chronic inflammation and the formation of granulomas, which are areas where the bacteria are contained but not destroyed. These are the facts that encoucouraged Dr. Susanna Grundstrom Brighenti at the Karolinska Institutet in Stockholm, Sweden, to examine the immune response in patients infected with tuberculosis. And this research is of great significance, since it is the first of its kind. The findings are really interesting and justify why the bacterium is getting resistance to the drugs. Following are the important conclusions by the researchers:

The immune cells responsible for killing the tuberculosis bacteria surrounded the granuloma, these cells had low levels of the molecules necessary to kill the TB. Instead, granulomas had high numbers of regulatory immune cells. These regulatory cells suppress the immune response, resulting in the survival of the tuberculosis bacteria and perhaps contributing to persistent long-term infection. Compartmentalization of the immune response in human TB could be part of the reason why infection is never completely eradicated but instead develops into a chronic disease. Congrats for the interesting findings and wish them further success in their future research...

TB disease mechanism and the molecule to block It - discovered ......

We know about the drug resistant tuberculosis and the havoc its causing, so there is an urgent need to  develop new drugs that can be useful. (have covered some articles on  drug development  for drug resistant TB in my earlier blogs). Many groups have tried to explain the resistance,  but now  researchers from Indiana University School of Medicine have identified a mechanism used by the tuberculosis bacterium to evade the body's immune system and have identified a compound that blocks the bacterium's ability to survive in the host, which could lead to new drugs to treat tuberculosis. 

The focus of the research was TB actions inside macrophages (infection fighting cells in the body's immune system). Macrophage cells' tools include the production of special proteins called cytokines to attack foreign invaders. Infected macrophages can also initiate a self-destruction mechanism called apoptosis, which signals other immune system cells to mount a defense against the infection. 

TB bacteria are able to disable the macrophage defenses by secreting virulent factors into the host. The IU team found that the actions of a particular virulent factor a protein phosphatase enzyme called mPTPB  blocked both the production of the infection-fighting cytokines, and the macrophage's self-destruct system. 

As for as my knowledge goes,  phosphatases  (VE-PTP, Cdc25A, PTP1b, VHR, Shp-2, MptpA und MptpB) the  key regulators of various life processes are being studied for the diverse activities. The following is the brief summary ;

a). VE-TPT inhibition is very promising in the development of antiangiogenesis inhibitors in cancer therapy.
b). Cdc25A influences cell cycle regulation and may also be a target of interest in cancer therapy.
c). The phosphatase MptpB, from Mycobacterium tuberculosis, influences the host's immune 
     reaction in a tuberculosis infection.
d) VHR dephosphorylates MAP kinases in the activation loop THX, which plays an important role in signal
    transduction processes.
e) Inhibiting MptpB and Shp-2 opens up new directions in the search for antibiotics and
f) The Ptp1B enzyme plays an important role in developing a medicine against type 2 diabetes and the
   metabolic syndrome.

Though many researchers  tried to study the mechanism of action by which the  tuberculosis bacterium is getting resistance,  this group has come up with a drug and this is of great significance in my opinion.

Using combinatorial chemical synthesis and high-throughput screening, (HTS) the researchers developed the I-A09 compound, which successfully blocked the action of mPTPB. Tests involving live TB bacteria were conducted at the Institute of Tuberculosis Research, University of Illinois at Chicago. 

As per the claim by the lead researcher, Dr. Zhong-Yin Zhang, compound I-A09 is being evaluated in a TB animal model at the Johns Hopkins University School of Public Health. More potent forms of the I-A09 compound are being pursued by the IU team for possible future clinical testing. Hope the team  will come up with a solution to this problem in the days to come...

Ref : http://www.medicine.indiana.edu/news_releases/viewRelease.php4?art=1232

New substance (Benzothiazin derivative) to tackle drug resistant tuberculosis...

Project NM4TB which gathers 18 research teams from 13 countries, discovered a novel class of substances, called benzothiazinones (BTZ-see structure), that could be used in the treatment of tuberculosis and drug resistant tuberculosis.

Prof Stewart Cole, Dr Vadim Makarov, Dr Ute Möllmann, Prof Giovanna Riccardi, and their colleagues have identified a novel class of compounds called benzothiazinones (BTZ) that act by preventing the TB bacterium from constructing its cell wall. In particular, one member of the class, BTZ043 was extremely potent, killing the TB agent, both in test tube experiments and in mouse models of the disease. BTZ043 is as effective as the two main drugs (Isoniazid and Rifampicin) in reducing the bacterial levels in the lungs and spleens of infected mice. The target of the new class of compounds is a component of Mycobacterium’s cell-wall-building machinery that has never before been used as a drug target. The most advanced compound of this new class, BTZ043, is a candidate for inclusion in combination therapies for both drug-sensitive and extensively drug-resistant TB. 

These substances act by preventing the bacteria that cause tuberculosis from constructing their cell wall. This discovery represents an important breakthrough in the battle against tuberculosis as the most advanced compound of this new class, BTZ043, is also effective against extensively drug resistant tuberculosis (XDR-TB).

More... : 

Improved efficacy of tuberculosis vaccine ?

We know that BCG (Bacille Calmette-Guérin) is a live but weakened form of a bacterium, M. bovis, which causes tuberculosis in cattle. It is sufficiently related to the human pathogen to stimulate production of specialized immune cells that fight off TB infection when it is injected into a person as a vaccine. The bacilli have retained enough strong antigenicity to become a somewhat effective vaccine for the prevention of human tuberculosis. At best, the BCG vaccine is 80% effective in preventing tuberculosis for a duration of 15 years, however, its protective effect appears to vary according to geography.

Many attempts have been made to improve the vaccine by incorporating antigens (molecular components of the bacteria) to induce a stronger immune response. However, tuberculosis and BCG have evasive mechanisms that prevent the development of stronger immune responses. We read oftenly in news paper, about the drug resistant strains and use of combined drugs. Now thanx to the two research groups from UT Health Science Center at Houston. The importance of this research is in the fact that the two groups investigated mechanisms by which BCG evades immune stimulating mechanisms and devised two means to neutralize them.

1. scientists used genetically-modified organisms and
2. a drug used for organ transplantation (Rapamycin, see the structure)to block BCG's evasive mechanisms, causing it to induce stronger immune responses.

This dual approach to the BCG vaccine was associated with a tenfold increase in the number of TB organisms killed and a threefold increase in the duration of protection in tests with an NIH-approved mouse model, Dr. Jagannath said.

The research is of great importance because of the fact that "it has countered the ability of TB organisms to subvert immunization", (Tuberculosis hides in cells so the antigens are not recognized by the immune system. The BCG vaccine also does the same thing). The role of the drug is of great importance, i.e., it modulates the movement of particles in cells, would cause BCG antigens to enter pathways leading to improved immunization. I would say one more significant contribution(or else one more serendipity !) of the drug apart from bieng used in 1. treatment of cancer and inflammation 2. in significantly reducing the frequency of acute kidney transplant rejection.

Though further research to substantiate the claim is essential. Its a good beginning in this direction for the improved efficay of the vaccine.. Congrats Dr. Jagannath and group.. More...

Methionine Aminopeptidases from Mycobacterium tuberculosis as Novel Antimycobacterial Targets ..

Suspecting that a particular protein in tuberculosis was likely to be vital to the bacteria's survival, Johns Hopkins scientists screened 175,000 small chemical compounds and identified a potent class of compounds that selectively slows down this protein's activity and, in a test tube, blocks TB growth, demonstrating that the protein is indeed a vulnerable target.

 

This class of chemical compounds attacks TB by inhibiting methionine aminopeptidase (MetAP), an essential enzyme found in organisms ranging from bacteria to humans, and that clearly has been conserved throughout evolution because of its important task of ensuring the proper manufacture of proteins.

Methionine aminopeptidase (MetAP) is a metalloprotease that removes the N-terminal methionine during protein synthesis. To assess the importance of the two MetAPs in Mycobacterium tuberculosis, researchers overexpressed and purified each of the MetAPs to near homogeneity and showed that both were active as MetAP enzymes in vitro. 

 

Researchers screened a library of 175,000 compounds against MtMetAP1c and identified 2,3-dichloro-1,4-naphthoquinone class of compounds as inhibitors of both MtMetAPs. It was found that the MtMetAP inhibitors were active against replicating and aged nongrowing M. tuberculosis. Overexpression of either MtMetAP1a or MtMetAP1c in M. tuberculosis conferred resistance of bacterial cells to the inhibitors. As per the claim by the researchers, knockdown of MtMetAP1a, but not MtMetAP1c, resulted in decreased viability of M. tuberculosis and they conclude  that MtMetAP1a is a promising target for developing antituberculosis agents.

 

The scientists cautioned that although the MetAP inhibitors prevent TB growth in test tubes, they have a long way to go before being declared safe and effective to treat TB patients...

 

"Judging from potency, a MetAP inhibibitor alone probably won't wipe out TB," Liu says. "TB is so hard to treat that the standard therapy involves a cocktail of multiple drugs; no single compound is powerful enough. Our hope is that someday an inhibitor of MetAP will become a new component to enhance the existing therapy."

Ref : Jun O. Liu et.al., Chemistry & Biology, Volume 17, Issue 1, 29 January 2010, Pages 86-97

Self-Poisoning of Mycobacterium tuberculosis by targeting GlgE in an a-glucan pathway...

In the past few years, extremely drug resistant strains of TB have arisen that can’t be eliminated by any drugs, so new strategies for attacking TB are urgently needed.

Now, researchers at Albert Einstein College of Medicine of Yeshiva University have found two novel ways of killing the bacteria that cause tuberculosis.

In searching for a new Achilles’ heel for M. tuberculosis, Dr. Jacobs and colleagues focused on an enzyme called GlgE. Previous research had suggested  that GlgE might be essential for the growth of TB bacteria.        (building polysaccharides) GlgE would also be an excellent drug target because there are no enzymes similar to it in humans or in the bacteria of the human gut.

Using genetic and biochemical approaches, William Jacobs and colleagues identified four enzymes involved in a pathway that converts a naturally-occurring sugar compound into polysaccharides called alpha-glucans. The scientists found that inactivating one of these enzymes, TreS, was not lethal to the bacteria, indicating that this pathway is not required for growth. 

However, inactivating GlgE was lethal, causing the buildup of toxic levels of the enzyme's sugar substrate, maltose-1-phosphate. In addition, the scientists found that the combined inactivation of TreS and an enzyme for an alternate alpha-glucan biosynthetic pathway was lethal, highlighting the important roles of alpha-glucan's in M. tuberculosis growth.

Sure enough, when the researchers inhibited GlgE, the bacteria underwent "suicidal self-poisoning": a sugar called maltose 1-phosphate accumulated to toxic levels that damaged bacterial DNA, causing the death of TB bacteria grown in Petri dishes as well as in infected mice.

The researchers discovered a second way of killing TB after observing a crucial connection between their novel alpha glucan pathway and a second pathway that also synthesizes alpha glucans. 

When the researchers knocked out one of the other enzymes in their novel pathway, the pathway's shutdown didn't kill the bacteria; similarly, inactivating an enzyme called Rv3032 in the second alpha glucan pathway failed to kill the microbes. But inactivating both of those enzymes caused what the researchers term synthetic lethality: two inactivations that separately were nonlethal but together cause bacterial death. 

Though the biological role of the GlgE pathway remains to be elucidated, GlgE and the alpha-glucan pathways more generally, are possible drug targets that can now be tested in in vivo models of tuberculosis infection....

"The bacteria that cause TB need to synthesize alpha glucans," notes Dr. Jacobs. "And from the bacterial point of view, you can't knock out both of these alpha glucan pathways simultaneously or you're dead. So if we were to make drugs against GlgE and Rv3032, the combination would be extremely potent. And since TB bacteria need both of those alpha glucan pathways to live, it's very unlikely that this combination therapy would leave behind surviving bacteria that could develop into resistant strains."

Ref :  http://www.nature.com/nchembio/journal/vaop/ncurrent/pdf/nchembio.340.pdf

Mycobacterium tuberculosis is extraordinarily sensitive to killing by a vitamin C-induced Fenton reaction : Nature Communications : Nature Publishing Group

In a striking, unexpected discovery, researchers at Albert Einstein College of Medicine of Yeshiva University have determined that vitamin C kills drug-resistant tuberculosis (TB) bacteria in laboratory culture. The finding suggests that vitamin C added to existing TB drugs could shorten TB therapy, and it highlights a new area for drug design.

Dr. Jacobs and his colleagues observed that isoniazid-resistant TB bacteria were deficient in a molecule called mycothiol. "We hypothesized that TB bacteria that can't make mycothiol might contain more cysteine, an amino acid," said Dr. Jacobs. 

"So, we predicted that if we added isoniazid and cysteine to isoniazid-sensitive M. tuberculosis in culture, the bacteria would develop resistance. Instead, we ended up killing off the culture  something totally unexpected."

The Einstein team suspected that cysteine was helping to kill TB bacteria by acting as a "reducing agent" that triggers the production of reactive oxygen species (sometimes called free radicals), which can damage DNA.

"To test this hypothesis, we repeated the experiment using isoniazid and a different reducing agent vitamin C," said Dr. Jacobs. "The combination of isoniazid and vitamin C sterilized the M. tuberculosis culture. We were then amazed to discover that vitamin C by itself not only sterilized the drug-susceptible TB, but also sterilized MDR-TB and XDR-TB strains."

To justify testing vitamin C in a clinical trial, Dr. Jacobs needed to find the molecular mechanism by which vitamin C exerted its lethal effect. More research produced the answer: Vitamin C induced what is known as a Fenton reaction, causing iron to react with other molecules to create reactive oxygen species that kill the TB bacteria.

"We don't know whether vitamin C will work in humans, but we now have a rational basis for doing a clinical trial," said Dr. Jacobs. "It also helps that we know vitamin C is inexpensive, widely available and very safe to use. At the very least, this work shows us a new mechanism that we can exploit to attack TB.".....

Ref : http://www.einstein.yu.edu/news/releases/907/study-finds-vitamin-c-can-kill-drug-resistant-tb/


Mycobacterium tuberculosis is extraordinarily sensitive to killing by a vitamin C-induced Fenton reaction : Nature Communications : Nature Publishing Group

Novel iron complexes (quinoxaline) as potential antitubercular agents...

A team of researchers from Spain and Latin America have synthesized two iron compounds(complex with qunoxaline derivative below structure)  that inhibit the in vitro growth of Mycobacterium tuberculosis, the bacteria that causes tuberculosis. Due their low level of toxicity in mammel cells, the compounds could be used in the future as therapeutic agents and hospital disinfectants.  

As per the claim by the researchers, the complexes are better than the second line drugs (we know already about drug resistant tubercular species and tuberculosis is being considered as re-emerging disease due to the increase in the number of people with HIV and other viruses that attack the immune system, as well as to the increasing consumption of immunosuppressive and recreational drugs).  Another advantage of the iron compounds is that they show low toxicity in mammal cells, as demonstrated by the experiments performed with mice cells.

"That is why these compounds are useful as hospital disinfectants or therapeutic agents," the Uruguayan researchers highlight, albeit recalling that, at present, they in vitro trials "and the line of research remains open to learn more about how they act."

Researchers conclude that, the novel complexes showed in vitro growth inhibitory activity on Mycobacterium tuberculosis H₃₇Rv (ATCC 27294), together with very low unspecific cytotoxicity on eukaryotic cells (cultured murine cell line J774). Both complexes showed higher inhibitory effects on M. tuberculosis than the “second-line” therapeutic drugs....

Ref : Dinorah Gambino et.al., Journal of Inorganic Biochemistry Volume 104, Issue 11

Multitarget TB drug could treat other diseases, evade resistance -- ScienceDaily

A drug under clinical trials to treat tuberculosis could be the basis for a class  of broad-spectrum drugs that act against various bacteria, fungal infections and parasites, yet evade resistance, according to a study. The team determined the different ways the drug SQ109 attacks the tuberculosis bacterium, how the drug can be tweaked to target other pathogens from yeast to malaria  and how targeting multiple pathways reduces the probability of pathogens becoming resistant.

Led by U. of I. chemistry professor Eric Oldfield, the team determined the different ways the drug SQ109 attacks the tuberculosis bacterium, how the drug  can be tweaked to target other pathogens from yeast to malaria -- and how targeting multiple pathways reduces the probability of pathogens becoming resistant. SQ109 is made by Sequella Inc., a pharmaceutical company. 

"Drug resistance is a major public health threat," Oldfield said. "We have to make new antibiotics, and we have to find ways to get around the resistance problem. And one way to do that is with multitarget drugs. Resistance in many cases arises because there's a specific mutation in the target protein so the drug will no longer bind. Thus, one possible route to attacking the drug resistance problem will be to devise drugs that don't have just one target, but
two or three targets."

Oldfield read published reports about SQ109 and realized that the drug would likely be multifunctional because it had chemical features similar to those found in other systems he had investigated. The original developers had identified one key action against tuberculosis -- blocking a protein involved in building the cell wall of the bacterium -- but conceded that the drug could have other actions within the cell as well since it was found to kill other bacteria and
fungi that lacked the target protein. Oldfield believed he could identify those actions  and perhaps improve upon SQ109. 

"I was reading Science magazine one day and saw this molecule, SQ109, and I thought, that looks a bit like molecules we've been studying that have multiple targets," Oldfield said. "Given its chemical structure, we thought that some of the enzymes that we study as cancer and antiparasitic drug targets also could be SQ109 targets. We hoped that we could make some analogs that would be more potent against tuberculosis, and maybe even against parasites.

More : http://pubs.acs.org/doi/abs/10.1021/jm500131s

Multitarget TB drug could treat other diseases, evade resistance

Eliminating inherent drug resistance in tuberculosis....

In continuation of my update on drug resistant TB and the drug development for TB, I found this info interesting to share with.

Dr. John Blanchard of the Albert Einstein College of Medicine has come up with really  interesting  findings about how to "eliminate inherent drug resistance in tuberculosis".   

When the M. tuberculosis genome was sequenced a few years ago, the presence of  beta-lactamase enzyme was discovered. Most scientists didn't pay much attention to this discovery and beta-lactams   never have been systematically used to treat TB. However Dr. John,  thought it would be an attractive therapeutic target, considering several beta-lactamase inhibitors had been developed for other bacteria.

If we could inactivate this inactivator enzyme, it would expose TB bacteria to a whole new range of antibiotics," he says. 

While M. tuberculosis was resistant to most beta-lactamase inhibitors,  Blanchard's group found that the drug clavulanate was effective in shutting down the TB enzyme. 

The combination of clavulanate (see above right structure- its potassium salt) with the beta-lactam   meropenem (see below: left structure) could effectively sterilize laboratory cultures of TB within two weeks, including several XDR-strains (XDR strains are even more resilient than multi-drug resistant (MDR) strains).  Blanchard notes this finding was exciting since, despite such high rates of drug resistance, research into new TB drugs is not a high priority in industrialized countries (for socio-economic reasons), and thus the best short-term approach might be identifying other already FDA approved antibiotics that are effective against TB -like meropenem and clavulanate.

Blanchard is currently progressing with the next steps of the therapeutic process, which includes both detailed animal studies and setting up some small-scale trials with XDR-TB patients in developing nations...

(Source : a presentation at the American Society for Biochemistry and Molecular Biology’s annual meeting, titled “Drug resistance in tuberculosis,” by Dr. John Blanchard).

Ref : http://www.asbmb.org/News.aspx?id=7470&terms=John+Blanchard

Stroke drug kills bacteria that cause ulcers and tuberculosis

Now researchers  found that, a compound called ebselen (see structure) effectively inhibits the thioredoxin reductase system in a wide variety of bacteria, including Helicobacter pylori which causes gastric ulcers and Mycobacterium tuberculosis which causes tuberculosis. Thioredoxin and thioredoxin reductase proteins are essential for bacteria to make new DNA, and protect them against oxidative stress caused by the immune system. Targeting this system with ebselen, and others compounds like it, represents a new approach toward eradicating these bacteria.

Building on previous observations where ebselen has shown antibacterial properties against some bacteria, Holmgren and colleagues hypothesized that the bacteria sensitive to ebselen relied solely on thioredoxin and thioredoxin reductase for essential cellular processes. They investigated this by testing it on strains of E. coli with deletions in the genes for thioredoxin, thioredoxin reductase and the glutaredoxin system. They found that strains with deletions in the genes coding for glutaredoxin system were much more sensitive than normal bacteria. Researchers further tested ebselen againstHelicobacter pylori andMycobacterium tuberculosis, which both naturally lack the glutaredoxin system and are frequently resistant to many commonly used antibiotics, and found both to be sensitive to ebselen.

"As rapidly as these organisms evolve, we need new drugs sooner rather than later," said Gerald Weissmann, M.D., Editor-in-Chief of The FASEB Journal. "The fact that these scientists have found a new target for killing some of the most resistant bacteria is great news, but the fact that we already have at least one drug which we could possibly use now makes the news even better."

Ref : http://www.fasebj.org/content/early/2012/12/17/fj.12-223305

Stroke drug kills bacteria that cause ulcers and tuberculosis