Experimental drug tested against multi-drug resistant TB

"Researchers who tested a novel type of antibiotic against multi-drug-resistant tuberculosis [MDR-TB] are reporting that nearly half of patients who got the new drug cleared the bacteria from their lung fluid in two months," according to a study published  in the New England Journal of Medicine. Japanese pharmaceutical company Otsuka developed the experimental drug, delamanid (see structure), and "also designed and financed the clinical trial, which took place in 17 medical centers across nine countries." 

 "'We've invested a lot of time and money to develop this drug, but we are not seeking robust sales growth immediately,' Masuhiro Yoshitake, Otsuka's head of tuberculosis projects, said in an interview," Bloomberg Businessweek reports. "We want to begin selling to people who know how to use the drug," he added, the news service notes. "Doctors must balance the need to fight hard-to-treat cases against prolonging the medicine's potency,"

More : http://www.nejm.org/doi/full/10.1056/NEJMoa1112433

Experimental drug tested against multi-drug resistant TB

Novel two-drug combination cures young patient with extensively drug-resistant tuberculosis

The combination of meropenem (above structure)  with clavulanate (right structure-potassium salt)  has high antimycobacterial activity in vitro against extensively drug-resistant Mycobacterium tuberculosis strains. Researchers report the successful use of this combination in association with linezolid (below structure)  in the management of an advanced extensively drug-resistant tuberculosis disease with complex second-line drug resistance in a 14-year-old teenager.

Ref : 1.Meropenem/Clavulanate and Linezolid Treatment for Extensively Drug-Resistant Tuberculosis

    2. http://www.einstein.yu.edu/uploadedFiles/PHD/2010%20Faculty%20Research%20Book.pdf

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... : 

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

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

PA-824 - Aerosol: New Tool Against Tuberculosis?

We know the epidemic rates of HIV/TB coinfection as well as emerging multidrug-resistant  (MDR) and extensively drug-resistant (XDR) TB strains those are contributing to increased TB-associated deaths worldwide. 

Now PA-824 (see structure), a compound capable of being formulated into a dry powder, has not only shown promising activity against MDR (multidrug-resistant tuberculosis) and XDR (extensively drug-resistant tuberculosis, or latent TB) but has also proven safe and effective in patients coinfected with HIV and TB. Previous studies showed that PA-824 was well-tolerated in tablet form, however, side effects such as headache and stomach discomfort were reported. Aerosol delivery of PA-824 directly to the primary site of infection would limit systemic exposure and ultimately eliminate potentially bothersome side effects.

About  PA-824 :

Nitroimidazoles are widely used drugs in humans for a variety of primarily anaerobic microbial infections. Metronidazole, a 5-nitroimidazole, is an important bactericidal agent for the treatment of anaerobic infections  and shows excellent selective toxicity toward anaerobic bacterial and protozoal pathogens. This class of compounds has only recently begun to be explored for Mtb, because only anaerobic activity of metronidazole against Mtb has been reported. Bicyclic 4-nitroimidazoles such as PA-824 (a nitroimidazo-oxazine) and CGI-17341 (a nitroimidazo-oxazole) have inhibitory activity against aerobically growing and nonreplicating anaerobic Mtb. Although anaerobic conditions have not been demonstrated during TB disease in humans, various authors have suggested that an anaerobic microenvironment may contribute to a nonreplicating state that may be linked with latent disease in humans. Thus, PA-824 has been developed, in part, because it may be a promising lead for therapy against latent disease that may be linked to anaerobically persisting bacilli. The Global Alliance for TB Drug Development has recently initiated phase-I clinical trials with PA-824 

Researchers from the University of North Carolina School of Pharmacy, Chapel Hill, North Carolina; and Harvard School of Engineering and Applied Sciences, Cambridge, Massachusetts, lead by  Dr. Anthony J Hickey  have achieved this interesting finding, i.e., potential use of PA-824 dry powder aerosols in the treatment of TB.

In the study guinea pigs were used to evaluate the effects of PA-824 aerosols on TB infection. One month following infection with TB some guinea pigs received high daily aerosol treatments while others received low daily treatments for 4 weeks. Lung and spleen analysis of guinea pigs receiving the high dose of aerosol PA-284 showed less inflammation, bacterial burden and tissue damage.

"The present studies indicate the potential use of PA-824 dry powder aerosols in the treatment of TB,” say the researchers".

Ref : http://aac.asm.org/cgi/content/abstract/54/4/1436.

UT Southwestern researchers find clues to TB drug resistance.....

In continuation of my update on TB and its challenges...

Now researchers from the University of Texas Southwestern Medical Center at Dallas, have come up with some interesting info. i.e.,  a type of blood pressure medication shows promise at overcoming some drug-resistant tuberculosis, at least in the laboratory. 

Dr. Gumbo (lead researcher) and his colleagues used an experimental apparatus to simulate the way TB bacteria grow in the human lung. When they exposed the bacteria to drugs commonly used to treat the disease (ethambutol and isoniazid),  the bacterial cells activated a cellular mechanism that pumps each drug out of the cells. 

"The pumping action enables the rapid emergence of high-level resistance to the drugs whether administered together as well as individually, Dr. Gumbo said".

As per the claim by the researchers, resistance was drastically reduced  when the researchers gave the blood-pressure drug reserpine – which is known to block this pumping action – to the TB cells before administering ethambutol and isoniazid.

Researchers now want to test all the first-line drug treatments together with the pump blocker in humans. Hope they will come up with positive results.....

Ref  : http://www.utsouthwestern.edu/utsw/cda/dept37389/files/582308.html

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

New insight for design of novel antibiotic derivatives for drug resistant microorganisms...

Viomycin and Capreomycin (a group of nonribosomal peptide antibiotics) belong to the tuberactinomycin (an essential component in the drug cocktail currently used to fight infections of Mycobacterium tuberculosis) Are among the most effective antibiotics against multidrug-resistant tuberculosis. Viomycin was the first member of the tuberactinomycins to be isolated and identified and was used to treat TB until it was replaced by the less toxic, but structurally related compound, Capreomycin. The tuberactinomycins target bacterial ribosomes, binding RNA and disrupting bacterial protein biosynthesis.

Now Dr. Steitz and his colleagues at Yale's Department of Molecular Biophysics and Biochemistry, have identified two structures of tuberactinomycins bound to the ribosome. The researchers claims that,   the identification of these structures provides an insight for the design of novel antibiotic derivatives that could be effective against a variety of drug resistant microorganisms.

As per the claim by Dr.Steitz, both antibiotics (Viomycin and Capreomycin) bind to the same site on the ribosome, which lies at the interface between helix 44 of the small ribosomal subunit and helix 69 of the large ribosomal subunit. The structures of these complexes suggest that the tuberactinomycins inhibit translocation by stabilizing the tRNA in the A site in the pretranslocation state. In addition, these structures show that the tuberactinomycins bind adjacent to the binding sites for the paromomycin and hygromycin B antibiotics, which may enable the development of new derivatives of tuberactinomycins that are effective against drug-resistant strains. The authors have presented two crystal structures of the 70S ribosome in complex with three tRNAs and bound to either viomycin or capreomycin at 3.3-and 3.5-Å resolution, respectively in "Nature Structural & Molecular Biology 14 February 2010 ".

Interestingly, Dr. Steitz was awarded the 2009 Nobel Prize in Chemistry   for his groundbreaking work determining a high resolution crystal structure of the 50S subunit of the ribosome which has proved to be a major target for antibiotic development.

Hope this discovery will lead to a new insight for design of novel antibiotic derivatives that could be effective against a variety of drug-resistant microorganisms ....

Ref: http://www.rib-x.com/news_and_events/release_2010_02_16

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

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...

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……

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...

A new avenue for TB therapy !

TB bacteria actually sends signals that encourage the growth of those organized granuloma structures, and for good reason: each granuloma serves as a kind of hub for the infectious bugs in the early stages of infection, allowing them to expand further and spread throughout the body. Which is something interesting in he sense that the earlier believed fact (i.e., masses of immune cells that form as a hallmark of tuberculosis (TB) have long been thought to be the body's way of trying to protect itself by literally walling off the bacteria) is being ruled out?. Scientists thought they were protective, but they are not - at least not in early infection. The bacteria use them to reproduce and disseminate themselves.
Not only do the bacteria expand themselves within the first granuloma to form, she added, but some of the immune cells in that initial mass leave to start new granulomas elsewhere. Those new granulomas then also serve as breeding grounds for the bacteria. The finding (Lalita Ramakrishnan and J.Davis). suggests a new avenue for TB therapy at an important time in the struggle against TB infection (not only the increasing number of patients, AIDS with TB and drug resistant TB). So if one can prevent granulomas that might be therapeutic either by intercepting the bacterial signal that spurs granulomas' formation or by manipulating the human immune system in some other way. Hope this research will go a long way in finding the solution to the epidemic drug resistant TB........