Tag Archives: guinea pig

Fighting the White Death: A new treatment for drug resistant TB

For most people born in the United States in the past half century tuberculosis (TB) is a disease you only read about in the history books, to which it was consigned by the development of antibiotics such as streptomycin in the aftermath of the second world war. However, the reality of TB in the world today is very different; this is a disease that still kills over a million people every year, mostly in developing countries.  Many of these deaths are due to the way TB infects people who are HIV positive, indeed TB is a leading cause of death among people with AIDS. Current treatments are ultimately effective in most cases, but the treatment regimes often require the patient to take the drugs for up to 2 years, which leads to problems of adherence as patients – many of them poor – struggle to cope with the expense of visiting clinics and with the side effects of the antibiotics over the months of treatment. In addition to these deficiencies in the current treatment regimes, the HIV/AIDS epidemic has also seen the emergence of strains of TB that are resistant to currently available antibiotics, as HIV infection increases vulnerability to TB and standard TB therapies often interact badly with antiretroviral therapy for HIV, a development which threatens the hard-won gains made against the disease over the past decades.

But thanks to animal research TB has a new enemy.

Last week the TB Alliance – a global alliance whose mission is to discover and develop better, faster-acting, and affordable drugs to fight tuberculosis – announced that the new multidrug combination therapy regime PaMZ had performed very well in an early clinical trial, clearing over 99% of the Mycobacterium tuberculosis bacteria that cause TB in 2 weeks. The results indicate that the new drug combination will have fewer side effects than current treatments, require only 4 months of treatment, be more compatible with anti-retroviral therapy for HIV, and cost far less than current first and second line treatments for TB.

PA-824 is one of several new TB drugs whose development has been funded by the NIH’s National Institute of Allergy and Infectious Diseases (NIAID)

A key ingredient in PaMZ is PA-824, a new drug that has not yet been approved by the FDA, and a novel aspect of the development of this therapy is that rather than seeking FDA approval for PA-824  on its own and then carrying out further studies in combination with other drugs, a lengthy process, the this therapy has been developed as a combination therapy with moxifloxacin, an antibiotic approved by the FDA for treating pneumonia and sinus infections and commonly used as a 2nd line treatment for multi-drug resistant TB, and pyrazinamide, a drug which has been used to treat TB since the 1950’s. This novel approach to drug development, which should shorten the development time for the multi-drug therapy be several years,  was made possible by a recent change in the FDA regulations that is intended to make it easier to develop new combination therapies for infectious diseases and cancers. An added advantage is that licencing PA-824 for use only in combination with other anti-TB drugs will make it far more difficult for the bacteria will evolve resistance to it.

The development of PA-824 began when a class of molecules named bicyclic nitroimidazofurans were observed to have activity against M. tuberculosis in vitro, and subsequently in mice infected with M. tuberculosis.  A series of derivatives of these compounds were synthesised, and over 100 found to have some anti-TB activity in vitro tests.  PA-824 was one of the derivatives that performed well in vitro, but was not as potent as several other compounds in the series. However, when the more promising drugs were evaluated in mice infected with TB, PA-824 was found to have the best anti-TB activity when administered orally, and was therefore selected for further evaluation.

This was only the beginning of the road for PA-824, further studies in both mice and guinea pigs –  whose response to TB infection more closely mimics that of humans than mice do – demonstrated that it could eliminate TB infection at doses well below those that caused side effects.  In combination with the ability of PA-824 to kill a wide range of drug-resistant M. tuberculosis strains in vitro, these results indicated that PA-824 was an excellent candidate for inclusion in a multi-drug combination pill for TB (1). Finally a study published in 2008 examining the efficiency of several multi-antibiotic combinations reported that a combination of PA-824, moxifloxacin and pyrazinamide could clear M. tuberculosis infection more quickly than the standard first line therapy (2), paving the way for the trial whose result was announced last week.

Of course animal studies also played a key role in the evaluation of the anti-TB potential of the other two drugs used in this combination, particularly the effectiveness of pyrazinamide in treating TB in guinea pigs, and the high activity of moxifloxacin in combination therapy against a highly-virulent M. tuberculosis strain in mice.

It’s a very promising therapy, and if approved PA-824 will be the first new antibiotic approved for treating TB in over 40 years, but also a reminder that when it comes to fighting disease we must never allow ourselves to become complacent.

Paul Browne

1)      Lenaerts AJ et al.”Preclinical testing of the nitroimidazopyran PA-824 for activity against Mycobacterium tuberculosis in a series of in vitro and in vivo models.” Antimicrob Agents Chemother. (2005) Vol. 49(6), pages 2294-2301. PMCID: PMC1140539

2)      Nuermberger E et al. “Powerful bactericidal and sterilizing activity of a regimen containing PA-824, moxifloxacin, and pyrazinamide in a murine model of tuberculosis.” Antimicrob Agents Chemother. 2008 Vol. 52(4), pages 1522-1524. PMCID: PMC2292539

The Golden Goose Awards

Politicians sometimes deride research based on the what they perceive as being “silly” titles of federal funded grants.  If they spot a title that deals with “games”, for example, they may assume it deals with some sort of amusement of little value to society, instead of a deep, powerful branch of mathematics that describes the behavior of competing rational agents with much relevance to voting, economics, cooperation, and so on.  Animal rights activists also enjoy the hobby.  The latest example is IDA’s list of “ridiculous research” ,whose claims were sadly repeated by far too many news journalists who were clearly too lazy check if they were accurate.  There were some honorable exceptions, notably an excellent editorial entitled “When the facts ruin a good spin” in the Times Union, which discusses a project on the role of music as a conditioning stimulus for drug use ends with a statement with which we heartily agree:

What’s “ridiculous,” to borrow the press release’s language, is that we fall for it, over and over, egged on by politicians eager to score easy points. And what’s “wasteful” is the time and energy that could be so much better spent on something other than a cheap shot.”

Back in 1976 the House Committee on Appropriations asked the National Science Foundation “Why does the Foundation persist in supporting research whose results have no apparent value to the American people?”  The NSF responded in part that:

Basic research seeks an understanding  of the laws of nature  without  initial  regard  for specific  utilitarian  value. Ultimately, however, it  is of the  most important  practical significance, because in a broad sense it is the foundation upon  which rests  all technological development.  Applied research builds on the results of basic research, seeking detailed  information  about  a specific situation  whose general laws have  been  discovered by  basic  research.  The  final step  toward  utilization  of research-development is  the systematic  application  of knowledge to  the  design  of  end products. […]

As we  increase  our  knowledge  of nature  and  mankind,  in order  to adjust  nature  to our survival, safety,  comfort and convenience, we must  depend  upon  scientific research  to clarify the  relationships  of many, many things.  Thus,  we study  atoms,  even  though  they  will never  be seen  by an  unaided  human  eye.  We study  stars  too  faint  to  be  seen without  a  telescope  and  with  wavelengths  which  can  only be  detected  with  radio  receivers  or  photographic  plates. To  understand  geology, we must  look  at  geologic formations  and processes in many  parts  of the world where different  conditions have existed.  To understand  more about the  phenomena  of life, we must  study  the  behavior  of viruses,  single  cells,  plants,  and  animals  of  many  species.

A book was compiled covering various areas of research with Isaac Asimov writing an essay defending the value of basic research.

Thus, it was with some surprise and delight that we read in the news about Rep. Jim Cooper (D-Tenn) understanding the value of basic research.  The Washington Post reports that:

On Wednesday afternoon, Cooper rose to the defense of taxpayer-funded research into dog urine, guinea pig eardrums and, yes, the reproductive habits of the parasitic flies known as screwworms–all federally supported studies that have inspired major scientific breakthroughs.

Together with two colleagues he created the Annual Golden Goose Awards to honor federally funded research  “whose work may once have been viewed as unusual, odd, or obscure, but has produced important discoveries benefiting society in significant ways.”

Studying dog urine, among other stuff deem crazy by animal rights cranks, led to major medical discoveries

The article goes on to describe how research on dog urine led to an understanding of the effects of hormones on the human kidney, how studies in the guinea pig led to a treatment for hearing loss in infants, and how studies on the screwworm led to the effective control of the a deadly parasite that targets cattle.  All these provide additional examples refuting the notion that learning about life processes from animals cannot yield knowledge applicable to human health.

The Golden Goose Award has the backing of the American Association for the Advancement of ScienceAssociation of American Universities (who in 2011 published a series of “Scientific Inquirer” articles skewering dubious politically-motivated attacks on basic science) and the Progressive Policy Institute, who are to be congratulated for this excellent initiative to highlight the importance of basic research.

At the press conference to launch the award Rep. Robert Dold told reporters that “When we invest in science, we also invest in jobs. Research and development is a key part to any healthy economy,” while  Rep. Charlie Dent (R-Penn.) added “It’s critical, and the federal government has an important role to play,” who went on to describe how injecting horses with snake venom might “seem peculiar” but led to the discovery of the first anti-venom.

Taking us, once again, to the concluding words of Asimov’s essay:

Unless we continue with science and gather knowledge, whether or not it seems useful on the spot, we will be buried under our problems and find no way out.  Today’s science is tomorrow’s solution — and tomorrow’s problems , too — and, most of all, it is mankind’s greatest adventure, now and forever.

Heart failure breakthrough: animal research paved the way!

Heart failure, where the heart is unable to maintain a sufficient blood flow to supply the body’s needs, is a leading cause of death, especially among the over 65’s. Half of all chronic heart failure patients die within four years of diagnosis. It can have a number of causes, for example damage to heart tissue after a heart attack, and leads to a variety of problems in patients. Fatigue and muscle weakness are common as the muscles receive insufficient oxygen, and because waste products cannot be removed from tissues quickly enough fluid can build up in the lungs and other parts of the body, often the legs and abdomen. The extra strain placed on the heart as it tries to maintain adequate blood pressure can lead to further damage to the heart and ultimately cardiac arrest.

Ivabradine can lower the heart rate while maintaining a normal blood pressure - good news for heart failure patients. Image courtesy of the CDC Public Health Image Library.

In heart failure the rate at which the heart beats is often increased, and group of scientists led by Karl Svedberg and Michael Komajda set up the SHIfT study, to evaluate whether a drug called Ivabradine, which lowers the heart rate, could reduce risk of death or hospitalization in a group of patients who had heart failure accompanied by an elevated resting heart rate.  Significantly fewer patients taking Ivabradine in addition to their existing treatments required hospital admission during the course of the study, compared to a control group who were given a placebo in addition to their existing treatment. The most striking outcome was that Ivabradine cut the risk of death by 26%.

So what is Ivabradine, and where does it come from?

Ivabradine slows the heart rate by inhibiting an electrical current known as the If current* which is a major regulator of the activity of the sinoatrial node – better known as the pacemaker. Inhibiting the If current slows the generation of the electrical impulses by the sinoatrial node that trigger heart contraction, and therefore slows the heart rate itself. Ivabradine, then known as S16257, was first developed in the early 1990’s when it was found to be able to block the If current in-vitro in sinoatrial node tissue from rabbits and guinea pigs, and slowed the generation of electrical impulses in a manner that was safer than other bradycardic drugs (1). Ivabradine was then evaluated in live rats and dogs, where it safely reduced the heart rate, and moreover did so without reducing the blood pressure (2,3). While beta-blockers such as Propranolol can reduce the heart rate they also lower the blood pressure – indeed they are used to treat hypertension – and hence are not suitable for many patients, so the development of a drug that could reduce heart rate without affecting blood pressure was very welcome.

Following the successful animal studies Ivabradine entered human clinical trials and in 2005 was approved for the treatment of angina pectoris. In angina pectoris the heart muscle receives too little oxygen, a problem exacerbated by a fast heart beat that increases the need for oxygen, so lowering of the heart rate by Ivabradine reduced oxygen demand and prevents angina attacks. The success of Ivabradine in the treatment of angina pectoris in turn led to its evaluation in heart failure.

The successful outcome of SHIfT study is a major boost to the development of better treatment regimes for heart failure, and if it is confirmed by further clinical trials will improve and prolong the lives of many heart failure patients.

* Hence the name of the SHIfT study – Systolic Heart failure treatment with the If inhibitor ivabradine Trial

Paul Browne

1) Thollon C. et al. “Electrophysiological effects of S 16257, a novel sino-atrial node modulator, on rabbit and guinea-pig cardiac preparations: comparison with UL-FS 49.” Br J Pharmacol. Volume 112(1), Pages 37-42 (1994) PubMedCentral:PMC1910295

2) Gardiner S.M. et al. “Acute and chronic cardiac and regional haemodynamic effects of the novel bradycardic agent, S16257, in conscious rats.”  Br J Pharmacol. Volume 115(4):579-586 (1995) PubMedCentral:PMC1908496

3) Simon L. et al. “Coronary and hemodynamic effects of S 16257, a new bradycardic agent, in resting and exercising conscious dogs.”  J Pharmacol Exp Ther. Volume 275(2), Pages 659-666 (1995) PubMed:7473152

A shield against the nightmare: Ebola virus vaccine success

There must be few diseases that can conjure up images of horror the way Ebola virus can. Since it was first identified in Zaire (now the Democratic Republic of the Congo) in the mid-1970’s there have been several outbreaks that have left hundreds of people dead, but it is the potential for far worse outbreaks that has epidemiologists worried. Ebola infection causes a viral hemorrhagic fever characterised by rapid onset of fever, followed within days by vomiting and diarrhea, and eventually bleeding from bodily orifices and injection sites; mortality varies between 50 and 90% depending on the strain of Ebola. There is no specific treatment or cure available for Ebola virus, although through research on mice and guinea pigs scientists at the U.S. Army Medical Research Institute of Infectious Diseases developed a morpholino based treatment that protected 75% of rhesus monkeys exposed to Ebola virus. Subsequent studies showed that these morpholino based therapies – AVI-6002 and AVI-6003 – could confer protection against Ebola and Marburg viruses respectively when administered within an hour of infection, and further studies are under way to determine if they can offer protection when administered later.

Transmission electron micrograph of Ebola virus. Courtesy of the Centers for Disease Control and Prevention

While efforts to improve the efficiency of this treatment are ongoing other scientists have turned to developing a vaccine against Ebola virus.  So far we have been quite lucky with Ebola, most outbreaks have occurred in remote areas and due to the rapid progression of the disease – and the fact that no strains have been capable of airborne infection – the outbreaks have tended to burn themselves out quite quickly once travel restrictions and containment protocols were implemented, but we can’t rely on being lucky forever.

A difficulty with designing vaccines against Ebola is that the antibody-producing B-cells of the immune system that many vaccines stimulate can only recognize one strain at a time, so for each new strain of Ebola that emerges you would need a new vaccine.  This would obviously result in a significant delay between reporting of an outbreak and getting the vaccine into the areas where it’s needed, so scientists have been studying another vaccination strategy that stimulates the cellular arm of the immune system that is capable of recognizing a wider range of virus strains. The two part “Prime-Boost” strategy they developed involves first administering a “prime”, a DNA vaccine that codes for part of the surface proteins of the “Zaire” and “Sudan” strains of Ebola, followed several months later by administration of a “boost” vaccine based on a weakened adenovirus (cold virus) that also produces fragments of the Ebola surface proteins that are then recognized as foreign by the immune system. This strategy successfully protected cynomolgus macaques from the Zaire strain of Ebola virus (1) and has since been shown to be safe to stimulate an immune response in small scale human trials (2).

The question remained as to whether this vaccine strategy would be able to protect against Ebola strains other than “Zaire” and “Sudan”, and the opportunity to test this came in 2007 when a new strain of Ebola was identified in the Bundibugyo region of Uganda. The outbreak burnt itself out before any program of vaccination could be implemented, but the new strain did offer the opportunity to re-evaluate the prime-boost vaccination strategy.  In a report, published yesterday in the open access journal PloS Pathogens, Dr Nancy J. Sullivan and colleagues at the National Institute of Allergy and Infectious Diseases report that the prime-boost strategy can protect cynomolgus macaques from the otherwise fatal Bundibugyo Ebola virus, demonstrating that it can protect against several different strains of the disease.

This is great news and brings us a lot closer to the goal of a vaccine that can protect us against Ebola virus, in particular it is possible that this vaccine could be used to immunize people living in areas where Ebola is a threat even before an outbreak is detected.  It is not just humans who may benefit from this vaccine research, in the past decade tens of thousands of chimpanzees and gorillas have died from Ebola, and the disease now poses a significant threat to the their very survival.  A vaccine against Ebola would help reduce death toll among these endangered apes, though even with an effective vaccine developing and implementing a successful immunization program will be neither cheap nor easy.

Paul Browne

1)      Sullivan N. J. et al. (2000) Development of a preventive vaccine for Ebola virus infection in primates. Nature 408: 605–609. DOI:10.1038/35046108

2)      Martin J.E., et al. (2006) A DNA vaccine for Ebola virus is safe and immunogenic in a phase I clinical trial. Clin Vaccine Immunol 13: 1267–1277. DOI:10.1128/CVI.00162-06

3)      LE Hensley et al. Demonstration of cross-protective vaccine immunity against an emerging pathogenic Ebolavirus species. PLoS Pathogens Online open-access publication (2010) DOI: 10.1371/journal.ppat.1000904