TB treatment and diagnostics pipeline: once empty, suddenly offers new hope for TB care

After decades with little tuberculosis (TB) research and development, news on several new TB drugs; a new vaccine against TB, and a partnership to develop a ‘point-of-care’ diagnostic test were released at this year’s World Conference on Lung Health (the World Conference), held in October in Paris.

The tools currently being used to detect, prevent and treat TB are in desperate need of updating. “We have a diagnostic test for TB that predates the age of flight,” said Dr Helene Gayle of the Bill and Melinda Gates Foundation. “As a result, we are using a 100-year old diagnostic test that misses half of all the cases. We use a vaccine that predates television; and the last time there was a new drug for TB, the majority of people on this earth were not born. We need faster, better, easier, more broadly effective tests, combined with better, faster, easier, and less expensive treatment. And we need a better vaccine.”

But in comparison to HIV and other disease, funding to develop new tools for fighting tuberculosis has been minimal. In the last several years, the Gates Foundation has strived to change this.

“At the Gates Foundation,” Dr Gayle continued, “we believe that technology offers the opportunity to solve problems that may have seemed intractable.”

Gate Foundation has made some important grants in an effort to encourage the development of new tools. These grants include:

• $25 million to the Global Alliance for TB Drug Development (GATB) to develop and ensure global access to improved TB drug regimens.
• $83 million to the Aeras Global TB Vaccine Foundation to develop and license an improved vaccine against TB (January 2004).
• $23 million to the Foundation for Innovative New Diagnostics to develop diagnostic tests for infectious diseases including tuberculosis (December 2003).
• Almost one million dollars for the TB/HIV Project — an effort to mobilize community-based treatment advocacy and foster treatment literacy projects targeting people with TB. It is hoped that such social mobilisation will put pressure on governments and markets to generate more funding to TB research and management.

These grants appear to be producing some results and, as Dr Gayle announced “several pieces of good news about our fighting tuberculosis.”

First, GATB has formed a partnership with Bayer Healthcare AG to conduct a clinical trial programme exploring the potential for an existing antibiotic, moxifloxacin, to shorten the standard six-month course of TB treatment. Preliminary studies have shown that the drug, which is already approved in more than 100 countries to treat bacterial respiratory and skin infections, may reduce treatment time to three or four months.

The clinical trials will enrol close to 2,500 patients in Brazil, Canada, South Africa, Spain, Tanzania, Uganda, the United States and Zambia. Bayer will donate moxifloxacin for each trial site and will cover the costs of regulatory filings, while the TB Alliance will coordinate and pay for the clinical trials with additional support from the U.S. Centers for Disease Control and Prevention (CDC), the Orphan Products Development Center of the Food & Drug Administration (FDA), the European and Developing Countries Clinical Trials Partnership (EDCTP), and the British Medical Research Council.

Current World Health Organization (WHO) and national TB programme guidelines for TB treatment recommend two months of intensive, directly observed treatment (DOTS) with four drugs - isoniazid, rifampicin, ethambutol and pyrazinamide. Treatment then continues with either four months of rifampicin and isoniazid (preferably given via directly observed therapy), or six months of isoniazid and ethambutol (which may be given on a monthly outpatient basis). A recently published study demonstrated that the six-month course is more effective (see aidsmap news report), however, the need for six months of direct observed therapy places great financial and logicistical burdens on both the patient and national TB programmes.

Preclinical studies have shown that moxifloxacin has potent anti-TB activity (Nuermberger^a). Although a subsequent studies in mice found that the additive effect of moxifloxacin to the standard regimen (in place of ethambutol) was minimal, they also reported that when moxifloxacin was used in combination with rifampicin and pyrazinamide — in place of isoniazid — the sterilizing activity of the regimen was much greater than that of the standard isoniazid-containing regimen (Nuermberger^b). These studies suggest that moxifloxacin could reduce treatment time by at least two months when substituted for isoniazid.

A poster at the World Conference reported that six months of moxifloxacin combined with either pyrazinamide, ethambutol, ethionamide, M.leprae hsp65 DNA (new TB vaccine) or another new drug PA-824 (see below) were at least as effective (and generally superior to) six months of isoniazid for the treatment of latent TB. The combination with PA-824 was particularly potent — sterilising the infection in 9 out of 9 treated mice — without any relapses three months after treatment discontinued (compared to a 100% relapse rate on isoniazid (p<0.01). The author noted that all of these combinations would be effective in drug-resistant TB and that other mice studies suggest that combinations of moxifloxacin with more than one of these other drugs could represent an alternative to the standard rifampicin/isoniazid-containing regimens (Grosset).

But how will these preclinical studies translate to TB treatment in humans? So far, it seems well. In early phase one studies in smear-positive patients, moxifloxacin has demonstrated early bactericidal activity (EBA) comparable to rifampicin (Gosling) and isoniazid (Pletz). (Early bactericidal activity is only one measure of TB drug activity, preclinical studies suggest that moxifloxacin also has a sterilising effect (Lounis)). In another study, 20 patients with tuberculosis were treated with moxifloxacin in combination with rifampicin and isoniazid for six months. Patients “experienced no toxicity, almost complete sterilisation and remission of the disease. Sterilisation was obtained in 15 days.” (Valerio).

The new GATB studies will evaluate whether the substitution of moxifloxacin for one of the standard TB drugs (ethambutol or isoniazid) eliminates TB infection faster than the current standard therapy. Some studies where moxifloxacin is being substituted for ethambutol are already underway (or enrolling), however, based on preclinical studies, it would appear that the studies where it will be substituted for isoniazid offer the most hope of shortening the length of TB therapy.

According to Bayer, moxifloxacin has been used in more than 35 million people, so the drug’s safety profile is well characterised. In general, it seems much safer than isoniazid or rifampicin, however, there may be complications in patients with heart problems, and the drug has some rare CNS side-effects. The drug has been used widely in treatment of bacterial infections in people with HIV and has no drug interactions with antiretrovirals.

However, of crucial importance, the safety and effectiveness of moxifloxacin has yet to be established in paediatric patients, adolescents (less than 18 years of age), pregnant women, and lactating women. It is shocking that Bayer has managed to get the drug approved in so many countries without conducting basic safety studies in these other populations. The TB Alliance and the Gates Foundation need to remedy this treatment gap before moxifloxacin becomes part of the standard TB regimen — which, if the studies are successful could be within the next five years — otherwise, they will be developing a drug for use primarily by adult men.

* Going into phase I studies within the next 6 months

One such drug is gatifloxacin, which is the furthest along in clinical development for tuberculosis. The drug is licensed to Bristol-Myers Squibb in the developed world, where it is marketed to treat a variety of bacterial infections. Like moxifloxacin, it has been widely used in people with HIV and has no interactions with antiretrovirals.

Gatifloxacin is a very similar fluoroquinolone drug to moxifloxacin and the two drugs probably work in the same way. Older fluoroquinolones such as levofloxacin and ofloxacin have long been known to possess some activity against tuberculosis, but were relegated to treatment of drug-resistant TB after studies suggested that they might not be as promising in first line regimens. However, both gatifloxacin and moxifloxacin have demonstrated dramatically greater activity in preclinical studies (Sulochana). The two drugs are likely to be cross-resistant though (Cheng).

Conflicting results have been reported about gatifloxacin’s activity when added to isoniazid or rifampicin in cell cultures, with one study suggesting synergy but another reporting little additive effect (Bhusal; Paramasivan). However, it is not clear how applicable these test tube studies are to what would happen in vivo.

Studies in mice have been encouraging. One study suggests that gatifloxacin in combination with ethionamide or pyrazinamide, could be an alternative regimen to cure active TB, which could be used instead of the standard isoniazid/rifampicin containing regimen in patients with susceptible or drug-resistant tuberculosis (Cynamon and Sklankey).

Early clinical indications of gatifloxacin’s anti-TB activity have been promising as well, with identical activity to moxifloxacin and similar (though not quite as potent) EBA to isoniazid (see online http://www.cwru.edu/affil/tbru/trials.htm). The drug’s toxicity and drug-drug interaction profile is similar to moxifloxacin’s. Likewise, the drug has not been adequately evaluated in children and pregnant or lactating women.

A large multicentre phase III clinical trial is currently evaluating whether the use of gatifloxacin (in place of ethambutol) can shorten the standard TB treatment in adults to four months. Sponsored by the Institut de Recherche pour le Developpement, the WHO and the European Commission, the study plans to enroll over 2000 patients at trial sites in South Africa, Senegal, Kenya, Benin, and Guinea. The trial is using a generic formulation made by Lupin Pharmaceuticals of India, which hopes to market a fixed-dose combination containing gatifloxacin.

Moxifloxacin is just the tip of the iceberg for new TB drug development. According to Dr Mel Spigelman, Director of Research and Development for GATB, there are six new TB drugs in clinical trials, and a number of others in the development pipeline (see Table). Although, many of these compounds may not succeed, having so many candidates represents a dramatic change. “If we had put up this chart even four years ago,” said Spigelman. “It would have been almost empty.”

According to Spigelman, GATB drug development efforts are focused on “shortening therapy of active disease — six months is still a pretty long time.” The goal is first to, “shorten six month down to 2-3 months, [then to] simplify it to a weekly regimen and in the process move from 130 administrations down to [around] 10.”

“The next target is to decrease the drug-drug interactions. The strategy that we employ here is that we up-front the drugs with no p450 interactions.” p450 is the liver enzyme system which metabolises many HIV drugs and the TB drug rifampicin.

“Even if they do not shorten therapy but they still are active drugs against TB, then they will still be useable for patients with HIV because they do not have the drug-drug interactions,” said Spigelman.

The next drug in the pipeline comes from Tibotec/Johnson and Johnson. It is a diarylquinoline (a quinolone derivative) called TMC207 (formerly R207910) with a mechanism of action that targets a new TB drug target. TMC appears to interfere with the proton pump used for mycobacterial ATP synthase — thus depleting the main energy source that mycobacteria use to grow (Andries). The drug’s unique mechanism of action explains the lack of cross-resistance observed in preclinical studies to any of the current TB drugs, including moxafloxacin.

In cell culture and mice studies, TMC has extremely potent anti-TB activity, more active than the combination of rifampicin, isoniazid, and pyrazinamide even when used as monotherapy. When substituted for either rifampicin or isoniazid in combination therapy, TMC207 halved treatment time, leading to complete TB sterilisation within two months.

Preliminary studies in healthy human volunteers suggest that the drug may be safe and has a halflife of more than 24 hours, which may permit once weekly dosing. The drug is currently in early clinical activity studies in patients with tuberculosis.

In addition to moxifloxaxin, GATB is conducting clinical evaluations of a promising novel anti-TB compound, called PA-824 from the nitroimidazopyran class of compounds. GATB licensed PA-824 from Chiron for TB in January 2002, and has since funded the compound’s preclinical and early clinical development. If development is successful, the drug will be marketed royalty free in lesser-developed nations.

The compound’s novel anti-tuberculosis activity was first identified in 2000 when a preclinical study suggested that the compound interrupted mycobacterial protein and cell wall synthesis. Since that time, preclinical studies, directed by GATB, indicate that it has both potent bactericidal and sterilizing activity (Tyagi). PA-824 could potentially be substituted for either isoniazid (which is bactericidal) or rifampicin (which is sterilizing) — or possibly even both. Studies also suggest it has potential for the treatment of latent TB (Grosset; Lenaerts).

A report at the World Conference found that in the murine tuberculosis model PA-824 was more potent than rifampicin when used in combination with moxifloxacin and pyrazinamide, and that when all four drugs were used together, the duration of treatment could be reduced to 3 months or less. “Remarkably, [the PA-824/moxifloxacin/pyrazinamide combination] may have the potential to rapidly cure MDR-TB”, wrote the author.

The drug has no P450 interactions and thus is not expected to interfere with antiretroviral treatment.

A Phase I dose-ranging study is ongoing to evaluate the safety, tolerability, and pharmacokinetics of PA-824 in healthy, male volunteers.

This lead compound from Otsuka Pharmaceuticals in Japan is currently in phase I studies. The company reports that OPC 67683 has potent in vitro activity against MTB, may shorter duration of therapy in active TB/MDR-TB and is more effective than current drugs for ATT.

However, very little has actually been published on the compound to date. A number of presentations on preclinical and early phase I studies with OPC 67683 are scheduled for this year’s Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC), which was postponed until December due to Hurricane Katrina.

Lupin Limited, the same Indian company that is developing the generic formulation of gatifloxacin, has identified a lead compound called sudoterb, which against sensitive and resistant strains of M.tuberculosis. [Sudoterb belongs to a class of compounds known as pyrroles, which are commonly found in alkaloids from plants, including, incidentally, lupins. Lupin has previously developed synthetic analogues of active compounds isolated from plants used in traditional Ayurvedic medicine.]

At last year’s ICAAC, sudoterb was reported to have potent anti-TB activity in vitro and in vivo (mice and guinea pig) studies. In vitro, sudoterb has bactericidal activity similar to isoniazid and is synergistic with rifampicin (Arora). The combination of sudoterb with isoniazid, rifampicin, and pyrazinamide led to complete sterilisation of sensitive and resistant M.TB strains in infected mice within two months. In combination with rifampicin and pyrazinamide, sudoterb also cured TB in all animals after three months of treatment (Sinha).

Thus, sudoterb could potentially cut the time of TB treatment down to two or three months. Early reports are that the drug exhibits good oral bioavailability with once daily dosing.

Sudoterb was scheduled to enter EBA studies in October of this year.

The gains in diagnostic technology have been less impressive but it remains a focus for the Gates Foundation. “We recognize, that any work we do to improve and expand treatment programmes will still face a bottleneck if advances aren’t made in diagnostics,” said Dr Gayle.

She announced that the Foundation for Innovative New Diagnostics headed by Dr Giorgio Roscigno has begun a new collaboration with Eiken Chemicals, with the goal of developing a rapid and simple test for the detection of tuberculosis [in] HIV infected patients. The TB test will use Eiken’s Loop-Mediated Isothermal Amplification (LAMP) method to detect M.TB DNA directly from clinical samples in less than two hours with minimal instrumentation.

LAMP is a novel nucleic acid amplification method that works rapidly under isothermal conditions. When targeted DNA is detected in a clinical sample, a fluorescent chelating reagent should become visible by the naked eye when placed under an ultraviolet light. Working jointly with FIND, Eiken plans to develop a LAMP test for tuberculosis simple enough to be used in any site that currently uses microscopy.

While it should be simple enough to incorporate DNA probes for MTB into a LAMP test, a potential drawback of this approach may be the tests the ability to distinguish between active and latent TB, and depending upon the genes used, between MTB and other mycobacteria and or vaccination products.

Dr Gayle also told conference-goers about an important development in the area of vaccine work, “Aeras Global TB Vaccine Foundation has formed a new partnership with Glaxo SmithKline (GSK) Biologics,” she said “to bring GSK’s promising vaccine candidate to phase two trials in Africa and other locations. Already this vaccine has been shown high levels of cellular immunity against TB in early stage clinical trials. Our hope is that this cooperation between public and private sector will accelerate the development, testing and ultimately the delivery of an effective vaccine for those who need it the most.”

The vaccine Mtb72F/AS02A consists of a recombinant fusion protein (Mtb72F) formulated in a proprietary GSK adjuvant system (AS02A) that appears to induce strong, long lasting cellular and humoral immune responses. It has shown promising results in preclinical studies (Skeiky). In addition, the vaccine has shown a good safety and immunogenicity profile in early-stage clinical trials conducted by GSK.

In the next few months, GSK and Aeras plan to start additional safety and immunogenicity trials in Europe in adults who have been previously infected with TB or vaccinated with Bacillus Calmette-Guérin (BCG). The plan is then to begin larger studies in Africa and other locations to test the safety and efficacy of the vaccine candidate in populations with a high burden of TB.