New drugs for tuberculosis treatment

Clofazimine inhibits innate immunity against Mycobacterium tuberculosis by NF-κB

Tuberculosis (TB) remains one of the infectious diseases with high incidence and high mortality. About a quarter of the population has been latently infected with Mycobacterium tuberculosis. At present, the available TB treatment strategies have the disadvantages of too long treatment duration and serious adverse reactions. The sustained inflammatory response leads to permanent tissue damage. Unfortunately, the current selection of treatment regimens does not consider the immunomodulatory effects of various drugs. In this study, we preliminarily evaluated the effects of commonly used anti-tuberculosis drugs on innate immunity at the cellular level. The results showed that clofazimine (CFZ) has a significant innate immunosuppressive effect. CFZ significantly inhibited cytokines and type I interferons (IFNα and IFNβ) expression under both lipopolysaccharide stimulation and CFZ-resistant strain infection. In further mechanistic studies, CFZ strongly inhibited the phosphorylation of nuclear factor kappa B (NF-κB) p65 and had no significant effect on the phosphorylation of p38. In conclusion, our study found that CFZ suppresses innate immunity against Mycobacterium tuberculosis by NF-κB, which should be considered in future regimen development.

IMPORTANCE

The complete elimination of Mycobacterium tuberculosis (Mtb), the etiologic agent of TB, from TB patients is a complicated process that takes a long time. The excessive immune inflammatory response of the host for a long time causes irreversible organic damage to the lungs and liver. Current antibiotic-based treatment options involve multiple complex drug combinations, often targeting different physiological processes of Mtb. Given the high incidence of post-tuberculosis lung disease, we should also consider the immunomodulatory properties of other drugs when selecting drug combinations.

[New tuberculosis drugs in resistant and multiresistant tuberculosis]

Drug-resistant tuberculosis is a globally emerging problem with a rising incidence. According to the WHO in 2008, 17% of strains of Mycobacterium tuberculosis, in untreated cases were resistant to at least one drug and 3.6% were resistant to rifampicin and isoniazid, which is called multidrug-resistant tuberculosis. The problem is greater in patients previously treated and in some countries, where rates of multidrug resistance reach 60%. Approximately 5% of multidrug-resistant tuberculosis patients are also resistant to any fluoroquinolone and at least one injectable drug, being called extensively drug-resistant tuberculosis. The treatment of these forms of tuberculosis requires the use of second-line drugs, which causes higher cost, higher toxicity and a longer duration of treatment. There is a need for new compounds with efficacy and safety profiles better than those currently used to treat these forms of tuberculosis. In the last decade different drugs have being reassessed and appeared, which are at different stages of development.

In vitro characterization of the anti-bacterial activity of SQ109 against Helicobacter pylori

The most evident challenge to treatment of Helicobacter pylori, a bacterium responsible for gastritis, peptic ulcers and gastric cancer, is the increasing rate of resistance to all currently used therapeutic antibiotics. Thus, the development of novel therapies is urgently required. N-geranyl-N'-(2-adamantyl) ethane-1, 2-diamine (SQ109) is an ethylene diamine-based antitubercular drug that is currently in clinical trials for the treatment of tuberculosis (TB). Previous pharmacokinetic studies of SQ109 revealed that persistently high concentrations of SQ109 remain in the stomach 4 hours post oral administration in rats. This finding, combined with the need for new anti-Helicobacter therapies, prompted us to define the in vitro efficacy of SQ109 against H. pylori. Liquid broth micro-dilution was used for susceptibility studies to determine the antimicrobial activity of SQ109 against a total of 6 laboratory strains and 20 clinical isolates of H. pylori; the clinical isolates included a multi-drug resistant strain. All strains tested were susceptible to SQ109 with MIC and MBC ranges of 6-10 µM and 50-60 µM, respectively. SQ109 killing kinetics were concentration- and time-dependent. SQ109 killed H. pylori in 8-10 h at 140 µM (2MBCs) or 4-6 h at 200 µM (~3MBCs). Importantly, though the kinetics of killing were altered, SQ109 retained potent bactericidal activity against H. pylori at low pH. Additionally, SQ109 demonstrated robust thermal stability and was effective at killing slow growing or static bacteria. In fact, pretreatment of cultures with a bacteriostatic concentration of chloramphenicol (Cm) synergized the effects of typically bacteriostatic concentrations of SQ109 to the level of five-logs of bacterial killing. A molar-to-molar comparison of the efficacy of SQ109 as compared to metronidazole (MTZ), amoxicillin (AMX), rifampicin (RIF) and clarithromycin (CLR), revealed that SQ109 was superior to MTZ, AMX and RIF but not to CLR. Finally, the frequency of resistance to SQ109 was low and electron microscopy studies revealed that SQ109 interacted with bacterial inner membrane and cytoplasmic content(s). Collectively, our in vitro data demonstrate that SQ109 is an effective monotherapy against susceptible and multi-drug resistant strains of H. pylori and may be useful alone or in combination with other antibiotics for development as a new class of anti-Helicobacter drugs.

Potent rifamycin-sparing regimen cures guinea pig tuberculosis as rapidly as the standard regimen

Strategies involving new drug combinations, as well as new uses of existing drugs, are urgently needed to reduce the time required to cure patients with drug-sensitive or multidrug-resistant (MDR) tuberculosis (TB). We compared the sterilizing activity of the standard first-line antitubercular regimen, rifampin-isoniazid-pyrazinamide (RHZ), with that of the novel regimen PA-824-moxifloxacin-pyrazinamide (PaMZ), which is currently being studied in clinical trials (NCT01498419), in the guinea pig model of chronic TB infection, in which animals develop necrotic granulomas histologically resembling their human counterparts. Guinea pigs were aerosol infected with ~2 log10 bacilli of wild-type Mycobacterium tuberculosis H37Rv, and antibiotic treatment was initiated 6 weeks after infection. Separate groups of animals received RHZ, PaMZ, or single or two-drug components of the latter regimen administered at human-equivalent doses 5 days/week for a total of 8 weeks. Relapse rates were assessed 3 months after discontinuation of treatment to determine the sterilizing activity of each combination regimen. PaMZ given at human-equivalent doses was safe and well tolerated for the entire treatment period and rendered guinea pig lungs culture negative more rapidly than RHZ did. After 1 month of treatment, 80% and 50% of animals in the RHZ and PaMZ groups, respectively, had lung culture-positive relapse. Both combination regimens prevented microbiological relapse when administered for a total of 2 months. Our data support the use of PaMZ as a novel isoniazid- and rifamycin-sparing regimen suitable for treatment of both drug-sensitive TB and MDR-TB.

Determining quantitative targets for public funding of tuberculosis research and development

South Africa's expenditure on tuberculosis (TB) research and development (R&D) is insignificant relative to both its disease burden and the expenditure of some comparator countries with a minimal TB incidence. In 2010, the country had the second highest TB incidence rate in the world (796 per 100,000 population), and the third highest number of new TB cases (490,000 or 6% of the global total). Although it has a large TB treatment program (about $588 million per year), TB R&D funding is small both in absolute terms and relative to its total R&D expenditure. Given the risk and the high cost associated with drug discovery R&D, such neglect may make strategic sense. However in this analysis it is shown that TB R&D presents a unique opportunity to the national treasuries of all high-burden countries. Using two separate estimation methods (global justice and return on investment), it is concluded that most countries, including South Africa, are under-investing in TB R&D. Specific investment targets for a range of countries, particularly in areas of applied research, are developed. This work supports the outcome of the World Health Organization's Consultative Expert Working Group on Research and Development: Financing and Coordination, which has called for "a process leading to the negotiation of a binding agreement on R&D relevant to the health needs of developing countries".