In vitro activity of the new quinolone lomefloxacin against Mycobacterium tuberculosis

Recognizing drug targets using evolutionary information: implications for repurposing FDA-approved drugs against Mycobacterium tuberculosis H37Rv

Drug repurposing to explore target space has been gaining pace over the past decade with the upsurge in the use of systematic approaches for computational drug discovery. Such a cost and time-saving approach gains immense importance for pathogens of special interest, such as Mycobacterium tuberculosis H37Rv. We report a comprehensive approach to repurpose drugs, based on the exploration of evolutionary relationships inferred from the comparative sequence and structural analyses between targets of FDA-approved drugs and the proteins of M. tuberculosis. This approach has facilitated the identification of several polypharmacological drugs that could potentially target unexploited M. tuberculosis proteins. A total of 130 FDA-approved drugs, originally intended against other diseases, could be repurposed against 78 potential targets in M. tuberculosis. Additionally, we have also made an attempt to augment the chemical space by recognizing compounds structurally similar to FDA-approved drugs. For three of the attractive cases we have investigated the probable binding modes of the drugs in their corresponding M. tuberculosis targets by means of structural modelling. Such prospective targets and small molecules could be prioritized for experimental endeavours, and could significantly influence drug-discovery and drug-development programmes for tuberculosis.

New anti-tuberculosis agents amongst known drugs

Mycobacterium tuberculosis has an on-going impact on global public health and new therapeutics to treat tuberculosis are urgently required. The emergence of drug resistant tuberculosis poses a serious threat to the control of this pathogen, and the development of drugs that are active against the resistant strains is vital. A medium-throughput assay using the Alamar Blue reagent was set-up to identify novel inhibitors of M. tuberculosis from a library of known drugs, for which there has already been extensive research investigating their suitability and safety as human therapeutics. Of the 1514 compounds screened, 53 were demonstrated to possess inhibitory properties against M. tuberculosis at a concentration of 5microM or below. Of these, 17 were novel inhibitors while 36 were known tuberculosis drugs or had been previously described as possessing anti-tuberculosis activity. Five compounds were selected as those which represent the most promising starting points for new anti-tuberculosis agents. It was demonstrated that all five were active against intracellular M. tuberculosis in a macrophage model of infection. The anti-tuberculosis agents identified in this screen represent promising new scaffolds on which future drug development efforts can be focused.

Fluoroquinolones and tuberculosis

Tuberculosis (TB) remains one of the main causes of morbidity worldwide, and the emergence of multi-drug resistant (MDR) Mycobacterium tuberculosis strains in some parts of the world has become a major concern. The decrease in activity of the major anti-TB drugs, such as isoniazid and rifampicin, is an important threat and alternative therapies are urgently required. The anti-TB activity of the fluoroquinolones has been under investigation since the 1980s. Many are active in vitro but only a few, including ofloxacin, ciprofloxacin, sparfloxacin, levofloxacin and lomefloxacin, have been clinically tested. Fluoroquinolones can be used in co-therapy with the available anti-TB drugs. However, the choice of fluoroquinolone should be based not only on the in vitro activity, but also on the long-term tolerance. Fluoroquinolones are novel anti-TB drugs to be used when a patient is infected with a MDR-TB strain.

The role of fluoroquinolones in tuberculosis today

Tuberculosis is a growing international health concern; it is the leading infectious cause of death in the world today. The fluoroquinolones are the most recent class of drugs offering hope in the fight against this disease. Ciprofloxacin, ofloxacin, levofloxacin and sparfloxacin are currently the most commonly used agents used against Mycobacterium tuberculosis (TB), with in vitro minimum inhibitory concentrations (MICs) of 0.1 to 4 mcg/ml. Resistance in TB to fluoroquinolones may occur spontaneously or may be acquired, especially when these agents are used inappropriately. Cross-resistance among the fluoroquinolones has been shown in TB. The fluoroquinolones offer a favourable pharmacokinetic profile for the treatment of TB. Most demonstrate excellent oral bioavailability and achieve maximum (peak) serum concentrations well above the MIC. They are also distributed widely, including intracellularly. The fluoroquinolones are cleared renally and/or hepatically, with varying serum half-lives. Fluoroquinolones are most effective when the peak concentration (Cmax) to MIC ratio is maximised. Fluoroquinolones such as ciprofloxacin and ofloxacin have been used in regimens for the prevention of TB, but have been poorly tolerated when used in combination with pyrazinamide. Favourable responses with fluoroquinolones in regimens used in the treatment of clinical TB disease have been seen. They, however, are not to be considered as equal replacements for isoniazid or rifampicin (rifampin) and should be used with at least 2 other antituberculous agents. Therapeutic drug monitoring of fluoroquinolones is beneficial in assuring that maximum Cmax to MIC ratios are being achieved, especially in patients at risk for malabsorption, such as those infected with HIV. Higher, once-daily doses of most fluoroquinolones are becoming more common in treating TB. Fluoroquinolones are generally well tolerated with long term use in treating TB, but rare, serious adverse effects have been reported with general fluoroquinolone use. The most common drug interactions with fluoroquinolones in TB therapy include the malabsorption interactions associated with multivalent cations and cytochrome P450 interactions with ciprofloxacin. An increased risk of central nervous system effects with concomitant cycloserine has been reported and seen clinically. When using fluoroquinolones to treat TB, careful consideration of individual susceptibility patterns, pharmacokinetic and toxicity profiles should be taken. The aid of a TB expert may also be warranted. The exact role of the fluoroquinolones in treating TB remains to be determined.

In vitro activity of four fluoroquinolones against Mycobacterium tuberculosis

The in vitro activity of ciprofloxacin, ofloxacin, levofloxacin and moxifloxacin against strains of Mycobacterium tuberculosis was studied. Moxifloxacin and levofloxacin showed the greatest activity having an MIC(90) of 1 mg/l. The MIC(90) for ofloxacin was 2 mg/l and for ciprofloxacin 4 mg/l. Further studies should be made to determine the role played by these compounds in the treatment of tuberculosis.

Infection caused by Mycobacterium tuberculosis

OBJECTIVE

To update readers on the clinical management of infections caused by Mycobacterium tuberculosis, to provide a general description of the organism, culture and susceptibility testing, and clinical manifestations of the disease, and to provide several aspects of the treatment of the disease, including historical perspective, current approaches, and research opportunities for the future.

DATA SOURCES

The current medical literature, including abstracts presented at recent international meetings, is reviewed. References were identified through MEDLINE, MEDLARS II, Current Contents, and published meeting abstracts.

STUDY SELECTION

Data regarding the epidemiology, clinical manifestations, culture and susceptibility testing, and treatment of tuberculosis are cited. Specific attention has been focused on the clinical management of patients with noncontagious infection and potentially contagious active disease (TB) caused by M. tuberculosis.

DATA EXTRACTION

Information contributing to the discussion of the topics selected by the authors is reviewed. Data supporting and disputing specific conclusions are presented.

DATA SYNTHESIS

The incidence of TB is increasing in the US, despite the fact that available technologies are capable of controlling the vast majority of existing cases. Fueling the fire is the problem of coinfection with HIV and M. tuberculosis. Very few drugs are available for the treatment of TB, and few of these approach the potency of isoniazid and rifampin. Preventive therapy of patients exposed to multiple-drug-resistant M. tuberculosis (MDR-TB) is controversial and of unknown efficacy. Treatment of active disease caused by MDR-TB requires up to four times longer, is associated with increased toxicity, and is far less successful than the treatment of drug-susceptible TB. Strategies for the management of such cases are presented. The rising incidence of TB in the US reflects a breakdown in the healthcare systems responsible for controlling the disease, which reflects the past budgetary reductions. Although TB control is one of the most cost-effective public health strategies, funding has been cut repeatedly despite the fact that TB was never eliminated. This has helped to produce the current crisis, including the spread of MDR-TB in many urban areas. The elimination of TB will now take decades longer, cost hundreds of millions of dollars more, and result in vastly higher morbidity and mortality rates than would have occurred with timely, adequate measures.

CONCLUSIONS

Tremendous effort and far more funding will be required to eliminate TB in the US. The selection of drug therapy must be based on the susceptibility data for each isolate. Multiple-drug therapy must be continued for 6 to > or = 24 months, and patient adherence to prescribed regimens must be verified in all cases of TB. Significant antimycobacterial drug malabsorption has been documented in AIDS patients with TB, and may result in treatment failure. New agents are needed to improve the clinical outcome in patients with MDR-TB.

Ciprofloxacin susceptibility testing by MIC and disk elution of drug-resistant Mycobacterium tuberculosis and Mycobacterium avium complex

The ability to provide susceptibility data for certain species of mycobacteria can be clinically useful. In this study, the disk elution method for susceptibility testing was adapted for testing ciprofloxacin against mycobacterial isolates. Of the 75 Mycobacterium tuberculosis isolates tested, including 23 multiply drug-resistant isolates, 96% were susceptible to ciprofloxacin at a breakpoint concentration of 2 micrograms/ml.