Intracellular bactericidal activity of ciprofloxacin and ofloxacin against Mycobacterium tuberculosis H37Rv multiplying in the J-774 macrophage cell line

Liposome delivery of ciprofloxacin against intracellular Francisella tularensis infection

The effect of liposome delivery on the controlled release and therapeutic efficacy of ciprofloxacin against intracellular Francisella tularensis infection in vivo was evaluated in this study. Ciprofloxacin was encapsulated in small unilamellar vesicles by a remote loading procedure using an ammonium sulfate gradient. This procedure produced uniform sized liposomes (100 nm) with an entrapment rate of 90+/-3.5%. Following administration of unencapsulated or liposome-encapsulated ciprofloxacin by intravenous injection or aerosol inhalation, levels of ciprofloxacin in sera, lungs, liver and spleen were determined using 14C-ciprofloxacin as radiotracer for ciprofloxacin. Intravenous injection of liposome-encapsulated ciprofloxacin resulted in higher serum levels of drug in serum, as well as increased drug retention in lungs, liver and spleen, compared to that of free encapsulated drug. Aerosol administration of liposome-encapsulated ciprofloxacin by jet nebulization resulted in significantly higher drug levels and prolonged drug retention in the lower respiratory tract compared to the free drug. Aerosol inhalation of liposome-encapsulated ciprofloxacin, given either prophylactically or therapeutically, provided complete protection to mice against a pulmonary lethal infection model of F. tularensis. In contrast, ciprofloxacin given in its free form, was ineffective. These results suggest that liposome encapsulation of ciprofloxacin enhances drug delivery to the primary site of infection and results in increasing therapeutic efficacy against F. tularensis.

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.

Comparison of antimycobacterial activity of grepafloxacin against Mycobacterium avium with that of levofloxacin: accumulation of grepafloxacin in human macrophages

The bactericidal activity of two new quinolones, grepafloxacin and levofloxacin, against five strains of Mycobacterium avium was investigated in vitro. The minimum inhibitory concentrations (MICs) of these two quinolones, determined by the broth microdilution method, were comparable for all strains tested. In contrast, grepafloxacin suppressed the intracellular growth of all the strains in monocyte-derived macrophages more strongly than levofloxacin, when the cells infected with these strains were incubated for 7 days in the presence of various concentrations of the two new quinolones. To find the reason for the strengthened intracellular killing activity of grepafloxacin, we determined the ratio of the concentration of the new quinolones in the cells to that in the medium (C/M concentration ratio). The C/M concentration ratio of grepafloxacin was increased to 34.7 by 7 days, whereas that of levofloxacin at 7 days was only 12.3. These data suggested that a higher level of intraphagocytic accumulation of grepafloxacin endows it with greater mycobactericidal activity.

Fluoroquinolone action against clinical isolates of Mycobacterium tuberculosis: effects of a C-8 methoxyl group on survival in liquid media and in human macrophages

When the lethal action of a C-8 methoxyl fluoroquinolone against clinical isolates of Mycobacterium tuberculosis in liquid medium was measured, the compound was found to be three to four times more effective (as determined by measuring the 90% lethal dose) than a C-8-H control fluoroquinolone or ciprofloxacin against cells having a wild-type gyrA (gyrase) gene. Against ciprofloxacin-resistant strains, the C-8 methoxyl group enhanced lethality when alanine was replaced by valine at position 90 of the GyrA protein or when aspartic acid 94 was replaced by glycine, histidine, or tyrosine. During infection of a human macrophage model by wild-type Mycobacterium bovis BCG, the C-8 methoxyl group lowered survival 20- to 100-fold compared with the same concentration of a C-8-H fluoroquinolone. The C-8 methoxyl fluoroquinolone was also more effective than ciprofloxacin against a gyrA Asn94 mutant of M. bovis BCG. In an M. tuberculosis-macrophage system the C-8 methoxyl group improved fluoroquinolone action against both quinolone-susceptible and quinolone-resistant clinical isolates. Thus, a C-8 methoxyl group enhances the bactericidal activity of quinolones with N1-cyclopropyl substitutions; these data encourage further refinement of fluoroquinolones as antituberculosis agents.

Mechanism underlying levofloxacin uptake by human polymorphonuclear neutrophils

The mechanism of radiolabeled levofloxacin ([3H]levofloxacin) uptake by human polymorphonuclear neutrophils (PMNs) was investigated by a classical velocity centrifugation technique. PMNs were incubated with levofloxacin for 5 to 180 min under various conditions before centrifugation through an oil cushion. Radioactivity was measured in the cell pellet to determine the amount of cell-associated drug. The uptake of levofloxacin was moderate with a cellular concentration/extracellular concentration ratio of about 4 to 6. Levofloxacin accumulated in PMNs parallel to the extracellular concentration, without saturation, over the range of 2.5 to 200 mg/liter (linear regression analysis: r = 0.92; P < 0.001). The activation energy was low (36 +/- 7.2 kJ/mol). Levofloxacin uptake was increased in Ca(2+)-depleted, EGTA-containing medium by approximately 33% (P = 0.022), while Ni2+, a Ca2+ channel inhibitor, inhibited it in a concentration-dependent manner, with the concentration that inhibited 50% of control uptake being approximately 2.65 mM. Verapamil (an L-type Ca2+ channel inhibitor) and other pharmacologic agents which modify Ca2+ homeostasis did not modify levofloxacin uptake. Interestingly, Ca2+ and Mg2+ inhibited levofloxacin uptake in a concentration-dependent manner. EGTA, Ni2+, and verapamil did not modify levofloxacin efflux; thapsigargin, a Ca2+ pool-releasing agent, modestly increased the intracellular retention of levofloxacin. In addition, contrary to other fluoroquinolones, probenecid at 1 to 10 mM did not modify either levofloxacin uptake or efflux. These data are consistent with a mechanism of passive accumulation of levofloxacin in PMNs. Extracellular Ca2+ and Mg2+ may influence the structural conformation of levofloxacin or the lipophilicity of PMN membranes, thus explaining their effect on levofloxacin uptake.

In vitro activities of levofloxacin used alone and in combination with first- and second-line antituberculous drugs against Mycobacterium tuberculosis

By using the radiometric BACTEC 460-TB methodology, the inhibitory and bactericidal activity of the optically active L-isomer of ofloxacin (levofloxacin) was compared with those of the D-isomer and the commercially available mixture containing equal amounts of DL-isomers (ofloxacin) against the Mycobacterium tuberculosis complex (type strain H37Rv, a panel of drug-susceptible and -resistant clinical isolates including multidrug-resistant isolates of M. tuberculosis, as well as M. africanum, M. bovis, and M. bovis BCG). Levofloxacin MICs (range 0.50 to 0.75 microgram/ml) were about 1 dilution lower than those of ofloxacin (MIC range, 0.75 to 1.00 microgram/ml) and 5 to 6 dilutions lower than those of the D-isomer (MIC range, 32 to 60 micrograms/ml). The MICs of levofloxacin, ofloxacin, and D-ofloxacin at which 90% of the strains are inhibited were 0.50, 1.00, and 64 micrograms/ml, respectively. The multidrug-resistant M. tuberculosis strains resistant to first-line drugs were as susceptible to quinolones as the wild-type drug-susceptible isolates. Levofloxacin at 0.5 microgram/ml showed bactericidal activity comparable to the activities of 1.0 microgram of ofloxacin per ml and 64 micrograms of D-ofloxacin per ml, with MBCs within the range of 0.5 to 2.0 micrograms/ml, compared with MBCs of 0.75 to 4.0 micrograms of ofloxacin per ml for M. tuberculosis, M. africanum, M. bovis BCG. Combination testing of sub-MICs of levolofoxacin with other first-line (isoniazid, rifampin, and ethambutol) and second-line (amikacin and clofazimine) antituberculous drugs was evaluated with various two-, three-, and four-drug combinations; enhanced drug activity was observed in 8 of 25, 12 of 20, and 8 of 15 tests, respectively, indicating that levofloxacin acts in synergy with other antituberculous drugs.

Activities of poloxamer CRL8131 against Mycobacterium tuberculosis in vitro and in vivo

A poloxamer surfactant, CRL8131, was evaluated for activity against Mycobacterium tuberculosis (Erdman) by itself and in combination with antibiotics in broth culture, in a macrophage cell line assay, and in testing with mice. In the broth culture, CRL8131 suppressed the growth of M. tuberculosis and produced synergistic effects in combination with isoniazid, rifampin, and streptomycin. It also displayed synergy with isoniazid and rifampin against two drug-resistant isolates. In the macrophage cell line assay, CRL8131 produced a synergistic effect on intracellular killing of M. tuberculosis by isoniazid, rifampin, streptomycin, pyrazinamide, thiacetazone, D-cycloserine, ethionamide, amikacin, clindamycin, and p-aminosalicylic acid. It demonstrated no synergy or antagonism with ethambutol, gentamicin, kanamycin, ciprofloxacin, or nalidixic acid. Finally, with C57BL/6 mice infected with M. tuberculosis, a combination of CRL8131 and either thiacetazone or pyrazinamide produced 100% survival at 40 days whereas the antibiotics produced only 33% survival and CRL8131 produced 0% survival when used as single agents. This improved survival rate was associated with a significant reduction in the number of organisms in the lungs and spleens of infected mice.

Comparison of activities of fluoroquinolones in murine macrophages infected with Mycobacterium tuberculosis

In this study the compounds levofloxacin and sparfloxacin, as well as three experimental compounds (AMQ2, AMQ4, and AMQ5), were compared with isoniazid and rifabutin in terms of their capacity to inhibit the intracellular growth of the drug-susceptible Mycobacterium tuberculosis strain Erdman and the isoniazid-resistant katG gene-negative strain 24 within monolayers of mouse bone marrow-derived macrophages. Both levofloxacin and sparfloxacin, as well as compound AMQ4, had substantial activity in this physiologically relevant model, further confirming the potential usefulness of this class of compounds in the therapy of tuberculosis.

Antimycobacterial spectrum of sparfloxacin and its activities alone and in association with other drugs against Mycobacterium avium complex growing extracellularly and intracellularly in murine and human macrophages

The MICs and MBCs of the new difluorinated quinolone drug sparfloxacin against type strains belonging to 21 species of mycobacteria were screened. The MICs and MBCs were within the range of 0.1 to 2.0 and 0.1 to 4.0 micrograms/ml, respectively (with an MBC/MIC ratio of 1 to 2), and against 18 of the 21 species tested, the drug showed significant bactericidal activity (at least 99% killing or more of the initial inoculum added) at concentrations well within the reported peak concentrations in serum (Cmax) in humans. MICs of sparfloxacin for 7 of 10 Mycobacterium avium complex strains were below the Cmax, with MBC/MIC ratios within the range of 2 to 4. Enhancement of its activity by ethambutol, rifampin, amikacin, and clarithromycin (which were used at sublethal concentrations) assessed by using BACTEC radiometry revealed that its activity was further enhanced in 2 of 10 strains by rifampin and in 7 of 10 strains by ethambutol. The bactericidal effects of various drugs used alone as well as two-drug combinations used at Cmax levels were also screened against four strains of M. avium complex growing intracellularly in two different macrophage systems, namely, mouse bone marrow-derived macrophages and peripheral blood monocyte-derived human macrophages. Our results showed a satisfactory correlation between the extracellular and intracellular drug activity data.

In vitro activity of the new difluorinated quinolone sparfloxacin (AT-4140) against Mycobacterium tuberculosis compared with activities of ofloxacin and ciprofloxacin

MICs of the new fluoroquinolone drugs ofloxacin, ciprofloxacin, and sparfloxacin (AT-4140) for 10 strains of Mycobacterium tuberculosis were determined by using both a BACTEC radiometric method and testing on solid 7H11 agar medium. Radiometric MICs by 7H12 broth testing ranged from 0.5 to 1.0, 0.25 to 0.5, and 0.1 to 0.2 microgram/ml for ofloxacin, ciprofloxacin, and sparfloxacin respectively, whereas MICs in solid medium ranged from 0.5 to 1.0, 0.5 to 1.0, and 0.2 to 0.5 microgram/ml, respectively. The bactericidal action of the quinolones compared with their reported peak concentrations in human serum showed that sparfloxacin is the most bactericidal, followed by ciprofloxacin and ofloxacin. Our results suggest the potential of the new difluorinated quinolone sparfloxacin for use against the tubercle bacillus and indicate that further determination of its antimycobacterial spectrum and intracellular efficacy may be fruitful.