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

Fluoroquinolone heteroresistance, antimicrobial tolerance, and lethality enhancement

With tuberculosis, the emergence of fluoroquinolone resistance erodes the ability of treatment to interrupt the progression of MDR-TB to XDR-TB. One way to reduce the emergence of resistance is to identify heteroresistant infections in which subpopulations of resistant mutants are likely to expand and make the infections fully resistant: treatment modification can be instituted to suppress mutant enrichment. Rapid DNA-based detection methods exploit the finding that fluoroquinolone-resistant substitutions occur largely in a few codons of DNA gyrase. A second approach for restricting the emergence of resistance involves understanding fluoroquinolone lethality through studies of antimicrobial tolerance, a condition in which bacteria fail to be killed even though their growth is blocked by lethal agents. Studies with Escherichia coli guide work with Mycobacterium tuberculosis. Lethal action, which is mechanistically distinct from blocking growth, is associated with a surge in respiration and reactive oxygen species (ROS). Mutations in carbohydrate metabolism that attenuate ROS accumulation create pan-tolerance to antimicrobials, disinfectants, and environmental stressors. These observations indicate the existence of a general death pathway with respect to stressors. M. tuberculosis displays a variation on the death pathway idea, as stress-induced ROS is generated by NADH-mediated reductive stress rather than by respiration. A third approach, which emerges from lethality studies, uses a small molecule, N-acetyl cysteine, to artificially increase respiration and additional ROS accumulation. That enhances moxifloxacin lethality with M. tuberculosis in culture, during infection of cultured macrophages, and with infection of mice. Addition of ROS stimulators to fluoroquinolone treatment of tuberculosis constitutes a new direction for suppressing the transition of MDR-TB to XDR-TB.

THP-1 cell line model for tuberculosis: A platform for in vitro macrophage manipulation

Macrophages are large mononuclear phagocytic cells that play a vital role in the immune response. They are present in all body tissues with extremely heterogeneous and plastic phenotypes that adapt to the organs and tissues in which they live and respond in the first-line against invading microorganisms. Tuberculosis (TB) is caused by the pathogenic bacteria Mycobacterium tuberculosis (Mtb), which is among the top 10 global infectious agents and the leading cause of mortality, ranking above human immunodeficiency virus (HIV), as a single infectious agent. Macrophages, upon Mtb infection, not only phagocytose the bacteria and present the antigens to T-cells, but also react rapidly by developing antimycobacterial immune response depending highly on the production of cytokines. However, Mtb is also capable of intracellular survival in instances of sub-optimal activation of macrophages. Hence, several systems have been established to evaluate the Mtb-macrophage interaction, where the THP-1 monocytes have been developed as an attractive model for in vitro polarized monocyte-derived macrophages. This model is extensively used for Mtb as well as other intracellular bacterial studies. Herein, we have summarized the updated implications of the THP-1 model for TB-related studies and discussed the pros and cons compared to other cell models of TB.

Antiproliferative Activity of 8-methoxy Ciprofloxacin-Hydrozone/Acylhydrazone Scaffolds

AIMS

A series of 8-methoxy ciprofloxacin- hydrazone/acylhydrazone hybrids were evaluated for their activity against a panel of cancer cell lines including HepG2 liver cancer cells, MCF-7, doxorubicin- resistant MCF-7 (MCF-7/DOX) breast cancer cells, DU-145 and multidrug-resistant DU145 (MDR DU-145) prostate cancer cells to seek for novel anticancer agents.

BACKGROUND

Ciprofloxacin with excellent pharmacokinetic properties as well as few side effects, is one of the most common used antibacterial agents. Notably, Ciprofloxacin could induce cancer cells apoptosis, and cell cycle arrest at the S/G2 stage. The structure-activity relationship reveals that the introduction of the methoxy group into the C-8 position of the fluoroquinolone moiety has resulted in a greater binding affinity to the binding site, and 8-methoxy ciprofloxacin derivatives have proved a variety of biological activities even against drug-resistant organisms. However, to the best of our current knowledge, there are no studies that have reported the anticancer activity of 8-methoxy ciprofloxacin derivatives so far. Furthermore, many fluoroquinolone-hydrazone/acylhydrazone hybrids possess promising anticancer activity. Thus, it is rational to screen the anticancer activity of 8-methoxy ciprofloxacin derivatives.

OBJECTIVE

To enrich the structure-activity relationship and provide new anticancer candidates for further investigations.

METHODS

The desired 8-methoxy ciprofloxacin-hydrazone/acylhydrazone hybrids 5 and 6 were screened for their in vitro anticancer activity against liver cancer cells HepG2, breast cancer cells MCF-7, MCF7/DOX, prostate cancer cells DU-145 and MDR DU-145 by MTT assay.

RESULTS

Some of 8-methoxy ciprofloxacin-hydrazone hybrids showed potential activity against HepG2, MCF-7, MCF-7/DOX, DU-145 and MDR DU-145 cancer cell lines, low cytotoxicity towards VERO cells and promising inhibitory activity on tubulin polymerization.

CONCLUSION

Compounds 5d and 5f showed promising anticancer activity, low cytotoxicity, and potential tubulin polymerization inhibitory activity, were worthy of investigation. Other: The structure-activity relationship was enriched.

Synthesis and In Vitro Antimycobacterial and Antibacterial Activity of 8-OMe Ciprofloxacin-Hydrozone/Azole Hybrids

A series of novel 8-OMe ciprofloxacin (CPFX)-hydrazone/azole hybrids were designed, synthesized, and evaluated for their in vitro biological activities. Our results reveal that all of the hydrozone-containing hybrids (except for 7) show potency against Mycobacterium tuberculosis (MTB) H₃₇Rv (minimum inhibitory concentration (MIC): <0.5 μM), which is better than the parent drug CPFX, and comparable to moxifloxacin and isoniazid, some of the tested Gram-positive strains (MIC: 0.06-4 μg/mL), and most Gram-negative strains (MIC: ≤0.03-4 μg/mL).

Azide-alkyne cycloaddition towards 1H-1,2,3-triazole-tethered gatifloxacin and isatin conjugates: Design, synthesis and in vitro anti-mycobacterial evaluation

Twelve novel 1H-1,2,3-triazole-tethered gatifloxacin (GTFX) isatin conjugates 5a-l with greater lipophilicity compared with GTFX were designed, synthesized and evaluated for their in vitro anti-mycobacterial activities against M. tuberculosis (MTB) H₃₇Rv and MDR-TB as well as cytotoxicity. The preliminary results showed that all the targets (MIC: 0.10-8 μg/mL) exhibited excellent inhibitory activity against MTB H₃₇Rv and MDR-TB, but eight of them (CC₅₀: 7.8-62.5 μg/mL) were much more toxic than the parent GTFX (CC₅₀: 125 μg/mL). Among them, 5g (MIC: 0.10 μg/mL) was 4-8 times more potent in vitro than the references GTFX (MIC: 0.78 μg/mL) and RIF (MIC: 0.39 μg/mL) against MTB H₃₇Rv, but less active than INH (MIC: 0.05 μg/mL). The most potent 5g and 5h (MIC: 0.25 μg/mL) were 4->512 times more active than the three references (MIC: 1.0->128 μg/mL) against MDR-TB. Unfortunately, both of the two hybrids (CC₅₀: 7.8 μg/mL) were much more cytotoxic than the other derivatives, need to be further optimized.

Emerging drugs and drug targets against tuberculosis

Mycobacterium tuberculosis (M. tuberculosis), the causative agent of tuberculosis, uses various tactics to resist on antibiotics and evade host immunity. To control tuberculosis, antibiotics with novel mechanisms of action are urgently needed. Emerging new antibiotics and underlying novel drug targets are summarized in this paper.

Moxifloxacin Improves Treatment Outcomes in Patients with Ofloxacin-Resistant Multidrug-Resistant Tuberculosis

It is unclear whether the use of moxifloxacin (MFX), a newer synthetic fluoroquinolone, results in better outcomes in patients with ofloxacin (OFX)-resistant multidrug-resistant tuberculosis (MDR-TB). During the period from April 2006 to December 2013, a total of 2,511 patients with culture-confirmed tuberculosis (TB) were treated at a TB referral hospital in southern Taiwan. Of the 2,511 patients, 325 (12.9%) had MDR-TB, and of those 325 patients, 81 (24.9%) had OFX-resistant MDR-TB and were included in the study. Among the 81 patients with OFX-resistant MDR-TB, 50 (61.7%) were successfully treated and 31 (38.3%) had unfavorable outcomes, including treatment failure (n = 25; 30.9%), loss to follow-up (n = 2; 2.5%), and death (n = 4; 4.9%). Patients treated with MFX had a significantly higher rate of treatment success (77.3% versus 43.2%; odds ratio [OR] = 4.46, 95% confidence interval [CI] = 1.710 to 11.646, P = 0.002) than patients not treated with MFX, especially among those infected with MFX-susceptible isolates (40.7%) or isolates with low-level resistance to MFX (28.4%). Multivariate logistic regression analysis showed that treatment with MFX (adjusted odds ratio = 6.54, 95% CI = 1.44 to 29.59, P = 0.015) was the only independent factor associated with treatment success. Mutation at codon 94 in the gyrA gene was the most frequent mutation (68.0%) associated with high-level MFX resistance. Multivariate Cox proportional hazards regression analysis showed that treatment with MFX was also an independent factor associated with early culture conversion (hazard ratio = 3.12, 95% CI = 1.48 to 6.54, P = 0.003). Our results show that a significant proportion of OFX-resistant MDR-TB isolates were susceptible or had low-level resistance to MFX, indicating that patients with OFX-resistant MDR-TB benefit from treatment with MFX.

Fluoroquinolone interactions with Mycobacterium tuberculosis gyrase: Enhancing drug activity against wild-type and resistant gyrase

Mycobacterium tuberculosis is a significant source of global morbidity and mortality. Moxifloxacin and other fluoroquinolones are important therapeutic agents for the treatment of tuberculosis, particularly multidrug-resistant infections. To guide the development of new quinolone-based agents, it is critical to understand the basis of drug action against M. tuberculosis gyrase and how mutations in the enzyme cause resistance. Therefore, we characterized interactions of fluoroquinolones and related drugs with WT gyrase and enzymes carrying mutations at GyrA(A90) and GyrA(D94). M. tuberculosis gyrase lacks a conserved serine that anchors a water-metal ion bridge that is critical for quinolone interactions with other bacterial type II topoisomerases. Despite the fact that the serine is replaced by an alanine (i.e., GyrA(A90)) in M. tuberculosis gyrase, the bridge still forms and plays a functional role in mediating quinolone-gyrase interactions. Clinically relevant mutations at GyrA(A90) and GyrA(D94) cause quinolone resistance by disrupting the bridge-enzyme interaction, thereby decreasing drug affinity. Fluoroquinolone activity against WT and resistant enzymes is enhanced by the introduction of specific groups at the C7 and C8 positions. By dissecting fluoroquinolone-enzyme interactions, we determined that an 8-methyl-moxifloxacin derivative induces high levels of stable cleavage complexes with WT gyrase and two common resistant enzymes, GyrA(A90V) and GyrA(D94G). 8-Methyl-moxifloxacin was more potent than moxifloxacin against WT M. tuberculosis gyrase and displayed higher activity against the mutant enzymes than moxifloxacin did against WT gyrase. This chemical biology approach to defining drug-enzyme interactions has the potential to identify novel drugs with improved activity against tuberculosis.

Levofloxacin: update and perspectives on one of the original ‘respiratory quinolones’

The fluoroquinolone class of antimicrobials has enjoyed enormous clinical and marketing success over the past 20 years. These drugs have proven to be extremely useful in a broad range of clinical indications including both common community-acquired as well as nosocomial bacterial infections. Levofloxacin (Levaquin, Tavanic), like ciprofloxacin (Cipro), has established an enviable record of safe and efficacious use, and in many ways has become the agent against which all of the newer fluoroquinolones are judged. New clinical indications in complicated skin and skin structure infections, nosocomial pneumonia and chronic bacterial prostatitis continue to expand the important role of this already versatile drug. In addition, the use of 'short-course, high-dose' therapies are being studied in indications, such as community-acquired pneumonia, in an effort to optimize the efficacy and convenience of the drug while minimizing the future development of resistance. As the use of levofloxacin continues to expand, future challenges will include the threat of increasing antimicrobial resistance and the availability of newer alternative agents, both newer fluoroquinolones as well as agents of other antibiotic classes.

Analysis of mutations in the gyrA and gyrB genes and their association with the resistance of Mycobacterium tuberculosis to levofloxacin, moxifloxacin and gatifloxacin

The purpose of the present study was to analyse mutations in the gyrA and gyrB genes of Mycobacterium tuberculosis and define the possible correlation between these mutations and resistance to levofloxacin (LVX), moxifloxacin (MFX) and gatifloxacin (GAT), based on their MICs. One hundred and forty-two M. tuberculosis clinical isolates were collected from pulmonary tuberculosis patients in the Moscow region. All M. tuberculosis strains were tested for drug susceptibility to rifampicin and isoniazid using the BACTEC MGIT 960 System and to ofloxacin (OFX) using the absolute concentration method on solid Lowenstein-Jensen slants. All in all, 68 strains were selected at random (38 strains were resistant and 30 were susceptible to OFX) for further analysis using the TB-BIOCHIP-2 test system and DNA sequence analysis. The MICs of LVX, MFX and GAT for selected strains were determined using the BACTEC MGIT 960 System. Mutations in the gyrA gene were observed in 36 out of 38 (94.7 %) OFX-resistant M. tuberculosis strains. Asn538Asp and Asp500His substitutions in the gyrB gene only were found in two (5.3 %) strains. Twenty-nine out of 30 OFX-sensitive M. tuberculosis strains had no mutations in either gene. One (3.3 %) OFX-sensitive M. tuberculosis strain carried an Arg485His substitution in gyrB. The results of our investigation showed that there is no clear correlation between the type of mutation in the genes gyrA and gyrB, and the MIC levels of LVX, MFX and GAT for resistant strains. Mutations in gyrA and Asn538Asp, and Asp500His substitutions in gyrB were associated with cross-resistance of M. tuberculosis to fluoroquinolones. The substitution Arg485His in gyrB does not confer resistance to LVX, MFX and GAT in M. tuberculosis.

Fluoroquinolone resistance in Mycobacterium tuberculosis: an assessment of MGIT 960, MODS and nitrate reductase assay and fluoroquinolone cross-resistance

OBJECTIVES

The aim of this study was to assess the sensitivity, specificity and time to results of mycobacterial growth indicator tube (MGIT) 960, microscopic observation drug susceptibility (MODS) assay and nitrate reductase assay (NRA) compared with the gold standard agar proportion method (PM), and to determine whether there is cross-resistance between older-generation fluoroquinolones and moxifloxacin.

METHODS

Mycobacterium tuberculosis isolates from culture-confirmed tuberculosis patients from 2002 to 2007 were tested for ofloxacin (2 mg/L) resistance by PM and MGIT 960. All isolates from 2005 and 2006 were also tested by MODS and NRA. Ofloxacin-resistant isolates by PM were further tested by all four methods using ciprofloxacin, levofloxacin and moxifloxacin. For each ofloxacin-resistant isolate, two ofloxacin-susceptible isolates were tested against all three fluoroquinolones using all four methods.

RESULTS

Of the 797 M. tuberculosis isolates, 19 (2.4%) were ofloxacin-resistant by PM. MGIT 960 had 100% sensitivity (95% CI, 83%-100%) and specificity (95% CI, 99.5%-100%). Of the 797 isolates, 239 were from 2005 to 2006 and 6 of these (2.5%) were resistant by PM. MODS had 100% sensitivity (95% CI, 61%-100%) and specificity (95% CI, 98%-100%). NRA had 100% sensitivity (95% CI, 61%-100%) and 98.7% specificity (95% CI, 96%-99.6%). The median time to results was shorter using MGIT 960 (8 days), MODS (6 days) or NRA (9 days) compared with PM (21 days) (P < 0.001). All 19 ofloxacin-resistant isolates were resistant to ciprofloxacin, levofloxacin and moxifloxacin by PM.

CONCLUSIONS

MGIT 960, MODS and NRA are sensitive and specific and more rapid than PM for identifying fluoroquinolone resistance in M. tuberculosis. Ofloxacin resistance was associated with cross-resistance to ciprofloxacin, levofloxacin and moxifloxacin.

Importance of the efflux pump systems in the resistance of Mycobacterium tuberculosis to fluoroquinolones and linezolid

OBJECTIVE

Our aim was to study the influence of efflux pump systems in the resistance of Mycobacterium tuberculosis to fluoroquinolones and linezolid.

METHODS

We studied the mutations in gyrA and gyrB genes and the influence of efflux pump systems with 2 inhibitors (reserpine and MC 207.110).

RESULTS

The effect of the active efflux system on the decrease in sensitivity to ciprofloxacin, moxifloxacin, levofloxacin, ofloxacin, gatifloxacin and linezolid was studied by investigating the variation in the in vitro activity of these compounds when assayed in association with reserpine and MC 207.110. These inhibitors exhibit activity both in strains that are resistant and in strains that are susceptible to these antibiotics. However, they are seen to be most active in resistant strains, since the minimum inhibitory concentration of the antibiotics studied in these strains was reduced between 2- and 6-fold.

CONCLUSIONS

Therefore, these mechanisms are involved in the resistance to both compounds. It would be of interest to carry out further studies to determine to what extent these active efflux systems influence resistance to the different groups of drugs used in the treatment of tuberculosis, with a view to the possibility of using the inhibitors of these systems in future therapeutic applications.

Synthesis and antitubercular activity of lipophilic moxifloxacin and gatifloxacin derivatives

Fluoroquinolone (FQ) has a broad spectrum of activity against several bacteria, mycobacteria, parasites, and other diseases. Moxifloxacin and gatifloxacin are a new generation of fluoroquinolone agents with improved activity against Gram-negative and positive bacteria. As lipophilicity is an important consideration in the design and activity of novel antibacterial agents, we report in this work the synthesis and biological evaluation of 12 lipophilic moxifloxacin or gatifloxacin derivatives, by reaction of 1-cyclopropyl-6,7-difluoro-1,4-dihydro-8-methoxy-4-oxoquinoline-3-carboxylic acid 13 with several N-monoalkyl 1,2-ethanediamine or 1,3-propanediamine.

Susceptibility Testing of Clinical Isolates of Pseudomonas aeruginosa to Levofloxacin, Moxifloxacin, and Gatifloxacin as a Guide to Treating Pseudomonas Ocular Infections

PURPOSE

Pseudomonas aeruginosa ocular infections most frequently originate from an environmental source; successful treatment with various ocular antibiotics is well established. However, emergence of resistant clones to available antibiotics poses a real threat to successful treatment. The purpose of this study was to evaluate the antibiotic susceptibilities of 100 random clinical isolates of P. aeruginosa to levofloxacin, moxifloxacin, and gatifloxacin, potential agents for the treatment of ocular infections caused by this microorganism.

METHODS

One hundred consecutive strains of P. aeruginosa were isolated from clinical specimens submitted to the clinical microbiology hospital laboratory. Duplicate isolates were not included. The minimum inhibitory concentrations (MICs) of these isolates were determined by using Etests, performed according to the manufacturer's instructions. American Type Culture Collection (ATCC) strains of Escherichia coli, P. aeruginosa, and Staphylococcus aureus served as reference controls.

RESULTS

Although most isolates were susceptible to levofloxacin, moxifloxacin, and gatifloxacin and the MICs were not significantly different, significant numbers were resistant. The standardized controls rendered expected MICs. The susceptibility of the isolates varied with regard to source, and resistant strains showed increased resistance.

CONCLUSIONS

Based on the data, the treatment of ocular infections caused by P. aeruginosa with levofloxacin, moxifloxacin, and gatifloxacin still has a high likelihood of success. However, six of the isolates collected were resistant to all three of the fluoroquinolones tested. Based on the data, clinicians must be aware that clinical resistance can occur even with the newer fluoroquinolones.

Activity of RBx 7644 and RBx 8700, new investigational oxazolidinones, against Mycobacterium tuberculosis infected murine macrophages

The decision to develop a new chemical entity should not only be based on its ability to inhibit multidrug-resistant tuberculosis (MDR-TB) strains but also on its ability to enter macrophages and be active against intracellular bacteria. RBx 7644 and RBx 8700, two novel extended spectrum oxazolidinones, were investigated for their activity against sensitive and MDR isolates of Mycobacterium tuberculosis and for activity against bacteria within a macrophage cell line. RBx 8700 showed excellent in vitro activity against sensitive as well as MDR M. tuberculosis strains with MIC(50) and MIC(90) values of 0.032 and 0.25mg/L (sensitive) and 0.25 and 1.0mg/L (MDR) strains. The corresponding MIC(50) and MIC(90) values of RBx 7644, linezolid, rifampicin and isoniazid were 8 and 16; 32 and 64; 64 and 64; 64 and 64 mg/L, respectively. RBx 8700 and rifampicin were bactericidal at 0.5 and 0.25mg/L when tested intracellularly whereas linezolid reduced the count by 100-fold at a concentration of 8 mg/L. In combination studies with standard antimycobacterial drugs, RBx 8700 did not show any antagonistic effect.

Which agents should we use for the treatment of multidrug-resistant Mycobacterium tuberculosis?

The inappropriate treatment of drug-susceptible tuberculosis can lead to the selection and transmission of multidrug-resistant tuberculosis (MDR-TB), indicating resistance to at least isoniazid and rifampicin. In the treatment of MDR-TB, residual first-line drugs, such as ethambutol, pyrazinamide and streptomycin must be appropriately combined with additional second-line drugs, guided by individual susceptibility patterns. The clinical pharmacology of these second-line antituberculous drugs is reviewed. Fluoroquinolones represent the only substantial therapeutic advance in the last 20 years. Many factors potentially affect the outcome of MDR-TB. Treatment adherence, prior exposure to antituberculous drugs, the number of drugs to which the infection is still susceptible and the time since the first diagnosis of tuberculosis are the most relevant. The management of MDR-TB requires considerable expertise. When initiating or revising therapy for MDR-TB, the process of selecting drugs should rely on prior treatment history, results of susceptibility testing and an evaluation of the patient's adherence. In making drug selection, we propose to follow a hierarchy based on the intrinsic activity against Mycobacterium tuberculosis and the clinical evidence of efficacy of the available active compounds.

In vitro activities of mutant prevention concentration-targeted concentrations of fluoroquinolones against Staphylococcus aureus in a pharmacodynamic model

To test the validity of the mutant selection window, we simulated mutant prevention concentration-targeted fluoroquinolone concentrations using an in vitro model with infected fibrin clots. Therapeutic ciprofloxacin (peak 5 microg/mL; t(1/2) 4 h), gatifloxacin (3.5 microg/mL; 8h), gemifloxacin (1.25 microg/mL; 8 h), levofloxacin (6 microg/mL; 6 h) and moxifloxacin (4.5 microg/mL; 12 h) were tested against methicillin-susceptible and -resistant Staphylococcus aureus, as were mutant prevention concentration (MPC)-targeted regimens achieving a trough of 1/4x or 2x MPC. MIC/MPC for MSSA K553 were 0.125/2, 0.03/0.125, 0.03/0.063, 0.125/1 and 0.015/0.25 microg/mL for ciprofloxacin, gatifloxacin, gemifloxacin, levofloxacin and moxifloxacin, respectively. Corresponding values for MRSA 494 were 0.125/1, 0.063/0.125, 0.03/0.063, 0.125/0.5 and 0.063/0.125 microg/mL. All regimens produced efflux mutants of MSSA K553. For MRSA 494, therapeutic and 1/4x MPC levofloxacin regimens produced resistance, whereas only 1/4x MPC regimens of gatifloxacin, gemifloxacin, and moxifloxacin produced resistance. All ciprofloxacin regimens produced resistance. Ciprofloxacin 1/4x MPC and therapeutic levofloxacin caused outgrowth of GrlA mutants (S80Y amino acid substitution); efflux mutants were isolated in all other cases. Overall, gatifloxacin, gemifloxacin, and moxifloxacin displayed a lesser propensity to select resistant isolates of S. aureus than ciprofloxacin and levofloxacin. The mutant selection window premise appeared valid for MRSA only. Additional studies are necessary to define the applicability of the MPC.

Treatment and Outcome Analysis of 205 Patients with Multidrug-resistant Tuberculosis

Multidrug-resistant tuberculosis, a disease caused by Mycobacterium tuberculosis strains that are resistant at least to rifampin and isoniazid, entails extended treatment, expensive and toxic regimens, and higher rates of treatment failure and death. We retrospectively analyzed the outcomes in 205 patients treated at our center for multidrug-resistant tuberculosis, with strains resistant to a median of six drugs, and compared the results with those of our previous series. Logistic regression and survival analysis were used to evaluate short- and long-term outcomes, respectively. Initial favorable response, defined as at least three consecutive negative sputum cultures over a period of at least 3 months, was 85% compared with 65% in the prior cohort. The current cohort had greater long-term success rates, 75% versus 56%, and lower tuberculosis death rates, 12% versus 22%, than the earlier one. Surgical resection and fluoroquinolone therapy were associated with improved microbiological and clinical outcomes in the 205 patients studied after adjusting for other variables. The improvement was statistically significant for surgery and among older patients for fluoroquinolone therapy.

Multiplex PCR amplimer conformation analysis for rapid detection of gyrA mutations in fluoroquinolone-resistant Mycobacterium tuberculosis clinical isolates

A new strategy known as multiplex PCR amplimer conformation was developed for detection of mutation in the gyrA gene of 138 clinical isolates of Mycobacterium tuberculosis. The method generated a single-stranded and heteroduplex DNA banding pattern of multiplex PCR amplimers of the region of interest that was extremely sensitive to specific mutations, thus enabling much more sensitive and reliable mutation analysis compared to the standard single-stranded conformation polymorphism technique. The genetic profiles of the gyrA gene of the 138 isolates as detected by MPAC were confirmed by nucleotide sequencing and were found to correlate strongly with the in vitro susceptibilities of the mutant strains to six fluoroquinolones (ofloxacin, levofloxacin, sparfloxacin, moxifloxacin, gatifloxacin, and sitafloxacin). All 32 isolates that contained gyrA mutations exhibited cross-resistance to the six fluoroquinolones (ofloxacin MIC for 90% of strains > 16 mg/liter), although moxifloxacin, gatifloxacin, and sitafloxacin (MIC for 90% of strains </= 4 mg/liter) were apparently more active than ofloxacin, levofloxacin, and sparfloxacin (MIC for 90% of strains >/==" BORDER="0"> 16 mg/liter). All gyrA mutations were clustered in codons 90, 91, and 94, and aspartic acid 94 was most frequently mutated. Twenty-three isolates without gyrA mutations were also found to exhibit reduced susceptibility to ofloxacin (MIC for 90% of strains = 4 mg/liter), but largely remained susceptible to other drugs (MIC for 90% of strains </= 1 mg/liter). Another 83 isolates without mutations were fully susceptible to all six fluoroquinolones (ofloxacin MIC for 90% of strains = 1 mg/liter). In conclusion, high-level phenotypic resistance to fluoroquinolones among M. tuberculosis clinical isolates, which appears to be predominantly due to gyrA mutations, may be readily detected by genotyping techniques such as multiplex PCR amplimer conformation.

Posttranscriptional Inhibition of Gene Expression byMycobacterium tuberculosisOffsets Transcriptional Synergism with IFN-γ and Posttranscriptional Up-Regulation by IFN-γ

Host defense against Mycobacterium tuberculosis requires the cytokine IFN-gamma and IFN regulatory factor 1 (IRF-1), a transcription factor that is induced to high levels by IFN-gamma. Therefore, we chose to study regulation of IRF-1 expression as a model for effects of M. tuberculosis on response to IFN-gamma. We found that IRF-1 mRNA abundance increased far more than transcription rate in human monocytic THP-1 cells stimulated by IFN-gamma, but less than transcription rate in cells infected by M. tuberculosis. IFN-gamma stimulation of infected cells caused a synergistic increase in IRF-1 transcription, yet IRF-1 mRNA abundance was similar in uninfected and infected cells stimulated by IFN-gamma, as was the IRF-1 protein level. Comparable infection by Mycobacterium bovis bacillus Calmette-Guérin failed to induce IRF-1 expression and had no effect on the response to IFN-gamma. We also examined the kinetics of transcription, the mRNA t(1/2), and the distribution of IRF-1 transcripts among total nuclear RNA, poly(A) nuclear RNA, and poly(A) cytoplasmic RNA pools in cells that were infected by M. tuberculosis and/or stimulated by IFN-gamma. Our data suggest that infection by M. tuberculosis inhibits RNA export from the nucleus. Moreover, the results indicate that regulated entry of nascent transcripts into the pool of total nuclear RNA affects IRF-1 expression and that this process is stimulated by IFN-gamma and inhibited by M. tuberculosis. The ability of infection by M. tuberculosis to limit the increase in IRF-1 mRNA expression that typically follows transcriptional synergism may contribute to the pathogenicity of M. tuberculosis.

Activities of mutant prevention concentration-targeted moxifloxacin and levofloxacin against Streptococcus pneumoniae in an in vitro pharmacodynamic model

The differential effects of moxifloxacin and levofloxacin on the development of resistance in four Streptococcus pneumoniae isolates were examined by using an in vitro pharmacodynamic model. Therapeutic regimens (moxifloxacin: peak, 4.5 micro g/ml; half-life [t(1/2)], 12 h; and levofloxacin: peak, 6 micro g/ml; t(1/2), 6 h) were tested against two fluoroquinolone-susceptible isolates (strains 79 and ATCC 49619) and KD2138 and KD2139 (parC and gyrA mutants, respectively, of ATCC 49619). Mutant prevention concentration (MPC)-targeted regimens with modified pharmacokinetics of each drug were simulated to match the area under the concentration-time curve (AUC) above the MPC for the two fluoroquinolones. Moxifloxacin MICs and MPCs (MIC/MPC) for isolates 79, ATCC 49619, KD2138, and KD2139, respectively, were 0.125 and 0.5, 0.125 and 0.5, 0.25 and 8, and 0.25 and 4 micro g/ml. Levofloxacin MICs and MPCs for the same isolates were 1 and 4, 0.5 and 2, 1 and 64, and 0.5 and 32 micro g/ml, respectively. Therapeutic levofloxacin concentrations led to isolation of mutants of ATCC 49619 (S79Y in ParC), KD2138 (S81Y in GyrA), and KD2139 (S79Y in ParC). Therapeutic moxifloxacin concentrations against the gyrA mutant KD2139 resulted in outgrowth of a mutant with a ParC substitution (S79Y) but caused no emergence of mutants of the other three isolates. MPC-targeted moxifloxacin (lower-than-normal peak = 0.75 to 1.5 micro g/ml, administered at levofloxacin's t(1/2)) caused growth of a GyrA variant (S81Y) of KD2138 and a ParC variant (S79Y) of KD2139, while no mutants of ATCC 49619 were recovered. MPC-targeted levofloxacin (higher-than-normal peak = 14.5 to 29.5 micro g/ml, administered at moxifloxacin's t(1/2)) against KD2138 and KD2139 did not prevent the development of the mutations observed in therapeutic regimens, but resistance in the fluoroquinolone-susceptible ATCC 49619 was no longer noted. Normalization of the respective AUC/MPC ratios of moxifloxacin and levofloxacin did not eliminate differences in resistance selectivity of the two agents in all cases. We conclude that the reduced recovery of resistant mutants of S. pneumoniae following moxifloxacin exposure compared to levofloxacin may be due to intrinsic differences between the drugs. Increasing the concentration and exposure (t(1/2)) to exceed the MPC may prevent mutations from occurring in fluoroquinolone-susceptible strains. However, this strategy did not prevent the selection of secondary mutants in strains with preexisting mutations. Further study of the MPC concept to evaluate these relationships is warranted.

Inhibition of response to alpha interferon by Mycobacterium tuberculosis

We previously reported that infection by Mycobacterium tuberculosis, the causative agent of tuberculosis, leads to secretion of alpha/beta interferon (IFN-alpha/beta). While IFN-alpha/beta ordinarily stimulates formation of signal transducer and stimulator of transcription-1 (STAT-1) homodimers and IFN-stimulated gene factor-3 (ISGF-3), only ISGF-3 is found in infected human monocytes and macrophages. We have now investigated the basis for this unusual profile of transcription factor activation and its consequences for regulation of transcription, as well as the impact of infection on response to IFN-alpha. After infection, IFN-alpha stimulation of STAT-1 homodimers is inhibited in monocytes and macrophages, while stimulation of ISGF-3 increases in monocytes but tends to decline in macrophages. Effects of infection on the abundance of ISGF-3 subunits, STAT-1, STAT-2, and interferon regulatory factor 9, and on tyrosine phosphorylation of STAT-1 and STAT-2 explain the observed changes in DNA-binding activity, which correlate with increased or inhibited transcription of genes regulated by ISGF-3 and STAT-1. Infection by Mycobacterium bovis BCG does not inhibit IFN-alpha-stimulated tyrosine phosphorylation of STAT-1, formation of homodimers, or transcription of genes regulated by STAT-1 homodimers, suggesting that inhibition of the response to IFN-alpha/beta by M. tuberculosis is an aspect of pathogenicity. Thus, this well-known feature of infection by pathogenic viruses may also be a strategy employed by pathogenic bacteria.

Synergic activity of fluoroquinolones and linezolid against Mycobacterium tuberculosis

We evaluated the in vitro activity against Mycobacterium tuberculosis of the combination of fluoroquinolones and linezolid with classical drugs. The combination of isoniazid with fluoroquinolones had synergic activity in nine of the ten isoniazid-susceptible strains. We also found synergism between rifampicin and linezolid in five of the 15 strains susceptible to rifampicin. The clinical significance of these findings should be evaluated.

Contribution of the 8-methoxy group to the activity of gatifloxacin against type II topoisomerases of Streptococcus pneumoniae

The inhibitory activities (50% inhibitory concentrations [IC(50)s]) of gatifloxacin and other quinolones against both DNA gyrase and topoisomerase IV of the wild-type Streptococcus pneumoniae IID553 were determined. The IC(50)s of 10 compounds ranged from 4.28 to 582 microg/ml against DNA gyrase and from 1.90 to 35.2 microg/ml against topoisomerase IV. The inhibitory activity against DNA gyrase was more varied than that against topoisomerase IV among fluoroquinolones. The IC(50)s for DNA gyrase of the 8-methoxy quinolones gatifloxacin and AM-1147 were approximately seven times lower than those of their 8-H counterparts AM-1121 and ciprofloxacin, whereas the IC(50)s for topoisomerase IV were 1.5 times lower. Moreover, the IC(50) ratios (IC(50) for DNA gyrase/IC(50) for topoisomerase IV) of gatifloxacin, AM-1147, and moxifloxacin, which possess 8-methoxy groups, were almost the same. The 8-methoxy quinolones showed higher antibacterial activity and less mutant selectivity against IID553 than their 8-H counterparts. These results suggest that the 8-methoxy group enhances both target inhibition, especially for DNA gyrase, leading to potent antipneumococcal activity and dual inhibition against both DNA gyrase and topoisomerase IV in the bacterial cell.

In vitro activity of moxifloxacin, levofloxacin, gatifloxacin and linezolid against Mycobacterium tuberculosis

The in vitro activity of moxifloxacin, gatifloxacin, levofloxacin and linezolid was evaluated against 234 strains of Mycobacterium tuberculosis isolated in the Southeast of Spain. All drugs tested showed good activity, with an MIC(90) of less than 1 mg/l, and were active against isociacide and rifampicin resistant strains. Three strains were resistant to isoniazid and to the fluoroquinolones, which suggested the existence of mechanisms of resistance not yet described. These new compounds may prove to be therapeutic alternatives for treatment of multi-resistant tuberculosis and further studies should be done to demonstrate their true usefulness.

Dual targeting of DNA gyrase and topoisomerase IV: target interactions of garenoxacin (BMS-284756, T-3811ME), a new desfluoroquinolone

We determined the target enzyme interactions of garenoxacin (BMS-284756, T-3811ME), a novel desfluoroquinolone, in Staphylococcus aureus by genetic and biochemical studies. We found garenoxacin to be four- to eightfold more active than ciprofloxacin against wild-type S. aureus. A single topoisomerase IV or gyrase mutation caused only a 2- to 4-fold increase in the MIC of garenoxacin, whereas a combination of mutations in both loci caused a substantial increase (128-fold). Overexpression of the NorA efflux pump had minimal effect on resistance to garenoxacin. With garenoxacin at twice the MIC, selection of resistant mutants (<7.4 x 10(-12) to 4.0 x 10(-11)) was 5 to 6 log units less than that with ciprofloxacin. Mutations inside or outside the quinolone resistance-determining regions (QRDR) of either topoisomerase IV, or gyrase, or both were selected in single-step mutants, suggesting dual targeting of topoisomerase IV and gyrase. Three of the novel mutations were shown by genetic experiments to be responsible for resistance. Studies with purified topoisomerase IV and gyrase from S. aureus also showed that garenoxacin had similar activity against topoisomerase IV and gyrase (50% inhibitory concentration, 1.25 to 2.5 and 1.25 micro g/ml, respectively), and although its activity against topoisomerase IV was 2-fold greater than that of ciprofloxacin, its activity against gyrase was 10-fold greater. This study provides the first genetic and biochemical data supporting the dual targeting of topoisomerase IV and gyrase in S. aureus by a quinolone as well as providing genetic proof for the expansion of the QRDRs to include the 5' terminus of grlB and the 3' terminus of gyrA.

Synthesis of variously substituted 1,8-naphthyridine derivatives and evaluation of their antimycobacterial activity

A series of 1,8-naphthyridine derivatives variously substituted in the 2, 3, 4 and 7 positions were synthesized for in vitro evaluation of antimycobacterial activity in accordance with an international program with the tuberculosis antimicrobial acquisition and coordinating facility (TAACF). Several compounds 4, 8, 12, 14, 19, 29 and 30, when tested at a concentration of 6.25 microg/ml against Mycobacterium tuberculosis H37Rv, showed an interesting activity with % inhibition in the range 38-96%. The most effective substituent in position 2, 4 or 7 of the 1,8-naphthyridine nucleus seem to be the piperidinyl group.

Host defense responses to infection by Mycobacterium tuberculosis. Induction of IRF-1 and a serine protease inhibitor

Alveolar macrophages and newly recruited monocytes are targets of infection by Mycobacterium tuberculosis. Therefore, we examined the expression of interferon regulatory factor 1 (IRF-1), which plays an important role in host defense against M. tuberculosis, in undifferentiated and differentiated cells. Infection induced IRF-1 in both. IRF-1 from undifferentiated, uninfected monocytic cell lines was modified during extraction to produce specific species that were apparently smaller than intact IRF-1. After infection by M. tuberculosis or differentiation, intact IRF-1 was recovered. Subcellular fractions were assayed for the ability to modify IRF-1 or inhibit its modification. A serine protease on the cytoplasmic surface of an organelle or vesicle in the "lysosomal/mitochondrial" fraction from undifferentiated cells was responsible for the modification of IRF-1. Thus, the simplest explanation of the modification is cleavage of IRF-1 by the serine protease. Recovery of intact IRF-1 correlated with induction of a serine protease inhibitor that was able to significantly reduce the modification of IRF-1. The inhibitor was present in the cytoplasm of M. tuberculosis-infected or -differentiated cells. It is likely that induction of both IRF-1 and the serine protease inhibitor in response to infection by M. tuberculosis represent host defense mechanisms.

In vitro and in vivo activities of gatifloxacin against Mycobacterium tuberculosis

Gatifloxacin (GAT) and moxifloxacin (MXF) were evaluated in vitro to determine their activities against Mycobacterium tuberculosis. GAT was subsequently compared in a dose range study to isoniazid (INH) in a murine tuberculosis model. GAT was somewhat less active than INH. GAT and MXF were evaluated in mice infected with M. tuberculosis and were found to have similar activities. GAT was studied alone and in combination with ethambutol, ethionamide (ETA), and pyrazinamide (PZA) and compared to INH and rifampin (RIF). GAT appears to have sufficient activity alone and in combination with ETA with or without PZA to merit evaluation for treatment of tuberculosis.

Anti-Mycobacterium tuberculosis activities of new fluoroquinolones in combination with other antituberculous drugs

OBJECTIVES

Studies were undertaken in order to assess the anti- Mycobacterium tuberculosis (MTB) activities of newly developed fluoroquinolones in combination with other antituberculous drugs.

METHODS

A new C-8-methoxyl fluoroquinolone, gatifloxacin (GFLX), and a new C-8-chloro fluoroquinolone, sitafloxacin (STFX), in combination with other drugs were examined for their activities against extracellular growing MTB organisms and those replicating in RAW264.7 macrophages (RAW-M phis s).

RESULTS

STFX but not GFLX potentiated the activities of rifampin and rifalazil against extracellular MTB. Both GFLX and STFX exhibited combined activities against intramacrophage MTB, when used in combination with rifampin, rifalazil, isoniazid, pyrazinamide, ethambutol, streptomycin, or clofazimine.

CONCLUSIONS

Although the observed combined effects varied to some extent from case to case depending on drug combinations, the present findings suggest the usefulness of these new fluoroquinolones in multi-drug regimens for tuberculosis patients.

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.

Antimicrobial activities of clarithromycin, gatifloxacin and sitafloxacin, in combination with various antimycobacterial drugs against extracellular and intramacrophage Mycobacterium avium complex

We studied the activities of clarithromycin and fluoroquinolones (gatifloxacin, sitafloxacin, levofloxacin) in combination with other antimycobacterial drugs against extracellular and intramacrophage Mycobacterium avium complex (MAC). Clarithromycin potentiated the activities of rifampicin and rifalazil against both extracellular and intramacrophage MAC. In contrast, all the test quinolones exhibited antagonistic effects against extracellular MAC when combined with either clarithromycin or rifamycins. Such an antagonism was not observed for the activity of these combinations against intramacrophage MAC. Combined effects were observed with combinations of these fluoroquinolones with either ethambutol or streptomycin. Similar profiles were seen for the activities of two-drug combinations of clarithromycin or fluoroquinolones with other drugs against intramacrophage MAC isolated from pulmonary and disseminated MAC infections.

Selection of Streptococcus pneumoniae mutants having reduced susceptibility to moxifloxacin and levofloxacin

With Streptococcus pneumoniae, moxifloxacin was 4- and 10-fold more effective than levofloxacin at restricting selection of resistant mutants and at killing resistant mutants, respectively. The selection frequency for first-step topoisomerase mutants was 1,000 times lower for moxifloxacin than for levofloxacin; this difference was lost when second-step mutants were selected.

Fluoroquinolones: place in ocular therapy

The fluoroquinolones have become widely used antibacterial agents in the treatment of ocular infections, with topical, intravitreal and systemic routes of administration being used. In general, fluoroquinolones (such as ciprofloxacin, ofloxacin, lomefloxacin and norfloxacin) have good activity against gram-negative and gram-positive bacteria. Therapeutic concentrations are achieved in the cornea after topical administration so that the fluoroqinolones have largely replaced combination therapy for the treatment of bacterial keratitis. However, a second line agent is needed when resistance is likely, such as in disease caused by streptococcal species. Reversal of resistance to quinolones may not occur with withdrawal of the antibacterial. This stresses the importance of prudent prescribing to reduce the occurrence of resistance to quinolones. When used in therapeutic topical dosages, corneal toxicity does not occur. Similarly, retinal toxicity is not seen when fluoroquinolones are used at therapeutic dosages, systemically or topically. Corneal precipitation occurs, particularly with ciprofloxacin and to a lesser extent norfloxacin, but does not appear to interfere with healing. In the treatment of endophthalmitis there is reasonable penetration of systemic fluoroquinolones into the vitreous but sufficiently high concentrations to reach the minimum inhibitory concentration for 90% of isolates (MIC90) of all important micro-organisms may not be guaranteed. Systemic administration may be useful for prophylaxis after ocular trauma.