WQ-3810: A new fluoroquinolone with a high potential against fluoroquinolone-resistant Mycobacterium tuberculosis

WQ-3810, a fluoroquinolone with difluoropyridine derivative as the R1 group exerts high potency against quinolone-resistant Campylobacter jejuni

Quinolone-resistant Campylobacter jejuni have been increasing worldwide. Quinolones exert their antibacterial activity by inhibiting DNA gyrase, but most of the isolates acquire quinolone resistance via an amino acid substitution in the A subunit of DNA gyrase. WQ-3810 is a quinolone antibiotic that has been reported to have high potency even to DNA gyrase with amino acid substitutions in several bacterial species; however, there was no information on C. jejuni. Hence, this study aimed to evaluate the activity of WQ-3810 to inhibit wild-type/mutant DNA gyrases of C. jejuni and the bacterial growth for accessing the potency for the treatment of quinolone-resistant C. jejuni infection. The inhibitory activity of WQ-3810 was assessed and compared with ciprofloxacin and nalidixic acid by calculating the half maximal inhibitory concentration (IC50) against wild-type/mutant DNA gyrases. Next, the minimum inhibitory concentration (MIC) of WQ-3810 and five other quinolones was determined for C. jejuni including quinolone-resistant strains with amino acid substitutions in GyrA. Furthermore, the interaction between WQ-3810 and wild-type/mutant DNA gyrase was speculated using docking simulations. The IC50 of WQ-3810 against wild-type DNA gyrase was 1.03 µg/mL and not different from that of ciprofloxacin. However, those of WQ-3810 against mutant DNA gyrases were much lower than ciprofloxacin. The MICs of WQ-3810 ranged <0.016-0.031 µg/mL and were the lowest against both quinolone-susceptible and quinolone-resistant strains among the examined quinolones. The results obtained by the docking simulation agreed well with this observation. WQ-3810 seems to be a promising antimicrobial agent for the infections caused by quinolone-resistant C. jejuni.

IMPORTANCE

WQ-3810, a relatively new quinolone antibiotic, demonstrates exceptional antibacterial properties against certain pathogens in previous studies. However, its efficacy against quinolone-resistant Campylobacter jejuni was not previously reported. The prevalence of quinolone-resistant C. jejuni as a cause of foodborne illnesses is increasing, prompting this investigation into the effectiveness of WQ-3810 as a countermeasure. This study revealed high inhibitory activity of WQ-3810 against both wild-type and mutant DNA gyrases of C. jejuni. WQ-3810 was equally efficacious as ciprofloxacin against wild-type DNA gyrases but showed superior effectiveness against mutant DNA gyrases. WQ-3810 also demonstrated the lowest minimum inhibitory concentrations, highlighting its enhanced potency against both susceptible and resistant strains of C. jejuni. This observation was well supported by the results of the in silico analysis. Consequently, WQ-3810 exhibits a higher level of bactericidal activity compared to existing quinolones in combating both susceptible and resistant C. jejuni isolates.

Effect of WQ-3334 on Campylobacter jejuni carrying a DNA gyrase with dominant amino acid substitutions conferring quinolone resistance

INTRODUCTION

Campylobacteriosis stands as one of the most frequent bacterial gastroenteritis worldwide necessitating antibiotic treatment in severe cases and the rise of quinolones-resistant Campylobacter jejuni poses a significant challenge. The predominant mechanism of quinolones-resistance in this bacterium involves point mutations in the gyrA, resulting in amino acid substitution from threonine to isoleucine at 86th position, representing more than 90% of mutant DNA gyrase, and aspartic acid to asparagine at 90th position. WQ-3334, a novel quinolone, has demonstrated strong inhibitory activity against various bacteria. This study aims to investigate the effectiveness of WQ-3334, and its analogues, WQ-4064 and WQ-4065, with a unique modification in R1 against quinolones-resistant C. jejuni.

METHODS

The structure-activity relationship of the examined drugs was investigated by measuring IC50 and their antimicrobial activities were accessed by MIC against C. jejuni strains. Additionally, in silico docking simulations were carried out using the crystal structure of the Escherichia coli DNA gyrase.

RESULT

WQ-3334 exhibited the lowest IC50 against WT (0.188 ± 0.039 mg/L), T86I (11.0 ± 0.7 mg/L) and D90 N (1.60 ± 0.28 mg/L). Notably, DNA gyrases with T86I substitutions displayed the highest IC50 values among the examined WQ compounds. Moreover, WQ-3334 demonstrated the lowest MICs against wild-type and mutant strains. The docking simulations further confirmed the interactions between WQ-3334 and DNA gyrases.

CONCLUSION

WQ-3334 with 6-amino-3,5-difluoropyridine-2-yl at R1 severed as a remarkable candidate for the treatment of foodborne diseases caused by quinolones-resistant C. jejuni as shown by the high inhibitory activity against both wild-type and the predominant quinolones-resistant strains.

The Impact of Substitutions at Positions 1 and 8 of Fluoroquinolones on the Activity Against Mutant DNA Gyrases of Salmonella Typhimurium

Although many drug-resistant nontyphoidal Salmonella (NTS) infections are reported globally, their treatment is challenging owing to the ineffectiveness of the currently available antimicrobial drugs against resistant bacteria. It is therefore essential to discover novel antimicrobial drugs for the management of these infections. In this study, we report high inhibitory activities of the novel fluoroquinolones (FQs; WQ-3810 and WQ-3334) with substitutions at positions R-1 by 6-amino-3,5-difluoropyridine-2-yl and R-8 by methyl group or bromine, respectively, against wild-type and mutant DNA gyrases of Salmonella Typhimurium. The inhibitory activities of these FQs were assessed against seven amino acid substitutions in DNA gyrases conferring FQ resistance to S. Typhimurium, including high-level resistant mutants, Ser83Ile and Ser83Phe-Asp87Asn by in vitro DNA supercoiling assay. Drug concentrations of WQ compounds with 6-amino-3,5-difluoropyridine-2-yl that suppressed DNA supercoiling by 50% (IC50) were found to be ∼150-fold lower than ciprofloxacin against DNA gyrase with double amino acid substitutions. Our findings highlight the importance of the chemical structure of an FQ drug on its antimicrobial activity. Particularly, the presence of 6-amino-3,5-difluoropyridine-2-yl at R-1 and either methyl group or bromine at R-8 of WQ-3810 and WQ-3334, respectively, was associated with improved antimicrobial activity. Therefore, WQ-3810 and WQ-3334 are promising candidates for use in the treatment of patients infected by FQ-resistant Salmonella spp.

Characterization of DNA Gyrase Activity and Elucidation of the Impact of Amino Acid Substitution in GyrA on Fluoroquinolone Resistance in Mycobacterium avium

Mycobacterium avium, a member of the M. avium complex (MAC), is the major pathogen contributing to nontuberculous mycobacteria (NTM) infections worldwide. Fluoroquinolones (FQs) are recommended for the treatment of macrolide-resistant MACs. The association of FQ resistance and mutations in the quinolone resistance-determining region (QRDR) of gyrA of M. avium is not yet clearly understood, as many FQ-resistant clinical M. avium isolates do not have such mutations. This study aimed to elucidate the role of amino acid substitution in the QRDR of M. avium GyrA in the development of FQ resistance. We found four clinical M. avium subsp. hominissuis isolates with Asp-to-Gly change at position 95 (Asp95Gly) and Asp95Tyr mutations in gyrA that were highly resistant to FQs and had 2- to 32-fold-higher MICs than the wild-type (WT) isolates. To clarify the contribution of amino acid substitutions to FQ resistance, we produced recombinant WT GyrA, GyrB, and four GyrA mutant proteins (Ala91Val, Asp95Ala, Asp95Gly, and Asp95Tyr) to elucidate their potential role in FQ resistance, using them to perform FQ-inhibited DNA supercoiling assays. While all the mutant GyrAs contributed to the higher (1.3- to 35.6-fold) FQ 50% inhibitory concentration (IC50) than the WT, Asp95Tyr was the most resistant mutant, with an IC50 15- to 35.6-higher than that of the WT, followed by the Asp95Gly mutant, with an IC50 12.5- to 17.6-fold higher than that of the WT, indicating that these amino acid substitutions significantly reduced the inhibitory activity of FQs. Our results showed that amino acid substitutions in the gyrA of M. avium contribute to FQ resistance. IMPORTANCE The emergence of fluoroquinolone (FQ) resistance has further compounded the control of emerging Mycobacterium avium-associated nontuberculous mycobacteria infections worldwide. For M. avium, the association of FQ resistance and mutations in the quinolone resistance-determining region (QRDR) of gyrA is not yet clearly understood. Here, we report that four clinical M. avium isolates with a mutation in the QRDR of gyrA were highly resistant to FQs. We further clarified the impact of mutations in the QRDR of GyrA proteins by performing in vitro FQ-inhibited DNA supercoiling assays. These results confirmed that, like in Mycobacterium tuberculosis, mutations in the QRDR of gyrA also strongly contribute to FQ resistance in M. avium. Since many FQ-resistant M. avium isolates do have these mutations, the detailed molecular mechanism of FQ resistance in M. avium needs further exploration.

Effectiveness of Fluoroquinolones with Difluoropyridine Derivatives as R1 Groups on the Salmonella DNA Gyrase in the Presence and Absence of Plasmid-Encoded Quinolone Resistance Protein QnrB19

Aims: WQ-3810 has strong inhibitory activity against Salmonella and other fluoroquinolone-resistant pathogens. The unique potentiality of this is attributed to 6-amino-3,5-difluoropyridine-2-yl at R1 group. The aim of this study was to examine WQ-3810 and its derivatives WQ-3334 and WQ-4065 as the new drug candidate for wild-type Salmonella and that carrying QnrB19. Materials and Methods: The half maximal inhibitory concentrations (IC₅₀s) of WQ-3810, WQ-3334 (Br atom in place of methyl group at R8), and WQ-4065 (6-ethylamino-3,5-difluoropyridine-2-yl in place of 6-amino-3,5-difluoropyridine-2-yl group at R1) in the presence or absence of QnrB19 were assessed by in vitro DNA supercoiling assay utilizing recombinant DNA gyrase and QnrB19. Results: IC₅₀s of WQ-3810, WQ-3334, and WQ-4065 against Salmonella DNA gyrase were 0.031 ± 0.003, 0.068 ± 0.016, and 0.72 ± 0.39 μg/mL, respectively, while QnrB19 increased IC₅₀s of WQ-3810, WQ-3334, and WQ-4065 to 0.44 ± 0.05, 0.92 ± 0.34, and 9.16 ± 2.21 μg/mL, respectively. Conclusion: WQ-3810 and WQ-3334 showed stronger inhibitory activity against Salmonella Typhimurium DNA gyrases than WQ-4065 even in the presence of QnrB19. The results suggest that 6-amino-3,5-difluoropyridine-2-yl group at R1 is playing an important role and WQ-3810 and WQ-3334 to be good candidates for Salmonella carrying QnrB19.

Point mutation in the stop codon of MAV_RS14660 increases the growth rate of Mycobacterium avium subspecies hominissuis

Mycobacterium avium subspecies hominissuis (MAH) is a pathogen that causes various non-tuberculous mycobacterial diseases in humans and animals worldwide. Among the genus, MAH is characterized by relatively slow growth. Here, we isolated a rapidly growing variant of the MAH 104 strain. The variant strain (named N104) exhibited an enhanced growth rate and higher motility compared to the parent MAH 104 strain (P104). Whole-genome sequencing analysis of N104 revealed the loss of the stop codon of MAV_RS14660 due to a single nucleotide replacement, resulting in the substitution of the codon for tryptophan. Notably, exclusion of the stop codon ligated the open reading frames and caused the fusion of two adjacent proteins. A revertant parent strain, in which a mutation was introduced to restore the stop codon, revealed that elimination of the stop codon in MAV_RS14660 was responsible for the N104 phenotype. Furthermore, we analysed the phenotypes of the parent and mutated strains by determining the functions of the MAV_RS14660 and MAV_RS14655 coding regions flanking the stop codon. The mutant strains, expected to express a fusion protein, exhibited increased resistance to antimicrobial drugs and exogenous copper toxicity compared to that of the parent strains. These findings suggest that the fusion of the MAV_RS14660- and MAV_RS14655-encoding regions in the mutant N104 strain could be related to the modified functions of these intrinsic proteins.

Abattoir survey of bovine tuberculosis in tanta, centre of the Nile delta, with in silico analysis of gene mutations and protein-protein interactions of the involved mycobacteria

Bovine tuberculosis is a transboundary disease of high economic and public health burden worldwide. In this study, post-mortem examination of 750 cattle and buffalo in Tanta abattoir, Centre of the Nile Delta, revealed visible TB in 4% of animals and a true prevalence of 6.85% (95% CI: 5.3%-8.9%). Mycobacterial culture, histopathology and RT-PCR targeting all members of M. tuberculosis complex were performed, upon which 85%, 80% and 100% of each tested lesions were confirmed as TB, respectively. Mpb70-targeting PCR was conducted on ten RT-PCR positive samples for sequencing and identified nine Mycobacterium (M.) bovis strains and, interestingly, one M. tuberculosis (Mtb) strain from a buffalo. Bioinformatics tools were used for prediction of mutations, nucleotide polymorphisms, lineages, drug resistance and protein-protein interactions (PPI) of the sequenced strains. The Mtb strain was resistant to rifampicin, isoniazid and streptomycin, and to the best of our knowledge, this is the first report of multidrug resistant (MDR)-Mtb originating from buffaloes. Seven M. bovis strains were resistant to ethambutol and ethionamide. Such resistances were associated with KatG, rpoB, rpsL, embB and ethA genes mutations. Other mutations and nucleotide polymorphisms were also predicted, some are reported for the first time and require experimental work for validation. PPI revealed more interactions than what would be expected for a random set of proteins of similar size and had dense interactions between nodes that are biologically connected, as a group. Two M. bovis strains belonged to BOV AFRI lineage (Spoligotypes BOV 1; BOV 2) and eight strains belonged to East-Asian (Beijing) lineage. In conclusion, visible TB was prevalent in the study area, RT-PCR is the best to confirm the disease, MDR-Mtb is associated with buffalo TB, and mycobacteria of different lineages carry many resistance genes to chemotherapeutic agents used in treatment of human TB constituting a major public health risk.

Pulmonary Targeting of Inhalable Moxifloxacin Microspheres for Effective Management of Tuberculosis

In the present study, the objective was to attain a localized lung delivery of an anti-tubercular fluoroquinolone, moxifloxacin (MXF), targeting the alveolar macrophages through a non-invasive pulmonary route using inhalable microspheres as a dry powder inhaler approach. MXF-loaded poly (lactic-co-glycolic acid) (PLGA) microspheres (MXF-PLGA-MSs) were fabricated by solvent evaporation technique and optimized by using a central composite statistical design. The morphology and particle size, as well as the flowability of the optimized microspheres, were characterized. In addition, the aerosolization performance of the optimized formula was inspected using an Andersen cascade impactor. Furthermore, in vivo fate following intrapulmonary administration of the optimized formula was evaluated. The optimized MXF-PLGA-MSs were spherical in shape with a particle size of 3.16 µm, drug loading of 21.98% and entrapment efficiency of 78.0%. The optimized formula showed a mass median aerodynamic diameter (MMAD) of 2.85 ± 1.04 µm with a favorable fine particle fraction of 72.77 ± 1.73%, suggesting that the powders were suitable for inhalation. Most importantly, in vivo studies revealed that optimized MXF-PLGA-MSs preferentially accumulated in lung tissue as manifested by a two-fold increase in the area under the curve AUC_0–24h, compared to plain drug. In addition, optimized MXF-PLGA-MS sustained drug residence in the lung for up to 24 h following inhalation, compared to plain drug. In conclusion, inhalable microspheres of MXF could be a promising therapeutic approach that might aid in the effective eradiation of tuberculosis along with improving patient adherence to the treatment.