Seconeolitsine, the Novel Inhibitor of DNA Topoisomerase I, Protects against Invasive Pneumococcal Disease Caused by Fluoroquinolone-Resistant Strains.

Antibiotic resistance in Streptococcus pneumoniae has increased worldwide, making fluoroquinolones an alternative therapeutic option. Fluoroquinolones inhibit the type II DNA topoisomerases (topoisomerase IV and gyrase). In this study we have evaluated the in vivo activity of seconeolitsine, an inhibitor of topoisomerase I. Levofloxacin (12.5 to 50 mg/kg) or seconeolitsine (5 to 40 mg/kg) were administered every 12 h during two days in mice infected with a serotype 8-resistant strain. At 48 h, a 70% protection was obtained with seconeolitsine (40 mg/kg; p < 0.001). However, survival with levofloxacin was 20%, regardless of the dose. In addition, seconeolitsine decreased bacteremia efficiently. Levofloxacin had higher levels in serum than seconeolitsine (Cmax of 14.7 vs. 1.6; p < 0.01) and higher values of area under the serum concentration-time curve (AUC0-12h of 17.3 vs. 5; p < 0.01). However, seconeolitsine showed higher levels of time to peak concentration and elimination half-life. This is consistent with the higher binding of seconeolitsine to plasma proteins (40% and 80% when used at 1 µg/mL and 50 µg/mL, respectively) in comparison to levofloxacin (12% at 5 µg/mL and 33% at 50 µg/mL). Our results suggest that seconeolitsine would be a promising therapeutic alternative against pneumococcal isolates with high fluoroquinolone resistance levels.

An increase in negative supercoiling in bacteria reveals topology-reacting gene clusters and a homeostatic response mediated by the DNA topoisomerase I gene.

We studied the transcriptional response to an increase in DNA supercoiling in Streptococcus pneumoniae by using seconeolitsine, a new topoisomerase I inhibitor. A homeostatic response allowing recovery of supercoiling was observed in cells treated with subinhibitory seconeolitsine concentrations. Supercoiling increases of 40.7% (6 µM) and 72.9% (8 µM) were lowered to 8.5% and 44.1%, respectively. Likewise, drug removal facilitated the recovery of cell viability and DNA-supercoiling. Transcription of topoisomerase I depended on the supercoiling level. Also specific binding of topoisomerase I to the gyrase A gene promoter was detected by chromatin-immunoprecipitation. The transcriptomic response to 8 µM seconeolitsine had two stages. An early stage, associated to an increase in supercoiling, affected 10% of the genome. A late stage, manifested by supercoiling recovery, affected 2% of the genome. Nearly 25% of the early responsive genes formed 12 clusters with a coordinated transcription. Clusters were 6.7-31.4 kb in length and included 9-22 responsive genes. These clusters partially overlapped with those observed under DNA relaxation, suggesting that bacteria manage supercoiling stress using pathways with common components. This is the first report of a coordinated global transcriptomic response that is triggered by an increase in DNA supercoiling in bacteria.

Identification of Haemophilus haemolyticus in clinical samples and characterization of their mechanisms of antimicrobial resistance.

OBJECTIVES: The objectives of this study were to establish the frequency of Haemophilus haemolyticus in clinical samples, to determine the antimicrobial resistance rate and to identify the mechanisms of resistance to ß-lactams and quinolones. METHODS: An updated database was used to differentiate between MALDI-TOF MS results for Haemophilus influenzae and H. haemolyticus. Antimicrobial susceptibility was studied by microdilution, following EUCAST criteria. The ß-lactamase types were identified by PCR analysis of isolates that tested positive for nitrocefin hydrolysis. Mutations in the ftsI gene were identified in isolates with ampicillin MICs ≥0.25 mg/L. Mutations in the quinolone resistance-determining region (QRDR) were identified in isolates with ciprofloxacin MICs ≥0.5 mg/L. RESULTS: Overall, we identified 69 H. haemolyticus isolates from 1706 clinical isolates of Haemophilus spp. from respiratory, genital, invasive, and other infection sources. The frequency of H. haemolyticus was low in respiratory samples compared with that of H. influenzae, but in genital-related samples, the frequency was similar to that of H. influenzae. We found low antimicrobial resistance rates among H. haemolyticus isolates, with 8.7% for ampicillin, 8.7% for co-trimoxazole, 7.2% for tetracycline and 4.3% for ciprofloxacin. Mutations in the ftsI gene classified the isolates into four groups, including the newly described Group Hhae IV, which presents mutations in the ftsI gene not identified in H. influenzae and H. haemolyticus type strains. Three ciprofloxacin-resistant H. haemolyticus isolates with mutations affecting GyrA and ParC were identified. CONCLUSIONS: The frequency of H. haemolyticus was low, especially in respiratory samples, where H. influenzae is the main pathogen of this genus. Although antimicrobial resistance rates were low, three ciprofloxacin-resistant H. haemolyticus clinical isolates have been identified for the first time.

Molecular characterization of fluoroquinolone resistance in nontypeable Haemophilus influenzae clinical isolates.

Nontypeable Haemophilus influenzae (NTHi) is a common cause of respiratory infections in adults, who are frequently treated with fluoroquinolones. The aims of this study were to characterize the genotypes of fluoroquinolone-resistant NTHi isolates and their mechanisms of resistance. Among 7,267 H. influenzae isolates collected from adult patients from 2000 to 2013, 28 (0.39%) were ciprofloxacin resistant according to Clinical and Laboratory Standards Institute (CLSI) criteria. In addition, a nalidixic acid screening during 2010 to 2013 detected five (0.23%) isolates that were ciprofloxacin susceptible but nalidixic acid resistant. Sequencing of their quinolone resistance-determining regions and genotyping by pulse-field gel electrophoresis and multilocus sequence typing of the 25 ciprofloxacin-resistant isolates available and all 5 nalidixic acid-resistant isolates were performed. In the NTHi isolates studied, two mutations producing changes in two GyrA residues (Ser84, Asp88) and/or two ParC residues (Ser84, Glu88) were associated with increased fluoroquinolone MICs. Strains with one or two mutations (n = 15) had ciprofloxacin and levofloxacin MICs of 0.12 to 2 µg/ml, while those with three or more mutations (n = 15) had MICs of 4 to 16 µg/ml. Long persistence of fluoroquinolone-resistant strains was observed in three chronic obstructive pulmonary disease patients. High genetic diversity was observed among fluoroquinolone-resistant NTHi isolates. Although fluoroquinolones are commonly used to treat respiratory infections, the proportion of resistant NTHi isolates remains low. The nalidixic acid disk test is useful for detecting the first changes in GyrA or in GyrA plus ParC among fluoroquinolone-susceptible strains that are at a potential risk for the development of resistance under selective pressure by fluoroquinolone treatment.

Inhibition of fatty acid metabolism reduces human myeloma cells proliferation.

Multiple myeloma is a haematological malignancy characterized by the clonal proliferation of plasma cells. It has been proposed that targeting cancer cell metabolism would provide a new selective anticancer therapeutic strategy. In this work, we tested the hypothesis that inhibition of ß-oxidation and de novo fatty acid synthesis would reduce cell proliferation in human myeloma cells. We evaluated the effect of etomoxir and orlistat on fatty acid metabolism, glucose metabolism, cell cycle distribution, proliferation, cell death and expression of G1/S phase regulatory proteins in myeloma cells. Etomoxir and orlistat inhibited ß-oxidation and de novo fatty acid synthesis respectively in myeloma cells, without altering significantly glucose metabolism. These effects were associated with reduced cell viability and cell cycle arrest in G0/G1. Specifically, etomoxir and orlistat reduced by 40-70% myeloma cells proliferation. The combination of etomoxir and orlistat resulted in an additive inhibitory effect on cell proliferation. Orlistat induced apoptosis and sensitized RPMI-8226 cells to apoptosis induction by bortezomib, whereas apoptosis was not altered by etomoxir. Finally, the inhibitory effect of both drugs on cell proliferation was associated with reduced p21 protein levels and phosphorylation levels of retinoblastoma protein. In conclusion, inhibition of fatty acid metabolism represents a potential therapeutic approach to treat human multiple myeloma.

Low-density lipoprotein cholesterol suppresses apoptosis in human multiple myeloma cells.

Multiple myeloma (MM) is an incurable disease accompanied by low plasma levels of low-density lipoprotein cholesterol (LDL-c). The significance of altered cholesterol metabolism in the pathophysiology of MM remains elusive. Although it has been hypothesized that myeloma cells depend on exogenous cholesterol for its survival, the role of LDL-c on myeloma cells has not been elucidated. To evaluate the impact of exogenous LDL-c on cell viability, three human myeloma cell lines (RPMI-8226, NCI-H929, and U-266B1) were grown in the presence or absence of lipoproteins. Cell viability was markedly reduced in the absence of lipoproteins in sera. However, exogenous LDL-c improved cell viability. We showed that reduced cell viability was associated with increased levels of cleaved caspase-3, whereas proliferation rate remained unchanged. Interestingly, exogenous LDL-c counteracted apoptosis in human myeloma cell lines and primary cultures of human myeloma cells. Thus, our results demonstrated that LDL-c is an important anti-apoptotic factor for myeloma cells and begin to explain the hypocholesterolemia observed in patients with MM.