The well established assay was carried out with the permanent mouse fibroblast see more cell line L929 according to a published procedure [11] with some modifications [12]. In the assay cell viability is determined by the reduction of the yellow MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazoliumbromid) to the MDV3100 cell line violet formazan by the action of ER- and mitochondrial

enzymes. Concentrations of the active compounds vz0825, vz0500 and 1541–0004 from 0.003 to 370 μM were used and effects on the fibroblasts were analyzed after 24 hours and 5 days of incubation. The IC50 values are shown in Table  5. The two most active compounds vz0825 and vz0500 showed cytotoxic (inhibition after 24 hours of incubation) and anti-proliferative (inhibition

after 5 days of incubation) IC50 values at low micromolar concentrations. Compound 1541–0004 is less cytotoxic, but has also a strong antiproliferative activity. Table 5 Cytotoxic (24 h) and antiproliferative (5 d) activity of the most active compounds according to MTT test with L929 cells Compound IC50 [μM] 24 h 5 d vz0825 14 6 vz0500 3 1 1541-0004 170 14 Generation of resistant mutants against vz0825 Mutants against vz0825 were generated by selection of variants of the wild type strain NM06-058 that are able to grow on agar plates containing 8 μM vz0825. After one round of selection, 15 resistant mutants were picked and analyzed individually. They displayed 4–16 fold reduced sensitivities (MIC 6.3 – 25 μM) against vz0825 compared to the wild type strain. In order to obtain an indication if vz0825 has a mode of action that is different selleck compound FER from standard antimicrobials, eight

established antibiotics against the major different antibacterial targets were tested with the resistant mutants. The addressed targets and their inhibitors were i) cell wall synthesis (ampicillin), ii) protein biosynthesis (tetracycline), iii) DNA-replication (ciprofloxacin), iv) DNA-dependent RNA polymerase (rifampicin), v) translation (chloramphenicol, erythromycin) and vi) synthesis of folic-acid (trimethoprim/sulfamethoxazol). The V. cholerae wild type strain NM06-058 and resistant mutants did not show differences in their MIC values against all tested antibiotics (data not shown), suggesting that vz0825 has a mode of action that is different from the classical antibiotics. Target identification This result initiated a further investigation of the mode of action of vz0825 by the comparative genome sequence analysis approach. The method makes use of whole genome sequence analysis of resistant mutants that were generated against an active compound and the comparison of the genome of the wild type and the mutant strain [13]. The genomes of the 15 resistant V. cholerae mutants were isolated, pooled and analyzed via paired-end sequencing. In parallel, the genome of the wild type strain from which the resistant mutants have been generated was also sequenced by the same method.