3.2. Inhibition of MurE ligase
The effect of compound 1 was tested against the recombinant MurE ligase from M. tuberculosis, a key enzyme that participates in the early stages of peptidoglycan biosynthesis. This enzyme is conserved in all bacterial species but selects its natural substrates in a species-specific manner [24]. Compound 1 exhibited moderate inhibition of the activity of M. tuberculosis MurE ligase, with an IC50 of 75M (data not shown).
3.3. Cytotoxicity evaluation
The IC50 values of compound 1 were determined for MCF7 (human breast carcinoma; Fig. 2), A549 (human lung carcinoma) and WI38 (human fibroblast) cells using the sulforhodamine B assay and were 12.5, 10.5 and 8.9M, respectively.
3.4. 14C-enoxacin accumulation
Compound 1 demonstrated a concentration-dependent effect on the accumulation of 14C-enoxacin by S. aureus SA-1199B, with increasing concentrations resulting in gradually increasing accu- mulation (Fig. 3). Both reserpine and compound 1 at 50M increased enoxacin accumulation significantly compared with the control (P=0.03 and P=0.002, respectively) and there was a trend towards compound 1 at 50M being more effective than reserpine (P=0.08). Enoxacin accumulation data were validated by time–kill assays, which revealed no effect of 50M of compound 1 on the viabil- ity of S. aureus SA-1199B over a 10-min exposure period (data not shown). This period of time was the same as that employed in the accumulation assays.