Fluoroquinolones are broad spectrum
antibiotics widely indicated in the treatment of both human and
animal diseases. The primary objective of this study was to assess short and long term affinities of
gemifloxacin towards efflux transporters (P-gp, MRP2) and
nuclear hormone receptor (PXR). Uptake and dose dependent inhibition studies were performed with [(14)C]
erythromycin (0.25 μCi/ml) on MDCKII-MDR1 and MDCKII-MRP2 cells. Cellular accumulation of
calcein-AM was further determined to confirm the affinity of
gemifloxacin towards P-gp and MRP2. Transport studies were conducted to determine bi-directional permeability and to assess efflux ratio of
gemifloxacin. LS-180 cells were treated with three different concentrations of
gemifloxacin for 72 h and real-time PCR analysis was performed to study the quantitative gene expression levels of PXR, MDR1 and MRP2. Further, [(14)C]
erythromycin uptake was also performed on LS-180 treated cells to better delineate the functional activity of efflux transporters. Results from our study suggest that
gemifloxacin may be a substrate of both the efflux transporters studied. This compound inhibited both P-gp and MRP2 mediated efflux of [(14)C]
erythromycin in a dose dependent manner with IC(50) values of 123 ± 2 μM and 16 ± 2 μM, respectively. The efflux ratio of [(14)C]
erythromycin lowered from 3.56 to 1.63 on MDCKII-MDR1 cells and 4.93 to 1.26 on MDCKII-MRP2 cells. This significant reduction in efflux ratio further confirmed the substrate specificity of
gemifloxacin towards P-gp and MRP2. Long term exposure significantly induced the expression of PXR (18 fold), MDR1 (6 fold) and MRP2 (6 fold). A decrease (20%) in [(14)C]
erythromycin uptake further confirmed the elevated functional activity of P-gp and MRP2. In conclusion, our studies demonstrated that
gemifloxacin is effluxed by both P-gp and MRP2. Long term exposure induced their gene expression and functional activity. This substrate specificity of
gemifloxacin towards these efflux transporters may be one of the major factors accounting for low oral bioavailability (71%). Better understanding of these mechanistic interactions may aid in the development of newer strategies to achieve adequate therapeutic levels and higher bioavailability.