Is Ciprofloxacin a Substrate of P-glycoprotein?

Area of Science:

• Pharmacokinetics and Drug Transport
• Cell Biology
• Molecular Pharmacology

Background:

• Previous studies suggest ciprofloxacin is not a substrate of P-glycoprotein (P-gp).
• However, contradictory results arise from transport studies using different P-gp overexpressing cell lines.
• This highlights the need for careful cell line characterization in drug transport studies.

Purpose of the Study:

• To investigate whether ciprofloxacin is a substrate of P-glycoprotein (P-gp).
• To evaluate ciprofloxacin transport in MDCKI cells transfected with human MDR1 cDNA.
• To reconcile conflicting data on ciprofloxacin's interaction with P-gp.

Main Methods:

• Semi-quantitative RT-PCR to assess MDR1 mRNA levels.
• Western blot analysis for P-gp, MRP1, and MRP2 protein expression.
• Bidirectional transport assays of ciprofloxacin across various cell monolayers (MDCKI, MDCKI-MDR1, MDCKII, MDCKII-MDR1, MDCKII-MRP2, LLC-PK1, L-MRP1, L-MDR1).

Main Results:

• Ciprofloxacin exhibited net secretion in MDCKI-MDR1 cells but net absorption in MDCKI cells.
• P-gp inhibitors modulated ciprofloxacin transport in MDCKI-MDR1 cells, consistent with P-gp substrate activity.
• No significant differences in ciprofloxacin transport were observed between MDCKII/MDCKII-MDR1, LLC-PK1/L-MDR1, LLC-PK1/L-MRP1, and MDCKII/MDCKII-MRP2 cell pairs.

Conclusions:

• Transport data in MDCKI and MDCKI-MDR1 cells suggest ciprofloxacin is a P-gp substrate.
• Conversely, data from MDCKII, LLC-PK1, and derived cell lines indicate ciprofloxacin is not a P-gp substrate.
• Discrepancies necessitate further characterization of P-gp overexpressing cell lines and ciprofloxacin transport mechanisms.