Daunomycin secretion by killfish renal proximal tubules

Area of Science:

• Renal Physiology
• Drug Transport Mechanisms
• Molecular Pharmacology

Background:

• Daunomycin, a fluorescent anthracycline, is used in chemotherapy.
• Understanding its renal tubule uptake is crucial for efficacy and toxicity.
• Killifish renal proximal tubules offer a model for studying drug secretion.

Purpose of the Study:

• To investigate the mechanisms of daunomycin uptake and secretion in killifish renal proximal tubules.
• To determine the role of multidrug-resistance (MDR) transporters and organic cation transporters in daunomycin transport.
• To assess the influence of pH and transporter modifiers on daunomycin accumulation.

Main Methods:

• Epifluorescence microscopy and video-image analysis.
• Incubation of intact killifish renal proximal tubules with daunomycin.
• Exposure to MDR transporter modifiers (verapamil, CSA), TEA, NaCN, and vanadate.
• Manipulation of buffer solution pH.

Main Results:

• Daunomycin accumulated in both cells and tubular lumen, with higher luminal concentration at steady state.
• Luminal accumulation was reduced by MDR modifiers (verapamil, CSA) and NaCN/vanadate, but not TEA at pH 8.25.
• Cellular accumulation was largely unaffected by most modifiers, except slight reduction by NaCN.
• At pH 7.25, TEA affected both cellular and luminal accumulation, while CSA still reduced luminal accumulation.

Conclusions:

• Daunomycin is actively secreted in killifish proximal tubules via at least two mechanisms.
• At pH 8.25, secretion involves MDR transporters, with basolateral entry via diffusion.
• At pH 7.25, basolateral uptake includes diffusion and organic cation transport, with luminal secretion by MDR transporters and an organic cation/H+ exchanger.