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Furosemide reverses multidrug resistance status in bladder cancer cells in vitro

¹ Department of Biomedical Sciences, University of Portsmouth, Portsmouth, UK
² Department of Urology, Southampton University Hospitals NHS Trust, Southampton, UK

Correspondence to:
B A Lwaleed
Department of Urology, Central block, Level E, West Wing, Mailpoint 67, Southampton University Hospitals NHS Trust, Tremona Road, Southampton, SO16 6YD, UK; bashir{at}soton.ac.uk Background: Multidrug resistance (MDR) has a potentially serious influence on cancer treatment and should be taken into consideration in the design and application of therapeutic regimens. It is mediated through the activity of cellular pumps.

Aim: To investigate whether furosemide, itself a pump-blocker, reverses MDR in an in vitro model.

Materials and methods: An MDR bladder cancer cell line (MGH-u 1R) and its parental (drug sensitive) clone were exposed to epirubicin and furosemide, with the concentration of one drug fixed and that of the other serially diluted in a 96-well plate format. Both drugs formed the variable component in separate experiments. After a 1-h exposure, the cells were washed and replenished with fresh medium. To examine the toxicity of epirubicin and furosemide separately and in combination, monotetrazolium-based assays were carried out. Intracellular epirubicin distribution was assessed by confocal microscopy as a second index of resistance status after in vitro exposure.

Results: MGH-u 1R cells incubated with furosemide showed distribution of drug similar to that in the parental cells (MGH-u 1 sensitive). Controls (without furosemide) continued to show a resistant pattern of fluorescence. In cytotoxicity assays furosemide appeared substantially non-toxic. Resistant cells in the toxicity titration experiments showed increased resistance to levels of furosemide over 500 µg/ml. Parental cells were made only marginally more sensitive against increased background toxicity.

Conclusion: Furosemide is effective in reversing MDR status in bladder cancer cell lines in vitro. It may also have an increment of intrinsic cytotoxicity, but only at higher concentrations. We propose a potential for further investigation of furosemide as an adjunct to chemotherapy for superficial bladder cancer.

Abbreviations: ATP, adenosine triphosphate; MDR, multidrug resistance; MGH-u 1R, MDR bladder cancer cell line; P-gp, P-glycoprotein