Urine protects urothelial cells against killing with nanosecond pulsed electric fields

The quest for safe and effective ablation resulted in the development of nanosecond pulsed electric fields (nsPEF) technology for tumor treatment. For future applications of nsPEF in urothelial cancer treatment, we evaluated the effect of urine presence at the ablation site. We prepared artificial urine (AU) with compounds commonly present in the healthy human urine at physiological concentrations. We compared nsPEF cytotoxicity for cancerous (T24) and non-cancerous (SV-HUC-1) human urothelial cell lines pulsed either in the AU or in a physiological solution (PS). Cell monolayers were exposed to trains of 300-ns, 10-Hz pulses using a two-needle electrode assembly placed orthogonal to the monolayer. The assembly produced the electric field gradually weakening with the distance from the electrodes. The electric field which killed 50 % of cells (LD50) was measured by staining with propidium iodide and matching the stained area with the simulated electric field strength. nsPEF exposure in PS was more cytotoxic to cancer cells. The AU protected both healthy and cancer urothelial cells, increasing their LD50 1.4 and 1.6 times, respectively. Omitting urea from the AU reduced the LD50 for healthy and cancer urothelial cells. Testing the role of other AU components, we found that it was the high concentration of phosphates what also rendered the protective effect of the AU. Our findings suggest that the nsPEF ablation of bladder cancer will be less efficient if the bladder is filled with urine.