Minimization of Cancellation Effect with Nisin During Bipolar Nanosecond Electrochemotherapy

Bipolar cancellation (BPC) is an efficiency-limiting phenomenon in bipolar nanosecond pulsed electric field (nsPEF) exposures, in which the second, opposite-polarity phase reduces or partially reverses the electroporation induced by the first phase. Nisin, a cationic antibiotic peptide, has been reported to interact with lipid membranes in bacterial systems and artificial bilayer models, where it may contribute to membrane destabilization and increased permeability during pulsed electric field exposure. This study investigated whether nisin may enhance the efficacy of bleomycin electrochemotherapy (ECT) in the presence of bipolar nanosecond pulses, which are typically associated with pronounced BPC effects. Pulsed electric field (PEF) parameters and drug concentrations were selected based on preliminary viability and Yo-Pro-1 uptake experiments in CLS-354 human squamous cell carcinoma cells. To evaluate the effect of nisin, cell viability and membrane permeabilization were assessed following exposure to 300 ns pulses across a range of bipolar PEF protocols, with or without nisin, while identical unipolar pulses were used for comparison. Nisin (50 µg/mL) increased membrane permeabilization across the tested range of field amplitudes (9-15 kV/cm) and burst repetition frequencies (0.1-1.66 MHz). The presence of nisin was also associated with increased efficacy of bleomycin-based ECT under both unipolar and symmetrical bipolar PEF conditions. Under the optimized parameters tested (13 kV/cm; 150 pulses of 300 ns at 1.66 MHz), bipolar nsPEFs in combination with nisin reached levels of efficacy comparable to those observed with unipolar waveforms, suggesting a potential attenuation of bipolar cancellation effects.