Millimeter-Wave Pulsed Heating in Vitro: Effect of Pulse Duration

The aim of this work is to compare the response of A375 melanoma cells following 90 min of exposure to trains of 1.5 or 6 s millimeter-waves (MMW)-induced thermal pulses with the same temperature dynamics. Phosphorylation of heat shock protein 27 (HSP27) and activation of cleaved Caspase-3 were used as markers of cellular stress and apoptosis, respectively. Immunofluorescence was used to observe and precisely quantify the cellular response as a function of the spatial distribution within the exposed area. Results show that cellular response was stronger when cells were exposed to a train of 1.5 s compared to 6 s heat pulses despite the same average temperature dynamics. Cellular apoptosis induced by 1.5 s pulses was about 50% greater compared to the one induced by 6 s pulses in the area of maximal thermal stress. Similarly, HSP27 phosphorylation was approximately 20% stronger than the one induced by 6 s pulses, and mainly focused within a small area of a few mm ² . Cellular response to MMW induced by pulsed heating does not only depend on the peak, average, and minimum temperature. It is a function of combination of the pulse parameters, including duration, peak power, and period. MMW-induced heat pulses can be efficiently used to induce cellular stress and apoptosis in melanoma cells as a promising innovative tool for the treatment of superficial skin cancer. Adaptative therapies might be envisaged by tuning the pulse shape as a function of the desired effect.