Millimeter-Wave Heating In Vitro: Local Microscale Temperature Measurements Correlated to Heat Shock Cellular Response

Abstract

Cellular sensitivity to heat is highly variable depending on the cell line. The aim of this paper is to assess the cellular sensitivity of the A375 melanoma cell line to continuous (CW) millimeter-waves (MMW) induced heating at 58.4 GHz, between 37 • C and 47 • C to get a deeper insight into optimization of thermal treatment of superficial skin cancer. Methods: Phosphorylation of heat shock protein 27 (HSP27) was mapped within an area of about 30 mm 2 to visualize the variation of heat-induced cellular stress as a function of the distance from the waveguide aperture (MMW radiation source). A multiphysics computational approach was then adopted to yield both electromagnetic and thermal field distributions as well as corresponding specific absorption rate (SAR) and temperature elevation. Induced temperature rise was experimentally measured using a micro-thermocouple (µTC). Results: Coupling of the incident electromagnetic (EM) field with µTC leads was first characterized, and optimal µTC placing was identified. HSP27 phosphorylation was induced at temperatures ≥ 41 • C, and its level increases as a function of the thermal dose delivered, remaining mostly focused within 3 mm 2 . Conclusion: Phosphorylation of HSP27 represents a valuable marker of cellular stress of A375 melanoma cells under MMW exposure, providing both quantitative and spatial information about the distribution of the thermal stress. Significance: These results may contribute to the design of thermal treatments of superficial melanoma through MMWinduced heating in the hyperthermic temperature range.

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

“…The exposure system as well as the electromagnetic dosimetry were described in detail in [10], [20]. Briefly, a thin cell monolayer cultured in a well of a 12-well tissue culture plate was exposed from the bottom 5 mm away from an open-ended rectangular WR15 waveguide (WG) antenna (aperture size 3.81×1.905 mm 2 ), used as a source of the MMW radiation.…”

“…Numerical simulations were performed using the finite integration technique (FIT) solver of CST Microwave Studio 2018 (Computer Simulation Technology [CST]; Dassault Systemes, Darmstadt, Germany) as detailed in [10], [20]. Due to the shallow penetration of the MMW, the specific absorption rate (SAR) distribution in the exposed cell monolayer rapidly decreases along all the directions of the well [10], [20]. Computed local SAR in the cell monolayer, at the center of the exposure -aligned with the boresight axis of the open-ended WG -is equal to 19.8 W/kg per 1 W of incident power.…”

“…Heating of biological tissues may be achieved by means of different power sources such as ultrasound or electromagnetic waves, including radiofrequency (RF), microwave (MW), ultraviolet (photothermal therapy), and light (lasers). Our recent results suggest that the upper part of the millimeter-wave (MMW) band may be used for thermal treatment of superficial skin cancer, such as spreading melanoma, located within the MMW penetration depth (i.e., ∼ 0.5 mm at 60 GHz) [9], [10], [11]. We showed that continuous wave (CW) MMW-induced heating at temperatures higher than 46 °C may minimize cellular thermotolerance while inducing apoptosis [10].…”

“…Our recent results suggest that the upper part of the millimeter-wave (MMW) band may be used for thermal treatment of superficial skin cancer, such as spreading melanoma, located within the MMW penetration depth (i.e., ∼ 0.5 mm at 60 GHz) [9], [10], [11]. We showed that continuous wave (CW) MMW-induced heating at temperatures higher than 46 °C may minimize cellular thermotolerance while inducing apoptosis [10]. Moreover, MMW-induced heat pulses with duration of 1.5 s, period of 20 s, amplitude of 10 °C, and peak steady-state temperature > 48 °C were able to induce a significant cellular injury in melanoma cells compared to CW-induced heating with the same average temperature rise of about 42 °C [9], [11].…”

“…The main objective of this study is to extend the current knowledge about the heat-induced modifications in melanoma cells by MMW-pulsed heating as a function of the heat pulse duration for adaptative therapies. To this end, results previously obtained using short 1.5 s pulses [9], [10], were compared, for the first time, to longer pulses (6 s), with the same minimum, peak, and average temperature rise. Cellular response was quantified in terms of cellular injury after 90 min of exposure mediated by the activation of cleaved Casp-3 and compared to heat shock response mediated by phosphorylation of HSP27.…”