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Cytotoxicity of hepatocellular carcinoma cells to hyperthermic and ablative temperature exposures: In vitro studies and mathematical modelling

Abstract Purpose: Image-guided ablative therapies use temperatures greater than 45 °C to kill abnormal cells. There is limited published data of cell survival after ablative temperature exposures, which is of importance to predict ablation zone dimensions. The objective of this study was to determine and mathematically model survival of hepatocellular carcinoma cells following ablative temperature exposures (45–60 °C). Materials and methods: Hepatocellular carcinoma (HCC) cell lines were plated in 96-well plates, and heated between 45 and 60 °C for 0–32 min. Heating was applied by a rapid media exchange with heated Hank’s balanced salt solution (HBSS) in a temperature-controlled water bath. Cell viability was determined by MTS assay. Survival data was modelled by the Arrhenius model, and the thermal isoeffective dose (TID) model where kinetic parameters were determined via non-linear optimisation. Results: Results suggest that the thermal dose based on cumulative equivalent minutes and parameters as used for hyperthermia exposures (<43 °C) is not applicable for ablative exposures. We found R = 0.72 for temperatures between 45–60°C for the TID model. The Arrhenius parameters were frequency factor A = 3.25E43 1/s, and activation energy Ea = 281 kJ/mol. These parameters correlate well with a prior study in the same cell line, and with threshold temperatures for necrosis from in vivo studies. Conclusions: Our results suggest that standard TID model kinetic parameters based on hyperthermia studies, often also used at ablation temperatures, are not applicable at these higher temperatures for HCC cells.