Experimental method for the hyperthermic treatment of cells in tissue culture: initial application to pancreatic cancer cells

Hyperthermia is attractive as a potential adjunctive modality in the treatment of cancer, especially those cancers that are more resistant to conventional modalities. In the present study, we characterized the response of two pancreatic cancer cell lines to hyperthermia alone. In so doing, we utilized and characterized a novel exposure system that heats by 915-MHz continuous wave microwave (MW) radiation, with microprocessor control of the power input via temperature monitoring of the sample and simultaneous visualization and recording of temperature parameters. Samples, consisting of cells in 25-cm2 culture flasks with 10 ml of medium, were exposed to MWs in a stripline for 1 h at MW-induced temperatures of 37, 41.5, 42.5, 43.5, or 44.5 degrees C. The specific absorption rate was 132 W/kg for all temperatures. In addition, 37 degrees C waterbath controls were concurrently run. The colony formation assay was used to assess cytotoxicity. No significant difference was found between 37 degrees C waterbath and 37 degrees C MW controls. Significant differences in the thermosensitivity of the two cell lines were found, with the most drug-sensitive cell line showing the greatest thermosensitivity. However, hyperthermia alone was not very effective as a single cytotoxic modality in either cell line. The MW-hyperthermia-induction system provided precise, automated temperature control (+/- 0.2 degrees C), and ease of utilization and data management.