A predictive assay for human tumor cellular response to hyperthermia using dansyl lysine staining and flow cytometry

The heat response of five human tumor biopsies has been examined using the fluorescent probe dansyl lysine and multiparameter flow cytometry. Dansyl lysine has previously been shown to possess specificity for heat killed mammalian cells. The human tumors tested included a cervical squamous cell carcinoma, malignant melanoma, colon adenocarcinoma, ovarian carcinoma, and a mesothelioma. The samples were excised, mechanically disrupted into single cell suspensions and heated in vitro for various lengths of time at 45 degrees C. The cells were returned to 37 degrees C incubation for 12 to 15 hours prior to staining with dansyl lysine. The fraction of cells staining dansyl lysine was quantitated by flow cytometry after gating on high forward angle light scatter and 90 degrees C light scatter. This gate excluded much of the normal cell contamination within the tumor sample. The data show that the heat response of human tumor biopsies varied significantly, with cervical carcinoma and malignant melanoma being the most resistant and the mesothelioma and ovarian carcinoma the most heat sensitive. Finally, evidence is presented for the expression of thermotolerance in ovarian carcinoma and mesothelioma biopsies pre-heated in vitro. Dansyl lysine appears to be useful in measuring the intrinsic cellular heat sensitivity of human tumors and in determining the kinetics of decay of thermotolerance following an initial heat exposure.