Schedule-dependent efficiency of thermochemotherapy in vitro with etoposide and heating at 43 degrees C.

We have investigated the effect of hyperthermia (HT) treatment on the extent of etoposide-induced apoptosis in human leukemia HL-60 cells. The cells were heated at 43 degrees C for 15 to 60 min. Relative quantitative changes in the apoptotic (Ap) fractions were monitored by flow cytometry, HT treatment for 15 min prior to or concurrently with etoposide exposure had no effect on the Ap fraction generated by the drug alone, whereas, 60 min heating resulted in an increase in the Ap fraction. Heating of the cells at 6 to 24 hr after drug exposure enhanced the Ap fraction. Taken collectively, the results indicate that appropriately scheduled HT and etoposide treatments may lead to a thermochemotherapy protocol that will result in increased etoposide-induced death of human leukemia cells.