Inhibition of thermotolerance observed on tsAF8 cells

Effect of Withaferin A on the development and decay of thermotolerance in B16F1 melanoma: a preliminary study

Protein synthesis inhibitors can suppress the development of thermotolerance in tumor tissues during [corrected] repeated heating. Withaferin A (WA), isolated from Withania somnifera has cytotoxic and inhibitory action on protein synthesis. In the present investigation, effect of WA on development and decay of thermotolerance in B16F1 melanoma was studied in C57BL mice. Tumors of 100 +/- 10 [corrected] mm(3) size were subjected to repeated hyperthermia (HT) at 43 degrees C for 30 minutes. WA was injected after first hyperthermia treatment. The tumor response was assessed by calculating the tumor growth delay (GD). The GD increased with increase in time gap between two hyperthermia treatments and was significantly higher (p < 0.05 to p < 0.001) in WA treated groups at all the respective time gaps (except at 0h and 120h) compared to hyperthermia alone group. WA increases the tumor response during repeated hyperthermia by reducing the magnitude of thermotolerance developed and by decreasing the recovery time from thermotolerance.

Effects of PKC inhibitors on suppression of thermotolerance development in tsAF8 cells

Effects of protein kinase C (PKC) inhibitors (H7, staurosporine, calphostin C) on thermotolerance development were investigated in temperature sensitive tsAF8 cells derived from Syrian hamster BHK21 cells. Cells were pre-heated at 45 degrees C for 20 min, incubated at 34 degrees C with PKC inhibitors for varying lengths of time, i.e. 1.25-10.0 h, and then heated at 45 degrees C for 30 min. Increasing survival fractions after the second heat treatment was inhibited by the treatment with H7 (40-160 microM), with staurosporine (0.05-1.0 microM), and with calphostin C (0.8, 1.2 microM) in a concentration dependent manner. When the concentrations of these PKC inhibitors were low, the restraint of increasing survival fractions was temporary, since survival fractions increased 3-7.5 h after pre-heating. However, the survival fractions were almost constant by the treatment with 160 microM H7 and 1.0 microM staurosporine. Induction of HSP72 after heat stress was investigated in tsAF8 and BHK21 cells. Cells were heated at 45 degrees C for 20 min and incubated at 34 or 39.7 degrees C (tsAF8), at 37 degrees C (BHK21). Intensity of intracellular fluorescence from HSP72 was measured by flow cytometry. HSP72 was induced in BHK21 cells, but there was no definite induction of HSP72 in tsAF8 cells at either 39.7 or 34 degrees C. These results suggest that PKC is related with the thermotolerance development in tsAF8 cells; however, HSP72 is not involved in the thermotolerance development in tsAF8 cells.