The thermosensitivity of human gingival squamous carcinoma ca9-22 cells with oncogeneerbB-1/EGFR

Abstract

The heat sensitivity of Human gingival squamous carcinoma Ca9-22 cells with oncogeneerbB-1/EGFR and Chinese hamster V79 cells of normal thermosensitivity as control was investigated. Colony formitig ability of the treated cells was assayedin vitro. Heat-treatment period-survival and the concerned curves were drawn. The slopes of exponentially regressing parts of the survival curves were estimated in the T0 values of cellular thermosensitivity and subjected to Arrhenius analysis. The 42–44°C time-survival curves of Ca9-22 Cells showed biphasic slopes which indicated the presence of thermotolerance induction during continuous heating even at 44°C while for the V79 cells the biphasic slopes due to thermotolerance induction were shown in temperatures at and before 42°C. In comparison of T0 values with V79 cells, those of Ca9-22 cells were longer (less thermosensitive) by about 2.1 fold at 43°C and 1.2 fold at 44°C Both V79 and Ca9-22 cells were sensitized by 44–42°C step-down heating (SDH). 42°C heat treatment period-survival curves of 44°C ( 5 minute) preheated V79 cells; while Ca9-22 cells under the same treatment condition for not only 5 minutes but 20 minutes showed biphasic slope, which indicated the presence of thermotolerance. The thermosensitization ratio (TSR) of Ca9-22 cells were smaller than V79 cells. Arrhenius curves a breaking points at 44°C and 43°C for Ca9-22 and V79 cells, respectively. The activation energies of V79 cells were 145kcal/molc and 400 kcal/mole above and below 43°C (P < 0.05), respectively, while those of Ca9-22 cells were 200 kcal/mole and 250 kcal/mole above and below 44°C (P <0.05), respectively. These data suggested that oncogeneerbB-1 /EGFRcontained in Ca9-22 cells may contribute to reduce thermosensitivity and variety in term of G1 phase as shown in fractionated Hydroxyurea treatment.