Effects of a combined thermochemotherapy on markers of apoptosis, differentiation and adhesion in the human mammary carcinoma MX-1

The susceptibility to apoptotic stimuli, the degree of differentiation and the adhesive properties are important determinants of a tumor's biological behavior and of the possibility of it's being influenced by treatment. In this study we examined the effects of a combined thermochemotherapy, consisting of the administration of the alkylating agents ifosfamide or mafosfamide combined with hyperthermia at 41 degrees C for one hour, applied to the human mammary carcinoma MX-1. We concentrated our observations on the apoptosis-associated proteins bax and bcl-2, on cytokeratin and vimentin as markers of differentiation, on desmosomes and on the antiadhesive epithelial membrane antigen episialin. These proteins were visualized immunohistochemically in cultured cells in vitro as well as in xenotransplants growing in nude mice in vivo. We found that the susceptibility of the surviving cells to apoptotic stimuli, measured by the bax/bcl-2 ratio, was much higher after a combined thermochemotherapy than after chemotherapy or thermotherapy alone. Many of these cells could probably be forced into apoptosis by later applying another kind of anticancer therapy. With regard to the expression of episialin after thermochemotherapy, fewer cells possessed an antiadhesive and, therefore, potentially invasive capacity. The number of desmosomes seemed not to be affected. As to their higher expression of cytokeratin and their unchanged expression of vimentin, the surviving cells appear to be more differentiated. Since these results could be observed in vivo as well as in vitro, it seems likely that, apart from its influence on the perfusion of the tumor, the amplification of the cytostatic efficacy of the chemotherapy by hyperthermia must be mediated by a direct mechanism.