Novel insights into hyperthermia’s therapeutic effectiveness in treating malignant melanoma
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Malignant melanoma is one of the most aggressive types of human cancers and one of the deadliest malignancies with steadily increasing incidence rates globally. Although early detection and increased surveillance have undoubtedly contributed to the elevation of survival rates, its mortality rates still remain high as the disease does not respond to current therapeutic strategies. Hyperthermia, defined as the application of exogenous heat induction, is one of the most common therapeutic modalities and acts by either directly killing tumor cells and/or sensitizing them against other therapeutic means. Numerous reports have provided proof that it can trigger the activation of cell death pathways in various skin cancer cell lines. Hence, in the present study we have aimed to establish a hyperthermia-induced experimental platform in order to assess its therapeutic efficacy in an in vitro human skin cancer model consisting of (1) immortalized keratinocytes (non-malignant), (2) malignant melanoma and (3) epidermoid carcinoma (non-melanoma) cells as well as an in vivo mouse model of malignant melanoma (mice injected with mouse malignant melanoma cells). According to our kinetic analyses using our in vitro skin cancer model, the optimal hyperthermic experimental conditions range between 430C-450C, for 2 hours, as there was a significant cell death induction in malignant melanoma cells, whereas, interestingly, non-malignant cells seem to be more resistant. Furthermore, we utilized a real-time PCR microarray-based gene expression profiling system to identify critical gene targets involved at various stages of the apoptotic pathway(s). Moreover, in order to fully characterize the interactions and cross-talks between the different apoptotic cascades (intrinsic, extrinsic, ER- stress mediated), we studied changes in protein expression levels of various genes implicated in those pathways by means of Western immunoblotting. According to our results, there is differential regulation of gene expression of several pro- and anti-apoptotic genes which appears to depend on the hyperthermic exposure conditions. Finally, our previous findings were evaluated by utilizing an in vivo mouse malignant melanoma model and according to our data there was a considerable inhibition of tumor growth for both hyperthermic conditions accompanied by the respective changes in several apoptotic genes' expression levels. The results of this study further support hyperthermia's effectiveness in treating malignant melanoma by identifying the underlying molecular mechanisms and various molecules responsible for hyperthermia's beneficial effects on tumor growth inhibition.