AIM To investigate the response to hyperthermia and chemotherapy, analyzing apoptosis, cytotoxicity, and cisplatin concentration in different digestive system malignancy cells. cells; and additive and antagonistic effects in T3M4 cells. Combined treatment enhanced initiation of cell apoptosis in AGS, Caco-2, and T3M4 cells by 61%, 20%, and 19% respectively. The increase of intracellular cisplatin concentration was observed at 43 C by 30%, 20%, and 18% in AGS, Caco-2, and T3M4 cells, respectively. CONCLUSION In addition to cisplatin, hyperthermia up to 43 C does not impact the viability of malignancy cells in a synergistic manner. results suggest that optimal heat has to be taken into consideration for achieving optimal therapeutic effect. In addition to cisplatin, hyperthermia up to 43 C does not impact the viability of AGS, Caco-2, and T3M4 cells in a synergistic manner. However, some regimens of hyperthermia and cisplatin treatment are beneficial regarding an increase in intracellular cisplatin concentration and enhancement apoptosis of gastrointestinal malignancy cells. INTRODUCTION For the past two decades, hyperthermal intraperitoneal chemotherapy (HIPEC) has been considered as a treatment option AB1010 enzyme inhibitor for peritoneum invading gastrointestinal cancers[1]. Various studies have exhibited improved survival rates for gastric[2] and colorectal cancers[3-5]. The clinical application of hyperthermia is based on the assumption that it may enhance the effect of the chemotherapy, especially cisplatin-based treatments[6-8]. There are some experimental studies providing evidence that hyperthermia can affect cell membranes, cytoskeletons, synthesis of macromolecules, increase drug-induced DNA damage, and inhibit the repair of drug-induced DNA damage[9]. Hyperthermia may provide higher local cisplatin concentrations in tissues, indicating the pharmacokinetic advantage of its use and reduction of systemic toxicity[10]. Hyperthermia-induced PARP blockade can increase chemotherapy-induced damage in BRCA-competent cells of ovarian and colon cancer[11]. However, the results of available studies around the synergy of AB1010 enzyme inhibitor hyperthermia and cisplatin chemotoxicity, initiation of apoptosis, and intracellular accumulation of cisplatin in different gastrointestinal malignancy cells are controversial. The opposite effect of hyperthermia on cisplatin sensitivity was observed in mismatch repair deficiency and mismatch repair proficiency in colon cancer cell lines[12]. Isolated hyperthermia only temporarily inhibited cell proliferation without cytotoxic effects on gastric malignancy cell lines. However, a synergistic effect of hyperthermia and chemotherapy on inhibiting proliferation and induction of cell death via the apoptotic pathway was reported[13]. Interestingly, the hyperthermia-mediated increase of cellular accumulation of cisplatin and prolonged DNA damage in gastric malignancy cells was observed only with the addition of tumor necrosis factor[14]. The expression of warmth shock genes and AB1010 enzyme inhibitor proteins provides an adaptive mechanism for stress tolerance, allowing cells to survive non-physiologic conditions. However, the same adaptive mechanism can ultimately favor malignant transformation by interfering with pathways that regulate cell growth and apoptosis. Cytoprotection and thermotolerance AB1010 enzyme inhibitor raised the concern that heat-treated tumor cells might also be resistant to attack by immune effector mechanisms[15]. Data around the additive effect of AB1010 enzyme inhibitor hyperthermia in terms of enhanced chemo-cytotoxicity in malignancy cells of pancreatic origin are scarce. Therefore, the aim of this study was to analyze the additivity of hyperthermia to cisplatin effects in gastric, pancreatic, and colorectal malignancy cell lines evaluating cell cytotoxicity, apoptosis, and intracellular cisplatin concentration. MATERIALS AND METHODS Human cancer cell lines The AGS and Caco-2 cell lines were purchased from American Type Cell Culture (ATCC Manassas, VA, United States). AGS cell line is derived from a gastric adenocarcinoma of the stomach of a 54 year-old Caucasian female with no prior anti-cancer treatment. Caco-2 cells were isolated from Pf4 a primary colonic tumor in a 72-year-old Caucasian male using the explant culture technique. Forms moderately well differentiated adenocarcinomas consistent with colonic primary grade II, in nude mice. T3M4 cell line was obtained as a gift from the European Pancreas Center (Heidelberg, Germany). This cell line was derived from a lymph node metastasis of the Japanese male patient, diagnosed with pancreatic ductal adenocarcinoma. It is characterized as pancreatic adenocarcinoma producing CEA, K-ras activated, and with slow cell growth. Cells were grown in RPMI medium (Gibco/Invitrogen, Carlsbad, CA, United States) with the addition of 10% fetal bovine serum (Gibco/Invitrogen) and 1% penicillin/streptomycin solution (Gibco/Invitrogen). Flasks with cells were cultured in a humid incubator with a CO2 level of 5% and temperature of 37 C. Design of experiment Cancer cells were cultivated for 24 h in the conditions described above. Afterwards, cells were treated by one of two separate factors: temperature (37 C, 38 C, 39 C, 40 C, 41 C, 42 C,.