Thermal cycling as a novel thermal therapy to synergistically enhance the anticancer effect of propolis on PANC‑1 cells

Hyperthermia (HT) has shown potential in cancer therapy. In particular, it appears to sensitize cancer cells to chemotherapy. However, a major concern associated with HT is that the thermal dosage applied to the tumor cells may also harm the normal tissue cells. Besides, the drugs used in HT are conventional chemotherapy drugs, which may cause serious side effects. The present study demonstrated a novel methodology in HT therapy called thermal cycle (TC)-HT. With this strategy, a therapeutic window with a maximum synergistic effect was created by combining TC-HT with natural compounds, with minimal unwanted cell damage. The natural compound propolis was selected, and the synergistic anticancer effect of TC-HT and propolis was investigated in pancreatic cancer cells. The present results demonstrated for the first time that TC-HT could enhance the anticancer effect of propolis on PANC-1 cancer cells through the mitochondria-dependent apoptosis pathway and cell cycle arrest. Combined treatment greatly suppressed mitochondrial membrane potential, which is an important indicator of damaged and dysfunctional mitochondria. Furthermore, the cell cycle-regulating protein cell division cycle protein 2 was downregulated upon combined treatment, which prevented cellular progression into mitosis. The present study offers the first report, to the best of our knowledge, on the combination of TC-HT with a natural compound for pancreatic cancer treatment. It is anticipated that this methodology may be a starting point for more sophisticated cancer treatments and may thereby improve the quality of life of many patients with cancer.