Autophagy and enhanced chemosensitivity in experimental pancreatic cancers induced by noninvasive radiofrequency field treatment.

BACKGROUND: Patients with pancreatic ductal adenocarcinoma (PDAC) have limited therapeutic options and poor response to the standard gemcitabine (GCB)-based chemotherapy. In the current study, the authors investigated the feasibility of noninvasive short-wave radiofrequency (RF) electric fields to improve the cytotoxic effect of GCB on PDAC cells and determined its mechanism of action. METHODS: The cytotoxicity of RF alone and in combination with GCB was studied in vitro on normal pancreatic human pancreatic ductal epithelial cells and different PDAC cell lines by flow cytometry, and in vivo on ectopic and orthotopic human PDAC xenograft models in mice. The mechanism of RF activity was studied by Western blot analysis and immunohistochemistry. Toxicity was determined by histopathology. RESULTS: Exposure of different PDAC cells to 13.56-megahertz radio waves resulted in a substantial cytotoxic effect, which was accompanied by the induction of autophagy but not apoptosis. These effects of RF were found to be absent in normal cells. Excessive numbers of autophagosomes in cancer cells persisted 24 to 48 hours after RF exposure and then declined. The addition of a subtoxic dose of GCB to RF treatment inhibited the recovery of cancer cells from the RF-induced autophagy and enhanced the cytotoxic effect of the latter on cancer cells. The treatment of PDAC in situ in mice with the combination of noninvasive RF and GCB was found to have a superior antitumor effect compared with the use of RF or GCB alone, yet there was no evidence of systemic toxicity. CONCLUSIONS: Noninvasive RF treatment induced autophagy but not apoptosis in cancer cells and demonstrated potential as an enhancer of chemotherapy for treating patients with pancreatic cancer without toxicity to normal cells.

Noninvasive radiofrequency treatment effect on mitochondria in pancreatic cancer cells.

BACKGROUND: The development of novel therapeutic approaches for cancer therapy is important, especially for tumors that have poor response or develop resistance to standard chemotherapy and radiation. We discovered that noninvasive radiofrequency (RF) fields can affect cancer cells but not normal cells, inhibit progression of tumors in mice, and enhance the anticancer effects of chemotherapy. However, it remains unclear what physiological and molecular mechanisms this treatment induces inside cells. Here, we studied the effect of RF treatment on mitochondria in human pancreatic cancer cells. METHODS: The morphology of mitochondria in cells was studied via electron microscopy. The alteration of mitochondrial membrane potential (Δψ) was accessed using a Mitotracker probe. The respiratory activity of mitochondria was evaluated by analyzing changes in oxygen consumption rates determined with a Mito Stress Test Kit. The production of intracellular reactive oxygen species was performed using flow cytometry. The colocalization of mitochondria and autophagosome markers in cells was performed using fluorescence immunostaining and confocal microscopy analysis. RESULTS: RF fields treatment changed the morphology of mitochondria in cancer cells, altered polarization of the mitochondrial membrane, substantially impaired mitochondrial respiration, and increased reactive oxygen species production, indicating RF-induced stress on the mitochondria. We also observed frequent colocalization of the autophagosome marker LC3B with the mitochondrial marker Tom20 inside cancer cells after RF exposure, indicating the presence of mitochondria in the autophagosomes. This suggests that RF-induced stress can damage mitochondria and induce elimination of damaged organelles via autophagy. CONCLUSION: RF treatment impaired the function of mitochondria in cancer cells. Therefore, mitochondria can represent one of the targets of the RF treatment.

The effects of non-invasive radiofrequency treatment and hyperthermia on malignant and nonmalignant cells.

BACKGROUND: Exposure of biological subjects to electromagnetic fields with a high frequency is associated with temperature elevation. In our recent studies, we reported that non-invasive radiofrequency (RF) treatment at 13.56 MHz with the field ranging from 1 KeV to 20 KeV/m2 inhibits tumor progression in animals with abdominal tumor xenografts and enhances the anticancer effect of chemotherapy. The RF treatment was followed by temperature elevation in tumors to approximately 46 °C during 10 min of exposure. In contrast, the temperature of normal tissues remained within a normal range at approximately 37 °C. Whether all biological effects of RF treatment are limited to its hyperthermic property remains unclear. Here, we compared how RF and hyperthermia (HT) treatments change the proliferation rate, oxygen consumption and autophagy in malignant and nonmalignant cells. METHODS: In the current study, cancer and nonmalignant cells of pancreatic origin were exposed to the RF field or to conventional HT at 46 °C, which was chosen based on our previous in vivo studies of the tumor-specific RF-induced hyperthermia. RESULTS: Only RF treatment caused declines in cancer cell viability and proliferation. RF treatment also affected mitochondrial function in cancer cells more than HT treatment did and, unlike HT treatment, was followed by the elevation of autophagosomes in the cytoplasm of cancer cells. Importantly, the effects of RF treatment were negligible in nonmalignant cells. CONCLUSION: The obtained data indicate that the effects of RF treatment are specific to cancer cells and are not limited to its hyperthermic property.

Tumor selective hyperthermia induced by short-wave capacitively-coupled RF electric-fields.

There is a renewed interest in developing high-intensity short wave capacitively-coupled radiofrequency (RF) electric-fields for nanoparticle-mediated tumor-targeted hyperthermia. However, the direct thermal effects of such high-intensity electric-fields (13.56 MHZ, 600 W) on normal and tumor tissues are not completely understood. In this study, we investigate the heating behavior and dielectric properties of normal mouse tissues and orthotopically-implanted human hepatocellular and pancreatic carcinoma xenografts. We note tumor-selective hyperthermia (relative to normal mouse tissues) in implanted xenografts that can be explained on the basis of differential dielectric properties. Furthermore, we demonstrate that repeated RF exposure of tumor-bearing mice can result in significant anti-tumor effects compared to control groups without detectable harm to normal mouse tissues.