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

Abstract

Background Patients with pancreatic adenocarcinoma (PDAC) have limited therapeutic options and poor response to the standard gemcitabine (GCB)-based chemotherapy. We investigated the feasibility of non-invasive short-wave RF electric fields to improve cytotoxic effect of GCB on PDAC cells and determined its mechanism of action. Methods Cytotoxicity of RF alone and in combination with GCB was studied in vitro on normal pancreatic HPDE cells and different PDAC cell lines by flow cytometry, and in vivo on ectopic and orthotopic human PDAC xenograft models in mice. Mechanism of RF activity was studied by western blot and immunohistochemistry analysis. Toxicity was determined by histopathology. Results Exposure of different PDAC cells to 13.56 MHz radiowaves resulted in substantial cytotoxic effect, which was accompanied by induction of autophagy, but not apoptosis. These effects of RF were absent in normal cells. Excessive numbers of autophagosomes in cancer cells persisted 24-48 h after RF exposure and then declined. Addition of a subtoxic dose of GCB to RF treatment inhibited the recovery of cancer cells from the RF-induced autophagy and enhanced cytotoxic effect of the latter on cancer cells. Treatment of PDAC cancer in situ in mice with combination of non-invasive RF and GCB had superior antitumor effect than RF or GCB alone, yet had no evidence of systemic toxicity. Conclusions Non-invasive RF treatment induced autophagy, not apoptosis in cancer cells and showed a potential as an enhancer of chemotherapy for treating pancreatic cancer without toxicity to normal cells.

Noninvasive radiofrequency treatment effect on mitochondria in pancreatic cancer cells

“…Increased levels of LC3B green fluorescent puncta were noticed only in cells exposed to the RF field, indicating an increased presence of autophagosomes in cells after RF exposure (Fig. ) and correlating with our previous studies in which we performed a thorough investigation of RF‐induced autophagy . Red fluorescence staining with Tom20 antibody designating mitochondria was similar in both treated and untreated cells.…”

“…Recent studies by other investigators have demonstrated that deprivation of ATP production can stimulate an autophagy mechanism in cells for alternative energy sources . In our previous studies, we were able to show that RF treatment of cancer cells was followed by induction of autophagy . Data obtained in the current study indicate that substantial reduction of oxygen consumption in RF‐treated cancer cells could be one of the initiating signals for autophagy activation, as seen by the increase in green LC3B puncta signals in Fig.…”

“…In our previous studies, we already observed the ability of RF treatment to change cellular morphology by causing shrinking and detachment of cancer cells, which was followed by significant reduction of their viability. 16 Here examination of cellular organelles under electron microscopy revealed the most significant morphological changes in mitochondria (Fig. 2).…”

“…In our recent studies, we reported that noninvasive RF treatment at 13.56 MHz with the noninvasive field ranging from 1 KeV to 20 KeV/m 2 inhibits the growth of orthotopic hepatocellular carcinoma in mice and enhances the anticancer effect of gemcitabine chemotherapy in a murine model of orthotopic pancreatic cancer . Investigation of the RF‐induced cell death mechanism in cells indicated its ability to affect cancer cells via autophagy . Importantly, this effect was not observed in normal cells.…”

“…16 Investigation of the RF-induced cell death mechanism in cells indicated its ability to affect cancer cells via autophagy. 16 Importantly, this effect was not observed in normal cells. Autophagy is one of the mechanisms used by cells for processing damaged organelles.…”