Radiofrequency currents exert cytotoxic effects in NB69 human neuroblastoma cells but not in peripheral blood mononuclear cells

Response of human cancer cells to simultaneous treatment with sorafenib and radiofrequency current

Due to their alleged analgesic, anti-inflammatory and tissue regenerative effects, capacitive-resistive electrothermal therapy (CRET), which is based on non-invasive exposure to radiofrequency (RF) currents, is often applied to chemotherapeutically treated patients with cancer. Our previous studies have demonstrated that subthermal CRET currents can elicit a number of cell responses, including anti-proliferative effects, in the human liver cancer cell line HepG2. Such effects involve significant changes in the regulation of proteins involved in MAPK signaling pathways, which are also implicated in the cancer cell response to standard anticancer drugs such as sorafenib. This overlap in response pathways may lead to competitive, neutralizing or blocking interactions between the electrical and chemical treatments, thus raising questions on the advisability of CRET treatment for their analgesic, anti-inflammatory or other purposes in patients undergoing chemotherapy. The present study analyzed the effects of simultaneous treatment with sorafenib and 448-kHz, subthermal CRET current on the proliferation and viability of HepG2 cell cultures. Cell viability was assessed through Trypan blue or XTT assays, while flow cytometry was applied for cell cycle and apoptosis analysis. The expression of proteins involved in cell proliferation were assessed by immunoblotting and immunofluorescence. The results revealed no evidence to suggest that the electrical treatment counteracted or neutralized the cellular response to sorafenib at the different conditions evaluated. Furthermore, at the standard pharmacological sorafenib concentration, 5 µM, the combined treatment elicited an anti-proliferative response significantly stronger than that induced by each of the treatments when applied separately in HepG2 cells. These data do not support the hypothesis that CRET exposure may inhibit or diminish the effects of a chemotherapeutic drug used in cancer treatment, and highlights the requirement for further investigation into the cell response to the combined action of electrical and chemical treatments.

Response of neuroblastoma cells to RF currents as a function of the signal frequency

BACKGROUND

Capacitive-resistive electric transfer (CRET) is a non-invasive therapeutic strategy that applies radiofrequency electric currents within the 400-600 kHz range to tissue repair and regeneration. Previous studies by our group have shown that 48 h of intermittent exposure to a 570 kHz CRET signal at a subthermal density of 50 μA/mm² causes significant changes in the expression and activation of cell cycle control proteins, leading to cycle arrest in human cancer cell cultures. The present study investigates the relevance of the signal frequency in the response of the human neuroblastoma cell line NB69 to subthermal electric treatment with four different signal frequency currents within the 350-650 kHz range.

METHODS

Trypan blue assay, flow cytometry, immunofluorescence and immunoblot were used to study the effects of subthermal CRET currents on cell viability, cell cycle progression and the expression of several marker proteins involved in NB69 cell death and proliferation.

RESULTS

The results reveal that among the frequencies tested, only a 448 kHz signal elicited both proapoptotic and antiproliferative, statistically significant responses. The apoptotic effect would be due, at least in part, to significant changes induced by the 448 kHz signal in the expression of p53, Bax and caspase-3. The cytostatic response was preceded by alterations in the kinetics of the cell cycle and in the expression of proteins p-ERK1/2, cyclin D1 and p27, which is consistent with a potential involvement of the EGF receptor in electrically induced changes in the ERK1/2 pathway. This receives additional support from results indicating that the proapototic and antiproliferative responses to CRET can be transiently blocked when the electric stimulus is applied in the presence of PD98059, a chemical inhibitor of the ERK1/2 pathway.

CONCLUSION

The understanding of the mechanisms underlying the ability of slowing down cancer cell growth through electrically-induced changes in the expression of proteins involved in the control of cell proliferation and apoptosis might afford new insights in the field of oncology.

Antiadipogenic effects of subthermal electric stimulation at 448 kHz on differentiating human mesenchymal stem cells

The 448 kHz capacitive‑resistive electric transfer (CRET) is an electrothermal therapy currently applied in anticellulite and antiobesity treatments. The aim of the present study was to determine whether exposure to the CRET electric signal at subthermal doses affected early adipogenic processes in adipose‑derived stem cells (ADSC) from human donors. ADSC were incubated for 2 or 9 days in the presence of adipogenic medium, and exposed or sham‑exposed to 5 min pulses of 448 kHz electric signal at 50 µA/mm2 during the last 48 h of the incubation. Colorimetric, immunofluorescence, western blotting and reverse transcription‑quantitative polymerase chain reaction assays were performed to assess adipogenic differentiation of the ADSC. Electric stimulation significantly decreased cytoplasmic lipid content, after both 2 and 9 days of differentiation. The antiadipogenic response in the 9 day samples was accompanied by activation of mitogen‑activated protein kinase kinase 1/2, decreased expression and partial inactivation of peroxisome proliferator‑activated receptor (PPAR) γ, which was translocated from the nucleus to the cytoplasm, together with a significant decrease in the expression levels of the PPARG1 gene, perilipin, angiopoietin‑like protein 4 and fatty acid synthase. These results demonstrated that subthermal stimulation with CRET interferes with the early adipogenic differentiation in ADSC, indicating that the electric stimulus itself can modulate processes controlling the synthesis and mobilization of fat, even in the absence of the concomitant thermal and mechanical components of the thermoelectric therapy CRET.

Molecular mechanisms underlying antiproliferative and differentiating responses of hepatocarcinoma cells to subthermal electric stimulation

Capacitive Resistive Electric Transfer (CRET) therapy applies currents of 0.4–0.6 MHz to treatment of inflammatory and musculoskeletal injuries. Previous studies have shown that intermittent exposure to CRET currents at subthermal doses exert cytotoxic or antiproliferative effects in human neuroblastoma or hepatocarcinoma cells, respectively. It has been proposed that such effects would be mediated by cell cycle arrest and by changes in the expression of cyclins and cyclin-dependent kinase inhibitors. The present work focuses on the study of the molecular mechanisms involved in CRET-induced cytostasis and investigates the possibility that the cellular response to the treatment extends to other phenomena, including induction of apoptosis and/or of changes in the differentiation stage of hepatocarcinoma cells. The obtained results show that the reported antiproliferative action of intermittent stimulation (5 m On/4 h Off) with 0.57 MHz, sine wave signal at a current density of 50 µA/mm², could be mediated by significant increase of the apoptotic rate as well as significant changes in the expression of proteins p53 and Bcl-2. The results also revealed a significantly decreased expression of alpha-fetoprotein in the treated samples, which, together with an increased concentration of albumin released into the medium by the stimulated cells, can be interpreted as evidence of a transient cytodifferentiating response elicited by the current. The fact that this type of electrical stimulation is capable of promoting both, differentiation and cell cycle arrest in human cancer cells, is of potential interest for a possible extension of the applications of CRET therapy towards the field of oncology.