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

Abstract

Recently, a number of electric and electrothermal therapies have been applied to the treatment of specific cancer types. However, the cellular and molecular mechanisms involved in the response to such therapies have not been well characterized yet. Capacitive-resistive electric transfer (CRET) therapy uses electric currents at frequencies within the 0.45–0.6 MHz range to induce hyperthermia in target tissues. Preliminary trials in cancer patients have shown consistent signs that CRET could slow down growth of tumor tissues in brain gliomas, without inducing detectable damage in the surrounding healthy tissue. Previous studies by our group have shown that subthermal treatment with 0.57-MHz electric currents can induce a cytostatic, not cytotoxic response in HepG2 human hepatocarcinoma cells; such effect being mediated by cell cycle alterations. In contrast, the study of the response of NB69 human neuroblastoma cells to the same electric treatment revealed consistent indications of cytotoxic effects. The present study extends the knowledge on the response of NB69 cells to the subthermal stimulus, comparing it to that of primary cultures of human peripheral blood mononuclear cells (PBMC) exposed to the same treatment. The results showed no sensitivity of PBMC to the 0.57 MHz subthermal currents and confirmed that the treatment exerts a cytotoxic action in NB69 cells. The data also revealed a previously undetected cytostatic response of the neuroblastoma cell line. CRET currents affected NB69 cell proliferation by significantly reducing the fraction of cells in the phase G2/M of the cell cycle at 12 h of exposure. These data provide new information on the mechanisms of response to CRET therapy, and are consistent with a cytotoxic and/or cytostatic action of the electric treatment, which would affect human cells of tumor origin but not normal cells with a low proliferation rate.

Molecular Mechanisms Underlying Antiproliferative and Differentiating Responses of Hepatocarcinoma Cells to Subthermal Electric Stimulation

“…These alterations in cell cycle progression were mediated by changes in the expression of cyclins D1, A and B1 and of cyclin-dependent kinase inhibitor p27 kip1 [15] , [16] . Similar effects were observed in human neuroblastoma NB69 cells, in which the same CRET treatment caused cell cycle arrest, accompanied with increased necrosis [17] , [18] . On the basis of those results, the present work was aimed to analyze whether the CRET stimulus can also influence cellular and molecular processes involved in HepG2 cell death regulation.…”

“…Although it has been reported that CRET stimulation induces necrosis in human neuroblastoma cells NB69 [17], [18], in HepG2 the observed decrease in the number of alive cells is not accompanied with increased rates of necrosis [15]. Thus, the present work investigated the potential apoptotic action of CRET in HepG2.…”

Electric Stimulation at 448 kHz Promotes Proliferation of Human Mesenchymal Stem Cells

“…Indeed, our late passage cells showed a number of genetic abnormalities, including aneuploidy (data not shown) that are characteristic of senescent cultures. The possibility that CRET elicits antiproliferative effects in senescent ADSC could take partial support from previous studies by our group, which report that CRET treatment causes antiproliferative effects in hepatocarcinoma HepG2 and neuroblastoma NB69 [32,33,34,35,36], two human cancer cell lines known to carry a variety of genetic alterations [52,53]. …”

“…For sham-exposure, the electrode pairs inserted in control dishes were also connected to the generator, but not energized. The stimulation pattern consisted of 5-minute pulses of 448 kHz sine wave current, at a subthermal density of 50 μA/mm 2 , separated by 4-h interpulse lapses, along a total period of 48 h. Such exposure parameters have been proven to affect cell proliferation in previous studies by our group [32,33,34,35,36]. The cultures were grown in two separate, identical CO 2 incubators (Thermo Fisher Scientific, Waltham, MA, USA).…”

“…However, evidence exists indicating that, at least at the cellular level, the CRET effects are not limited to the thermal ones. In fact, previous studies by our group have shown that CRET stimulation at subthermal doses can induce anti-proliferative and cytotoxic responses in cultured human cancer cell lines, but not in primary cultures of human peripheral blood mononuclear cells [32,33,34,35,36]. These results can be interpreted as an experimental support to the evidence that the effects of CRET medical therapies are not due exclusively to temperature increase in the exposed tissues, but also to direct cellular responses to the electric stimulus itself.…”