Abstract

The temperature-independent effects of electromagnetic fields (EMF) have been controversial for decades. Here, we critically analyze the available literature on non-thermal effects of radiofrequency (RF) and microwave EMF. We present a literature review of preclinical and clinical data on non-thermal antiproliferative effects of various EMF applications, including conventional RF hyperthermia (HT, cRF-HT). Further, we suggest and evaluate plausible biophysical and electrophysiological models to decipher non-thermal antiproliferative membrane effects. Available preclinical and clinical data provide sufficient evidence for the existence of non-thermal antiproliferative effects of exposure to cRF-HT, and in particular, amplitude modulated (AM)-RF-HT. In our model, transmembrane ion channels function like RF rectifiers and low-pass filters. cRF-HT induces ion fluxes and AM-RF-HT additionally promotes membrane vibrations at specific resonance frequencies, which explains the non-thermal antiproliferative membrane effects via ion disequilibrium (especially of Ca2+) and/or resonances causing membrane depolarization, the opening of certain (especially Ca2+) channels, or even hole formation. AM-RF-HT may be tumor-specific owing to cancer-specific ion channels and because, with increasing malignancy, membrane elasticity parameters may differ from that in normal tissues. Published literature suggests that non-thermal antiproliferative effects of cRF-HT are likely to exist and could present a high potential to improve future treatments in oncology.

Highlights

  • Conventional radiofrequency (RF) hyperthermia (HT, cRF-HT) or microwave (MW) HT has been evaluated in clinical studies [1] and is used in the treatment of soft tissue sarcoma in combination with neoadjuvant chemotherapy [2], and for the treatment of cervical cancer [3,4,5] and superficial tumors [6,7,8,9], when combined with radiation therapy (RT)

  • The researchers applied clinical systems like mEHT. These studies have in common according to the general understanding of hyperthermia that temperature increases are below 40 C and the observed effects are to be regarded as non-thermal

  • Clinical and preclinical data suggest the existence of antiproliferative non-thermal effects (Sections 3 and 4), which can damage tumor cells at lower temperatures (

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Summary

Introduction

Conventional radiofrequency (RF) hyperthermia (HT, cRF-HT) or microwave (MW) HT has been evaluated in clinical studies [1] and is used in the treatment of soft tissue sarcoma in combination with neoadjuvant chemotherapy [2], and for the treatment of cervical cancer [3,4,5] and superficial tumors [6,7,8,9], when combined with radiation therapy (RT). The researchers applied clinical systems like mEHT (modulated electro-hyperthermia [23,24], TTF (tumor treating fields) [25] and the TheraBionic device [26,27]. These studies have in common according to the general understanding of hyperthermia that temperature increases are below 40 C and the observed effects are to be regarded as non-thermal. We hypothesize that additional non-thermal effects of the electromagnetic fields (EMF) exist and are clinically validated This hypothesis is controversial as it challenges current textbook knowledge and has a high potential to impact clinical practice. We summarize the current information regarding the non-thermal effects of EMF

Methods
Clinical studies
Preclinical studies
RF-EMF in the intermediate-frequency range 100–300 kHz
Model approaches to describe non-thermal antiproliferative effects
Nanoheating
Biophysical processes on transmembrane ion channels
 1010 2  109 2  109 3  104 3  104
Frequency-dependent effects on cells
Findings
Discussion and prospects for oncologic applications

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