Comparison of biological effects of modulated electro-hyperthermia and conventional heat treatment in human lymphoma U937 cells

Abstract

Loco-regional hyperthermia treatment has long history in oncology. Modulated electro-hyperthermia (mEHT, trade name: oncothermia) is an emerging curative treatment method in this field due to its highly selective actions. The impedance-matched, capacitive-coupled modulated radiofrequency (RF) current is selectively focused in the malignant cell membrane of the cancer cells. Our objective is studying the cell-death process and comparing the cellular effects of conventional water-bath hyperthermia treatment to mEHT. The U937 human histiocytic lymphoma cell line was used for the experiments. In the case of conventional hyperthermia treatment, cells were immersed in a thermoregulated water bath, whereas in the case of mEHT, the cells were treated using a special RF generator (LabEHY, Oncotherm) and an applicator. The heating dynamics, the maximum temperature reached (42 °C) and the treatment duration (30 min) were exactly the same in both cases. Cell samples were analysed using different flow cytometric methods as well as microarray gene expression assay and western blot analysis was also used to reveal the molecular basis of the induced effects. Definite difference was observed in the biological response to different heat treatments. At 42 °C, only mEHT induced significant apoptotic cell death. The GeneChip analysis revealed a whole cluster of genes, which are highly up-regulated in case of only RF heating, but not in conventional heating. The Fas, c-Jun N-terminal kinases (JNK) and ERK signalling pathway was the dominant factor to induce apoptotic cell death in mEHT, whereas the cell-protective mechanisms dominated in case of conventional heating. This study has clearly shown that conventional hyperthermia and RF mEHT can result in different biological responses at the same temperature. The reason for the difference is the distinct, non-homogenous energy distribution on the cell membrane, which activates cell death-related signalling pathways in mEHT treatment but not in conventional heat treatment.

Energy Absorption by the Membrane Rafts in the Modulated Electro-Hyperthermia (mEHT)

“…The selectively heated rafts excite numerous signal transduction pathways [44], and produce extrinsic apoptosis signals [45]. In the case of well-applied excitations, these create a spatiotemporal production of particular molecules (damage-associated molecular pattern, DAMP), and its consequence could be immunogenic cell-death (ICD), [46].…”

Hyperthermia Dosing and Depth of Effect

“…In temperature scale, the aim in this matching technology is to reach at least 43˚C temperature in the Tx effective percentages of the tumor treatment. In the current-matching case, the goal is apoptosis and excitation of the actual membrane rafts [41] [42], initialize immunogenic cells death, [43]. The difference between the two matching methods in capacitive coupling techniques well observable and proven [44].…”

Evolving Paradigms in HIV Malignancies: Review of Ongoing Clinical Trials

“…18 mEHT utilizes the principles of extracellular hyperthermia using low frequency modulated direct electroic field, but not temperature-dependent, effects of electromagnetic fields and special modulation, the effect of which may exceed that of the overall heating (macroscopic temperature elevation) by 3- to 4-fold. 19 mEHT does not require hyperthermia-range temperature and may be performed safely, without invasive thermal control. 20 …”