  We have developed a novel in vitro instrument that can deliver intermediate
frequency (100 - 400 kHz), moderate intensity (up to and exceeding 6.5 V/cm
pk-pk) electric fields (EFs) to cell and tissue cultures generated using
induced electromagnetic fields (EMFs) in a solenoid coil. A major application
of these EFs is as an emerging cancer treatment modality. In vitro studies by
Novocure Ltd. reported that intermediate frequency (100 - 300 kHz), low
amplitude (1 - 3 V/cm) EFs, which they called "Tumor Treating Fields"
(TTFields), had an anti-mitotic effect on glioblastoma multiforme (GBM) cells.
The effect was found to increase with increasing EF amplitude. Despite
continued theoretical, preclinical, and clinical study, the mechanism of action
remains incompletely understood. Previous in vitro studies of "TTFields" have
used attached, capacitively coupled electrodes to deliver alternating EFs to
cell and tissue cultures. This contacting delivery method suffers from a poorly
characterized EF profile and conductive heating that limits the duration and
amplitude of the applied EFs. In contrast, our device delivers EFs with a
well-characterized radial profile in a non-contacting manner, eliminating
conductive heating and enabling thermally regulated EF delivery. To test and
demonstrate our system, we generated continuous 200 kHz EMF with an EF
amplitude profile spanning 0 - 6.5 V/cm pk-pk and applied them to human thyroid
cell cultures for 72 hours. We observed moderate reduction in cell density (<
10%) at low EF amplitudes (< 4 V/cm) and a greater reduction in cell density of
up to 25% at higher amplitudes (4 - 6.5 V/cm). Our device can be extended to
other EF frequency and amplitude regimes. Future studies with this device
should contribute to the ongoing debate about the efficacy and mechanism(s) of
action of "TTFields" by better isolating the effects of EFs.
