DC electrical field-induced c-fos expression and growth stimulation in multicellular prostate cancer spheroids

Abstract

The effects of electrical direct current (DC) field pulses on c-fos expression, growth kinetics and vitality patterns of multicellular tumour spheroids (MCSs) were studied. Monitoring the membrane potential of MCSs by di-8-ANNEPS staining and confocal microscopy during DC electrical field treatment revealed a hyperpolarization at the anode-facing side and a depolarization at the cathode-facing side. When a single 500 V m-1 electrical field pulse with a duration of 60 s was applied to MCSs (150-350 μm in diameter) an enhancement of the growth kinetics within a period of 6 days post pulse was observed. Whereas the volume doubling time amounted to 4-5 days in control samples, it was reduced to 1-2 days in electropulsed MCSs. At day 6 post pulse the diameter of the necrotic core was significantly smaller than the control. The critical diameter for the first appearance of central necrosis amounted to 350 ± 50 μm in the control and 450 ± 50 μm in the electropulsed MCSs. Coincidentally, the proliferating rim was increased to 107 ± 11 μm in electropulsed MCSs as compared with 60 ± 6 μm in the control. The growth stimulation may be mediated by the proto-oncogene c-fos as its expression increased by a factor of 2.5 within 2 h post pulse. c-fos expression declined towards control values within 8 h post pulse.