Strong synergy of heat and modulated electromagnetic field in tumor cell killing.
OBJECTIVE
Hyperthermia is an emerging complementary method in radiooncology. Despite many positive studies and comprehensive reviews, the method is not widely accepted as a combination to radiotherapy. Modulated electrohyperthermia (mEHT; capacitive, electric field modulated, 13.56 MHz) has been used in clinical practice for almost 2 decades in Germany, Austria and Hungary. This in vivo study in nude mice xenograft tumors compares mEHT with "classic" radiative hyperthermia (radHT).


METHODS
Nude mice were xenografted with HT29 human colorectal carcinoma cells. 28 mice in four groups with seven animals each and two tumors per animal (totally 56 tumors) were included in the present study: group 1 as untreated control; group 2 treated with radHT at 42 degrees C; group 3 treated with mEHT at identical 42 degrees C; group 4 treated with mEHT at 38 degrees C (by intensively cooling down the tumor). 24 h after treatment, animals were sacrificed and the tumor cross sections studied by precise morphological methods for the respective relative amount of "dead" tumor cells.


RESULTS
The effect of mEHT established a double effect as a synergy between the purely thermal (temperature-dependent) and nonthermal (not directly temperature-dependent) effects. The solely thermal enhancement ratio (TER) of cell killing was shown to be 2.9. The field enhancement ratio (FER) at a constant temperature of 42 degrees C was measured as 3.2. Their complex application significantly increased the therapeutic enhancement to 9.4.


CONCLUSIONS
mEHT had a remarkable cancer cell-killing effect in a nude mice xenograft model.
Andocs
Gabor
G
"Frederic Joliot Curie" National Research Institute for Radiobiology and Radiohygiene, Budapest, Hungary.
Renner
Helmut
H
Balogh
Lajos
L
Fonyad
Laszlo
L
Jakab
Csaba
C
Szasz
Andras
A
D000818:Animals; D017209:Apoptosis / Q000528:radiation effects*; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000473:pathology* / Q000532:radiotherapy*; D003131:Combined Modality Therapy; D004574:Electromagnetic Fields; D006801:Humans; D006979:Hyperthermia, Induced / Q000379:methods*; D055909:Magnetic Field Therapy / Q000379:methods*; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D016896:Treatment Outcome