Book of abstract 2008

Tumor blood flow modifying changes after application of different sets
of electric pulses
Simona Kranjc1, Urška Kamenšek1, Suzana Mesojednik1, Gregor Tevž1, Andrej Cör2, Maja
Čemažar1, Gregor Serša1
1Dept. of Experimental Oncology, Institute of Oncology Ljubljana, Zaloška 2, SI-1000 Ljubljana,
Slovenia; 2Faculty of Medicine, University of Ljubljana, Korytkova 2, SI-1000 Ljubljana, Slovenia
Electroporation is a method that by application of direct current electric pulses to the
tumors induces cell permeabilization which is nowadays widely used to increase cell uptake
of poorly permeant chemotherapeutic drugs and molecules such as DNA, antibodies,
enzymes and dyes. Besides increased drug delivery, application of electric pulses to the
tumors induces tumor blood flow modifying effect and vascular disrupting effect. The
aim of this study was to determine the effects of different sets of electric pulses on tumor
blood flow and their relation to antitumor effectiveness.
Subcutaneous SA-1 tumors were exposed to four different sets of electric pulses; the first
two were composed of 8 high voltage electric pulses, at 1300 V/cm, 100 μs, with electric
pulse repetition frequencies of 1 Hz or 5 kHz; the third was the combination of 1 high
(1300 V/cm) and 8 low (140 V/cm, 50 ms, 2 Hz) voltage pulses and the fourth was composed
of 8 electric pulses at 600 V/cm, 5 ms and 1 Hz. The first two sets of electric pulses
are usually used in drug delivery (ECT, electrochemotherapy) and the last two sets are
used for delivery of DNA molecules (EGT, electrogene therapy). The changes in tumor
perfusion were measured by tumor staining with Patent blue. In addition, stereological
analysis on whole area of tumor sections stained with hematoxylin and eosin to estimate
necrosis and caspase-3 to estimate apoptosis were performed.
Electroporation of SA-1 tumors with all sets of electric pulses induced an immediate
and profound reduction in tumor perfusion (80-90%). Tumors treated with ECT pulses
started
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to reperfuse very quickly thereafter and within h reached approximately the
70% perfused tumor area compared to pretreatment value. In contrast, the kinetics of
tumor reperfusion after treatment with the sets of EGT pulses with lower amplitude and
longer duration resumed more slowly and tumor blood flow was 5 days after the treatment
still reduced up to 47%. The decreased tumor blood flow correlated with increased rate
(up to 2-times) of tumor necrosis and apoptosis after the treatment. ECT pulses induced
fast changes in tumor histology observed already h after the treatment, whereas the
tumor histological changes caused by EGT pulses gradually increased with maximal peak
72 h after the treatment.
Electroporation of tumors with (ECT and EGT pulses) high and low voltage electric
pulses induced immediate and profound reduction in tumor blood flow. The duration
of tumor blood flow reduction was more pronounced after application of EGT pulses.
Consequently, the lack of nutrients and oxygen supply as well as changes in tumor and
endothelial cells after the electroporation lead to tumor cell killing by necrosis and
apoptosis, which correlated well with antitumor effectiveness.
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