Antitumor Efficiency of Electrochemotherapy by High and Low Frequencies and Repetitive Therapy in the Treatment of Invasive Ductal Carcinoma in Balb/c Mice

OBJECTIVE: In electrochemotherapy (ECT), there is an unpleasant sensation of muscle contraction when using a low frequency (1 Hz). Therefore, by increasing the pulse frequency above the tetanic frequency this painful sensation can be reduced. The aim of the present study is to compare the treatment efficiencies of low and high frequency ECT, and estimate the effect of its repeated sessions. MATERIALS AND METHODS: We transplanted invasive ductal carcinoma into the flanks of female Balb/c mice. ECT was performed on the mice by the use of 8 pulses, 1000 v/cm, of 100 µs duration at 1 Hz and 5 kHz repetition frequencies along with intra-tumoral injections of bleomycin. We also used this ECT protocol for the second therapy session six days after tumour regrowth. The effect of treatment was measured by calculating the tumor volumes for 24 days following treatment. Statistical analysis was performed with ANOVA. RESULTS: ECT at 1 Hz and 5 kHz pulse frequencies demonstrated significant inhibition of tumor growth, but after the first treatment the tumours began to regrow. Repetitive ECT sessions increased the curability of tumors up to 40% in the group treated by 1 Hz frequency and 60% in the group treated with 5 kHz frequency. CONCLUSION: Our results demonstrate that the effects of 1 Hz and 5 kHz pulse repetition frequencies are comparable for inhibited tumour growth. Repetitive treatment can improve the effectiveness of ECT.