The intratumoral field, which determines the efficiency of electric field-mediated
drug and gene delivery, can differ significantly from the applied field. Therefore, we investigated the distribution of the electric field in mouse
tumors and tissue phantoms exposed to a large range of electric stimuli, and quantified the resistances of
tumor, skin, and
electrode-tissue interface. The samples used in the study included 4T1 and B16.F10
tumors, mouse skin, and tissue phantoms constructed with 1%
agarose gel with or without 4T1 cells. When pulsed electric fields were applied to samples using a pair of parallel-plate
electrodes, we determined the electric field and resistances in each sample as well as the resistance at the
electrode-tissue interface. The electric fields in the center region of tissue phantoms and
tumor slices ex vivo were macroscopically uniform and unidirectional between two parallel-plate
electrodes. The field strengths in
tumor tissues were significantly lower than the applied field under both ex vivo and in vivo conditions. During in vivo stimulation, the ratio of intratumoral versus applied fields was approximately either 20% or 55%, depending on the applied field. Meanwhile, the total resistance of skin and
electrode-tissue interface was decreased by approximately 70% and the electric resistance at the center of both
tumor models was minimally changed when the applied field was increased from 50 to 400 V/cm. These results may be useful for improving electric field-mediated
drug and gene delivery in solid
tumors.