| Electric field-mediated gene delivery is currently plagued by its inefficiency. From local injection to expression of a transgene, several barriers, namely, interstitial transport, cellular uptake, intracellular transport, and nuclear uptake, impede the process. However, in order to determine the limiting steps in the treatment, or to design new treatment strategies, each of the aforementioned barriers must be characterized and understood.; Since diffusion is negligible in the interstitial and intracellular regions, electrophoresis of DNA is the primary mode of transport in these regions. Also, the permeability of the cell membrane is increased in response to the local electric field in tumor tissues. Therefore, since the local electric field ultimately determines the extent of DNA electrophoresis or cellular electroporation, the inefficiency of electric field-mediated gene delivery may, in part, be explained in terms of the properties of the fields around and within the target cells.; In the past, the local electric field that exists in tumors during treatment has been poorly characterized. In fact, in many studies, the local electric field in tumors was assumed to be equal to the applied field. To this end, this work aims to quantitatively assess the fields that exist during electric field-mediated gene delivery on both the macroscopic (i.e. tissue) and microscopic (i.e. cellular) levels.; Experimental and theoretical studies were conducted to characterize the electric field that exists in tumor tissue and around and within tumor cells in response to an applied external electric stimulus. The results show that in ex vivo tumor tissue slices and in tissue phantoms, the macroscopic electric field is relatively uniform, and unaffected by the presence of cells. However, the magnitude of the electric field in tumor tissues was significantly lower than the applied field during both ex vivo and in vivo stimulation. During in vivo stimulation, the ratio of the intratumoral versus the applied field was a sigmoidal function of the applied field. In fact, the field in tumors can be as low as ∼25% of the applied field during in vivo stimulation. During electroporation, the magnitude of the field in tumors increases, but asymptotically reaches only ∼50% of the applied field.; The resistances of the skin and electrode interface and the tumor were also experimentally determined during in vivo stimulation. The resistance of the skin and electrode-tissue interface decreased exponentially when the applied field was increased from 50 V/cm to 400 V/cm, but the resistance at the center of tumors was independent of the applied field.; The microscopic electric field was determined using a 3D model to determine the electric field that exists in both the extracellular and intracellular domains of a 10-mum spherical cell exposed to an applied field of 100 V/cm. Electroporation was modeled as a decrease in cell membrane resistivity over a specified angle. The results showed that the extracellular and membrane fields and the extracellular currents are less sensitive to electroporation, compared to the intracellular field and currents. Also, the extent of electroporation affects the transmembrane potential flanking the pore region, which may have consequences for pore growth. The results also showed that extracellular field redirection occurs only in a small volume when pores are formed in the cell membrane, which may help explain some of the inefficiencies currently seen during electric field-mediated gene delivery. Finally, the percent changes in the total current flow are relatively small compared to the changes in the current flow inside the cell. |
