Tissue Engineered Scaffolds and Three Dimensional Tumor Constructs to Evaluate Pulsed Electric Field Treatments

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Date
2018-09-19
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Virginia Tech
Abstract

This work investigates the use of irreversible electroporation (IRE) for tissue engineering applications and as a cancer ablation therapy. IRE uses short, high-intensity electric pulses to create pores in a cell's membrane and disrupt its stability. At a certain energy level, damage to the cell becomes too great and it leads to cell death. The particular mechanisms that drive this response are still not completely understood. Thus, further characterization of this behavior for cell death induced by pulsed electric fields (PEFs) will advance the understanding of these types of therapies and encourage their use to treat unresectable tumors that can benefit from the non-thermal mechanism of action which spares critical blood vessels and nerves in the surrounding area. We evaluate the response to PEFs by different cell types through experimental testing combined with computer simulations of these treatments. We show that IRE can be used to kill a specific type of bacteria that produce cellulose which can be used as an implantable material to repair damaged tissues. By killing these bacteria at particular times and locations during their cellulose production, we can create conduits in the overall structure of this material for the transport of oxygen and nutrients to the cells within the area after implantation. The use of tissue models also plays a key role in the investigation of various cancer treatments by providing a controlled environment which can mimic the state of cells within a tumor. We use tumor models comprised of a mix of collagen and cancer cells to evaluate their response to IRE based on the parameters that induce cell death and the time it takes for this process to occur. The treatment of prostate and pancreatic cancer cells with standard monopolar (only positive polarity) IRE pulses resulted in different time points for a full lesion (area of cell death) to develop for each cell type. These results indicate the presence of secondary processes within a cell that induce further cell death in the border of the lesion and cause the lesion to increase in size several hours after treatment. The use of high-frequency irreversible electroporation (H-FIRE)--comprised of short bursts of high-intensity, bipolar (both positive and negative polarity) pulses--can selectively treat cancer cells while keeping healthy cells in the neighboring areas alive. We show that H-FIRE pulses can target tumor-initiating cells (TICs) and late-stage, malignant cancer cells over non-malignant cells using a mouse ovarian cancer model representative of different stages of disease progression. To further explore the mechanisms that drive this difference in response to IRE and H-FIRE, we used more complex tumor models. Spheroids are a type of 3D cell culture model characterized by the aggregation of one or more types of cells within a single compact structure; when embedded in collagen gels, these provide cell-to-cell contact and cell-to-matrix adhesion by interactions of cells with the collagen fibers (closely mimicking the tumor microenvironment). The parameters for successful ablation with IRE and H-FIRE can be further optimized with the use of these models and the underlying mechanisms driving the response to PEFs at the cellular level can be revealed.

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Keywords
pulsed electric fields, tissue engineering, electroporation, cancer therapy, tumor models, hydrogels, high frequency bipolar pulses
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