Irreversible Electroporation (IRE) has gained increasing popularity in the cancer treatment field during the past decade due to many advantages over other focal therapies. Despite early success in pre-clinical and clinical IRE trials, in vivo studies have shown that IRE suffers from an inability to destroy large volumes of cancer tissue without repeating treatment and/or increasing the applied electrical dose to dangerous levels. There are approaches to expand the treatment volume by IRE with the addition of chemotherapeutic or cytotoxic agents. While these studies demonstrated improved cell killing, the focus was on enhancing the ability of chemotherapeutic drugs or cytotoxic agents to enter and kill the cancer cells rather than enhancing the efficacy of IRE itself. Therefore, the aim of this work is to investigate the ability to increase the destructive capability of IRE without relying on cytotoxic drugs. Specifically, mechanisms that directly modify membrane properties should reduce the voltage threshold for lethal permeabilization and therefore increase the efficacy of cell killing and therefore the volume treated after a given IRE level. Two methods to achieve these changes are proposed in this study: 1) addition of surfactant (e.g. Dimethyl sulfoxide, or DMSO) to directly interact with membrane lipids thereby changing membrane line tension and surface tension, and 2) use of pulse timing (i.e. introduction and persistence of defects in the membrane between pulses). Here then we began by Investigation of IRE enhancement in vitro to understand the impacts of our proposed mechanisms and their ideal working parameters. We found that the best enhancement effect was achieved with addition of 5% v/v DMSO, which resulted in a significant increase of 75% more cell destruction compared to baseline IRE. Similarly with pulse timing, when dividing the pulses into three trains with 30s delays in between, an enhancement of 67% more cell destruction was achieved compared to baseline IRE. Next we tested our IRE enhancement approaches in an in vivo dorsal skin fold chamber (DSFC) model of prostate cancer with optimal parameters selected from our in vitro experiments. The results reproducibly showed that more than 120% and 101% enhancement in the treatment volume were achieved by the addition of DMSO and pulse timing, respectively, with two independent injury assessment methods (histological and perfusion defect). Finally, we translated one of the enhancement approaches (pulse timing) to an in vivo hind limb model of prostate cancer and demonstrated that more than 33% additional tumor destruction and 2 weeks longer tumor growth delay could be achieved compared to baseline IRE treatment without relying on any cytotoxic drugs or agents. Because DMSO is commercially available and regularly used at low concentrations (<10% v/v) in clinic, this approach could easily be integrated into current IRE procedures to increase the treatment efficacy. In addition, introducing pulse timing delays in IRE also increases the destructive potential of IRE without the introduction of any foreign agents into the body. Further opportunities exist in improving the adjuvant delivery methods, optimizing the pulse timing delivery approach and understanding the fundamental mechanisms of IRE. Nevertheless, we suggest that the simple and safe nature of our proposed approaches compared with cytotoxic drugs may help to translate IRE into the clinic.
University of Minnesota Ph.D. dissertation. May 2014. Major: Mechanical Engineering. Advisor: John Bischof. 1 computer file (PDF); xiii, 126 pages.
Membrane-Targeting Approaches for Enhanced Cell Destruction with Irreversible Electroporation.
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