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Autophagy is an intracellular recycling mechanism that helps cells to survive against environmental stress and nutritional
starvation. We have recently shown that prostate cancers undergo metabolic stress and caspase-independent cell death
following exposure to arginine deiminase (ADI, an enzyme that degrades arginine in tissue). The aims of our current
investigation into the application of ADI as a novel cancer therapy are to identify the components mediating tumor cell
death, and to determine the role of autophagy (stimulated by ADI and/or rapamycin) on cell death. Using advanced
fluorescence microscopy techniques including 3D deconvolution and superresolution structured-illumination microscopy
(SIM), we show that prostate tumor cells that are killed after exposure to ADI for extended periods, exhibit a
morphology that is distinct from caspase-dependent apoptosis; and that autophagosomes forming as a result of ADI
stimulation contain DAPI-stained nuclear material. Fluorescence imaging (as well as cryo-electron microscopy) show a
breakdown of both the inner and outer nuclear membranes at the interface between the cell nucleus and aggregated
autophagolysosomes. Finally, the addition of N-acetyl cysteine (or NAC, a scavenger for reactive oxygen species)
effectively abolishes the appearance of autophagolysosomes containing nuclear material. We hope to continue this
research to understand the processes that govern the survival or death of these tumor cells, in order to develop methods
to improve the efficacy of cancer pharmacotherapy.
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