Plethora of studies has reiterated the importance of chemoprevention in the reduction of prostate cancer (PCa) incidence and death rate in recent years. However an estimated 220,800 new prostate cancer cases and 27,540 deaths are expected to occur in US men by the end of 2015. Beta-lapachone is a promising anticancer bioreductive ortho-naphthoquinone that was initially isolated from the bark of the South American Lapacho tree. Recent studies suggest that β-lap kills cancer cells targeting the NAD(P)H:quinone oxidoreductase (NQO1) enzyme levels in cancer tissues. But LNCaP, a cell line of primary and metastatic hormone dependent PCa is deficient in NQO1 enzyme. In this study, the potential role of very low doses of x-ray radiation (VLDR) from a portable pyroelectric generator at 20mGy/hr in enhancing the chemopreventive effects of beta-lapachone in LNCaP cells were investigated. This generator uses the pyroelectric principle to generate low doses of low energy radiation from polarized pyroelectric crystal when heated or cooled. Chemosensitivity by exposing LNCaP (and/or PC3) cells to 20mGy/hr of x-ray radiation prior to treatment with varied dose concentrations of beta-lapachone, we assessed the using MTT and Trypan blue exclusion assays. Dicoumarol (an NQO1 inhibitor) was administered to assess the effect of VLDR on NQO1 activation. Nitroblue tetrazolium assay was used to assess the intracellular ROS levels. Fluorescence microscopy and DNA Fragmentation were used to assess the mode of cell death. LNCaP cells were found to be slightly more radiosensitive compared to PC3 cells after exposure to VLDR. The data suggests that VLDR induced a rise in ROS levels, followed by upregulation in NQO1 levels. The major mode of cell death by this combination therapy was found to be via Apoptosis. In conclusion, our results confirm that VLDR-induced NQO1 levels contribute to LNCaP cell death by enhancing the chemopreventive effects of beta-lapachone.
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