Exploration of effects of emodin in selected cancer cell lines: enhanced growth inhibition by ascorbic acid and regulation of LRP1 and AR under hypoxia-like conditions

• Published in: Journal of applied toxicology Vol. 34; no. 1; pp. 95 - 104
• Main Authors: Masaldan, Shashank, Iyer, Vidhya V.
• Format: Journal Article
• Language: English
• Published: England Blackwell Publishing Ltd 01.01.2014; Wiley Subscription Services, Inc
• Subjects: androgen receptor; anticancer; antioxidant; ascorbic acid; Ascorbic Acid - pharmacology; Cancer; Cell Line, Tumor; Chemotherapy; Down-Regulation - drug effects; emodin; Emodin - pharmacology; Gene Expression Regulation, Neoplastic; Humans; Hypoxia; Hypoxia - metabolism; LDL receptor-related protein 1; Low Density Lipoprotein Receptor-Related Protein-1 - genetics; Low Density Lipoprotein Receptor-Related Protein-1 - metabolism; Male; prostate cancer; Prostatic Neoplasms - genetics; Prostatic Neoplasms - metabolism; Proteins; reactive oxygen species; Reactive Oxygen Species - metabolism; Receptors, Androgen - genetics; Receptors, Androgen - metabolism; Toxicology; Up-Regulation - drug effects; antioxidant; ascorbic acid; prostate cancer; androgen receptor; LDL receptor-related protein 1; reactive oxygen species; anticancer; emodin
• ISSN: 0260-437X; 1099-1263
• DOI: 10.1002/jat.2838

ABSTRACT This study explores the link between the antiproliferative activity of emodin through the generation of reactive oxygen species (ROS) in various cancer cell lines and the expression of the androgen receptor (AR) in the prostate cancer cell lines LNCaP (androgen‐sensitive) and PC‐3 (androgen‐refractory), as well as the pro‐metastatic low‐density lipoprotein receptor‐related protein 1 (LRP1) in the above prostate cancer cells and the nonprostate cell lines A549 (lung), HCT‐15 (colon) and MG‐63 (bone) under normoxic and hypoxia‐like conditions. Among all cell lines, emodin showed most growth inhibition in LNCaP, followed by A549. The mechanism of cytotoxicity of emodin was postulated to be the widely reported ROS generation, based on the observations of poor in vitro radical‐scavenging activity and increased growth inhibition of emodin by ascorbic acid (AA) pre‐treatment owing to the additive effects of ROS generation by emodin and pro‐oxidant effects of AA. Emodin downregulated AR in LNCaP under normoxic and hypoxia‐like conditions (simulated by CoCl2) and LRP1 under normoxia. Emodin upregulated LRP1 in other cell lines, except HCT‐15, under normoxic, and even more markedly under hypoxia‐like conditions. The downregulation of AR in LNCaP and upregulation of LRP1 in all cell lines, except HCT‐15, under hypoxia‐like conditions along with growth inhibition by emodin, suggests that emodin may be a useful therapeutic option against androgen‐sensitive prostate cancer and other such LRP1‐expressing cancers to attempt the targeting of the elevated LRP1 levels to allow the uptake of emodin and/or any other accompanying therapeutic agents by LRP1. Copyright © 2012 John Wiley & Sons, Ltd. Ascorbic acid (AA) pre‐treatment increased growth inhibition by emodin in AR‐positive LNCaP, PC‐3, HCT‐15, MG‐63 and A549 cancer cells, all with varying LRP1 levels, probably owing to ROS generation by emodin and the pro‐oxidant activity of AA. Marked increase in LRP1 expression and growth inhibition of these cancer cells by emodin under hypoxia‐like conditions may point to a strategy to target hypoxic tumors through the LRP1 protein by increased uptake of emodin, alone or along with other chemotherapeutic agents.