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  • Title: DHL‑TauZnNa, a newly synthesized α-lipoic acid derivative, induces autophagy in human colorectal cancer cells.
    Author: Hiratsuka T, Inomata M, Kono Y, Yokoyama S, Shiraishi N, Kitano S.
    Journal: Oncol Rep; 2013 Jun; 29(6):2140-6. PubMed ID: 23588820.
    Abstract:
    In recent years, several antioxidant substances have been found to have an antiproliferative effect on various types of carcinomas. α-lipoic acid (ALA) induces apoptosis in several types of cancer cell lines, but it is difficult to apply α-lipoic acid in clinical use as it is easily oxidized and unstable. Recently, we succeeded in synthesizing the α-lipoic acid derivative sodium N-[6,8-dimercaptooctanoyl]-2-aminoethanesulfonate zinc complex (DHL-TauZnNa), which has highly stable antioxidant effects. We investigated whether DHL-TauZnNa elicits its antiproliferative effects in vivo and in vitro by inducing apoptosis, autophagy or cell cycle arrest, and we analyzed the expression of proteins related to these phenomena and their phosphorylation in HT-29 human colon cancer cells. Subcutaneously administered DHL-TauZnNa treatment applied daily for 41 days significantly inhibited tumor growth by 43% in a xenograft mouse model (P=0.0271). DHL-TauZnNa significantly reduced cell viability over that of controls in the trypan-blue exclusion test in a time- and dose-dependent manner (P<0.05). DHL-TauZnNa increased the proportion of cells in S phase and decreased that of cells in G0/G1 phase in the cell cycle analysis of HT-29 cells. Although DHL-TauZnNa did not increase caspase-3/7 activity and DNA fragmentation in flow cytometry analysis, it increased the expression of microtubule-associated protein light chain 3-II. Autophagosomes and autolysosomes were observed by electron microscopy in the cytoplasm of HT-29 cells treated with DHL-TauZnNa. These results suggest that DHL-TauZnNa inhibited the proliferation of HT-29 cells through the mechanisms of G2/M cell cycle arrest and autophagy but not that of apoptosis. The newly synthesized ALA derivative DHL-TauZnNa may be expected to become a novel cancer therapeutic strategy through its induction of autophagy.
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