Abstract 2788: Antiproliferative schweinfurthins reveal a role of the trans-Golgi-network in mTOR-AKT signaling and cancer cell survival
Authors: Bao Xingfeng , Hata Naoko , Agarwala Kishan , Wang Zichun , Lee Winnie , Parent Lana , Cheng Hongsheng , Qiu Dayong , Shen Yongchun , Du Bingfan , Zheng Wanjun , Zhao Nanding , Postema Maarten , Jappe Mary Woodall , Takase Yasutaka , Uenaka Toshimitsu , Nomoto Kenichi 
Published: May 2015

Abstract
The schweinfurthin class of natural compounds showed selective and potent anti-proliferative activities in the NCI-60 cancer cell panel1,2). Recent work by Burgett et al3) suggested that schweinfurthins may bind to oxysterol-binding protein-related proteins (ORPs) for their anti-proliferative activity. However, the mechanism of the selectivity and potency is still unknown. Here we show that schweinfurthins preferentially inhibited cell proliferation of PTEN-deficient cancer cells across different cancer types, and specifically inhibited AKT phosphorylation in both PTEN wild-type and mutant cancer cells. Intracellularly, a fluorescent schweinfurthin probe localized within the endosome/lysosome structure. Treatment of cells with active schweinfurthins caused fragmentation of the trans-Golgi-network (TGN), a vesicular trafficking system, in a dose- and time-dependent manner, without impacting the cis, med or trans-Golgi matrix structures. An inactive trimethylated analog of schweinfurthins did not display this activity. Using biotinylated probes, we found that schweinfurthins bind to the sterol-binding domain of ORPs; the capacity of binding to ORPs was positively correlated with both TGN fragmentation activity and anti-proliferative activity. These results are consistent with the recent observation that knockdown of specific ORP proteins leads to TGN trafficking disruption4). The fragmentation of TGN by schweinfurthins resulted in specific inhibition of mTOR-AKT pathway signaling in two ways: 1) disruption of lipid raft organization at the plasma membrane, evidenced by diminished trafficking of ceramide, GM1 and sphingomyelin, which inhibited PDK1 phosphorylation; and 2) dislocation of mTOR from its active sites at endosomes and/or lysosomes. Furthermore, we found that PTEN-deficient DLBCL cancer cells were highly sensitive to schweinfurthin treatment in vitro (IC50 values &lt; 10 nM). Normal human fibroblasts were 1000 times less sensitive than the DLBCL cells. Taken together, our results disclosed an important role of the TGN, which was specifically targeted by schweinfurthins, in mTOR-AKT signaling and in cancer cell survival, suggesting that analogs of schweinfurthin might offer promising novel therapeutics for treating mTOR-AKT signaling-addicted cancer cells such as PTEN-deficient DLBCL.
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Citation Format: Xingfeng Bao, Naoko Hata, Kishan Agarwala, Zichun Wang, Winnie Lee, Lana Parent, Hongsheng Cheng, Dayong Qiu, Yongchun Shen, Bingfan Du, Wanjun Zheng, Nanding Zhao, Maarten Postema, Mary Woodall Jappe, Yasutaka Takase, Toshimitsu Uenaka, Kenichi Nomoto. Antiproliferative schweinfurthins reveal a role of the trans-Golgi-network in mTOR-AKT signaling and cancer cell survival. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2788. doi:10.1158/1538-7445.AM2014-2788