A Small Molecule Screen Exposes mTOR Signaling Pathway Involvement in Radiation-Induced Apoptosis

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• 作者：Elizabeth R. Sharlow ; Stephanie Leimgruber ; Ana Lira ; Michael J. McConnell ; Andrés Norambuena ; George S. Bloom ; Michael W. Epperly ; Joel S. Greenberger ; John S. Lazo
• 刊名：ACS Chemical Biology
• 出版年：2016
• 出版时间：May 20, 2016
• 年：2016
• 卷：11
• 期：5
• 页码：1428-1437
• 全文大小：614K
• 年卷期：0
• ISSN：1554-8937

文摘

Individuals are at risk of exposure to acute ionizing radiation (IR) from a nuclear accident or terrorism, but we lack effective therapies to mitigate the lethal IR effects. In the current study, we exploited an optimized, cell-based, high throughput screening assay to interrogate a small molecule library comprising 3437 known pharmacologically active compounds for mitigation against IR-induced apoptosis. Thirty-three library compounds significantly reduced apoptosis when administered 1 h after 4 Gy IR. Two- or three-dimensional computational structural analyses of the compounds indicated only one or two chemical clusters with most of the compounds being unique structures. The mechanistic target of rapamycin complex 1 (mTORC1) inhibitor, rapamycin, was the most potent compound, and it mitigated apoptosis by 50% at 200 ± 50 pM. Other mTOR inhibitors, namely everolimus, AZD8055, and torin 1, also suppressed apoptosis, providing additional pharmacological evidence for mTOR pathway involvement in regulating cell death after IR. Everolimus and torin 1 treatment after IR decreased the S phase population and enforced both G₁ and G₂ phase arrest. This prorogation of cell cycle progression was accompanied by decreased IR-induced DNA damage measured by γH2AX phosphorylation at Ser139. RNA interference-mediated knockdown of the respective mTORC1 and mTORC2 subunits, Raptor or Rictor, also mitigated IR-induced apoptosis. Collectively, this study suggests a central role for the mTOR signaling in the cytotoxic response to IR and offers a useful platform to probe for additional agents.