Autophagy induction with RAD001 enhances chemosensitivity and radiosensitivity through met inhibition in papillary thyroid cancer

Chi Iou Lin, Edward E. Whang, David B. Donner, Jinyan Du, Jochen Lorch, Frank He, Xiaofeng Jiang, Brendan D. Price, Francis D. Moore, Daniel T. Ruan

Research output: Contribution to journalArticlepeer-review

88 Scopus citations

Abstract

Although autophagy is generally considered a prosurvival mechanism that preserves viability, there is evidence that it could drive an alternative programmed cell death pathway in cells with defects in apoptosis. Because the inhibition of autophagic activity promotes resistance to both chemotherapy and external beam radiation in papillary thyroid cancer (PTC), we determined if RAD001, a potent activator of autophagy, improves the efficacy of either therapy. We found that RAD001 increased the expression level of light chain 3-II, a marker for autophagy, as well as autophagosome formation in cell lines and in human PTC ex vivo. RAD001 sensitized PTC to doxorubicin and external beam radiation in a synergistic fashion, suggesting that combination therapy could improve therapeutic response at less toxic concentrations. The effects of RAD001 were abrogated by RNAi knockdown of the autophagy-related gene 5, suggesting that RAD001 acts, in part, by enhancing autophagy. Because the synergistic activity of RAD001 with doxorubicin and external radiation suggests distinct and complementary mechanisms of action, we characterized how autophagy modulates signaling pathways in PTC. To do so, we performed kinome profiling and discovered that autophagic activation resulted in Src phosphorylation and Met dephosphorylation. Src inhibition did not reverse the effects of RAD001, whereas Met inhibition reversed the effects of autophagy blockade on chemosensitivity. These results suggest that the anticancer effects of autophagic activation are mediated largely through Met. We conclude that RAD001 induces autophagy, which enhances the therapeutic response to cytotoxic chemotherapy and external beam radiation in PTC.

Original languageEnglish (US)
Pages (from-to)1217-1226
Number of pages10
JournalMolecular Cancer Research
Volume8
Issue number9
DOIs
StatePublished - Sep 2010
Externally publishedYes

ASJC Scopus subject areas

  • Molecular Biology
  • Oncology
  • Cancer Research

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