PDK1-SGK1 signaling sustains AKT-independent mTORC1 activation and confers resistance to PI3Kα inhibition

Pau Castel, Haley Ellis, Ruzica Bago, Eneda Toska, Pedram Razavi, F. Javier Carmona, srinivasaraghavan kannan, Chandra S. Verma, Maura Dickler, Sarat Chandarlapaty, Edi Brogi, Dario Alessi, Jose Baselga (Lead / Corresponding author), Maurizio Scaltriti (Lead / Corresponding author)

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166 Citations (Scopus)
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PIK3CA, the gene encoding the alpha isoform of PI3K (PI3Kα), is frequently mutated and oncogenic in breast cancer. PI3Kα inhibitors are in clinical development and despite promising early clinical activity, primary and acquired resistance is frequent among patients. We have previously reported that residual downstream mTORC1 activity upon treatment with PI3Kα inhibitors drives resistance to these agents. However, the underlying mechanisms that mediate this phenotype are not fully understood. Here we show that in cancer cells resistant to PI3Kα inhibition, PDK1 blockade restores sensitivity to these therapies. SGK1, which is activated by PDK1, contributes to the maintenance of residual mTORC1 activity and cell survival through direct phosphorylation and inhibition of TSC2. Targeting either PDK1 or SGK1 prevents mTORC1 activation and restores the antitumoral effects of PI3Kα inhibition in resistant cancer cells.
Original languageEnglish
Pages (from-to)229-242
Number of pages14
JournalCancer Cell
Issue number2
Early online date21 Jul 2016
Publication statusPublished - 8 Aug 2016


  • breast cancer
  • PI3K pathway
  • kinase
  • Targeted Therapy
  • drug resistance
  • PDK1
  • SGK1
  • mTOR


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