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Cancer Cell. 2012 Dec 11;22(6):796-811. doi: 10.1016/j.ccr.2012.10.023.

JAK2/STAT5 inhibition circumvents resistance to PI3K/mTOR blockade: a rationale for cotargeting these pathways in metastatic breast cancer.

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Friedrich Miescher Institute for Biomedical Research, Basel, CH-4058, Switzerland.


Hyperactive PI3K/mTOR signaling is prevalent in human malignancies and its inhibition has potent antitumor consequences. Unfortunately, single-agent targeted cancer therapy is usually short-lived. We have discovered a JAK2/STAT5-evoked positive feedback loop that dampens the efficacy of PI3K/mTOR inhibition. Mechanistically, PI3K/mTOR inhibition increased IRS1-dependent activation of JAK2/STAT5 and secretion of IL-8 in several cell lines and primary breast tumors. Genetic or pharmacological inhibition of JAK2 abrogated this feedback loop and combined PI3K/mTOR and JAK2 inhibition synergistically reduced cancer cell number and tumor growth, decreased tumor seeding and metastasis, and also increased overall survival of the animals. Our results provide a rationale for combined targeting of the PI3K/mTOR and JAK2/STAT5 pathways in triple-negative breast cancer, a particularly aggressive and currently incurable disease.

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