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Dual inhibition of the mTORC1 and mTORC2 signaling pathways is a promising therapeutic target for adult T-cell leukemia.

ABSTRACT: Adult T-cell leukemia (ATL) has a poor prognosis as a result of severe immunosuppression and rapid tumor progression with resistance to conventional chemotherapy. Recent integrated-genome analysis has revealed mutations in many genes involved in the T-cell signaling pathway, suggesting that the aberration of this pathway is an important factor in ATL pathogenesis and ATL-cell proliferation. We screened a siRNA library to examine signaling-pathway functionality and found that the PI3K/Akt/mTOR pathway is critical to ATL-cell proliferation. We therefore investigated the effect of mammalian target of rapamycin (mTOR) inhibitors, including the dual inhibitors PP242 and AZD8055 and the mTORC1 inhibitors rapamycin and everolimus, on human T-cell leukemia virus type 1 (HTLV-1)-infected-cell and ATL-cell lines. Both dual inhibitors inhibited the proliferation of all tested cell lines by inducing G1-phase cell-cycle arrest and subsequent cell apoptosis, whereas the effects of the 2 mTORC1 inhibitors were limited, as they did not induce cell apoptosis. In the ATL-cell lines and in the primary ATL samples, both dual inhibitors inhibited phosphorylation of AKT at serine-473, a target of mTORC2, as well as that of S6K, whereas the mTORC1 inhibitors only inhibited mTORC1. Furthermore, AZD8055 more significantly inhibited the in vivo growth of the ATL-cell xenografts than did everolimus. These results indicate that the PI3K/mTOR pathway is critical to ATL-cell proliferation and might thus be a new therapeutic target in ATL.

SUBMITTER: Kawata T

PROVIDER: S-EPMC5765289 | biostudies-other | 2018 Jan

REPOSITORIES: biostudies-other

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Dual inhibition of the mTORC1 and mTORC2 signaling pathways is a promising therapeutic target for adult T-cell leukemia.

Kawata Takahito T Tada Kohei K Kobayashi Masayuki M Sakamoto Takashi T Takiuchi Yoko Y Iwai Fumie F Sakurada Maki M Hishizawa Masakatsu M Shirakawa Kotaro K Shindo Keisuke K Sato Hironori H Takaori-Kondo Akifumi A

Cancer science 20171122 1

Adult T-cell leukemia (ATL) has a poor prognosis as a result of severe immunosuppression and rapid tumor progression with resistance to conventional chemotherapy. Recent integrated-genome analysis has revealed mutations in many genes involved in the T-cell signaling pathway, suggesting that the aberration of this pathway is an important factor in ATL pathogenesis and ATL-cell proliferation. We screened a siRNA library to examine signaling-pathway functionality and found that the PI3K/Akt/mTOR pa ...[more]

PMID: 29077243

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Project description:The mammalian target of rapamycin (mTOR) regulates cell growth and survival by integrating nutrient and hormonal signals. These signaling functions are distributed between at least two distinct mTOR protein complexes: mTORC1 and mTORC2. mTORC1 is sensitive to the selective inhibitor rapamycin and activated by growth factor stimulation via the canonical phosphoinositide 3-kinase (PI3K)-->Akt-->mTOR pathway. Activated mTORC1 kinase up-regulates protein synthesis by phosphorylating key regulators of mRNA translation. By contrast, mTORC2 is resistant to rapamycin. Genetic studies have suggested that mTORC2 may phosphorylate Akt at S473, one of two phosphorylation sites required for Akt activation; this has been controversial, in part because RNA interference and gene knockouts produce distinct Akt phospho-isoforms. The central role of mTOR in controlling key cellular growth and survival pathways has sparked interest in discovering mTOR inhibitors that bind to the ATP site and therefore target both mTORC2 and mTORC1. We investigated mTOR signaling in cells and animals with two novel and specific mTOR kinase domain inhibitors (TORKinibs). Unlike rapamycin, these TORKinibs (PP242 and PP30) inhibit mTORC2, and we use them to show that pharmacological inhibition of mTOR blocks the phosphorylation of Akt at S473 and prevents its full activation. Furthermore, we show that TORKinibs inhibit proliferation of primary cells more completely than rapamycin. Surprisingly, we find that mTORC2 is not the basis for this enhanced activity, and we show that the TORKinib PP242 is a more effective mTORC1 inhibitor than rapamycin. Importantly, at the molecular level, PP242 inhibits cap-dependent translation under conditions in which rapamycin has no effect. Our findings identify new functional features of mTORC1 that are resistant to rapamycin but are effectively targeted by TORKinibs. These potent new pharmacological agents complement rapamycin in the study of mTOR and its role in normal physiology and human disease.

Dataset Information

Dual inhibition of the mTORC1 and mTORC2 signaling pathways is a promising therapeutic target for adult T-cell leukemia.

Publications

Dual inhibition of the mTORC1 and mTORC2 signaling pathways is a promising therapeutic target for adult T-cell leukemia.

Similar Datasets

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