ATP-site binding inhibitor effectively targets mTORC1 and mTORC2 complexes in glioblastoma

Abstract

Abstract. The PI3K-AKT-mTOR signaling axis is central to the transformed phenotype of glioblastoma (GBM) cells, due to frequent loss of tumor suppressor PTEN (phosphatase and tensin homolog deleted on chromosome 10). The mechanistic target of rapamycin (mTOR) kinase is present in two cellular multi-protein complexes, mTORC1 and mTORC2, which have distinct subunit composition, substrates and mechanisms of action. Targeting the mTOR protein is a promising strategy for GBM therapy. However, neither of these complexes is fully inhibited by the allosteric inhibitor of mTOR, rapamycin or its analogs. Herein, we provide evidence that the combined inhibition of mTORC1/2, using the ATP-competitive binding inhibitor PP242, would effectively suppress GBM growth and dissemination as compared to an allosteric binding inhibitor of mTOR. GBM cells treated with PP242 demonstrated significantly decreased activation of mTORC1 and mTORC2, as shown by reduced phosphorylation of their substrate levels, p70 S6K Thr389 and AKT Ser473, respectively, in a dosedependent manner. Furthermore, insulin induced activation of these kinases was abrogated by pretreatment with PP242 as compared with rapamycin. Unlike rapamycin, PP242 modestly activates extracellular regulated kinase (ERK1/2), as shown by expression of pERK Thr202/Tyr204 . Cell proliferation and S-phase entry of GBM cells was significantly suppressed by PP242, which was more pronounced compared to rapamycin treatment. Lastly, PP242 significantly suppressed the migration of GBM cells, which was associated with a change in cellular behavior rather than cytoskeleton loss. In conclusion, these results underscore the potential therapeutic use of the PP242, a novel ATP-competitive binding inhibitor of mTORC1/2 kinase, in suppression of GBM growth and dissemination.

Spleen tyrosine kinase (SYK) blocks autophagic Tau degradation in vitro and in vivo

“…The effect of the mTOR inhibitor KU0063794 on Akt phosphorylation is expected and has been described before (34). In fact, Akt (Ser-473) is a known substrate of mTOR, and mTOR has been shown to regulate Akt phosphorylation at that site (35)(36)(37)(38).…”

mTOR: A Cellular Regulator Interface in Health and Disease

“…The second generation of inhibitors targets both TORC1 as well as TORC2 by competing with ATP at the catalytic site of the mTOR kinase, which is present in both complexes [202,203]. Similar to rapalogs, they can decrease protein translation and attenuate cell proliferation in several cancer cell lines [204,205].…”

Mice endometrium receptivity in early pregnancy is impaired by maternal hyperinsulinemia

“…Insulin could serve its roles though mTOR (28,29). Neil et al determined that insulin may induce activation of mTOR signaling in glioblastoma cells (41). Fritzen et al observed that mTOR signaling via unc-51 like autophagy activating kinase 1 may mediate the autophagy-inhibiting effect of insulin in human skeletal muscle (42).…”