RAD 001 (everolimus) prevents mTOR and Akt late re-activation in response to imatinib in chronic myeloid leukemia.

The mammalian target of rapamycin (mTOR) is one target of BCR-ABL fusion gene of chronic myeloid leukemia (CML). Moreover, it drives a compensatory route to Imatinib mesylate (IM) possibly involved in the progression of leukemic progenitors towards a drug-resistant phenotype. Accordingly, mTOR inhibitors are proposed for combined therapeutic strategies in CML. The major caveat in the use of mTOR inhibitors for cancer therapy comes from the induction of an mTOR-phosphatidylinositol 3 kinase (PI3k) feedback loop driving the retrograde activation of Akt. Here we show that the rapamycin derivative RAD 001 (everolimus, Novartis Institutes for Biomedical Research) inhibits mTOR and, more importantly, revokes mTOR late re-activation in response to IM. RAD 001 interferes with the assembly of both mTOR complexes: mTORC1 and mTORC2. The inhibition of mTORC2 results in the de-phosphorylation of Akt at Ser(473) in the hydrophobic motif of C-terminal tail required for Akt full activation and precludes Akt re-phosphorylation in response to IM. Moreover, RAD 001-induced inhibition of Akt causes the de-phosphorylation of tuberous sclerosis tumor suppressor protein TSC2 at 14-3-3 binding sites, TSC2 release from 14-3-3 sigma (restoring its inhibitory function on mTORC1) and nuclear import (promoting the nuclear translocation of cyclin-dependent kinase [CDK] inhibitor p27(Kip1), the stabilization of p27(Kip1) ligand with CDK2, and the G(0)/G(1) arrest). RAD 001 cytotoxicity on cells not expressing the BCR-ABL fusion gene or its p210 protein tyrosine kinase (TK) activity suggests that the inhibition of normal hematopoiesis may represent a drug side effect.

Mancini M ，Petta S ，Martinelli G ，Barbieri E ，Santucci MA ... -  《-》

Compensatory PI3-kinase/Akt/mTor activation regulates imatinib resistance development.

Burchert A ，Wang Y ，Cai D ，von Bubnoff N ，Paschka P ，Müller-Brüsselbach S ，Ottmann OG ，Duyster J ，Hochhaus A ，Neubauer A ... -  《LEUKEMIA》

mTOR inhibitor RAD001 (Everolimus) enhances the effects of imatinib in chronic myeloid leukemia by raising the nuclear expression of c-ABL protein.

Constitutive tyrosine kinase (TK) activity of p210 BCR-ABL fusion protein of chronic myeloid leukemia (CML) usurps physiological functions of normal p145 c-ABL protein. Accordingly, its inhibition by imatinib mesylate (IM) lets p145 c-ABL translocate into the nuclear compartment, which drives cell growth arrest and apoptotic death. Here we show that IM and the mammalian target of rapamycin (mTOR) inhibitor RAD001 (Everolimus) have additive effects on BCR-ABL-expressing cells. Those effects are at least partly conditional upon the enhanced nuclear accumulation of p145 c-ABL through events encompassing post-translational modifications of p145 c-ABL (Thr(735) phosphorylation) precluding its nuclear export and of 14-3-3 sigma (Ser(186) phosphorylation by c-Jun N-terminal kinase [JNK]) promoting p145 c-ABL nuclear re-import.

Mancini M ，Corradi V ，Petta S ，Martinelli G ，Barbieri E ，Santucci MA ... -  《-》

Novel pathway in Bcr-Abl signal transduction involves Akt-independent, PLC-gamma1-driven activation of mTOR/p70S6-kinase pathway.

Markova B ，Albers C ，Breitenbuecher F ，Melo JV ，Brümmendorf TH ，Heidel F ，Lipka D ，Duyster J ，Huber C ，Fischer T ... -  《-》

Molecular characterization and sensitivity of STI-571 (imatinib mesylate, Gleevec)-resistant, Bcr-Abl-positive, human acute leukemia cells to SRC kinase inhibitor PD180970 and 17-allylamino-17-demethoxygeldanamycin.

Nimmanapalli R ，O'Bryan E ，Huang M ，Bali P ，Burnette PK ，Loughran T ，Tepperberg J ，Jove R ，Bhalla K ... -  《CANCER RESEARCH》