Dual mTORC2/mTORC1 Targeting Results in Potent Suppressive Effects on Acute Myeloid Leukemia (AML) Progenitors

Abstract

Purpose To determine whether mTORC2 and RI-mTORC1 complexes are present in AML cells and to examine the effects of dual mTORC2/mTORC1 inhibition on primitive AML leukemic progenitors. Experimental Design Combinations of different experimental approaches were used, including immunoblotting to detect phosphorylated/activated forms of elements of the mTOR pathway in leukemic cell lines and primary AML blasts; cell proliferation assays; direct assessment of mRNA translation in polysomal fractions of leukemic cells; and clonogenic assays in methylcellulose to evaluate leukemic progenitor colony formation. Results mTORC2 complexes are active in AML cells and play critical roles in leukemogenesis. Rapamycin insensitive (RI) mTORC1 complexes are also formed and regulate the activity of the translational repressor 4E-BP1 in AML cells. OSI-027, blocks mTORC1 and mTORC2 activities and suppresses mRNA translation of cyclin D1 and other genes that mediate proliferative responses in AML cells. Moreover, OSI-027 acts as a potent suppressor of primitive leukemic precursors from AML patients and is much more effective than rapamycin in eliciting antileukemic effects in vitro. Conclusions Dual targeting of mTORC2 and mTORC1 results in potent suppressive effects on primitive leukemic progenitors from AML patients. Inhibition of the mTOR catalytic site with OSI-027 results in suppression of both mTORC2 and RI-mTORC1 complexes and elicits much more potent antileukemic responses than selective mTORC1 targeting with rapamycin.

Targeting of mTORC1/2 by the mTOR kinase inhibitor PP242 induces apoptosis in AML cells under conditions mimicking the bone marrow microenvironment

“…Most importantly, PP242, but not rapamycin derivative temsirolimus, induced cell death in stromal cocultures, which otherwise reliably support viability of leukemic blasts (supplemental Figure 1) and reduce efficacy of traditional anti-AML chemotherapy agents. 35 These data support the recently reported evidence of the superior antileukemic potency of mTOR kinase inhibitors 36,37 or dual P13K/ mTORK inhibitors 38 through suppression of rapamycin-resistant mTORC1 and mTORC2 complexes compared with allosteric mTOR inhibitors. These findings indicate that mTOR signaling plays an essential role in the stroma-leukemia cell interaction, and its blockade is sufficient to abrogate the stroma-mediated survival advantage of leukemic cells.…”

AZD1208, a potent and selective pan-Pim kinase inhibitor, demonstrates efficacy in preclinical models of acute myeloid leukemia

“…[23][24][25] In vivo studies were treated with either vehicle or AZD1208, with 3 mice per dose and time point, and tumors were harvested and lysed for immunoblot analysis. pBAD protein levels were quantified by using the phospho/total-BAD MULTI-SPOT Assay System from Meso Scale Discovery.…”

Targeting the PI3K/AKT/mTOR Signaling Axis in Children with Hematologic Malignancies

“…Because constitutive activation of AKT is the most common pathway abnormality in AML, dual PI3K/mTOR inhibitors (PI-103, BEZ235), mTORC1/2 inhibitors (OSI-027, PP242), and AKT inhibitors (perifosine) have been investigated in preclinical models and, at least in vitro, appear to be more effective than rapalogs. [183][184][185][186][187] Based on these results, early-phase clinical trials are ongoing in adults.…”