Dual PI3K/mTOR inhibition shows antileukemic activity in MLL-rearranged acute myeloid leukemia

Abstract

In acute myeloid leukemia (AML), several signaling pathways such as the phosphatidylinositol-3-kinase/AKT and the mammalian target of rapamycin (PI3K/AKT/mTOR) pathway are deregulated and constitutively activated as a consequence of genetic and cytogenetic abnormalities. We tested the effectiveness of PI3K/AKT/mTOR-targeting therapies and tried to identify alterations that associate with treatment sensitivity. By analyzing primary samples and cell lines, we observed a wide range of cytotoxic activity for inhibition of AKT (MK-2206), mTORC1 (rapamycin) and PI3K/mTORC1/2 (BEZ-235) with a high sensitivity of cells carrying an MLL rearrangement. In vivo PI3K/mTOR inhibition delayed tumor progression, reduced tumor load and prolonged survival in an MLL-AF9(+)/FLT3-ITD(+) xenograft mouse model. By performing targeted amplicon sequencing in 38 MLL-AF9(+) and 125 cytogenetically normal AML patient samples, we found a high additional mutation rate for genes involved in growth factor signaling in 79% of all MLL-AF9(+) samples, which could lead to a possible benefit of this cohort. PI3K/mTOR inhibition for 24 h led to the cross-activation of the ERK pathway. Further in vitro studies combining PI3K/mTOR and ERK pathway inhibition revealed highly synergistic effects in apoptosis assays. Our data implicate a possible therapeutic benefit of PI3K/mTOR inhibition in the MLL-mutated subgroup. Inhibiting rescue pathways could improve the therapeutic efficacy of PI3K-targeted therapies in AML.

The transcriptomic landscape and directed chemical interrogation of MLL-rearranged acute myeloid leukemias

“…IDH2 mutations, present in 3 of 31 samples in this cohort, had not been detected in previous reports, possibly reflecting a great heterogeneity in this disease. Finally, rare mutations in genes encoding splicing factors have been described in the MLL-MLLT3 subtype 10 . In our cohort, we found three mutations in SRSF2 in non-MLL-MLLT3 samples, indicating that these events occur in various MLL-F ALL subtypes.…”

“…The previous analysis, however, showed that MLL-F AMLs have the lowest frequency of mutations among all the AML subtypes 9 . Targeted analyses of larger MLL-F AML cohorts have identified frequent KRAS and NRAS mutations in this disease 7,10 . Consistent with these observations, recent studies have indicated that MLL-F AMLs are possibly more sensitive to mitogen-activated protein kinase kinase (MEK) inhibitors than control leukemias, raising the possibility that the RAS-ERK pathway is sensitized in MLL-F AMLs 11 .…”

Targeting mTOR signaling pathways and related negative feedback loops for the treatment of acute myeloid leukemia

“…34 Notably, there was particular sensitivity among the AML blasts with MLL translocations, a subset in which 52% contained an NRAS or KRAS mutation as compared to 28% in cytogenetically normal AML blasts. 34 These results are in agreement with reports showing that RAS mutations can activate the PI3K/AKT/mTOR pathway. 35 As another example of the regulatory complexity of this pathway, treatment with BEZ-235 resulted in increased phosphorylation of ERK (extracellular regulated kinase) suggesting an escape mechanism for PI3K/AKT/mTOR inhibition.…”

“…33 The similarities between the PI3K p110 subunit and mTOR catalytic domains have allowed the development of dual PI3K/mTOR dual inhibitors including BEZ-235. 34 BEZ-235 was found to induce significant apoptosis of primary AML blasts to a greater magnitude than the selective AKT and mTOR inhibitors, MK-2206 and rapamycin, respectively. 34 Notably, there was particular sensitivity among the AML blasts with MLL translocations, a subset in which 52% contained an NRAS or KRAS mutation as compared to 28% in cytogenetically normal AML blasts.…”

“…34 BEZ-235 was found to induce significant apoptosis of primary AML blasts to a greater magnitude than the selective AKT and mTOR inhibitors, MK-2206 and rapamycin, respectively. 34 Notably, there was particular sensitivity among the AML blasts with MLL translocations, a subset in which 52% contained an NRAS or KRAS mutation as compared to 28% in cytogenetically normal AML blasts. 34 These results are in agreement with reports showing that RAS mutations can activate the PI3K/AKT/mTOR pathway.…”