Cancer cells require glutamine to adapt to increased biosynthetic activity. The limiting step in intracellular glutamine catabolism involves its conversion to glutamate by glutaminase (GA). Different GA isoforms are encoded by the genes GLS1 and GLS2 in humans. Herein, we show that glutamine levels control mitochondrial oxidative phosphorylation (OXPHOS) in AML cells. Glutaminase C (GAC) is the GA isoform that is most abundantly expressed in AML. Both knockdown of GLS1 expression and pharmacological GLS1 inhibition by the drug CB-839 can reduce OXPHOS, leading to leukemic cell proliferation arrest and apoptosis without causing cytotoxic activity against normal human CD34⁺ progenitors. Strikingly, a GLS1-knockdown dramatically inhibited AML development in NSG mice. The anti-leukemic activity of CB-839 was abrogated by both the expression of a hyperactive GAC^K320A allele and the addition of the TCA cycle product α-ketoglutarate, indicating the critical function of GLS1 in AML cell survival. Finally, glutaminolysis inhibition activated mitochondrial apoptosis and synergistically sensitized leukemic cells to priming with the BCL-2 inhibitor ABT-199. These findings show that targeting glutamine addiction via GLS1 inhibition offers a potential novel therapeutic strategy for AML.

The PI3K/AKT and mTOR signaling pathways are activated in acute myeloid leukemia, including in the more immature leukemic populations. Constitutive PI3K activation is detectable in 50% of acute myeloid leukemia samples whereas mTORC1 is activated in all cases of this disease. In leukemic cells, the PI3K activity relates to the expression of the p110delta isoform of class IA PI3K. Constitutive PI3K activation is the result of autocrine IGF-1/IGF-1R signaling in 70% of acute myeloid leukemia samples but specific inhibition of this pathway does not induce apoptosis. Specific inhibition of PI3K/AKT or mTORC1 alone in vitro has anti-leukemic effects which are essentially exerted via the suppression of proliferation. However, as mTORC1 activation is independent of PI3K/AKT in acute myeloid leukemia, dual PI3K and mTOR inhibitors may induce apoptosis in blast cells. Moreover, mTORC1 inhibition using sirolimus overactivates PI3K/AKT via the upregulation of IRS2 expression and by favoring IGF-1/IGF-1R autocrine signaling. Recent data also indicate that mTORC1 does not control protein translation in acute myeloid leukemia. These results open the way for the design of direct inhibitors of protein synthesis as novel acute myeloid leukemia therapies and also for the development of second generation mTOR inhibitors (the TORKinhibs).

Key Points: Glutamine removal and knockdown of the glutamine transporter SLC1A5 have antileukemic activity in AML. The glutaminase activity of l-asparaginase inhibits mTORC1 and protein synthesis and induces a strong autophagy in AML.

Objective Real-life studies on patients with primary CNS lymphoma (PCNSL) are scarce. Our objective was to analyze, in a nationwide population-based study, the current medical practice in the management of PCNSL. Methods The French oculo-cerebral lymphoma network (LOC) database prospectively records all newly diagnosed PCNSL cases from 32 French centers. Data of patients diagnosed between 2011 and 2016 were retrospectively analyzed. Results We identified 1,002 immunocompetent patients (43% aged >70 years, median Karnofsky Performance Status [KPS] 60). First-line treatment was high-dose methotrexate-based chemotherapy in 92% of cases, with an increasing use of rituximab over time (66%). Patients 60 years of age, WBRT and HCT-ASCT consolidation were administered in only 9% and 2%, respectively. The complete response rate to initial chemotherapy was 50%. Median progression-free survival was 10.5 months. For relapse, second-line chemotherapy, HCT-ASCT, WBRT, and palliative care were offered to 55%, 17%, 10%, and 18% of patients, respectively. The median, 2-year, and 5-year overall survival was 25.3 months, 51%, and 38%, respectively (60 years: 15.4 months, 44%, and 28%). Age, KPS, sex, and response to induction CT were independent prognostic factors in multivariate analysis. Conclusions Our study confirms the increasing proportion of elderly within the PCNSL population and shows comparable outcome in this population-based study with those reported by clinical trials, reflecting a notable application of recent PCNSL advances in treatment.

The phosphatidylinositol 3-kinase (PI3K)/Akt and mTORC1 pathways are frequently activated, representing potential therapeutic targets in acute myeloid leukemia (AML). In 19 AML samples with constitutive PI3K/Akt activation, the rapamycin derivative inhibitor everolimus (RAD001) increased Akt phosphorylation. This mTOR C1-mediated Akt up-regulation was explained by an insulin-like growth factor-1 (IGF-1)/IGF-1 receptor autocrine loop: (1) blast cells expressed functional IGF-1 receptors, and IGF-1-induced Akt activation was increased by RAD001, (2) a neutralizing anti-IGF-1R α-IR3 monoclonal antibody reversed the RAD001-induced Akt phosphorylation, and (3) autocrine production of IGF-1 was detected in purified blast cells by quantitative reverse transcription-polymerase chain reaction and immunofluorescence. This RAD001-induced PI3K/Akt up-regulation was due to an up-regulated expression of the IRS2 adaptor. Finally, we observed that concomitant inhibition of mTORC1 and PI3K/Akt by RAD001 and IC87114 induced additive antiproliferative effects. Our results suggest that dual inhibition of the mTORC1 complex and the IGF-1/IGF-1R/PI3K/Akt pathway in AML may enhance the efficacy of mTOR inhibitors in treatment of this disease.