Ablation of PI3K blocks BCR-ABL leukemogenesis in mice, and a dual PI3K/mTOR inhibitor prevents expansion of human BCR-ABL+ leukemia cells
Michael G. Kharas, … , Kevan M. Shokat, David A. Fruman
Michael G. Kharas, … , Kevan M. Shokat, David A. Fruman
Published August 14, 2008
Citation Information: J Clin Invest. 2008;118(9):3038-3050. https://doi.org/10.1172/JCI33337.
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Ablation of PI3K blocks BCR-ABL leukemogenesis in mice, and a dual PI3K/mTOR inhibitor prevents expansion of human BCR-ABL+ leukemia cells

Abstract

Some cases of pre–B cell acute lymphoblastic leukemia (pre–B-ALL) are caused by the Philadelphia (Ph) chromosome–encoded BCR-ABL oncogene, and these tend to have a poor prognosis. Inhibitors of the PI3K/AKT pathway reduce BCR-ABL–mediated transformation in vitro; however, the specific PI3K isoforms involved are poorly defined. Using a murine model of Ph+ pre–B-ALL, we found that deletion of both Pik3r1 and Pik3r2, genes encoding class IA PI3K regulatory isoforms, severely impaired transformation. BCR-ABL–dependent pre/pro-B cell lines could be established at low frequency from progenitors that lacked these genes, but the cells were smaller, proliferated more slowly, and failed to cause leukemia in vivo. These cell lines displayed nearly undetectable PI3K signaling function and were resistant to the PI3K inhibitor wortmannin. However, they maintained activation of mammalian target of rapamycin (mTOR) and were more sensitive to rapamycin. Treatment with rapamycin caused feedback activation of AKT in WT cell lines but not PI3K-deficient lines. A dual inhibitor of PI3K and mTOR, PI-103, was more effective than rapamycin at suppressing proliferation of mouse pre–B-ALL and human CD19+CD34+ Ph+ ALL leukemia cells treated with the ABL kinase inhibitor imatinib. Our findings provide mechanistic insights into PI3K dependency in oncogenic networks and provide a rationale for targeting class IA PI3K, alone or together with mTOR, in the treatment of Ph+ ALL.

Authors

Michael G. Kharas, Matthew R. Janes, Vanessa M. Scarfone, Michael B. Lilly, Zachary A. Knight, Kevan M. Shokat, David A. Fruman

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Figure 8

Short-term in vivo administration of PI-103 combined with imatinib suppresses leukemic cell expansion more effectively than imatinib alone.

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Short-term in vivo administration of PI-103 combined with imatinib suppr...
(A) Lethally irradiated syngeneic recipients were transplanted with p190 L-CFCs (hCD4+) together with normal BM, then treated on days 11–13 after injection (i.p.; 2 days of treatment) with single and combination doses of imatinib (70 mg/kg, b.i.d.) and rapamycin (7 mg/kg, once per day) or imatinib and PI-103 (40 mg/kg, b.i.d.) or double placebo control (diH2O and 75%/25% DMSO/saline mixture, b.i.d.) prior to sacrifice. Spleen weights after treatment regimen are reported. (B) Percent apoptosis in the BM and spleen was determined by annexin V/7AAD staining of hCD4+ blasts after 2-day treatment regimen. (C) Two hours prior to sacrifice, mice were injected with 5-ethynyl-2′-deoxyridine (EdU; i.p., 1.125 mg) and assayed for cycling cells that incorporated EdU in the BM and spleen with Click-iT EdU AF647 azide and propidium iodide staining (left and right panels). Representative depiction of cycling cells in the BM (left panel). *P < 0.05, ‡P < 0.01, **P < 0.001 versus control; #P < 0.05, †P < 0.01 versus imatinib; 1-way ANOVA; mean values ± SEM are shown; n = 5 mice per treatment group.