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Effective and selective targeting of leukemia cells using a TORC1/2 kinase inhibitor

Abstract

Targeting the mammalian target of rapamycin (mTOR) protein is a promising strategy for cancer therapy. The mTOR kinase functions in two complexes, TORC1 (target of rapamycin complex-1) and TORC2 (target of rapamycin complex-2); however, neither of these complexes is fully inhibited by the allosteric inhibitor rapamycin or its analogs. We compared rapamycin with PP242, an inhibitor of the active site of mTOR in both TORC1 and TORC2 (hereafter referred to as TORC1/2), in models of acute leukemia harboring the Philadelphia chromosome (Ph) translocation. We demonstrate that PP242, but not rapamycin, causes death of mouse and human leukemia cells. In vivo, PP242 delays leukemia onset and augments the effects of the current front-line tyrosine kinase inhibitors more effectively than does rapamycin. Unexpectedly, PP242 has much weaker effects than rapamycin on the proliferation and function of normal lymphocytes. PI-103, a less selective TORC1/2 inhibitor that also targets phosphoinositide 3-kinase (PI3K), is more immunosuppressive than PP242. These findings establish that Ph+ transformed cells are more sensitive than normal lymphocytes to selective TORC1/2 inhibitors and support the development of such inhibitors for leukemia therapy.

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Figure 1: PP242 induces apoptosis of p190 BCR-ABL–transformed mouse hematopoietic progenitors and human Ph+ B-ALL cells in vitro.
Figure 2: PP242 completely inhibits TORC1 and TORC2 signaling in BCR-ABL+ cells, whereas rapamycin partially suppresses TORC1 and drives elevated PI3K-AKT signaling.
Figure 3: Immunofluorescence analysis shows that PP242 induces Foxo1 nuclear entry without affecting PIP3 abundance.
Figure 4: PP242 selectively suppresses leukemic expansion in vivo and extends survival.
Figure 5: PP242 enhances the efficacy of dasatinib and the combination causes regression of human Ph+ B-ALL xenografts.
Figure 6: In vitro and in vivo effects of PP242 compared to rapamycin in assays of normal immune cell proliferation and function.

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Acknowledgements

We thank K. Shokat, T. Wilson, and M. Kharas for support and helpful discussions and R. Nguyen for constructing BCR-ABL mutants. For access to the LSM710 Zeiss confocal microscope we thank E. Gratton's laboratory in the Department of Biomedical Engineering, University of California–Irvine. The SUP-B15 cells stably expressing firefly luciferase (SUP-B15ffLuc) were a kind gift from M. Jensen (City of Hope). Technical assistance was provided through the Optical Biology Core facility of the Developmental Biology Center, a shared resource supported in part by the Cancer Center Support Grant (CA-62203) and the Center for Complex Biological Systems Support Grant (GM-076516) at the University of California–Irvine. The Lumina IVIS bioluminescent imager was supported by a grant to the University of California–Irvine from the California Institute of Regenerative Medicine. This work was supported by US National Institutes of Health training grant T32-CA009054 (to M.R.J.), National Institutes of Health Minority Access to Research Careers grant T34GM069337 (to M.A.C.), a Research Scholar Grant from the American Cancer Society (to D.A.F.), a Discovery Grant from the University of California Industry–University Cooperative Research Program (to D.A.F.), a sponsored research agreement from Intellikine, Inc. (to D.A.F.) and a Bridge award from the Chao Family Comprehensive Cancer Center. M.R.J. is an awardee of the Jackie Murphy and Carol Malouf Scholar Achievement Rewards for College Scientists.

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M.R.J. designed and performed experiments, analyzed data and wrote the manuscript. J.J.L., L.S., J.C. and C.V. designed and performed experiments and analyzed data. M.A.C., R.J.L. and S.M. performed experiments and analyzed data. M.B.L., S.T.O. and M.K. provided clinical samples, analyzed data and edited the manuscript. M.B.M. and P.R. provided materials and supervised groups performing chemical synthesis and formulation. Y.L. and C.R. designed and supervised experiments and edited the manuscript. D.A.F. designed and supervised experiments and wrote the manuscript.

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Correspondence to David A Fruman.

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Competing interests

M.B.M., P.R., Y.L. and C.R. are employees of Intellikine, a company developing mTOR inhibitors for therapeutic use. D.A.F. is a member of the Scientific Advisory Board of Intellikine.

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Janes, M., Limon, J., So, L. et al. Effective and selective targeting of leukemia cells using a TORC1/2 kinase inhibitor. Nat Med 16, 205–213 (2010). https://doi.org/10.1038/nm.2091

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