PP2A-activating drugs selectively eradicate TKI-resistant chronic myeloid leukemic stem cells
Paolo Neviani, … , Guido Marcucci, Danilo Perrotti
Paolo Neviani, … , Guido Marcucci, Danilo Perrotti
Published September 3, 2013
Citation Information: J Clin Invest. 2013;123(10):4144-4157. https://doi.org/10.1172/JCI68951.
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Research Article Oncology

PP2A-activating drugs selectively eradicate TKI-resistant chronic myeloid leukemic stem cells

Abstract

The success of tyrosine kinase inhibitors (TKIs) in treating chronic myeloid leukemia (CML) depends on the requirement for BCR-ABL1 kinase activity in CML progenitors. However, CML quiescent HSCs are TKI resistant and represent a BCR-ABL1 kinase–independent disease reservoir. Here we have shown that persistence of leukemic HSCs in BM requires inhibition of the tumor suppressor protein phosphatase 2A (PP2A) and expression — but not activity — of the BCR-ABL1 oncogene. Examination of HSCs from CML patients and healthy individuals revealed that PP2A activity was suppressed in CML compared with normal HSCs. TKI-resistant CML quiescent HSCs showed increased levels of BCR-ABL1, but very low kinase activity. BCR-ABL1 expression, but not kinase function, was required for recruitment of JAK2, activation of a JAK2/β-catenin survival/self-renewal pathway, and inhibition of PP2A. PP2A-activating drugs (PADs) markedly reduced survival and self-renewal of CML quiescent HSCs, but not normal quiescent HSCs, through BCR-ABL1 kinase–independent and PP2A-mediated inhibition of JAK2 and β-catenin. This led to suppression of human leukemic, but not normal, HSC/progenitor survival in BM xenografts and interference with long-term maintenance of BCR-ABL1–positive HSCs in serial transplantation assays. Targeting the JAK2/PP2A/β-catenin network in quiescent HSCs with PADs (e.g., FTY720) has the potential to treat TKI-refractory CML and relieve lifelong patient dependence on TKIs.

Authors

Paolo Neviani, Jason G. Harb, Joshua J. Oaks, Ramasamy Santhanam, Christopher J. Walker, Justin J. Ellis, Gregory Ferenchak, Adrienne M. Dorrance, Carolyn A. Paisie, Anna M. Eiring, Yihui Ma, Hsiaoyin C. Mao, Bin Zhang, Mark Wunderlich, Philippa C. May, Chaode Sun, Sahar A. Saddoughi, Jacek Bielawski, William Blum, Rebecca B. Klisovic, Janelle A. Solt, John C. Byrd, Stefano Volinia, Jorge Cortes, Claudia S. Huettner, Steffen Koschmieder, Tessa L. Holyoake, Steven Devine, Michael A. Caligiuri, Carlo M. Croce, Ramiro Garzon, Besim Ogretmen, Ralph B. Arlinghaus, Ching-Shih Chen, Robert Bittman, Peter Hokland, Denis-Claude Roy, Dragana Milojkovic, Jane Apperley, John M. Goldman, Alistair Reid, James C. Mulloy, Ravi Bhatia, Guido Marcucci, Danilo Perrotti

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Figure 1

PP2A activity is inhibited in CML HSCs.

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PP2A activity is inhibited in CML HSCs. (A) Left: PP2A phosphatase assay...
(A) Left: PP2A phosphatase assay (mean ± SD) in CD34+CD38– and CD34+CD38+ cell fractions from NBM and CML donor BM. 32Dcl3 and 32D-BCR-ABL cells were used as controls. Right: SET levels, measured by intracellular flow staining and expressed as MFI (mean ± SD), in CD34+CD38– and CD34+CD38–CD90+ NBM and CML BM cells. (B) Left: Confocal microphotographs showing SET-PP2A association (red signals), as well as quantitative proximity ligation assays (PLA; n = 3), on untreated (UNT) and FTY720-treated (24 hours) CD34+CD38– CML cells. Original magnification, ×630. Right: Western blots showing endogenous SET-PP2Ac association in untreated (lane 1) and FTY720-treated (lane 2) K562 cells. Immunoprecipitation with nonrelated IgG (lane 3) was used as control. *P < 0.05, **P < 0.01, ***P < 0.001.