Targeting compensatory MEK/ERK activation increases JAK inhibitor efficacy in myeloproliferative neoplasms
Simona Stivala, … , Ross L. Levine, Sara C. Meyer
Simona Stivala, … , Ross L. Levine, Sara C. Meyer
Published February 7, 2019
Citation Information: J Clin Invest. 2019;129(4):1596-1611. https://doi.org/10.1172/JCI98785.
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Research Article Hematology Oncology

Targeting compensatory MEK/ERK activation increases JAK inhibitor efficacy in myeloproliferative neoplasms

Abstract

Constitutive JAK2 signaling is central to myeloproliferative neoplasm (MPN) pathogenesis and results in activation of STAT, PI3K/AKT, and MEK/ERK signaling. However, the therapeutic efficacy of current JAK2 inhibitors is limited. We investigated the role of MEK/ERK signaling in MPN cell survival in the setting of JAK inhibition. Type I and II JAK2 inhibition suppressed MEK/ERK activation in MPN cell lines in vitro, but not in Jak2V617F and MPLW515L mouse models in vivo. JAK2 inhibition ex vivo inhibited MEK/ERK signaling, suggesting that cell-extrinsic factors maintain ERK activation in vivo. We identified PDGFRα as an activated kinase that remains activated upon JAK2 inhibition in vivo, and PDGF-AA/PDGF-BB production persisted in the setting of JAK inhibition. PDGF-BB maintained ERK activation in the presence of ruxolitinib, consistent with its function as a ligand-induced bypass for ERK activation. Combined JAK/MEK inhibition suppressed MEK/ERK activation in Jak2V617F and MPLW515L mice with increased efficacy and reversal of fibrosis to an extent not seen with JAK inhibitors. This demonstrates that compensatory ERK activation limits the efficacy of JAK2 inhibition and dual JAK/MEK inhibition provides an opportunity for improved therapeutic efficacy in MPNs and in other malignancies driven by aberrant JAK-STAT signaling.

Authors

Simona Stivala, Tamara Codilupi, Sime Brkic, Anne Baerenwaldt, Nilabh Ghosh, Hui Hao-Shen, Stephan Dirnhofer, Matthias S. Dettmer, Cedric Simillion, Beat A. Kaufmann, Sophia Chiu, Matthew Keller, Maria Kleppe, Morgane Hilpert, Andreas S. Buser, Jakob R. Passweg, Thomas Radimerski, Radek C. Skoda, Ross L. Levine, Sara C. Meyer

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Figure 3

Combined JAK2 and MEK inhibition provides superior therapeutic efficacy in a Jak2V617F MPN mouse model.

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Combined JAK2 and MEK inhibition provides superior therapeutic efficacy ...
(A) Combined ruxolitinib 60 mg/kg and binimetinib 10–30 mg/kg for 1 week completely inhibited STAT and ERK phosphorylation in Jak2V617F splenocytes, whereas ruxolitinib alone resulted in maintained ERK activation. (B) Binimetinib 30 mg/kg for 4 weeks moderately reduced splenomegaly, although to a lesser extent than ruxolitinib 60 mg/kg. Combined binimetinib/ruxolitinib showed a superior effect compared with either single agent. (C) Combined binimetinib/ruxolitinib for 4 weeks reduced the elevated hematocrit (Hct), which was not seen with either monotherapy. (D) Hematocrit was only slightly reduced after combined binimetinib/ruxolitinib for 1 week. (E) Combined binimetinib/ruxolitinib reduced elevated reticulocytes at 1 week of treatment, superior to single-agent therapies. (F) Expanded Lin–Sca1–Kit+ multipotent myeloid progenitors (MPs) were more completely reduced by combined treatment than with single agents. (G) Reduction of CD71+ erythroid progenitors was more complete with combined binimetinib/ruxolitinib than with either treatment alone. Representative FACS plots (top) and quantitation (bottom) are shown. (H) Representative FACS plots showing superior reduction of Lin–Sca1–Kit+CD41–FcgR–CD150+CD105– megakaryocytic/erythroid progenitors (Pre-MegE) and Lin–Sca1–Kit+CD41–FcgR–CD150+CD105+ erythroid progenitors (Pre-CFU-E) by combined binimetinib/ruxolitinib. (I) Quantitation of treatment effects on myelo-erythroid progenitor populations upon 1 week of therapy. (J) Reduction of mutant allele burden as reflected by the fraction of Jak2V617F CD45.2 BM cells was superior by combined binimetinib/ruxolitinib versus single-agent therapies. Results are from recipients of Jak2V617F (CD45.2) and Jak2 wild-type (CD45.1) BM treated for 4 weeks (filled plots, n = 5 per group) or for 1 week (open plots, n = 5–6 per group). Quantitative results were analyzed by 1-way ANOVA with P ≤ 0.05 considered significant and are shown as mean ± SD (I) or as medians with boxes representing 25th to 75th percentiles and whiskers indicating minimum and maximum values (B–G and J). *P < 0.05, **P < 0.01, ***P < 0.005, ****P < 0.0001.