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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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 1

ERK activation is maintained in the presence of JAK2 inhibition in vivo, but inhibited ex vivo.

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ERK activation is maintained in the presence of JAK2 inhibition in vivo,...
(A) Type I JAK2 inhibition by ruxolitinib at 1 μM inhibits STAT and ERK phosphorylation promptly and over 48 hours in JAK2V617F SET-2 cells (n = 4). (B) Type II JAK2 inhibition by CHZ868 at 1–4 μM for 4 hours dose-dependently inhibits STAT and ERK phosphorylation in JAK2V617F SET-2 cells (n = 3). (C and D) Type I JAK2 inhibitor ruxolitinib at 60 mg/kg (n = 6) and type II JAK2 inhibitor CHZ868 at 40 mg/kg (n = 6) administered orally to primary Jak2V617F mice for 3–5 doses inhibit STAT phosphorylation, whereas ERK phosphorylation is fully maintained in comparison with vehicle-treated mice (n = 6–7). (E and F) Type I JAK2 inhibitor ruxolitinib at 90 mg/kg (n = 16) and type II JAK2 inhibitor CHZ868 at 40 mg/kg (n = 6) administered orally to MPLW515L transplanted mice for 3–5 doses inhibit STAT phosphorylation, whereas ERK phosphorylation remains fully maintained in comparison with vehicle-treated mice (n = 8–13). (G) Schematic of ex vivo experiments. Primary MPN mouse splenocytes were exposed to ruxolitinib at 0.5–2 μM for 6–8 hours to differentiate cell-intrinsic versus cell-extrinsic mechanisms of JAK2-independent ERK activation. (H) Ruxolitinib at 2 μM inhibited STAT and ERK phosphorylation in primary Jak2V617F splenocytes upon ex vivo exposure for 8 hours (n = 4). (I) Ruxolitinib at 0.5–2 μM dose-dependently inhibited STAT and ERK phosphorylation upon 8 hours of ex vivo exposure in PBMCs of JAK2V617F mutant MPN patients (n = 2). (J) Ruxolitinib at 0.5 μM inhibited STAT and ERK phosphorylation upon ex vivo exposure in splenocytes of MPLW515L transplanted mice for 6 hours (n = 9) as compared with vehicle-treated mice (n = 8).