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 2

PDGF-BB–PDGFRα signaling bypasses JAK2 inhibition, mediating JAK2-independent ERK activation.

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PDGF-BB–PDGFRα signaling bypasses JAK2 inhibition, mediating JAK2-indepe...
(A) RTK arrays of Jak2V617F splenocytes treated with vehicle (top) or ruxolitinib (middle) show primarily activation of PDGFRα (blue, in duplicate) versus C57BL/6 (bottom, n = 1–2 per condition). Additional RTKs in the array are specified in Supplemental Figure 2, A and B. (B) PDGFRα remains activated in Jak2V617F mouse splenocytes upon 60 mg/kg ruxolitinib (n = 1–2 per condition). (C) Expression of Pdgfa, Pdgfb, and Pdgfra in Jak2V617F mouse BM is maintained upon 60 mg/kg ruxolitinib (n = 5 per group). (D) Expression of Pdgfa, Pdgfb, and Pdgfra in Jak2V617F mouse splenocytes is maintained upon 60 mg/kg ruxolitinib (n = 5 per group). (E) PDGF-BB levels are higher than PDGF-AA levels in BM, spleen interstitial fluid, and serum of untreated Jak2V617F mice (n = 5 per group). (F) PDGF-BB levels are higher than PDGF-AA levels in BM, spleen interstitial fluid, and serum of Jak2V617F mice upon ruxolitinib 60 mg/kg (n = 5 per group). (G) Jak2V617F mouse BM was exposed ex vivo to ruxolitinib 1 μM and PDGF-AA 100 ng/ml or PDGF-BB 200 ng/ml without (left) or with (right) ruxolitinib pretreatment for 6 hours. PDGF-BB maintained ERK phosphorylation in the presence of ruxolitinib. (H) Densitometries confirm increased ERK phosphorylation by PDGF-BB in the presence of ruxolitinib in Jak2V617F BM ex vivo (n = 3–4). (I) Pdgfa, Pdgfb, and Pdgfra expression levels in megakaryocyte-erythroid progenitors (MEPs) of Jak2V617F BM are elevated upon ruxolitinib treatment (n = 4–7 per group). (J) Pdgfa, Pdgfb, and Pdgfra expression levels in common myeloid progenitors (CMPs) of Jak2V617F BM are elevated upon ruxolitinib treatment (n = 3–6 per group). Quantitative results were analyzed by 1-way ANOVA with P ≤ 0.05 considered significant and are shown as mean ± SD (C, D, H–J) or as medians with boxes representing 25th to 75th percentiles and whiskers indicating minimum and maximum values (E and F). *P < 0.05, ***P < 0.005.