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Purpose:The Philadelphia chromosome–negative myeloproliferative neoplasms (MPN) polycythemia vera, essential thrombocythemia, and primary myelofibrosis are characterized by JAK/STAT pathway activation. JAK inhibitors are approved for MPN treatment, but persistence has been observed, due to JAK/STAT reactivation.Experimental Design:Using MPN patient samples, JAK2-mutated cell lines, and MPN mouse models, we examined both the efficacy and mechanism by which crizotinib, the ALK/MET/RON/ROS1 inhibitor approved for the treatment of non–small cell lung cancer, alters MPN cell proliferation and JAK/STAT activation.Results:We found that crizotinib suppresses proliferation and activation of JAK/STAT signaling, and decreases the disease burden in the JAK2V617F mouse model of MPN. Furthermore, we found that crizotinib could overcome JAK inhibitor persistence to ruxolitinib. Interestingly, phosphorylation of the crizotinib target RON kinase was enhanced in ruxolitinib-persistent cells. We show that phospho-JAK2 and phospho-RON can physically interact to sustain JAK/STAT signaling, and that the combination of crizotinib and ruxolitinib disrupts this interaction. Furthermore, RON knockdown suppresses proliferation and activation of JAK/STAT signaling in JAK2-mutated cells, and RON deletion in a JAK2V617F mouse MPN model decreases the disease burden. We also observed RON hyperactivation in MPN patient cells, suggesting that RON may be an important target of crizotinib in MPN.Conclusions:In summary, we demonstrate that crizotinib has preclinical efficacy in MPN patient cells, JAK2-mutated cell lines, and a JAK2-mutated mouse model, and that the combination of crizotinib with JAK inhibitors suppresses JAK inhibitor persistence. Our work suggests that crizotinib should be investigated for the treatment of patients with MPN.

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Purpose:The Philadelphia chromosome–negative myeloproliferative neoplasms (MPN) polycythemia vera, essential thrombocythemia, and primary myelofibrosis are characterized by JAK/STAT pathway activation. JAK inhibitors are approved for MPN treatment, but persistence has been observed, due to JAK/STAT reactivation.Experimental Design:Using MPN patient samples, JAK2-mutated cell lines, and MPN mouse models, we examined both the efficacy and mechanism by which crizotinib, the ALK/MET/RON/ROS1 inhibitor approved for the treatment of non–small cell lung cancer, alters MPN cell proliferation and JAK/STAT activation.Results:We found that crizotinib suppresses proliferation and activation of JAK/STAT signaling, and decreases the disease burden in the JAK2V617F mouse model of MPN. Furthermore, we found that crizotinib could overcome JAK inhibitor persistence to ruxolitinib. Interestingly, phosphorylation of the crizotinib target RON kinase was enhanced in ruxolitinib-persistent cells. We show that phospho-JAK2 and phospho-RON can physically interact to sustain JAK/STAT signaling, and that the combination of crizotinib and ruxolitinib disrupts this interaction. Furthermore, RON knockdown suppresses proliferation and activation of JAK/STAT signaling in JAK2-mutated cells, and RON deletion in a JAK2V617F mouse MPN model decreases the disease burden. We also observed RON hyperactivation in MPN patient cells, suggesting that RON may be an important target of crizotinib in MPN.Conclusions:In summary, we demonstrate that crizotinib has preclinical efficacy in MPN patient cells, JAK2-mutated cell lines, and a JAK2-mutated mouse model, and that the combination of crizotinib with JAK inhibitors suppresses JAK inhibitor persistence. Our work suggests that crizotinib should be investigated for the treatment of patients with MPN.

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Background: Myelofibrosis (MF) pts often exhibit suboptimal response to chronic ruxolitinib therapy, possibly due to persistent PI3K pathway activation. In the ongoing phase 2 INCB 50465-201 trial (NCT02718300), add on parsaclisib (potent, highly selective PI3Kδ inhibitor) is showing preliminary efficacy in MF pts with suboptimal ruxolitinib response. JAK inhibitors (eg, ruxolitinib), are associated with thrombocytopenia; therefore, pts with low PC are commonly more difficult to treat. We present a subgroup analysis of efficacy and safety data from INCB 50465-201 by baseline PC. Methods: Eligible adults had primary/secondary MF with suboptimal response (palpable spleen >10 cm below left subcostal margin [LSM]; or palpable spleen 5-10 cm below LSM and active symptoms) after ≥6 months of ruxolitinib monotherapy (5-25 mg BID; stable dose ≥8 wks). Pts remained on their last stable ruxolitinib dose and received add on parsaclisib (10 or 20 mg QD for 8 wks; same dose QW thereafter) or parsaclisib (5 or 20 mg QD for 8 wks; 5 mg QD thereafter). For this analysis, spleen volume (SV), total symptom score (TSS) assessed by Myelofibrosis-Symptoms Assessment Form (MFSAF) v3.0 daily diary, and safety, were evaluated by baseline PC (low PC, 50- Results: At data cutoff (8/27/2020), 67 pts were enrolled (low PC, n=21; higher PC, n=46; median age 68 y). For low vs higher PC, median prior duration of ruxolitinib use was 34.7 vs 14.9 months; baseline symptoms were worse for low PC vs higher PC (median [range] MFSAF-TSS, 21.4 [0.6-47] vs 10 [0-43]). For low vs higher PC, 9/18 (50.0%) vs 15/38 (39.4%) pts had SV reduction (SVR) ≥10% at wk 12; percentages of pts with SVR ≥10% were similar at wk 24 (6/17 [35.2%] vs 13/35 [37.1%]); 0 vs 1 pt had SVR ≥35% at wk 12; 2 vs 1 pt had SVR ≥35% at wk 24. Of pts with ≥10% SVR at wk 24, 4/6 with low PC and 9/13 with higher PC were on all daily dosing regimens. For low vs higher PC, median (range) percentage change in MFSAF-TSS was −20.5 (−56.6 to +17.1) vs −22.2 (−100 to +500) at wk 12; −26.1 (−54.7 to +2.4) vs −23.1 (−91.3 to +222.5) at wk 24. In both subgroups, nonhematologic treatment-emergent adverse events (TEAEs) were mostly grade 1/2. Most common (≥20%) TEAEs were dyspnea (33%), falls (33%), peripheral edema (29%), and nasal congestion (24%) for low PC; diarrhea (28%), nausea (24%), abdominal pain (24%), cough (20%), and fatigue (20%) for higher PC. For low vs higher PC, 9/21 (43%) vs 3/46 (7%) pts had parsaclisib dose interruption due to thrombocytopenia; 1 pt with low PC had ruxolitinib interruption due to thrombocytopenia. Conclusion: Add-on parsaclisib showed efficacy in pts from both low and higher baseline PC groups. Given the acceptable safety profile and efficacy of add-on parsaclasib, MF pts with both low and higher PC may be able to benefit from parsaclisib-ruxolitinib combination therapy. Citation Format: Abdulraheem Yacoub, Uma Borate, Raajit Rampal, Haris Ali, Eunice Wang, Aaron Gerds, Gabriela Hobbs, Marina Kremyanskaya, Elliott Winton, Casey O’Connell, Swati Goel, Stephen Oh, Gary Schiller, Albert Assad, Sue Erickson-Viitanen, Feng Zhou, Naval Daver. Efficacy and safety of parsaclisib-ruxolitinib combination therapy in myelofibrosis patients (Pts) with low vs higher baseline platelet count (PC): A subgroup analysis of data from a phase 2 study [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr CT541.