Abstract 4369: Rearrangements of the erythropoietin receptor are recurrent in Ph-like acute lymphoblastic leukemia and are sensitive to Jak2 inhibition
Authors: Iacobucci Ilaria , Roberts Kathryn G. , Li Yongjin , Zhang Jinghui , Harvey Richard C. , Payne-Turner Debbie , Valentine Marcus , McCastlain Kelly , Easton John , Chen I-Ming , Rusch Michael , Kornblau Steven M. , Konopleva Marina , Paietta Elisabeth , Rowe Jacob M. , Pui Ching-Hon , Gastier-Foster Julie M. , Reshmi Shalini , Loh Mignon L. , Willman Cheryl , Downing James R. , Hunger Stephen P. , Mullighan Charles G. 
Published: August 2015

Abstract
Introduction: Ph-like acute lymphoblastic leukemia (ALL) is characterized by a diverse range of genetic alterations that activate cytokine receptor and kinase signaling. We recently identified (Roberts KG, NEJM 2014) rearrangements of the erythropoietin receptor (EPOR) with immunoglobulin heavy (IGH) or kappa (IGK) chain loci in 154 Ph-like ALL. Here, we aimed to investigate their spectrum and recurrence in an extended cohort, as well as their pathogenic role and therapeutic potential in childhood Ph-like ALL.
Methods: Whole transcriptome sequencing, real-time quantitative PCR (qPCR) and Sanger sequencing were performed to detect and map the EPOR rearrangements in 307 Ph-like ALL. Wild-type or EPOR rearranged alleles were expressed in IL-3-dependent mouse hematopoietic Ba/F3 cells and IL-7-dependent pre-B cells harboring alterations of Arf and/or the dominant negative IKZF1 allele IK6. Proliferation and downstream EPOR signaling were examined in absence or presence of erythropoietin (EPO). Leukemic growth was monitored in C57BL/6 mice transplanted with Arf-/- pre-B cells expressing rearranged EPOR. Luciferase-marked xenografts were established in NOD-SCID-IL2R gamma (NSG) null mice. Signaling, EPO-dependent proliferation and sensitivity to the JAK inhibitors were assessed ex vivo and in vivo.
Results: EPOR rearrangements were identified in 8.3% of Ph-like ALL as the result of: i) inversion and cryptic insertion under the promoter region of IGH/IGK; ii) reciprocal translocation; or iii) fusion to 5′ LAIR1. All rearrangements resulted in ectopic overexpression of a C-terminal truncated receptor, confirmed by qPCR, that retained the phosphorylation site required for STAT5 activation, but lacked multiple tyrosine residues required for normal negative regulation. The rearranged alleles were expressed at higher and more prolonged levels than wild-type EPOR in Ba/F3 and Arf-/- mouse pre-B cells, and sustained cell proliferation with increased STAT5 phosphorylation following exogenous EPO stimulation. In vivo, the truncated receptor promoted leukemia development in C57BL/6 mice. Xenografted EPOR-rearranged leukemic cells exhibited high levels of truncated EPOR, STAT5 phosphorylation and ex vivo sensitivity to JAK2 inhibition using ruxolitinib, fedratinib, momelotinib, or pacritinib alone or in combination with daunrobucin, vincristine or dexamethasone (synergistic effect). The efficacy of Jak2 inhibition and the synergistic effect of combining ruxolitinib and dexamethasone were subsequently demonstrated in vivo.
Conclusions: EPOR rearrangements are recurrent in Ph-like ALL and result in ectopic expression of truncated EPOR and activation of JAK2-STAT5 signaling pathway, sustaining leukemia development in vivo. Xenografted EPOR-rearranged leukemia cells exhibit ex vivo and in vivo sensitivity to JAK2 inhibitors alone or in combination with chemotherapy.
Citation Format: Ilaria Iacobucci, Kathryn G. Roberts, Yongjin Li, Jinghui Zhang, Richard C. Harvey, Debbie Payne-Turner, Marcus Valentine, Kelly McCastlain, John Easton, I-Ming Chen, Michael Rusch, Steven M. Kornblau, Marina Konopleva, Elisabeth Paietta, Jacob M. Rowe, Ching-Hon Pui, Julie M. Gastier-Foster, Shalini Reshmi, Mignon L. Loh, Cheryl Willman, James R. Downing, Stephen P. Hunger, Charles G. Mullighan. Rearrangements of the erythropoietin receptor are recurrent in Ph-like acute lymphoblastic leukemia and are sensitive to Jak2 inhibition. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4369. doi:10.1158/1538-7445.AM2015-4369