Abstract 665: MEN1703/SEL24 exhibits promising antitumoral activity in preclinical models of myelofibrosis both as single agent and combined with ruxolitinib

Abstract Myelofibrosis (MF) is a pathological chronic bone marrow (BM) condition characterized by abnormal growth of erythroid and megakaryocytic precursors and deposition of fibrotic tissue. The JAK/STAT pathway plays an important role in MF (Cardoso 2015), and multiple JAK1/2 inhibitors (JAKis) are approved for MF treatment. Despite initially limiting disease symptoms, JAKis often fail due to persistent JAK2 activation and survival of MF-driving cells, hence new treatment strategies are highly needed. PIM kinases also contribute to MF pathogenesis. PIM1 is highly overexpressed in granulocytes, peripheral blood mononuclear cells (PBMCs), and BM of patients with MF. PIM1/2 expression is dependent upon JAK2 signaling in myeloproliferative neoplasms (MPNs). Hence, PIM inhibitors represent potential therapeutic targets for MPNs and have been evaluated in several preclinical and clinical studies (Rampal 2021). MEN1703/SEL24 (MEN) is an oral, first-in-class, dual PIM/FLT3 kinase inhibitor in development for hematologic malignancies. This study aims to investigate the efficacy of MEN alone and in combination with the JAKi ruxolitinib (RUX) in preclinical MF models and to elucidate the underlying signaling pathways. MF cell lines (JAK2V617F and JAK2 wild type) were used in MTS assays to assess the in vitro cytotoxicity of MEN alone and in combination with RUX, compared with the PIM inhibitor TP-3654 (Dutta 2022). Cell cycle distribution and signaling pathways were analyzed via propidium iodide/FACS analysis and immunocapillary electrophoresis, respectively, upon treatment with the single agents and MEN + RUX. In vivo efficacy was assessed in a murine xenograft model treated with MEN +/- RUX. In vitro studies showed single agent MEN activity with an IC50 ranging from 0.3 to 2.3 µM. Moreover, a synergistic drug interaction was found with MEN + RUX in all tested cell lines (Combination Index [CI] range 0.41-0.80). MEN presented cytotoxic and cytostatic capacity, inducing apoptosis and arresting a proportion of cells in G2/M phase. This effect was maintained in combination with RUX. Signaling pathway analysis showed that MEN inhibits phosphorylation of STAT proteins and decreases Mcl1 protein expression. These effects were enhanced with MEN + RUX. Compared with TP-3654, MEN was more effective both as a single agent (IC50 2-3 fold lower than TP-3654) and in combination with RUX (mean CI of 0.77-0.80 compared to 0.79-0.98 with TP-3654). MEN showed anti-tumoral efficacy in MF preclinical models, moderately higher than TP-3654, exhibiting in vitro activity at clinically relevant concentrations. Importantly, MEN combined with the standard of care RUX was synergistic, and molecular analyses confirmed the role of PIM downstream target inhibition. Our results support the therapeutic potential and relevance of MEN in MF treatment strategies. Citation Format: Maria Luisa Iannitto, Diego Bisignano, Sonia Zicari, Francesco Belli, Alessio Fiascarelli, Simone Talucci, Giuseppe Merlino, Vittoria Nicolis di Robilant, Clelia Irrissuto, Mario Bigioni, Alessandro Bressan, Daniela Bellarosa, Monica Binaschi. MEN1703/SEL24 exhibits promising antitumoral activity in preclinical models of myelofibrosis both as single agent and combined with ruxolitinib [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 665.