Abstract 6274: Preclinical characterization of the BET inhibitor, INCB057643, in combination with ruxolitinib for treatment of myeloproliferative neoplasms (MPN)

Abstract Patients with MPNs share common characteristics including overproduction of myeloid cells and chronic inflammation. In MPNs, bromodomain and extra-terminal (BET) proteins can bind to acetylated chromatin to regulate the activity of transcription factors such as NF-kB, leading to overproduction of inflammatory cytokines. Dysregulation of transcriptional gene expression can drive disease defining characteristics, therefore, targeting BET proteins could be an attractive therapeutic approach. In preclinical models, BET inhibitors decreased inflammatory cytokine production and restored hematopoietic cell differentiation. Combination of BET inhibitors with the JAK1/2 inhibitor, ruxolitinib, resulted in further reduction in cytokine production and bone marrow fibrosis (Kleppe M. Cancer Cell 2018). Here, we investigate a novel, orally bioavailable BET inhibitor, INCB057643, for the treatment of MPN in combination with ruxolitinib. INCB057643 is a potent and selective inhibitor of the BET family. In binding assays, INCB057643 selectively inhibited both BRD4 bromodomains, BD1 and BD2, with IC50 values of 39 nM and 6 nM, respectively. INCB057643 comparably inhibited both NF-kB reporter activity and MYC protein levels. Nascent transcript analysis on the JAK2 V617F-mutant cell line SET2 showed decreased transcription of genes linked to inflammation, alone and in combination with ruxolitinib. These data suggest that INCB057643 and ruxolitinib can be used in combination to effectively suppress the pathogenic gene program driving chronic inflammation. Functionally, INCB057643 inhibited proliferation of SET2 cells at nanomolar concentrations. In a SET2 xenograft model, combination of INCB057643 and ruxolitinib potently inhibited tumor growth. Similarly, in the MPLW515L-driven MPN mouse model, INCB057643 in combination with ruxolitinib resulted in a greater reduction in spleen volume, compared to that achieved with single agent treatment. Meso scale discovery assays on MPN-patient-derived CD34+ cells and whole blood using INCB057643 showed inhibition of NF-kB-mediated production of cytokines such as IL-8. In addition, flow cytometry-based analysis on MPN-patient-derived CD34+ cells showed that INCB057643 in combination with ruxolitinib decreased pathogenic megakaryopoiesis, and increased terminal erythroid differentiation. Our data demonstrate that the combination of the BET inhibitor, INCB057643, with ruxolitinib can restore normal hematopoietic differentiation, reduce inflammatory gene expression, and inhibit pathogenic cell differentiation in preclinical models of MPN. INCB057643 is currently being evaluated in clinical studies as monotherapy and in combination with ruxolitinib in patients with MPN. Acknowledgments: Michelle Pusey and Gaurang Trivedi contributed equally to this study. Citation Format: Michelle Pusey, Gaurang Trivedi, Bob Collins, Nina Zolotarjova, Pat Feldman, Monica Bomber, Jacob Ellis, Kristy Stengel, Cynthia Timmers, Hamza Celik, Matt Stubbs, Jeff Jackson, Scott Hiebert, Susan Wee, Sunkyu Kim. Preclinical characterization of the BET inhibitor, INCB057643, in combination with ruxolitinib for treatment of myeloproliferative neoplasms (MPN). [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6274.