Progress of investigational bromodomain and extra-terminal domain inhibitors for myelofibrosis therapy.

INTRODUCTION: Myelofibrosis (MF) is a BCR-ABL1-negative myeloproliferative neoplasm (MPN) driven by recurrent acquired somatic mutations in hematopoietic stem cells and characterized by progressive bone marrow fibrosis, cytopenias, and extramedullary hematopoiesis. Janus kinase inhibitors (JAKi) improve splenomegaly and MF symptom burden but without achieving molecular remission or clear disease course modification. Novel therapies targeting epigenetic dysregulation through bromodomain and extra-terminal domain (BET) proteins have emerged as a key therapeutic approach, aimed at reducing pro-inflammatory and oncogenic transcription to deepen clinical responses in combination with JAKi therapy.

AREAS COVERED: This review summarizes the biology, preclinical data, and emerging clinical data in the development of novel BET inhibitor (BETi). Trials assessing the efficacy of pelabresib, ABBV-744, INCB057643, BMS-986158, and OPN-2853 are detailed herein.

EXPERT OPINION: BET protein inhibition is a promising therapeutic target complementing JAK inhibition by co-targeting inflammatory pathways, fibrosis, and clonal proliferation. Pelabresib is a pan-BETi furthest in development demonstrating clinical benefit with ongoing trials. Research into novel pan-and selective-BETis both as monotherapy and in combination with JAKis or other mechanism-based therapies is ongoing. Whether BETi therapy in MF will ultimately deliver substantial anti-clonal activity to modify disease biology and meaningfully impact clinical outcomes is yet to be determined.