Targeting nuclear export and Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) signalling in myelofibrosis: A novel combinatorial strategy that impacts intrinsic and microenvironment-related pathways.

Myelofibrosis (MF) is a chronic myeloproliferative neoplasm (MPN) characterized by splenomegaly, constitutional symptoms, marrow fibrosis, cytopenias and inflammation. Janus kinase 2 (JAK2) inhibitors, such as ruxolitinib, reduce splenomegaly and alleviate symptoms but have limited disease-modifying activity, and resistance frequently develops. Selinexor, an oral selective exportin (XPO1) inhibitor, restores nuclear retention of tumour suppressors and inhibitors of inflammatory signalling. Dual XPO1/JAK2 inhibition targets complementary downstream pathways, enhancing suppression of MF progenitor cell fitness. We evaluated selinexor plus ruxolitinib in MF models, including JAK2V617F or calreticulin (CALR) exon 9-mutant MPN cell lines and samples from patients with MF. The combination showed greater anti-proliferative activity than JAK2 inhibition alone and suppressed colony formation from MF Cluster of Differentiation 34 (CD34)+ cells. Selinexor remained active in a ruxolitinib-resistant MPN cell line, inducing G1 arrest and apoptosis. Multi-omic analyses demonstrated increased nuclear retention of p53 and disruption of Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) signalling, complementing and extending ruxolitinib-targeted pathways. The combination suppressed NF-κB transcriptional activity and reduced Tumor Necrosis Factor alpha (TNFα), Interleukin-6 (IL-6) and Monocyte Chemoattractant Protein-1 (MCP-1) secretion from MF patient peripheral blood mononuclear cells. These findings highlight that selinexor plus ruxolitinib affects both MF haematopoietic cell-intrinsic and microenvironment-related pathways, providing a novel disease-modifying strategy with the potential to improve clinical outcomes in patients with MF.