Disrupting a new NFkB-IL-6-JAK2-STAT cascade with novel NFkB inhibitors reduces primary myelofibrosis growth Free

Introduction: Primary myelofibrosis (PMF), a myeloproliferative neoplasm (MPN), features bone marrow fibrosis, splenomegaly, and abnormal blood cell production. Aberrant JAK/STAT signaling, elevated cytokines or hyperactive NFκB are implicated in MPN pathogenesis; however, their interplay remains unclear. JAK inhibitors (JAKi) alleviate PMF symptoms, but they don't fully address disease progression or mitigate cytokine storms. NFκB inhibitors have shown promise in MPN models but are associated with off-target effects and toxicities. This study aims to elucidate the mechanisms of JAKi resistance and develop novel therapeutic strategies targeting hyperactive NFκB in vitro and in vivo, offering potential benefits beyond current JAKi therapies.

Methods: To investigate JAKi resistance in PMF, ruxolitinib-resistant HEL cells were generated and NFκB/JAK2/STAT signaling was examined by Western blot. Biomarkers associated with JAKi response were identified in PMF patients treated with BMS-9115437 (Gangat et al, Blood Cancer J, 2023) via Western blot. Molecular mechanisms of MPN pathogenesis were further elucidated using Affymetrix HG-U133Plus2 assay on RNA from treatment-naïve PMF, essential thrombocythemia (ET), polycythemia vera (PV) patients and healthy donors, followed by KEGG and gene set enrichment (GSE) analysis. In vitro, NFκB was inactivated by shRNA, Ixazomib or emetine followed by Western blot for NFκB/JAK2/STAT phosphorylation as well as flow cytometry and clonogenic assays for cell growth. NFκB DNA binding activity was determined by electrophoretic mobility-shift assays (EMSA). The therapeutic and preventive effects of Ixazomib and emetine were evaluated in HEL-engrafted nude mice by assessing tumor formation, development, and underlying mechanisms using Western blot, H&E and IHC staining.

Results: Short-term JAKi (BMS-911543, ruxolitinib) exposure altered JAK2 phosphorylation, increasing Tyr1008 phosphorylation and decreasing Tyr221, Tyr570, and STAT5 phosphorylation. Notably, JAK2, STAT3 and STAT5 were phosphorylated in ruxolitinib-resistant HEL cells or after treatment cessation, implying sustained signaling activity. Western blot analysis and clinical data in PMF patients (n=3) receiving BMS-911543 showed no hyperphosphorylation of JAK2 Tyr1008 with diverse responses independent of JAK2^V617F status. A lack of correlation between JAK2 and STAT5 expression/phosphorylation suggests that other factors contribute to hyperactive STAT5 in PMF. Symptomatic improvement in a JAK2^V617F-positive patient correlated with decreased STAT5 protein expression and phosphorylation, potentially serving as a predictor for JAKi response. Transcriptomic analysis in MPN patients (PMF (n=11), ET (n=6), PV (n=4), HD (n=5)) pinpointed the transcriptomic dissimilarities between PMF and PV or ET, and highlighted the higher NFκB activity in PMF compared to PV or ET. The importance of NFκB in PMF was further evidenced by the network analysis for the overproduction of circulating cytokines in PMF patients (Tefferi et al, JCO, 2011). In vitro studies revealed that NFκB overexpression promotes cell proliferation and inhibits apoptosis through enhanced IL-6/IL-6R expression and JAK2/STAT5 phosphorylation. Inactivating NFκB using shRNA, emetine, or ixazomib reversed these effects. Further, IL-6 treatment increased JAK2 phosphorylation. In vivo studies showed that Ixazomib significantly reduces tumor volume (734 ±133 to 98 ±14 mm³; P <0.001) and weight (582 ±156 to 87 ±22 mg; P =0.0005) compared to controls. Emetine similarly suppressed tumor growth dose-dependently without affecting spleen weight and even prevented tumor formation when administered prior to cell engraftment. Mechanistically, both Ixazomib and emetine inhibited NFκB and JAK2 phosphorylation while increasing cleaved caspase-3 in tumors.

Conclusions: We discovered that STAT inactivation independently predicts improved outcomes in PMF and that NFκB hyperactivity holds particular significance for PMF compared to other MPN subtypes. We identified a NFκB-IL-6-JAK2-STAT axis in regulating PMF growth regardless of JAK2^V617F status. Targeting NFκB with novel inhibitors Ixazomib and emetine disrupts the NFκB-IL-6-JAK2-STAT axis, suppressing PMF growth and offering potential therapeutic alternatives to overcome current JAKi limitations.