Ruxolitinib is a JAK1/2 inhibitor that is effective in managing symptoms and splenomegaly related to myelofibrosis (MF). Unfortunately, many patients must discontinue ruxolitinib, at which time treatment options are not well defined. In this study, we investigated salvage treatment options and clinical outcomes among MF patients who received and discontinued ruxolitinib outside the context of a clinical trial. Among 145 patients who received ruxolitinib, 23 died while on treatment, 58 remained on treatment at time of analysis, leaving 64 people available for analysis. Development of cytopenias was the most common reason for discontinuation (38%) after median treatment time of 3.8 months (mo). The majority of patients received some form of salvage therapy after ruxolitinib discontinuation (n = 42; 66%), with allogeneic hematopoietic stem cell transplant (alloHSCT) (n = 17), being most commonly employed. Lenalidomide, thalidomide, hydroxyurea, interferon, and danazol were used with similar frequency. The response rate to salvage treatment was 26% (8 responses) and responses were most often seen with lenalidomide or thalidomide. Improved outcomes were observed in patients who underwent alloHSCT or received salvage therapy compared to those who did not receive additional therapy. Median overall survival (OS) after ruxolitinib discontinuation was 13 months. These findings show that salvage therapy can provide clinical responses after ruxolitinib discontinuation; however, these responses are rare and outcomes in this patient population are poor. This represents an area of unmet clinical need in MF.

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To elucidate mechanisms of tumor necrosis factor alpha (TNF-alpha)-induced proliferation of a number of human leukemia and lymphoma cell lines, we examined the role of p38 mitogen-activated protein kinase (MAPK) in TNF-alpha signaling in Mo7e and Hut-78 cells. TNF-alpha-dependent p38 MAPK activation was detected in both Mo7e and Hut-78 cells and was blocked by the p38 MAPK inhibitor, SB203580. Ablation of p38 MAPK activity by SB203580 abrogated TNF-alpha-induced Mo7e cell proliferation and TNF-alpha-dependent autocrine growth of Hut-78. As we have shown previously that activation of the nuclear factor kappaB (NF-kappaB) is also required for TNF-alpha-induced Mo7e cell proliferation, the involvement of p38 MAPK in NF-kappaB activation was assessed. SB203580 did not affect TNF-alpha-signaled nuclear translocation and DNA-binding activity of NF-kappaB, and inhibition of NF-kappaB function did not affect TNF-alpha-induced p38 MAPK activation, indicating that these events are not dependent on each other. However, SB203580 depressed the expression of NF-kappaB-dependent genes, as monitored by a kappaB-driven reporter gene. Our findings demonstrate that activation of both p38 MAPK and NF-kappaB plays a critical role in TNF-alpha-mediated survival and proliferation of human leukemia and lymphoma cells, and p38 MAPK acts at least in part by facilitating the transcriptional activation function of NF-kappaB.