Paradoxical activation of chronic lymphocytic leukemia cells by ruxolitinib in vitro and in vivo

Introduction: Chronic lymphocytic leukemia (CLL) is characterized by an aberrant cytokine network that can support tumor growth by triggering janus kinase (JAK)/STAT pathways. Targeting cytokine-signaling should then be a rational therapeutic strategy but the JAK inhibitor ruxolitinib failed to control and seemingly accelerated the disease in clinical trials. Methods: The effect of ruxolitinib on primary human CLL cells was studied in vitro and in vivo. Results: Ruxolitinib increased phosphorylation of IRAK4, an important toll-like receptor (TLR)- signaling intermediate, in circulating CLL cells in vitro. It also enhanced p38 and NFKB1 phosphorylation while lowering STAT3 phosphorylation in CLL cells activated with TLR-7/8 agonists and IL-2. Among the cytokines made by activated CLL cells, high levels of IL-10 contributed strongly to STAT3 phosphorylation and inhibited TLR7 activity. Ruxolitinib limited TLR-mediated IL10 transcription and markedly reduced IL-10 production in vitro. It also decreased blood levels of IL-10 while increasing TNF alpha along with phospho-p38 expression and gene sets associated with TLR-activation in CLL cells in vivo. The bruton's tyrosine kinase inhibitor ibrutinib decreased IL-10 production in vitro but, in contrast to ruxolitinib, blocked initial IL10 transcription induced by TLR-signaling in vitro, decreased TNFa production, and deactivates CLL cells in vivo. Discussion: These findings suggest the possible benefits of inhibiting growth factors with JAK inhibitors in CLL are outweighed by negative effects on potential tumor suppressors such as IL-10 that allow unrestrained activation of NF kappa B by drivers such as TLRs. Specific inhibition of growth-promoting cytokines with blocking antibodies or infusing suppressive cytokines like IL-10 might be better strategies to manipulate cytokines in CLL.

Automated summary

The study investigated the effect of ruxolitinib on CLL cells and found that it increased IRAK4 phosphorylation, enhanced p38 and NFKB1 phosphorylation, and reduced STAT3 phosphorylation. High levels of IL-10 contributed to STAT3 phosphorylation and inhibited TLR7 activity. Ruxolitinib limited TLR-mediated IL-10 transcription and reduced IL-10 production. The study suggests that targeting growth factors with JAK inhibitors in CLL may have negative effects on tumor suppressors like IL-10. Specific inhibition of growth-promoting cytokines or infusion of suppressive cytokines like IL-10 might be better strategies for manipulating cytokines in CLL.