Efficacy of JAK1/2 inhibition in murine myeloproliferative neoplasms is mediated mainly by targeting pro-inflammatory cytokine signaling not oncogenic signaling

In this study, we evaluated the mechnasim of ruxolitinib action is directly on malignant cell or not. For this purpose, we evaluated whether the drug primarily blocks the proliferation of the malignant clone or exerts its effects also by targeting non-malignant cells. Therefore, we developed two JAK2-V617F-driven myeloproliferative neoplasm (MPN) mouse models harboring ruxolitinib resistance mutations. Mice carrying ruxolitinib-resistant JAK2-V617F-driven MPN responded to ruxolitinib treatment similar to mice with ruxolitinib-sensitive JAK2-V617F MPN with respect to reduction of spleen size, leukocyte count and pro-inflammatory cytokines in the serum. Ruxolitinib also reduced pro-inflammatory cytokines both in stromal cells and non-malignant hematopoietic cells. Using a rigorous ruxolitinib resistance mutation approach we can prove that ruxolitinib acts independent of oncogenic JAK2-V617F signaling and reduces the main features of MPN disease such as spleen size and leukocyte counts. Our findings characterize the mechanism of action for ruxolitinib in MPN. To prove our hypothesis, we developed a ruxolitinib sensitive MPN variant (JAK2-V617F) and resistant variant (JAK2-L902Q) and measured the inflamatory cytokine land scape in different cellular origin from spleen and bone marrow after ruxolitinib treatment in these groups of mice.