Pharmacological targeting of P-selectin to halt the progression of myelofibrosis in the Gata1low mouse model

Primary myelofibrosis is a clonal hematopoietic disorder characterized by marked degrees of systemic inflammation. The release of pro-inflammatory factors by clonal hematopoietic cell populations cause the remodeling of a specialized microenvironment, defined niche, in which the hematopoietic stem cells reside. The main source of pro-inflammatory cytokines is represented by malignant megakaryocytes. The bone marrow and spleen from myelofibrosis patients, as well as those from the Gata1low mouse model of the disease, contain increased number of abnormal megakaryocytes. These cells express on their surface high levels of the adhesion receptor P-selectin that, by triggering a pathological megakaryocyte-neutrophil emperipolesis, lead to increased bioavailability of TGF-β1 in the microenvironment and disease progression. Gata1low mice develop with age a phenotype similar to that of patients with myelofibrosis. We previously demonstrated that deletion of the P-selectin gene in Gata1low mice prevented the development of the myelofibrotic phenotype in these mice. In the current study, we tested the hypothesis that pharmacological inhibition of P-selectin may rescue the fibrotic phenotype of Gata1low mice. To test this hypothesis, we have investigated the phenotype expressed by old Gata1low mice treated with the anti-mouse monoclonal antibody against P-selectin RB40.34, alone or in combination with the JAK2 inhibitor Ruxolitinib. The results showed that the combined therapy normalized the phenotype of Gata1low mice with limited toxicity by reducing fibrosis, TGF-β1 and CXCL1 content in the BM and spleen and by restoring hematopoiesis in the bone marrow and the normal architecture of the spleen. In conclusion, pharmacological inhibition of P-selectin was effective in targeting malignant megakaryocytes and the microenvironmental abnormalities that affect the hematopoietic stem cell compartment in this model. These results suggest that P-selectin and JAK1/2 inhibitors in combination may represent a valid therapeutic option for patients with myelofibrosis.