Microenvironment and therapeutic modulation of myelofibrosis in an experimental mouse model.

Primary myelofibrosis(PMF) is the most severe form of Philadelphia-negative myeloproliferative neoplasms(MPNs), characterized by splenomegaly, extramedullary hematopoiesis and bone marrow(BM) fibrosis, with disease progression to leukemia and low survival. The best therapy currently available includes treatment with a JAK inhibitor(Ruxolitinib), which only ameliorates symptoms. Unfortunately, the pathogenesis of the disease is still poorly understood. It has been hypothesized that its progression may be determined by the presence of inflammatory cytokines produced by the bone marrow microenvironment that promote fibrosis. The three aims of this PhD thesis, using the Gata1low mouse model of myelofibrosis, were: 1. Investigate the presence of different cytokines in the bone marrow microenvironment; 2. Test the efficacy of treatment with Reparixin, a CXCR1/2 receptor inhibitor; 3. Test the efficacy of treatment with RB40.34 (P-selectin inhibitor), alone and in combination with Ruxolitinib. In the first study, we demonstrated by immunohistochemistry(IHC) the presence in the BM of Gata1low mice of elevated levels of CXCL1, and its receptors CXCR1/2, and TGF-β1. Particularly, the cells with higher expression of these cytokines were the megakaryocytes. In the second study, we found that treatment with Reparixin in Gata1low mice showed dose-dependent efficacy in reducing bone marrow and splenic fibrosis. Furthermore, by IHC analysis we demonstrated that the treatment induced a decrease in the expression of TGF-β1. In the third study, we found that treatment with RB40.34 in combination with Ruxolitinib normalizes the phenotype of Gata1low mice, reducing fibrosis and the content of TGF-β and CXCL1 in the bone marrow, and restoring the architecture of hematopoiesis in the bone marrow and spleen. In summary, these data provide preclinical evidence that treatment with Reparixin and RB40.34 in combination with Ruxolitinib are effective on reversing the myelofibrotic trait in the Gata1low mouse model and encourage clinical trials to validate these compounds in human patients with PMF.