Ruxolitinib

Ruxolitinib (INCB18424) is an orally active and selective JAK1/2 inhibitor with IC₅₀s of 3.3 nM and 2.8 nM in cell-free assays, and has 130-fold selectivity for JAK1/2 over JAK3^[1]. Ruxolitinib induces autophagy and kills tumor cells through toxic mitophagy^[3]. IC50 & Target:IC50: 3.3 nM (JAK1), 2.8 nM (JAK2) In Vitro:Ruxolitinib potently and selectively inhibits JAK2V617F-mediated signaling and proliferation, markedly increases apoptosis in a dose dependent manner, and at 64 nM results in a doubling of cells with depolarized mitochondria in Ba/F3 cells.
Ruxolitinib demonstrates remarkable potency against erythroid colony formation with IC₅₀ of 67 nM, and inhibits proliferating of erythroid progenitors from normal donors and polycythemia vera patients with IC₅₀ values of 407 nM and 223 nM, respectively^[1]. In Vivo:Ruxolitinib (180 mg/kg, orally, twice a day) results in survive rate of greater than 90% by day 22 and markedly reduces splenomegaly and circulating levels of inflammatory cytokines, and preferentially eliminated neoplastic cells, resulting in significantly prolonged survival without myelosuppressive or immunosuppressive effects in a JAK2V617F-driven mouse model^[1].
In the Ruxolitinib group, the primary end point is reached in 41.9% of patients, as compared with 0.7% in the placebo group in the double-blind trial of myelofibrosis. Ruxolitinib results in maintaining of reduction in spleen volume and improvement of 50% or more in the total symptom score^[2].