Our novel oral kinase inhibitor with specificity for JAK2 and IRAK1, without inhibiting JAK1, is approved for the treatment of myelofibrosis patients with cytopenic myelofibrosis, that is patients with a platelet count below 50 x 109/L.
Myelofibrosis is a rare, heterogeneous, debilitating, progressive bone marrow cancer that disrupts the normal production of healthy blood cells resulting in formation of fibrous scar tissue in the bone marrow, cytopenias or low blood counts (thrombocytopenia and anemia), weakness, fatigue and an enlarged spleen.

Within the U.S, there are approximately 21,000 patients with myelofibrosis, 7,000 of which have severe thrombocytopenia (defined as blood platelet counts of <50 x 109/L). Patients with severe thrombocytopenia have a poor prognosis with greater disease burden, increased rates of anemia, red blood cell transfusion dependence and shorter overall survival.

Cytopenic myelofibrosis (thrombocytopenia and anemia) presents a significant treatment challenge for physicians due to the limitations of approved therapies, as these therapies commonly worsens cytopenias, leading to dose reductions to sub-therapeutic levels that offer minimal benefit for patients.

Pacritinib’s unique MOA, which targets JAK2 and IRAK1 without inhibiting JAK1, has demonstrated the ability to improve a comprehensive set of debilitating symptoms associated with other JAK inhibitors.

The JAK family of enzymes are a central component in signal transduction pathways, which are critical to normal blood cell growth and development, as well as inflammatory cytokine expression and immune responses. There are currently no myelofibrosis therapies approved for patients with cytopenic myelofibrosis. Pacritinib is the only drug to have included these patients as part of a Phase 3 trial and to demonstrate clinical activity in this subgroup of patients.

Pacritinib is an oral kinase inhibitor with specificity for JAK2 and IRAK1, without inhibiting JAK1. Inhibition of JAK1 has been associated with immune dysfunction and lymphomas, and may also worsen thrombocytopenia and anemia. Pacritinib’s unique mechanism of action (JAK2/IRAK1) may allow for reductions of both splenomegaly and constitutional symptoms and may reduce the risk of cytopenias and immune dysfunction associated with other JAK inhibitors.