The investigational agent pacritinib appears active against myelofibrosis without the risk of myelosuppression, a common side effect of many drugs used to treat myelofibrosis and other myeloproliferative neoplasms (MPN). The developers of pacritinib, CTI BioPharma Corp and Baxter International Inc, announced these findings from a Phase III clinical trial called PERSIST-1.

Myelofibrosis is a type of blood cancer known as a myeloproliferative neoplasm. It involves the abnormal development and function of bone marrow cells that produce blood cells which leads to the formation of scar tissue in the bone marrow. This can cause anemia, enlargement of the spleen and liver, fatigue, and other problems. In some patients with myelofibrosis, the condition progresses to acute myeloid leukemia.

Proteins known as JAK1 and JAK2 may play a role in the development of MPNs, including myelofibrosis, by causing the body to make the wrong number of blood cells. Drugs that suppress JAK1 and JAK2 are used to treat different forms of MPN by reducing the number of abnormal blood cells associated with these disorders. JAK1/JAK2 inhibitors can, however, result in too much suppression of the bone marrow’s production of blood cells. Known as myelosuppression, this condition can negatively impact patient health and quality of life.

Pacritinib is designed to fight myelofibrosis by interfering with the kinases JAK2 and FLT3 to potentially keep tumors from developing. Unlike other JAK inhibitors, pacritinib does not cause myelosuppression, which, if safe and effective, could offer an advantage to patients.

The researchers measured pacritinib’s anticancer activity by comparing patients treated with pacritinib with patients treated with best available therapy (BAT) for myelofibrosis. They evaluated treatments by monitoring spleen volume (an enlarged spleen is a symptom of myelofibrosis). The researchers measured spleen volume of all patients after six months of treatment; they found that more patients receiving pacritinib had spleen volume decreased by 35% or more compared with those on BAT. Patients with more severe disease experienced the most significant results on pacritinib. In addition, many patients who entered the study needing regular red blood cell transfusions to treat myelofibrosis were able to stop transfusions after treatment with pacritinib. Pacritinib was considered beneficial enough that 79% of patients on BAT were allowed to switch to treatment with pacritinib.

Researchers did not find any new side effect information for pacritinib compared with earlier studies. It appeared that very few patients had to stop treatment due to side effects.

Pacritinib looks to be a very promising therapy for patients with myelofibrosis. Not only is it active against the disease, it also does not pose a risk of myelosuppression. As a result, pacritinib might offer effective treatment for patients who previously had no or few options.

Reference: CTI BioPharma and Baxter Announce Positive Top-Line Results from Phase 3 Persist-1 Trial Of Pacritinib for Patients with Myelofibrosis [press release]. CTI BioPharma website. Available at: Accessed March 17, 2015.


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