CTI Biopharma Posts Positive Myelofibrosis Study Results
SEATTLE (TheStreet) -- CTI Biopharma's (CTIC) - Get Report experimental drug pacritinib significantly reduced the spleen size in patients with myelofibrosis compared to patients treated with best alternative care, according to results from a phase III study announced by the company on Monday.
The relative benefit observed in myelofibrosis patients treated with pacritinib was large enough to meet the primary endpoint of the study, CTI Biopharma said, although details were not provided. A second phase III study is still underway.
CTI Biopharma shares were up 20% to $3.18 in pre-market trading.
Myelofibrosisis is a disorder in which abnormal bone marrow stem cells produce scar tissue that replaces healthy marrow. Patients with myelofibrosis suffer from anemia and enlarged spleens. Approximately 3,500 people in the U.S. are diagnosed with myelofibrosis annually and about one-third of these patients develop acute myeloid leukemia or bone marrow failure.
Pacritinib is a pill designed to inhibit enzymes known as JAK2 and FLT3 believed to play a role in diseases like myelofibrosis that cause bone marrow cells to grow uncontrollably. Incyte (INCY) - Get Report and Novartis (NVS) - Get Report currently sell a similar pill, Jakafi, approved to treat myelofibrosis and related diseases.
In the "PERSIST-1" study conducted by CTI Biopharma, 327 patients with myelofibrosis were randomized to receive treatment with pacritinib or best alternative care. Patients could not be treated with another JAK inhibitor, including Jakafi. The primary endpoint of the study was spleen response, defined as the 35% or greater reduction in the size of the spleen measured after 24 weeks of treatment.
Pacritinib demonstrated a statistically significant spleen response compared to best alternative therapy, the company said. The precise response rates were withheld pending presentation at a future medical meeting.
CTI Biopharma did say that phase III spleen response rates observed in pacritinib-treated patients were "consistent" with results from prior phase II studies. In those older studies, which enrolled 65 patients, pacritinib demonstrated a 27% spleen response.
Based on a cross-trial comparison, Incyte's Jakafi, with spleen response rates of 32% at 24 weeks in similar patients, appears more potent. But the biggest knock on Jakafi is that the drug causes significant suppression of blood platelets, a condition known as thrombocytopenia. Some myelofibrosis patients with low blood platelets cannot tolerate Jakafi, while others must reduce the dose of the drug used.
Pacritinib appears to cause less thrombocytopenia. CTI Biopharma says the greatest spleen response in the phase III study was observed in patients with the lowest platelet counts at baseline.
The most significant side effects tied to pacritinib are diarrhea, nausea and vomiting. Three patients discontinued therapy and nine patients required dose reduction for diarrhea in the phase III study.
The second, ongoing phase III study, dubbed PERSIST-2, compares pacritinib against best alternative care. Importantly, patients in the control arm will be allowed to be treated with Incyte's Jakafi.
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