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Will the FDA Approve Pacritinib for Myelofibrosis?

Will the FDA Approve Pacritinib for Myelofibrosis?
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Published on May 19, 2021

Pacritinib Could Fill an Unmet Need in Myelofibrosis

A new therapy for patients with myelofibrosis (MF) may soon be available. CTI BioPharma has submitted an application to the U.S. Food and Drug Administration (FDA) seeking the approval of pacritinib as a treatment for patients with myelofibrosis who have severe thrombocytopenia. The Seattle-based biopharmaceutical company hopes to make the drug commercially available by the end of 2021.

“[Pacritinib] is a welcome addition to the treatment armamentarium for myelofibrosis,” John Mascarenhas, MD, associate professor of medicine at Icahn School of Medicine and director of the Adult Leukemia Program at Mount Sinai, told Patient Power. “It serves an urgent unmet need that has gone on for too long.” Dr. Mascarenhas has been an advisory board member for CTI BioPharma and his institution has received research funding from the company.

Thrombocytopenia in Patients with Myelofibrosis

Myelofibrosis is a chronic blood cancer that causes excessive scar tissue to form in the bone marrow, impairing the body’s ability to produce normal blood cells. It is part of a group of related blood cancers called myeloproliferative neoplasms (MPNs) that affect the production of white blood cells, red blood cells, and platelets.

Thrombocytopenia (low platelet count) is a common side effect of myelofibrosis. Patients with severe thrombocytopenia (less than 50,000 platelets per microliter) are at risk for early death. They are also at a higher risk for developing acute myeloid leukemia (AML), a type of blood and bone marrow cancer that progresses rapidly.

The FDA has approved two JAK inhibitors — ruxolitinib (Jakafi) and fedratinib (Inrebic) — for treating myelofibrosis. However, neither is considered safe for patients with severe thrombocytopenia, leaving this high-risk group without a viable treatment option.

“It’s tragic that this patient population has been excluded from the benefits of JAK inhibitors,” said Dr. Mascarenhas. “We can’t safely deliver the current JAK inhibitors that are approved to this patient population. [Pacritinib] would give them symptom relief and improve their ability to function. Personally, I think this drug should have been approved already.”

What is Pacritinib?

Pacritinib is an oral kinase inhibitor that has been in clinical trials for several years. It inhibits the JAK2, FLT3, and IRAK-1 mutations. After showing early promise and being touted as an emerging therapy at the 2015 American Society of Clinical Oncology (ASCO) annual meeting, the FDA placed pacritinib on a full clinical hold in 2016. That means that the drug manufacturer had to halt all clinical trials until they could show that the potential benefits from the drug exceeded the potential risks.

“There was a concern about excessive bleeding risk and cardiovascular events that led the FDA to put a full clinical hold [on pacritinib] in 2016,” Dr. Mascarenhas said. “At that point, the FDA was looking at early data. After a more rigorous review of the full data set, they found that the adverse effects were no different than for patients on other therapies. And considering the patient population we are treating, a patient population in need, the benefits clearly outweigh the risks.”

After reviewing findings from the phase 3 PERSIST-1 and PERSIST-2 trials, the FDA removed the clinical hold on pacritinib in January 2017. Shortly after, CTI BioPharma began a new phase 2 trial, PAC203, for patients with advanced myelofibrosis who were resistant to or could not tolerate ruxolitinib. Promising results from PAC203 led to PACIFICA, an ongoing phase 3 trial to evaluate the safety and efficacy of 200 mg of pacritinib administered twice daily, potentially paving the way for an FDA approval later this year.

Pacritinib is also being investigated as a treatment for cytokine storms in patients who are hospitalized with severe cases of COVID-19. Dr. Mascarenhas said the ability of pacritinib to inhibit IRAK-1 is noteworthy.

“[Pacritinib] may not simply be another JAK2 inhibitor,” he said. “It addresses an unmet need in patients with low platelet counts, but there may be additional benefits.”

For more information about pacritinib, please contact your doctor. We will continue to update you on this developing story.

~Suzanne Mooney

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