Pacritinib has been granted Fast Track designation by the FDA ( Food and Drug Administration ) for the treatment of intermediate and high risk myelofibrosis, including but not limited to patients with disease related thrombocytopenia, patients experiencing treatment emergent thrombocytopenia on other JAK2 therapy or patients who are intolerant to or whose symptoms are sub-optimally managed on other JAK2 therapy.
The drug candidate is currently being evaluated in two Phase 3 clinical trials, known as the PERSIST program, for patients with myelofibrosis.

The Fast Track process is designed to facilitate the development, and expedite the review of drugs to treat serious conditions and fill an unmet medical need. An unmet need is a condition whose treatment or diagnosis is not addressed adequately by available therapy. The purpose of the Fast Track designation is to make important new drugs available to the patient earlier. The Fast Track program also enables a company to submit sections of the NDA on a rolling basis as data becomes available. This enables the FDA to review sections of the NDA as they are received, rather than waiting until every section of the application is completed before the entire application can be reviewed. NDA review usually does not begin until the company has submitted the entire application to the FDA. A drug program with Fast Track designation enables the company to have early and frequent communication with the FDA in the development and review of the product candidate, often leading to faster drug approval and access by patients.

Pacritinib is an oral tyrosine kinase inhibitor with dual activity against JAK2 and FLT3. The JAK family of enzymes is 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. Mutations in these kinases have been shown to be directly related to the development of a variety of blood-related cancers, including myeloproliferative neoplasms, leukemia and lymphoma. Pacritinib may offer an advantage over other JAK inhibitors through effective treatment of symptoms while having less treatment-emergent thrombocytopenia and anemia than has been seen in currently approved and in-development JAK inhibitors.

Myelofibrosis is classified as a myeloproliferative neoplasm and is a chronic bone marrow disorder. Myelofibrosis is caused by the accumulation of malignant bone marrow cells that triggers an inflammatory response, scarring the bone marrow and limiting its ability to produce red blood cells, prompting the spleen and liver to take over this function. Symptoms that arise from this disease include enlargement of the spleen, anemia, extreme fatigue and pain.

PERSIST phase 3 development Program of Pacritinib

Based on Pacritinib's efficacy and tolerability profile demonstrated, two phase 3 clinical trials are ongoing for patients with myelofibrosis: one in a broad set of patients without limitations on blood platelet counts, the PERSIST-1 trial, and the other in patients with low platelet counts, the PERSIST-2 trial.

PERSIST-1 trial was designed to enroll approximately 320 patients and is a randomized, open-label, multicenter trial comparing the efficacy and safety of Pacritinib with that of best available therapy, other than JAK inhibitors, in patients with primary myelofibrosis, post-polycythemia vera myelofibrosis or post-essential thrombocythemia myelofibrosis, without exclusion for low platelet counts. The primary endpoint is the percentage of patients achieving a greater than or equal to 35% reduction in spleen volume measured by MRI or CT from baseline to 24 weeks of treatment.

PERSIST-2 trial, which is evaluating Pacritinib compared to best available therapy, including approved JAK2 inhibitors that are dosed according to product label, in patients with myelofibrosis whose platelet counts are less than or equal to 100,000/uL. The trial is designed to enroll up to 300 patients in North America, Europe, Australia and New Zealand. The co-primary endpoints are the percentage of patients achieving a 35% or greater reduction in spleen volume measured by MRI or CT scan from baseline to 24 weeks of treatment and the percentage of patients achieving a Total Symptom Score ( TSS ) reduction of 50% or greater using six key symptoms as measured by the modified Myeloproliferative Neoplasm Symptom Assessment ( MPN-SAF TSS 2.0 ) diary from baseline to 24 weeks. ( Xagena )

Source: CTI BioPharma, 2014

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