For the first 28 day cycle, all patients will be treated with single agent pacritinib at 200 mg twice daily. The investigators chose this starting dose based on the previous three phase I studies of pacritinib as a single agent which showed that the maximum tolerated dose (MTD) to be 500 mg, and subsequently, the dose of 400 mg daily was recommended for the phase II studies.
Recently, the results of the phase III PERSIST-1 trial comparing pacritinib to best available therapy (BAT) in patients with MF was reported at the 2015 American Society of Clinical Oncology (ASCO) annual meeting. Pacritinib was found to be significantly more effective than BAT at reducing spleen volume at 24 weeks of therapy and improving constitutional symptoms.
Low dose decitabine has demonstrated depletion of DNMT1 in normal hematopoietic stem cells (HSC) without cytotoxicity and subcutaneous (SC) instead of intravenous (IV) administration may avoid high peak levels that can cause apoptosis. Furthermore, the low toxicity associated with low dose decitabine would allow for more frequent (1 to 3 times weekly) administration of the drug which would catch more cells in S-phase via greater exposure time. Based on these findings, a starting dose of decitabine 5 mg/m2 SC twice weekly should be well tolerated and effective in patients with MF and MPN/MDS syndromes when combined with pacritinib 400 mg daily.