Protagonist Therapeutics, Inc. (NASDAQ:PTGX) today announced initial data from the ongoing Phase 2 study of PTG-300 in patients with polycythemia vera. The current results demonstrate that treatment with PTG-300 at individualized doses ranging from 10 mg to 80 mg for up to 28 weeks provided dose-related control of hematocrit levels and eliminated the need for phlebotomy in all six out of six patients that received the dosing as per protocol. A seventh patient with 12 weeks of treatment had an unintended dose interruption, received a single phlebotomy, and remains on the study. In addition, positive symptomatic measurements related to the ability of PTG-300 to address iron deficiency in these frequently phlebotomized patients were observed, with increases in serum ferritin values approaching the range observed in healthy subjects. Patients enrolled in the current study had received at least three phlebotomies within a 24 week period prior to PTG-300 treatment and were treated for up to 28 weeks as of the cutoff date of May 1, 2020 (range of 4 to 28 weeks, n=7 evaluable for efficacy). Enrollment in the study continues and a total of eight patients have enrolled to date.
"While further follow up and data from additional patients will be needed to confirm the continuity of the robust clinical responses observed to date, we believe that this study provides a compelling rationale to initiate planning for a pivotal program in polycythemia vera," commented Samuel Saks, M.D., Protagonist Chief Medical Officer. "As a peptide mimetic of the natural hepcidin hormone, PTG-300 is believed to limit the excess number of red blood cells in polycythemia vera by reducing iron available for red blood cell production. In the near term, we are expanding the current study to include additional patients as the Company focuses on these encouraging results. We will also be hosting a scientific planning meeting with leaders in the field of myeloproliferative neoplasms and working with patient advocates to discuss pivotal and future studies in polycythemia vera. Our goal with these studies is to work to address the broad populations of patients that may benefit from this new non-cytoreductive treatment."
"These initial data demonstrate the potential of PTG-300 to almost entirely avoid the need for phlebotomy in the treatment of polycythemia vera by persistent control of hematocrit levels to below 45 percent," commented Ronald Hoffman, M.D., Director of the Myeloproliferative Diseases Program at The Icahn School of Medicine at Mount Sinai and an investigator in the PTG-300 polycythemia vera study. "Previous studies have repetitively demonstrated that patients undergoing phlebotomy in addition to other therapies spend far too much time above the target hematocrit levels of 45 percent in the clinical guidelines. This is despite the fact that hematocrit levels above this target are associated with significant cardiovascular events such as heart attack and stroke. PTG-300 offers the possibility of maintaining patients consistently below 45 percent hematocrit levels with weekly administration of a mimetic of the endogenous iron regulator without the up and down excursions inherent in typical phlebotomy therapy. In addition, the reduction in phlebotomy may allow sufficient iron to be available systemically to avoid symptoms related to iron deficiency. The potential for weekly self-administration with PTG-300 is a meaningful advantage of this approach to treatment. These early results are very encouraging and suggest the potential for a paradigm shift for the treatment of polycythemia vera. We look forward to additional data from the expanded study in the future."
Administration of PTG-300 was well tolerated and the safety profile was generally similar with results of prior studies, with injection site reactions and bruise as the only observed adverse events. With eight subjects enrolled to date, the study continues to accrue patients and none of the patients have discontinued treatment with PTG-300.
The study is designed to monitor the safety profile and to obtain evidence of efficacy in patients requiring frequent phlebotomies. Based on the initial findings, the study is being expanded and is now expected to enroll approximately 50 patients. The study design consists of a 16-week open-label dose escalation, reduction, or maintenance stage every four weeks from 10 mg to 80 mg and a 12-week maintenance period at doses that generate desired hematocrit levels followed by a randomized and blinded withdrawal stage up to 12 weeks. The study has an open-label extension for up to one year to monitor long-term safety and other effects. The primary endpoint is the proportion of responders during the blinded randomized withdrawal period. Other endpoints of this clinical proof-of-concept study include measurement of blood parameters (hematocrit and hemoglobin levels), reductions or delay in phlebotomy requirements and improvements in quality-of-life symptoms. Additional information is available at https://clinicaltrials.gov/ct2/show/NCT04057040.