Protagonist Wins FDA Approval for MIMRYLO in Rare Blood Cancer Treatment

Key Points

• FDA approval: Protagonist Therapeutics received U.S. approval for MIMRYLO (rusfertide) to treat erythrocytosis in adults with polycythemia vera, marking its second approved medicine this year.
• Clinical results: In the Phase III VERIFY trial, MIMRYLO achieved a 76.9% clinical response rate, improved hematocrit control, reduced phlebotomy needs and addressed fatigue; the most common adverse events were injection-site reactions and anemia.
• Financial impact: Takeda will commercialize the treatment, with Protagonist receiving $275 million in approval-related payments and remaining eligible for up to $875 million in milestones plus tiered royalties of 14% to 29% on worldwide sales.

Protagonist Therapeutics NASDAQ: PTGX said the U.S. Food and Drug Administration has approved rusfertide, to be marketed as MIMRYLO, for the treatment of erythrocytosis in adults with polycythemia vera, or PV.

The approval marks the company’s second FDA-approved medicine this year, following the March approval of ICOTYDE, an oral IL-23 receptor blocker partnered with Johnson & Johnson. MIMRYLO is partnered with Takeda Pharmaceutical, which is now solely responsible for the product’s commercialization and ongoing clinical development following Protagonist’s opt-out election.

PV is a rare blood cancer characterized by excessive red blood cell production. Protagonist Chief Executive Officer Dinesh Patel said the central treatment objective is to lower and maintain hematocrit below 45%. Existing care can include phlebotomy and cytoreductive therapies, but Patel said no prior therapy had specifically targeted erythrocytosis.

Mechanism and Phase III Results

MIMRYLO is a peptide mimetic of hepcidin, a hormone that regulates iron homeostasis. By regulating iron availability, the therapy is designed to help normalize red blood cell production and maintain hematocrit levels.

Chief Medical Officer Arturo Molina said FDA approval was based on the Phase III VERIFY study, a 32-week, double-blind, placebo-controlled trial in patients receiving standard care who continued to require frequent phlebotomies because of uncontrolled hematocrit. Patients in the investigational arm received rusfertide in addition to ongoing treatment.

The study met its primary endpoint of clinical response during weeks 20 through 32, as well as four key secondary endpoints, according to the company. MIMRYLO produced a 76.9% response rate during that period and demonstrated hematocrit control and reduced phlebotomy. Improvement in fatigue, measured using the PROMIS Fatigue Short Form 8a, was included in the approved label.

Molina said the most common adverse events were injection-site reactions and anemia. The label does not include a boxed warning. Injection-site reactions were reported in 56% of MIMRYLO-treated patients, with most reported as Grade 1 or 2; 0.7% were Grade 3. Thrombocytosis was reported in 8% of patients, with all cases Grade 1 or 2. Discontinuations tied to adverse events were low, the company said.

Broad Label and Commercial Outlook

Protagonist said MIMRYLO’s label allows use either as a monotherapy or in combination with other PV treatments. Molina cited company-described real-world data indicating that approximately 78% of treated PV patients experience elevated hematocrit despite current therapy.

The company estimated that PV affects approximately 155,000 people in the United States, including roughly 78,000 people currently receiving some form of treatment. Molina said a comparable number of patients are in Europe.

Management characterized MIMRYLO as an add-on option that can be used alongside phlebotomy or cytoreductive treatment where appropriate. During the call, executives said most patients in clinical studies self-administered the treatment after the initial months of therapy. Monitoring is more frequent during dose titration, but patients in longer-term studies had blood counts monitored every 12 weeks, according to the company.

In long-term follow-up from the Phase II REVIVE study and the THRIVE extension study, 44 of 46 patients who entered the extension remained on MIMRYLO at three years, while 41 of 46 remained on treatment at four years.

Takeda has previously guided to potential peak annual sales of $1 billion to $2 billion for MIMRYLO. Protagonist executives said Takeda will provide further details on launch timing, pricing, reimbursement and commercialization. The company said it expects the launch to take roughly six to 12 months to establish a more regular cadence, based on management’s view of prior product launches.

Partnership Economics and Pipeline Plans

Chief Financial Officer Asif Ali said Protagonist had approximately $850 million in cash, cash equivalents and marketable securities as of June 30. MIMRYLO’s approval triggered $275 million in additional payments, including a $200 million opt-out fee and a $75 million milestone payment. Ali said the company expects to recognize at least a significant portion of those payments in the third quarter.

Protagonist remains eligible for up to $875 million in future MIMRYLO milestones and tiered royalties of 14% to 29% on worldwide net sales. Ali said the royalty rate is a weighted average of 21% at $1.5 billion in annual sales and rises to 29% on sales above that level.

For ICOTYDE, Protagonist remains eligible for another $580 million in potential milestones and royalties of 6% to 10%. The company said it has earned approximately $1.2 billion to date from upfront payments, milestones and opt-out-related payments across its partnerships.

Ali said management does not anticipate needing equity financing in the foreseeable future and may consider share repurchases over time, though research and development remains its primary capital-allocation priority. The company said a potential buyback announcement by year-end remains its expected timeline.

Protagonist also outlined wholly owned pipeline programs in inflammation and immunology, obesity and hematology. The company expects to initiate a Phase II psoriasis study for PN-881, an oral IL-17A and IL-17F antagonist, in the first quarter of 2027. Its PN-477 GLP-1/GIP/glucagon triple agonist is in Phase I development, while an oral Phase I plan is expected in the first half of 2027. PN-8047, an oral hepcidin mimetic, is expected to enter Phase I in the first quarter of 2027.

About Protagonist Therapeutics (NASDAQ:PTGX)

Protagonist Therapeutics, Inc NASDAQ: PTGX is a clinical-stage biopharmaceutical company focused on the development of novel, orally administered peptide-based therapies for immune-mediated and other serious diseases. The company leverages its proprietary Peptide 2.0 platform to design peptides that target G protein–coupled receptors and cytokine receptors, with the goal of combining the potency of biologics with the convenience of oral administration. Protagonist's approach aims to address unmet medical needs in areas where injectable therapies have been the standard of care.

Among its lead programs is PTG-100, an oral α4β7 integrin antagonist intended to block leukocyte migration to the gut in ulcerative colitis and Crohn's disease.

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