Newly approved injection therapy gives PV patients a new option

The U.S. Food and Drug Administration’s (FDA) recent approval of Takeda‘s injection therapy Mimrylo (rusfertide) to treat excessive blood cell production in adults with polycythemia vera (PV) “means we have more options for our patients, said Andrew Kuykendall, MD, a hematologist-oncologist and associate member in the hematology department at Moffitt Cancer Center in Tampa, Florida.

“More options means that we can individualize care better than we did before,” Kuykendall told Rare Cancer News. “We know that we don’t have a one-size-fits-all treatment for PV and every patient has a unique experience with their disease. Having more options allows us to listen to patients and come up with an individual treatment plan that makes sense.”

PV is a form of blood cancer marked by erythrocytosis, the term for when the body produces too many red blood cells. To manage the disease, patients often require regular phlebotomies (blood draws) to remove excess blood cells.

Mimrylo is a weekly, under-the-skin injection therapy that works by mimicking the activity of hepcidin, a naturally occurring signaling molecule that helps regulate iron distribution in the body.

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“You need iron to make red blood cells and patients with PV rapidly use up whatever iron they have to make more and more red blood cells,” Kuykendall said. “Unfortunately, the body senses that lack of iron and tries to compensate by mobilizing more iron (by downregulating hepcidin). Ultimately, this just feeds the fire.”

Mimrylo mimics hepcidin, “which decreases the delivery of iron to the bone marrow which stops this chain reaction and controls the erythrocytosis,” he said.

Takeda’s application seeking FDA approval of Mimrylo was based largely on data from a Phase 3 clinical trial called VERIFY (NCT05210790), which tested the therapy against a placebo in nearly 300 adults with PV who required regular phlebotomies.

“Patients who were enrolled on the VERIFY studies required repeated phlebotomies to control their hematocrit [blood cell counts] at a goal level,” said Kuykendall, an investigator on the study. “This was regardless of whether they were on another medication that was aiming to control their blood counts or not.”

“Reliance on phlebotomy meant that these patients were regularly getting their blood drawn and going to an infusion center or lab to have [about half a liter] of blood removed,” he said. “Then, once they were done, assuming they were able to tolerate the removal of blood well, they went home knowing they would have to do it all again in perhaps a week, or a month, or two months.”

Results from VERIFY showed that Mimrylo outperformed placebo at reducing the need for phlebotomies. In fact, most patients given the therapy didn’t need phlebotomy at any time during a year of follow-up.

That “showed that there was an alternative [to phlebotomies] where a medication could be self-administered and – in the majority of patients – eliminate the need to have those repeated phlebotomies,” Kuykendall said.

Patients who received Mimrylo in VERIFY also tended to report more symptom easing compared with those given a placebo.

“In the phase 3 study, when patients were blinded to whether they were on placebo or [Mimrylo], we assessed how symptoms changed and, encouragingly, patients randomized to [Mimrylo] reported significant improvements in fatigue and disease-related symptoms,” Kuykendall said. “To me, this means that some patients can expect that [Mimrylo] may improve their overall quality of life.”

According to its prescribing information, the most common side effects of Mimrylo are injection site reactions and anemia (low red blood cell counts). Kuykendall said these side effects “typically are mild and don’t require any change to treatment.”

Kuykendall noted that to minimize safety complications, it’s recommended that Mimrylo be started at a low dose, with regular monitoring to tailor treatment to each individual’s response.

“Anemia makes sense [as a side effect]  since our goal is to reduce [red blood cell counts], but we don’t want to go too far,” he said. “This is why [Mimrylo]  is recommended to start at a relatively low dose and [increase the dose] upwards to make sure we find the right dose for each patient without overshooting.”

Mimrylo may also increase platelet counts. Platelets are cell fragments that initiate and form the core of a blood clot.

“Typically, patients are recommended to have labs done every 2-4 weeks after starting [Mimrylo] with this becoming less frequent once an optimal dose is established,” Kuykendall said.

Overall, he said, the newly approved PV treatment “is another tool in our toolbox that allows patients the opportunity to live independently, be less reliant upon the healthcare system, and, perhaps, live with fewer symptoms related to their disease.”