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In the wake of Pfizer’s voluntary market withdrawal of the popular sickle cell disease therapy,
BioSpace
looks at five investigational drugs currently making their way through the pipeline.
A recent fumble has left the sickle cell disease community
reeling
. Last month,
Pfizer
abruptly
pulled
Oxbryta from all global markets after new data showed a higher risk of deaths and complications in treated patients.
“[Oxbryta] was one of four medications which we would describe as disease-modifying,” Clifford Takemoto, director of clinical hematology at St. Jude Children’s Research Hospital, told
BioSpace
. Since the
approval
of Bristol Myers Squibb’s hydroxyurea for sickle cell disease (SCD) in 1998, only three disease-modifying medications have entered the market, he said.
Oxbryta, which won FDA
accelerated approval
in November 2019, was one of these. Another, Novartis’ Adakveo, has also been called into question after
failing
to reduce vaso-occlusive crises (VOC) in people with SCD in a Phase III trial last year. EU regulators formally
revoked
Adakveo’s approval in August 2023, but it remains available in the U.S.
“We were optimistic that things were changing,” Takemoto said. “People had hoped that these medications would make a difference.”
SCD
affects
more than 100,000 people in the U.S. and 8 million worldwide. With so few treatment options, it remains a seriously
underserved population
. Takemoto said the Oxbryta withdrawal has left some patients a “bit angry” and distrustful of new medications, and the question for the community remains: “What’s next?”
For Takemoto, the ultimate hope for SCD treatment lies in next-gen transplantation and gene therapy. With the
approval
of bluebird bio’s Lyfgenia and Vertex and CRISPR Therapeutics’ Casgevy, the potential for gene therapies in SCD is there, even if the
rollout is slow
and for most, not very accessible, he said. St. Jude is developing its own gene therapy, which the research hospital hopes to move into clinical trials sometime next year.
Takemoto also pointed to work being done in bone marrow transplantation intended to reduce toxicity and improve success rates. St. Jude is working on a process that will utilize a “half match,” where a parent’s bone marrow can be used instead of a sibling. These treatments could be transformative, Takemoto said.
Here,
BioSpace
looks at five investigational therapies making their way through the SCD pipeline.
Pfizer’s Inclacumab and Osivelotor
Oxbryta is not the only SCD asset Pfizer brought onboard with its 2022
acquisition of Global Blood Therapeutics
. Two other investigational therapies, inclacumab and osivelotor, were also part of the deal.
Inclacumab, a P-selectin inhibitor, is currently being assessed in a
Phase III trial
to determine its safety and efficacy in reducing VOC. The drug works by binding to P-selectin, a cell adhesion molecule found on platelets. According to Pfizer, this prevents platelets from aggregating, which in turn, is expected to help maintain normal blood flow.
Like Oxbryta, osivelotor is a sickle hemoglobin polymerization inhibitor, but with a next-generation design. The asset is currently being studied in a
Phase II/III
study slated for completion in 2028. While Pfizer has not stated whether the recent findings related to Oxbryta will impact the development of osivelotor, Leerink Partners
noted
that a Phase II study raised safety concerns, with treatment-emergent adverse events seen in 8 out of 35 patients.
Agios Pharmaceuticals’ Mitapivat
Agios Pharmaceuticals
is developing mitapivat, a pyruvate kinase (PK) activator that is already approved for the treatment of hemolytic anemia in adults with PK deficiency, for SCD. Red blood cells require the PK enzyme for energy, Takemoto explained.
In December 2023, the company
presented
positive data from the Phase II portion of its pivotal RISE UP study. The annualized rate of sickle cell pain crises for patients in the higher dose treatment arm was 0.51 compared to 1.71 for participants in the placebo arm. Takemoto said the oral medication seems to benefit red blood cell health in general and noted that the data look favorable for patients with SCD and other hemolytic anemias.
But not everyone is as convinced. Leerink Partners analysts wrote last month of concerns that similar physiological effects could be seen with both Oxbryta and mitapivat. A Phase III readout is expected next year, and the company is targeting a label expansion in 2026.
Novo Nordisk’s Etavopivat
In 2022,
Novo Nordisk
paid $1.1 billion to
acquire
Forma Therapeutics, gaining a lead SCD asset, etavopivat, in the deal. Like mitapivat, etavopivat is also a PK activator, but Novo’s candidate comes with a potential
advantage
—once daily dosing, versus mitapivat’s twice daily regimen. Etavopivat is currently being studied in a Phase III trial
slated
for completion in 2026.
Phase I data
presented
by Forma at the American Society of Hematology’s annual meeting in 2021 showed a “sustained increase in hemoglobin and improvement in biomarkers of hemolysis and red blood cell health.” The results, from 15 patients dosed for up to 12 weeks, also showed a trend toward decreasing VOC compared to the 12 months prior to their entering the trial.
Takemoto said the candidate “looks very promising” so far but acknowledged that “there are things we don’t know about it. We may learn new side effects as it’s used.” St. Jude will serve as a site for the Phase III trial.
Fulcrum Therapeutics’ Pociredir
Fulcrum Therapeutics
’ pociredir, a polycomb repressive complex 2 (PRC2) inhibitor, is
designed
to induce expression of fetal hemoglobin to compensate for the mutated hemoglobin that occurs in SCD.
The development path for pociredir has not been without bumps. In February 2023, the FDA slapped Fulcrum with a clinical hold based on previously submitted preclinical data and non-clinical and clinical evidence of hematological malignancies observed with other PRC2 inhibitors. The hold was
released
six months later.
The small molecule, which is currently being studied in a Phase Ib trial, has been well-tolerated in people with SCD with no treatment-related adverse events reported after up to three months exposure, according to a press release announcing the lifted clinical hold.
