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Dive Brief:
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The biotechnology company Rallybio is discontinuing its lead candidate for a rare blood disorder in pregnant women after disappointing data from a mid-stage study, sending shares down sharply Tuesday morning.
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The drug, dubbed RLYB212, was in testing to treat the disorder known as fetal and neonatal alloimmune thrombocytopenia, or FNAIT, which has no approved treatment available in the U.S. Development was also supported from Johnson & Johnson, which provided Rallybio with an equity investment of $6.6 million, an upfront payment of $500,000 and additional funding of up to $3.7 million to support a natural history study.
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Rallybio said Tuesday the drug did not meet expectations in a Phase 2 pharmacokinetic study and all screening of trial participants has stopped. The biotech will now focus on development of another candidate, RLYB116, and other preclinical programs.
Dive Insight:
Rallybio, spearheaded by former Alexion Pharmaceuticals leaders Steve Uden and Martin Mackay, has already faced tough decisions over the years including switching lead candidates and cutting its workforce by half to stay afloat.
RLYB212 was viewed as a major opportunity, however. After completing an epidemiological analysis of the risk of FNAIT across diverse ancestries, Rallybio estimated the drug’s commercial opportunity was greater than $1.6 billion.
In FNAIT, the mother’s immune cells are not compatible with the fetus’ platelets, so allo-antibodies can attack blood-clotting cells in the fetus leading to thrombocytopenia, or low platelet levels. The disease can be life-threatening or lead to miscarriages or neurological disabilities of the infant. Platelet transfusion is typically first line of treatment, but there are no other preventions available.
RLYB212 is a monoclonal antibody targeting “HPA-1a,” a protein thought to cause alloimmunization. Diagnostic tests for the disease include testing the mother for anti-HPA antibodies.
The Phase 2 trial assessed pharmacokinetics and safety in pregnant women at higher risk of HPA-1a alloimmunization and FNAIT. In testing, the drug did not achieve predicted target concentration levels, nor did it meet the bar set for efficacy. The company said it did not seem feasible to adjust the dose.
Rallybio said it believes HPA-1a antigen expression on the placenta could have impacted plasma concentrations of the antibody.