Rallybio’s lead program has crashed out. Racing toward a $1.6 billion market, the biotech stopped work on RLYB212 in a rare maternal immune disorder in response to phase 2 data.
RLYB212, an anti-HPA-1a antibody, was in phase 2 development for the prevention of fetal and neonatal alloimmune thrombocytopenia (FNAIT). The condition occurs when a mother’s immune system identifies her baby’s platelets as foreign and mounts an attack. No drugs are approved to prevent or treat FNAIT, which Rallybio has valued as a $1.6 billion opportunity.
Rallybio ended its pursuit of the opportunity on Tuesday, sending the company's struggling shares down 50% in pre-market trading to 21 cents from a Monday closing price of 42 cents.
The biotech stopped development of RLYB212 after concentrations of the drug in the first person enrolled in the phase 2 trial fell short of the target range.
Researchers predicted target concentrations of 6 ng/mL to 10 ng/mL in the second trimester. Rallybio set 3 ng/mL as the minimum concentration required for efficacy. When the data came in, the biotech found the values were near or below the assay’s lower limit of quantitation.
Rallybio CEO Steve Uden, M.D., discussed the prospect of concentrations missing the bottom end of the range at a TD Cowen event last month. In that scenario, the data would inform changes to the dose to ensure Rallybio hit the range in the next cohort, the CEO said. However, the candidate missed the mark by such a wide margin that Rallybio opted against trying to adjust the dose on feasibility grounds.
The biotech’s current hypothesis is that HPA-1a antigen expression on the placenta may be impacting plasma concentrations of RLYB212. Whatever the reason, the result is that Rallybio has shifted its focus to its once-weekly low-volume C5 inhibitor RLYB116 and its preclinical programs. Uden and other people at Rallybio know the C5 space well from their time at Alexion.
Rallybio is working to start dosing RLYB116 in a confirmatory pharmacokinetic/pharmacodynamic study in the second quarter. The biotech is aiming to share results from the first two cohorts in the third and fourth quarters. Rallybio wants to see complete and sustained complement inhibition with improved tolerability to support its positioning of RLYB116 as a drug that patients can self-administer at home.