Omeros plunges deeper after FDA rejects rare disease drug, asking for more information
Omeros practically warned investors that a complete response letter was coming when it disclosed that the FDA found deficiencies in its BLA for narsoplimab. But the agency did not elaborate on the specifics of those deficiencies for the drug, which was being positioned as a treatment for the rare but serious blood clotting disease known as hematopoietic stem cell transplant-associated thrombotic microangiopathy (HSCT-TMA).
The other shoe has now dropped.
In the CRL, the FDA “expressed difficulty in estimating the treatment effect of narsoplimab in HSCT-TMA and asserted that additional information will be needed to support regulatory approval,” according to Omeros.
While it wouldn’t be entirely surprising to some, the rejection still startled other investors, who sent shares $OMER down 27.04% to $5.64.
TMA — a constellation of symptoms caused by the formation of tiny blood clots in the body — is one of the conditions that can plague patients who have gone through an HSCT. Omeros believes it’s largely because stem cell transplants trigger endothelial damage, which in turns activates the complement system, primarily through the lectin complement pathway.
By blocking an enzyme on the lectin pathway dubbed MASP-2, narsoplimab was designed to address that exact cause.
It’s not exactly alone in pinning the blame on the complement system. Alexion’s C5 inhibitor Soliris is often prescribed off-label for this use as well as transplant-associated TMA; in fact, some of the indications it’s approved in can be characterized as TMA. But narsoplimab was the first candidate to be submitted specifically for HSCT-TMA.
For its part, Omeros says it remains confident about its drugs’ efficacy and safety data — from a single-arm pivotal trial that was compared to historical controls, and employed clinical response as the primary endpoint — and plans to request a Type A meeting with regulators.
“There were no chemistry, manufacturing and controls (CMC), safety, or non-clinical issues precluding approval raised in the CRL,” the company added, while noting the drug is adorned with breakthrough and orphan designations.
