Silence sees fast-track tag as proof of FDA confidence in blood cancer drug that faced trial troubles

Silence Therapeutics’ efforts to push SLN124 as a potential treatment for myelodysplastic syndrome (MDS) may have hit a roadblock earlier this year, but the FDA appears to have faith in the therapy’s abilities for another type of blood cancer.

The agency granted SLN124 a fast-track tag to treat polycythemia vera (PV) ahead of a planned phase 1/2 study later this year, the company announced Thursday morning.

SLN124 is designed to temporarily silence TMPRSS6, a gene that stops the liver from making hepcidin. As deficiency of hepcidin, a hormone that controls iron levels, is a driver of both MDS and thalassemia, Silence targeted both indications when it began testing SLN124 last year.

The MDS route came to naught, with the biotech blaming difficulties recruiting patients for dropping a phase 1 trial in March. That left potential avenues in the blood disorder thalassemia—for which the drug is being evaluated in another phase 1 trial—as well as PV. The FDA has already granted orphan-disease tags for both indications.

Of the three conditions SLN124 was being sized up for, PV is the most widespread. The rare disease, in which blood becomes thicker, affects around 150,000 people in the U.S.

"The granting of fast track designation represents an important recognition by the FDA of SLN124’s potential to address a significant unmet need in the treatment of PV," said Silence CEO Craig Tooman. "We plan to leverage fast track to expedite our development path as we seek to provide an important new treatment option to those suffering from this very serious and chronic genetic disease."