Phase 3 Trial of Apitegromab for SMA Type 2, 3 on Track for This Year

Yedida Y Bogachkov PhD avatar

by Yedida Y Bogachkov PhD |

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Scholar Rock is on track to initiate a pivotal Phase 3 trial of apitegromab in non-ambulatory patients with type 2 and type 3 spinal muscular atrophy (SMA) by the end of 2021, according to a company press release.

The planned randomized, double-blind, and placebo-controlled trial will focus on people with these later-onset types of SMA who are on either Spinraza (nusinersen) or Evrysdi (risdiplam), both approved disease-modifying therapies in the U.S. Apitegromab will be given as an add-on to patients’ maintenance medications.

According to Scholar Rock, apitegromab is the first muscle-directed therapy for the disease, as current SMA treatments work to increase the levels of SMN, the protein that’s missing or at low levels in patients.

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Early Work Supports Apitegromab’s Safety as SMA Muscle Therapy

Apitegromab works by selectively inhibiting the activity of myostatin, a protein that suppresses muscle growth and that is produced mainly by skeletal muscle cells (cells involved in movement). By blocking myostatin, apitegromab is expected to increase muscle strength and function in people with SMA.

Latest results from the Phase 2 TOPAZ trial (NCT03921528), announced in June, found apitegromab led to improvements in motor function, as measured by the Hammersmith functional motor scale expanded (HFMSE) that is used to assess physical abilities in types 2 and 3 SMA.

In the trial, apitegromab was tested — largely as an add-on therapy to Spinraza — in 58 children and young adults (ages 2 to 21) with type 2 or 3 SMA. The therapy was given as intravenous (into-the-vein) infusions once every four weeks for up to one year.

A greater improvement in motor function was seen in younger patients, ages 2–6, with type 2 SMA, as compared to the older group, ages 7–21, with type 2 or 3. Additionally, data showed that the HFMSE scores after one year were greater than those seen at six months, indicative that apitegromab can continually improve motor function over time.

The most frequent treatment-related adverse side effects reported in the TOPAZ trial were headache, fever, upper respiratory tract infection, cough, and cold symptoms.

According to Scholar Rock, the full design for the planned Phase 3 trial should be announced by month’s end.