Scholar Rock will soon start enrolling participants for a phase 3 clinical trial of apitegromab, a new muscle therapy. For the trial — dubbed SAPPHIRE — apitegromab will be tested alongside other medications for people with type 2 and type 3 SMA who are nonambulatory (unable to walk).
During the study, apitegromab will be tested in tandem with two existing SMA treatments: Spinraza (nusinersen) and Evrysdi (risdiplam). This usage of an additional treatment may be referred to as add-on, adjuvant, or augmentation therapy. The trial will test whether apitegromab is safe for people with SMA to take and whether the drug is effective at improving motor skills.
Currently, the trial is estimated to begin in February 2022 and last for 12 months. Participants will then have a 20-week follow-up period or have the option to enroll into an extension study.
Apitegromab works differently than other SMA drugs. Current treatment options like nusinersen and risdiplam work by helping nerve cells make more survival motor neuron (SMN) protein, which helps protect the nerves from dying. Apitegromab, on the other hand, targets muscle cells. It blocks a protein called myostatin that prevents muscles from growing.
In theory, a treatment plan that includes both apitegromab and other SMA treatments may help protect both nerve cells and muscle cells, leading to better motor function in people with SMA. However, additional clinical trials are needed to test the safety and effectiveness of this treatment plan.
In an initial study, researchers gave apitegromab to 58 people with type 2 or type 3 SMA. The study participants received apitegromab intravenously (through an IV) once every four weeks.
The researchers found that apitegromab was safe and effective. More than half of the study participants had improvements in physical function, and the researchers didn’t find any major side effects that seemed to be associated with the drug.
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Scholar Rock has laid out details about the new apitegromab clinical trial. The company expects to enroll about 156 people between the ages of 2 and 12 with type 2 or 3 SMA.
During the 12-month trial, each participant will receive standard SMA treatments in addition to one of the following options:
As participants receive treatment, researchers will collect information about motor function, developmental milestones, and side effects.
Scholar Rock will also conduct a smaller study with 48 people with type 2 or 3 SMA who are between the ages of 13 and 21. These participants will either receive a high dose of apitegromab or placebo.