The U.S. Food and Drug Administration (FDA) runs a number of programs designed to facilitate research and drug development for serious conditions. One such program is the Fast Track program; its Fast Track designation seeks to expedite drug development and review to help patients receive treatments quicker. According to a recent news release, biopharmaceutical company Scholar Rock shared that its investigational treatment, apitegromab, recently received Fast Track designation. Currently, Scholar Rock is exploring apitegromab as a potential treatment for spinal muscular atrophy (SMA).

Apitegromab

According to Scholar Rock, apitegromab is:

a selective inhibitor of the activation of latent myostatin. Rather than the traditional approach of blocking already-activated, mature myostatin or the receptor, apitegromab selectively targets the precursor, or inactive, form of myostatin to block its activation in the muscle.

Normally, myostatin is expressed within skeletal muscle cells. Prior studies have shown that blocking myostatin improves muscle strength and muscle mass. Thus, by inhibiting myostatin using apitegromab, researchers hope that patients with SMA could improve muscle strength and motor function.

Beyond Fast Track status, apitegromab also received Orphan Drug and Rare Pediatric Disease designations within the United States, as well as PRIME and Orphan Drug designations within Europe.

Scholar Rock believes the designation hinged upon data from the Phase 2 TOPAZ clinical trial. As the company expresses:

The TOPAZ Phase 2 proof-of-concept trial investigated apitegromab in patients with Type 2 and Type 3 SMA over a 12-month treatment period. Positive 12-month top-line results were announced in April 2021 and support further development of apitegromab as a potential muscle-directed therapy intended to be used in conjunction with available SMN upregulator therapies to help improve motor function for individuals with SMA.

Learn more about the TOPAZ trial.

Spinal Muscular Atrophy (SMA)

SMN1 gene mutations cause spinal muscular atrophy (SMA), a rare genetic and neuromuscular disorder. Ultimately, these gene mutations cause motor neuron loss in the brainstem and spinal cord. As these nerve cells die, they cause muscle weakness and wasting. Typically, muscle weakness more highly affects proximal muscles, or muscles near the center of the body. An estimated 1 in every 10,000 people has SMA.

SMA Subtypes

• Type 0. This is often considered the most severe form of SMA. Patients with type 0 SMA are diagnosed in the womb, as symptoms become apparent before birth. Within the womb, infants do not move much. Symptoms include joint deformities, low muscle tone, respiratory distress/failure, and congenital heart defects. Sadly, type 0 is fatal and patients often do not survive infancy.
• Werdnig-Hoffman disease (type I). Type I SMA is typically considered the most common form. It is diagnosed at or soon after birth, and has severe symptoms. Patients are often unable to independently sit or support their head. Other symptoms include a bell-shaped chest, difficulty feeding or breathing, poor growth, and difficulty swallowing. Unfortunately, patients with type I SMA often do not survive past early childhood.
• Type II SMA. For patients with type II, the condition is often diagnosed between ages 6-12 months. In this form, patients are usually unable to stand or walk independently. However, they can sit without support. Throughout their lives, muscle weakness progressively worsens. Additional symptoms include scoliosis (abnormal spinal curvature), respiratory muscle weakness, and tremors. While overall lifespan varies, many patients survive through their 20s-30s.
• Kugelberg-Welander syndrome (type III). In this form, muscle weakness develops in early childhood or adolescence. While walking or climbing stairs becomes progressively more difficult, patients are able to walk, sit, and stand without assistance. As the condition progresses, patients often require mobility aids. However, in this form, patients have a normal lifespan.
• Type IV SMA. The final form of SMA, type IV, begins in adulthood. Typically, this means past 30 years old. This rare form also results in a normal lifespan. Symptoms include mild muscle weakness, tremors or muscle twitches, and some breathing problems. For those with this form, muscle weakness usually affects the upper arms or legs.