Scholar Rock’s Phase 3 SMA Trial Achieves Success

Scholar Rock Inc has announced that the phase 3 trial of Apitegromab for spinal muscular atrophy treatment has come through with its primary result. Despite this, the higher dosage did not achieve the desired therapeutic effect and the company omitted an important secondary endpoint. However it has still motivated investors as the proposed therapy is different from other SMA drugs which are working on the neurological aspect of the disease, but it’s all about muscular strength.

The phase 3 study recruited 156 nonambulatory SMA patients aged between 2 and 12 years to receive either a placebo or one of two doses of apitegromab. When the data from both the doses were combined the pooled analysis indicated an improvement of motor function of 1.8 points, this was significantly different from the placebo after 52 weeks, p=0.0192. This news triggered a massive increase in its stock price to north of $23 in premarket trading.
In Scholar Rock’s statistical analysis the plan was to compare the pooled data and the 20-mg/kg dose separately to placebo. To make the trial a complete success, both p-values had to be reduced to low values for them to be clinically significant. Where the pooled analysis was successful the higher 20-mg/kg dose did not quite hit the intended mark with an improvement in motor function of only 1.4 points and a statistical significance p-value of 0.1149. However, the smaller 10 mg/kg dose saw a greater improvement by 2.2 points in the motor function which made it easier for the pooled analysis to meet this success criteria.
It is important to note that while Scholar Rock failed to reach the two-point improvement on the trial to detect, according to the trial 30.4% of the patients in the treatment group achieved a three-point or better in comparison to 12.5% of the placebo group. During Scholar Rock’s CFO Edward Myles interview, he pointed out that the upper limb function is also used as the second output even for patients who are unable to walk. However, the company has not been particularly clear on whether or not this goal was achieved in the top-line numbers.

Scholar Rock will now have to persuade the payers to reimburse for apitegromab, which will presumably be administered together with other pricey SMA treatments. Further, the market competitor is likely to be brought about by other muscle-directed treatments on offer by other firms. For example, Biohaven still anticipates reporting topline phase 3 data this year; as for Roche, it has a treatment under development through a phase 2/3 trial. Scholar Rock remains buoyant about its approach here, it is all about being able to hit the latent form of myostatin but competitors are bringing other differentiating factors to their own candidates.

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