caused by superoxide dismutase 1 (SOD1) gene mutations.
The 1-year results, presented at the European Network for the Cure of Amyotrophic Lateral Sclerosis (ENCALS) 2022 meeting, show a deceleration in functional decline that is similar, but “more pronounced” than the previously reported 6-month results, which were not statistically significant, said lead investigator Timothy Miller, MD, PhD, professor of neurology and director of the ALS Center, Washington University, St. Louis.
“What I thought we saw in the first data cut is confirmed by what we saw in the longer data,” he said in an interview. “There were trends [showing] those treated with tofersen did a bit better, but it was hard to be sure. It was hard to be confident in what we were seeing at that early time point.”
Now, with 6 more months of data, Dr. Miller says he is confident that tofersen is slowing down the neurodegenerative disease process. “I see results that I’m encouraged by,” he said. “As a clinician who treats people with ALS with this mutation I would want this drug to be available to people that I see in my clinic.”
One-year VALOR study results
The primary efficacy objective of the VALOR study was to show the 28-week impact of 100 mg tofersen (three doses given about 2 weeks apart, then five doses given every 4 weeks), versus placebo, on function, measured on the Amyotrophic Lateral Sclerosis Functional Rating Scale–Revised (ALSFRS-R). The open-label extension switched placebo-treated patients to tofersen (delayed-start group) and continued to compare them with the early-start group up to 1 year. This open-label extension phase included 49 patients who had been on early-start tofersen and 18 patients in the delayed-start group.
For the primary endpoint, change from baseline in 48-point ALSFRS-R score, there was a statistically significant benefit for the early-start patients with these patients scoring 3.5 points higher than the delayed-start group (P = .0272, 95% confidence interval [CI], 0.4-6.7). This means that both groups declined in function, which is expected in ALS, but the early-start group declined more slowly.
There was also a benefit associated with early-start tofersen for a number of secondary endpoints, including change from baseline in total SOD1 cerebrospinal fluid concentration (CSF SOD1), plasma neurofilament light chain (NfL) levels, and respiratory function.
“This drug targets the MRNA of SOD1, so it lowers the MRNA and then the SOD1 protein falls,” explained Dr. Miller, adding that these levels dropped 21% in the delayed start group, and 33% in the early-start group. “I think the data pretty clearly show that [tofersen] does what it is supposed to do, and that is the first step.”
Neurofilament light chain, a marker of neurodegeneration, also dropped by 41% in the delayed-start group, and 51% in the early-start group.
Respiratory function, as measured by percent predicted slow vital capacity (SVC), also declined 9.2% more slowly in the early- versus delayed-start group (P = .0159).
Finally, muscle strength, as measured by handheld dynamometry (HHD) score, declined more slowly in the early-start group compared with the late-start group, with an adjusted mean difference in score of 2.8 (P = 0.0186).
Dr. Miller said that the data show that it takes time for tofersen to impact clinical function, but there are signs of benefit before that. “I think what you see is that just starting on the drug, the first thing that happens is SOD1 goes down, the next thing is that neurofilament decreases, but clinical function is not yet changing. It takes time. What I see in these data is that it takes time for us to see that effect on clinical function.”