new research suggests.
The phase 2 KINETIC trial involved patients with essential tremor. Among patients treated with SAGE-324 for 28 days, there was a statistically significant reduction in upper-limb tremors on day 29 – meeting the primary endpoint of the study.
However, moderate to severe treatment-emergent adverse events (TEAEs) led to many treatment and/or study discontinuations, the investigators reported.
The findings were presented at the International Congress of Parkinson’s Disease and Movement Disorders.
Mechanism of action
Essential tremor affects an estimated 6.4 million adults in the United States. Available drugs are not helpful for 30%-50% of these patients. No new drug for this condition has been approved by the Food and Drug Administration for the past 50 years. Of the several drugs used to treat essential tremor, propranolol is the only one that has been approved, according to the American Academy of Neurology.
Deficits in inhibitory signaling via the gamma-aminobutyric acid system may have a role in the pathophysiology of essential tremor because the GABAergic system is the major neuroinhibitory system in the brain.
SAGE-324 is a steroid-positive allosteric modulator of the GABAA receptor. It acts on the receptor distant from the neuronal synapse to enhance GABAergic (inhibitory) signaling.
In the phase 2 multicenter KINETIC trial, investigators enrolled 69 patients aged 18-80 years. The patients had moderate to severe essential tremor, as determined on the basis of their having a score of 10 or higher on item 4 of the Essential Tremor Rating Assessment Scale (TETRAS) on screening day and at baseline/day 1 of the trial.
Participants did not take medications for essential tremor during the 28-day washout period. They were randomly assigned in a 1:1 ratio to receive SAGE-324 60 mg (n = 34) or placebo (n = 35) once daily. Dose reductions were allowed.
The groups were reasonably matched for age (mean, 69.4 years for SAGE-324 vs. 64.7 years for placebo) and dominant hand (right, 85.3% for SAGE-324 vs. 88.6% for placebo). Women composed 35.3% of the drug group and 57.1% of the placebo group.
The primary endpoint of the trial was change from baseline for the active drug in comparison with placebo on day 29 (1 day after the final dose) for upper-limb tremor, as measured by item 4 of TETRAS. There was also a 2-week follow-up with assessments on day 42.
Primary endpoint met, high dropout rate
Baseline mean TETRAS Performance Subscale item 4 scores were 12.82 for the SAGE-324 group and 12.28 for the placebo group.
On day 29, the least squares mean difference from baseline was –2.31 with SAGE-324 (n = 21) versus –1.24 with placebo (n = 33; P = .049). There was no difference between the SAGE-324 and placebo groups on day 42.
“Their significant reduction in upper-limb tremor score at day 29 corresponds to a 36% reduction from baseline in tremor amplitude in patients receiving SAGE-324, compared with a 21% reduction in tremor amplitude in patients receiving a placebo,” said lead investigator Kemi Bankole, MBBCh, of Sage Therapeutics.
“A reduction in tremor amplitude of 36% is a clinically significant improvement for most patients with essential tremor. For patients with moderate-severe tremor, a 41% improvement would be clinically noticeable and appreciated,” said Helen Colquhoun, MBChB, vice president at Sage.
“We believe patients with more severe tremor, that is, a TETRAS score of greater than 12, represent the majority of [essential tremor] patients getting diagnosed and seeking treatment today,” Dr. Colquhoun said.
There was an even greater reduction in tremor amplitude for the subgroup of patients with more severe tremor at baseline, meaning those with a median TETRAS score of 12 or greater (–2.75 for SAGE-324 vs. –1.05 for placebo; P = .0066).
These figures represented a 41% reduction from baseline in tremor amplitude for the SAGE-324 group, versus an 18% reduction in the placebo group. Again, the effect had disappeared in comparison with placebo at the 2-week off-drug follow-up on day 42.
Tolerability of SAGE-324 was a major problem, leading to dose reductions, treatment discontinuations, and study discontinuations. Of the 34 patients who received SAGE-324, 13 dropped out of the study, compared with 2 of 35 patients who received placebo.
Most TEAEs were moderate or severe in the SAGE-324 group, whereas most were mild in the placebo group.
The most common TEAEs for participants who received SAGE-324 were somnolence (67.6%) and dizziness (38.2%), followed by balance problems, diplopia, dysarthria, and gait disturbance. In the placebo group, somnolence affected 5.7%, and dizziness affected 11.4%. There were no deaths in either group.
Dr. Colquhoun said these findings “are in line with our expectations for the 60-mg dose.”
More than one-third of the SAGE-324 group discontinued treatment before the end of the trial, and continuing treatment often required dose reductions. Only 24% completed the trial while taking the 60-mg dose; 15% completed the trial while taking 45 mg; and 24% did so while taking 30 mg.
Dr. Colquhoun noted that the company plans to initiate a phase 2b dose-ranging study later this year to optimize the dosing regimen with regard to tolerability and sustained tremor control.