Experimental Therapy Shows Promise in Early-Stage Huntington’s Disease

LOS ANGELES—IONIS-HTTRx, an antisense oligonucleotide (ASO), effectively reduced levels of the protein responsible for Huntington’s disease in early-stage patients, according to findings presented at the American Academy of Neurology’s 70th Annual Meeting.

“ASO technology has the potential to provide disease-modifying benefits to patients with neurodegenerative diseases,” said lead author Sarah Tabrizi, BSc, MBChB, PhD, Professor of Clinical Neurology at the University College London Institute of Neurology, and colleagues. “In this phase I/IIa trial in patients with early-stage Huntington’s disease, IONIS-HTTRx delivered via intrathecal injection was well tolerated with no study-drug-related adverse safety signals during the treatment or follow-up periods.” In addition, significant dose-dependent reductions in CSF mutant huntingtin protein (mHTT) were observed, suggesting that IONIS-HTTRx is a promising therapeutic for the treatment of Huntington’s disease.

Sarah Tabrizi, BSc, MBChB, PhD

Huntington’s disease is caused by CAG repeat expansion in the HTT gene resulting in polyglutamine expansion in the mHTT with a toxic gain-of-function disease mechanism. A comprehensive drug discovery effort, including extensive preclinical testing, was undertaken to design a well-tolerated ASO with high specificity to human HTT mRNA that could potently suppresses mHTT production.

In the present study—a first-in-human, multicenter, double-blind clinical trial—46 patients were randomized (3:1) to receive four doses of IONIS-HTTRx or placebo by monthly bolus intrathecal injection, followed by a four-month untreated period. Five ascending-dose cohorts were enrolled with independent Data Safety Monitoring Board review of safety, pharmacokinetics, and target engagement prior to dose escalation.

Dr. Tabrizi reported that IONIS-HTTRx was well tolerated at all doses tested. Adverse events were mostly mild and unrelated to the study drug. There were no adverse trends in laboratory parameters. No patients prematurely discontinued the treatment. ASO was measurable in CSF and plasma, and concentrations were generally aligned with predictions from a linked pharmacokinetic/pharmacodynamic preclinical model. Significant, dose-dependent reductions in CSF mHTT were observed. At the highest dose of the ASO, 40% to 60% reductions in CSF mHTT were observed. “When we looked more carefully at the data with exploratory analyses, we found a link between lowering of CSF mHTT and improvement in total motor scores and neurologic function,” Dr. Tabrizi said.