LOS ANGELES – Results from the first-in-human trial of the investigational antisense oligonucleotide therapy IONIS-HTTRx showed strong dose-dependent reductions in the toxic huntingtin protein in Huntington’s disease patients’ cerebrospinal fluid when compared with placebo.

An exploratory analysis also showed signals of clinical improvement among patients receiving the therapy, the study’s lead author, Sarah Tabrizi, MD, PhD, of University College London, reported at the annual meeting of the American Academy of Neurology.

The findings represent a potential breakthrough in the way Huntington’s – and possibly other neurodegenerative diseases – are treated, said Dr. Tabrizi of University College London. The intrathecally-delivered drug binds to mutant huntingtin protein mRNA to reduce the level of the toxic protein being made.

In the phase 1/2a trial, Dr. Tabrizi and her colleagues enrolled 46 patients with early-stage Huntington’s disease and randomized them to four doses of IONIS-HTTRx or placebo. Patients received four monthly injections of the study drug into the cerebrospinal fluid followed by a 4-month untreated follow-up period. IONIS-HTTRx was delivered in five ascending-dose cohorts.

IONIS-HTTRx was safe and well tolerated and all patients completed the study, Dr. Tabrizi reported. “Our results show that we had significant lowering of the toxic mutant huntingtin protein in the spinal fluid of the patients,” she said, noting that patients receiving the highest doses saw 40%-60% lowering of the protein, which preclinical work suggests correlates to reductions of the protein in the brain.

Dr. Tabrizi stressed that the main outcome measures in the study were reduction of the mutant protein in the CSF and safety and tolerance of the study drug. The investigators did not expect to see clinical measures to change in such a short, small study, she said.

“But then when we looked more carefully at the data with exploratory analysis we found a link between lowering of CSF mutant huntingtin and improvement in total motor score, which is a measure of neurological function, and also, improvement in the Symbol Digit Modalities Test.”

The clinical results are exploratory and require confirmation in larger studies, Dr. Tabrizi stressed.

The study was supported by Ionis Pharmaceuticals. Roche will develop the drug in further clinical trials.

SOURCE: Tabrizi S et al. AAN 2018 abstract CT.002.

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