Alnylam Pharmaceuticals this week released preclinical data from its ongoing neurology programs in Huntington’s disease, neuropathic pain, Parkinson’s disease, and dystonia at this year’s Society for Neuroscience annual meeting in Atlanta.
None of the programs are in the company’s official pipeline, which is currently limited to candidates for pandemic influenza and respiratory syncytial virus. However, Alnylam has said it intends to unveil its third formal drug-development program before the end of the year.
Huntington’s disease is a member of the polyglutamine disease family and is caused by the expansion of a CAG repeat in exon 1 of the gene huntingtin. According to Alnylam, the majority of the siRNAs targeting this gene that have been tested in cell culture were able to reduce huntingtin protein levels while cutting mRNA levels by up to 70 percent.
The company, along with partner Medtronic, also conducted in vivo experiments in which fluorescently labeled siRNAs against huntingtin were delivered into rat brains via continuous, 14-day intrastriatal infusion using Durect’s Alzet osmotic pumps. Both unconjugated and cholesterol-conjugated siRNAs were evaluated.
Alnylam said that following administration, the fluorescent label was present in areas around the injection site and into the overlying cortex, and that both neuronal cell bodies and fibers were intensely labeled.
“Outside of the striatum, discrete cellular labeling was also observed in the substantia nigra and thalamus consistent with retrograde transport of siRNA to structures with known projections into the striatum,” the company said in a poster from the Society for Neuroscience meeting. “The distribution of labeled siRNA [to both] local and distant structures was similar for conjugated and unconjugated forms, although the former yielded more discrete labeling of neuronal structures.”
Alnylam said that the biological activity of the siRNAs in knocking down huntingtin after direct infusion into the brain is under investigation, but that these preclinical results suggest that continuous delivery to the striatum is able to move siRNA to brain structures relevant for the treatment of Huntington’s disease, supporting further studies of RNAi-based treatments for the disorder.
In its neuropathic pain program, Alnylam is targeting sodium channel V1.8, a sodium channel subtype that the company said is “expressed selectively in nociceptive sensory neurons, underlies hyperactivity in these neurons in neuropathic pain states, and contributes to the maintenance of neuropathic pain.”
Although this target has proven undruggable by small molecules and proteins, Alnylam has identified it as a candidate for RNAi-based therapeutic intervention. The program is currently unpartnered, but Alnylam collaborator and shareholder Novartis has been interested in the use of siRNAs for neuropathic pain since at least early 2004 as evidenced by a paper from that year in Nucleic Acids Research.
Working with researchers at the University of Arizona, Alnylam has found that an intrathecal injection of an siRNA targeting sodium channel V1.8 led to a greater than 75-percent reduction in pain in a model of chronic inflammatory pain. Knockdown of sodium channel V1.8 mRNA was found to be dose-dependent, and siRNAs were found to be stable in cerebrospinal fluid.
“We anticipate that an siRNA targeting [sodium channel V1.8] would normalize altered physiology of nociceptive sensory neurons in pathological conditions and alleviate neuropathic pain with a much greater therapeutic window than the non-selective [sodium channel V] antagonists presently used in the clinic,” Alnylam said in a meeting poster.
Parkinson’s disease has been linked to certain autosomal dominant mutations in the alpha-synuclein gene, and recently duplications and triplications of the wild-type alpha-synuclein gene have been shown to lead to the condition, according to Alnylam.
The company, along with collaborators at the Mayo Clinic and with the support of a grant from the Michael J. Fox Foundation (see RNAi News, 8/19/2005), have developed several lines of a mouse model in which wild-type human alpha-synuclein is conditionally expressed.
“We anticipate that an siRNA targeting [sodium channel V1.8] would normalize altered physiology of nociceptive sensory neurons in pathological conditions and alleviate neuropathic pain.”
Alnylam said that experiments delivering siRNAs into the brain of mice were able to cut alpha-synuclein levels, and that two complementary delivery methods also resulted in a “significant lowering of alpha-synuclein mRNA levels in vivo, suggesting the applicability of RNAi therapeutics as a possible disease-modifying therapy for Parkinson’s disease.”
Alnylam is also collaborating with Medtronic on its Parkinson’s disease program.
Dystonia is a neurological disorder in which muscles involuntarily contract. Alnylam has so far not publicly mentioned its interest in researching the condition, but said in a poster at the Society for Neuroscience meeting that it is working with researchers from Massachusetts General Hospital to investigate whether siRNAs can be used to silence the mutant form of the dystonia gene torsinA.
The company generated siRNAs targeting wild-type torsinA, which were transfected into cultured cells and yielded between 50- and 75-percent knockdown of both mRNA and torsinA protein levels, according to the poster.
Alnylam said that studies are ongoing to evaluate siRNAs specific for the mutant form of torsinA gene in culture
It is unclear whether Alnylam has a partner for its dystonia program, although the company has a number of undisclosed programs under development through its alliances with Novartis and Medtronic.