SLS-004 Lowered Alpha-synuclein Levels in Mice
SLS-004, Seelos Therapeutics’ experimental epigenetic editing therapy for Parkinson’s disease, effectively reduced the production of alpha-synuclein — the protein that accumulates in toxic clumps in Parkinson’s — in the brains of healthy mice.
Epigenetic modifications refer to the addition of chemical marks to DNA by a group of specialized enzymes that influence genes’ activities without altering their underlying DNA sequence.
In contrast to gene-editing therapies, which add, remove, or change specific DNA sections, epigenetic editing allows medium- to long-term regulation of a gene’s activity, and thereby the production of its resulting protein. That leaves the underlying genetic sequence intact.
Overproduction of alpha-synuclein “has been implicated as a highly significant risk factor for Parkinson’s and the accumulation of this protein is a [disease-related] hallmark” of Parkinson’s and other synucleinopathies, Mehra said. Synucleinopathies are conditions associated with toxic alpha-synuclein clumps.
Ornit Chiba-Falek, PhD, the co-inventor of SLS-004 at Duke University School of Medicine, said that “this pilot experiment in mice showed promising results with an effect on SNCA [alpha-synuclein] reduction within the presumed target therapeutic window.”
“We are continuing the preclinical studies to further the development of epigenome-editing targeting SNCA towards precision medicine for Parkinson’s disease,” Chiba-Falek added.
“We plan to further validate the safety and efficacy of our lentivirus-based epigenome-editing approach in a full-range preclinical study under our Sponsored Research Agreement with Seelos, with the aim of reversing the Parkinson’s disease-related [mechanisms],” said Boris Kantor, PhD, also a co-inventor of SLS-004 at Duke.
Under this agreement, Seelos, which acquired SLS-004’s rights in 2019, is sponsoring proof-of-concept preclinical studies at Duke to investigate whether the therapy can safely and effectively prevent and/or delay disease progression in a mouse model of Parkinson’s.
Other preclinical models are expected to be used in the future to further validate the therapy’s potential.
Nerve cell loss in Parkinson’s disease is triggered mainly by the toxic buildup of clumps of alpha-synuclein, a protein abundant in the brain and thought to help regulate nerve cell function and communication.
Patients with impaired regulation of the SNCA gene show as high as 200% levels of alpha-synuclein protein, and a reduction of 25–50% in SNCA messenger RNA (mRNA) and alpha-synuclein protein levels is expected to be sufficient to restore normal levels of the protein, Seelos stated.
mRNA is the intermediate molecule derived from DNA that guides protein production.
SLS-004 uses a modified, harmless virus, known as a lentivirus, to deliver CRISPR-dCas9 epigenetic-editing components and the DNA methyltransferase 3A (DNMT3A) enzyme to cells.
The original CRISPR-Cas9 system, discovered in bacteria as a defense mechanism, allows researchers to add, remove, or change specific sections of a DNA sequence. CRISPR-dCas9 is a modified version of the original system that, instead of modifying a particular genetic sequence, can regulate gene activity by guiding epigenetic modifications to that sequence.
Guided by the CRISPR-dCas9 elements, DNMT3A “turns off” the SCNA gene, which provides instructions to produce the alpha-synuclein protein, by adding an epigenetic marker (called methyl group) to a specific region of the gene.
By specifically turning off SCNA’s activity, SLS-004 is expected to reduce alpha-synuclein production, thereby limiting or preventing the formation of toxic clumps inside nerve cells. These clumps, also called Lewy bodies, damage and eventually kill the cells.
Earlier preclinical studies showed that SLS-004 effectively suppressed SCNA’s activity and lowered alpha-synuclein levels in dopamine-producing neurons derived from a Parkinson’s patient. The therapy also improved neuronal survival and reduced disease-related changes. Dopamine-producing neurons are the cells progressively lost in Parkinson’s.
In the current study, Duke researchers treated healthy adult mice with either SLS-004 or a similar lentivirus and CRISPR-dCas9-based approach that uses a potent gene activity repressor, KRAB-MeCp2, instead of DNMT3A.
Both treatments, as well as empty, harmless lentiviruses (control condition), were injected directly into the substantia nigra on the left brain hemisphere of the animals, using the right hemisphere as an internal control for each mouse. Susbtantia nigra, a brain region filled with dopamine-producing neurons and involved in motor control, is the key region affected by Parkinson’s neurodegeneration.
Results showed that SLS-004 treatment led to a mean 10% reduction in the levels of SNCA mRNA and a 20% drop in alpha-synuclein levels in the left substantia nigra, relative to the untreated side.
Greater effects were observed with the KRAB-MeCp2 approach (a repressor that is attached to the CRISPR-dCas9 elements), as it resulted in a mean 27% drop in SNCA mRNA levels and a reduction of 40% in alpha-synuclein. This was consistent with previous results in human cells, where the use of DNMT3A led to a 35% reduction in SNCA mRNA, compared with a 55% drop with KRAB-MeCp2.
The control condition showed no major differences in SNCA mRNA and protein levels between the injected and the non-injected substantia nigra.
The animal showed no abnormalities within 10 days since the single injection. The researchers currently are performing a complete analysis of all non-injected (control) brain structures, as well as repeating the experiment in more mice, while confirming the specificity of the site injection.
Seelos also is testing SLS-007, another Parkinson’s therapy candidate that aims to lessen alpha-synuclein aggregation.