Neuron-specific modulation of gene expression using systemically administered bispecific antibody-ASO conjugates

The ability to selectively modulate the expression of one or more neuronal genes is critical for defining pathways that govern normal brain physiology and diverse disease phenotypes. Anti-sense oligonucleotides (ASOs) are attractive agents for manipulating neuronal gene expression, especially given their clear advantages relative to

gene therapy, including that ASO therapy is reversible, nonimmunogenic, and independent of gene size. However, progress has been limited by the need for invasive routes of administration [e.g., intracerebroventricular (ICV) injection], limited cellular uptake, and lack of cell-type specificity. A technology

capable of delivering ASOs across the blood-brain barrier (BBB) and specifically into neurons following intravenous (IV) administration – resulting in modulation of neuronal gene expression – would be incredibly useful. Therefore, we have developed a bispecific antibody (bAb) shuttle that targets CD98hc, the heavy chain

of the large neutral amino acid transporter (LAT1), and mediates delivery of IgGs across the BBB. We observe superior brain retention of IgGs shuttled via CD98hc, as compared to shuttling via transferrin receptor (TfR-1). Moreover, we do not observe cellular uptake of CD98hc bAbs in the brain parenchyma unless targeted to specific

cell types, which is unique relative to TfR-1 bAbs. We have also developed a first-generation CD98hc bAb that targets glycoprotein M6A, which is selectively internalized into neurons in the mouse brain. Finally, we have optimized the conjugation of azide-functionalized ASOs to our bAbs. Therefore, the first objective is to test the

efficacy of our first-generation, neuron-specific bAb – when conjugated to a Scn1a ASO that increases the expression of NaV1.1 – for increasing the threshold of temperature-sensitive seizures and restoring intrinsic excitability of parvalbumin-expressing inhibitory neurons in a mouse model of Dravet syndrome (Scn1a+/-). The

second objective is a method development study aimed at developing second-generation bAbs that target different cell-surface proteins enriched on neurons and evaluating their specificity for reducing Malat1 gene expression as bAb-ASOs using single-cell RNA-seq and single-molecule fluorescent in situ hybridization.

Therefore, in Aim 1, we propose to evaluate the efficacy of first-generation bAb-ASOs for increasing neuronal expression of NaV1.1 and improving associated phenotypes in Scn1a+/- mice. We will generate M6A/CD98hc bAbs conjugated to our validated NaV1.1 ASO and evaluate their impact on temperature-sensitive seizures and

intrinsic excitability of parvalbumin-expressing inhibitory neurons in Scn1a+/- mice. Next, in independent Aim 2, we will evaluate gene silencing of second-generation bAb-ASOs that target different cell-surface proteins enriched on neurons (e.g., synaptophysin, GRIA1, CHRM3). We propose to use a validated ASO against a non-

coding gene (Malat1) given that this gene is expressed in all brain cell types and its knockout does not produce a phenotype. A key expected outcome is the characterization of bAb-ASOs that selectively modulate gene expression in neuronal cells after IV administration, which has a staggering number of potential applications.