Associate Director New Modalities, BioPharmaceuticals R&D, AstraZeneca
Senior Director Chemistry, BioPharmaceuticals R&D, AstraZeneca
Executive Research Fellow, Ionis Pharmaceuticals Inc.
Recent advances in genomics have led to a myriad of new targets and with them, the opportunity to drug them using nucleotide-based therapeutics, such as oligonucleotides. Oligonucleotides modify the protein levels associated by disease-driving mechanisms. Both single-stranded antisense oligonucleotides (ASOs) and double-stranded small interfering RNA (siRNA) are designed to bind with high specificity to a specific RNA sequence, including pre-mRNA and mRNA and, among other mechanisms, can breakdown the mRNA to reduce associated protein levels.
The uptake of oligonucleotides in the cells is limited and remains a barrier for broadening the scope of this therapeutic modality.1 Phosphorothioated ASOs predominantly distribute to the liver and to a lesser extent in the kidney. Much lower concentrations are observed in other organs. The double stranded siRNA has no significant uptake into any cell type without the assistance from a delivery vehicle or conjugation to a targeting ligand that steers the distribution to the relevant cell type and ensures internalisation into the cell.
We have a specific interest in identifying targeting ligands that can act as tags for specific cell types and facilitate the oligonucleotide uptake by an active mechanism.
The state of the art targeting ligand is the N-acetylgalactosamine (GalNAc), which targets the asialoglycoprotein receptor which is highly expressed on hepatocytes in the liver. GalNac conjugation to ASOs or siRNAs results in strong targeting and subsequent downregulation or deactivation (known as know down) of specific mRNA in the liver. At AstraZeneca, we are using this technology as part of our research into advanced ligand conjugated ASOs to ‘silence’ PNPLA3 with the aim of restoring fat break down in the liver.
To realise the full potential of oligonucleotide therapeutics, we aim to find targeting ligands to other cell types by utilising specific cell-surface receptors that facilitate up-take by the targeted cells.
Pancreatic beta cells represent a cell population with high potential for therapeutic intervention using oligonucleotides due to their role in diabetes. Previously, we published breakthrough research in Science Advances that demonstrated genes in insulin-secreting pancreatic beta cells could be ‘silenced’ using targeted delivery of ASOs in in vivo models.2 This research demonstrated for the first time how uptake of ASOs into pancreatic beta cells can be enabled by tagging them to a peptide (peptide conjugation) recognised and internalised by the glucagon-like peptide 1 receptor (GLP1R) which is highly expressed on pancreatic beta cells.2
In our latest publication in the Journal of the American Chemical Society we share our detailed understanding for the targeted delivery of ASOs to pancreatic beta cells and expanded on the medicinal chemistry optimisation we have undertaken. The construct is made up of three parts: the peptide which is targeting the GLP1R in the beta cells, the linker and the ASO. We demonstrated in this research that the linker design and spacer between the oligonucleotide and peptide is critical to optimise to ensure optimal targeted delivery of the conjugate especially in an in vivo context.2 This work highlights the importance to combine a good balance of stability during the biodistribution phase and efficient intracellular processing to efficiently release the metabolites responsible for effective knock down. In addition, despite GLP1 peptide agonists being well researched and understood, we demonstrate that punctual modification of the N terminal of different agonist sequences can lead to dramatic differences in in vivo efficacy.3
Reprinted with permission from J Am Chem Soc. 2021; 143(9):3416-3429. Copyright 2021 American Chemical Society.
We hope to soon be able to share how these promising early studies translate to animal models and the validation in human beta cells. The medicinal chemistry strategies used to refine the ligand and linker properties and efficiency will inform us in our effort of applying targeted delivery towards other cell types and receptors and open the door for future oligonucleotide-based therapeutics in patients within cardiovascular, renal and metabolism diseases.
The study was conducted as part of AstraZeneca’s collaboration with Ionis Pharmaceuticals to discover and develop novel antisense therapies for cardiovascular, renal and metabolic diseases.
1. Valeur E, et al. (2017). Targeted delivery for regenerative medicines: an untapped opportunity for drug conjugates. Drug Discov Today 22(6):841-847.
2. Ämmälä C, et al. (2018). Targeted delivery of antisense oligonucleotides to pancreatic beta-cells. Sci Adv 4(10): eaat3386
3. Knerr L; et al. (2021). Glucagon Like Peptide 1 Receptor Agonists for Targeted Delivery of Antisense Oligonucleotides to Pancreatic Beta Cell. J. Am. Chem. Soc. 2021, https://doi.org/10.1021/jacs.0c12043