Our GalXCTM Technology Platform: Enhancing the Utility of DsiRNA-EX Molecules
Delivering DsiRNAs to the Liver.
GalXCTM is a proprietary technology platform that advances the development of next-generation RNAi-based therapies designed to silence disease-driving genes in the liver. Compounds produced via GalXC are intended to be broadly applicable across multiple therapeutic areas, including rare diseases, chronic liver diseases, cardiovascular diseases and viral infectious diseases
Our GalXC molecules are structured to be processed by the enzyme Dicer, the initiation point for RNAi in the human cell cytoplasm. Unlike earlier generation RNAi molecules, which mimic the output product of Dicer processing, all our DsiRNAs, including GalXC molecules, enter the RNAi pathway prior to Dicer processing. This can result in preferential use of the correct strand of a double-stranded RNA molecule, and therefore increase the efficacy of the RNAi mechanism. We have found in animal tests that this benefit both increases the potency of our GalXC molecules relative to other RNAi-inducing molecules and enables more sequences to be used compared to other RNAi-inducing molecules. In addition, all our DsiRNAs, including GalXC molecules, have an extended structure relative to conventional RNAi inducing molecules. This extended region presents multiple sites for chemical modification and conjugation compared to earlier RNAi technologies. At these sites, we can use modifications that enhance the drug-like properties on our molecules. Specifically, we can employ modifications that enhance the pharmacokinetic profile and/or suppress immunostimulatory activity.
Our GalXC RNAi platform is designed to enable convenient subcutaneous delivery for our emerging pipeline of liver-targeted RNAi investigational therapies. The GalXC RNAi platform does not involve lipid nanoparticles (LNPs) or other formulation components that facilitate drug delivery, which simplifies the platform and eliminates any requirement for functional excipients. Instead, our GalXC molecules are stabilized by chemical modifications and utilize a four base sequence known as a tetraloop, where each base is conjugated to a simple sugar, N-acetylgalactosamine (GalNAc), that is specifically recognized by a receptor on the surface of hepatocyte liver cells. With the GalXC RNAi platform, we believe that a full human dose may be administered via a single subcutaneous injection. After injection, the GalXC molecules enter the bloodstream and are exposed to the liver hepatocytes expressing the GalNAc receptor. After binding to the receptor, the GalXC molecules are internalized by the hepatocyte, ultimately enabling the GalXC molecules to access the RNAi machinery inside the hepatocyte. To date, we have demonstrated in vivo gene silencing activity with GalXC molecules after subcutaneous administration against nearly three dozen disease-associated genes in the liver.
GalXC enables subcutaneous delivery of Dicerna’s RNAi therapies to hepatocytes in the liver and may offer several distinct benefits, as shown in animal models. These potential benefits include:
- potency that is on par with or better than comparable platforms
- exquisite specificity to gene targets
- long duration of action versus other modalities
- simple, infrequent dosing regimen
For delivery to the liver, we attach N-acetylgalactosamine (GalNAc) sugars to one or more points on GalXC compounds, yielding multiple effective and proprietary conjugate delivery configurations. These molecules specifically bind to highly expressed asialoglycoprotein (ASGPR) receptors on the target cells, leading to internalization and access to the RNAi machinery within the cells. GalXC allows us to screen and optimize therapeutic leads with greater efficiency, and to apply them to a wide variety of gene targets associated with liver-related diseases.
GalNAc has been used as a liver-targeting delivery vehicle since the early 1990s. We invented the DsiRNA-EX molecular structures and started developing the GalXC structures in 2008. With GalXC, our proprietary implementation of the GalNAc technology, the GalNAc sugar molecules are chemically conjugated to specific bases on the DsiRNA-EX RNA duplexes in a configuration that is unique to Dicerna. GalXC compounds have been our core focus since 2013.
Many of our conjugates produced via GalXC technology incorporate a folded motif known as a tetraloop in the extended region. The tetraloop configuration, which is unique to Dicerna’s GalXC compounds, interfaces effectively with the RNAi machinery. The GalXC platform allows flexible and efficient conjugation to the targeting ligands, and stabilizes the RNAi duplex to enable effective delivery of our GalXC RNAi-inducing molecules directly to the liver.
Dicerna’s Proprietary GalXC Configuration Interfaces Effectively with the RNAi Machinery
Our unique, proprietary tetraloops incorporate specific design principles (e.g., sequence and chemistry features) accumulated from our research data, relevant literature and 3D modeling to maximize their efficiency and optimization. Our data suggest that in the tetraloop format, the Dicer protein presents the RISC machinery with a pre-formed Guide Strand:
GalXC Technology Platform: Potential Therapeutic Applications
As Dicerna reported during its 2016 Investor Day presentation, subcutaneously delivered GalXC compounds silenced 12 different disease targets in animal models, highlighting the long duration of action, infrequent dosing and tolerability of GalXC-based compounds. Use of the GalXC platform yielded gene silencing of greater than 90% for multiple genes in non-human primates (NHPs) after a single dose. In an NHP model of an undisclosed rare disease gene target, a single 3 mg/kg dose achieved a maximum gene silencing of 94%, with an average gene silencing of approximately 88%. Another single 3 mg/kg dose NHP study resulted in an average of 97% silencing of an undisclosed rare disease gene target.
Future Directions for the GalXC Technology Platform
Our GalXC compounds incorporate our unique, proprietary tetraloop technology and are broadly applicable across multiple therapeutic areas, including rare diseases, chronic liver diseases, cardiovascular disease, and viral infectious diseases. These compounds may be used to develop additional therapeutic agents targeting other cell types in the future.
Optimization of our GalXC Molecules
For therapeutic use in humans, our GalXC molecules are optimized both with respect to base sequence and chemical modifications to increase stability and mask them from mechanisms that recognize foreign RNAs, inducing immune system stimulation. Our optimization process begins with an analysis of the target gene sequence using our proprietary GalXC prediction algorithm, which we have developed based on the results of testing thousands of sequences for RNAi activity. We select the sequences with the highest predicted RNAi activity and apply patterns of chemical modification, including a GalNAc-linked tetraloop stem-loop structure, which design-in enhanced stability and hepatocyte delivery specificity and engineers-out immunostimulatory activity. Our GalXC molecules routinely achieve high potencies, with EC50 values in the liver (the amount of material required to silence a target gene by 50 percent) typically in the 0.1 to 1.0 milligram per kilogram bodyweight (mg/kg) range in in vivo studies in mice. We have routinely generated GalXC molecules of this potency within 30 days of doing the initial algorithmic gene sequence analysis, which allows us to explore a large number of potential target genes when selecting our programs.