Breaking Through Synthesis Challenges: Hongene Accelerates Clinical Translation of Dual-Targeting Oligonucleotide Drugs!

In recent years, dual-targeting oligonucleotide drugs have become one of the hottest fields in the global pharmaceutical industry due to their advantages of synergistic effects and avoiding combination therapy. Despite their promising future, the synthesis and production of these drugs face multiple technical bottlenecks, which have become key obstacles hindering pipeline advancement.

Currently, numerous pharmaceutical companies worldwide are intensively laying out their strategies in the field of dual-targeting oligonucleotide drugs, pushing drug development towards clinical application. Particularly, dual-targeting siRNA (small interfering RNA) drugs, leveraging their breakthrough advantage of "simultaneously silencing multiple key disease-causing genes," have become a crucial solution to overcome the limitations of single-target interventions. This trend is fully evidenced by recent industry developments:

On September 2, Corsera Health, founded by RNAi pioneer John Maraganore, announced that its dual-targeting siRNA drug is planned to enter clinical trials by the end of 2025. This drug simultaneously targets PCSK9 and AGT for the treatment of hyperlipidemia.

Following closely, on September 17, Mabwell Biotech successfully out-licensed a preclinical dual-targeting siRNA pipeline through a "NewCo model", securing a potential total deal value of up to $1 billion with Kalexo.

Around the same time at the 18th International IgA Nephropathy Symposium, Frontier Biotech unveiled preclinical data for a potentially first-in-class dual-targeting siRNA drug. This drug demonstrated inhibition rates as high as ~95% against both targets and promises a groundbreaking dosing interval of once every 4-6 months.

Most recently, on October 21, Siran Biotech's self-developed dual-targeting siRNA drug SA1211 officially received NMPA approval for clinical trials, becoming the first dual-targeting siRNA pipeline for chronic HBV (hepatitis B) treatment globally to enter the clinical stage.

The excitement reflected in the above cases stems from the advantages conferred by the unique design of dual-targeting siRNA. Traditional siRNA consists of complementary sense and antisense strands (Figure 1, A), whereas dual-targeting siRNA utilizes a linker to concatenate two siRNA units (Figure 1, B), forming a single entity. The antisense strand a and antisense strand b can be designed to target different mRNA targets, achieving dual-targeting.

Figure 1. Schematic diagram of traditional siRNA (A) and dual-targeting siRNA (B) structures.

This dual-targeting design offers the following therapeutic advantages:

1. Synergistic Effects, Breaking Through Single-Target Limitations. Many diseases are not driven by a single factor. The dual-targeting design enables coordinated intervention across multiple pathways in the disease process. Taking Shian Biotech's SA1211 as an example, this HBV-targeting dual-targeting siRNA simultaneously targets the HBX gene (HBV X protein) and the PD-L1 gene (programmed death-ligand 1). Inhibiting HBX mRNA and PD-L1 mRNA respectively can block viral replication while "awakening" the immune system, reducing HBV immune evasion.
2. Avoiding Combination Therapy, Reducing Dose-Related Toxicity. Compared to using two different siRNAs in combination, dual-targeting siRNA requires a lower total dose, thereby avoiding toxicity associated with high doses and improving safety.
3. Controllable In Vivo Exposure, Avoiding Dual-Peak Phenomenon. From a PK (pharmacokinetics) perspective, two separate siRNAs would have different absorption and clearance rates, leading to "dual-peak" plasma concentration curves for the two drugs. As a single molecule, dual-targeting siRNA does not exhibit this phenomenon, allowing for synchronized silencing of both targets and achieving better synergistic efficacy.

While dual-targeting siRNA brings the aforementioned advantages, it also introduces significant synthesis challenges, becoming key obstacles for pipeline progression:

1. Doubled-Length Sense Strand. Because the sense strand of a dual-targeting siRNA needs to be complementary to two antisense strands, its length reaches around 40 nt, twice that of a traditional siRNA sense strand. Consequently, the solid-phase synthesis requires more coupling steps, and the cumulative yield is significantly reduced.
2. Additional Linker Modification. Unlike traditional siRNA, the sense strand also requires the introduction of a linker modification. Taking a TEG (tetraethylene glycol) linker as an example, using TEG phosphoramidite for synthesis not only increases the number of coupling steps but also further reduces synthesis efficiency due to the steric hindrance it introduces.
3. Large-Scale Production. Corsera Health's recent announcement of clinical plans for its hyperlipidemia-targeting dual-targeting siRNA drug marks the entry of dual-targeting siRNA into the field of common metabolic diseases. This implies broader patient coverage and greater demand for scaled-up production in the future. Given the aforementioned synthesis challenges, large-scale production of dual-targeting siRNA will become a major hurdle.

As a globally leading supplier of gene monomers, Hongene has been deeply involved in the nucleic acid field for nearly 30 years. While continuously improving our existing solid-phase synthesis platform, we are also pioneering a chemoenzymatic ligation synthesis platform to facilitate the industrialization of dual-targeting siRNA.

Solid-Phase Synthesis Platform. Leveraging our full-industry-chain advantage in nucleic acids, Hongene ensures complete quality control from upstream raw materials (e.g., phosphoramidites / GalNAc / NTPs) to downstream purification and formulation. This enables us to provide high-quality, low-cost, and stable nucleic acid products. Furthermore, Zhaowei's solid-phase synthesis platform is equipped with industry-leading large-scale 1800 mmol synthesizers, with GMP-scale production capacity reaching kilogram levels.

Figure 2. Chemoenzymatic ligation synthesis strategy for dual-targeting siRNA.
(A) Shorter fragments are obtained using solid-phase synthesis.
(B) Fragments are hybridized to create ligation sites.
(C) A ligase is used to connect the fragments, forming the complete dual-targeting siRNA.

Chemoenzymatic Ligation Synthesis Platform. Figure 2 illustrates Hongene's latest chemoenzymatic ligation synthesis platform. This platform avoids synthesizing the entire long sense strand in one go. Instead, it first uses solid-phase synthesis to obtain multiple shorter fragments (Figure 2, A), ensuring synthesis quality and yield. Subsequently, a ligase is employed to join these fragments together, forming the complete dual-targeting siRNA (Figure 2, C). This synthesis strategy features the following characteristics:

1. Higher Yield. By shortening the length required for solid-phase synthesis, the purity and yield of each short fragment are guaranteed, especially for sense strand 2 carrying the linker modification (Figure 2, A). The reduction in coupling steps also correspondingly lowers reagent costs.
2. One-Pot Enzymatic Ligation. The enzymatic ligation reaction does not require stepwise operations; instead, a one-pot method converts the individual fragments into the complete double-stranded siRNA product.
3. Simplified Purification Process. Typically, each short fragment needs chromatographic purification after synthesis (Figure 2, A). Zhaowei's chemoenzymatic ligation platform can adopt a post-ligation purification scheme, eliminating the need for purification after solid-phase synthesis, thereby reducing costs and improving overall yield.

Currently, Hongene's dual platforms have successfully supported multiple projects advancing into clinical stages. This includes assisting Siran Biotech in gaining clinical approval for the world's first single-molecule dual-targeting siRNA drug and supporting Dingle Xinwei in obtaining clinical approval for the world's first siRNA drug using an enzymatic process!

Dual-targeting oligonucleotide drugs are ushering in a new era of innovative therapies. As a leader deeply rooted in the oligonucleotide CDMO field, Hongene employs a dual-platform technology matrix of "Chemoenzymatic Ligation + Solid-Phase Synthesis" to tackle the core challenges of synthesis efficiency, large-scale production, and purity control.

Moving forward, Hongene will continue to iterate its technology platforms, providing more efficient and reliable CDMO services to assist global innovative pharmaceutical companies in accelerating the R&D and commercialization of dual-targeting oligonucleotide drugs. Our goal is to bring more breakthrough therapies to patients sooner.