As one of the most vital directions in modern drug discovery, following small molecules and antibodies, nucleic acid therapeutics have demonstrated enormous potential in the era of precision medicine. Currently, commercialized nucleic acid drugs are primarily classified into Antisense Oligonucleotides (ASOs), Small Interfering RNAs (siRNAs), and Nucleic Acid Aptamers. Although the former two maintain strong market enthusiasm, nucleic acid aptamers, recognized as highly differentiated "chemical antibodies," are approaching a brand-new inflection point in commercialization and technological evolution.

What are Aptamers?

Aptamers are short, single-stranded oligonucleotides (DNA or RNA), typically 15 to 60 bases in length, that bind to targets with high affinity and specificity by folding into tertiary structures. It is a novel nucleic acid molecule with recognition function, which is usually developed in vitro by a very defined iterative procedure, called Systematic Evolution of Ligands by Exponential enrichment (SELEX).

Compared to traditional protein antibodies, aptamers offer prominent advantages, including a smaller size (6–30 kDa, 2 nm) and flexible structure, a broader target spectrum (capable of identifying small molecules, toxins, viruses, and whole cells), low immunogenicity, excellent thermal stability, lower synthesis costs, and minimal batch-to-batch variation.

Despite these advantages, aptamer therapeutics face several development challenges, including rapid renal clearance, susceptibility to nuclease degradation, and limited systemic exposure. Covalent attachment of PEG to aptamers—termed PEGylation— addresses these major limitations.

Approved Aptamer Drugs: The Critical Role of PEG

To date, two nucleic acid aptamer drugs have received FDA approval. Both target age-related macular degeneration (AMD) in ophthalmology and rely heavily on PEGylation technology.

Pegaptanib (Macugen®): The First Approved Aptamer Drug

Approved in 2004 for wet age-related macular degeneration (wet AMD), Macugen was the world's first nucleic acid aptamer drug to enter clinical practice. It features a 28-mer RNA aptamer covalently conjugated to two 20 kDa PEG chains (branched PEG) via a lysine residue in order to increase the half-life of the drug in the vitreous cavity. 

By highly selectively binding to the VEGF-165 isoform, it halts neovascularization. However, visual gains were not as impressive as those of later, less specific anti-VEGF agents, and pegaptanib is no longer commonly used for subretinal neovascularisation.

Figure 1. Structure of Pegaptanib, Source: Reference [2]

Avacincaptad pegol (Izervay®) - The Modern Commercial Blockbuster

Avacincaptad pegol (Izervay) is another clinically aptamer therapy approved by the FDA in 2023 for geographic atrophy secondary to AMD. It is a 39-mer aptamer, covalently bound to an approximately 43-kiloDalton (kDa) branched PEG molecule and inhibits complement protein C5. By inhibiting C5, avacincaptad pegol may prevent its cleavage to C5a and C5b thus decreasing membrane attack complex (MAC) formation.

Figure 2. Structure of Avacincaptad pegol, Source: Reference [3]

How to Choose the Ideal PEG Linker for Aptamers?

As a specialized PEG Linker supplier, Huateng Pharma understands that selecting the appropriate PEGylation strategy during the early stages of aptamer R&D directly determines the drug's in vivo exposure and targeting efficiency. Key technical considerations include:

• ● Molecular Weight & Architecture: Typically, 20 kDa or larger PEGs (such as single-chain Linear PEG or two-arm Branched PEG) are preferred. Branched PEGs provide superior steric hindrance compared to linear counterparts of equal molecular weight, effectively shielding the oligonucleotide backbone from nucleases.

• ● Customized Functional Groups: We offer various reactive derivatives, including amine, thiol, aminooxy, alkyne, aldehyde, and azide functional groups, ensuring excellent coupling efficiency and yields.

• ● Purity Control: For oligonucleotide therapeutics requiring stringent structural control, high-purity PEG derivatives are mandatory to minimize batch variation and satisfy regulatory criteria.

While aptamers face shared obstacles regarding in vivo stability, rapid renal clearance, and delivery efficiency, advanced chemical modifications are steadily unlocking their therapeutic future. In particular, the rise of Aptamer-Drug Conjugates (ApDCs)—utilizing aptamers as highly specific targeting ligands to deliver cytotoxic payloads or therapeutic oligonucleotides—promises a new frontier in targeted drug delivery. As your trusted PEG Linker partner, we are committed to providing the highest quality, compliant, and diversified portfolio of PEG linkers to accelerate your aptamer therapeutics from laboratory discovery to clinical success.

References:
[1] Ozer, I., Pitoc, G. A., Layzer, J. M., Moreno, A., Olson, L. B., Layzer, K. D., Hucknall, A. M., Sullenger, B. A., & Chilkoti, A. (2022). PEG-Like Brush Polymer Conjugate of RNA Aptamer That Shows Reversible Anticoagulant Activity and Minimal Immune Response. Advanced Materials, 34(10), 2107852. https://doi.org/10.1002/adma.202107852
[2] Moshfeghi AA, Puliafito CA. Pegaptanib sodium for the treatment of neovascular age-related macular degeneration. Expert Opin Investig Drugs. 2005 May;14(5):671-82. doi: 10.1517/13543784.14.5.671. PMID: 15926872.
[3] https://www.astellas.com/content/dam/astellas-com/global/en/documents/izervay_pi.pdf