AOC linkers are one of the key components in antibody-oligonucleotide conjugates (Figure 1) that connect an antibody with an oligonucleotide (payload) through a chemical bond. Just as antibody-drug conjugates (ADCs) target and deliver small-molecule drugs to tumor cells, AOCs leverage antibodies' specificity and robust tissue targeting to deliver genetic therapies-such as antisense oligonucleotides (ASOs) or small interfering RNAs (siRNAs)-to cells. These linkers critically influence in vivo performance, including stability in circulation, intracellular release, and delivery to target tissues (e.g., skeletal and cardiac muscles for muscular dystrophy therapy).
Figure 1. There are three major components of an AOC: the antibody, the linker, and the oligonucleotide payload to be delivered.
AOC linkers play central roles in dictating the success of an antibody-oligonucleotide conjugate. They can modulate:
Researchers have shown that customizing AOC linkers-whether cleavable (Figure 2, 3, 4) or non-cleavable (Figures 5 & 6), positioned at specific sites on the oligonucleotide or antibody, or combined with additional modifications such as monodispersed polyethylene glycol (PEG)-can substantially enhance therapeutic outcomes (Murphy). This targeted delivery can improve outcomes in conditions that involve gene dysregulation or mutation, such as the exon-skipping therapies for Duchenne muscular dystrophy and siRNA-based therapies for metabolic or oncologic diseases (Zambon).
Similar to ADC Linkers, AOC linkers commonly fall into two main categories:
Cleavable linkers can be designed to remain stable in systemic circulation and only break once the AOC enters target cells. For instance, certain disulfide-based linkers (Figure 2) release the oligonucleotide in reducing intracellular environments (Cochran). Moreover, modular cleavable linkers such as enzyme-labile peptides (Figure 3), sterically hindered disulfides (Figure 4) or pH-sensitive bonds allow precise tuning of AOC stability in circulation and the timing of intracellular payload release (Jiao). This linker flexibility directly influences pharmacokinetics (circulation half-life and clearance) and drug-to-antibody ratio, expanding the range of deliverable payloads (Jiao, Hsu).
Figure 2: Disulfide-based Linker, SPDB
Figure 3: Enzyme-labile Peptide Linker, MC-Val-Cit-PAB-PNP
Figure 4: Sterically Hindered Disulfide Linker, SPDMV
Non-cleavable linkers rely on intracellular degradation of the antibody or additional intracellular processes to release the oligonucleotide payload. Stable linkers (e.g., maleimide-based linkers such as MCC and BisMal) have become popular in AOC design. They resist premature cleavage in circulation, ensuring the oligonucleotide remains attached until it reaches sites of uptake, such as skeletal muscles or tumor tissues. Non-cleavable linkers like MCC (Figure 5) or BisMal (Figure 6) can be conjugated to multiple sites on both the antibody and the siRNA, including the 5' or 3' ends of the sense strand. These linkers remain intact until the antibody or other portions of the conjugate are degraded within the cell, thereby freeing the oligonucleotide (Cochran).
Figure 5: MCC Linker, SMCC
Figure 6: BisMal Linker, Bis-Mal-Lysine-PEG4-acid
PEG chains can be integrated into both cleavable and non-cleavable linkers to enhance the aqueous solubility, circulation half-life, and tissue delivery of AOCs. Recent studies have shown that sandwiching the oligonucleotide between the antibody and a PEG moiety can significantly increase tissue-specific delivery in muscles and tumors. The addition of PEG may also reduce potential off-target or nonspecific protein binding, further improving the safety profile (Cochran).
BroadPharm is at the forefront of linker technology for next-generation therapeutics, offering a wide selection of AOC linkers that build on our expertise with ADC linkers:
Our innovative linker designs can be leveraged for your advanced research, enabling accelerated development of antibody-oligonucleotide conjugates. Whether you are fine-tuning a cleavable AOC linker for siRNA-mediated gene silencing or stabilizing a non-cleavable linker for safer and more effective exon-skipping AOCs, BroadPharm stands ready to support your therapeutic discoveries.
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If you want to learn more about our AOC linker portfolio or discuss your next-generation conjugate design, please contact BroadPharm today at sales@broadpharm.com. We are committed to fueling your success in the rapidly evolving field of AOCs.
Cochran, M., Arias, D., Burke, R., Chu, D., Erdogan, G., Hood, M., ... & Doppalapudi, V. R. (2024). Structure-Activity Relationship of Antibody-Oligonucleotide Conjugates: Evaluating Bioconjugation Strategies for Antibody-siRNA Conjugates for Drug Development. Journal of medicinal chemistry, 67(17), 14852-14867.
Hsu, N. S., Lee, C. C., Kuo, W. C., Chang, Y. W., Lo, S. Y., & Wang, A. H. J. (2020). Development of a versatile and modular linker for antibody-drug conjugates based on oligonucleotide strand pairing. Bioconjugate Chemistry, 31(7), 1804-1811.
Jiao, J., Qian, Y., Lv, Y., Wei, W., Long, Y., Guo, X., ... & Zhang, W. (2024). Overcoming Limitations and Advancing the Therapeutic Potential of Antibody-Oligonucleotide Conjugates (AOCs): Current Status and Future Perspectives. Pharmacological Research, 107469.
Murphy, A., Hill, R., & Berna, M. (2024). Bioanalytical approaches to support the development of antibody-oligonucleotide conjugate (AOC) therapeutic proteins. Xenobiotica, 54(8), 552-562.
Zambon, A. A., Falzone, Y. M., Bolino, A., & Previtali, S. C. (2024). Molecular mechanisms and therapeutic strategies for neuromuscular diseases. Cellular and Molecular Life Sciences, 81(1), 198.