Novel Approaches to the Manufacturing of AOCs and Oligo-Peptide Conjugates

The manufacturing of antibody–oligonucleotide conjugates (AOCs) and oligo-peptide conjugates are transforming the precision, scalability, and therapeutic potential of targeted biologics. Advances in site-specific conjugation technologies—such as engineered cysteine residues, enzymatic tagging (e.g., Sortase or transglutaminase), and click chemistry—enable controlled drug-to-antibody or peptide-to-cargo ratios (DAR), improving product homogeneity and pharmacokinetics. Continuous flow synthesis and solid-phase peptide synthesis (SPPS) innovations have enhanced the efficiency and purity of oligo-peptide backbones, while automated oligonucleotide synthesizers now support high-fidelity, scalable production with modified nucleotides for stability and targeted delivery. Integration of cell-free protein synthesis platforms and modular bioconjugation strategies further streamlines manufacturing workflows, reducing batch variability and facilitating rapid prototyping. Together, these novel manufacturing paradigms are accelerating the clinical translation of AOCs and oligo-peptide conjugates, particularly in precision oncology and neuromuscular disease therapeutics.

Redefining Conjugation: From Stochastic to Programmable Architectures

Early conjugation strategies relied heavily on stochastic modification of lysine or cysteine residues, resulting in heterogeneous mixtures with variable drug-to-antibody ratios (DARs). This heterogeneity directly impacts pharmacokinetics, efficacy, and safety profiles.

Recent advances have shifted toward programmable, site-specific conjugation, including:

• Engineered cysteine platforms (e.g., THIOMAB-like systems) enabling defined conjugation stoichiometry
• Enzymatic ligation (Sortase A, microbial transglutaminase) for regioselective coupling
• Genetic code expansion incorporating noncanonical amino acids with orthogonal reactive handles
• Bioorthogonal click chemistries (SPAAC, IEDDA), allowing rapid, high-yield conjugation under physiological conditions

SPAAC: SPAAC (Strain-Promoted Azide–Alkyne Cycloaddition) is a copper-free, bioorthogonal “click” reaction between an azide and a strained cyclooctyne (e.g., DBCO or BCN) that forms a stable triazole linkage. It is widely used in live-cell imaging and bioconjugation because it operates efficiently at ambient temperature without the cytotoxicity associated with copper catalysts.

IEDDA: The inverse electron demand Diels–Alder reaction, or DAINV or IEDDA (10) is an organic chemical reaction, in which two new chemical bonds and a six-membered ring are formed.

A particularly novel paradigm is modular self-assembly of AOCs, where antibody and oligonucleotide components are synthesized independently and assembled via DNA scaffolds to yield highly homogeneous constructs with precise stoichiometry. This decoupled manufacturing strategy represents a shift from covalent conjugation toward supramolecular bioconjugation, potentially simplifying scale-up and enabling multi-valent or multi-payload designs.

Supramolecular bioconjugation: is a specialized strategy for linking biomolecules (such as proteins, DNA, or antibodies) with other functional entities (drugs, imaging agents, or polymers) using non-covalent interactions or reversible assembly methods, rather than traditional irreversible covalent bonds.

Oligonucleotide Manufacturing: Toward High-Fidelity, Scalable Platforms
The oligonucleotide component of AOCs introduces unique manufacturing challenges due to its susceptibility to degradation and the need for chemical modification. Modern solid-phase oligonucleotide synthesis (SPOS) has evolved to support:

• High-throughput, automated synthesis at GMP scale
• Incorporation of stabilizing chemistries (phosphorothioates, 2′-modifications)
• Sequence-specific optimization for target engagement and reduced immunogenicity

Despite these advances, cost and purity remain major bottlenecks, as oligonucleotide production requires high-purity reagents and extensive downstream purification. Emerging innovations include:

• Continuous-flow oligonucleotide synthesis, improving reaction efficiency and reducing reagent consumption
• Enzymatic oligonucleotide synthesis, which may eventually replace phosphoramidite chemistry for greener, scalable production
• AI-assisted sequence design, optimizing manufacturability alongside biological function

Advances in oligonucleotide synthesis have also been critical. Modern automated solid-phase oligonucleotide synthesis (SPOS) platforms now support scalable production of chemically modified nucleotides, such as phosphorothioates, 2′-O-methyl, and locked nucleic acids (LNAs), which enhance nuclease resistance and binding affinity (1). These improvements are particularly important for AOCs, where oligonucleotide stability and intracellular delivery efficiency are key determinants of therapeutic efficacy.

Advances in Peptide Conjugate Manufacturing

Solid-phase peptide synthesis (SPPS) has undergone significant innovation, including microwave-assisted synthesis, improved coupling reagents, and greener solvent systems, all of which enhance yield, reduce cycle times, and minimize impurities (2,4). Hybrid approaches that combine SPPS with recombinant expression systems are increasingly used to produce longer or more complex peptide scaffolds with site-specific functionalization handles.

Oligo-peptide conjugates benefit from decades of innovation in solid-phase peptide synthesis (SPPS), but recent developments have significantly enhanced scalability and sustainability:

• Microwave-assisted SPPS, reducing cycle times and aggregation
• Greener solvents and coupling reagents, addressing environmental and regulatory pressures
• Hybrid recombinant–synthetic approaches, enabling longer or structurally complex peptides

Additionally, peptide carriers are increasingly engineered with cell-penetrating motifs or receptor-targeting ligands, allowing them to serve as modular delivery vehicles analogous to antibodies but with improved tissue penetration.

Continuous and Integrated Manufacturing Systems

Emerging continuous flow manufacturing technologies are further revolutionizing the field by enabling real-time monitoring, improved reproducibility, and scalable production of both peptides and oligonucleotides. Flow-based synthesis allows tighter control over reaction parameters and facilitates integration with downstream purification processes, reducing batch-to-batch variability (5).

A major paradigm shift in the field is the move from batch-based production to continuous and integrated manufacturing platforms. These systems enable:

• Real-time monitoring of conjugation reactions (Process Analytical Technology, PAT)
• Reduced batch variability and improved reproducibility
• Integration of synthesis, conjugation, and purification into a single workflow

This is particularly important for AOCs, where multi-step processes (antibody production → oligo synthesis → conjugation → purification) must be tightly controlled to meet regulatory standards. Continuous processing also facilitates scalable production, addressing one of the primary barriers to commercialization.

Antibody Production

This is the starting point generating an antibody that specifically binds the target (antigen).

Key steps:

• Antigen design & preparation: Choose the protein/epitope desired to target.
• Immunization (for polyclonal/monoclonal antibodies): Animals (e.g., mice, rabbits) are exposed to the antigen.
• Hybridoma generation (monoclonal antibodies): B-cells are fused with myeloma cells to create immortal antibody-producing cells.
• Recombinant expression: Alternatively, antibodies can be engineered and produced in systems like mammalian cells (e.g., CHO cells).
• Screening & validation: Ensure specificity, affinity, and functionality.

Output: Purified antibody with known specificity.

Oligonucleotide (Oligo) Synthesis

Here, short DNA or RNA sequences are chemically synthesized.

Key steps:

• Sequence design: Tailored for the application (e.g., barcode, probe, linker).
• Solid-phase synthesis: Nucleotides are added stepwise on a solid support.
• Modification incorporation: Functional groups (e.g., amine, thiol, biotin, fluorophores) are added for later conjugation.
• Cleavage & deprotection: Oligo is released from the support and protecting groups are removed.

Output: Custom oligonucleotide with specific sequence and chemical modifications.

Conjugation (Antibody–Oligo Linking)

Common strategies:

• Amine-reactive chemistry: Targets lysine residues on antibodies (e.g., NHS esters).
• Thiol-reactive chemistry: Uses cysteine residues (e.g., maleimide linkers).
• Click chemistry: Bioorthogonal reactions for precise and efficient conjugation.
• Enzymatic conjugation: More site-specific (e.g., Sortase-mediated).

Considerations:

• Maintain antibody binding activity.
• Control the degree of labeling (DOL)—how many oligos per antibody.
• Avoid aggregation or steric hindrance.

Output: Antibody–oligonucleotide conjugate.

Purification

After conjugation, you need to isolate the correctly linked product.
Methods:

• Size-exclusion chromatography (SEC): Separates based on size (removes free oligos).
• Affinity chromatography: Uses antibody binding properties.
• Ion-exchange chromatography: Separates based on charge differences.
• Ultrafiltration/dialysis: Removes small molecules and buffers.

Quality control:

• Verify conjugation efficiency.
• Check purity and stability.
• Confirm functionality (binding + oligo accessibility).

Output: High-purity antibody–oligo conjugate ready for use.

Cell-Free and Modular Biomanufacturing

Cell-free protein synthesis (CFPS) platforms are gaining traction as flexible systems for producing antibody fragments or peptide carriers with noncanonical amino acids or reactive handles pre-installed, thereby simplifying downstream conjugation (7). When combined with modular bioconjugation strategies, CFPS enables rapid prototyping and iterative optimization of AOCs and oligo-peptide conjugates.

Cell-free protein synthesis (CFPS) is emerging as a disruptive platform for producing antibody fragments and peptide scaffolds with built-in conjugation handles. Advantages include:

• Rapid prototyping and on-demand production
• Direct incorporation of noncanonical amino acids
• Elimination of cell-based variability and contamination risks

When combined with modular bioconjugation strategies, CFPS enables a “plug-and-play” approach to AOC assembly, significantly shortening development timelines and enabling personalized or small-batch therapeutics.

Finally, the integration of modular and platform-based manufacturing workflows—including standardized linker chemistries, purification strategies, and analytical characterization methods—has streamlined development pipelines and reduced regulatory complexity. These advances collectively support the clinical translation of AOCs and oligo-peptide conjugates, particularly in areas such as precision oncology, rare genetic disorders, and neuromuscular diseases, where targeted delivery and molecular specificity are paramount.

Downstream Processing and Quality Control Innovations

Purification and analytical characterization remain among the most challenging aspects of AOC manufacturing. Key innovations include:

• Advanced chromatographic techniques (e.g., HIC, SEC, ion-exchange) adapted for conjugate separation
• Multi-attribute mass spectrometry (MAM) for simultaneous monitoring of DAR, aggregation, and modifications
• High-resolution LC-MS (Liquid Chromatography-Mass Spectroscopy) and capillary electrophoresis for oligonucleotide characterization

Maintaining critical quality attributes (CQAs)—including DAR distribution, linker stability, and absence of free oligonucleotide—is essential for regulatory approval and clinical translation.

Formulation and Stability Engineering

AOCs are inherently unstable due to the combination of protein and nucleic acid components. Novel formulation strategies include:

• PEGylation and lipid-based encapsulation to enhance stability and circulation time
• Cleavable linkers (pH-sensitive, enzymatic) to improve intracellular payload release
• Stabilizing excipients and lyophilized formulations to extend shelf life

These approaches aim to address key limitations such as endosomal trapping and degradation, which remain major barriers to efficacy.

Manufacturing Challenges and Future Directions

Despite rapid progress, several critical challenges remain:

• Scalability and cost: Multi-component synthesis and purification are resource-intensive
• Product heterogeneity: Even minor variability in conjugation impacts clinical performance
• Supply chain complexity: Dependence on high-quality antibodies and oligonucleotides creates bottlenecks
• Regulatory uncertainty: Lack of standardized guidelines for hybrid modalities

These challenges are compounded by the need for stringent CMC documentation and GMP compliance, which increase development timelines and costs.

Looking forward, the field is moving toward:

• Platform-based manufacturing (standardized linkers, conjugation chemistries)
• Automation and robotics in bioconjugation workflows
• Digital twins and AI-driven process optimization
• Personalized, small-batch production models for rare diseases

Toward Programmable and Scalable Precision Therapeutics

Antibody–oligonucleotide conjugates (AOCs) and oligo-peptide conjugates represent an emerging class of hybrid therapeutics that integrate the targeting specificity of biologics with the regulatory or signaling functions of nucleic acids and peptides. Recent advances in site-specific conjugation (3), oligonucleotide and peptide synthesis, and integrated manufacturing systems have enabled unprecedented control over product quality, scalability, and functionality. This review discusses the evolving technological landscape underpinning AOC and oligo-peptide conjugate manufacturing, highlighting innovations in programmable bioconjugation, continuous production, and modular design, as well as the remaining challenges in scalability, regulatory harmonization, and cost.

The convergence of biologics and nucleic acid therapeutics has catalyzed the development of AOCs and oligo-peptide conjugates as next-generation targeted delivery systems. Unlike traditional antibody–drug conjugates (ADCs), these constructs deliver genetic payloads (e.g., siRNA, ASOs) or functional peptides, enabling modulation of intracellular pathways previously considered “undruggable.” However, their structural complexity introduces substantial manufacturing challenges, necessitating innovations across upstream production, conjugation chemistry, and downstream processing.

From Stochastic to Programmable Conjugation

A defining shift in the field has been the transition from stochastic conjugation toward site-specific and programmable assembly. Conventional lysine- or cysteine-based conjugation yields heterogeneous mixtures with variable stoichiometry. In contrast, modern approaches enable:

• Defined conjugation sites via engineered residues or noncanonical amino acids
• Controlled stoichiometry (DAR), improving pharmacokinetics and efficacy
• Orthogonal chemistries, enabling multiplexed payload attachment

Emerging strategies extend beyond covalent conjugation to include DNA-guided self-assembly, where oligonucleotide hybridization directs precise and modular assembly of multi-component constructs. This enables multivalency and combinatorial payload design, which are difficult to achieve with traditional chemistries.

Advances in Oligonucleotide and Peptide Synthesis

Oligonucleotide platforms
Modern synthesis has evolved to support:

• Chemically stabilized backbones (phosphorothioate, LNA, 2′-modifications)
• High-throughput, GMP-compliant production
• Sequence-specific manufacturability optimization

Emerging enzymatic synthesis platforms (6) promise improved sustainability and scalability, potentially overcoming limitations of phosphoramidite chemistry.

Peptide synthesis innovations
Peptide manufacturing has been transformed by:
Microwave-assisted SPPS, reducing synthesis time
Continuous-flow peptide synthesis, enabling scale-up
Hybrid recombinant–synthetic approaches, allowing complex architectures

These advances are particularly important for cell-penetrating peptides (CPPs) and targeting ligands used in oligo-peptide conjugates.

Integrated and Continuous Manufacturing

The field is rapidly transitioning toward end-to-end integrated manufacturing systems, where synthesis, conjugation, and purification are unified.

Key features include:

• Continuous flow reactors for oligonucleotide and peptide synthesis
• Inline monitoring (PAT tools) for real-time quality control
• Automated conjugation modules, reducing human variability

Such systems improve reproducibility and reduce cost while enabling rapid process optimization and scale-up.

Cell-Free and Modular Biomanufacturing

Cell-free protein synthesis (CFPS) has emerged as a flexible alternative to traditional cell-based systems. It allows:

• Incorporation of noncanonical amino acids with reactive handles
• Rapid production of antibody fragments or peptide carriers
• On-demand, decentralized manufacturing

When integrated with modular conjugation toolkits, CFPS supports a plug-and-play paradigm, accelerating therapeutic development and enabling personalized medicine applications.

Downstream Processing and Analytical Control

Ensuring product quality requires advanced analytical tools capable of resolving highly complex conjugates:

• Multi-attribute mass spectrometry (MAM)
• Hydrophobic interaction chromatography (HIC) for DAR profiling
• Capillary electrophoresis and LC–MS for oligonucleotide analysis

These tools enable monitoring of critical quality attributes (CQAs) such as:

• Conjugation stoichiometry
• Aggregation
• Free payload contamination
• Linker stability

Formulation and Stability Engineering

AOCs and peptide conjugates are prone to instability due to their hybrid nature. Strategies to address this include:

• Cleavable linkers (pH-sensitive, enzymatic)
• Nanoparticle or lipid encapsulation
• Lyophilized formulations with stabilizing excipients

These approaches improve circulation time, intracellular delivery, and shelf stability.

Challenges and Future Directions

Despite progress, key barriers remain:

• Manufacturing cost and scalability
• Complex supply chains (biologics + oligonucleotides
• Regulatory uncertainty for hybrid modalities
• Endosomal escape inefficiency

Future directions include:

• AI-driven process optimization
• Standardized platform technologies
• Fully automated, closed manufacturing systems
• Personalized and decentralized production models

Conclusion

The manufacturing of AOCs and oligo-peptide conjugates is undergoing a fundamental transformation, driven by innovations in site-specific conjugation, nucleic acid and peptide synthesis, and integrated bioprocessing. The transition from heterogeneous, batch-based systems to modular, programmable, and continuous manufacturing paradigms is enabling greater control over product quality and scalability. While significant challenges remain—particularly in cost, standardization, and regulatory alignment—these emerging modalities/technologies are poised to accelerate the clinical translation of next-generation targeted therapeutics and redefine the landscape of precision medicine.

References and notes

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