Solving manufacturing bottlenecks through advanced ADC design

Downstream production bottlenecks in antibody-drug conjugate (ADC) development frequently originate years earlier during the discovery phase. Developers often treat payload selection, conjugation chemistry and commercial scale-up as isolated operations. This fragmented approach inevitably creates complex purification challenges, poor yields and supply chain vulnerabilities. Overcoming these hurdles requires engineering manufacturability into the earliest stages of advanced ADC design.

Supply chain resilience and the payload pool

The first generation of ADCs relied heavily on a highly restricted class of payloads, primarily microtubule and topoisomerase 1 (Topo1) inhibitors. This lack of diversity restricts clinical benefit and accelerates tumor resistance, but it also creates inherent sourcing vulnerabilities. Relying on a narrow set of highly toxic active pharmaceutical ingredients concentrates production risk into very specific raw materials. Incorporating a wider variety of specialized small molecules diversifies the chemical library and strengthens the overall supply chain. The wider breadth of ADC payloads that are currently being explored by developers will likely result in a more diverse manufacturing process, yet there are advantages as more robust route development can be included as an attribute to payload selection

Developers are actively shifting toward an approach that combines the targeting precision of the antibody with a payload that is intrinsically selective for specific tumor biology. This strategy enables the repurposing of “fallen angel” small molecules. These assets may have previously failed in the clinic as systemic therapies due to poor tissue penetration or on-target systemic toxicity, but they possess the exact properties needed for effective ADC payloads. 

Homogeneity and site-specific conjugation

Securing the supply chain is only the first step toward commercial viability. The industry must move away from stochastic conjugation techniques to ensure scalability. lysine or interchain disulfide targeting generates highly heterogeneous products with widely variable drug-antibody ratios (DARs). This inconsistency complicates quality control, reduces overall yield and challenges strict regulatory expectations.

Adopting site-specific conjugation techniques solves this issue at the chemical source. Approaches utilizing engineered cysteines, enzymatic reactions or non-canonical amino acid insertions yield homogeneous ADCs with consistent DARs. This precision minimizes the batch-to-batch variability that hinders traditional manufacturing pipelines and simplifies downstream analytical testing, saving significant bioprocessing time and preserving project budgets.

Linker engineering and aggregation control

Aggregation remains a persistent threat to commercial scale-up and formulation. As the industry explores novel molecular architectures, including dual-payload systems, the hydrophobicity of the overall conjugate often increases. Higher DARs combined with hydrophobic active agents amplify the precipitation risk, resulting in lost batches and ruined manufacturing yields.

Advanced linker engineering actively addresses this developability flaw. Innovative linker designs purposefully modify the solubility of the payload, utilizing hydrophilic elements like PEG groups or sugar moieties to reduce aggregation risk. Resolving solubility at the structural level ensures the integrity of the ADC during large-scale production and prolonged storage.

Multi-mechanism therapies and stoichiometry risks

The rise of dual-payload ADCs adds complexity to established manufacturing and developability challenges. Combining two distinct therapeutic agents, such as a Topo1 inhibitor to damage DNA alongside a second molecule blocking the DNA repair pathway, creates powerful synergistic effects against tumor resistance.

The stoichiometry of these constructs needs to be defined early and controlled tightly. If developers miscalculate the dual payload ratio, deciding between a 4:2 versus a 2:4 stoichiometry, for example, they face severe developability and formulation risks. Hydrophobicity can rise and solubility can drop, which can drive aggregation and reduce filtration headroom. It is nearly impossible to predict from a toxicity perspective which component will dominate once manufactured, potentially resulting in unmanageable adverse events or unstable batches. A strong biological rationale, supported by rigorous target-payload fit screening and structural biology evaluations, must guide these complex design choices long before they reach the bioprocessing stage.

Automation and early analytics

Late evaluation of complex biophysical traits guarantees expensive delays. Developers must deploy automated, high-throughput analytical tools earlier in the design-make-test-analyze (DMTA) process. 

Coupling this automation with techniques like hydrophilic ion chromatography (HIC), Mass sepctrometryand size exclusion chromatography (SEC) allows discovery teams to monitor DAR distribution and aggregation long before the asset reaches the manufacturing floor. Identifying stable, highly soluble candidates early prevents unscalable molecules from consuming development pipeline capacity.

An interdisciplinary framework for commercial success

The complexity of next-generation payloads demands an integrated development framework. Small molecule discovery relies on established frameworks like Lipinski’s rules to ensure a drug remains stable in the bloodstream. ADCs require an entirely opposite approach, where the highly toxic payload is ideally cleared immediately after release from the antibody. Developers can engineer metabolic soft spots into payloads to enhance the clearance rate of free drug from peripheral blood and prevent off-target toxicity.

Unifying small-molecule medicinal chemistry with large-molecule biochemistry creates a system that is inherently easier to manufacture. Homogeneous drug design, optimized linker solubility and automated biophysical characterization effectively remove the most significant barriers to scale-up. Discovery teams ensure resilient supply chains and deliver highly targeted therapeutics to patients without unnecessary delays by addressing these variables early. This proactive strategy directly prevents unscalable concepts from reaching the manufacturing floor. 

The new path to next-generation ADCs starts at the design stage rather than the bioreactor. An integrated biological and chemical strategy transforms these theoretical concepts into highly targeted, commercially viable therapeutics long before production begins.

Allan joined Sygnature Discovery in February 2019 as Vice President of Oncology Drug Discovery, delivering broad scientific oversight and mentorship of all Sygnature’s oncology projects. With 25+ years’ experience in medicinal chemistry and drug discovery, he has actively participated in almost 60 drug discovery projects, resulting in the delivery of fifteen pre-clinical candidates of which ten have entered human clinical trials. He led the chemistry teams which developed the first cell-active inhibitors of the DNA repair protein PARG, now in Phase I trials with Ideaya Biosciences and the first reversible, selective inhibitors of the epigenetic enzyme DNMT-1, in collaboration with GSK.

Joshua Greally has spent over 12 years in drug discovery, starting in small molecule medicinal chemistry and quickly moving into specialize in the development of conjugate therapies. On joining Sygnature discovery Josh’s combined academic and industry experience now informs his work at the interface of science and strategy, where he leads Antibody–Drug Conjugate (ADC) initiatives and supports scientific business development. Driven by a commitment to translating innovation into meaningful therapeutic advances, Joshua is focused on contributing to the development of next‑generation ADC therapies.