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ADC Discovery Considerations, Key Challenges, and Market Context

Supporting ADC drug development with MOA-driven antibody discovery, in vitro, and in vivo services

 

Antibody-drug conjugates (ADCs) have become an important drug class in oncology because they combine antibody-based targeting with the cell-killing activity of a cytotoxic payload. There is growing interest in antibody drug conjugates for breast cancer and other solid and hematologic malignancies. The design of ADCs can improve tumor selectivity but also makes development more complex than standard antibody programs. Target binding, ADC internalization, intracellular payload release, potency, exposure, safety, and ADC pharmacokinetics all need to align for successful development. In addition, factors such as ADC DAR (drug-to-antibody ratio), linker stability, and tissue distribution can significantly influence efficacy and tolerability. (Chen et al., 2025; FDA, 2024)

 

WuXi Biologics CRO Services can support ADC drug development from antibody discovery to in vitro and in vivo testing to help address these ADC-specific challenges. This page will guide readers through several practical areas of ADC drug discovery:

 

 

 

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Concept image of an antibody drug conjugate (ADC)

How ADC Discovery Differs from Standard Antibody Drug Discovery

ADC discovery begins with target and antibody selection, but success depends on more than identifying a high-affinity binder. Unlike naked mAb or bsAb, which may rely on signaling blockade or immune effector functions, antibody drug conjugates (ADCs) must function as an effective delivery vehicle, demonstrate efficient ADC internalization, maintain function and biophysical properties after conjugation, and achieve anti-tumor activity within an acceptable safety margin. In practice, this creates a multi-step workflow that connects antibody discovery, lead optimization, conjugation strategy, and ADC DAR optimization through both in vitro and in vivo evaluation. (Chen et al., 2025; Tang et al., 2025)

 

Key considerations in ADC antibody discovery and target selection

 

As a result, optimization and screening strategies in ADC discovery are broader in scope than in traditional antibody programs. Evaluation extends beyond binding properties to include ADC internalization, intracellular trafficking, payload sensitivity, and early safety-related signals. Target selection is also more stringent in ADC drug development, requiring careful evaluation of antigen density, tumor selectivity, and expression in normal tissues, since these factors directly influence the efficacy and tolerability of ADCs. (Chen et al., 2025; Tang et al., 2025; FDA, 2024)

 

Key considerations in ADC antibody discovery and target selection

This checklist reflects recurring themes in recent ADC reviews and in FDA clinical pharmacology guidance, which emphasize exposure-response, DAR, immunogenicity, and factors that can shift safety margins. (FDA, 2024; Koo et al., 2025)

 

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How We Support ADC Discovery

ADC discovery focuses on whether an antibody can serve as a reliable drug delivery scaffold after conjugation. In addition to binding quality, factors such as conjugation impact, internalization, cytotoxicity, PK assessment (including in vitro & in vivo total antibody and drug-to-antibody ratio (DAR) analysis), heterogeneity, and stability must be considered early, as they directly influence efficacy and safety. Here is what we can help:

 

Antibody Discovery
  • Multiple discovery methods to find optimal ADC binders
  • Select for affinity, specificity, and ADC internalization
  • Optimize for functionality and developability
Antibody Production
  • mg-g scale for screening, conjugation and in vitro / in vivo studies
  • Reliable quality (Purity ≥98% and endotoxin ≤0.2 EU/mg prior to conjugation)
  • TFC Quick ‘n’ Clean platform provides HTP tagless bsAb for bispecific ADC conjugation

 

 
In Vitro ADC Assays
  • Binding & competition (ELISA/SPR/BLI/FACS) to select high-affinity, well-behaved ADC binders
  • ADC cytotoxicity & internalization to confirm payload delivery and cell killing
  • Serum/Plasma stability to reduce conjugation and PK risks
In Vivo PK & Efficacy
  • PK assessment for total antibody and DAR analysis to track ADC stability and payload integrity
  • CDX efficacy models to assess tumor response across targets
  • PK/PD/Tox to support dose selection and clinical translation

 

Case Study 1: Multi-Cell Line FACS Binding and 34×34 Epitope Binning Enable Efficient Lead Selection in ADC Discovery

This case study demonstrates a high-throughput workflow for ADC discovery that combines multi-cell line FACS binding assays with large-scale epitope binning to accelerate ADC lead identification. Simultaneous binding evaluation across diverse tumor cell lines improves screening efficiency and helps identify antibodies with stronger potential for antibody drug conjugate development. In parallel, 34×34 pairwise epitope binning provides detailed epitope mapping to support the rational selection of optimal ADC candidates.

High-throughput ADC binding characterization and epitope binning

 

Case Study 2: High-Throughput BsAb Generation Enables Efficient ADC Conjugation, Binding, Internalization, and Cytotoxicity Evaluation

Bispecific antibody drug conjugates (bsADCs) have attracted significant attention in ADC drug development for their potential to improve selective delivery, enhance ADC internalization, and broaden tumor coverage through simultaneous engagement of two targets or epitopes. Although most bispecific ADC drugs remain in early clinical development, growing pipeline activity and increasing industry investment highlight bsADCs as an important direction for next-generation antibody drug conjugates. As of May 2026, more than 30 bispecific ADCs and 7 biparatropic ADCs have been administered to humans, with nearly all entering clinical studies within the past five years. (Conilh L et al., 2026)

 

The study below highlights a streamlined workflow for high-throughput production of 26 bispecific antibodies, followed by ADC conjugation and functional screening. Rapid generation and consistent quality support efficient ADC discovery by enabling evaluation across binding, ADC internalization assay, and cytotoxicity studies, helping accelerate the identification of high-performing ADC candidates.

High-throughput BsADC conjugation and internalization assays

 

Case Study 3: Re-Evaluating ADC Binding Activity After Conjugation Using Customized ELISA and SPR Assays

Customized ELISA and SPR assays were developed to evaluate ADC binding activity before and after conjugation, highlighting the importance of reassessing target engagement during ADC drug development. In one study, ELISA showed that ADC1 maintained a comparable EC50 to the naked antibody but exhibited reduced maximum binding, suggesting conjugation-related impact on binding efficacy and potential changes associated with ADC DAR (Figure A). In another study, SPR analysis demonstrated that ADC2 retained comparable binding kinetics and affinity before and after conjugation, supporting effective characterization strategies for ADC discovery and ADC pharmacokinetics assays (Figure B).

ADC binding evaluation before and after conjugation by ELISA and SPR

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Main ADC Discovery Challenges, and How In Vitro / In Vivo Studies Help to Address Them

Differentiation from existing drugs

As the ADC landscape becomes increasingly competitive, many new antibody drug conjugates are being developed against clinically validated targets such as HER2, TROP2, CD19, BCMA, and cMET, often using similar antibody scaffolds or payload classes. As a result, differentiating new ADC drugs from existing approved or clinical-stage therapies has become a major bottleneck in ADC drug development. Even antibody drug conjugates targeting the same antigen may show substantially different efficacy, safety, and therapeutic window due to differences in epitope binding, ADC internalization efficiency, linker stability, conjugation site, ADC DAR distribution, payload mechanism, PK, and tissue exposure.

 

Translational insight gap

A common challenge in ADC discovery is that promising in vitro activity does not always translate into strong in vivo efficacy or acceptable safety. This happens because ADC performance depends on several linked events, including target engagement, internalization, intracellular release, payload stability, systemic exposure, and clearance of released payload species. Recent FDA guidance reflects this complexity by emphasizing bioanalytical strategy, exposure-response analysis, intrinsic factors, immunogenicity, and drug-drug interaction risk. (FDA, 2024; Koo et al., 2025)

 

Narrow therapeutic window

Many ADCs are associated with a narrow therapeutic window. Toxicity may result from low-level target expression in normal tissues, unstable linker-payload behavior, or systemic exposure to released payload and metabolites. This means early screening should not focus only on potency; it also needs to identify factors that may compress the safety margin. (Zhou et al., 2025)

 

Greater analytical complexity

Antibody drug conjugates (ADCs) introduce greater analytical complexity than naked antibodies due to conjugation site effects on ADC DAR and molecular properties, the need to balance linker stability with efficient payload release, complex PK and tissue distribution profiles, and payload-related off-target toxicity. These factors require more comprehensive characterization strategies to support ADC drug development, including ADC optimization, differentiation, and translational assessment. In particular, LC-MS plays a critical role in ADC discovery and characterization in vitro and in vivo by enabling ADC DAR analysis, conjugation site confirmation, linker-payload stability assessment, free or released payload detection, payload-related catabolite analysis, and ADC pharmacokinetics assays for both total antibody and average DAR throughout preclinical development. (Koo et al., 2025; Zhou et al., 2025; FDA, 2024)

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How We Address the Above Challenges in ADC Discovery

In vitro and in vivo ADC studies can help address several major translational challenges in ADC drug development. In vitro ADC assays, including ADC internalization assay, cytotoxicity, bystander killing, and serum stability studies, can evaluate whether antibody binding efficiently translates into intracellular payload delivery and tumor cell killing while identifying potential liabilities early. In vivo PK and efficacy studies further assess how linker stability, payload release, systemic exposure, ADC DAR stability, and tumor antigen expression influence anti-tumor activity and tolerability under physiologically relevant conditions. By connecting mechanistic in vitro data with in vivo exposure-response and efficacy outcomes, these integrated workflows help reduce translational uncertainty, support therapeutic window optimization, and enable more comprehensive characterization of ADC developability and differentiation.

 

At WuXi Biologics CRO Services, we address key challenges in ADC drug discovery through fit-for-purpose in vitro and in vivo strategies that enable data-driven candidate selection. Our one-stop platform supports the full workflow from antibody discovery and engineering to comprehensive characterization, including in vitro assays such as internalization, cytotoxicity, and serum stability, alongside in vivo PK/PD, efficacy, and toxicology studies. By linking mechanistic insights with translational and safety-relevant data, we help identify ADC candidates with optimal efficacy, improved developability, and a more favorable therapeutic window.

 

 

In Vitro Internalization Assays

Measures ADC internalization using pHrodo assay, acid quench assay, and lysosome tracking, ideal for high-throughput screening, helping improve downstream translational insights
In Vitro ADC Cytotoxicity & Bystander Killing

Determine IC50 values across ADC leads; Utilize co-culture models to assess payload diffusion and the cytotoxic impact on antigen-negative cells; Select leads with better therapeutic window
In Vitro Serum Stability Assays

Evaluate in human, cyno, mouse, and rat plasma at 0, 1, 7, 14, and 21 days (37 °C); Utilize LC-MS to monitor total antibody, drug-to-antibody ratio (DAR), and PTMs and ELISA and FACS to assess binding of treated samples to antigen
In Vivo PK Studies & DAR Monitoring

Measure ADC and antibody levels to assess systemic exposure and payload stability; Utilize enzymatic hydrolysis and LC-MS to track DAR dynamics and total antibody over time.
In Vivo Custom CDX Models & Predictive Efficacy

Assess antitumor efficacy in strategically designed xenografts with high or medium target antigen expression; Generate dose-response curves to guide IND candidate selection.

 

Case Study 4: Comprehensive ADC Internalization Assay Suite

A complementary suite of ADC internalization assays designed to characterize ADC uptake, intracellular trafficking, and internalization kinetics across adherent and suspension cell models. pHrodo-based live-cell imaging using Operetta or Incucyte platforms enables real-time and kinetic visualization of ADC internalization and subcellular localization. FACS-based acid quenching assays are used for quantitative high-throughput analysis in suspension cells. These assays support high-throughput comparison of antibodies and ADCs before and after conjugation, enabling evaluation of how payload conjugation impacts target binding, cellular uptake, and intracellular processing to support ADC screening, lead selection, and optimization during ADC drug development.

ADC internalization assay for uptake and co-localization analysis

 

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Case Study 5: Correlation of hFab-MMAE Screening and Post-Conjugation ADC Cytotoxicity Profiles

CTG, MTT, or WST-based cytotoxicity assays were applied in a high-throughput workflow to evaluate ADC-mediated tumor cell killing across multiple cell models. hFab-MMAE was used as a surrogate screening approach by binding Fc regions of antibody leads and functionally mimicking ADC activity prior to payload conjugation. The cytotoxicity ranking of antibody leads observed in the hFab-MMAE assay was consistent with the ranking obtained after full ADC conjugation, supporting its value for early lead prioritization and efficient ADC screening.

High-throughput ADC cytotoxicity assay for antibody lead ranking

 

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Case Study 6: Evaluating ADC Serum/Plasma Stability Through Integrated DAR, Free Payload, and Functional Analysis

This workflow illustrates a comprehensive ADC serum/plasma stability assay used to evaluate linker stability, payload release, and functional integrity under physiologically relevant conditions. ADCs are incubated in serum or plasma from multiple species (human, cynomolgus monkey, mouse, and rat) and collected at defined time points to monitor stability over time.

 

Following incubation, ADC integrity is assessed through three complementary analyses:

 

  1. ADC DAR and Total Antibody Analysis: ADCs are recovered from serum/plasma by affinity purification and analyzed by Intact MS to determine changes in the drug-to-antibody ratio (DAR).
  2. Free Payload Quantification: LC-MS or LC-MS/MS is used to measure released free payload, providing insight into linker stability and premature payload release.
  3. Functional Assessment: Binding activity and ADC functionality are evaluated using ELISA, FACS, or quantitative ligand-binding assays.

 

This integrated approach supports characterization of ADC stability, payload retention, and functional performance across species, helping inform candidate selection and translational assessment.

 

ADC serum and plasma stability assay with DAR and free payload analysis

 

Case Study 7: Rationally Designed CDX Models Enable Integrated ADC Pharmacokinetics and Efficacy Evaluation

Rationally designed CDX models with different antigen expression levels were used to evaluate ADC antitumor efficacy and dose response in vivo. Integrated ADC pharmacokinetics evaluation further characterized antibody integrity, Fc-associated versus payload-associated exposure to measure average ADC DAR and total antibody over time, providing comprehensive insight into ADC efficacy, pharmacokinetics, and in vivo payload behavior to support lead selection and optimization.

In vivo ADC efficacy and PK characterization in CDX model

 

Case Study 8: Integrated In Vivo Toxicity Assessment Supports ADC Safety Evaluation

This case study highlights an integrated in vivo toxicity study workflow for antibody drug conjugates (ADCs), combining in-life observation, blood chemistry, and hematology analysis to evaluate tolerability and safety profiles. Parameters including body weight change, food intake, survival, liver function markers, and immune cell counts were monitored to assess systemic toxicity and treatment-related effects following ADC administration. These studies support early safety assessment and candidate differentiation during ADC drug development by helping identify toxicity liabilities and therapeutic window risks associated with linker-payload stability, systemic exposure, and payload-related off-target effects.

In vivo ADC toxicity study with hematology and blood chemistry analysis

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ADC Market Landscape and Emerging Trends

ADC remains one of the fastest-growing oncology modalities. A recent FDA-focused review reported that 14 ADCs had received FDA approval as of April 2025, with more than 100 candidates currently in clinical development worldwide. The FDA approval count increased further with the approvals of Datroway and Emrelis in 2025. Different market reports and reviews may report slightly different totals because some include withdrawn products, non-US approvals, or non-classical immunoconjugates. (Koo et al., 2025; FDA, 2025, Tang et al., 2025; World ADC 2026)

 

Approved drugs:

Practical note: the table below focuses on oncology ADCs commonly included in current market discussions. Some historical counts vary depending on whether withdrawn products or non-classical immunotoxins are included. Product characteristics are compiled from FDA approval pages, the Antibody Society resource, and recent ADC reviews. (Antibody Society, 2026; Koo, 2025; Tang et al., 2025). A more comprehensive table of approved ADCs and ADCs in regulatory review can be found in the recent review in Cell by Conilh L et al. 2026.

 

Key considerations in ADC antibody discovery and target selection

 

Future directions

The next generation of ADC drug development is moving beyond traditional “same-target, same-payload” strategies toward increasingly integrated and multifunctional conjugate designs. As HER2- and Trop-2-targeted antibody drug conjugates for breast cancer continue to drive ADC market growth, recent trends include the expansion of novel target classes such as B7-H3, PTK7, CLDN18.2, and cMET, alongside improved linker stability, site-specific conjugation technologies, and broader adoption of topoisomerase I inhibitor payloads such as DXd and exatecan derivatives to improve therapeutic window and enhance bystander killing effects. The field is also rapidly advancing toward more complex formats such as bispecific ADCs (bsADCs), dual-payload ADCs, and immune-stimulatory conjugates designed to address tumor heterogeneity, resistance mechanisms, and selective payload delivery. Experts at World ADC 2026 emphasized that future ADC development will increasingly depend on holistic optimization of antibody design, linker chemistry, conjugation strategy, payload selection, and translational strategy rather than improving individual components independently.

 

At the same time, the conjugate field is expanding beyond classical cytotoxic ADCs into broader targeted delivery platforms. Antibody-oligonucleotide conjugates (AOCs), which enable antibody-mediated delivery of siRNA or antisense oligonucleotides, are gaining significant momentum for neuromuscular, metabolic, and rare diseases, reflecting growing convergence between antibody engineering and RNA therapeutics. Emerging modalities such as radioconjugates, degrader-antibody conjugates, and immune-stimulating antibody conjugates (ISACs) carrying STING or TLR agonists are also attracting increasing attention as companies explore new mechanisms beyond direct cytotoxicity.

 

In parallel, biomarker-guided patient selection, translational PK/PD modeling, and early developability assessment are becoming increasingly important, as clinical differentiation now depends not only on potency, but on demonstrating advantages in selectivity, tolerability, manufacturability, and mechanistic rationale. These trends are driving demand for more advanced analytical characterization, internalization assays, DAR profiling, and translational in vitro and in vivo models throughout ADC discovery and preclinical development. (Yu et al., 2026; Wang R et al., 2025)

 

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References

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