July 2025: The Rise of Multi-Payload ADCs in Oncology

Cancer remains a leading cause of death globally, and the projected 77% increase in incidence by 2050 highlights the limitations of current therapies such as chemotherapy and radiation. Antibody-drug conjugates (ADCs), which couple monoclonal antibodies with cytotoxic drugs, emerged to improve tumor targeting and reduce off-target effects. However, conventional single-payload ADCs often face challenges like drug resistance, toxicity, and limited efficacy. To address these issues, recent innovations focus on dual- or multi-payload ADCs that combine different cytotoxic agents or integrate therapeutic radionuclides, yielding synergistic effects and enhancing antitumor responses in preclinical models. Dual-payload ADCs are specifically designed to deliver two distinct drugs on a single antibody backbone, offering the potential to overcome resistance that emerges from mono-agent pressure while preserving the tumor-targeting precision of conventional ADCs.

Various dual-payload ADCs, especially those targeting HER2+ cancers, have demonstrated superior efficacy by combining drugs with different mechanisms. These constructs leverage synergistic effects and bystander killing to overcome tumor heterogeneity. Preclinical models show strong antitumor activity and acceptable safety, supporting efforts to refine human dosing through pharmacokinetic modeling. Some dual ADCs also include immunomodulators to activate immune responses, effectively eradicating tumors in aggressive cancer models without added toxicity. However, synergy is not universal, highlighting the importance of optimizing linker design, drug-to-antibody ratio, and conjugation method.

Homogeneous dual-payload conjugates can be achieved through advanced site-specific techniques, such as the use of branched multifunctional linkers, orthogonal amino acid chemistries, and dual enzymatic tagging systems. One strategy involves using branched adapters with orthogonally protected cysteines, enabling sequential deprotection and conjugation of two distinct drugs, exemplified by a SEAGEN-developed anti-CD30 ADC loaded with both MMAE and MMAF, which outperformed single-payload counterparts in resistant and heterogeneous tumor models. MedImmune further developed a trifunctional linker bearing maleimide, azide, and ketone groups to enable stepwise attachment of two payloads via oxime ligation and click chemistry. Alternatively, approaches using non-canonical amino acids (such as pAcF and pAMF) allow for highly controlled site-specific conjugation, as demonstrated in a FolRα-targeting immunostimulant ADC incorporating cytotoxins and immune agonists on separate antibody chains with >90% conjugation efficiency.

These strategies also facilitate flexible tuning of drug-to-antibody ratios (DARs), a critical parameter for balancing potency and minimizing toxicity. Importantly, clinical data underscore the urgency of such innovations: patients previously treated with Topo1i-based ADCs exhibit significantly reduced responses to subsequent Topo1i therapies, regardless of target antigen, emphasizing the need to switch payload classes. Dual-payload ADCs offer a solution by combining payloads like microtubule inhibitors and topoisomerase inhibitors, or cytotoxins with DDR inhibitors or immune agonists, on a single scaffold, thereby maximizing therapeutic reach and immune activation while reducing the likelihood of cross-resistance and redundant toxicity.    

Beyond improving therapeutic potency, multi-payload ADCs are increasingly being explored as theranostic platforms, as agents that combine therapeutic and diagnostic capabilities. Emerging strategies fuse cytotoxins with radioisotopes or imaging probes, enabling real-time tracking of drug distribution and tumor response while delivering potent cytotoxic effects. These constructs can improve tumor accessibility profiling and guide treatment decisions, especially in resistant or heterogeneous cancers. The integration of payloads such as immune agonists or DNA damage response inhibitors alongside traditional chemotoxins may further amplify antitumor immunity and allow for patient-specific treatment customization. Additionally, using orthogonal conjugation chemistries and engineered antibody sites enables precise control over payload composition and location, minimizing systemic toxicity and improving manufacturing consistency.    

Preclinical Studies: Dual-Payload ADCs in Development

Several innovative multi-payload ADCs are advancing through preclinical and early clinical pipelines, demonstrating potential to overcome resistance, broaden therapeutic windows, and tackle tumor heterogeneity.

• Dual-Payload HER2 ADC (MediLink)

Aimed at tackling resistance to Topo1i-based ADCs like Enhertu, this dual-payload HER2 ADC combines a topoisomerase I inhibitor and a tubulin inhibitor. MediLink employed two conjugation strategies to fine-tune DAR ratios and payload placement. The ADC displayed robust cytotoxicity in HER2-low and drug-resistant tumor models, including those overexpressing ABC transporters, showing promise in overcoming multidrug resistance mechanisms.

• CTPH-02 (Celltrion Pharm)

This HER2-targeting dual-payload ADC was designed to increase therapeutic index and address efficacy in antigen-low tumors. It combines MMAE with a cell cycle-regulating agent identified for its synergy with MMAE. CTPH-02 showed enhanced cytotoxicity in HER2-low cell lines and drug-resistant models, suggesting its suitability for broader patient populations with low HER2 expression or low TPS/IHC scores.

• TJ101 (Phrontline Biopharma)

A bispecific ADC targeting EGFR and B7-H3, TJ101 uses a “knobs-into-holes” IgG1 backbone with reduced EGFR affinity to limit toxicity and a camptothecin-derived payload (PY-4car2) for potent cytotoxicity. In vitro and in vivo studies across NSCLC, HNSCC, and breast cancer models demonstrated strong synergistic internalization, durable regressions, and superior activity over single-target ADCs. It also showed favorable tolerability in non-human primates, supporting its advancement.

• JSKN021 (Alphamab Oncology)

JSKN021 is a bispecific ADC targeting EGFR and HER3, two receptors often co-expressed in cancers. It features site-specific glycan conjugation of two distinct payloads—T01 (a topoisomerase I inhibitor) and MMAE—via cleavable linkers. The dual-payload configuration enhances tumor inhibition by addressing heterogeneity, with preclinical studies indicating superior efficacy versus single-payload ADCs.

• JSKN022 (Alphamab Oncology)

This multi-specific ADC targets PD-L1 and integrins ITGB6/8 using a single-domain antibody format based on Envafolimab. The conjugation of T01 to Fc glycans via glycan-specific technology allows for precise and stable drug loading. JSKN022 was designed to overcome resistance to checkpoint inhibitors, and preclinical data suggest it offers a novel therapeutic angle for PD-L1–resistant cancers.