In vivo antibody-ADC click turns ADC design into a modular conjugation problem
The reported system uses two bioorthogonal handles. An EGFR-targeting antibody, panitumumab, is modified with trans-cyclooctene (TCO). A HER2-directed ADC, trastuzumab deruxtecan (T-DXd), is modified with tetrazine. The antibody is dosed first, followed 24 hours later by the tetrazine-bearing ADC. The two components are then covalently connected through inverse electron demand Diels-Alder (IEDDA) chemistry.
That sequence changes the development question. Instead of engineering a fixed bispecific ADC before dosing, the study treats the targeting antibody and cytotoxic ADC as separate modules that can be assembled after systemic delivery. The same concept was also explored with T-DM1, another HER2-directed ADC backbone, which makes the chemistry platform broader than a single linker-payload format.
The Nature paper is available through DOI: 10.1038/s41586-026-10789-w.
Why TCO-tetrazine pairing matters
IEDDA ligation is attractive because TCO and tetrazine can react rapidly under biological conditions without requiring native functional groups on proteins. In this study, that reaction is used to connect an EGFR-targeting antibody to a HER2-directed ADC after both molecules have reached the in vivo environment.
For a chemistry team, that creates several linked specifications. The TCO handle must remain sufficiently stable before reaction. The tetrazine handle must survive ADC modification and circulation long enough to meet the TCO-bearing antibody. The handle density must be high enough for ligation without damaging antibody behavior, ADC stability, or payload-related properties. Those are not generic formulation questions; they are conjugation-route and analytical-control questions.
This is where modular ADC design starts to depend on building-block quality. TCO derivatives, tetrazine derivatives, DBCO reagents, azide-installation chemistry, and glycan-remodeling steps become part of the same control strategy. Small changes in handle structure or installation site can affect reaction kinetics, hydrophobicity, aggregation risk, and biodistribution.
What the preclinical data showed
In a bilateral xenograft model, the authors paired a HER2-ultralow, EGFR-high A431 tumor with a HER2-positive, EGFR-low NCIN87 tumor. Single-antibody Cu-64 labeled trastuzumab-tetrazine showed about 3.75 %ID g-1 uptake in A431 tumors. With panitumumab-TCO mediated click pairing, A431 uptake increased to about 11.90 %ID g-1, a reported 3.2-fold increase.
The paper also reports preclinical activity in HER2-low heterogeneous breast cancer models and HER2-negative, EGFR-high pancreatic cancer models. T-DXd or T-DM1 alone, or antibody-plus-ADC combinations without covalent ligation, had limited activity in those models. Covalently ligated antibody-ADC click constructs reduced tumor volume and prolonged survival in the reported mouse studies.
For resistance-oriented experiments, EGFR protein levels were about 2.1-fold higher in tumors that did not respond to T-DXd than in responders. Switching T-DXd non-responding animals to panitumumab-TCO plus T-DXd-tetrazine reduced tumor growth in 5 of 9 mice. In a trastuzumab-resistant BT474 model, 6 of 10 mice were non-responders to T-DXd; pertuzumab-TCO plus T-DXd-tetrazine produced tumor suppression in 5 of those 6 non-responder mice.
These findings remain preclinical. They should be read as model-based evidence for a modular conjugation design, not as clinical translation or patient-response evidence.
Site-specific Fc-glycan installation is the process-relevant part
The study did not rely only on random antibody modification. The authors also installed click handles site-specifically through Fc-glycan engineering: azide groups were introduced enzymatically on Fc glycans, followed by azide-DBCO conjugation of tetrazine or TCO. The work reports reduced batch variability and about a twofold decrease in liver accumulation versus random conjugation.
That detail is highly relevant for ADC process development. Random conjugation can create heterogeneous distributions of modified species, which complicates batch comparability, analytical release, and interpretation of in vivo behavior. Fc-glycan-directed installation gives the conjugation team a defined region for handle placement while preserving the antigen-binding domains.
The approach was demonstrated across antibodies targeting HER2, EGFR, PD-L1, PSMA, and VEGF. That panel suggests the chemistry is not limited to one antibody sequence, although each antibody and ADC combination would still need its own stability, conjugation, and analytical qualification.
Development implications for modular ADC programs
A modular antibody-ADC click format shifts attention from one final construct to a controlled set of components. Development teams would need to characterize the antibody-handle intermediate, the ADC-handle intermediate, residual small-molecule reagents, conjugation efficiency, species distribution, aggregation, linker and payload stability, and the ligated product formed after click reaction.
Analytical methods also become more demanding. LC-MS, HIC, SEC, peptide mapping, glycan analysis, radiolabeling studies, and orthogonal purity assays may all be needed to connect material attributes with biological performance. The same applies to scale-up: a modular system is only useful if TCO/tetrazine installation can be reproduced with tight control over handle loading and impurity profiles.
The broader takeaway for CHEMOS readers is that ADC innovation is becoming more dependent on precise chemical handles and site-specific installation strategies. The biology defines the targeting problem, but the success of a modular format depends on whether the conjugation chemistry can be controlled, verified, and transferred into a robust development workflow.
FAQ
What is antibody-ADC click?
Antibody-ADC click is a modular strategy in which an antibody and an ADC are separately modified with compatible bioorthogonal handles, such as TCO and tetrazine, and then covalently ligated through click chemistry after administration in preclinical models.
Why are TCO and tetrazine used?
TCO and tetrazine participate in IEDDA ligation, a fast bioorthogonal reaction that can connect two modified biomolecules under biological conditions. Their stability, reaction rate, and installation chemistry are critical material attributes.
Why does Fc-glycan conjugation matter?
Fc-glycan-directed installation can place click handles in a more defined region of the antibody than random lysine or cysteine modification. That can reduce heterogeneity and make analytical control more tractable.
Is this a clinical ADC approach?
The reported work is preclinical. The findings support a modular conjugation concept in mouse models, but they do not establish clinical efficacy, safety, dosing, or patient benefit.
Reference
- Simo C., Vanover A. C., D'Oliveira Albanus R. et al. "Modular in vivo antibody-ADC click to reverse drug resistance in tumours." Nature, 2026. DOI: 10.1038/s41586-026-10789-w