Dual Payload ADC: Advances in Targeted Therapy

Dual-payload antibody-drug conjugates pack two different cancer-killing agents onto a single antibody, delivering both directly into tumor cells at once. This approach aims to solve a stubborn problem: patients treated with conventional ADCs, which carry only one type of drug, frequently develop resistance and relapse. By combining two mechanistically distinct warheads on the same targeting molecule, dual-payload ADCs function as a form of molecular combination therapy designed to raise the barrier to resistance and hit cancer through multiple pathways simultaneously.¹ The field is still largely preclinical, but the first candidates have entered human trials, and the underlying science has matured rapidly.

Why One Payload Is Not Always Enough

Single-payload ADCs have already changed cancer treatment in meaningful ways. Drugs like trastuzumab deruxtecan and sacituzumab govitecan have transformed outcomes across multiple solid tumors. But most patients eventually relapse. The escape routes are varied: tumor cells can lose the surface antigen the antibody targets, pump the drug back out through efflux transporters, alter the molecular target the payload is meant to hit, or simply be so genetically diverse within a single tumor that some cell populations were never vulnerable in the first place.¹ This creates what researchers describe as a “post-ADC treatment gap,” where patients who progress after an ADC have limited options, especially if the next therapy relies on the same type of payload.

That last point deserves emphasis. Clinical data have shown that patients previously treated with a topoisomerase I inhibitor-based ADC had only about a 15% response rate when switched to another ADC carrying the same class of payload, regardless of whether the antibody targeted a different antigen.² The resistance, in other words, was to the drug itself, not just the delivery address. Dual-payload ADCs confront this head-on by ensuring that even if cells develop resistance to one drug, the second warhead can still do its job.

How Two Payloads Work Together

The core logic is to pair drugs that attack cancer cells through completely different biological mechanisms, so resistance to one does not automatically confer resistance to the other. Several pairing strategies have emerged, each with its own rationale.

Topoisomerase I inhibitor plus microtubule inhibitor: One drug interferes with DNA replication while the other disrupts the structural scaffolding cells need to divide. A clinical combination study of sacituzumab govitecan (a topoisomerase I inhibitor ADC) and enfortumab vedotin (a microtubule inhibitor ADC) has already validated this concept by increasing response rates without significantly increasing toxicity.³ Building both payloads onto a single antibody takes this principle further.
Topoisomerase I inhibitor plus DNA-damage-response inhibitor: When a topoisomerase I inhibitor creates DNA breaks, a PARP inhibitor or similar agent blocks the cell’s repair machinery, compounding the damage.
Cell-permeable plus cell-impermeable payloads: Some drugs, like MMAE, freely cross cell membranes and kill neighboring tumor cells that the antibody never directly bound. Others, like MMAF, stay inside the cell they enter but are harder for efflux pumps to expel. Pairing them covers both angles: the membrane-permeable drug handles bystander killing of nearby cells, while the impermeable drug resists being pumped out by multidrug-resistance transporters.⁴
Cytotoxic plus immunostimulatory payloads: Instead of carrying two cell-killing drugs, some designs combine a traditional cytotoxic agent with a molecule that activates the immune system inside the tumor. One study paired an ADC carrying SN-38, a topoisomerase I inhibitor, with an immune-stimulating antibody conjugate delivering a STING agonist into immune cells. Mice treated with the combination had average tumor volumes roughly 40% of those in the ADC-only group by day 14.⁵

The emphasis on “non-overlapping resistance liabilities” keeps coming up across the literature. It is not enough to throw two potent drugs onto an antibody. The drugs need to be chosen so that the known escape mechanisms for one are irrelevant to the other.¹

Tackling Tumor Heterogeneity and the Bystander Effect

Tumors are not uniform masses of identical cells. A single tumor often contains subpopulations with different levels of the target antigen, different genetic mutations, and different vulnerabilities. This heterogeneity is one of the main reasons ADCs fail: the antibody binds and kills cells expressing the target, but leaves behind antigen-negative neighbors that can repopulate the tumor.

Dual-payload ADCs offer a built-in countermeasure through the bystander effect. When a cell-permeable payload is released inside a target-positive cell, some of it leaks out and kills surrounding cells, including those that lack the antigen. In a study using a heavy-chain antibody conjugate targeting Trop2, the dual-payload design showed superior cancer-cell killing and bystander activity not only in tumors with high Trop2 expression but also in mixed populations where some cells expressed the antigen and others did not.⁶ Similar bystander killing has been demonstrated with a bispecific construct targeting EGFR and c-MET, where cleavable linkers enabled the released drug to reach antigen-negative cells in mixed cultures.⁷

A related concept has emerged in small-molecule drug conjugates, where a dual-degrader payload showed improved targeted killing plus a strong bystander effect while significantly reducing the off-target uptake that can cause side effects in healthy tissue.⁸ Reducing nonspecific release is important because with two potent drugs on board instead of one, the consequences of unintended exposure to normal tissue become a bigger concern.

The Pharmacokinetic Puzzle of Two Drugs in One

Attaching two different drugs to the same antibody introduces a pharmacokinetic challenge that single-payload ADCs do not face: the two payloads may be released at very different rates. One platform that combined exatecan (a topoisomerase I inhibitor) with triptolide (a multi-target natural product) illustrates this clearly. In simulated blood plasma, triptolide-containing molecules dropped to about 38% after 24 hours, fell below 2% by one week, and became undetectable by three weeks. Exatecan-containing molecules, by contrast, still had roughly 46% remaining at three weeks.⁹

In monkeys, the picture was consistent: the triptolide component had a half-life of about 22.6 hours, while the exatecan component lasted roughly 56.2 hours.⁹ Rather than being a problem, the researchers suggested this “dual asynchronous release” may actually contribute to efficacy by exposing tumor cells to different drugs at different times, extending the window of vulnerability. But it does mean that dosing schedules, safety margins, and drug-to-antibody ratios need careful optimization for each payload independently, a degree of complexity that single-payload ADCs avoid.

Bispecific Antibodies Meet Dual Payloads

Some groups are layering another innovation on top: building dual-payload ADCs on bispecific antibodies, which bind two different antigens instead of one. This addresses two problems at once. The bispecific targeting reduces the chance that antigen loss on one marker will let cancer cells escape, while the dual payload reduces the chance that resistance to one drug will do the same. A platform combining MMAF and SN-38 on a bispecific antibody outperformed single-payload bispecific ADCs in killing cancer cells across multiple cell lines. It also inhibited non-dividing cells, which tend to resist traditional ADC payloads, and produced stronger tumor shrinkage in animal models.¹⁰

The bispecific EGFR/c-MET dual-payload construct IBI3028, developed by Innovent Biologics, has moved furthest toward the clinic among bispecific dual-payload ADCs and is described as the first clinical-stage molecule of its kind.⁷ Targeting two receptor tyrosine kinases that frequently co-drive cancer growth in lung and other solid tumors, IBI3028 represents the convergence of the bispecific and dual-payload trends into a single molecule.

Head-to-Head Preclinical Results

The critical question for dual-payload ADCs is whether carrying two drugs actually improves outcomes compared to single-payload designs, and the preclinical evidence is accumulating in their favor. The exatecan-triptolide ADC targeting TROP2 (called hRS7-E+T, now in human trials as KH815) was compared head-to-head against datopotamab deruxtecan, a single-payload ADC carrying a topoisomerase I inhibitor. In a lung cancer model with high TROP2 expression, datopotamab deruxtecan achieved a tumor growth inhibition rate of about 97% at 5 mg/kg. The dual-payload ADC at the same dose achieved over 105% inhibition, meaning tumors were shrinking beyond their starting size. At the highest dose tested, all five animals showed complete tumor regression by day 31.⁹

Dual-payload ADCs also outperformed single-payload versions specifically in models designed to mimic clinical resistance. In tumor models with low antigen expression or acquired resistance to topoisomerase I inhibitor ADCs, dual-payload constructs combining a topoisomerase I inhibitor with a microtubule inhibitor showed superior anti-tumor activity compared to either mono-payload ADC.³ In lung cancer cell-line studies, dual-target dual-payload ADCs using a microtubule agent and a topoisomerase I inhibitor were more effective at inhibiting cell growth across multiple lines and showed superior activity even in models normally resistant to ADC treatment.²

These results are encouraging but carry the usual caveats of preclinical work. Mice and cell lines do not always predict human outcomes, and the therapeutic window, meaning how much better the drug is at killing cancer than it is at harming normal tissue, is harder to evaluate in animal models than in patients.

Manufacturing Complexity and Design Trade-Offs

Building a dual-payload ADC is substantially harder than building a single-payload version. With one payload, the main manufacturing challenge is attaching a consistent number of drug molecules to the antibody at defined positions. With two payloads, you need to do that twice, on the same antibody, without the two conjugation reactions interfering with each other. This typically requires orthogonal chemistry, meaning two attachment strategies that are chemically independent and can be performed in sequence without cross-reacting.

A translational development roadmap for dual-payload ADCs emphasizes that successful design depends not just on picking two good drugs but on satisfying manufacturability requirements alongside pharmacological ones. The drug-to-antibody ratio for each payload matters for potency and toxicity, and the ratio between the two payloads matters for synergy.¹ Get the ratio wrong and the combination could be additive instead of synergistic, or one payload might dominate while the other is present in too low a quantity to contribute. Getting consistent, homogeneous products at manufacturing scale remains one of the field’s biggest practical hurdles.

The push toward site-specific conjugation, where payloads are attached at engineered, precisely defined positions on the antibody rather than at random surface sites, is helping address this. Site-specific methods produce more uniform products with more predictable pharmacokinetics, and they give chemists designated attachment points for each of the two payloads.¹¹

Dual-Payload ADCs Versus ADC Cocktails

An obvious question is: why bother building both drugs onto one antibody? Why not just give patients two separate ADCs at the same time? There are reasons the single-molecule approach might be preferable. When two ADCs are co-administered, each competes for the same antigen on the cell surface, potentially reducing the uptake of both. A dual-payload ADC ensures that every antibody molecule that binds a cancer cell delivers both drugs simultaneously. It also simplifies dosing: one molecule means one pharmacokinetic profile to manage (albeit a complicated one), rather than two independent drugs with their own dosing schedules and toxicities.

Dual-payload ADCs also guarantee that the two drugs reach the same individual cell. With an ADC cocktail, one cell might internalize mostly drug A while another gets mostly drug B, diluting any synergistic benefit. With a dual-payload molecule, every targeted cell receives both payloads in a fixed ratio.¹² That said, single-molecule combinations also lock in that ratio, and it may not be the ideal ratio for every patient or tumor type. Cocktails offer more dosing flexibility, even if they lack the co-delivery precision.

Where the Clinical Pipeline Stands

The field has moved beyond academic curiosity, but it is still early. The most advanced dual-payload ADC in clinical development is KH815, the exatecan-triptolide conjugate targeting TROP2, which has entered first-in-human trials.¹ IBI3028, the bispecific dual-payload ADC targeting EGFR and c-MET, is another first-in-class clinical-stage candidate.⁷ Both are being studied in advanced solid tumors where patients have limited remaining options.

No dual-payload ADC has yet received regulatory approval, and there are significant uncertainties ahead. Safety data from human trials are still sparse. The asynchronous release profiles seen in preclinical studies mean toxicologists are watching for delayed or overlapping side effects from the two payloads. And the manufacturing challenges described above will need to be solved at commercial scale, not just in research laboratories, before any of these molecules can reach patients broadly.

Patient Selection in a Two-Payload World

Figuring out which patients benefit most from a dual-payload ADC will likely require rethinking diagnostic approaches. Current companion diagnostics for single-payload ADCs typically measure how much of the target antigen a tumor expresses. For dual-payload ADCs, that remains important, but additional factors come into play. If one payload targets a DNA repair pathway, does the patient’s tumor have a relevant repair deficiency that would make it more sensitive? If one payload relies on the bystander effect, is the tumor heterogeneous enough that bystander killing matters?

The observation that payload-class resistance crosses antigen boundaries, with patients responding poorly to a second topoisomerase I inhibitor ADC even when it targeted a different protein, suggests that a patient’s prior treatment history might be as important as their tumor’s surface markers.² Dual-payload ADCs could be positioned specifically for patients who have already progressed on a single-payload ADC, using the second warhead to bypass the resistance their tumor has developed. But that positioning will require clinical trials designed to enroll post-ADC patients, and those studies are only beginning.

Immune-Activating Payloads and the Next Frontier

Perhaps the most conceptually ambitious direction for dual-payload ADCs moves beyond combining two cell-killing drugs and instead pairs a cytotoxic payload with a molecule designed to wake up the immune system inside the tumor. The idea is that the cytotoxic payload shrinks the tumor and releases fragments that the immune system can recognize, while the immunostimulatory payload, such as a STING agonist or a toll-like receptor agonist, primes nearby immune cells to mount a sustained attack. The study combining a CEA-targeting ADC with an immune-stimulating antibody conjugate delivering a STING agonist found that improved FcγR engagement allowed the immunostimulatory agent to be better delivered into immune cells, while the cytotoxic ADC component benefited from increased internalization driven by two non-competing antibodies binding the same antigen.⁵

This pairing raises the tantalizing possibility that a dual-payload ADC could produce durable responses by engaging both the drug and the patient’s own immune system. It also adds yet another layer of complexity: the pharmacokinetics, toxicology, and dosing considerations for an immune-activating payload are fundamentally different from those of a cytotoxic drug. The therapeutic window might be defined not by organ toxicity but by cytokine storms or autoimmune flares. The field is watching these combinations closely, but clinical data remain years away for most of them.

1
PubMed Central. From Unmet Medical Need to Drug Candidate: A Translational Therapeutic Development Roadmap Illustrated by Dual-Payload Antibody-Drug Conjugates
2
PubMed Central. Engineering the Future of ADCs in Non-Small Cell Lung Cancer
3
AACR Journals (Cancer Research). Abstract 2870: Enhancing Topo1i ADC efficacy: development of homogeneous dual-payload ADCs combining Topo1i with microtubule inhibitors or PARP inhibitors
4
The Oncologist. Overcoming resistance to antibody-drug conjugates: mechanisms and emerging strategies
5
PubMed Central. Dual Payload ADC: Advances in Targeted Therapy
6
Chemical Engineering Journal. A dual-payload heavy-chain antibody conjugate boosting bystander effect for heterogeneous tumor therapy
7
Journal of Clinical Oncology. Preclinical data of IBI3028, the first clinical-stage bispecific dual-payload ADC, targeting EGFR/c-MET–positive advanced solid tumors
8
PubMed. Dual-payload small-molecule drug conjugates enable bystander anticancer activity with reduced nonspecific release
9
Molecular Cancer Therapeutics. A Novel Dual-Payload ADC Platform Integrating Exatecan and Triptolide to Enhance Antitumor Efficacy and Overcome Resistance
10
PubMed Central. A Dual-Payload Bispecific ADC Improved Potency and Efficacy over Single-Payload Bispecific ADCs
11
PubMed Central. Homogeneous antibody-drug conjugates with dual payloads: potential, methods and considerations
12
PubMed. Dual-payload antibody-drug conjugates: Taking a dual shot