ADC Linker Payloads: 8 Most-Used Cytotoxic Agents in 2026

The payload is the business end of every antibody-drug conjugate. While antibody engineering and linker design receive considerable attention, the choice of cytotoxic warhead ultimately determines whether an ADC kills target cells effectively — or causes unacceptable off-target toxicity. With over 20 ADCs now approved globally and more than 200 in clinical trials, the field has converged on a handful of payload classes that balance potency, physicochemical properties, and manufacturability.

This article examines the eight ADC linker payloads dominating clinical and commercial pipelines in 2026, with attention to mechanism of action, potency ranges, approved products, and the linker chemistries that pair best with each warhead. For a broader overview of linker design principles, see our comprehensive guide to ADC linker technology.

Payload Comparison Table

Before examining each warhead individually, here is a side-by-side comparison of the eight most-used ADC cytotoxic payloads:

1. MMAE (Monomethyl Auristatin E)

Monomethyl auristatin E (MMAE) remains the most widely used ADC payload globally. This synthetic antimitotic agent binds to tubulin and prevents microtubule polymerization, arresting cells in the G₂/M phase and triggering apoptosis.

Potency and pharmacology. MMAE exhibits sub-nanomolar cytotoxicity (IC₅₀ typically 0.1–1 nM) against dividing cells. Its membrane permeability enables a pronounced bystander killing effect, where released MMAE diffuses into neighboring antigen-negative tumor cells — a property that proves advantageous in heterogeneous solid tumors.

Approved ADCs. Brentuximab vedotin (Adcetris) was the first MMAE-based ADC, approved in 2011 for Hodgkin lymphoma. Since then, polatuzumab vedotin (Polivy), enfortumab vedotin (Padcev), and tisotumab vedotin (Tivdak) have each demonstrated the versatility of this warhead across diverse target antigens.

Linker pairing. MMAE pairs predominantly with cleavable valine-citrulline (Val-Cit) dipeptide linkers featuring a para-aminobenzyloxycarbonyl (PAB) self-immolative spacer. Cathepsin B cleaves the Val-Cit bond inside the lysosome, triggering PAB elimination and clean MMAE release. PEG spacers between the maleimide and the Val-Cit-PAB unit improve solubility and reduce aggregation — particularly important at higher drug-to-antibody ratios. PurePeg’s Mal-PEG8-Val-Cit-PAB-MMAE provides an eight-unit monodisperse PEG spacer for precisely this purpose.

2. MMAF (Monomethyl Auristatin F)

Monomethyl auristatin F (MMAF) is the charged analog of MMAE. The C-terminal phenylalanine residue renders MMAF cell-impermeant, which eliminates bystander killing but significantly reduces off-target toxicity in normal tissues.

Potency and pharmacology. Free MMAF is roughly 10- to 100-fold less potent than MMAE in cell-based assays (IC₅₀ ~2–10 nM), but this comparison is somewhat misleading. Once released intracellularly following antibody internalization, the active metabolite achieves comparable tubulin binding. The lack of membrane permeability means cytotoxicity is confined strictly to antigen-positive cells.

Approved ADCs. Belantamab mafodotin (Blenrep), targeting BCMA for multiple myeloma, uses MMAF with a non-cleavable maleimidocaproyl (MC) linker. Although Blenrep had a complicated regulatory path, the MMAF payload itself continues to appear in multiple clinical candidates.

Linker pairing. MMAF is frequently paired with non-cleavable MC linkers, where the entire linker-payload fragment remains attached to a lysine residue after antibody degradation in the lysosome. For click-chemistry-based conjugation, PurePeg offers DBCO-PEG4-Val-Cit-PAB-MMAF for azide-bearing antibody constructs, and MC-Val-Cit-PAB-MMAF for conventional cysteine conjugation.

3. DM1 (Mertansine)

DM1 is a maytansinoid derivative that inhibits tubulin polymerization with exceptional potency (IC₅₀ 10⁻¹¹–10⁻¹⁰ M). It is 100- to 10,000-fold more potent than standard chemotherapy agents like doxorubicin.

Pharmacology. DM1 binds to the vinca alkaloid site on β-tubulin, suppressing microtubule dynamics. Its limited membrane permeability means that the bystander effect is modest compared to MMAE. The metabolite generated from non-cleavable linker degradation (lysine-SMCC-DM1) carries a charge that further restricts membrane transit.

Approved ADCs. Ado-trastuzumab emtansine (Kadcyla, T-DM1) is the benchmark, approved for HER2-positive breast cancer. T-DM1 uses a non-cleavable SMCC (succinimidyl 4-(N-maleimidomethyl)cyclohexane-1-carboxylate) linker conjugated to surface lysines. Despite being a first-generation conjugation approach with heterogeneous DAR, Kadcyla remains commercially successful.

Linker considerations. The non-cleavable SMCC linker provides excellent plasma stability. However, lysine-based conjugation produces heterogeneous mixtures (DAR 0–8), which is one reason newer DM1 programs are exploring site-specific conjugation methods with defined PEG spacers for improved homogeneity.

4. DM4 (Ravtansine)

DM4 is a sterically hindered maytansinoid with a methyl group adjacent to the disulfide bond, which modulates the rate of intracellular payload release.

Pharmacology. DM4 shares the tubulin-binding mechanism of DM1 but generates membrane-permeable metabolites upon intracellular reduction and S-methylation. This gives DM4-based ADCs a meaningful bystander killing effect — a deliberate design choice for targeting heterogeneous tumors where not all cells express the surface antigen.

Approved ADCs. Mirvetuximab soravtansine (Elahere), approved for FRα-positive ovarian cancer, uses DM4 with a cleavable sulfo-SPDB linker. The hindered disulfide provides tunable release kinetics: slow enough for plasma stability, fast enough for efficient intracellular processing.

Linker pairing. DM4 is typically linked through reducible disulfide bonds (SPDB or sulfo-SPDB linkers). The steric hindrance from the methyl groups flanking the disulfide controls the reduction rate, establishing a half-life of hours inside the reducing intracellular environment.

For a detailed discussion of how linker chemistry influences payload release kinetics, see our article on linker chemistry, ADC stability, and payload release.

5. SN-38

SN-38 is the active metabolite of irinotecan, a topoisomerase I inhibitor. Its use as an ADC payload represented a strategic departure from ultra-potent warheads toward moderately potent agents delivered at higher DAR values.

Pharmacology. SN-38 stabilizes the topoisomerase I–DNA cleavage complex, converting transient single-strand breaks into lethal double-strand breaks during DNA replication. With IC₅₀ values in the low nanomolar to sub-micromolar range (~1–50 nM depending on cell line), SN-38 is 100- to 1,000-fold less potent than auristatins or maytansinoids. The ADC compensates by achieving a high DAR of approximately 7.6.

Approved ADCs. Sacituzumab govitecan (Trodelvy) targets Trop-2 in triple-negative breast cancer and urothelial carcinoma. Its CL2A linker incorporates a pH-sensitive carbonate bond that hydrolyzes in the acidic lysosomal environment (pH ~5), releasing free SN-38. The moderate potency and high DAR strategy has proven effective in multiple solid tumor settings.

Linker pairing. The CL2A linker uses a short PEG spacer and a pH-labile carbonate linkage. The high DAR (~7.6) demands that the linker-payload not significantly increase hydrophobicity or cause aggregation — making hydrophilic PEG spacers particularly valuable. Explore PurePeg’s full catalog of cleavable linkers for reagents compatible with acid-labile conjugation strategies.

6. Dxd (Deruxtecan / DXd)

Dxd (also called DXd or MAAA-1181a) is the exatecan derivative used in Daiichi Sankyo’s DXd platform. It has arguably become the most consequential ADC payload of the past five years.

Pharmacology. Like SN-38, Dxd inhibits topoisomerase I, but with roughly 10-fold greater potency (IC₅₀ ~0.3–5 nM). Dxd is membrane-permeable and generates a substantial bystander effect. Its relatively short systemic half-life (~1.4 hours) limits toxicity from prematurely released payload — an elegant pharmacokinetic safety feature built into the molecular design.

Approved ADCs. Trastuzumab deruxtecan (Enhertu, T-DXd) has transformed the treatment of HER2-positive and HER2-low breast cancer, gastric cancer, and non-small cell lung cancer. Its clinical success has triggered a wave of Dxd-platform ADCs across the industry. Datopotamab deruxtecan (Dato-DXd) targets TROP2, and patritumab deruxtecan targets HER3.

Linker pairing. The Dxd platform uses a proprietary GGFG tetrapeptide cleavable linker with a maleimide-GGFG-NH spacer. Enzymatic cleavage by lysosomal peptidases releases Dxd cleanly. The DAR is tightly controlled at ~8 through site-specific conjugation to engineered interchain cysteines, yielding a homogeneous product despite the high drug loading. This approach sets the standard for next-generation ADC design.

7. PBD Dimers (Pyrrolobenzodiazepine Dimers)

Pyrrolobenzodiazepine (PBD) dimers are among the most potent ADC payloads in clinical use, with IC₅₀ values reaching the femtomolar range against some cell lines.

Pharmacology. PBD dimers bind covalently to the DNA minor groove, forming interstrand crosslinks at specific purine-guanine-purine sequences. Unlike alkylators that distort the DNA helix, PBDs fit snugly within the minor groove and do not significantly bend or unwind DNA — which makes them difficult for DNA repair machinery to detect. This stealth mechanism contributes to their extraordinary potency.

Approved ADCs. Loncastuximab tesirine (Zynlonta), targeting CD19 for relapsed/refractory diffuse large B-cell lymphoma, uses a PBD dimer payload (SG3199) connected through a Val-Ala dipeptide cleavable linker. The extreme potency of PBDs means that even low DAR values (typically 2–3) deliver sufficient cell killing.

Linker pairing. PBD-ADCs use cleavable peptide linkers, most commonly Val-Ala-PAB, with cathepsin-triggered release. Because of their extreme potency, precise DAR control is paramount — even modest over-conjugation can push the therapeutic index into unacceptable territory. Site-specific linker technologies become especially important here to achieve uniform DAR distributions.

8. Duocarmycin Analogs

Duocarmycins are DNA minor groove alkylating agents originally isolated from Streptomyces. Synthetic analogs like seco-DUBA and CC-1065 derivatives have been engineered for ADC applications, offering potency between that of auristatins and PBD dimers.

Pharmacology. Duocarmycins alkylate adenine at the N3 position within AT-rich DNA minor groove sequences. The resulting adducts disrupt DNA replication and trigger apoptosis. Several prodrug designs incorporate a self-immolative moiety that masks the alkylating seco-drug form until linker cleavage occurs inside the target cell.

Clinical status. While no duocarmycin ADC has reached regulatory approval as of mid-2026, multiple candidates are in Phase I/II trials. Trastuzumab duocarmazine (SYD985) and other constructs have shown activity in HER2-expressing tumors. The payload class remains of strong interest because duocarmycins are effective against both dividing and quiescent cells — addressing a limitation of tubulin-targeting warheads.

Linker pairing. Duocarmycin ADCs typically use cleavable Val-Cit or enzyme-labile linkers with PAB self-immolative spacers. The seco-drug design requires that the linker cleavage and cyclization cascade proceed in the correct sequence, which makes spacer chemistry and linker length critical parameters.

Choosing the Right Payload-Linker Combination

Payload selection is not simply about maximizing potency. Several factors interact:

• Target antigen expression level. Low-expression targets may require ultra-potent payloads (PBD dimers, duocarmycins) or high-DAR strategies (Dxd platform). High-expression targets can work with moderately potent warheads like auristatins.
• Tumor heterogeneity. Heterogeneous tumors benefit from bystander-competent payloads (MMAE, DM4, Dxd, SN-38) that can kill neighboring antigen-negative cells.
• Therapeutic index. Charged or cell-impermeant payloads (MMAF) limit off-target damage but sacrifice bystander activity.
• DAR requirements. The tolerable DAR depends on both payload hydrophobicity and linker design. Hydrophilic PEG spacers allow higher DAR without aggregation, as discussed in our ADC linker technology overview.

The linker is not a passive tether — it determines pharmacokinetics, release kinetics, conjugation site compatibility, and physicochemical properties of the whole construct. Monodisperse PEG spacers from PurePeg, such as endo-BCN-PEG4-Val-Cit-PAB-MMAE for click chemistry conjugation, provide defined molecular weight and consistent performance across batches.

What’s Next for ADC Payloads

Several trends are reshaping the ADC payload landscape heading into late 2026 and beyond:

Immunostimulatory payloads. Rather than direct cytotoxicity, some next-generation ADCs carry STING agonists or TLR ligands to activate antitumor immunity at the tumor site. These immunology-oriented payloads pair well with cleavable linkers that release the agonist specifically within the tumor microenvironment.

Dual-payload ADCs. Emerging designs conjugate two different payloads to the same antibody — for example, combining a tubulin inhibitor with a DNA-damaging agent to attack two independent survival pathways simultaneously.

Payload recycling. Some biparatopic ADC designs promote enhanced internalization and intracellular trafficking, which enables each antibody molecule to deliver payload across multiple internalization cycles.

These innovations will demand increasingly sophisticated linker chemistry. Consistent, well-characterized monodisperse PEG building blocks are essential for translating these concepts from bench to clinic.

Explore PurePeg’s ADC Linker Catalog

PurePeg offers a comprehensive portfolio of monodisperse PEG-based ADC linker-payloads, including MMAE and MMAF conjugates with various reactive handles. Browse our cleavable linker collection or contact our PEG specialists to discuss custom linker-payload requirements for your ADC program.