antibody-drug conjugate

Overview

Antibody-drug conjugates (ADCs) are a class of targeted cancer therapeutics that combine the antigen-binding specificity of monoclonal antibodies with the cytotoxic potency of small-molecule payloads, typically linked via a chemical linker. By directing cytotoxic agents — such as camptothecin derivatives or tubulin inhibitors — to tumour-associated antigens expressed on cancer cell surfaces, ADCs aim to selectively kill malignant cells while minimizing systemic toxicity compared to conventional chemotherapy. The canonical ADC architecture consists of three components: a tumour-associated antigen-specific antibody, a cleavable or non-cleavable linker, and a cytotoxic payload that disrupts key cellular mechanisms such as mitosis and DNA replication. Upon antigen binding and internalization, the linker is cleaved in the lysosomal compartment, releasing the active drug intracellularly. This "Trojan horse" mechanism enables delivery of highly potent agents — often too toxic for systemic administration alone — at therapeutically relevant concentrations within the tumour microenvironment.

Over the past decade, ADCs have transitioned from a niche concept to a central pillar of oncology drug development. As of the mid-2020s, twelve ADCs have received FDA approval spanning hematologic malignancies and solid tumours, including breast cancer, urothelial carcinoma, cervical cancer, and non-small cell lung cancer (NSCLC). Their clinical success has prompted broad investigation into next-generation designs featuring novel payloads, site-specific conjugation chemistries, optimized drug-to-antibody ratios (DARs), and combination strategies alongside bispecific T-cell engagers, checkpoint inhibitors, PARP inhibitors, and Cdk4/6 inhibitors.

Recent Publications Summary

Recent publications demonstrate antibody-drug conjugates (ADCs) as emerging therapeutic agents across diverse malignancies, targeting multiple surface antigens and showing activity in disease settings with limited treatment options. These agents have been evaluated in EGFR-mutant non-small cell lung cancer, where trophoblast cell-surface antigen 2 (TACSTD2/Trop-2)-directed ADCs have recently achieved regulatory approval for use after resistance to third-generation EGFR tyrosine kinase inhibitors 41730505Feb. Similarly, sacituzumab govitecan, a Trop-2-directed ADC, demonstrated clinical activity in a phase II trial of patients with advanced and recurrent endometrial cancer who had progressed on prior chemotherapy and/or immunotherapy, including those with aggressive histologies such as serous carcinoma, carcinosarcoma, and grade 3 endometrioid tumors 42132892May. ADCs have also been incorporated into emerging combination strategies for other malignancies; for example, a Nectin-4-targeted ADC is being evaluated in combination with KRAS G12D inhibitors in metastatic pancreatic cancer 42571010Aug, while HER2-targeting ADCs are part of the growing therapeutic arsenal for hormone receptor-positive, HER2-negative breast cancer 42266036Jun.

Beyond epithelial malignancies, IL1RAP-targeting ADCs have shown preclinical promise in oncofusion-driven Cancers including Ewing sarcoma, anaplastic large cell lymphoma, and ETV6-NTRK3-positive sarcomas, with engineered constructs carrying diverse cytotoxic payloads demonstrating potent tumor growth inhibition and durable regression in xenograft and syngeneic models 41973074Apr. These agents successfully reduced metastatic dissemination in vivo while showing a favorable safety profile, with no detectable normal tissue toxicity observed even in non-human primate studies 41973074Apr. ADCs have been included in novel therapeutic strategies for metastatic castration-resistant prostate cancer as agents to overcome resistance to conventional androgen receptor pathway inhibitors 41992975Apr.

A significant challenge limiting ADC efficacy is acquired resistance through subpopulation selection. In HER2-heterogeneous breast cancer, HER2-low tumor subpopulations drive resistance to HER2-targeted ADCs such as trastuzumab deruxtecan, while remaining sensitive to HER2 kinase inhibitors 41925564Apr. Mechanistic studies identified USP9X as a sensitizer of HER2-low cells to ADC therapy, with USP9X inhibition enhancing lysosomal targeting and payload release, thereby reducing tumor recurrence 41925564Apr. In EGFR-mutant lung cancer, novel combination strategies pairing chemotherapy with amivantamab or ivonescimab are being explored alongside ADCs to overcome resistance 41730505Feb.

A major limitation to broader ADC implementation is their restriction to intravenous administration, contrasting with monoclonal antibodies which have successfully transitioned to subcutaneous delivery 42002047Apr. The transition to subcutaneous ADC dosing faces specific technical barriers including tissue poroelasticity, extreme concentration requirements, non-Newtonian injectability challenges, route-dependent linker degradation, and payload-driven interfacial instability 42002047Apr. However, these barriers are increasingly recognized as tractable engineering targets amenable to advanced materials approaches, positioning subcutaneous ADC delivery as a potential future mechanism to enhance patient convenience and system efficiency in cancer care 42002047Apr.

What Changes, What Holds

1. TACSTD2 and Trop-2-directed ADCs extend approved indications to EGFR-mutant lung cancer and endometrial disease
REINFORCES Regulatory approval now extends to EGFR-mutant NSCLC and Trop-2 ADCs demonstrate activity across endometrial histologies, including aggressive subtypes 41730505Feb42132892May. Combination evaluation with KRAS inhibitors in pancreatic cancer and incorporation into HER2-negative breast cancer regimens continue the established strategy. These applications broaden the patient populations and therapeutic contexts the Overview already identifies, but neither the ADC mechanism nor the class principle shifts.

2. IL1RAP-targeting ADCs achieve durable tumor regression in fusion-driven sarcomas with favorable preclinical safety
REINFORCES IL1RAP-directed constructs induce tumor regression in Ewing sarcoma, anaplastic large cell lymphoma, and ETV6-NTRK3 sarcomas, with acceptable safety in non-human primates 41973074Apr. Fusion-driven sarcomas were not listed in the Overview's cancer scope, yet the mechanism—targeted toxin delivery to tumor-associated antigens—exactly matches the baseline description. Application to new tumor types and new targets reinforces rather than displaces the established ADC strategy.

3. Acquired HER2-low resistance to trastuzumab deruxtecan can be reversed by enhancing lysosomal trafficking through USP9X inhibition
NEW DIRECTION HER2-heterogeneous breast tumors develop resistance by selecting for HER2-low subpopulations, a failure mechanism the Overview does not discuss 41925564Apr. USP9X emerges as a molecular handle on the lysosomal delivery step the Overview describes—inhibiting it restores payload release in otherwise resistant cells. This identifies both how ADC efficacy can be lost and a pharmacologic pathway to recover it, expanding understanding of ADC reversibility beyond what the baseline addresses.

4. Subcutaneous ADC delivery is constrained by solvable materials-engineering barriers, not fundamental pharmacology
NEW DIRECTION IV-only administration sharply limits ADC accessibility compared to subcutaneous monoclonal antibodies; the barriers are not pharmacologic but physical—tissue poroelasticity, extreme concentration demands, non-Newtonian injectability, linker degradation, payload instability 42002047Apr. The baseline ignores route of administration entirely. Identifying these as engineerable problems rather than immutable constraints reframes subcutaneous delivery as a design frontier rather than an impossible goal, expanding the developmental scope of ADC deployment.

Overview update candidates: FDA-approved Trop-2 ADCs in EGFR-mutant NSCLC and endometrial Cancers; emerging combinations with KRAS inhibitors; IL1RAP-targeting ADCs in fusion-driven sarcomas; acquired HER2-low resistance mechanisms and USP9X-mediated reversal strategies; subcutaneous delivery as an engineering-solvable development frontier.