Antibody-drug conjugates (ADCs) have emerged as revolutionary agents in oncology, representing a precision-guided approach that targets cancer cells with high specificity while minimizing collateral damage to healthy tissues. This sophisticated therapy combines the selectivity of monoclonal antibodies with the potent cytotoxicity of chemotherapeutic payloads, effectively functioning as a “smart bomb” to eradicate malignant cells. Since the approval of the first ADC over 25 years ago, the field has witnessed the clinical introduction of more than 20 ADCs, showcasing their transformative potential. However, despite these advances, a major hurdle that continues to undermine the efficacy of ADCs is the development of tumor resistance mechanisms, which are multifaceted and complex.
Resistance to ADC therapy is not a singular phenomenon but an intricate network of adaptive processes employed by cancer cells to evade destruction. Tumors exhibit remarkable plasticity, often altering their surface antigen expression to reduce ADC binding or mutating target epitopes outright. This antigen modulation directly compromises the initial step of ADC action: antibody recognition and binding. Furthermore, resistance also manifests at the cellular internalization and trafficking level. Key proteins involved in endocytosis, such as caveolin-1, may be downregulated or functionally impaired, disrupting the internalization of ADCs and thereby limiting intracellular payload delivery.
Beyond the blockade at the membrane level, resistance mechanisms extend into intracellular organelle dysfunction. The lysosome, essential for proteolytic processing and payload liberation, can become impaired due to defective acidification, often caused by altered ionic homeostasis. Without proper lysosomal function, the cytotoxic payload remains entrapped and inactive, allowing cancer cells to survive despite ADC exposure. Additionally, cancer cells exploit efflux mechanisms mediated by ATP-binding cassette (ABC) transporters to actively pump out released cytotoxic agents before they can exert their lethal effects. This multidrug resistance phenotype complicates treatment by diminishing intracellular payload retention.
Compounding these cellular adaptations is the heterogeneity inherently present within tumor populations. Subsets of cancer cells lacking target antigen expression—antigen-negative subclones—serve as reservoirs of resistance. These resilient populations survive ADC treatment and drive disease relapse, highlighting the necessity for strategies capable of overcoming inter- and intratumoral heterogeneity. Importantly, resistance to ADCs is rarely attributable to a single mechanism. Rather, tumors coordinate multiple pathways simultaneously, forming a sophisticated defensive network against therapeutic assault.
Recognizing these challenges, researchers from Union Hospital, Tongji Medical College at Huazhong University of Science and Technology have compiled a comprehensive review that delves into the full gamut of ADC resistance mechanisms and the innovative counterstrategies emerging to overcome them. Their analysis spans every stage of ADC pharmacodynamics, from antigen-antibody engagement through intracellular payload release to eventual induction of cytotoxicity. This systematic exploration illuminates the complex biology of ADC resistance and directs the development of next-generation ADC therapeutics.
Among the forward-looking approaches detailed in the review, bispecific antibody-drug conjugates (BsADCs) represent a promising advancement. By simultaneously targeting two distinct tumor antigens, BsADCs address the problem of antigen heterogeneity and reduce the likelihood of tumor escape via antigen loss. Similarly, dual-payload ADCs, equipped with two complementary cytotoxic agents, aim to attack cancer cells through multiple mechanisms of cell death, thereby bypassing specific efflux or resistance pathways triggered by single-agent payloads.
This innovative review also casts light on immunostimulatory antibody conjugates (ISACs), a novel class of ADCs designed not only to kill cancer cells directly but also to reprogram the tumor microenvironment (TME) to enhance immunologic attack. By modulating immune components within the TME, ISACs help to overcome immune suppression, creating conditions that favor sustained anti-tumor responses in concert with ADC cytotoxicity.
The review further highlights the potential of rational combination regimens that synergize ADCs with established therapeutics. Combining ADCs with chemotherapy, targeted kinase inhibitors, anti-angiogenic agents, and immune checkpoint inhibitors represents an integrated strategy that attacks tumors on multiple fronts. A paramount clinical example is the EV-302 trial, where enfortumab vedotin combined with pembrolizumab demonstrated nearly double the progression-free survival compared to chemotherapy alone in urothelial carcinoma patients. This landmark trial underscores how combination therapies can potentiate ADC efficacy and delay resistance onset.
Deep mechanistic insights derived from this review underscore a crucial paradigm: ADC resistance is not a monolithic issue but a dynamic and multi-layered hurdle requiring multiplexed solutions. The authors stress that newly engineered ADCs must incorporate features such as bispecific antigen targeting, payload diversification capable of evading efflux pumps, and immune-modulatory functions to tip the balance in favor of tumor eradication. This holistic view extends beyond the tumor cell to include modulation of the surrounding microenvironment.
From a clinical perspective, the findings advocate for biomarker-guided patient selection as a pivotal step in maximizing ADC therapeutic benefit. Assessing levels of target antigen expression, evaluating lysosomal function, and measuring efflux pump activity could collectively inform predictions of treatment responsiveness. Equipping clinicians with such diagnostic tools is critical to personalize ADC therapies and circumvent futile treatments in resistant populations.
Moreover, the review cautions against the simplistic substitution of ADCs sharing the same cytotoxic payload class, emphasizing emerging evidence of cross-resistance among topoisomerase I inhibitor-based ADCs. This observation challenges the notion that ADCs are interchangeable and underscores the requirement for nuanced selection based on resistance profiles and payload mechanisms.
Ultimately, overcoming ADC resistance demands a fundamental shift toward integrated treatment regimens and next-generation ADC platforms with multi-mechanistic capabilities. By simultaneously targeting antigen heterogeneity, intracellular trafficking, efflux mechanisms, tumor microenvironment, and apoptotic pathways, these advanced therapeutics hold the promise to surmount the formidable defenses deployed by cancer. This integrated approach heralds a new era of precision oncology in which ADCs fulfill their promise as powerful and durable weapons against cancer.
The authors express guarded optimism: as we unravel the complex architecture of ADC resistance, the design of smarter ADC therapeutics—featuring bispecificity, payload innovation, and immunomodulation—provides a roadmap for conquering adaptive tumor resilience. This evolving understanding gears the oncology community toward more effective, tailored interventions capable of overcoming resistance and ultimately improving patient outcomes.
Subject of Research: Not applicable
Article Title: Drug resistance to antibody-drug conjugates: mechanisms, challenges, and perspectives
News Publication Date: 6-Apr-2026
References:
10.20892/j.issn.2095-3941.2025.0707
Image Credits: Cancer Biology & Medicine
Keywords: Drug resistance, Antibody-drug conjugates, Cancer therapy, Tumor heterogeneity, Bispecific ADCs, Dual-payload ADCs, Immunostimulatory antibody conjugates, ATP-binding cassette transporters, Lysosomal dysfunction, Tumor microenvironment, Combination therapy
