AKR1C1 Promotes ADC Resistance by Altering Uptake and Export

Although antibody–drug conjugates (ADC) have transformed the standard of care for patients with metastatic urothelial carcinoma, primary and acquired resistance remain major obstacles to achieving durable clinical benefit. To investigate potential mechanisms of resistance to the NECTIN4-targeting ADC enfortumab vedotin, Wang, Chen, Wang, and colleagues engrafted NECTIN4+ tumor cells from untreated patient tissues into humanized mice thereafter exposed to multiple cycles of ADC therapy. Single-cell RNA sequencing analysis before and after treatment highlighted a population of cancer cells within ADC-resistant tumors that retained abundant surface expression of the target yet accumulated significantly less intracellular levels of the cytotoxic payload. Resistant tumors exhibited suppression of genes involved in endocytosis and pathways previously reported to be involved in ADC receptor internalization, whereas there was an enrichment in pathways related to membrane shedding and vesicle secretion, suggesting that tumors become resistant, not by altering target expression but by mitigating ADC uptake. Mechanistically, AKR1C1 emerged as a key mediator of this phenomenon by directly binding the intracellular domain of NECTIN4 and blocking AP2M1-dependent clathrin-mediated endocytosis, thereby impairing ADC internalization and delivery to lysosomes. In parallel, AKR1C1 recruited WWP2, an ESCRT-related E3 ligase that promoted extracellular vesicle formation and subsequent export of NECTIN4–ADC complexes. Upstream of these processes, the transcription factor ELF3 was determined to drive this resistance program through coordinated upregulation of both NECTIN4 and AKR1C1. Importantly, single-cell spatial transcriptomic analyses of paired tumor specimens from patients with metastatic urothelial carcinoma pre- and post-ADC plus immune checkpoint blockade validated the human relevance of these observations, as NECTIN4high tumor cells with coordinated upregulation of AKR1C1 and ELF3 were enriched in post-treatment samples. Pharmacologic disruption of AKR1C1 restored ADC uptake, increased intracellular cytotoxic payload concentrations, enhanced tumor control, and improved survival in preclinical mouse models, with additional benefit observed when combined with PD-1 blockade. These findings position endocytic evasion as a clinically relevant mechanism of ADC resistance beyond target downregulation and suggest the therapeutic potential of targeting membrane trafficking for optimal ADC efficacy.Wang Y, Chen Z, Wang W, Jiang L, Liang X, Liu Z, et al. Endocytic evasion confers resistance to antibody-drug conjugates therapy in cancer. Cancer Cell 2026;44:1201–17.Note: Research Watch is written by Cancer Discovery editorial staff. Readers are encouraged to consult the original articles for full details. For more Research Watch, visit Cancer Discovery online at https://aacrjournals.org/cdnews.