Bohan Zhang, Lei Zhang, Cheng Liu, Tong Xie, Yifan Zhang, Xiao Wu, Yining Chen, Siyuan Cheng, Yang Feng, Yuxin Wang, Erke Gao, Hongquan Zhang, Lin Shen, Zhi Peng, Xiaofan Wei
Background: Trastuzumab deruxtecan (T-DXd) has revolutionized the therapeutic landscape for HER2-positive gastric cancer (GC). However, tumor heterogeneity poses a significant challenge in overcoming T-DXd resistance. This study aimed to delineate the mechanisms underlying primary and acquired resistance to T-DXd in GC. Methods: We performed single-cell RNA sequencing on GC tumor tissues from the DESTINY-Gastric06 study, including treatment-naive baseline samples and those with primary or acquired resistance to T-DXd. Dimensionality reduction and unsupervised clustering were applied to identify distinct cell clusters within the tumor tissues. High-dimensional weighted gene co-expression network analysis was employed to identify key gene modules associated with T-DXd resistance. Cell-cell communication was analyzed using CellChat. Key findings were experimentally validated through multiplex immunofluorescence, immunohistochemistry, and functional assays in cellular models. Results: Weighted gene co-expression network analysis identified the red and purple modules as being strongly correlated with primary and acquired T-DXd resistance, respectively. Notably, MUC3A was upregulated in patients with primary resistance and its overexpression was identified as a potential predictor of shorter progression-free survival in response to T-DXd therapy. Moreover, cystatin C, a gene implicated in linker cleavage, was upregulated during the development of acquired resistance. Tumor microenvironment profiling revealed that T-DXd initially promoted immune-cell infiltration and enhanced antigen presentation. However, with the development of resistance, the tumor microenvironment shifted to an immunosuppressive state, characterized by reactivation of transforming growth factor-beta signaling and upregulation of programmed cell death protein-1 (PD-1). Conclusion: These findings provide novel insights into mechanisms underlying T-DXd resistance and highlight potential therapeutic targets for overcoming T-DXd resistance in GC.