Identification of factors conferring resistance to trastuzumab deruxtecan in advanced gastric cancer: a translational study from the single-arm, phase II, DESTINY-Gastric06 trial.

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.