Spatial profiling of patient-matched HER2 positive gastric cancer reveals resistance mechanisms to targeted therapy.

Abstract

Human epidermal growth factor receptor 2 (HER2; <i>ERBB2</i>) is overexpressed or amplified in 15-20% of gastric cancers (HER2+ GC). Within individual HER2+ GCs, HER2/<i>ERBB2</i> expression is often variable. Although HER2 therapeutic targeting improves outcomes for HER2+ GC patients, acquired resistance is frequent. To spatially interrogate HER2+ GC interpatient and intrapatient heterogeneity and resistance mechanisms associated with HER2-targeting agents (trastuzumab, trastuzumab deruxtecan (T-DXd)). Spatial transcriptomic analysis (GeoMx Digital Spatial Profiler) was applied to >1500 regions of interest in 30 GCs-these contained 15 HER2+ GCs treated with trastuzumab and T-DXd subsequently. Analysis of patient-matched samples with acquired trastuzumab or T-DXd resistance revealed escape mechanisms. Results were validated by immunohistochemistry, independent cohorts and patient-derived xenografts and organoids. HER2+ tumours exhibited <i>PD-L1</i> expression within the spatial tumour microenvironment. We observed increased expression of CLDN18.2, a promising therapeutic target, in trastuzumab-resistant tumours. One-third of HER2+ GC patients developed epithelial-mesenchymal transition (EMT) on trastuzumab resistance, associated with <i>PD-L1</i> and <i>CCL2</i> upregulation. Another third of trastuzumab-resistant HER2+ GC patients activated the endoplasmic reticulum-associated degradation (ERAD) pathway including genes such as <i>GOLM1</i>. HLA loss and increases in oxidative phosphorylation pathways were observed in T-DXd-resistant GCs. Our results delineate multiple acquired resistance mechanisms to trastuzumab and T-DXd in HER2+ GC <i>in vivo</i>. This information may guide trials combining trastuzumab or T-DXd with new agents to enhance the efficacy and durability of HER2 blockade.