Targetable S100-RAGE signaling mediates intrinsic trastuzumab deruxtecan resistance in metastatic breast cancer.

PURPOSE: Trastuzumab deruxtecan (T-DXd) has improved outcomes in metastatic breast cancer; however, a substantial subset of patients experience early lack of clinical benefit that is not reliably predicted by routine clinicopathologic variables. In an institutional cohort of 109 T-DXd-treated metastatic lesions, HER2 expression level, ER/PR status, Ki-67 index, and metastatic site were not significantly associated with response, highlighting the need to define mechanistic determinants of intrinsic resistance.

EXPERIMENTAL

DESIGN

We performed spatial transcriptomic and proteomic profiling using NanoString GeoMx Digital Spatial Profiling on pretreatment bone, brain, and soft-tissue metastases from patients with clinical benefit (response) versus early progression (resistance) on T-DXd. Tumor (PanCK⁺) and immune (CD45⁺) compartments were analyzed to link tumor architecture and region-resolved signaling states with therapeutic response. Candidate resistance pathways were functionally evaluated in HER2-positive breast cancer cell lines and in vivo metastasis models treated with T-DXd alone or combined with the RAGE inhibitor TTP488.

RESULTS

Spatial proteogenomics revealed recurrent upregulation of S100 family alarmins in resistant tumor regions, associated with activation of a RAGE-centered pro-survival signaling program characterized by ERK, AKT, and STAT3 phosphorylation. Pharmacologic RAGE inhibition enhanced T-DXd-induced apoptosis, restored drug sensitivity in vitro, and significantly reduced metastatic burden in lung and brain metastasis models.

CONCLUSIONS

Spatial proteogenomics identifies a conserved S100-RAGE-driven survival state coupled to immune-excluded tumor architecture as a mechanism of intrinsic T-DXd resistance across metastatic niches. Targeting this pathway with an orally available RAGE antagonist restores T-DXd responsiveness and offers an immediately translatable strategy to overcome resistance in metastatic breast cancer.