Cytotoxic and immunogenic signals of small extracellular vesicles from melanoma cells exposed to auger targeted radionuclide therapy.

PURPOSE: Targeted radionuclide therapy (TRT) using beta emitters is an established tool for eradicating tumor cells; however, attention is increasingly focused on high-linear energy transfer particles, such as Auger electrons emitted during Auger TRT, due to their ability to generate bystander and immunological responses. In this context, we investigated whether extracellular vesicles (EVs) from cancer cells exposed to Auger TRT contribute to these responses.

MATERIALS AND

METHODS

EVs were purified from B16F10 melanoma cells exposed to TRT with the Auger emitter 125I-TA99 (TRT-EVs). The involvement of immunogenic cell death in TRT effect was investigated using immunocompetent and nude mice. TRT-EVs cytotoxic effect on recipient (non-exposed) B16F10 cells was investigated using clonogenic survival, γ-H2AX focus formation, apoptosis assays and EVs were characterized by proteomic analysis.

RESULTS

In vivo data showing that TRT with 125I-TA99 significantly delayed tumor growth in immunocompetent C57BL/6J mice, but not in T-cell-deficient athymic nude mice. Consistently, TRT-exposed cells exhibited enhanced extracellular ATP release and sequential cGAS-STING pathway activation. In vitro, TRT-EVs reduced recipient B16F10 cell clonogenic survival by 72 ± 15% and induced DNA double-strand breaks and micronuclei, but increased apoptosis only slightly. Proteomic analysis of TRT-EVs revealed an enrichment in proteins involved in immunogenic cell death and immune activation.

CONCLUSIONS

Overall, this study provides evidence that TRT-EVs contribute to cytotoxicity by delivering toxic and immunogenic signals that drive a T-cell-dependent antitumor response. Investigations are currently underway to identify the specific proteins that mediate this immune activation.