High-LET Alpha Particle Radiation Enhances the Potential of Tumor Cells to Activate an Anti-Tumor Immune Response Compared with Photons
Abstract
Purpose
High–linear energy transfer (LET) alpha-particle radiotherapy (RT) produces dense ionization tracks that generate complex DNA damage and may induce potent immunostimulatory signals. We compared alpha‑particle and photon RT across breast and pancreatic cancer models to determine modality‑specific effects on DNA damage response, innate immune sensing, inflammatory signaling, and tumor‑cell immune-activating potential.
Methods
Murine 4T1 (breast) and human pancreatic cancer cells (SUIT-2, TCC-Pan2) were irradiated with alphas (Americium-241) or photons (X-Rad320). Relative biological effectiveness was measured using clonogenic survival. Cell cycle distribution and DNA damage [γH2AX foci, micronuclei (MN)], and MN colocalized with cGAS were assessed. A 13-plex cytokine panel was used in culture supernatants to determine inflammatory signaling and flow cytometry to quantify immune-related surface proteins. Principal component analysis (PCA) was used to integrate DNA damage and immunologic variables to identify modality-specific multivariate signatures.
Results
Alpha RT induced more persistent DNA damage and higher MN and cGAS‑positive MN in 4T1 than photons. Under isoeffect conditions, alphas induced a more sustained G2/M arrest in SUIT‑2. Both modalities increased IFN‑β, while other cytokines showed non-significant trends. Alphas elicited broader immune-activating changes across cell lines, including higher calreticulin (CALR), major histocompatibility complex class I (MHC-I), CD80/CD86, and adaptive PD-L1 upregulation, even under isoeffect doses. PCA showed alpha-induced stronger immune‑activating tumor‑cell changes, higher levels of cytokines linked to early immune activation (GM‑CSF, MCP‑1), whereas photons produced an inflammatory pattern often associated with impaired T‑cell responses, characterized by IL‑1β, IL‑17, and LAG‑3 upregulation.
Conclusion
Alpha RT increased tumor-cell features consistent with engagement of innate- and adaptive-antitumor immune pathways. In contrast, photon RT favored an inflammatory profile less supportive of antitumor immunity. In the context of alpha-emitting radiopharmaceuticals and diffusing alpha-emitters radiotherapy, these findings highlight alpha RT as a promising immune‑stimulatory modality and support its combination with checkpoint inhibition.