Differential Radiobiological Effects of Αlpha- and Beta-Minus-Emitter Targeted Radionuclide Therapy: DNA Damage and...

Metastatic cancer remains a major challenge, demanding more effective and biologically informed therapeutic strategies. Targeted Radionuclide Therapy (TRT) holds significant promise, but its optimization is limited by insufficient understanding of treatment response and resistance. This work aims to enhance TRT efficacy and overcome radioresistance by dissecting how radionuclide properties, administered activity, and subcellular localization govern radiobiological outcomes. The objectives are to advance TRT for prostate cancer (PCa), overcome radioresistance, and generate mechanistic insights to guide radiopharmaceutical design and radionuclide selection.

PSMA-positive (LNCaP, C4-2) and PSMA-negative (PC-3) PCa cell lines were exposed to ²²⁵Ac- or ¹⁷⁷Lu-labeled PSMA radiopharmaceuticals or non-targeted radionuclides for 1 or 4 hours across activity ranges of α-emitters (1-100 kBq) and β⁻-emitters (100-5000 kBq), with external beam radiation therapy (EBRT; 0.5-2.5 Gy) serving as a reference. DNA double‑strand breaks (DSBs) were quantified by immunofluorescence‑based γH2AX analysis and complemented by cell viability assays. A proof‑of‑concept combination study with the DNA‑PK inhibitor Nedisertib® was performed.

The α-emitters outperformed the β⁻-emitters, inducing comparable DSBs at only 1% of the applied activity. PSMA‑mediated internalization strongly enhanced short‑range α‑TRT but had negligible impact for longer‑range β⁻‑TRT. α‑induced DSBs persisted for up to 72 h, whereas DSBs decreased over time after β⁻‑TRT and EBRT. Combination therapy with Nedisertib® significantly enhanced TRT efficacy in C4-2, enabling a 64‑fold (²²⁵Ac) versus 4‑fold (¹⁷⁷Lu) reduction in required activity. In the least radiosensitive PC-3 cells, viability decreased to below 50% following combined α-TRT and Nedisertib® treatment.

Our study defines key determinants for optimizing TRT. Cellular internalization is critical for short-range α-emitters, whereas β⁻-emitters depend on high binding affinity and retention, providing experimental guidance for radiopharmaceutical design and radionuclide selection. Distinct DNA repair kinetics underscore radionuclide‑specific biological effects. Combining TRT with DNA‑PK inhibition represents a promising strategy to enhance efficacy, enable activity de‑escalation, and potentially mitigate toxicity.