Differential Radiobiological Effects of α- and β⁻-Emitter Targeted Radionuclide Therapy: DNA Damage and Survival

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

Prostate-specific membrane antigen (PSMA)-positive (LNCaP [lymph node adenocarcinoma of the prostate] and C4-2) and PSMA-negative (PC-3) prostate cancer cell lines were exposed to ²²⁵Ac- or ¹⁷⁷Lu-labeled PSMA radiopharmaceuticals or nontargeted radionuclides for 1 or 4 hours across activity ranges for α-emitters (1-100 kBq) and β⁻-emitters (100-5000 kBq), with external beam radiation therapy (0.5-2.5 Gy) 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-dependent protein kinase (DNA-PK) inhibitor Nedisertib (M3814; Selleck Chemicals, Houston, TX, USA) 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 on longer‑range β⁻‑TRT. α‑Induced DSBs persisted for up to 72 hours, whereas DSBs decreased over time after β⁻‑TRT and external beam radiation therapy. Combination therapy with Nedisertib significantly enhanced TRT efficacy in C4-2 cells, 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 is a promising strategy to enhance efficacy, enable activity de‑escalation, and potentially mitigate toxicity.