Intracellular Sequestration of223Ra by the Iron-Storage Protein Ferritin

Differential responses to 223Ra and Alpha-particles exposure in prostate cancer driven by mitotic catastrophe

Introduction

Radium-223 (223Ra) has been shown to have an overall survival benefit in metastatic castration-resistant prostate cancer (mCRPC) involving bone. Despite its increased clinical usage, relatively little is known regarding the mechanism of action of 223Ra at the cellular level.

Methods

We evaluated the effects of 223Ra irradiation in a panel of cell lines and then compared them with standard X-ray and external alpha-particle irradiation, with a particular focus on cell survival and DNA damage repair kinetics.

Results

223Ra exposures had very high, cell-type-dependent RBE50% ranging from 7 to 15. This was significantly greater than external alpha irradiations (RBE50% from 1.4 to 2.1). These differences were shown to be partially related to the volume of 223Ra solution added, independent of the alpha-particle dose rate, suggesting a radiation-independent mechanism of effect. Both external alpha particles and 223Ra exposure were associated with delayed DNA repair, with similar kinetics. Additionally, the greater treatment efficacy of 223Ra was associated with increased levels of residual DNA damage and cell death by mitotic catastrophe.

Conclusions

These results suggest that 223Ra exposure may be associated with greater biological effects than would be expected by direct comparison with a similar dose of external alpha particles, highlighting important challenges for future therapeutic optimization.

Effect of Low-Level Laser on Some Metals Related to Redox State and Histological Alterations in the Liver and Kidney of Irradiated Rats

Low-level laser therapy (LLLT) is a type of medicine that uses laser light at low levels to activate the cellular chromophores and the initiation of cellular signaling. This study aimed to evaluate the photomodulation effect of LLL against ionizing radiation (IR)-induced metal disorders related to redox state in the liver and kidney of male rats. Rats were divided into 4 groups (control, LLLT, IR (7Gy), IR+LLLT). The results showed that LLLT 870 nm one time for 3 days post-irradiation revealed redistribution of iron (Fe), copper (Cu), zinc (Zn),calcium (Ca), magnesium (Mg), manganese (Mn), and selenium (Se) in the liver and kidney tissues. Moreover, LLLT attenuated the oxidative stress manifested by a marked reduction of hydrogen peroxide (H₂O₂), 4-hydroxynonenal (4-HNE), total oxidant state (TOS), and oxidative stress index (OSI) associated with a significant increase in total antioxidant status (TAS), glutathione (GSH) content, and glutathione peroxide (GPx), glutathione reductase (GRx), superoxide dismutase(SOD), and catalase (CAT) activities. Moreover, LLLT displayed an increase in glutathione-S-transferase (GSH-T) and ceruloplasmin activities and a decrease in the activity of gamma-glutamyl transferase (γ-GT). Besides, LLLT significantly attenuated the histological changes in the liver and kidney tissues, denoted by a reduction in the necrotic and degenerative changes of hepatocytes and an improvement in the corpuscles and tubules of the kidney. In conclusion, LLLT could be used as an adjuvant treatment post-exposure to radiation, while it is not beneficial to use it on the normal tissue.

Cellular and Genetic Determinants of the Sensitivity of Cancer to α-Particle Irradiation

Targeted α-particle-emitting radionuclides have great potential for the treatment of a broad range of cancers at different stages of progression. A platform that accurately measures cancer cellular sensitivity to α-particle irradiation could guide and accelerate clinical translation. Here, we performed high-content profiling of cellular survival following exposure to α-particles emitted from radium-223 (²²³Ra) using 28 genetically diverse human tumor cell lines. Significant variation in cellular sensitivity across tumor cells was observed. ²²³Ra was significantly more potent than sparsely ionizing irradiation, with a median relative biological effectiveness of 10.4 (IQR: 8.4-14.3). Cells that are the most resistant to γ radiation, such as Nrf2 gain-of-function mutant cells, were sensitive to α-particles. Combining these profiling results with genetic features, we identified several somatic copy-number alterations, gene mutations, and the basal expression of gene sets that correlated with radiation survival. Activating mutations in PIK3CA, a frequent event in cancer, decreased sensitivity to ²²³Ra. The identification of cellular and genetic determinants of sensitivity to ²²³Ra may guide the clinical incorporation of targeted α-particle emitters in the treatment of several cancer types. SIGNIFICANCE: These findings address limitations in the preclinical guidance and prediction of radionuclide tumor sensitivity by identifying intrinsic cellular and genetic determinants of cancer cell survival following exposure to α-particle irradiation.See related commentary by Sgouros, p. 5479.