288 T. Kisnanto et al.: Radioprotection 2025, 60( 3), 285 – 292
Table 3. Description of studies using the PICO method Articles Patients Intervention Comparison Outcome
Widjaja et al.( 2022), Germany
Derlin et al.( 2021), Germany
Twenty men with mCRPC undergoing 177Lu-PSMA therapy
Twenty-one patients with advanced gastroenteropancreatic neuroendocrine tumors( ten males and eleven females)
A median dose of 7.32 GBq( interquartile range 7.28 – 7.37) of 177Lu-PSMA was given every cycle. Treatment followed established procedural parameters, with cycles repeated every 6-8 weeks( median 42 days). A routine laboratory panel was evaluated before and throughout each cycle, including blood cell counts, liver enzymes, and PSA levels.
Eleven patients started peptide receptor radionuclide therapy( PRRT) with 7.4 GBq lutetium-177( 177Lu) labeled 1,4,7,10 tetraazacyclododecane-N, N’, N”, N”-tetraacetic acid-d-Phe( 1)-Tyr( 3) octreotate( 177Lu-DOTA-TATE), and 10 patients had previously received at least one PRRT cycle before( 6 ± 1). All patients suffered from grade 1( G1) or grade 2( G2) metastatic nonfunctioning gastroenteropancreatic neuroendocrine tumors. In addition, general laboratory examinations were performed, including hematology, liver enzymes, and serum CgA levels.
Blood samples for DDRmarker analysis were taken before, an hour after, and 24 hours after the 177Lu-PSMA injection DDR markers associated with intact lymphocyte cells were added and divided by the total number of cells to determine the number of foci per cell. PSA levels were measured before and 6-8 weeks after two cycles of therapy, and the percentage change from baseline was analyzed. The reliability of the analysis was confirmed in lymphoblastoid cells irradiated with a dose of 2 Gy from healthy donors and ataxia-telangiectasia syndrome( A – T) patients, the latter of whom showed a radiosensitivity phenotype. Blood samples of patients undergoing PRRT with 177 Lu-DOTA-TATE were
irradiated with a dose of 2 Gy as positive controls
Low baseline DDR marker( gamma-H2AX foci) levels before therapy may represent low individual radiosensitivity and be associated with earlier PSA-PD and shorter PSA-PFS.
The study found significant heterogeneity in gamma-H2AX foci induction and kinetics in PRRT patients’ PBLs, suggesting potential for stratification and treatment response prediction. However, the data was preliminary and called for larger prospective studies. weeks. Gamma-H2AX and 53BP1 foci growth in peripheral blood lymphocytes were assessed at baseline, one hour, and 24 h after PRRT 177Lu-DOTA-TATE delivery. 68Ga-DOTA- TATE PET / CT was used to evaluate therapy response before enrollment and after two cycles of PRRT. Individual radiosensitivity was assessed by the correlation between subclinical hematotoxicity and the onset of H2AX and 53 BP1 foci( Derlin et al., 2021).
3.1 DNA damage and formation of gamma-H2AX foci
“ DNA damage” refers to many lesions or damage to the DNA molecule. External sources, including radiation exposure, toxic chemicals, viral infections, and internal ones like DNA replication mistakes or undesired metabolic reactions, may damage DNA. DNA damage may result in genetic alterations, mutations, or cell death( Liu et al., 2022).
One of the reactions to DNA damage is the development of gamma-H2AX foci. Gamma-H2AX is a post-translational alteration of the histone H2AX after DNA damage( Willers et al., 2015). When DNA damage occurs, such as doublestrand breaks or other DNA lesions, the protein kinase ATM
( ataxia-telangiectasia mutated) is activated. This activation of ATM is the initial step in the signalling pathway responding to DNA damage. When active, ATM phosphorylates serine residues on the C-terminal tail of histone H2AX, producing gamma-H2AX. This creates scars that specifically mark sites of DNA damage in the genome. It is part of the cellular reaction to DNA damage, to repair the damage or, if the damage is too severe, directing the cell to apoptosis, also known as“ programmed cell death”( Song et al., 2023; Srivastava et al., 2009). DNA DSB signalling mechanism involves histone H2AX phosphorylation.
The formation of gamma-H2AX foci is critical for DNA damage detection and repair, as well as genomic stability. It is also employed in scientific studies as a marker to detect and quantify the extent of DNA damage in cells.
3.2 Gamma-H2AX as a biomarker of ionizing radiation exposure
The gamma-H2AX assay has gained popularity as a marker of radiation exposure due to its speed, sensitivity, ability to detect