ATM and RAD51 Repair Pathways in Human Lymphocytes Irradiated with 70 MeV Therapeutic Proton Beam

The repair of radiation-induced DNA damage is a key factor differentiating patients in terms of the therapeutic efficacy and toxicity to surrounding normal tissue. Proton energy substantially determines the types of cancers that can be treated. The present work investigated the DNA double-strand break repair systems, represented by phosphorylated ATM and Rad51. The status of proton therapy energy used to treat major types of cancer is summarized. Here, human lymphocytes from eight healthy donors (male and female) were irradiated with a spread-out Bragg peak using a therapeutic 70 MeV proton beam or with reference X rays. For both types of radiation, the kinetics of pATM and Rad51 repair protein activation (0–24 h) were estimated as determinants of homologous and non-homologous double-strand break repair. Additionally, γ-H2AX was used as the gold standard marker of double-strand breaks. Our results showed that at 30 min postirradiation there was significantly greater accumulation of γ-H2AX (0.6-fold), pATM (2.0-fold), and Rad51 (0.6-fold) in the proton-irradiated cells compared with the X-ray-treated cells. At 24 h post irradiation, for both types of radiation and all investigated proteins, the foci number was still significantly higher when compared with control. Furthermore, the mean value of pATM and Rad51 repair effectiveness was higher in cells exposed to protons than in cells exposed to X rays; however, the difference was significant only for pATM. The largest inter-individual differences in the repair capabilities were noted for Rad51. The association between the frequency of repair protein foci and the frequency of lymphocyte viability at 1 h post irradiation showed a positive correlation for protons but a negative correlation for X rays. These findings indicate that the accumulation of radiation-induced repair protein foci after proton versus X-ray irradiation differs between patients, consequently affecting the cellular responses to particle therapy and conventional radiation therapy.

The Effect of Atypical Nucleic Acids Structures in DNA Double Strand Break Repair: A Tale of R-loops and G-Quadruplexes

The fine tuning of the DNA double strand break repair pathway choice relies on different regulatory layers that respond to environmental and local cues. Among them, the presence of non-canonical nucleic acids structures seems to create challenges for the repair of nearby DNA double strand breaks. In this review, we focus on the recently published effects of G-quadruplexes and R-loops on DNA end resection and homologous recombination. Finally, we hypothesized a connection between those two atypical DNA structures in inhibiting the DNA end resection step of HR.

Integrated analysis reveals prognostic value of HLA-I LOH in triple-negative breast cancer

BackgroundTriple-negative breast cancers (TNBCs), especially those non-immune-inflamed tumors, have a poor prognosis and limited therapies. Human leukocyte antigen (HLA)-I not only contributes to antitumor immune response and the phenotype of the tumor microenvironment, but also is a negative predictor of outcomes after immunotherapy. However, the importance of HLA functional status in TNBCs remains poorly understood.MethodsUsing the largest original multiomics datasets on TNBCs, we systematically characterized the HLA-Ⅰ status of TNBCs from the perspective of HLA-Ⅰ homogeneity and loss of heterozygosity (LOH). The prognostic significance of HLA-I status was measured. To explain the potential mechanism of prognostic value in HLA-Ⅰ status, the mutational signature, copy number alteration, neoantigen and intratumoral heterogeneity were measured. Furthermore, the correlation between HLA-Ⅰ functional status and the tumor immune microenvironment was analyzed.ResultsLOH and homogeneity in HLA-I accounted for 18% and 21% of TNBCs, respectively. HLA-I LOH instead of HLA-I homogeneity was an independent prognostic biomarker in TNBCs. In particular, for patients with non-immune-inflamed tumors, HLA-I LOH indicated a worse prognosis than HLA-I non-LOH. Furthermore, integrated genomic and transcriptomic analysis showed that HLA-I LOH was accompanied by upregulated scores of mutational signature 3 and homologous recombination deficiency scores, which implied the failure of DNA double-strand break repair. Moreover, HLA-I LOH had higher mutation and neoantigen loads and more subclones than HLA-I non-LOH. These results indicated that although HLA-I LOH tumors with failure of DNA double-strand break repair were prone to produce neoantigens, their limited capacity for antigen presentation finally contributed to poor immune selection pressure.ConclusionOur study illustrates the genomic landscape of HLA-I functional status and stresses the prognostic significance of HLA-I LOH in TNBCs. For “cold” tumors in TNBCs, HLA-I LOH indicated a worse prognosis than HLA-I non-LOH.