C.A. Koch

Xrcc4 physically links DNA end processing by polynucleotide kinase to DNA ligation by DNA ligase IV

Nonhomologous end joining (NHEJ) is the major DNA double‐strand break (DSB) repair pathway in mammalian cells. A critical step in this process is DNA ligation, involving the Xrcc4–DNA ligase IV complex. DNA end processing is often a prerequisite for ligation, but the coordination of these events is poorly understood. We show that polynucleotide kinase (PNK), with its ability to process ionizing radiation‐induced 5′‐OH and 3′‐phosphate DNA termini, functions in NHEJ via an FHA‐dependent interaction with CK2‐phosphorylated Xrcc4. Analysis of the PNK FHA–Xrcc4 interaction revealed that the PNK FHA domain binds phosphopeptides with a unique selectivity among FHA domains. Disruption of the Xrcc4–PNK interaction in vivo is associated with increased radiosensitivity and slower repair kinetics of DSBs, in conjunction with a diminished efficiency of DNA end joining in vitro. Therefore, these results suggest a new role for Xrcc4 in the coordination of DNA end processing with DNA ligation.

Individual patient data meta-analysis shows a significant association between the ATM rs1801516 SNP and toxicity after radiotherapy in 5456 breast and prostate cancer patients

PURPOSE Several small studies have indicated that the ATM rs1801516 SNP is associated with risk of normal tissue toxicity after radiotherapy. However, the findings have not been consistent. In order to test this SNP in a well-powered study, an individual patient data meta-analysis was carried out by the International Radiogenomics Consortium. MATERIALS AND METHODS The analysis included 5456 patients from 17 different cohorts. 2759 patients were given radiotherapy for breast cancer and 2697 for prostate cancer. Eight toxicity scores (overall toxicity, acute toxicity, late toxicity, acute skin toxicity, acute rectal toxicity, telangiectasia, fibrosis and late rectal toxicity) were analyzed. Adjustments were made for treatment and patient related factors with potential impact on the risk of toxicity. RESULTS For all endpoints except late rectal toxicity, a significantly increased risk of toxicity was found for carriers of the minor (Asn) allele with odds ratios of approximately 1.5 for acute toxicity and 1.2 for late toxicity. The results were consistent with a co-dominant pattern of inheritance. CONCLUSION This study convincingly showed a significant association between the ATM rs1801516 Asn allele and increased risk of radiation-induced normal tissue toxicity.

Identification and Functional Characterization of a Ku-binding Motif in Aprataxin Polynucleotide Kinase/Phosphatase-like Factor (APLF)

Background: APLF interacts with Ku and facilitates nonhomologous end joining (NHEJ). Results: APLF possesses a Ku-binding motif, and disruption of the APLF-Ku interaction impairs both NHEJ and the nuclear retention of APLF. Conclusion: The APLF-Ku interaction is functionally important in DNA repair and may be important for APLF stability. Significance: The APLF Ku-binding motif appears to represent a general Ku-binding motif. Aprataxin polynucleotide kinase/phosphatase-like factor (APLF) facilitates nonhomologous end joining (NHEJ) and associates with the core NHEJ components XRCC4-DNA ligase IV and Ku. The APLF forkhead-associated (FHA) domain directs interactions with XRCC4, but the APLF-Ku interaction has not been well characterized. Here we describe an evolutionarily conserved amino acid motif within APLF that is required for mediating the physical interaction between APLF and Ku. This APLF Ku-binding motif possesses a similarity to regions identified in other NHEJ factors, WRN and XLF, which also direct interactions with Ku. Indeed, peptides derived from the Ku-binding region of APLF, WRN, or XLF were sufficient to reconstitute the interaction with Ku in vitro. Although APLF is localized predominantly to the nucleus, it does not possess a nuclear localization signal (NLS). Interestingly, the disruption of the APLF-Ku interaction by substituting key residues in the APLF Ku-binding motif was associated with increased relocalization of APLF to the cytoplasm and reduced association with XRCC4, which was rescued by the introduction of an NLS onto APLF. When human cells stably depleted of APLF were reconstituted with APLF Ku-binding mutants, or with an APLF FHA mutant that is known to disrupt interactions with XRCC4, APLF-dependent NHEJ and the retention of APLF at sites of laser-generated DNA damage were impaired. These data suggest functional requirements for Ku and XRCC4 in APLF-dependent NHEJ and a unique role for Ku as a factor required to facilitate the nuclear retention of APLF.

Patient-reported Acute Fatigue in Elderly Breast Cancer Patients Treated with and without Regional Nodal Radiation

Purpose Although regional nodal irradiation (RNI) improves outcomes in breast cancer (BC) patients, it is associated with increased toxicity. Therefore, controversy still exists surrounding its indications. The purpose of this study was to evaluate and compare patient-reported acute fatigue in elderly BC patients with and without regional nodal radiation (RNI). Methods Elderly breast cancer patients (≥ 65 years) treated with adjuvant radiotherapy (RT) between 2012 and 2017 were identified from a prospective database. The validated Edmonton Symptom Assessment System-revised (ESAS-r) questionnaire, which assesses fatigue, was completed prior to (baseline), during, at end of RT and first follow-up (3–6 months). Symptoms were rated on a 10-point Likert scale, with higher scores indicating higher fatigue. Patient’s treatment characteristics were also recorded prospectively. This was a retrospective study which identified elderly breast cancer patients who had received adjuvant radiation, completed ESAS-r prospectively and provided research consent for using ESAS-r. Patients were divided into two cohorts: those who received RNI (cohort 1) and those who did not (cohort 2). A minimal clinically important difference (MID) was defined using an anchor of ≥ 1-point compared to baseline. The proportion of patients reporting a change in fatigue at the end of RT was evaluated. To test the robustness of the results, dynamic changes of fatigue scores over time were further compared between the cohorts using a general linear mixed model (GLMM) after assuming individual patient with random effect. Univariate and multivariable logistic regression were conducted to assess the association between RNI and MID after adjusting for potential confounders. In addition to longitudinal analysis, a multivariable mixed effect model was developed to determine the association of RNI with fatigue after adjusting for potential confounders. A two-tailed p value ≤ 0.05 was considered statistically significant. Results Of the 1198 patients, 859 had provided research consent and completed the ESAS-r at baseline and any other timepoint and were included in the longitudinal analysis (cohort 1 = 159, cohort 2 = 700), while 637 (cohort 1 = 135, cohort 2 = 502) patients completed the ESAS-r at baseline and end of radiotherapy and were included in the anchor-based analysis. Mean age at diagnosis was similar between the groups: cohort 1; 71.5 ± 5.7 vs. cohort; 2 72 ± 5.4 years (total 71.8 ± 5.5). Overall, cohort 1 had higher stage (Stage 3: 32.7% vs 3.6%, p < 0.001) and reception of chemotherapy (68.6% vs. 16.1%, p < 0.001). Mean baseline fatigue was higher for cohort 1 vs. 2 (2.7 ± 2.5 vs. 2.1 ± 2.3, p = 0.006). On univariate and multivariable analyses, RNI was not associated with an increased odd of MID for fatigue at the end of RT (44% vs. 47%; OR 0.89, 95% CI 0.61–1.30, p = 0.56). After adjusting for confounders (age, duration of RT, endocrine therapy), treatment with RNI was not associated with increased odds of worse fatigue at the end of RT (OR 1.33, 95% CI 0.85–2.10, p = 0.22). Higher baseline fatigue (OR 0.86, 95% CI 0.79–0.92, p < 0.001) and receipt of chemotherapy had decreased odds (OR 0.50, 95% CI 0.32–0.86, p = 0.001) and were the only factors associated with decreased odds of MID. Dynamic changes showed a significant worsening of fatigue scores over time (p < 0.001) towards the end of RT and recovery at first follow-up (p < 0.001) with no difference between the cohorts (p = 0.38); both experienced parallel worsening of fatigue levels over time (cohort*time Jennifer Croke and Joelle Helou are joint senior authors. Electronic supplementary material The online version of this article (https ://doi.org/10.1007/s1054 9-020-05781 -5) contains supplementary material, which is available to authorized users. Extended author information available on the last page of the article Breast Cancer Research and Treatment 1 3 p = 0.71 and cohort*time2 p = 0.78). On multivariable analysis earlier stage, the absence of chemotherapy and higher baseline depression were independent predictors of worse fatigue scores over time (p = 0.01, p = 0.003, and p = 0.02, respectively). Conclusion The addition of RNI in elderly BC patients is not associated with a significant worsening of patient-reported fatigue. Predictors of acute fatigue will enable shared decision making between patients and clinicians.

PO-0676: Impact of IMN irradiation on the right coronary artery and OAR in right-sided post-mastectomy patients

Results: Of the 7 BCCT.core parameters, pBCE and pBCD were significantly related to patients’ score at 4 years. Patients with any difference in firmness rated their cosmesis worse than patients without any difference, even when the objective score (i.e. BCCT.core) was similar. This effect was larger by increasing difference. Worse perception of cosmetic outcome was also independently related to lower global QoL, lower emotional functioning and higher scores in the depression scale. The presence of rib pain had no influence.