Radiosensitization by hyperthermia in the chicken B-lymphocyte cell line DT40 and its derivatives lacking nonhomologous end joining and/or homologous recombination pathways of DNA double-strand break repair

Immunogenic Effect of Hyperthermia on Enhancing Radiotherapeutic Efficacy

Hyperthermia is a cancer treatment where tumor tissue is heated to around 40 °C. Hyperthermia shows both cancer cell cytotoxicity and immune response stimulation via immune cell activation. Immunogenic responses encompass the innate and adaptive immune systems, involving the activation of macrophages, natural killer cells, dendritic cells, and T cells. Moreover, hyperthermia is commonly used in combination with different treatment modalities, such as radiotherapy and chemotherapy, for better clinical outcomes. In this review, we will focus on hyperthermia-induced immunogenic effects and molecular events to improve radiotherapy efficacy. The beneficial potential of integrating radiotherapy with hyperthermia is also discussed.

Highlights on molecular targets for radiosensitization of breast cancer cells: Current research status and prospects

In the past, searching for effective radiotherapy sensitization molecular targets and improving the radiation sensitivity of malignant tumors was the hot topic for the oncologists, but with little achievements. We will summarize the research results about breast cancer irradiation sensitization molecular targets over the past two decades; we mainly focus on the following aspects: DNA damage repair and radiation sensitization, cell cycle regulation and radiation sensitization, cell autophagy regulation and radiation sensitization, and radiation sensitivity prediction and breast cancer radiotherapy scheme making. And based on this summary, we will put forward some of our viewpoints.

BRCA2 mutations should be screened early and routinely as markers of poor prognosis: evidence from 8,988 patients with prostate cancer

The aim of this study was to focus on clinicopathological characteristics and prognosis in men with prostate cancer (PCa) harboring a breast cancer 2 (BRCA2) gene mutation and to offer convincing evidence to consider BRCA2 mutation as a marker of poor prognosis in the molecular classification of PCa. We searched relevant articles from PubMed, Embase, Web of Science, and the Cochrane Library databases to evaluate the differences in the overall survival (OS) and cancer-specific survival (CSS) between BRCA2 mutation carriers and non-carriers in patients with PCa. We included 525 BRCA2 mutation-carriers and 8,463 non-carriers in total from 10 studies in our meta-analysis. The results showed that carrying a BRCA2 mutation was correlated with a reduced CSS and OS when compared with that of non-carriers, with pooled Hazard Ratios (HRs) of 2.53 (95% confidence interval (CI): 2.10–3.06, P < 0.001) and 2.21 (95% CI: 1.64–2.99, P < 0.001), respectively. The results also demonstrated that BRCA2 mutation-carriers harbored a higher Gleason Score (GS) (> 7), TNM stage (> T3, N1, M1), and risk level than non-carriers. Our meta-analysis showed that a BRCA2 mutation predicted poor survival outcomes in patients with prostate cancer, especially in those undergoing treatments with radiotherapy. Therefore, the use of BRCA2 mutation as a clinical prognostic factor could help stratify the high-risk patients and provide clinical strategies for more effective targeted treatments for patients with prostate cancer.

Homologous recombination preferentially repairs heat-induced DNA double-strand breaks in mammalian cells

PURPOSE

Heat shock induces DNA double-strand breaks (DSBs), but the precise mechanism of repairing heat-induced damage is unclear. Here, we investigated the DNA repair pathways involved in cell death induced by heat shock.

MATERIALS AND METHODS

B02, a specific inhibitor of human RAD51 (homologous recombination; HR), and NU7026, a specific inhibitor of DNA-PK (non-homologous end-joining; NHEJ), were used for survival assays of human cancer cell lines with different p53-gene status. Mouse embryonic fibroblasts (MEFs) lacking Lig4 (NHEJ) and/or Rad54 (HR) were used for survival assays and a phosphorylated histone H2AX at Ser139 (γH2AX) assay. MEFs lacking Rad51d (HR) were used for survival assays. SPD8 cells were used to measure HR frequency after heat shock.

RESULTS

Human cancer cells were more sensitive to heat shock in the presence of B02 despite their p53-gene status, and the effect of B02 on heat sensitivity was specific to the G₂ phase. Rad54-deficient MEFs were sensitive to heat shock and showed prolonged γH2AX signals following heat shock. Rad51d-deficient MEFs were also sensitive to heat shock. Moreover, heat shock-stimulated cells had increased HR.

CONCLUSIONS

The HR pathway plays an important role in the survival of mammalian cells against death induced by heat shock via the repair of heat-induced DNA DSBs.

Effects of hyperthermia as a mitigation strategy in DNA damage-based cancer therapies

Utilization of thermal therapy (hyperthermia) is defined as the application of exogenous heat induction and represents a concept that is far from new as it goes back to ancient times when heat was used for treating various diseases, including malignancies. Such therapeutic strategy has gained even more popularity (over the last few decades) since various studies have shed light into understanding hyperthermia's underlying molecular mechanism(s) of action. In general, hyperthermia is applied as complementary (adjuvant) means in therapeutic protocols combining chemotherapy and/or irradiation both of which can induce irreversible cellular DNA damage. Furthermore, according to a number of in vitro, in vivo and clinical studies, hyperthermia has been shown to enhance the beneficial effects of DNA targeting therapeutic strategies by interfering with DNA repair response cascades. Therefore, the continuously growing evidence supporting hyperthermia's beneficial role in cancer treatment can also encourage its application as a DNA repair mitigation strategy. In this review article, we aim to provide detailed information on how hyperthermia acts on DNA damage and repair pathways and thus potentially contributing to various adjuvant therapeutic protocols relevant to more efficient cancer treatment strategies.

Effects of hyperthermia on DNA repair pathways: one treatment to inhibit them all

The currently available arsenal of anticancer modalities includes many DNA damaging agents that can kill malignant cells. However, efficient DNA repair mechanisms protect both healthy and cancer cells against the effects of treatment and contribute to the development of drug resistance. Therefore, anti-cancer treatments based on inflicting DNA damage can benefit from inhibition of DNA repair. Hyperthermia – treatment at elevated temperature – considerably affects DNA repair, among other cellular processes, and can thus sensitize (cancer) cells to DNA damaging agents. This effect has been known and clinically applied for many decades, but how heat inhibits DNA repair and which pathways are targeted has not been fully elucidated. In this review we attempt to summarize the known effects of hyperthermia on DNA repair pathways relevant in clinical treatment of cancer. Furthermore, we outline the relationships between the effects of heat on DNA repair and sensitization of cells to various DNA damaging agents.

Electrophysiologic and cellular characteristics of cardiomyocytes after X-ray irradiation

The aim of this study was to investigate possible effects of ionizing irradiation on the electrophysiological functionality of cardiac myocytes in vitro. Primary chicken cardiomyocytes with spontaneous beating activity were irradiated with X-rays (dose range of 0.5-7 Gy). Functional alterations of cardiac cell cultures were evaluated up to 7 days after irradiation using microelectrode arrays. As examined endpoints, cell proliferation, apoptosis, reactive oxygen species (ROS) and DNA damage were evaluated. The beat rate of the cardiac networks increased in a dose-dependent manner over one week. The duration of single action potentials was slightly shortened. Additionally, we observed lower numbers of mitotic and S-phase cells at certain time points after irradiation. Also, the number of cells with γH2AX foci increased as a function of the dose. No significant changes in the level of ROS were detected. Induction of apoptosis was generally negligibly low. This is the first report to directly show alterations in cardiac electrophysiology caused by ionizing radiation, which were detectable up to one week after irradiation.

Misrepair of DNA double-strand breaks after exposure to heavy-ion beams causes a peak in the LET-RBE relationship with respect to cell killing in DT40 cells

To determine the radiobiological mechanisms underlying relative biological effectiveness (RBE) and the repair efficiencies of DNA double-strand breaks (DSBs) as a function of linear energy transfer (LET), we exposed cells of the chicken B-lymphocyte cell line DT40 and its DSB repair pathway-deficient derivatives to heavy-ion beams produced at the Heavy-Ion Medical Accelerator in Chiba (HIMAC) at the National Institute of Radiological Sciences (NIRS), Chiba, Japan. The relationship between LET and cell lethality was investigated in the DNA DSB repair gene knockouts Ku70(-/-), Rad54(-/-), and Ku70(-/-)Rad54(-/-), and in the wild-type cells. We found that cell-cycle stage and activity of the DNA DSB repair pathways influence LET-mediated biological effects. An expected LET-RBE relationship was observed in the cells capable of DNA repair, but no peak was found in the RBE with respect to cell survival in the Ku70(-/-)Rad54(-/-) cells or in Ku70(-/-) cells in the G1 and early S cell-cycle phases (when no sister chromatids were present and homologous recombination could not occur). These findings suggest that the peak in RBE is caused by deficient repair of the DNA DSBs.

Hyperthermia-induced DNA repair deficiency suggests novel therapeutic anti-cancer strategies

Local hyperthermia is an effective treatment modality to augment radio- and chemotherapy-based anti-cancer treatments. Although the effect of hyperthermia is pleotropic, recent experiments revealed that homologous recombination, a pathway of DNA repair, is directly inhibited by hyperthermia. The hyperthermia-induced DNA repair deficiency is enhanced by inhibitors of the cellular heat-shock response. Taken together, these results provide the rationale for the development of novel anti-cancer therapies that combine hyperthermia-induced homologous recombination deficiency with the systemic administration of drugs that specifically affect the viability of homologous recombination deficient cells and/or inhibit the heat-shock response, to locally sensitise cancer cells to DNA damaging agents.

Mild hyperthermia inhibits homologous recombination, induces BRCA2 degradation, and sensitizes cancer cells to poly (ADP-ribose) polymerase-1 inhibition

Defective homologous recombination (HR) DNA repair imposed by BRCA1 or BRCA2 deficiency sensitizes cells to poly (ADP-ribose) polymerase (PARP)-1 inhibition and is currently exploited in clinical treatment of HR-deficient tumors. Here we show that mild hyperthermia (41-42.5 °C) induces degradation of BRCA2 and inhibits HR. We demonstrate that hyperthermia can be used to sensitize innately HR-proficient tumor cells to PARP-1 inhibitors and that this effect can be enhanced by heat shock protein inhibition. Our results, obtained from cell lines and in vivo tumor models, enable the design of unique therapeutic strategies involving localized on-demand induction of HR deficiency, an approach that we term induced synthetic lethality.

Comparison of the kinetics of radiation-induced apoptosis in DT40 cells irradiated with low and high doses of X rays

In this study, we attempted to clarify the influence of the DNA repair genes RAD54 and KU70, components of the homologous recombination (HR) and non-homologous end-joining (NHEJ) pathways, respectively, on apoptosis induced by 1 Gy (low-dose) and 5 Gy (high-dose) irradiation. All experiments were performed using chicken B-lymphocyte DT40 cells and the DNA repair-deficient cell lines KU70(-/-), RAD54(-/-) and KU70(-/-)/RAD54(-/-). Morphological changes were detected by fluorescence methods, and the sub-G(1) fraction and the activated caspases in DT40 cells were analyzed by flow cytometry. Irradiation with 1 Gy significantly increased the level of apoptosis in cells with the defective DNA repair genes, with the maximum apoptosis occurring in double mutant cells, KU70(-/-)/RAD54(-/-), demonstrating that 1 Gy is enough to induce apoptosis in DNA repair-deficient DT40 cells, and that KU70 and RAD54 must have almost the same role in low-dose radiation-induced apoptosis. After 5 Gy, fast induction of apoptosis, within 2 h, was seen in both wild-type cells and RAD54(-/-) cells, indicating that functional KU70 must be important for the rescue of the cells from the induction of fast apoptosis.

Hyperthermia, cisplatin and radiation trimodality treatment: a promising cancer treatment? A review from preclinical studies to clinical application

This review discusses available clinical and experimental data and the underlying mechanisms involved in trimodality treatment consisting of hyperthermia, cisplatin and radiotherapy. The results of phase I/II clinical trials show that trimodality treatment is effective and feasible in various cancer types and sites with tolerable toxicity. Based on these results, phase III trials have been launched to investigate whether significant differences in treatment outcome exist between trimodality and standard treatment. In view of the clinical interest, it is surprising to find so few preclinical studies on trimodality treatment. Although little information is available on the doses of the modalities and the treatment sequence resulting in the largest degree of synergistic interaction, the results from in vivo and in vitro preclinical studies support the use of trimodality treatment for cancer patients. Animal studies show an improvement in treatment outcome after trimodality treatment compared with mono- and bimodality treatment. Studies in different human tumour cell lines show that a synergistic interaction can be obtained between hyperthermia, cisplatin and radiation and that this interaction is more likely to occur in cell lines which are more sensitive to cisplatin.

N/A

N/A

Activation-induced deaminase cloning, localization, and protein extraction from young VH-mutant rabbit appendix

Studies in mouse, human, and chicken suggest that activation-induced deaminase (AID) is involved in three known processes leading to antibody diversification: somatic hypermutation, gene conversion, and class-switch recombination. Developing rabbit appendix provides a particularly good site for studying all three of these B cell maturation events. We report here successful cloning of rabbit AID and isolation of AID protein from rabbit appendix-cell nuclear and cytoplasmic extracts. We succeeded in identifying and locating AID protein in cells by immunohistochemical and immunofluorescent staining techniques and examined colocalization of AID and other molecules important for Ab diversification. This report extends our knowledge about AID to a mammalian species that uses gene conversion to diversify rearranged Ig genes. Although much work remains to understand fully the mechanism of action of AID and its association with other cellular components, the rabbit system now offers a particularly useful model for future studies of these dynamics.