Typical cell signaling response to ionizing radiation: DNA damage and extranuclear damage

To treat many types of cancer, ionizing radiation (IR) is primarily used as external‐beam radiotherapy, brachytherapy, and targeted radionuclide therapy. Exposure of tumor cells to IR can induce DNA damage as well as generation of reactive oxygen species (ROS) and reactive nitrogen species (RNS) which can cause non‐DNA lesions or extracellular damage like lipid perioxidation. The initial radiation‐induced cell responses to DNA damage and ROS like the proteolytic processing, as well as synthesis and releasing ligands (such as growth factors, cytokines, and hormone) can cause the delayed secondary responses in irradiated and unirradiated bystander cells through paracrine and autocrine pathways.     

Radiation therapy induces the DNA damage response in peripheral blood

Stereotactic body radiation therapy (SBRT) is a radiotherapy modality that delivers highly conformal, ablative doses to a well-defined target. Here, using a semiquantitative multiplexed assay to analyze ATM and H2AX phosphorylation, we show that ATM kinase activity in peripheral blood mononuclear cells is induced following SBRT. This observation of a systemic ATM kinase-dependent DNA damage response in the peripheral blood is unprecedented and promotes the use of ATM serine-1981 phosphorylation as a predictive biomarker for DNA damaging modalities and ATM inhibitors.     

药物基因组学在非小细胞肺癌化疗耐药中的研究进展

非小细胞肺癌（non-small cell lungca Bcer,NSCLC）是目前肿瘤导致死亡的主要病因之一。应用化疗药物可以延长NSCLC患者的生存期,但耐药、副作用等情况限制了其临床应用。药物基因组学（pharmacogenomics）认为药物代谢过程中的相关基因突变会影响药物在体内的作用活性。本文总结了NSCLC常用化疗药物在药物基因组学方面的研究进展。     

克唑替尼治疗 ALK 融合基因阳性的晚期非小细胞肺癌患者的疗效分析

目的：探讨克唑替尼治疗中国 ALK 融合基因阳性的非小细胞肺癌（NSCLC）患者的疗效和安全性。方法14名患者接受至少4周的克唑替尼（250 mg,q12h）治疗,以评价治疗后的近期疗效、生活质量、不良反应。结果12例患者口服克唑替尼治疗后,11例（91.67%）获得部分缓解,1例（8.33%）获得疾病稳定,客观缓解率为91.67%;在生活质量评估中,患者的疲乏、气短、睡眠等均得到改善;不良反应主要为消化道症状,其次是谷丙转氨酶升高（64.29%）,视觉障碍（57.14%）,大部分为1～2级。结论克唑替尼作为 ALK 融合基因阳性的 NSCLC 患者的靶向治疗,具有良好的疗效及安全性,不良反应轻微。     

Aminoflavone induces oxidative DNA damage and reactive oxidative species-mediated apoptosis in breast cancer cells

Aminoflavone (5-amino-2-(4-amino-3-fluorophenyl)-6,8-difluoro-7-methylchromen-4-one; AF; NSC 686288), a novel anticancer candidate agent, is undergoing clinical evaluation. AF induces DNA-protein cross-links (DPCs), Gamma-H2AX phosphorylation, aryl hydrocarbon receptor (AhR) signaling, apoptosis and its own metabolism via cytochrome P4501A1 and 1A2 (CYP1A1/1A2) activation in sensitive estrogen receptor positive (ER+) MCF7 breast cancer cells. Estrogen receptor negative (ER-) breast cancer is typically more aggressive with a poorer prognosis. In this investigation, we evaluated the ability of AF to induce reactive oxygen species (ROS) formation, oxidative DNA damage and apoptosis in ER- MDA-MB-468 breast cancer cells. The antioxidant, N-acetyl-L-cysteine (NAC), attenuated the cytotoxic effects of AF in MDA-MB-468 cells; an effect is also observed in ER+ T47D breast cancer cells. Nonmalignant MCF10A breast epithelial cells were resistant to the cytotoxic effects of AF. AF increased intracellular ROS, an effect blocked by NAC and the CYP1A1/1A2 inhibitor, alpha-Naphthoflavone (alpha-NF). AF induced oxidative DNA damage as evidenced by increased 8-oxo-7,8-dihydroguanine (8-oxodG) levels and DPC formation in these cells. AF caused S-phase arrest corresponding to an increase in p21((waf1/cip1)) protein expression. AF induced caspase 3, 8 and 9 activation, caspase-dependent apoptotic body formation and poly [ADP-ribose] polymerase (PARP) cleavage. Pretreatment with the pan-caspase inhibitor, benzyloxycarbonyl-Val-Ala-DL-Asp(OMe)-fluoromethylketone inhibited apoptosis and partially inhibited ROS formation and oxidative DNA damage. Pretreatment with NAC attenuated AF-induced apoptotic body formation and caspase 3 activation. These studies suggest AF inhibits the growth of breast cancer cells in part, by inducing ROS production, oxidative DNA damage and apoptosis and has the potential to treat hormone-independent breast cancer.     

cGAS regulates the DNA damage response to maintain proliferative signaling in gastric cancer cells

The activation of some oncogenes promote cancer cell proliferation and growth, facilitate cancer progression and metastasis by induce DNA replication stress, even genome instability. Activation of the cyclic GMP-AMP synthase (cGAS) mediates classical DNA sensing, is involved in genome instability, and is linked to various tumor development or therapy. However, the function of cGAS in gastric cancer remains elusive. In this study, the TCGA database and retrospective immunohistochemical analyses revealed substantially high cGAS expression in gastric cancer tissues and cell lines. By employing cGAS high-expression gastric cancer cell lines, including AGS and MKN45, ectopic silencing of cGAS caused a significant reduction in the proliferation of the cells, tumor growth, and mass in xenograft mice. Mechanistically, database analysis predicted a possible involvement of cGAS in the DNA damage response (DDR), further data through cells revealed protein interactions of the cGAS and MRE11-RAD50-NBN (MRN) complex, which activated cell cycle checkpoints, even increased genome instability in gastric cancer cells, thereby contributing to gastric cancer progression and sensitivity to treatment with DNA damaging agents. Furthermore, the upregulation of cGAS significantly exacerbated the prognosis of gastric cancer patients while improving radiotherapeutic outcomes. Therefore, we concluded that cGAS is involved in gastric cancer progression by fueling genome instability, implying that intervening in the cGAS pathway could be a practicable therapeutic approach for gastric cancer.     

Breaking the DNA damage response to improve cervical cancer treatment

Every year, cervical cancer affects ∼500,000 women worldwide, and ∼275,000 patients die of this disease. The addition of platin-based chemotherapy to primary radiotherapy has increased 5-year survival of advanced-stage cervical cancer patients, which is, however, still only 66%. One of the factors thought to contribute to treatment failure is the ability of tumor cells to repair chemoradiotherapy-induced DNA damage. Therefore, sensitization of tumor cells for chemoradiotherapy via inhibition of the DNA damage response (DDR) as a novel strategy to improve therapy effect, is currently studied pre-clinically as well as in the clinic.Almost invariably, cervical carcinogenesis involves infection with the human papillomavirus (HPV), which inactivates part of the DNA damage response. This HPV-mediated partial inactivation of the DDR presents therapeutic targeting of the residual DDR as an interesting approach to achieve chemoradio-sensitization for cervical cancer. How the DDR can be most efficiently targeted, however, remains unclear. The fact that cisplatin and radiotherapy activate multiple signaling axes within the DDR further complicates a rational choice of therapeutic targets within the DDR. In this review, we provide an overview of the current preclinical and clinical knowledge about targeting the DDR in cervical cancer.     

RAD50 targeting impairs DNA damage response and sensitizes human breast cancer cells to cisplatin therapy

In tumor cells the effectiveness of anti-neoplastic agents that cause cell death by induction of DNA damage is influenced by DNA repair activity. RAD50 protein plays key roles in DNA double strand breaks repair (DSBs), which is crucial to safeguard genome integrity and sustain tumor suppression. However, its role as a potential therapeutic target has not been addressed in breast cancer. Our aim in the present study was to analyze the expression of RAD50 protein in breast tumors, and evaluate the effects of RAD50-targeted inhibition on the cytotoxicity exerted by cisplatin and anthracycline and taxane-based therapies in breast cancer cells. Immunohistochemistry assays on tissue microarrays indicate that the strong staining intensity of RAD50 was reduced in 14% of breast carcinomas in comparison with normal tissues. Remarkably, RAD50 silencing by RNA interference significantly enhanced the cytotoxicity of cisplatin. Combinations of cisplatin with doxorubicin and paclitaxel drugs induced synergistic effects in early cell death of RAD50-deficient MCF-7, SKBR3, and T47D breast cancer cells. Furthermore, we found an increase in the number of DSBs, and delayed phosphorylation of histone H2AX after cisplatin treatment in RAD50-silenced cells. These cellular events were associated to a dramatical increase in the frequency of chromosomal aberrations and a decrease of cell number in metaphase. In conclusion, our data showed that RAD50 abrogation impairs DNA damage response and sensitizes breast cancer cells to cisplatin-combined therapies. We propose that the development and use of inhibitors to manipulate RAD50 levels might represent a promising strategy to sensitize breast cancer cells to DNA damaging agents.     

DNA损伤应答通路研究现状

目的：分析不同DNA损伤诱导的细胞DNA修复和凋亡通路,以及相关因子在其中所起作用。方法：应用PubMed及CNKI全文数据库检索系统,以“DNA损伤、细胞凋亡和DNA修复”等为关键词,检索200601—201112的相关文献,共检索到1826篇,中文文献579篇。纳入标准：1）细胞对DNA损伤的监测;2）DNA损伤触发的DNA修复;3）DNA损伤触发的细胞凋亡。根据纳入标准符合分析的文献21篇。结果：细胞的DNA损伤应答是复杂的过程,DSBs或DNA复制阻滞是最常见DNA损伤性结构改变,其能启动多种信号通路,涉及的损伤识别因子主要有MRN、P13激酶ATM及ATR等,最终触发细胞周期抑制、DNA损伤修复或诱导细胞凋亡。结论：细胞能够识别具有潜在致死性的DNA损伤,进而激活特异的损伤通路以抑制细胞周期,增强DNA修复或诱导细胞凋亡。而因子p53和NF—KB的促细胞凋亡和促细胞存活双重作用对细胞的凋亡或者存活起决定作用。     

Dasatinib induces DNA damage and activates DNA repair pathways leading to senescence in non-small cell lung cancer cell lines with kinase-inactivating BRAF mutations

Improved therapies are greatly needed for non-small cell lung cancer (NSCLC) that does not harbor targetable kinase mutations or translocations. We previously demonstrated that NSCLC cells that harbor kinase-inactivating BRAF mutations (^KIBRAF) undergo senescence when treated with the multitargeted kinase inhibitor dasatinib. Similarly, treatment with dasatinib resulted in a profound and durable response in a patient with ^KIBRAF NSCLC. However, no canonical pathways explain dasatinib-induced senescence in ^KIBRAF NSCLC. To investigate the underlying mechanism, we used 2 approaches: gene expression and reverse phase protein arrays. Both approaches showed that DNA repair pathways were differentially modulated between ^KIBRAF NSCLC cells and those with wild-type (WT) BRAF. Consistent with these findings, dasatinib induced DNA damage and activated DNA repair pathways leading to senescence only in the ^KIBRAF cells. Moreover, dasatinib-induced senescence was dependent on Chk1 and p21, proteins known to mediate DNA damage-induced senescence. Dasatinib also led to a marked decrease in TAZ but not YAP protein levels. Overexpression of TAZ inhibited dasatinib-induced senescence. To investigate other vulnerabilities in ^KIBRAF NSCLC cells, we compared the sensitivity of these cells with that of ^WTBRAF NSCLC cells to 79 drugs and identified a pattern of sensitivity to EGFR and MEK inhibitors in the ^KIBRAF cells. Clinically approved EGFR and MEK inhibitors, which are better tolerated than dasatinib, could be used to treat ^KIBRAF NSCLC. Our novel finding that dasatinib induced DNA damage and subsequently activated DNA repair pathways leading to senescence in ^KIBRAF NSCLC cells represents a unique vulnerability with potential clinical applications.     

DNA损伤应答缺陷作为乳腺癌治疗靶点的研究进展

DNA损伤应答(DNA damage response,DDR)缺陷是近年来乳腺癌治疗研究的热门靶点之一。DDR通路负责DNA损伤后的识别、信号转导和修复,其功能异常可导致细胞的凋亡或基因组不稳定性的增加。目前进入临床研究阶段的乳腺癌DDR靶向药物主要包括多聚腺苷二磷酸核糖聚合酶[poly (ADP-ribose) polymerase,PARP]抑制剂、ATM抑制剂、CHEK1抑制剂、ATR抑制剂及WEE1抑制剂等。主要从DDR缺陷的概念、以DDR作为靶点的基本原理、DDR各类靶向药物的临床研究现状及其在临床应用中的难点与挑战等方面展开综述。     

Tribbles 2 mediates cisplatin sensitivity and DNA damage response in epithelial ovarian cancer

Aim was to identify methylated genes with functional involvement in cisplatin‐resistance development of epithelial ovarian cancer (EOC). Genome‐wide analyses of hypermethylated CpG‐islands in resistant cell lines in combination with qRT‐PCR analyses were used to identify epigenetically silenced genes. EOC‐Type‐II tumors were analyzed for gene methylation and expression and TCGA data were interrogated in‐silico. Experiments revealed 37 commonly hypermethylated genes in resistant cells of which Tribbles 2 (TRIB2) showed the most pronounced downregulation on mRNA level and was characterized further. TRIB2 showed a reactivation after 5′‐Aza‐Cytidine treatment in resistant cells but a cisplatin‐dependent, prominent upregulation on mRNA level in sensitive cells, only. Re‐expression in resistant A2780 cells increased the sensitivity to cisplatin and other DNA‐damaging agents, but not taxanes. Contrary, knockdown of TRIB2 increased resistance to cisplatin in sensitive cells. TRIB2 was involved in the induction of a cisplatin‐dependent cell cycle arrest and apoptosis by influencing p21 and survivin expression. An increased Pt‐DNA‐adduct formation in TRIB2 re‐expressing cells did not translate in higher levels of dsDNA damage (yH2AX‐foci). Thus, TRIB2 is potentially involved in the signal transduction from nucleotide excision repair of intrastrand cross links. Importantly, patient stratification of two homogenous cohorts of EOC‐Type‐II patients from Jena (n = 38) and the TCGA (n = 149) by TRIB2 mRNA expression consistently revealed a significantly decreased PFS for patients with low TRIB2 levels (log‐rank p < 0.05). Tumors from resistant patients expressed the lowest levels of TRIB2. Downregulation of TRIB2 contributes to platin‐resistance and TRIB2 expression should be validated as prognostic and predictive marker for EOC.     

Growth arrest and cell death in the breast tumor cell in response to ionizing radiation and chemotherapeutic agents which induce DNA damage

Breast tumor cells are relatively refractory to apoptosis in response to modalities which induce DNA damage such as ionizing radiation and the topoisomerase II inhibitor, adriamycin. Various factors which may modulate the apoptotic response to DNA damage include the p53 status of the cell, levels and activity of the Bax and Bcl-2 families of proteins, activation of NF-kappa B, relative levels of insulin like growth factor and insulin-like growth factor binding proteins, activation of MAP kinases and PI3/Akt kinases, (the absence of) ceramide generation and the CD95 (APO1/Fas) signaling pathway. Prolonged growth arrest associated with replicative senescence may represent an alternative and reciprocal response to DNA-damage induced apoptosis that is p53 and/or p21^waf1/cip1 dependent while delayed apoptosis may occur in p53 mutant breast tumor cells which fail to maintain the growth-arrested state. Clearly, the absence of animmediate apoptotic response to DNA damage does not eliminate other avenues leading to cell death and loss of self-renewal capacity in the breast tumor cell. Nevertheless, prolonged growth arrest (even if ultimately succeeded by apoptotic or necrotic cell death) could provide an opportunity for subpopulations of breast tumor cells to recover proliferative capacity and to develop resistance to subsequent clinical intervention.     

The DNA damage response in viral-induced cellular transformation

The DNA damage response (DDR) has emerged as a critical tumour suppressor pathway responding to cellular DNA replicative stress downstream of aberrant oncogene over-expression. Recent studies have now implicated the DDR as a sensor of oncogenic virus infection. In this review, we discuss the mechanisms by which tumour viruses activate and also suppress the host DDR. The mechanism of tumour virus induction of the DDR is intrinsically linked to the need for these viruses to promote an S-phase environment to replicate their nucleic acid during infection. However, inappropriate expression of viral oncoproteins can also activate the DDR through various mechanisms including replicative stress, direct interaction with DDR components and induction of reactive oxygen species. Given the growth-suppressive consequences of activating the DDR, tumour viruses have also evolved mechanisms to attenuate these pathways. Aberrant expression of viral oncoproteins may therefore promote tumourigenesis through increased somatic mutation and aneuploidy due to DDR inactivation. This review will focus on the interplay between oncogenic viruses and the DDR with respect to cellular checkpoint control and transformation.     

Non-coding RNAs in DNA damage response

Genome-wide studies have revealed that human and other mammalian genomes are pervasively transcribed and produce thousands of regulatory non-protein-coding RNAs (ncRNAs), including miRNAs, siRNAs, piRNAs and long non-coding RNAs (lncRNAs). Emerging evidences suggest that these ncRNAs also play a pivotal role in genome integrity and stability via the regulation of DNA damage response (DDR). In this review, we discuss the recent finding on the interplay of ncRNAs with the canonical DDR signaling pathway, with a particular emphasis on miRNAs and lncRNAs. While the expression of ncRNAs is regulated in the DDR, the DDR is also subjected to regulation by those DNA damage-responsive ncRNAs. In addition, the roles of those Dicer- and Drosha-dependent small RNAs produced in the vicinity of double-strand breaks sites are also described.     

MicroRNA-7对非小细胞肺癌表柔比星化疗的增敏作用

目的:研究microRNA-7(miR-7)对非小细胞肺癌A549和H1299细胞表柔比星(epirubicin,EPI)化疗的增敏作用及其机制。方法:EPI、miR-7 mimics单独或联合处理A549和H1299细胞后,CCK-8法检测A549和H1299细胞的增殖,Annexin-V/PI染色流式细胞术检测A549和H1299细胞的凋亡,实时定量PCR检测A549和H1299细胞中EGFR及Raf-1mRNA的表达。结果:单独使用EPI或转染miR-7 mimics均可抑制A549和H1299细胞的增殖(P<0.05),而转染miR-7 mim-ics后再以50～400 ng/ml EPI处理,较单独EPI处理显著增强对A549和H1299细胞增殖的抑制作用(P<0.05)。当miR-7mimics与EPI联用时,A549和H1299细胞的凋亡率则分别较EPI单独处理组增加(54.9±0.4)%和(67.2±0.5)%(均P<0.01),且伴随EGFR及Raf-1 mRNA表达量的显著下降(P<0.01),A549细胞中分别降低(68.0±6.0)%和(78.2±3.9)%,H1299细胞中分别降低(94.8±6.2)%和(87.8±4.3)%。结论:miR-7可通过下调EGFR及Raf-1 mRNA的表达,协同EPI抑制非小细胞肺癌A549和H1299细胞的增殖,并促进细胞凋亡。