Cancer Risk Related to Genetic Polymorphisms in Carcinogen Metabolism and DNA Repair

Abstract: Chemical carcinogenesis involves metabolism in the body of the carcinogen to the ultimate carcinogen and its interaction with DNA. There is considerable interindividual variation in the metabolic ability to activate as well as detoxify the carcinogens and in the ability to repair the carcinogen-DNA adducts. In many cases such differences occur as genetic polymorphisms and form the basis for variation in susceptibility to carcinogens and thereby to cancer risk. The activation mechanism is particularly related to the cytochromes P-450 (CYPs), and four of these are known to activate carcinogens: CYP1A1, CYP1A2, CYP2E1, and CYP3A4. Increased cancer risk has been related to polymorphisms in the CYPs and other activating enzymes. The DNA repair mechanisms show considerable complexity, and deficient repair mechanisms in certain human disorders are clearly related to increased cancer risk. Yet, there is no unambiguous epidemiological evidence available for cancer risk among individuals in general. In vivo methods have to be refined and developed for use in epidemiological studies.     

Regulation of miR-19 to Breast Cancer Chemoresistance Through Targeting PTEN

Purpose  

To explore whether miR-19 is involved in the regulation of multidrug resistance (MDR), one of the main causes of breast cancer mortality, and modulates sensitivity of tumor cells to chemotherapeutic agents.     

High Levels of Hyaluronic Acid Synthase-2 Mediate NRF2-Driven Chemoresistance in Breast Cancer Cells

Hyaluronic acid (HA), a ligand of CD44, accumulates in some types of tumors and is responsible for tumor progression. The nuclear factor erythroid 2-like 2 (NRF2) regulates cytoprotective genes and drug transporters, which promotes therapy resistance in tumors. Previously, we showed that high levels of CD44 are associated with NRF2 activation in cancer stem like-cells. Herein, we demonstrate that HA production was increased in doxorubicin-resistant breast cancer MCF7 cells (MCF7-DR) via the upregulation of HA synthase-2 (HAS2). HA incubation increased NRF2, aldo-keto reductase 1C1 (AKR1C1), and multidrug resistance gene 1 (MDR1) levels. Silencing of HAS2 or CD44 suppressed NRF2 signaling in MCF7-DR, which was accompanied by increased doxorubicin sensitivity. The treatment with a HAS2 inhibitor, 4-methylumbelliferone (4-MU), decreased NRF2, AKR1C1, and MDR1 levels in MCF7-DR. Subsequently, 4-MU treatment inhibited sphere formation and doxorubicin resistance in MCF7-DR. The Cancer Genome Atlas (TCGA) data analysis across 32 types of tumors indicates the amplification of HAS2 gene is a common genetic alteration and is negatively correlated with the overall survival rate. In addition, high HAS2 mRNA levels are associated with increased NRF2 signaling and poor clinical outcome in breast cancer patients. Collectively, these indicate that HAS2 elevation contributes to chemoresistance and sphere formation capacity of drug-resistant MCF7 cells by activating CD44/NRF2 signaling, suggesting a potential benefit of HAS2 inhibition.     

Repair and translesion DNA polymerases as anticancer drug targets

We have very recently highlighted possible connections between DNA polymerases, the main enzymes in the DNA metabolism, and human diseases (Ramadan, K., Maga, G. and Hübscher, U.: DNA polymerases and diseases, In: Genome Integrity: Facets and Perspectives ed. Lankenau, D.-H. Springer Verlag, Heidelberg Germany, Vol 1, pp. 69-102, 2007). Beside a role in DNA replication of the genome DNA polymerases have fundamental functions in other aspect of DNA metabolism, such as DNA repair, DNA recombination, translesion DNA synthesis and cell cycle checkpoint. In the last decade many novel DNA polymerases have been identified, but their exact cellular functions still await clarification. We know that many DNA polymerases have redundant functions. It is a fact that specific inhibition of certain DNA polymerases is a promising approach to develop anticancer drugs. In this review we will concentrate on DNA repair proteins and translesion DNA polymerases as possible targets for anti cancer drugs.     

外鼻皮肤癌手术切除及一期修复

目的探讨外鼻皮肤癌手术切除及一期修复的方法和效果。方法总结23例外鼻皮肤癌的临床资料。全部手术切除加一期修复。结果游离皮片修复12例,完全成活9例,边缘部分坏死3例,经换药等处理延期愈合。游离耳廓复合组织片修复的3例和各种皮瓣修复的8例全部成活。随访5年以上16例,3年以上7例,死亡2例,1例死于脑血管意外,1例死于心脏病。1例术后1年复发。其余病例全部存活无复发。结论外鼻皮肤癌采取手术切除和一期修复的方法是切实可行的。在彻底切除肿瘤的基础上,根据缺损的部位、大小和不同的情况,选择合适的修复材料,设计适当的修复方法,可以获得较好的效果。     

DNA链间交联修复与范可尼贫血发病机制的研究进展

范可尼贫血(Fanconi anemia,FA)是一种罕见的常染色体或X染色体隐性遗传病,临床表现为多样化先天畸形、进行性骨髓衰竭、色素沉着症、恶性血液系统肿瘤及实体瘤倾向。该病最典型的特征是对DNA交联剂具有高度敏感性,可产生DNA链间交联(Interstrand Cross-Links,ICL)。目前已发现至少15种FA基因,其编码的蛋白参与特有的DNA修复途径—FA途径,任何FA基因突变或缺失均可导致发病,与此同时DNA链间交联修复     

错配修复和微卫星不稳定性与食管癌的关系

目的探讨DNA错配修复基因、微卫星不稳定性与食管癌发生发展的关系。方法采用放射性同位素为基础的聚合酶链式反应(PCR)技术,对96例食管癌中错配修复基因和4个位点微卫星不稳定性进行了检测。结果 96例食管癌中hmsh3、hmsh6基因突变率分别为10.4%和25%,4个位点微卫星不稳定性阳性率分别为D2S123(12.5%)、BAT-26(18.8%)、D17S261(10.4%)、D17S799(8.3%),hmsh3、hmsh6基因突变和微卫星不稳定性多为分化不良的癌,而与患者的性别、淋巴结转移无关。结论错配修复基因突变与微卫星不稳定性是食管癌发生的早期分子事件,是除LOH致癌途径以外的又一新的致癌途径。     

8-甲氧补骨脂素诱导的四膜虫DNA损伤修复

用0.6 μg·ml~(-1)8-甲氧补骨脂素(8-methoxypsoralen,8-MOP)与365 nm UVA(紫外线)联合处理后,四膜虫DNA的修复反应,表现为细胞增殖反应受抑;DNA,RNA合成率在0 h受抑,(DNA为对照的5％,RNA为对照的20％),但经过一段修复后,DNA,RNA合成率均回升,在24h,DNA达70％,而RNA则几乎100％,同样条什下,用分子杂交等技术,观察到在0 h产生了分子交联(DNA双链在受热100℃时仍不能解链),经过24h培养后,有部分分子交联被去除(受热后DNA解链且被S1酶降解)。     

Repair of oxidative DNA damage in vitro: a tool for screening antioxidative compounds.

Reactive oxygen species (ROS) provoke the formation of base DNA alterations that are processed by an excision step of the lesion followed by a repair synthesis and ligation step to restore the strand continuity. We have reported previously the detection of DNA adducts by an in vitro chemiluminescence DNA repair synthesis assay (Salles et al., 1995) which allows the measurement of repair synthesis by cell-free extracts in damaged plasmid DNA adsorbed on sensitized microplate wells. The 3D (DNA damage detection) assay was performed in the presence of biotin-dUTP which was incorporated during the repair synthesis step. The extent of repair synthesis was measured in an ELISA reaction with ExtrAvidin-horse radish peroxidase and chemiluminescence detection. The 3D assay allows detection of any type of base alterations including base oxidation. Interestingly, under controlled production of ROS a screening procedure of antioxidants might be carried out with the 3D assay. By taking advantage of plasmid DNA adsorption, oxidative base damage can be recognized by the Escherichia coli Fpg protein which was detected in an ELISA reaction with specific antibody and chemiluminescence measurement (4D assay). With the sceening procedure of antioxidative compounds in mind, the development of such assays and their drawbacks are discussed.     

EDITORIAL REVIEW: MECHANISMS OF AMINOGLYCOSIDE NEPHROTOXICITY

Aminoglycosides continue to be widely used for the treatment of serious Gram-negative infections. Ten to fifteen per cent of all courses of therapy are complicated by declines in renal function, despite close monitoring of serum drug levels. The proposed pathogenesis and biochemical mechanisms of renal dysfunction caused by these commonly used therapeutic agents are discussed.     

Chemoresistance testing of human ovarian cancer cells and its in vitro model

Ovarian carcinoma represents the most common cause of death from gynecological malignancies in Europe and North America, being the third most frequent and the first as to the mortality. The standard chemotherapeutical regimen for ovarian cancer involves the administration of platinum derivate (carboplatin, cisplatin), in advanced stage is platinum derivate combined with paclitaxel. Introducing chemoresistance testing of ovarian tumour cells may help to choose optimal chemotherapeutic drug and customize the individual chemotherapeutical regimens in patients. One of approaches of individualization of chemotherapy is in vitro chemosensitivity testing. In our study, we evaluated the cytotoxic effects of selected chemotherapeutics in cells isolated from ovarian tumours and ascites of individual patients. Panel of chemotherapeutics used in the study included cisplatin, paclitaxel, carboplatin, topotecan, gemcitabine and etoposide and their effects on cell viability were determined by the MTT assay. In the total number of 32 clinical samples of tumour and ascites cells, the highest sensitivity showed cells to topotecan, sensitivity to cisplatin was higher than to carboplatin and paclitaxel used in clinical practice showed most often only the marginal reactivity. Resistance to carboplatin and most of the time to gemcitabine and etoposide was commonly present. When the same test on cells that have been frozen for several weeks was repeated it was found that in 20 cases chemosensitivity increased while in 18 cases decreased. In remaining cases there was no change in reactivity to cytostatics. Moreover, chemosensitivity of cells isolated from solid tumour and ascites from the same patient did not show any significant difference with exaption of paclitaxel.     

脉冲场凝胶电泳检测电离辐射诱发DNA损伤及其修复

目的：评价脉冲场凝胶电泳（PFGE）法检测电离辐射诱发小鼠脾细胞DNA损伤及其修复的可行性.方法：采用PFGE法测定不同剂量γ射线诱发小鼠脾细胞DNA单、双链断裂及4 Gyγ射线照射后不同时间脾细胞DNA单、双链断裂及其修复情况,并与未照射组（对照组）进行比较.结果：γ射线照射小鼠后,脾细胞DNA单、双链断裂数目随照射剂量的增加均呈增加趋势,单链断裂数目多于双链,1 Gy所致DNA双链断裂及2 Gy所致DNA单链断裂显著高于对照组（t=2.668,P＜0.05;t=5.117,P＜0.01）.以4 Gy照射后经过不同时间修复,单、双链断裂均呈下降趋势,起初DNA链断裂的修复为快速修复,1 h后大多数损伤已得到修复.单链断裂的修复速度高于双链,当修复时间超过2 h后,单链断裂又呈现上升趋势.结论：本实验方法有可能成为一种快速、敏感地检测活体动物细胞DNA损伤及其修复的方法.     

A Bacterial DNA Repair Test Evaluating the Genotoxicity of Light Sources

A DNA repair test was used in order to assess its applicability for detecting the genotoxicity of sunlight and of the light emitted by halogen lamps and fluorescent lamps. This experimental system compares the lethality of test agents in the Escherichia coli wild-type WP2 and its isogenic counterparts lacking, either individually or in combination, various DNA repair mechanisms. DNA repair-deficient strains included WP2uvrA (uvrA^-), WP67 (uvrA^- polA^-), CM561 (lexA^-), CM571 (recA^-), WP100 (uvrA^- recA^-), and CM871 (uvrA^- recA^- lexA^-). All light sources produced a substantial killing of repair-deficient strains, with a maximum activity in the triple mutant CM871, at doses that did not affect survival of the wild type. The genotoxicity of uncovered quartz halogen bulbs was particularly potent, compared to fluorescent lamps and sunlight. Moreover, the mechanisms involved in repairing the DNA damage induced by halogen lamps were similar to those of a 254 nm UV source. The spectrum of genetic damage produced by sunlight and fluorescent lamps was conversely more comparable to that of a 365 nm UV source. These data demonstrated a harmful emission of appreciable amounts of genotoxic far-UV wavelengths by halogen lamps, thereby confirming our previous results in the his^-Salmonella typhimurium mutagenicity test. Genotoxicity of halogen lamps could be easily prevented in both experimental systems by suitable glass or plastic covers. Compared to the mutagenicity end point, the differential lethality end point provided even more clear-cut results in detecting the DNA-damaging ability of all light sources. Moreover, parallel assays provided evidence that the bacterial DNA repair test was far more sensitive than the mutagenicity test in evaluating the genotoxicity of the light produced by halogen lamps. On the whole, the DNA repair test in E. coli is even simpler and faster (24 vs. 48 h) than the Salmonella mutagenicity test, and compares favorably in terms of sensitivity to genotoxic light sources.     

Polyamine–DNA Interactions: Possible Site of New Cancer Chemotherapeutic Intervention

The effects of polyamines on the structure of nucleic acids in cell-free systems and in cell culture systems are reviewed. Evidence suggests that polyamine depletion inhibits cell growth and may cause conformational changes in DNA. These effects may be exploited to cause changes in the action of drugs and may be used to advantage in combination treatment protocols. A discussion of theoretical models of the interactions, physicochemical evidence for conformational changes, and the effects of anticancer drugs in cells depleted of polyamines is presented.     

Strategies to Improve the Killing of Tumors Using Temozolomide: Targeting the DNA Repair Protein MGMT

Alkylating agents such as temozolomide (TMZ) are effective anticancer drugs for treating a variety of solid tumors including melanoma, glioma, and astrocytoma. TMZ exerts its effects mainly via the mutagenic product O6-methylguanine, a cytotoxic DNA lesion. This damage may be repaired by the DNA repair enzyme O6-methylguanine DNA methyltransferase (MGMT), a key player in the resistance of cancers to TMZ. Several strategies are presently being pursued to improve the killing of tumor cells by TMZ, with inhibition of MGMT being the most promising. In this review, we provide an overview of recent advances in this field.