Implications For Cancer Chemotherapy Research Articles

Morphine decreases cytotoxicity and mutagenicity of doxorubicin in vitro: Implications for cancer chemotherapy

Morphine is the most common opioid analgesic administered to treat pain in patients undergoing cancer chemotherapy. This study aimed to evaluate the cytotoxic and mutagenic effects of morphine alone and in combination with doxorubicin (Dox), an antineoplastic agent largely used in patients with solid cancers. Cytotoxicity was evaluated in neuroblastoma (SH-SY5Y) and fibroblast (V79) cells using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl tetrazolium bromide (MTT) colorimetric assay while mutagenicity was assessed using the Salmonella/microsome assay in the absence and in the presence of S9 mix. Morphine showed a cytotoxic effect mainly on SH-SY5Y cells and reduced the cytotoxic effects of Dox when evaluated in a co-treatment procedure. In the Salmonella/microsome assay, it was observed that morphine did not induce mutations and, in fact, decreased the mutagenic effects induced by Dox in TA98 and TA102 strains in the absence of metabolic activation. Furthermore, in the presence of metabolic activation, no induction of mutations was observed with morphine. In conclusion, morphine decreased Dox cytotoxicity in both neuronal and non-neuronal cells and showed antimutagenic effects in the TA102 strain which detects mutagens inducing DNA oxidative damages. However, morphine decreased frameshift mutations induced by Dox in non-cytotoxic concentrations, an effect suggesting interference of Dox intercalation activity that could decrease its chemotherapeutic efficacy. These compelling findings highlight the importance of conducting further studies to explore the potential implications of co-administering morphine and Dox during cancer chemotherapy.

DNA alkylation lesion repair: outcomes and implications in cancer chemotherapy.

Alkylated DNA lesions, induced by both exogenous chemical agents and endogenous metabolites, represent a major form of DNA damage in cells. The repair of alkylation damage is critical in all cells because such damage is cytotoxic and potentially mutagenic. Alkylation chemotherapy is a major therapeutic modality for many tumors, underscoring the importance of the repair pathways in cancer cells. Several different pathways exist for alkylation repair, including base excision and nucleotide excision repair, direct reversal by methyl-guanine methyltransferase (MGMT), and dealkylation by the AlkB homolog (ALKBH) protein family. However, maintaining a proper balance between these pathways is crucial for the favorable response of an organism to alkylating agents. Here, we summarize the progress in the field of DNA alkylation lesion repair and describe the implications for cancer chemotherapy.

Cell-cell contacts protect against t-BuOOH-induced cellular damage and ferroptosis in vitro.

Ferroptosis is a recently discovered pathway of regulated necrosis dependent on iron and lipid peroxidation. It has gained broad attention since it is a promising approach to overcome resistance to apoptosis in cancer chemotherapy. We have recently identified tertiary-butyl hydroperoxide (t-BuOOH) as a novel inducer of ferroptosis. t-BuOOH is a widely used compound to induce oxidative stress in vitro. t-BuOOH induces lipid peroxidation and consequently ferroptosis in murine and human cell lines. t-BuOOH additionally results in a loss of mitochondrial membrane potential, formation of DNA double-strand breaks, and replication block. Here, we specifically address the question whether cell-cell contacts regulate t-BuOOH-induced ferroptosis and cellular damage. To this end, murine NIH3T3 or human HaCaT cells were seeded to confluence, but below their saturation density to allow the establishment of cell-cell contacts without inducing quiescence. Cells were then treated with t-BuOOH (50 or 200 µM, respectively). We revealed that cell-cell contacts reduce basal and t-BuOOH-triggered lipid peroxidation and consequently block ferroptosis. Similar results were obtained with the specific ferroptosis inducer erastin. Cell-cell contacts further protect against t-BuOOH-induced loss of mitochondrial membrane potential, and formation of DNA double-strand breaks. Interestingly, cell-cell contacts failed to prevent t-BuOOH-mediated replication block or formation of the oxidative base lesion 8-oxo-dG. Since evidence of protection against cell death was both (i) observed after treatment with hydrogen peroxide, methyl methanesulfonate or UV-C, and (ii) seen in several cell lines, we conclude that protection by cell-cell contacts is a widespread phenomenon. The impact of cell-cell contacts on toxicity might have important implications in cancer chemotherapy.

Indibulin dampens microtubule dynamics and produces synergistic antiproliferative effect with vinblastine in MCF-7 cells: Implications in cancer chemotherapy

Indibulin, a synthetic inhibitor of tubulin assembly, has shown promising anticancer activity with a minimal neurotoxicity in preclinical animal studies and in Phase I clinical trials for cancer chemotherapy. Using time-lapse confocal microscopy, we show that indibulin dampens the dynamic instability of individual microtubules in live breast cancer cells. Indibulin treatment also perturbed the localization of end-binding proteins at the growing microtubule ends in MCF-7 cells. Indibulin reduced inter-kinetochoric tension, produced aberrant spindles, activated mitotic checkpoint proteins Mad2 and BubR1, and induced mitotic arrest in MCF-7 cells. Indibulin-treated MCF-7 cells underwent apoptosis-mediated cell death. Further, the combination of indibulin with an anticancer drug vinblastine was found to exert synergistic cytotoxic effects on MCF-7 cells. Interestingly, indibulin displayed a stronger effect on the undifferentiated neuroblastoma (SH-SY5Y) cells than the differentiated neuronal cells. Unlike indibulin, vinblastine and colchicine produced similar depolymerizing effects on microtubules in both differentiated and undifferentiated SH-SY5Y cells. The data indicated a possibility that indibulin may reduce chemotherapy-induced peripheral neuropathy in cancer patients.

Antibacterial and anticancer activity of the purified cashew nut shell liquid: implications in cancer chemotherapy and wound healing

The cashew nut shell liquid (CNSL) from the cashew nut shell of Anacardium occidentale L. has been used to treat skin infections, cracks on soles of feet and cancerous ulcers. In this study, we have purified the technical CNSL, systematically evaluated its anticancer, antibacterial and wound healing activity. The LC-MS data revealed that the purified CNSL contains the compounds, cardanol, anacardic acid and methylcardol. It inhibited the proliferation of HeLa cells with an IC50 of 0.004%(v/v) and caused moderate mitotic block with spindle abnormality. It induced apoptosis in HeLa cells and accelerated wound closure in L929 cells. It inhibited the growth of Bacillus subtilis with an IC50 of 0.35%(v/v) and the treated cells exhibited elongated morphology indicating that suppression of cell division is one of the possible mechanisms of its action. The study suggests that the purified CNSL might have potential applications in anticancer and antibacterial drug development.

Reversal effects of local anesthetics on P-glycoprotein-mediated cancer multidrug resistance.

The existence of multidrug resistance (MDR) is the main reason for failure in cancer chemotherapy. The main mechanism of MDR is the overexpression of P-glycoprotein (P-gp). P-gp, a 170 kDa transmembrane phosphorylated glycoprotein encoded by ABCB1 belonging to a member of the ATP-binding cassette (ABC) super-family of the membrane transporters, is also known as the MDR protein. Local anesthetics (LAs) are a major contributor to medical practice. As a cornerstone of analgesia, LAs provides myriad benefits. Recent studies have shown that the LAs can interfere with receptors other than the traditional sodium channel. LA can suppress the proliferation of several cancer cells. The inhibition of P-gp could reverse MDR. Interestingly, the LAs, such as lidocaine, can repress ABCB1 (P-gp) expression and reverse MDR. Also, LAs can modulate the tumor necrosis factor/AKT pathway, the tumor necrosis factor/Src pathway, epidermal growth factor receptor, the Wnt pathway, and the RASSF1A/MDM2/p53 pathway to interfere with P-gp function. This means that LAs could be potentially useful in reversing cancer MDR. The aim of this review is to report the nonanesthetic functions of LAs, with a special focus on their anti-MDR effects and their potential beneficial implications in cancer chemotherapy.

Phytochemicals mediated signalling pathways and their implications in cancer chemotherapy: Challenges and opportunities in phytochemicals based drug development: A review

Abstract Cancer is considered as major leading cause for death in India and around world. Modern drug-targeted therapies have undoubtedly improved treatment to the cancer patients but also evoke severe side effects. Organ failure and

Mobilization of Nuclear Copper by Green Tea Polyphenol Epicatechin-3-Gallate and Subsequent Prooxidant Breakage of Cellular DNA: Implications for Cancer Chemotherapy.

Epidemiological as well as experimental evidence exists in support of chemopreventive and anticancer properties of green tea and its constituents. The gallocatechin, epicatechin-3-gallate is a major polyphenol present in green tea, shown responsible for these effects. Plant-derived polyphenolic compounds are established natural antioxidants which are capable of catalyzing oxidative DNA degradation of cellular DNA, alone as well as in the presence of transition metal ions, such as copper. Here we present evidence to support that, similar to various other polyphenoic compounds, epicatechin-3-gallate also causes oxidative degradation of cellular DNA. Single cell alkaline gel electrophoresis (Comet assay) was used to assess DNA breakage in lymphocytes that were exposed to various concentrations of epicatechin-3-gallate. Inhibition of DNA breakage in the presence of scavengers of reactive oxygen species (ROS) suggested involvement of ROS generation. Addition of neocuproine (a cell membrane permeable Cu(I) chelator) inhibited DNA degradation, dose-dependently, in intact lymphocytes. In contrast, bathocuproine, which does not permeate cell membrane, was observed to be ineffective. We further show that epicatechin-3-gallate degrades DNA in cell nuclei, which can also be inhibited by neocuproine, suggesting mobilization of nuclear copper in this reaction as well. Our results are indicative of ROS generation, possibly through mobilization of endogenous copper ions, and support our long-standing hypothesis of a prooxidant activity of plant-derived polyphenols as a mechanism for their documented anticancer properties.

Design and synthesis of taxane derivatives of valproic acid as potent and selective cytotoxic agents

Resistance to anticancer agents has important implications for cancer chemotherapy. Small changes in chemical structures of cytotoxic agents can alter their biological interactions that can be beneficial in overcoming the drug resistance problem. Valproic acid, a well-known antiepileptic drug is in advanced clinical studies for cancer treatment. In the present study, valproic acid was incorporated into the taxane moiety at various positions and the new analogs were evaluated for their in vitro cytotoxicity. The novel analog, Valprotaxel showed comparable cytotoxicity in head and neck, and colon cancer cell lines with remarkable improvement in selectivity for cancer cells compared to paclitaxel and docetaxel.

The Induction and Repair of DNA Interstrand Crosslinks and Implications in Cancer Chemotherapy.

DNA interstrand crosslinks (ICLs) can be induced by numerous endogenous and exogenous chemical agents with the capacity of covalently binding to two base sites in the two strands of the DNA duplex. A series of normal DNA metabolism processes are affected by ICLs. For example, DNA replication and transcription are interfered during cell division, which is fatal to cell survival. In cancer cells, the induction of ICLs is a significant target for cancer chemotherapies. However, the formation of ICLs in cancer cells can be weakened by the repair mechanisms of DNA damage, which results in resistance to chemotherapies. Therefore, it is necessary to develop highly effective ICL agents for the purpose of achieving good chemotherapeutic effects. Furthermore, the combination of ICL agents with inhibitors of ICL repair is a promising strategy for the clinical treatment of cancer. This review summarizes the development of several types of ICL agents as chemotherapies over the past decades and the mechanisms underlying the repair of DNA ICLs. The potential of ICL repair inhibitors for combination therapy with ICL agents in cancer treatment is also discussed.

HDAC Inhibitors Target HDAC5, Upregulate MicroRNA-125a-5p, and Induce Apoptosis in Breast Cancer Cells

Histone deacetylase inhibitors (HDACi) are novel clinical anticancer drugs that inhibit HDAC gene expression and induce cell apoptosis in human cancers. Nevertheless, the detailed mechanism or the downstream HDAC targets by which HDACi mediates apoptosis in human breast cancer cells remains unclear. Here, we show that HDACi reduce tumorigenesis and induce intrinsic apoptosis of human breast cancer cells through the microRNA miR-125a-5p in vivo and in vitro. Intrinsic apoptosis was activated by the caspase 9/3 signaling pathway. In addition, HDACi mediated the expression of miR-125a-5p by activating RUNX3/p300/HDAC5 complex. Subsequently, miR-125a-5p silenced HDAC5 post-transcriptionally in the cells treated with HDACi. Thus, a regulatory loop may exist in human breast cancer cells involving miR-125a-5p and HDAC5 that is controlled by RUNX3 signaling. Silencing of miR-125a-5p and RUNX3 inhibited cancer progression and activated apoptosis, but silencing of HDAC5 had a converse effect. In conclusion, we demonstrate a possible new mechanism by which HDACi influence tumorigenesis and apoptosis via downregulation of miR-125a-5p expression. This study provides clinical implications in cancer chemotherapy using HDACi.

ABCC1 Is Related to the Protection of the Distal Nephron against Hyperosmolality and High Sodium Environment: Possible Implications for Cancer Chemotherapy

AimsGlutathione (GSH) plays an important role in protecting cells against oxidative damage. ABCC1 protein transports GSH. Although this protein is largely studied in cancer, due to multidrug resistance phenotype, its role in the tubular cells of the kidney is unknown. The goal of this study was to find out whether ABCC1 has a role in protecting cells from the distal nephron against the stress caused by high medullar osmolality.Main MethodsMA104 cells were treated with high concentrations of sodium chloride, urea, or both to raise the osmolality of the culture medium. Cell viability was accessed by MTT and trypan blue assays. ABCC1 expression and extrusion of carboxi-fluorescein (CF), a fluorescent ABCC1 substrate, were measured by flow cytometry.Key FindingsIncubation of MA104 cells in a high sodium concentration medium resulted in changes in cell granularity and altered expression and activity of ABCC1. Urea did not alter ABCC1 expression or activity, but reversed the observed NaCl effects. High sodium concentrations also had a negative effect on cell viability and urea also protected cells against this effect.SignificanceOur findings demonstrate that ABCC1 plays a significant role in the protection of kidney epithelial cells against the stress caused by high sodium environment present in renal medulla.

Cytotoxic Effects of Manganese in Human Prostate Carcinoma DU145 Cells

Manganese (Mn) is a micro‐nutrient essential for maintaining the normal functions of many enzymes and other proteins in mammalian cells and tissues. However, Mn is toxic when taken in excess. Our previous studies have shown that Mn induces cell death in human neural tumor cells by altering, in part, their energy metabolism leading to necrosis. To investigate the hypothesis that Mn generally exerts toxicity in cancer cells by inducing them to undergo apoptosis and/or necrosis, this study aims to determine the effects of Mn on human prostate carcinoma DU145 cells. Our results demonstrate that at pathophysiological levels Mn induced dose‐related decrease in survival of DU145 cells concomitant with alterations in their cellular morphology. Results from flow cytometry analysis and lactate dehydrogenase release assays obtained with DU145 cells treated with MnCl2 for 48 hours revealed that at lower treatment levels, Mn induced mainly apoptosis whereas at higher levels, it induced mainly necrosis in DU145 cells. Studies are ongoing to determine the signaling mechanisms underlying the Mn‐mediated effects. Thus, our findings may assume pathophysiological significance of Mn toxicity in prostate cancer and may have implications in cancer chemotherapy.

Cloning and characterization of polyA-RNA transcripts encoded by activated B1-like retrotransposons in mouse erythroleukemia MEL cells exposed to methylation inhibitors

We have previously identified a DNA silent region located downstream of the 3'-end of the β(major) globin gene (designated B1-559) that contains a B1 retrotransposon, consensus binding sites for erythroid specific transcription factors and shares the capacity to act as promoter in hematopoietic cells interacting with β-globin gene LCR sequences in vitro. In this study, we have cloned four new non-polyA RNA transcripts being detected upon blockade of murine erythroleukemia (MEL) cell differentiation to erythroid maturation by methylation inhibitors and demonstrated that two of them share high structural homology with sequences of B1 element found within the B1-559 region. Although it is not clear yet whether and how these RNAs interfere with induction of erythroid maturation, these data provide evidence for the first time showing that methylation inhibitors can activate silent repetitive DNA sequences in MEL cells and may have implications in cancer chemotherapy using demethylating drugs as antineoplastic agents.

Small Molecule Modifiers of MicroRNA miR-122 Function for the Treatment of Hepatitis C Virus Infection and Hepatocellular Carcinoma

MicroRNAs are a recently discovered new class of important endogenous regulators of gene function. Aberrant regulation of microRNAs has been linked to various human diseases, most importantly cancer. Small molecule intervention of microRNA misregulation has the potential to provide new therapeutic approaches to such diseases. Here, we report the first small molecule inhibitors and activators of the liver-specific microRNA miR-122. This microRNA is the most abundant microRNA in the liver and is involved in hepatocellular carcinoma development and hepatitis C virus (HCV) infection. Our small molecule inhibitors reduce viral replication in liver cells and represent a new approach to the treatment of HCV infections. Moreover, small molecule activation of miR-122 in liver cancer cells selectively induced apoptosis through caspase activation, thus having implications in cancer chemotherapy. In addition to providing a new approach for the development of therapeutics, small molecule modifiers of miR-122 function are unique tools for exploring miR-122 biogenesis.

Essential role of PI3-kinase pathway in p53-mediated transcription: Implications in cancer chemotherapy

The PI3-kinase pathway is the target of inactivation in achieving better cancer chemotherapy. Here, we report that p53-mediated transcription is inhibited by pharmacological inhibitors and a dominant-negative mutant of PI3-kinase, and this inhibition was relieved by a constitutively active mutant of PI3-kinase. Akt/PKB and mTOR, the downstream effectors of PI3-kinase, were also found to be essential. LY294002 (PI3-kinase inhibitor) pre-treatment altered the post-translational modifications and the sub-cellular localization of p53. Although LY294002 increased the chemosensitivity of cells to low concentrations of adriamycin (adriamycin-low), it protected the cells from cytotoxicity induced by high concentrations of adriamycin (adriamycin-high) in a p53-dependent manner. Further, we found that LY294002 completely abolished the activation of p53 target genes (particularly pro-apoptotic) under adriamycin-high conditions, whereas it only marginally repressed the p53 target genes under adriamycin-low conditions; in fact, it further activated the transcription of NOXA, HRK, APAF1 and CASP5 genes. Thus, the differential effect of PI3-kinase on p53 functions seems to be responsible for the differential regulation of DNA damage-induced cytotoxicity and cell death by PI3-kinase. Our finding becomes relevant in the light of ongoing combination chemotherapy trials with the PI3-kinase pathway inhibitors and underscores the importance of p53 status in the careful formulation of combination chemotherapies.

Abstract 96: Conformational and thermodynamics analyses of the regulation of trifluoperazine on camodulin binding to Fas: Implications for cancer chemotherapy

Abstract Fas-mediated signaling pathway is an important mechanism for apoptosis in a variety of cells, including cholangiocarcinoma and other cancer cells. The formation of death inducing signaling complex (DISC) is a critical step for Fas-mediated signaling. Recent experimental studies showed that calmodulin (CaM) binds to Fas and regulates Fas-mediated DISC formation and the binding of CaM to Fas is inhibited by the CaM antagonist, trifluoperazine (TFP) (J Cell Biochem, 103:788, 2008). The present study sought to determine the structural basis and molecular mechanisms of TFP regulation of Fas-mediated DISC formation. We used a combination of molecular dynamics simulations and binding free energy analyses to investigate the effect of TFP on CaM-Fas binding. We studied the interactions of different number(s) of TFP(s) with CaM and the effect of the resulting conformational changes of CaM on CaM/Fas binding. We found that the binding affinity of one TFP with CaM was affected by the sequential binding of other TFP(s) to CaM, which was consistent with near-UC circular dichroism data (Biochemistry 37:15300, 1998). The number of TFP(s) bound to CaM was shown to affect the conformational and motion changes of CaM, and thus directly affect CaM binding to Fas. Consistent with previous experimental observations that CaM-Fas binding was affected by TFP concentrations (J Biol Chem, 280:29964, 2005), we demonstrated that one TFP bound to CaM inhibited CaM-Fas binding while the subsequent two TFPs or four TFPs bound to CaM resulted in the recovery of CaM-Fas binding (Table 1). Results also showed that conformational and motional changes of Fas by binding to CaM were directly related to the number of TFPs bound to CaM, which could further affect Fas recruitment of FADD to the DISC. This study provides structural and thermodynamics evidence elucidating the role of the CaM antagonist, TFP, in regulating CaM-Fas binding and Fas-mediated DISC formation and apoptosis.Table 1.The change of CaM-Fas binding affinity by the CaM antagonist, TFP. CaM_Fas_WTCaM_1TFP_FasCaM_2TFPs_FasCaM_4TFPs_FasΔG−7.11±4.67−1.32±0.99−6.96±3.47−6.42±1.06ΔΔG 5.79*0.150.69All values in this table were expressed in terms of kcal/mol. ΔG is the binding free energy for the complex, and ΔΔG is the relative binding free energies with respect to the CaM-Fas complex without CaM antagonist TFP(s). * Differences are statistically significant (Student's t-test, p<0.05) Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 96.

Epidermal Growth Factor Receptor Phosphorylation Sites Ser991 and Tyr998 Are Implicated in the Regulation of Receptor Endocytosis and Phosphorylations at Ser1039 and Thr1041

Aberrant expression, activation, and down-regulation of the epidermal growth factor receptor (EGFR) have causal roles in many human cancers, and post-translational modifications including phosphorylation and ubiquitination and protein-protein interactions directly modulate EGFR function. Quantitative mass spectrometric analyses including selected reaction monitoring (also known as multiple reaction monitoring) were applied to the EGFR and associated proteins. In response to epidermal growth factor (EGF) stimulation of cells, phosphorylations at EGFR Ser991 and Tyr998 accumulated more slowly than at receptor sites involved in RAS-ERK signaling. Phosphorylation-deficient mutant receptors S991A and Y998F activated ERK in response to EGF but were impaired for receptor endocytosis. Consistent with these results, the mutant receptors retained a network of interactions with known signaling proteins including EGF-stimulated binding to the adaptor GRB2. Compared with wild type EGFR the Y998F variant had diminished EGF-stimulated interaction with the ubiquitin E3 ligase CBL, and the S991A variant had decreased associated ubiquitin. The endocytosis-defective mutant receptors were found to have elevated phosphorylation at positions Ser1039 and Thr1041. These residues reside in a serine/threonine-rich region of the receptor previously implicated in p38 mitogen-activated protein kinase-dependent stress/cytokine-induced EGFR internalization and recycling (Zwang, Y., and Yarden, Y. (2006) p38 MAP kinase mediates stress-induced internalization of EGFR: implications for cancer chemotherapy. EMBO J. 25, 4195–4206). EGF-induced phosphorylations at Ser1039 and Thr1041 were blocked by treatment of cells with SB-202190, a selective inhibitor of p38. These results suggest that coordinated phosphorylation of EGFR involving sites Tyr998, Ser991, Ser1039, and Thr1041 governs the trafficking of EGF receptors. This reinforces the notion that EGFR function is manifest through spatially and temporally controlled protein-protein interactions and phosphorylations.

Squalene: A natural antioxidant?

European Journal of Lipid Science and TechnologyVolume 111, Issue 5 p. 411-412 EditorialFree Access Squalene: A natural antioxidant? Ryszard Amarowicz, Ryszard Amarowicz Division of Food Science, Institute of Animal Reproduction and Food Research, Polish Academy of Sciences, Olsztyn, PolandSearch for more papers by this author Ryszard Amarowicz, Ryszard Amarowicz Division of Food Science, Institute of Animal Reproduction and Food Research, Polish Academy of Sciences, Olsztyn, PolandSearch for more papers by this author First published: 18 May 2009 https://doi.org/10.1002/ejlt.200900102Citations: 58AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. References 1 E. Psomiadou, M. Tsimidou: On the role of squalene in olive oil stability. J Agric Food Chem. 1999, 47, 4025– 4032. 2 C. I. G. Tuberoso, A. Kowalczyk, E. Sarritzu, P. Cabras: Determination of antioxidant compounds and antioxidant activity in comercial oilseeds for food use. Food Chem. 2007, 103, 1494– 1501. 3 Z.-R. Huang, Y.-K. Lin, J.-Y. Fang: Biological and pharmacological activities of squalene and related compounds: Potential uses in cosmetic dermatology. Molecules 2009, 14, 540– 554. 4 F. Conforti, G. Statti, M.R. Loizzo, G. Sacchetti, F. Poli, F. Menichini: In vitro antioxidant effect and inhibition of α-amylase of two varieties of Amaranthus caudatus seeds. Biol Pharm Bull. 2005, 28, 1098– 1102. 5 E. Psomiadou, M. Tsimidou: Stability of virigin olive oil. 2. Photo-oxidation studies. J Agric Food Chem. 2002, 50, 722– 727. 6 Y. Kohno, Y. Egawa, S. Itoh, S. Naganka, M. Takahashi, K. Mukai: Kinetik study of quenching reaction of singlet oxygen and scavenging reaction of free radical by squalene in n-butanol. Biochim Biophys Acta. 1995, 1256, 52– 56. 7 E. Finotti, M. D'Ambrosio, F. Paoletti, V. Vivanti, G. Quaglia: Synergestic effect of α-tocopherol, β-sitisterol and squalene on antioxidant activity assayed by crocin bleaching method. Nahrung 2000, 44, 373– 374. 8 M. A. Dessi, M. Deiana, B. W. Day, A. Rosa, S. Banni, F. P. Corongiu: Oxidative stability of polyunsaturated fatty acids: effect of squalene. Eur J Lipid Sci Technol. 2002, 104, 506– 512. 9 R. V. Tikekar, R. D. Ludescher, M. V. Karwe: Processing stability of squalene in amaranth and antioxidant potential of amaranth extract. J Agric Food Chem. 2008, 56, 10675– 10678. 10 R. Mateos, M. D. Domínguez, J. L. Espartero, A. Cert: Antioxidant effect of phenolic compounds, α-tocopherol, and other minor components in virgin olive oil. J Agric Food Chem. 2003, 51, 7170– 7175. 11 N. Dhandapani, B. Ganesan, R. Anandan, R. Jeyakumar, D. Rajaprabhu, R. A. Ezhilan: Synergistic effect of squalene and polyunsaturated fatty acid concentrate on lipid peroxidation and antioxidant status in isoprenaline-induced myocardial infarction in rats. African J Biotechnol. 2007, 6, 1021– 1027. 12 T. Hauß, S. Dante, N. A. Dencher, T. Haines: Squalene is in the midplane of lipid bilayer: implications for its function as aproton permeability barrier. Biochim Biophys Acta. 2002, 1556, 149– 154. 13 B. Das, H. Yeger, H. Baruchel, M. H. Freedman, G. Koren, S. Baruchel: In vitro cytoprotective activity of squalene on a bone marrow versus neuroblastoma model of cisplatin-induced toxicity: implications in cancer chemotherapy. Eur J Cancer 2003, 39, 2556– 2565. 14 P. Manzi, G. Panfili, M. Esti, L. Pizzoferrato: Natural antioxidants in the unsaponifiable fraction of virgin oils from different cultivars. J Sci Food Agric. 1998, 77, 115– 120. 15 E. Psomiadou, M. Tsimidou: Stability of virgin olive oil. 1. Autoxidation studies. J Agric Food Chem. 2002, 50, 716– 721. 16 K. Hrncirik, S. Fritsche: Relation of the endogenous antioxidant system and the quality of extra olive oil under accelerated storage conditions. J Agric Food Chem. 2005, 53, 2103– 2110. 17 Pan-frying of French fries in three different edible oils enriched with olive leaf extract: Oxidative stability and fate of microconstituents. LWT – Food Sci Technol. 2009, 42, 1090– 1097. Citing Literature Volume111, Issue5No. 5 May 2009Pages 411-412 ReferencesRelatedInformation

DNA binding, nucleotide flipping, and the helix-turn-helix motif in base repair by O6-alkylguanine-DNA alkyltransferase and its implications for cancer chemotherapy

O 6-Alkylguanine-DNA alkyltransferase (AGT) is a crucial target both for the prevention of cancer and for chemotherapy, since it repairs mutagenic lesions in DNA, and it limits the effectiveness of alkylating chemotherapies. AGT catalyzes the unique, single-step, direct damage reversal repair of O 6-alkylguanines by selectively transferring the O 6-alkyl adduct to an internal cysteine residue. Recent crystal structures of human AGT alone and in complex with substrate DNA reveal a two-domain α/β fold and a bound zinc ion. AGT uses its helix-turn-helix motif to bind substrate DNA via the minor groove. The alkylated guanine is then flipped out from the base stack into the AGT active site for repair by covalent transfer of the alkyl adduct to Cys145. An asparagine hinge (Asn137) couples the helix-turn-helix DNA binding and active site motifs. An arginine finger (Arg128) stabilizes the extrahelical DNA conformation. With this newly improved structural understanding of AGT and its interactions with biologically relevant substrates, we can now begin to unravel the role it plays in preserving genetic integrity and discover how it promotes resistance to anticancer therapies.