The antioxidant tempol transforms gut microbiome to resist obesity in female C3H mice fed a high fat diet

The nitroxide, Tempol, prevents obesity related changes in mice fed a high fat diet (HFD). The purpose of this study was to gain insight into the mechanisms that result in such changes by Tempol in female C3H mice. Microarray methodology, Western blotting, bile acid analyses, and gut microbiome sequencing were used to identify multiple genes, proteins, bile acids, and bacteria that are regulated by Tempol in female C3H mice on HFD. The effects of antibiotics in combination with Tempol on the gut microflora were also studied. Adipose tissue, from Tempol treated mice, was analyzed using targeted gene microarrays revealing up-regulation of fatty acid metabolism genes (Acadm and Acadl > 4-fold, and Acsm3 and Acsm5 > 10-fold). Gene microarray studies of liver tissue from mice switched from HFD to Tempol HFD showed down-regulation of fatty acid synthesis genes and up-regulation of fatty acid oxidation genes. Analyses of proteins involved in obesity revealed that the expression of aldehyde dehydrogenase 1A1 (ALDH1A1) and fasting induced adipose factor/angiopoietin-like protein 4 (FIAF/ANGPTL4) was altered by Tempol HFD. Bile acid studies revealed increases in cholic acid (CA) and deoxycholic acid (DCA) in both the liver and serum of Tempol treated mice. Tempol HFD effect on the gut microbiome composition showed an increase in the population of Akkermansia muciniphila, a bacterial species known to be associated with a lean, anti-inflammatory phenotype. Antibiotic treatment significantly reduced the total level of bacterial numbers, however, Tempol was still effective in reducing the HFD weight gain. Even after antibiotic treatment Tempol still positively influenced several bacterial species such as as Akkermansia muciniphila and Bilophila wadsworthia. The positive effects of Tempol moderating weight gain in female mice fed a HFD involves changes to the gut microbiome, bile acids composition, and finally to changes in genes and proteins involved in fatty acid metabolism and storage.

Pharmacological Inhibition of HSP90 Radiosensitizes Head and Neck Squamous Cell Carcinoma Xenograft by Inhibition of DNA Damage Repair, Nucleotide Metabolism, and Radiation-Induced Tumor Vasculogenesis

PURPOSE

Recent preclinical studies suggest combining the HSP90 inhibitor AT13387 (Onalespib) with radiation (IR) against colon cancer and head and neck squamous cell carcinoma (HNSCC). These studies emphasized that AT13387 downregulates HSP90 client proteins involved in oncogenic signaling and DNA repair mechanisms as major drivers of enhanced radiosensitivity. Given the large array of client proteins HSP90 directs, we hypothesized that other key proteins or signaling pathways may be inhibited by AT13387 and contribute to enhanced radiosensitivity. Metabolomic analysis of HSP90 inhibition by AT13387 was conducted to identify metabolic biomarkers of radiosensitization and whether modulations of key proteins were involved in IR-induced tumor vasculogenesis, a process involved in tumor recurrence.

METHODS AND MATERIALS

HNSCC and non-small cell lung cancer cell lines were used to evaluate the AT13387 radiosensitization effect in vitro and in vivo. Flow cytometry, immunofluorescence, and immunoblot analysis were used to evaluate cell cycle changes and HSP90 client protein's role in DNA damage repair. Metabolic analysis was performed using liquid chromatography-Mass spectrometry. Immunohistochemical examination of resected tumors post-AT13387 and IR treatment were conducted to identify biomarkers of IR-induced tumor vasculogenesis.

RESULTS

In agreement with recent studies, AT13387 treatment combined with IR resulted in a G2/M cell cycle arrest and inhibited DNA repair. Metabolomic profiling indicated a decrease in key metabolites in glycolysis and tricarboxylic acid cycle by AT13387, a reduction in Adenosine 5'-triphosphate levels, and rate-limiting metabolites in nucleotide metabolism, namely phosphoribosyl diphosphate and aspartate. HNSCC xenografts treated with the combination exhibited increased tumor regrowth delay, decreased tumor infiltration of CD45 and CD11b+ bone marrow-derived cells, and inhibition of HIF-1 and SDF-1 expression, thereby inhibiting IR-induced vasculogenesis.

CONCLUSIONS

AT13387 treatment resulted in pharmacologic inhibition of cancer cell metabolism that was linked to DNA damage repair. AT13387 combined with IR inhibited IR-induced vasculogenesis, a process involved in tumor recurrence postradiotherapy. Combining AT13387 with IR warrants consideration of clinical trial assessment.

Abstract 3587: Targeting cancer metabolism: A novel approach for improved radiotherapy

One key distinguishing hallmark of cancer cells includes a deregulated cellular metabolism that can be reprogrammed to preferentially exhibit dependence on glycolysis over oxidative phosphorylation (OXPHOS) even in the presence of oxygen (commonly known as “Aerobic Glycolysis” or the Warburg Effect). The bi-directional conversion of glucose to lactate in the presence of oxygen is mainly driven by the activity of the lactate dehydrogenase enzyme (LDH), of which, its A isoform is highly overexpressed in a variety of tumors. In the present study we characterized two novel LDH inhibitors (NCI-006 and NCI-737) in combination with ionizing radiation (IR) for their anti-cancer and radio-sensitization effects across tumor types. This study primarily examined effects of this novel combination therapy in cell lines of Pancreatic (MiaPaca, Hs766T, Panc-1), Lung (H460, A549), Head and Neck (FaDU, UMSCC-1), and Prostate (DU145, PC3) origin. Our preliminary results indicated that targeting LDH in conjunction with IR can enhance radiosensitivity under both hypoxic and normoxic conditions across glycolytic tumor cell lines while not affecting non-glycolytic/normal cells (1522, skin fibroblast) in vitro. Further we established that this enhanced radiosensitivity could be attributed to reduced DNA repair as seen by enhanced expression of y-H2AX and reduced ATP generation. Our results also indicated that increased expression of lactate and glucose transporters, combined with cellular bioenergetics changes, leads to a reprogramming of cells to OXPHOS. Lastly, we found that inhibition of OXPHOS and NAD+ in conjunction with these novel LDH inhibitors promotes metabolic synthetic lethality in vitro. As cancer patients continue to receive radiation for local tumor control, we hope that future studies targeting cancer metabolic vulnerabilities in combination with IR in vivo will enhance the therapeutic ratio of radiotherapy.

*The LDH inhibitors used in this study were provided by the NCI Experimental Therapeutics (NExT) Program

Citation Format: Suchet Taori, Sarwat Naz, Janet Gamson, Askale Mathias, John Cook, James B. Mitchell. Targeting cancer metabolism: A novel approach for improved radiotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3587.

Abemaciclib, a Selective CDK4/6 Inhibitor, Enhances the Radiosensitivity of Non-Small Cell Lung Cancer In Vitro and In Vivo

Purpose: To characterize the ionizing radiation (IR) enhancing effects and underlying mechanisms of the CDK4/6 inhibitor abemaciclib in non-small cell lung cancer (NSCLC) cells in vitro and in vivoExperimental Design: IR enhancement by abemaciclib in a variety of NSCLC cell lines was assessed by in vitro clonogenic assay, flow cytometry, and target inhibition verified by immunoblotting. IR-induced DNA damage repair was evaluated by γH2AX analysis. Global metabolic alterations by abemaciclib and IR combination were evaluated by LC/MS mass spectrometry and YSI bioanalyzer. Effects of abemaciclib and IR combination in vivo were studied by xenograft tumor regrowth delay, xenograft lysate immunoblotting, and tissue section immunohistochemistry.Results: Abemaciclib enhanced the radiosensitivity of NSCLC cells independent of RAS or EGFR status. Enhancement of radiosensitivity was lost in cell lines deficient for functional p53 and RB protein. After IR, abemaciclib treatment inhibited DNA damage repair as measured by γH2AX. Mechanistically, abemaciclib inhibited RB phosphorylation, leading to cell-cycle arrest. It also inhibited mTOR signaling and reduced intracellular amino acid pools, causing nutrient stress. In vivo, abemaciclib, when administered in an adjuvant setting for the second week after fractionated IR, further inhibited vasculogenesis and tumor regrowth, with sustained inhibition of RB/E2F activity, mTOR pathway, and HIF-1 expression. In summary, our study signifies inhibiting the CDK4/6 pathway by abemaciclib in combination with IR as a promising therapeutic strategy to treat NSCLC.Conclusions: Abemaciclib in combination with IR enhances NSCLC radiosensitivity in preclinical models, potentially providing a novel biomarker-driven combination therapeutic strategy for patients with NSCLC. Clin Cancer Res; 24(16); 3994-4005. ©2018 AACR.

Abstract 5861: Enhanced radiosenistivity of EGFR-TKI sensitive and resistant NSCLC cells by abemaciclib is mediated by altered DNA repair and metabolic pathways

Dysregulation of the p16(INK4a)-CyclinD-CDK4/6-Rb pathways in patients with NSCLC (Non-Small Cell Lung Cancer) is a rational therapeutic target. The current study investigated the radiosensitizing potential of a novel CDK4/6 inhibitor, LY2835219 (LY, Abemaciclib) in NSCLC cell lines with varied genomic context to identify genomic and metabolic biomarkers that are predictive of a response over conventional EGFR-tyrosine kinase inhibitor (EGFR-TKI) therapy. NSCLC cell lines were exposed to LY (0-10uM) for 24 hr immediately after 0-10 Gy radiation. Cell survival was assessed by clonogenic assay and cell cycle distribution was quantified by flow cytometry. Dose modifying factors (DMF) were calculated at 10% survival from radiation survival curves. Altered DNA repair pathways and metabolic profiling of cells post LY treatment was assessed by immunoblot and LC/MS mass spectrometry analysis. LY treatment enhanced radiosensitivity of EGFR-TKI sensitive (HCC827, PC9) and EGFR-TKI resistant (H820 and H1975) cell lines with DMF of 1.3 (±0.06), 1.4 (±0.30), 1.5 (±0.51) and 1.3 (±0.02), respectively. Values in the parenthesis indicates standard deviation. Wild type EGFR expressing cells (A549 and H460) also showed enhanced radiosensitivity by LY with DMF of 1.6 (±0.09) and 1.75(±0.15), respectively. Interestingly, no radiation enhancement by LY was observed for cells deficient in functional PTEN (H1650), Rb (H82) and p53 (H460 DNp53 and H1299) protein. Radiosensitization was also observed for cells made resistant to third generation EGFR-TKI, AZD9291. Flow cytometry analysis of majority of cell types exposed to LY exhibited 55% to 94% G1 arrest (depending on cell type). Mechanistically, the combinatorial treatment in radiosensitive cells showed elevated phosphorylated-γH2Ax. Combination treatment also reduced expression of ATR, ATM, DNA-PK, Rad51 and Chk-2 suggestive of reduced DNA repair compared to radiation alone. LY treatment brought major changes in the glycolysis/TCA/ total amino acids. LY increased significantly Acetyl-CoA, fumarate and malate, indicating enhanced oxidative phosphorylation. LY significantly elevated Uric acid levels suggestive of oxidative stress and elevated nucleotide degradation. Finally, administration of 100mg/kg LY2835219 for five days in combination with fractionated dose of radiation (3 Gy) significantly delayed tumor regrowth in H460 xenograft (p< 0.014). Collectively, our pre-clinical data indicates altered Rb, p53 and PTEN status are distinct predictive biomarkers of response for LY mediated radiosensitivity and provides an alternative therapeutic option in overcoming EGFR-TKI resistance in NSCLC.

Note: This abstract was not presented at the meeting.

Citation Format: Sarwat Naz, William DeGraff, Anastasia Sowers, Rajani Choudhuri, Maria Wissler, Janet Gamson, John Cook, James B. Mitchell. Enhanced radiosenistivity of EGFR-TKI sensitive and resistant NSCLC cells by abemaciclib is mediated by altered DNA repair and metabolic pathways [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5861. doi:10.1158/1538-7445.AM2017-5861

Abstract 1593: Cellular effects of the mitochondrially-directed antioxidant Tempol

The mitochondrial respiratory chain is a major source of reactive oxygen species, making it a high-yield target for antioxidants and potential radioprotection. The lipophilic cation triphenylphosphonium (TPP) has been used to target antioxidants to the mitochondrial membrane. Its lipophilicity permits it free passage through biological membranes while its positive charge traps it in the mitochondrial membrane, which is characterized by a large membrane potential. Among the agents localized to mitochondria via TPP have been stable nitroxide radicals, superoxide dismutase mimetics which also demonstrate the ability to scavenge free radicals. 4-Hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl, or Tempol (TP), is a nitroxide which is radioprotective both in vitro and in vivo when present during ionizing radiation. As with most chemical radioprotectors, relatively high concentrations of Tempol are required for protection. We questioned whether mito-Tempol (MTP), Tempol directed to mitochondria via TPP, would provide protection against radiation or hydrogen peroxide (HP) cytotoxicity as measured by the clonogenic assay in Chinese hamster V79 cells. MTP (10-500 μM) present 10 min prior to, during, and 4 hr after 12 Gy provided no radioprotection. MTP exhibited no cytotoxicity alone. In contrast, both TP and MTP (500 μM), when present immediately before and during a 1 hr exposure to HP, provided significant protection against HP cytotoxicity. We next evaluated the effects of continuous exposure to TP or MTP (100 μM) on the growth rate of several human tumor cell lines (MCF7, HT29, 786-0). TP had little effect on growth of these cell lines while MTP completely inhibited cell growth. The effects of the TPP-carbon linker alone will be presented; in short-term studies it did not exhibit cytotoxicity to V79 cells. These preliminary data with mitochondrial targeting of Tempol demonstrate that MTP exhibited antioxidant properties similar to TP with regard to protection against HP; at concentrations up to 500 μM, however, MTP did not protect against radiation. The latter finding is consistent with the requirement that chemical radioprotectors be present in sufficient concentration in the nucleus to afford radioprotection. Additional studies will be presented addressing the mechanism of MTP-mediated growth inhibition in human tumor cell lines.

Citation Format: Aparna H. Kesarwala, William DeGraff, Janet Gamson, Rajani Choudhuri, John A. Cook, Murali C. Krishna, James B. Mitchell. Cellular effects of the mitochondrially-directed antioxidant Tempol. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1593. doi:10.1158/1538-7445.AM2013-1593

Guggulsterone-mediated enhancement of radiosensitivity in human tumor cell lines

Purpose: To observe the effect of guggulsterone (GS) on the radiation response in human cancer cell lines. Materials and methods: The radiation response of cancer cells treated with GS was observed by cell survival studies, cell growth assay, NF-κB activity assay, western blotting of some key growth promoting receptors, the DNA repair protein γH2AX, and flow cytometry for DNA analyses. Results: GS inhibited radiation induced NF-κB activation and enhanced radiosensitivity in the pancreatic cell line, PC-Sw. It reduced both cell cycle movement and cell growth. GS reduced ERα protein in MCF7 cells and IGF1-Rβ protein in colon cancer cells and pancreatic cancer cells and inhibited DNA double strand break (DSB) repair following radiation. Conclusion: GS induced radiation sensitization may be due to several different mechanisms including the inhibition of NF-κB activation and reductions in IGF1-Rβ. In addition, GS induced γH2AX formation, primarily in the S-phase, indicates that DNA DSB's in the S-phase may be another reason for GS induced radiosensitivity. ERα down-regulation in response to GS suggests that it can be of potential use in the treatment of estrogen positive tumors that are resistant to tamoxifen.

Factors influencing nitroxide reduction and cytotoxicity in vitro

Nitroxides have been shown to be effective antioxidants, radiation protectors, and redox-active probes for functional electron paramagnetic resonance (EPR) imaging. More recently, the nitroxide 4-hydroxy-2,2,6,6-tetramethylpiperidinyl-N-oxyl (Tempol) has been shown to exert differential cytotoxicity to tumor compared with normal cell counterparts. Nitroxides are readily reduced in tissues to their respective hydroxylamines, which exhibit less cytotoxicity in vitro and do not provide radiation protection or an EPR-detectable signal for imaging. In order to better understand factors that influence nitroxide reduction, the rate of reduction of Tempol in mouse and human cell lines and in primary cultures of tumor cells was measured using EPR spectroscopy. Additionally, the cytotoxicity of high concentrations of Tempol and the hydroxylamine of Tempol (Tempol-H) was evaluated in wild-type and glucose-6-phosphate dehydrogenase (G6PD)-deficient Chinese hamster ovary cells. The results show that in general Tempol was reduced at a faster rate when cells were under hypoxic compared with aerobic conditions. Neither depletion of intracellular glutathione nor treatment of cells with sodium cyanide influenced Tempol reduction rates. G6PD-deficient cells were found to reduce Tempol at a significantly slower rate than wild-type cells. Likewise, Tempol-induced cytotoxicity was markedly less for G6PD-deficient cells compared with wild-type cells. Tempol-H exhibited no cytotoxicity to either cell type. Tempol-mediated cytotoxicity was enhanced by glutathione depletion and inhibition of 6-phosphogluconate dehydrogenase in wild-type cells, but was unaltered in G6PD-deficient cells. Collectively, the results indicate that while the bioreduction of Tempol can be influenced by a number of factors, the hexose monophosphate shunt appears to be involved in both nitroxide reduction as well as cytotoxicity induced by high levels of exposure to Tempol.

Redox generation of nitric oxide to radiosensitize hypoxic cells

PURPOSE

Previous studies have shown that nitric oxide (NO) delivered from NO donor agents sensitizes hypoxic cells to ionizing radiation. In the present study, nitroxyl (NO-), a potential precursor to endogenous NO production, was evaluated for hypoxic cell radiosensitization, either alone or in combination with electron acceptor agents.

METHODS AND MATERIALS

Radiation survival curves of Chinese hamster V79 lung fibroblasts under aerobic and hypoxic conditions were assessed by clonogenic assay. Hypoxia induction was achieved by metabolism-mediated oxygen depletion in dense cell suspensions. Cells were treated with NO- produced from the nitroxyl donor Angeli's salt (AS, Na2N2O3, sodium trioxodinitrate), in the absence or presence of electron acceptor agents, ferricyanide, or tempol. NO concentrations resulting from the combination of AS and ferricyanide or tempol were measured under hypoxic conditions using an NO-sensitive electrode.

RESULTS

Treatment of V79 cells under hypoxic conditions with AS alone did not result in radiosensitization; however, the combination of AS with ferricyanide or tempol resulted in significant hypoxic radiosensitization with SERs of 2.5 and 2.1, respectively. Neither AS alone nor AS in combination with ferricyanide or tempol influenced aerobic radiosensitivity. The presence of NO generated under hypoxic conditions from the combination of AS with ferricyanide or tempol was confirmed using an NO-sensitive electrode.

CONCLUSION

Combining NO- generated from AS with electron acceptors results in NO generation and substantial hypoxic cell radiosensitization. NO- derived from donor agents or endogenously produced in tumors, combined with electron acceptors, may provide an important strategy for radiosensitizing hypoxic cells and warrants in vivo evaluation.

The cytotoxicity of nitroxyl: possible implications for the pathophysiological role of NO

In addition to the broad repertoire of regulatory functions nitric oxide (NO) serves in mammalian physiology, the L-arginine:NO pathway is also involved in numerous pathophysiological mechanisms. While NO itself may actually protect cells from the toxicity of reactive oxygen radicals in some cases, it has been suggested that reactive nitrogen oxide species formed from nitric oxide synthase (NOS) can be cytotoxic. In addition to NO, the one electron reduction product NO- has been proposed to be formed from NOS. We investigated the potential cytotoxic role of nitroxyl (NO-), using the nitroxyl donor Angelis's salt, (AS; sodium trioxodinitrate, Na2N2O3) as the source of NO-. As was found to be cytotoxic to Chinese hamster V79 lung fibroblast cells over a concentration range of 2-4 mM. The presence of equimolar ferricyanide (Fe(III)-(CN6)3-), which converts NO- to NO, afforded dramatic protection against AS-mediated cytotoxicity. Treatment of V79 cells with L-buthionine sulfoximine to reduce intracellular glutathione markedly enhanced AS cytotoxicity, which suggests that GSH is critical for cellular protection against the toxicity of NO-. Further experiments showed that low molecular weight transition metal complexes associated with the formation of reactive oxygen species are not involved in AS-mediated cytotoxicity since metal chelators had no effect. However, under aerobic conditions, AS was more toxic than under hypoxic conditions, suggesting that oxygen dramatically enhanced AS-mediated cytotoxicity. At a molecular level, AS exposure resulted in DNA double strand breaks in whole cells, and this effect was completely prevented by coincubation of cells with ferricyanide or Tempol. The data in this study suggest that nitroxyl may contribute to the cytotoxicity associated with an enhanced expression of the L-arginine:NO pathway under different biological conditions.

Nitric oxide and some nitric oxide donor compounds enhance the cytotoxicity of cisplatin

A major emphasis in cancer therapy research is finding mechanisms to enhance the effectiveness of clinically used chemotherapeutic agents. In this report, we show the effects of direct NO exposure or NO delivery agents such as NONOate NO donors, DEA/NO ((C2H5)2N[N(O)NO]-Na+) and PAPA/ NO (NH2(C3H6)(N[N(O)NO]C3H7)), or S-nitrosothiol NO donors (GSNO, S-nitrosoglutathione, and SNAP, S-nitroso-N-acetylpenicillamine) on the cytotoxicity of cisplatin with Chinese hamster V79 lung fibroblast cells. Cells pretreated with bolus NO or NO delivered from NONOate NO donors were markedly sensitized to subsequent cisplatin treatment, whereas S-nitrosothiol NO donors exerted little effect. The enhancement in cisplatin cytotoxicity from pretreatment with DEA/NO and PAPA/ NO persisted for approximately 180 and 240 min, respectively; thereafter cytotoxicity returned to a level consistent with cisplatin treatment alone. Pretreatment of cells with GSNO or SNAP did not enhance cisplatin cytotoxity. To discern why there were differential effects among the different NO donors, formation of NO over the time course of the experiment was assessed by the nitrosation of 2,3-diaminonaphthylene. Bolus NO, DEA/NO, and PAPA/NO produced more reactive nitrogen oxide species (RNOS) than did treatment with GSNO or SNAP. Previously reported electrochemical studies revealed that temporal NO concentrations measured from DEA/NO and PAPA/NO (1 mM) were greater than 5 microM. It appears that the flux of NO, as well as the amount of RNOS, is important in the NO-mediated enhancement of cisplatin cytotoxicity. Our results demonstrate the importance of NO delivery systems in the enhancement of cisplatin cytotoxicity and may provide insights into strategies for participation of NO donors and nitric oxide synthase with cisplatin therapy.

The effect of various nitric oxide-donor agents on hydrogen peroxide-mediated toxicity: a direct correlation between nitric oxide formation and protection

The role that nitric oxide (NO) plays in various degenerative and disease states has remained a mystery since its discovery as a biological messenger, prompting the question, "NO, friend or foe?" Some reports have suggested that NO is cytotoxic, and yet others have shown that it possesses protective properties against reactive oxygen species (ROS). Many studies have used various NO donor complexes arriving at seemingly different conclusions. This report will address the effects of various NO donor compounds on ROS-mediated toxicity. Consistent with our previous study, the NO donor compound, DEA/NO ((C2H5)2N[N(O)NO]-Na+), afforded protection against hydrogen peroxide-mediated cytotoxicity in V79 Chinese hamster lung fibroblasts at concentrations as low as 10 microM DEA/NO. Furthermore, a survey of other NO donor complexes revealed that some either protected or potentiated hydrogen peroxide-mediated cytotoxicity. 3-Morpholinosynodiomine.HCl (SIN-1) and sodium nitroprusside (SNP) enhanced hydrogen peroxide-mediated cytotoxicity, while S-nitrosoglutathione (GSNO), and S-nitroso-N-acetylpenicillamine (SNAP) afforded protection. Electrochemical detection of NO in cell culture medium revealed that neither 1000 microM SIN-1 nor SNP yielded appreciable NO concentrations (<0.3 microM). In contrast, DEA/NO, SNAP, and GSNO yielded fluxes of NO >1.0 microM. Thus, a direct correlation between inhibition of hydrogen peroxide cytotoxicity and NO production was observed: agents that release NO during hydrogen peroxide treatment afford significant protection, whereas agents that do not release NO do not protect. Similar results were observed for NO donors studied when hypoxanthinesolidusxanthine oxidase was used as the source for ROS, although the S-nitrosothiol agents were much less protective. These results demonstrate that NO possesses properties which protect against ROS toxicity and demonstrate how the use of different NO donor compounds can lead to different conclusions about the role that NO can play in the cytotoxicity of ROS.

Radiation sensitisation by nitric oxide releasing agents

Previous studies have shown that nitric oxide (NO) sensitises hypoxic cells to ionising radiation. In the present study, four different nitric oxide (NO) donor agents were evaluated for both NO release and hypoxic radiosensitisation. The S-nitrosothiol NO donor agents, S-nitrosoglutathione (GSNO) and S-nitroso-N-acetylpenicillamine (SNAP), were shown to release sustained NO concentrations (microM) and significantly radiosensitise hypoxic cells. The extent of hypoxic radiosensitisation by both of these agents at 1.0 mM concentration was similar to that obtained with molecular oxygen. In contrast, neither 3-morpholinosydnonimine (SIN-1) nor sodium nitroprusside (SNP) released detectable NO concentrations and neither agent enhanced the hypoxic radiation response to the extent of that observed for GSNO or SNAP. NO-mediated hypoxic cell radiosensitisation by NO donor drugs may offer a new approach for clinical consideration, particularly if such agents can be selectively delivered to hypoxic cells.

Nitric oxide protects against alkyl peroxide-mediated cytotoxicity: further insights into the role nitric oxide plays in oxidative stress

Endogenously formed nitric oxide (NO) possesses diverse properties such as regulating physiological functions, exerting specific toxic effects, and protecting against various toxic substances. Recent studies suggest that in the presence of reactive oxygen species, NO can serve as an antioxidant. We show here that NO delivered from the NO donor compound, PAPA/NO (NH2(C3H6)(N[N(O)NO](C3H7)), protects Chinese hamster V79 lung fibroblasts from the cytotoxicity of t-butyl hydroperoxide and cumene hydroperoxide. In contrast, the other end products of PAPA/NO degradation in aqueous solution, NH2(C3H6)NH(C3H7) and nitrite, did not protect. The NONOate DEA/NO releases NO six times faster than PAPA/NO, yet did not afford protection, which implies that NO must be present throughout the alkyl hydroperoxide exposure. Measurements of NO concentrations released from PAPA/NO suggest that micromolar levels protect against cytotoxicity induced by alkyl hydroperoxides. These findings demonstrate that the flux of NO sustained over the duration of the peroxide exposure determines protection and not the total of NO delivered. These results suggest that concentrations of NO produced in the microenvironment of endothelial cells are high enough to protect cells from Fenton-type-mediated toxicity and support the premise that NO may exert a salutary effect in certain diseases associated with membrane damage.

Hypoxic mammalian cell radiosensitization by nitric oxide

The bioregulatory molecule, nitric oxide (NO), was evaluated as a hypoxic cell radiosensitizer. Authentic NO gas was nearly as effective as oxygen in radiosensitizing hypoxic Chinese hamster V79 lung cells as evaluated using clonogenic assays. When NO was delivered to hypoxic Chinese hamster V79 cells using the NO-releasing agent (C2H5)2N[N(O)-NO]- Na+, radiosensitization was also observed with a sensitizer enhancement ratio of 2.4 (1 mM (C2H5)2N[N(O)NO]-Na+). Aerobic radiosensitivity was not affected at this concentration. The hypoxic cell radiosensitization properties of (C2H5)2N[N(O)NO]-Na+, coupled with the vasodilatory effects of NO on tumor vasculature, suggest that such agents open a new avenue of research in radiation oncology.

Nitric oxide protects against cellular damage and cytotoxicity from reactive oxygen species

Nitric oxide, NO, which is generated by various components of the immune system, has been presumed to be cytotoxic. However, NO has been proposed to be protective against cellular damage resulting during ischemia reperfusion. Along with NO there is often concomitant formation of superoxide/hydrogen peroxide, and hence a synergistic relationship between the cytotoxic effects of nitric oxide and these active oxygen species is frequently assumed. To study more carefully the potential synergy between NO and active oxygen species in mammalian cell cytotoxicity, we utilized either hypoxanthine/xanthine cell cytotoxicity, we utilized either hypoxanthine/xanthine oxidase (a system that generates superoxide/hydrogen peroxide) or hydrogen peroxide itself. NO generation was accomplished by the use of a class of compounds known as "NONOates," which release NO at ambient temperatures without the requirement of enzyme activation or biotransformation. When Chinese hamster lung fibroblasts (V79 cells) were exposed to hypoxanthine/xanthine oxidase for various times or increasing amounts of hydrogen peroxide, there was a dose-dependent decrease in survival of V79 cells as measured by clonogenic assays. However, in the presence of NO released from (C2H5)2N[N(O)NO]-Na+ (DEA/NO), the cytotoxicity resulting from superoxide or hydrogen peroxide was markedly abrogated. Similarly, primary cultures of rat mesencephalic dopaminergic cells exposed either to hydrogen peroxide or to hypoxanthine/xanthine oxidase resulted in the degradation of the dopamine uptake and release mechanism. As was observed in the case of the V79 cells, the presence of NO essentially abrogated this peroxide-mediated cytotoxic effect on mesencephalic cells.

Identification of nitroxide radioprotectors

The nitroxide Tempol, a stable free radical, has recently been shown to protect mammalian cells against several forms of oxidative stress including radiation-induced cytotoxicity. To extend this observation, six additional water-soluble nitroxides with different structural features were evaluated for potential radioprotective properties using Chinese hamster V79 cells and clonogenic assays. Nitroxides (10 mM) were added 10 min prior to radiation exposure and full radiation dose-response curves were determined. In addition to Tempol, five of the six nitroxides afforded in vitro radioprotection. The best protectors were found to be the positively charged nitroxides, Tempamine and 3-aminomethyl-PROXYL, with protection factors of 2.3 and 2.4, respectively, compared with Tempol, which had a protection factor of 1.3. 3-Carboxy-PROXYL, a negatively charged nitroxide, provided minimal protection. DNA binding characteristics as studied by nonequilibrium dialysis of DNA with each of the nitroxides demonstrated that Tempamine and 3-amino-methyl-PROXYL bound more strongly to DNA than did Tempol. Since DNA is assumed to be the target of radiation-induced cytotoxicity, differences in protection may be explained by variabilities in affinity of the protector for the target. This study establishes nitroxides as a general class of new nonthiol radioprotectors and suggests other parameters that may be exploited to find even better nitroxide-induced radioprotection.

Inhibition of oxygen-dependent radiation-induced damage by the nitroxide superoxide dismutase mimic, tempol

Stable nitroxide radicals have been previously shown to function as superoxide dismutase (SOD)2 mimics and to protect mammalian cells against superoxide and hydrogen peroxide-mediated oxidative stress. These unique characteristics suggested that nitroxides, such as 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (Tempol), might protect mammalian cells against ionizing radiation. Treating Chinese hamster cells under aerobic conditions with 5, 10, 50, and 100 mM Tempol 10 min prior to X-rays resulted in radiation protection factors of 1.25, 1.30, 2.1, and 2.5, respectively. However, the reduced form of Tempol afforded no protection. Tempol treatment under hypoxic conditions did not provide radioprotection. Aerobic X-ray protection by Tempol could not be attributed to the induction of intracellular hypoxia, increase in intracellular glutathione, or induction of intracellular SOD mRNA. Tempol thus represents a new class of non-thiol-containing radiation protectors, which may be useful in elucidating the mechanism(s) of radiation-induced cellular damage and may have broad applications in protecting against oxidative stress.

Evaluation of nitroimidazole hypoxic cell radiosensitizers in a human tumor cell line high in intracellular glutathione

Five nitroimidazole hypoxic cell radiosensitizers were evaluated in a human lung adenocarcinoma cell line (A549) whose GSH level was 8-fold higher than Chinese hamster V79 cells. One millimolar concentrations of Misonidazole (MISO), SR-2508, RSU-1164, RSU-1172, and Ro-03-8799 sensitized hypoxic A549 cells to radiation, with Ro-03-8799 giving the highest sensitizer enhancement ration (SER) (2.3). However, MISO, SR-2508 and Ro-03-8799 were less effective in this cell line than in V79 cells, presumably due to higher GSH content of the A549 cells. Increased hypoxic radiosensitization was seen with 0.1 mM Ro-03-8799 after GSH depletion by BSO as compared to 0.1 mM Ro-03-8799 alone (SER-1.8 vs 1.3). The combination of GSH depletion and 0.1 mM Ro-03-8799 was considerably more toxic than 0.1 mM or 1.0 mM Ro-03-8799 alone. This sensitivity was much greater than has been observed for SR-2508. These data show that Ro-03-8799 was the most efficient hypoxic cell radiosensitizer in a human tumor cell line considerably higher in GSH than the rodent cell lines often used in hypoxic radiosensitization studies. Thus, Ro-03-8799 may be a more effective hypoxic cell sensitizer in human tumors that are high in GSH.

Radiation sensitivity of human lung cancer cell lines

X-Ray survival curves were determined using a panel of 17 human lung cancer cell lines, with emphasis on non-small cell lung cancer (NSCLC). In contrast to classic small cell lung cancer (SCLC) cell lines, NSCLC cell lines were generally less sensitive to radiation as evidenced by higher radiation survival curve extrapolation numbers, surviving fraction values following a 2 Gy dose (SF2) and the mean inactivation dose values (D) values. The spectrum of in vitro radiation responses observed was similar to that expected in clinical practice, although mesothelioma was unexpectedly sensitive in vitro. Differences in radiosensitivity were best distinguished by comparison of SF2 values. Some NSCLC lines were relatively sensitive, and in view of this demonstrable variability in radiation sensitivity, the SF2 value may be useful for in vitro predictive assay testing of clinical specimens.

Free radical formation and cell lysis induced by ultrasound in the presence of different rare gases

The effect of varying the temperature of cavitation bubbles in aqueous solutions of different rare gases on free radical formation and shearing stress induced by ultrasound was investigated. After sonication with 50kHz ultrasound the yield of hydroxyl radicals was measured by spin trapping with 5,5-dimethyl-1-pyrroline-N-oxide and the cell lysis of cultured mammalian cells was investigated. The hydroxyl radical yields were in the order Xe greater than Kr greater than Ar greater than Ne greater than He, in accord with the higher temperatures of the cavitation bubbles. However, cell lysis induced by shearing stress was the same for all of the rare gases, and independent of their thermal conductivity and the temperature of the cavitation bubbles.

Radiation sensitivity and study of glutathione and related enzymes in human colorectal cancer cell lines

A panel of 13 human colorectal cell lines was studied, with these lines exhibiting a histological profile similar to that observed in clinical practice. In the five lines tested, variable sensitivity to radiation was observed, from the relatively sensitive NCI-H716 to the highly resistant line NCI-H630, with the latter cell line derived from a patient who had previously received radiation treatment. Glutathione levels and glutathione related enzyme activity varied widely between all 13 cell lines, showing no relationship to radiation sensitivity. The variability observed suggests that some colonic tumours may be responsive to radiation, although their identification remains difficult. However, this may prove possible by incorporation of recently developed cell adhesive matrix assays using survival following a 2 Gy radiation dose as a parameter of radiation sensitivity. This panel of human cancer cell lines offers an ideal model for the study of parameters affecting the radiosensitivity and chemosensitivity pattern of colorectal cancer cells.

Chemosensitivity testing of human lung cancer cell lines using the MTT assay

Thirty human lung cancer cell lines were tested for chemosensitivity using the semi-automated, non-clonogenic MTT assay. The tumour cell lines came from three major categories of patients: untreated small cell lung cancer (SCLC); SCLC relapsing on chemotherapy; and non-SCLC predominantly from untreated patients. From these data IC50 values were derived for each drug in each cell line. While some inter-experimental variability was observed, the rank order of chemosensitivity of each cell line within this panel was significantly correlated between experiments. These results show that tumour cell lines derived from untreated small cell lung cancer patients were the most chemosensitive for adriamycin, melphalan, vincristine and VP16 compared to the other cell types. In addition, untreated SCLC was more sensitive than non-SCLC to BCNU and cis-platin, while vincristine was the only drug to which treated SCLC was more sensitive compared to the non-SCLC lines. In contrast, no significant differences between the lung cancer types were observed for vinblastine. Thus, this panel of lung cancer cells exhibited a drug sensitivity profile paralleling that observed in clinical practice. These results suggest that this lung cancer cell line panel in combination with a relatively simple but reproducible chemosensitivity assay, such as the MTT assay, has potential for the testing of drug combinations and evaluating new anti-cancer agents in vitro.

212Bismuth linked to an antipancreatic carcinoma antibody: model for alpha-particle-emitter radioimmunotherapy

For comparison of cytotoxicity from alpha-particle irradiation with that from conventional x-irradiation, 212Bi, an alpha-emitting radionuclide, was attached to a monoclonal antibody that recognizes a cell surface antigen on human pancreatic carcinoma cells. For a given level of survival, the 212Bi-antibody complex was found to be approximately 20 times more efficient in cell killing than x-irradiation and 5 times more cytotoxic when compared with the cytotoxicity of an antigen-negative cell line or an isotype-matched control antibody. High linear energy transfer radioimmunotherapy using alpha emitters linked to monoclonal antibodies may be useful in vivo and in vitro for selectively killing target cell populations, especially those resistant to other forms of treatment.

Potentiation of chemotherapy cytotoxicity following iododeoxyuridine incorporation in Chinese hamster cells

This study reports on the potentiation of selected chemotherapy drugs following halogenated pyrimidine incorporation into cellular DNA. Exponentially growing cultures of Chinese hamster V79 cells were exposed to 10(-5) M IdUrd or BrdUrd for 17 hr (approximately 2 cell doublings). This exposure resulted in approximately 16% replacement of thymidine by IdUrd or BrdUrd in the cellular DNA. Following the IdUrd exposure, dose response curves were determined for a 1 hr exposure to the various drugs. IdUrd pre-treatment was shown to enhance the cytotoxicity of melphalan, adriamycin, cisplatin, and neocarzinostatin with enhancement ratios at 1% survival of 1.5, 1.8, 1.5, and 1.4 respectively. BrdUrd pre-treatment also enhanced cisplatin cytotoxicity. A combination of BrdUrd pretreatment, cisplatin, and X rays was shown to yield additive survival effects. These findings are discussed in the context of possible clinical application of local drug perfusion of tumor-containing organs.

Depletion of cellular glutathione by exogenous spermine in V79 cells: implications for spermine-induced hyperthermic sensitization

The relationship between spermine-induced thermosensitization and modulation in the cellular redox state as measured by glutathione levels was studied using Chinese hamster V79 cells. Marked cellular glutathione depletion was observed for cells treated with exogenous 1 mM spermine at 37 degrees C or 43 degrees C. Glutathione depletion and thermal sensitization by spermine were found to be cell density dependent with maximum depletion and sensitization observed at low cell densities. These findings are discussed in the context that treatment of cells with exogenous polyamines such as spermine can result in cellular oxidative stress which may in part contribute to spermine-induced thermal sensitization.

The effects of cellular glutathione elevation on the oxygen enhancement ratio

The radiation responses at various oxygen tensions were evaluated in V79 Chinese hamster cells under conditions where their nonprotein thiols, primarily glutathione (GSH), were elevated by 2-oxothiazolidine-4-carboxylate (OTZ). OTZ, when cleaved by intracellular oxoprolinase, provides the cell with cysteine which stimulates GSH synthesis. A 2-hr pretreatment with 10 mM OTZ elevated GSH to 200% of controls. This elevation in GSH offered no protection to aerated cells; however, for O2 tensions less than or equal to 40,000 ppm modest protection was observed as evidenced by an increase in oxygen enhancement ratio. GSH elevation afforded maximal protection between 1000 and 10,000 ppm O2; however, the extent of protection was relatively small (protection factor = 1.3).

Oxygen dependence of hematoporphyrin derivative-induced photoinactivation of Chinese hamster cells

The oxygen dependence of hematoporphyrin derivative (HPD)-induced photoinactivation of Chinese hamster V79 cells was examined. Cells were treated with HPD (25 micrograms/ml) for 2 h and subsequently exposed to red light (greater than 590 nm) under either aerated or hypoxic (less than 10 ppm O2) conditions. Hypoxic cells were found to be extremely resistant to the lethal effects of HPD and light. The electron-affinic X-ray hypoxic cell sensitizer, SR-2508, did not sensitize hypoxic HPD-treated cells to light. The clinical implications of these findings are discussed, with consideration of the possibility that hypoxic areas in tumors may limit HPD phototherapy.