Multiple Infusion Start Time Mass Spectrometry Imaging of Dynamic SIL-Glutathione Biosynthesis Using Infrared Matrix-Assisted Laser Desorption Electrospray Ionization.

Due to the high association of glutathione metabolism perturbation with a variety of disease states, there is a dire need for analytical techniques to study glutathione kinetics. Additionally, the elucidation of microenvironmental effects on changes in glutathione metabolism would significantly improve our understanding of the role of glutathione in disease. We therefore present a study combining a multiple infusion start time protocol, stable isotope labeling technology, infrared matrix-assisted laser desorption electrospray ionization, and high-resolution accurate mass-mass spectrometry imaging to study spatial changes in glutathione kinetics across in sectioned mouse liver tissues. After injecting a mouse with the isotopologues [2-13C,15N]-glycine, [1,2-13C2]-glycine, and [1,2-13C2,15N]-glycine at three different time points, we were able to fully resolve and spatially map their metabolism into three isotopologues of glutathione and calculate their isotopic enrichment in glutathione. We created a tool in the open-source mass spectrometry imaging software MSiReader to accurately compute the percent isotope enrichment (PIE) of these labels in glutathione and visualize them in heat-maps of the tissue sections. In areas of high flux, we found that each label enriched an approximate median of 1.6%, 1.8%, and 1.5%, respectively, of the glutathione product pool measured in each voxel. This method may be adapted to study the heterogeneity of glutathione flux in diseased versus healthy tissues.

Flow-Encoded Oxygen Control to Track the Time-Dependence of Molecular Changes Induced by Static or Cycling Hypoxia.

Detecting the effects of low oxygen on cell function is often dependent on monitoring the expression of a number of hypoxia markers. The time dependence of the appearance and stability of these markers varies between cell lines. Assessing cellular marker dynamics is also critical to determining how quickly cells respond to transient changes in oxygen levels that occurs with cycling hypoxia. We fabricated a manifold designed to use flow-encoding to produce sequential changes in gas mixtures delivered to a permeable-bottom 96-well plate. We show how this manifold and plate design can be used to expose cells to either static or cycling hypoxic conditions for eight different time periods thereby facilitating the study of the time-response of cells to altered oxygen environments. Using this device, we monitored the time-dependence of molecular changes in human PANC-1 pancreatic carcinoma and Caco-2 colon adenocarcinoma cells exposed to increasing periods of static or cycling hypoxia. Using immunohistochemistry, both cell lines show detectable levels of the marker protein hypoxia-inducible factor-1α (HIF-1α) after 3 h of exposure to static hypoxia. Cycling hypoxia increased the expression level of HIF-1α compared to static hypoxia. Both static and cycling hypoxia also increased glucose uptake and aldehyde dehydrogenase activity. This new device offers a facile screening approach to determine the kinetics of cellular alterations under varying oxygen conditions.

Mixing and delivery of multiple controlled oxygen environments to a single multiwell culture plate.

Precise oxygen control is critical to evaluating cell growth, molecular content, and stress response in cultured cells. We have designed, fabricated, and characterized a 96-well plate-based device that is capable of delivering eight static or dynamically changing oxygen environments to different rows on a single plate. The device incorporates a gas-mixing tree that combines two input gases to generate the eight gas mixtures that supply each row of the plate with a different gas atmosphere via a removable manifold. Using air and nitrogen as feed gases, a single 96-well plate can culture cells in applied gas atmospheres with Po2 levels ranging from 1 to 135 mmHg. Human cancer cell lines MCF-7, PANC-1, and Caco-2 were grown on a single plate under this range of oxygen levels. Only cells grown in wells exposed to Po2 ≤37 mmHg express the endogenous hypoxia markers hypoxia-inducible factor-1α and carbonic anhydrase IX. This design is amenable to multiwell plate-based molecular assays or drug dose-response studies in static or cycling hypoxia conditions.

Pleiotropic effects of HIF-1 blockade on tumor radiosensitivity.

We have previously shown that radiation increases HIF-1 activity in tumors, causing significant radioprotection of the tumor vasculature. The impact that HIF-1 activation has on overall tumor radiosensitivity, however, is unknown. We reveal here that HIF-1 plays an important role in determining tumor radioresponsiveness through regulating four distinct processes. By promoting ATP metabolism, proliferation, and p53 activation, HIF-1 has a radiosensitizing effect on tumors. Through stimulating endothelial cell survival, HIF-1 promotes tumor radioresistance. As a result, the net effect of HIF-1 blockade on tumor radioresponsiveness is highly dependent on treatment sequencing, with "radiation first" strategies being significantly more effective than the alternative. These data provide a strong rationale for pursuing sequence-specific combinations of HIF-1 blockade and conventional therapeutics.

In vivo MR studies of glycine and glutathione metabolism in a rat mammary tumor.

The metabolism of glycine into glutathione was monitored noninvasively in vivo in intact rat mammary adenocarcinomas (R3230Ac) by MRI and MRS. Metabolism was tracked by following the isotope label from intravenously infused [2-(13)C]-glycine into the glycinyl residue of glutathione. Signals from [2-(13)C]-glycine and γ-glutamylcysteinyl-[2-(13)C]-glycine ((13)C-glutathione) were detected by nonlocalized (13)C spectroscopy, as these resonances are distinct from background signals. In addition, using spectroscopic imaging methods, heterogeneity in the in vivo tumor distribution of glutathione was observed. In vivo spectroscopy also detected isotope incorporation from [2-(13)C]-glycine into both the 2- and 3-carbons of serine. Analyses of tumor tissue extracts showed single- and multiple-label incorporation from [2-(13)C]-glycine into serine from metabolism through the serine hydroxymethyltransferase and glycine cleavage system pathways. Mass spectrometric analysis of extracts also showed that isotope-labeled serine is further metabolized via the trans-sulfuration pathway, as (13)C isotope labels appear in both the glycinyl and cysteinyl residues of glutathione. Our studies demonstrate the use of MRI and MRS for the monitoring of tumor metabolic processes central to oxidative stress defense.

In vivo selection of tumor-targeting RNA motifs.

In an effort to target the in vivo context of tumor-specific moieties, we screened a large library of nuclease-resistant RNA oligonucleotides in tumor-bearing mice to identify candidate molecules with the ability to localize to hepatic colon cancer metastases. One of the selected molecules is an RNA aptamer that binds to p68, an RNA helicase that has been shown to be upregulated in colorectal cancer.

Role of oxidative stress in a rat model of radiation-induced erectile dysfunction.

INTRODUCTION: Chronic oxidative stress is one of the major factors playing an important role in radiation-induced normal tissue injury. However, the role of oxidative stress in radiation-induced erectile dysfunction (ED) has not been fully investigated. Aims. To investigate role of oxidative stress after prostate-confined irradiation in a rat model of radiation-induced ED. METHODS: Fifty-four young adult male rats (10-12 weeks of age) were divided into age-matched sham radiotherapy (RT) and RT groups. Irradiated animals received prostate-confined radiation in a single 20 Gy fraction. MAIN OUTCOME MEASURES: Intracavernous pressure (ICP) measurements with cavernous nerve electrical stimulation were conducted at 2, 4, and 9 weeks following RT. The protein expression of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase subunits (Nox4 and gp91(phox)), markers of oxidative DNA damage (8-hydroxy-2'-deoxyguanosine [8-OHdG]), lipid peroxidation (4-hydroxynonenal [4HNE]), and inflammatory response including inducible nitric oxide synthase, macrophage activation (ED-1), and nitrotyrosine, and endogenous antioxidant defense by nuclear factor erythroid 2-related factor (Nrf2) were evaluated in irradiated prostate tissue and corpora cavernosa (CC). In addition, we investigated the relationships between results of ICP/mean arterial pressure (MAP) ratios and expression level of oxidative stress markers. RESULTS: In the RT group, hemodynamic functional studies demonstrated a significant time-dependent decrease in ICP. Increased expression of Nox4, gp91(phox), 8-OHdG, and 4HNE were observed in the prostate and CC after RT. Similarly, expressions of inflammatory markers were significantly increased. There was a trend for increased Nrf2 after 4 weeks. ICP/MAP ratio negatively correlated with higher expression level of oxidative markers. CONCLUSION: NADPH oxidase activation and chronic oxidative stress were observed in irradiated prostate tissue and CC, which correlated with lower ICP/MAP ratio. Persistent inflammatory responses were also found in both tissues after RT. These findings suggest that oxidative stress plays a crucial role in the development of radiation-induced ED.

Mapping glycine uptake and its metabolic conversion to glutathione in mouse mammary tumors using functional mass spectrometry imaging.

Although glutathione plays a key role in cancer cell viability and therapy response there is no clear trend in relating the level of this antioxidant to clinical stage, histological grade, or therapy response in patient tumors. The likely reason is that static levels of glutathione are not a good indicator of how a tissue deals with oxidative stress. A better indicator is the functional capacity of the tissue to maintain glutathione levels in response to this stress. However, there are few methods to assess glutathione metabolic function in tissue. We have developed a novel functional mass spectrometry imaging (fMSI) method that can map the variations in the conversion of glycine to glutathione metabolic activity across tumor tissue sections by tracking the fate of three glycine isotopologues administered in a timed sequence to tumor-bearing anesthetized mice. This fMSI method generates multiple time point kinetic data for substrate uptake and glutathione production from each spatial location in the tissue. As expected, the fMSI data shows glutathione metabolic activity varies across the murine 4T1 mammary tumor. Although glutathione levels are highest at the tumor periphery there are regions of high content but low metabolic activity. The timed infusion method also detects variations in delivery of the glycine isotopologues thereby providing a measure of tissue perfusion, including evidence of intermittent perfusion, that contributes to the observed differences in metabolic activity. We believe this new approach will be an asset to linking molecular content to tissue function.

Targeting lactate-fueled respiration selectively kills hypoxic tumor cells in mice.

Tumors contain oxygenated and hypoxic regions, so the tumor cell population is heterogeneous. Hypoxic tumor cells primarily use glucose for glycolytic energy production and release lactic acid, creating a lactate gradient that mirrors the oxygen gradient in the tumor. By contrast, oxygenated tumor cells have been thought to primarily use glucose for oxidative energy production. Although lactate is generally considered a waste product, we now show that it is a prominent substrate that fuels the oxidative metabolism of oxygenated tumor cells. There is therefore a symbiosis in which glycolytic and oxidative tumor cells mutually regulate their access to energy metabolites. We identified monocarboxylate transporter 1 (MCT1) as the prominent path for lactate uptake by a human cervix squamous carcinoma cell line that preferentially utilized lactate for oxidative metabolism. Inhibiting MCT1 with alpha-cyano-4-hydroxycinnamate (CHC) or siRNA in these cells induced a switch from lactate-fueled respiration to glycolysis. A similar switch from lactate-fueled respiration to glycolysis by oxygenated tumor cells in both a mouse model of lung carcinoma and xenotransplanted human colorectal adenocarcinoma cells was observed after administration of CHC. This retarded tumor growth, as the hypoxic/glycolytic tumor cells died from glucose starvation, and rendered the remaining cells sensitive to irradiation. As MCT1 was found to be expressed by an array of primary human tumors, we suggest that MCT1 inhibition has clinical antitumor potential.

RNA aptamer-targeted inhibition of NF-kappa B suppresses non-small cell lung cancer resistance to doxorubicin.

Due to the prevalence of tumor chemoresistance, the clinical response of advanced non-small cell lung cancer (NSCLC) to chemotherapy is poor. We suppressed tumor resistance to doxorubicin (Dox) in A549 cells, a human NSCLC cell line, both in vitro and in vivo in a lung tumor xenograft model, using a novel adenoviral expression system to deliver an RNA aptamer (A-p50) that specifically inhibits nuclear factor-kappaB (NF-kappaB) activation. By achieving selective, targeted, and early inhibition of NF-kappaB activity, we demonstrate that NF-kappaB plays a critical role in Dox-induced chemoresistance by regulating genes involved in proliferation (Ki-67), response to DNA damage (GADD153), antiapoptosis (Bcl-XL), and pH regulation (CA9). This Dox-induced NF-kappaB activation and subsequent chemoresistance is dependent on expression of p53. We also demonstrate that NF-kappaB promotes angiogenesis in the presence of Dox via the hypoxia-inducible factor-1alpha/vascular endothelial growth factor (HIF-1alpha/VEGF) pathway, revealing a previously unknown mechanism of NSCLC resistance to Dox. These studies provide important insights into the mechanisms of Dox-induced chemoresistance, and they demonstrate a novel, effective, and clinically practical strategy for interfering with these processes.

Small molecular inhibitor of transforming growth factor-beta protects against development of radiation-induced lung injury.

PURPOSE: To determine whether an anti-transforming growth factor-beta (TGF-beta) type 1 receptor inhibitor (SM16) can prevent radiation-induced lung injury. METHODS AND MATERIALS: One fraction of 28 Gy or sham radiotherapy (RT) was administered to the right hemithorax of Sprague-Dawley rats. SM16 was administered in the rat chow (0.07 g/kg or 0.15 g/kg) beginning 7 days before RT. The rats were divided into eight groups: group 1, control chow; group 2, SM16, 0.07 g/kg; group 3, SM16, 0.15 g/kg; group 4, RT plus control chow; group 5, RT plus SM16, 0.07 g/kg; group 6, RT plus SM16, 0.15 g/kg; group 7, RT plus 3 weeks of SM16 0.07 g/kg followed by control chow; and group 8, RT plus 3 weeks of SM16 0.15 g/kg followed by control chow. The breathing frequencies, presence of inflammation/fibrosis, activation of macrophages, and expression/activation of TGF-beta were assessed. RESULTS: The breathing frequencies in the RT plus SM16 0.15 g/kg were significantly lower than the RT plus control chow from Weeks 10-22 (p <0.05). The breathing frequencies in the RT plus SM16 0.07 g/kg group were significantly lower only at Weeks 10, 14, and 20. At 26 weeks after RT, the RT plus SM16 0.15 g/kg group experienced a significant decrease in lung fibrosis (p = 0.016), inflammatory response (p = 0.006), and TGF-beta1 activity (p = 0.011). No significant reduction was found in these measures of lung injury in the group that received SM16 0.7 g/kg nor for the short-course (3 weeks) SM16 at either dose level. CONCLUSION: SM16 at a dose of 0.15 g/kg reduced functional lung damage, morphologic changes, inflammatory response, and activation of TGF-beta at 26 weeks after RT. The data suggest a dose response and also suggest the superiority of long-term vs. short-term dosing.

H1 RNA polymerase III promoter-driven expression of an RNA aptamer leads to high-level inhibition of intracellular protein activity.

Aptamers offer advantages over other oligonucleotide-based approaches that artificially interfere with target gene function due to their ability to bind protein products of these genes with high affinity and specificity. However, RNA aptamers are limited in their ability to target intracellular proteins since even nuclease-resistant aptamers do not efficiently enter the intracellular compartments. Moreover, attempts at expressing RNA aptamers within mammalian cells through vector-based approaches have been hampered by the presence of additional flanking sequences in expressed RNA aptamers, which may alter their functional conformation. In this report, we successfully expressed a 'pure' RNA aptamer specific for NF-kappaB p50 protein (A-p50) utilizing an adenoviral vector employing the H1 RNA polymerase III promoter. Binding of the expressed aptamer to its target and subsequent inhibition of NF-kappaB mediated intracellular events were demonstrated in human lung adenocarcinoma cells (A549), murine mammary carcinoma cells (4T1) as well as a human tumor xenograft model. This success highlights the promise of RNA aptamers to effectively target intracellular proteins for in vitro discovery and in vivo applications.

Tumor necrosis factor-alpha is a potent endogenous mutagen that promotes cellular transformation.

Tumor necrosis factor-alpha (TNF-alpha) is an important inflammation cytokine without known direct effect on DNA. In this study, we found that TNF-alpha can cause DNA damages through reactive oxygen species. The mutagenic effect of TNF-alpha is comparable with that of ionizing radiation. TNF-alpha treatment in cultured cells resulted in increased gene mutations, gene amplification, micronuclei formation, and chromosomal instability. Antioxidants significantly reduced TNF-alpha-induced genetic damage. TNF-alpha also induced oxidative stress and nucleotide damages in mouse tissues in vivo. Moreover, TNF-alpha treatment alone led to increased malignant transformation of mouse embryo fibroblasts, which could be partially suppressed by antioxidants. As TNF-alpha is involved in chronic inflammatory diseases, such as chronic hepatitis, ulcerative colitis, and chronic skin ulcers, and these diseases predispose the patients to cancer development, our results suggest a novel pathway through which TNF-alpha promotes cancer development through induction of gene mutations, in addition to the previously reported mechanisms, in which nuclear factor-kappaB activation was implicated.

Long-term administration of a small molecular weight catalytic metalloporphyrin antioxidant, AEOL 10150, protects lungs from radiation-induced injury.

PURPOSE: To determine whether administration of a catalytic antioxidant, Mn(III) tetrakis(N,N'-diethylimidazolium-2-yl) porphyrin, AEOL 10150, with superoxide dismutase (SOD) mimetic properties, reduces the severity of radiation-induced injury to the lung from single-dose irradiation (RT) of 28 Gy. METHODS AND MATERIALS: Rats were randomly divided into four different dose groups (0, 1, 10, and 30 mg/kg/day of AEOL 10150), receiving either short-term (1 week) or long-term (10 weeks) drug administration via osmotic pumps. Rats received single-dose irradiation (RT) of 28 Gy to the right hemithorax. Breathing rates, body weights, blood samples, histopathology, and immunohistochemistry were used to assess lung damage. RESULTS: There was no significant difference in any of the study endpoints between the irradiated controls and the three groups receiving RT and short-term administration of AEOL 10150. For the long-term administration, functional determinants of lung damage 20 weeks postradiation were significantly worse for RT + phosphate-buffered saline (PBS) and RT + 1 mg/kg/day of AEOL 10150 as compared with the irradiated groups treated with higher doses of AEOL 10150 (10 or 30 mg/kg/day). Lung histology at 20 weeks revealed a significant decrease in structural damage and collagen deposition in rats receiving 10 or 30 mg/kg/day after radiation in comparison to the RT + PBS and 1 mg/kg/day groups. Immunohistochemistry demonstrated a significant reduction in macrophage accumulation, oxidative stress, and hypoxia in rats receiving AEOL 10150 (10 or 30 mg/kg/day) after lung irradiation compared with the RT + PBS and 1 mg/kg/day groups. CONCLUSIONS: The chronic administration of a novel catalytic antioxidant, AEOL 10150, demonstrates a significant protective effect from radiation-induced lung injury. AEOL 10150 has its primary impact on the cascade of events after irradiation, and adding the drug before irradiation and its short-term administration have no significant additional benefits.

Low molecular weight catalytic metalloporphyrin antioxidant AEOL 10150 protects lungs from fractionated radiation.

The objective of this study was to determine whether administration of a catalytic antioxidant, Mn(III) tetrakis(N,N'-diethylimidazolium-2-yl) porphyrin, AEOL10150, reduces the severity of long-term lung injury induced by fractionated radiation (RT). Fisher 344 rats were randomized into five groups: RT+AEOL10150 (2.5 mg/kg BID), AEOL10150 (2.5 mg/kg BID) alone, RT+ AEOL10150 (5 mg/kg BID), AEOL10150 (5 mg/kg BID) alone and RT alone. Animals received five 8 Gy fractions of RT to the right hemithorax. AEOL10150 was administered 15 min before RT and 8 h later during the period of RT treatment (5 days), followed by subcutaneous injections for 30 days, twice daily. Lung histology at 26 weeks revealed a significant decrease in lung structural damage and collagen deposition in RT+AEOL10150 (5 mg/kg BID) group, in comparison to RT alone. Immunohistochemistry studies revealed a significant reduction in tissue hypoxia (HIF1alpha, CAIX), angiogenic response (VEGF, CD-31), inflammation (ED-1), oxidative stress (8-OHdG, 3-nitrotyrosine) and fibrosis pathway (TGFbeta1, Smad3, p-Smad2/3), in animals receiving RT+ AEOL10150 (5 mg/kg BID). Administration of AEOL10150 at 5 mg/kg BID during and after RT results in a significant protective effect from long-term RT-induced lung injury. Low dose (2.5 mg/kg BID) delivery of AEOL10150 has no beneficial radioprotective effects.

Noninvasive in vivo detection of glutathione metabolism in tumors.

Magnetic resonance spectroscopic imaging has been used to follow glutathione metabolism and evaluate glutathione heterogeneity in intact tumor tissue. Stable isotope-labeled glutathione was detected in s.c. implanted fibrosarcoma tumors in anesthetized rats following infusion of [2-13C]glycine. Using 1H-decoupled 13C magnetic resonance spectroscopy, the appearance of [2-13C]glycine at 42.4 ppm and the subsequent incorporation of this isotope label into the glycyl residue of glutathione at 44.2 ppm can be detected. The identity and relative concentrations of labeled metabolites observed in the in vivo spectrum were confirmed in studies of tissue extracts. The high level of isotopic enrichment and the concentration of glutathione in tumor tissue allow for collection of spatially localized spectra using 13C chemical shift imaging methods. These data provide the first direct images of glutathione in intact tumor tissue and show metabolic heterogeneity. This method may lead to the ability to monitor changes in tumor tissue redox state that may ultimately affect diagnosis, monitoring, and treatment.

Stable RNA interference-mediated suppression of cyclophilin A diminishes non-small-cell lung tumor growth in vivo.

Cyclophilin A (CypA) was recently reported to be overexpressed in non-small-cell lung cancer, and represents a potentially novel therapeutic target. To determine the role of CypA in oncogenesis, stable RNA interference (RNAi)-mediated knockdown of CypA was established in two non-small-cell lung cancer cell lines (ADLC-5M2 and LC-103H), and these cells were grown as xenografts in severe combined immunodeficient mice. Tumor cell proliferation, apoptosis, and angiogenesis were measured by Ki67, terminal deoxyribonucleotidyl transferase-mediated dUTP nick-end labeling, and CD31 immunohistochemistry, respectively. Tumor glucose metabolism was assessed by fluorodeoxyglucose positron emission tomography imaging. Knockdown of CypA correlated in vivo with slower growth, less fluorodeoxyglucose uptake, decreased proliferation, and a greater degree of apoptosis in the tumors. These results establish the relevance of CypA to tumor growth in vivo, specifically to proliferation and apoptosis. Elucidation of the precise role of CypA in these pathways may lead to new targeted therapies for lung cancer.

Erythropoietin inhibits apoptosis in breast cancer cells via an Akt-dependent pathway without modulating in vivo chemosensitivity.

Evidence for erythropoietin signaling has been shown in several nonhematopoietic tissues, including many tumor types. Clinically, recombinant erythropoietin treatment of malignancy-related anemia has yet to be definitively associated with any modulation of chemotherapy or radiotherapy efficacy. Preclinically, recombinant erythropoietin has been shown to increase tumor oxygenation, but the direct effects of recombinant erythropoietin on tumor cells that express erythropoietin receptor are not yet fully characterized. This study examined the effects of exogenous recombinant erythropoietin on rodent mammary adenocarcinoma cells (R3230) in vitro and in vivo, and determined the effects of systemic recombinant erythropoietin on tumor growth delay in Taxol treatment. We showed that systemic recombinant erythropoietin treatment of rats bearing R3230 mammary carcinomas induced an increase in phospho-Akt levels within tumor cells. This was associated with a decrease in the frequency of apoptotic cells in tumors from recombinant erythropoietin-treated animals, but did not noticeably affect tumor growth rate. In vitro studies revealed that not only does recombinant erythropoietin induce Akt phosphorylation, but it also stimulates phosphorylation of p44/42 mitogen-activated protein kinases, Erk1 and Erk2. Activation of erythropoietin-mediated signaling in R3230 cells was associated with dose-dependent inhibition of apoptosis in response to Taxol treatment and serum starvation, an effect that was blocked by the addition of a phosphatidylinositol-3-kinase inhibitor. Despite its cytoprotective effects in vitro, recombinant erythropoietin did not significantly affect tumor growth delay in Taxol treatment. This study shows direct recombinant erythropoietin-mediated activation of specific intracellular signaling pathways in mammary adenocarcinoma cells in vivo and in vitro. Modulation of tumor apoptosis pathways by recombinant erythropoietin may have negative consequences by decreasing the chemosensitivity and radiosensitivity of erythropoietin receptor-positive breast tumors, although it did not have any obvious effects on growth with or without chemotherapy in this model.

Enhancement of hypoxia-induced tumor cell death in vitro and radiation therapy in vivo by use of small interfering RNA targeted to hypoxia-inducible factor-1alpha.

Hypoxia-inducible factor-1alpha (HIF-1alpha) is an important transcriptional factor that is activated when mammalian cells experience hypoxia, a tumor microenvironmental condition that plays pivotal roles in tumor progression and treatment. In this study, we examined the idea of down-regulating HIF-1alpha in tumor cells for therapeutic gain. We show that the expression levels of HIF-1alpha can be significantly attenuated by use of the recently established small interfering RNA technology in combination with adenovirus-mediated gene transfer. Down-regulation of the HIF-1alpha protein enhanced hypoxia-mediated tumor cell apoptosis in vitro. Subcutaneous tumor growth was also prevented from cells with attenuated HIF-1alpha expression. In addition, intratumoral injection of adenovirus encoding the HIF-1alpha-targeted small interfering RNA had a small but significant effect on tumor growth when combined with ionizing radiation. Therefore, our results provide proof of HIF-1alpha as an effective target for anticancer therapy. They also suggest that an adenovirus-based small interfering RNA gene transfer approach may be a potentially effective adjuvant strategy for cancer treatment.

A manganese porphyrin superoxide dismutase mimetic enhances tumor radioresponsiveness.

PURPOSE: To determine the effect of the superoxide dismutase mimetic Mn(III) tetrakis(N-ethylpyridinium-2-yl)porphyrin (MnTE-2-PyP(5+)) on tumor radioresponsiveness. METHODS AND MATERIALS: Various rodent tumor (4T1, R3230, B16) and endothelial (SVEC) cell lines were exposed to MnTE-2-PyP(5+) and assayed for viability and radiosensitivity in vitro. Next, tumors were treated with radiation and MnTE-2-PyP(5+)in vivo, and the effects on tumor growth and vascularity were monitored. RESULTS: In vitro, MnTE-2-PyP(5+) was not significantly cytotoxic. However, at concentrations as low as 2 mumol/L it caused 100% inhibition of secretion by tumor cells of cytokines protective of irradiated endothelial cells. In vivo, combined treatment with radiation and MnTE-2-PyP(5+) achieved synergistic tumor devascularization, reducing vascular density by 78.7% within 72 h of radiotherapy (p < 0.05 vs. radiation or drug alone). Co-treatment of tumors also resulted in synergistic antitumor effects, extending tumor growth delay by 9 days (p < 0.01). CONCLUSIONS: These studies support the conclusion that MnTE-2-PyP(5+), which has been shown to protect normal tissues from radiation injury, can also improve tumor control through augmenting radiation-induced damage to the tumor vasculature.