Anti-metastatic gene therapy utilizing subcutaneous inoculation of EC-SOD gene transduced autologous fibroblast suppressed lung metastasis of Meth-A cells and 3LL cells in mice

Imperative connotation of SODs in cancer: Emerging targets and multifactorial role of action

Superoxide dismutase (SOD) is a crucial enzyme responsible for the redox homeostasis inside the cell. As a part of the antioxidant defense system, it plays a pivotal role in the dismutation of the superoxide radicals (O 2 - ) generated mainly by the oxidative phosphorylation, which would otherwise bring out the redox dysregulation, leading to higher reactive oxygen species (ROS) generation and, ultimately, cell transformation, and malignancy. Several studies have shown the involvement of ROS in a wide range of human cancers. As SOD is the key enzyme in regulating ROS, any change, such as a transcriptional change, epigenetic remodeling, functional alteration, and so forth, either activates the proto-oncogenes or aberrant signaling cascades, which results in cancer. Interestingly, in some cases, SODs act as tumor promoters instead of suppressors. Furthermore, SODs have also been known to switch their role during tumor progression. In this review, we have tried to give a comprehensive account of SODs multifactorial role in various human cancers so that SODs-based therapeutic strategies could be made to thwart cancers.

Optimizing an Antioxidant TEMPO Copolymer for Reactive Oxygen Species Scavenging and Anti-Inflammatory Effects in Vivo

Oxidative stress is broadly implicated in chronic, inflammatory diseases because it causes protein and lipid damage, cell death, and stimulation of inflammatory signaling. Supplementation of innate antioxidant mechanisms with drugs such as the superoxide dismutase (SOD) mimetic compound 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) is a promising strategy for reducing oxidative stress-driven pathologies. TEMPO is inexpensive to produce and has strong antioxidant activity, but it is limited as a drug due to rapid clearance from the body. It is also challenging to encapsulate into micellar nanoparticles or polymer microparticles, because it is a small, water soluble molecule that does not efficiently load into hydrophobic carrier systems. In this work, we pursued a polymeric form of TEMPO [poly(TEMPO)] to increase its molecular weight with the goal of improving in vivo bioavailability. High density of TEMPO on the poly(TEMPO) backbone limited water solubility and bioactivity of the product, a challenge that was overcome by tuning the density of TEMPO in the polymer by copolymerization with the hydrophilic monomer dimethylacrylamide (DMA). Using this strategy, we formed a series of poly(DMA-co-TEMPO) random copolymers. An optimal composition of 40 mol % TEMPO/60 mol % DMA was identified for water solubility and O2•- scavenging in vitro. In an air pouch model of acute local inflammation, the optimized copolymer outperformed both the free drug and a 100% poly(TEMPO) formulation in O2•- scavenging, retention, and reduction of TNFα levels. Additionally, the optimized copolymer reduced ROS levels after systemic injection in a footpad model of inflammation. These results demonstrate the benefit of polymerizing TEMPO for in vivo efficacy and could lead to a useful antioxidant polymer formulation for next-generation anti-inflammatory treatments.

Extracellular Superoxide Dismutase: Growth Promoter or Tumor Suppressor?

Extracellular superoxide dismutase (SOD3) gene transfer to tissue damage results in increased healing, increased cell proliferation, decreased apoptosis, and decreased inflammatory cell infiltration. At molecular level, in vivo SOD3 overexpression reduces superoxide anion (O₂⁻) concentration and increases mitogen kinase activation suggesting that SOD3 could have life-supporting characteristics. The hypothesis is further strengthened by the observations showing significantly increased mortality in conditional knockout mice. However, in cancer SOD3 has been shown to either increase or decrease cell proliferation and survival depending on the model system used, indicating that SOD3-derived growth mechanisms are not completely understood. In this paper, the author reviews the main discoveries in SOD3-dependent growth regulation and signal transduction.

Extracellular superoxide dismutase regulates the expression of small gtpase regulatory proteins GEFs, GAPs, and GDI

Extracellular superoxide dismutase (SOD3), which catalyzes the dismutation of superoxide anions to hydrogen peroxide at the cell membranes, regulates the cellular growth in a dose-dependent manner. This enzyme induces primary cell proliferation and immortalization at low expression levels whereas it activates cancer barrier signaling through the p53-p21 pathway at high expression levels, causing growth arrest, senescence, and apoptosis. Because previous reports suggested that the SOD3–induced reduction in the rates of cellular growth and migration also occurred in the absence of functional p53 signaling, in the current study we investigated the SOD3-induced growth-suppressive mechanisms in anaplastic thyroid cancer cells. Based on our data, the robust over-expression of SOD3 increased the level of phosphorylation of the EGFR, ERBB2, RYK, ALK, FLT3, and EPHA10 receptor tyrosine kinases with the consequent downstream activation of the SRC, FYN, YES, HCK, and LYN kinases. However, pull-down experiments focusing on the small GTPase RAS, RAC, CDC42, and RHO revealed a reduced level of growth and migration signal transduction, such as the lack of stimulation of the mitogen pathway, in the SOD3 over-expressing cells, which was confirmed by MEK1/2 and ERK1/2 Western blotting analysis. Interestingly, the mRNA expression analyses indicated that SOD3 regulated the expression of guanine nucleotide-exchange factors (RHO GEF16, RAL GEF RGL1), GTPase-activating proteins (ARFGAP ADAP2, RAS GAP RASAL1, RGS4), and a Rho guanine nucleotide-disassociation inhibitor (RHO GDI 2) in a dose dependent manner, thus controlling signaling through the small G protein GTPases. Therefore, our current data may suggest the occurrence of dose-dependent SOD3–driven control of the GTP loading of small G proteins indicating a novel growth regulatory mechanism of this enzyme.

Extracellular superoxide dismutase induces mouse embryonic fibroblast proliferative burst, growth arrest, immortalization, and consequent in vivo tumorigenesis

AIMS

Rat sarcoma virus (RAS)-induced tumorigenesis has been suggested to follow a three-stage model consisting of an initial RAS activation, senescence induction, and evasion of p53-dependent senescence checkpoints. While reactive oxygen species act as second messengers in RAS-induced senescence, they are also involved in oncogenic transformation by inducing proliferation and promoting mutations. In the current work, we investigated the role of extracellular superoxide dismutase (SOD3) in RAS-induced senescence and immortalization in vitro and in vivo. We used a mouse embryonic fibroblast (MEF) primary cell model along with immortalized and transformed human cell lines derived from papillary and anaplastic thyroid cancer.

RESULTS

Based on our data, sod3 RNA interference in H-RasV12-transduced cells markedly inhibited cell growth, while sod3 over-expression in MEFs initially caused a proliferative burst followed by the activation of DNA damage checkpoints, induction of p53-p21 signal transduction, and senescence. Subsequently, sod3-transduced MEF cells developed co-operative p21-p16 down-regulation and acquired transformed cell characteristics such as increased telomerase activity, loss of contact inhibition, growth in low-nutrient conditions, and in vivo tumorigenesis. Interestingly, as previously reported with RAS, we showed a dose-dependent response to SOD3 in vitro and in vivo involving transcriptional and non-transcriptional regulatory mechanisms.

INNOVATION

SOD3 may mediate H-RasV12-induced initiation of primary cell immortalization.

CONCLUSIONS

Our results indicate that SOD3 influences growth signaling in primary and cancer cells downstream of the ras oncogene and could serve as a therapy target at an early tumorigenesis phase.

Intracellular superoxide dismutase activity defines invasiveness of the murine T-lymphoma cell line L5187Y-ML25 in vitro and in vivo

Superoxide anion in the tumor microenvironment promotes a malignant phenotype. Here, we examined superoxide in a murine T-lymphoma cell line L5187Y-ML25. Clones with high and low intracellular superoxide dismutase (SOD) activities were obtained from parental L5187Y-ML25 cells and were subjected to assays determining cell invasiveness, motility, and in vivo dissemination. Cells with lower SOD activity exhibited higher invasiveness in vitro and in vivo. NADPH oxidase inhibitor suppressed intracellular free radical levels and cell motility, suggesting NADPH oxidase as a source of superoxides that stimulates cell motility. These results implicate superoxide as a potential anti-metastatic therapy for hematopoietic cell malignancies.

Modulation of redox signaling promotes apoptosis in epithelial ovarian cancer cells

OBJECTIVE

Epithelial ovarian cancer (EOC) cells are known to be resistant to apoptosis through a mechanism that may involve alteration in their redox balance. NADPH oxidase is a major source of intracellular superoxide, which is converted to the less toxic product by superoxide dismutase (SOD). Superoxide contributes to hypoxia inducible factor (HIF)-1α stabilization. We sought to determine the effects of inhibiting the generation of intracellular reactive oxygen species (ROS) on apoptosis of EOC cells.

METHODS

Diphenyleneiodonium (DPI), an irreversible ROS inhibitor, was used to inhibit the generation of ROS in EOC cell lines, SKOV-3 and MDAH-2774, followed by assessment of apoptosis, NADPH oxidase, SOD3 and HIF-1α expression. A combination of immunohistochemistry, immunoprecipitation/western blot, and real-time RT-PCR were utilized to evaluate the expression of these enzymes in EOC cells as well as normal ovarian tissue and ovarian cancer tissue specimens.

RESULTS

DPI treatment significantly induced apoptosis in both EOC cell lines as evident by increased caspase-3 activity and TUNEL assay. Additionally, both EOC cell lines were found to express NADPH oxidase, HIF-1α, and SOD3, which were highly sensitive to DPI treatment. DPI treatment resulted in reduced NADPH oxidase, SOD3 and HIF-1α levels. Furthermore, ovarian cancer tissues were found to manifest higher NADPH oxidase levels as compared to normal ovarian tissues.

CONCLUSIONS

These data suggest that lowering oxidative stress, possibly through the inhibition of NADPH oxidase, induces apoptosis in ovarian cancer cells and may serve as a potential target for cancer therapy.

Essential role of protein kinase C zeta in transducing a motility signal induced by superoxide and a chemotactic peptide, fMLP

Under various pathological conditions, including infection, malignancy, and autoimmune diseases, tissues are incessantly exposed to reactive oxygen species produced by infiltrating inflammatory cells. We show augmentation of motility associated with morphological changes of human squamous carcinoma SASH1 cells, human peripheral monocytes (hPMs), and murine macrophage-like cell line J774.1 by superoxide stimulation. We also disclose that motility of hPMs and J774.1 induced by a chemotactic peptide (N-formyl-methionyl-leucyl-phenylalanine [fMLP]) was inhibited by superoxide dismutase or N-acetylcystein, indicating stimulation of motility by superoxide generated by fMLP stimulation. In these cells, protein kinase C (PKC) ζ was activated to phosphorylate RhoGDI-1, which liberated RhoGTPases, leading to their activation. These events were inhibited by dominant-negative PKCζ in SASH1 cells, myristoylated PKCζ peptides in hPMs and J774.1, or a specific inhibitor of RhoGTPase in SASH1, hPMs, and J774.1. These results suggest a new approach for manipulation of inflammation as well as tumor cell invasion by targeting this novel signaling pathway.

Amelioration of murine dextran sulfate sodium-induced colitis by ex vivo extracellular superoxide dismutase gene transfer

BACKGROUND

Although the etiology of inflammatory bowel disease has not been fully clarified, reactive oxygen species is speculated to be involved. Extracellular superoxide dismutase (EC-SOD), an isozyme of SODs, is known to function mainly in body fluids. We investigated the efficacy of an ex vivo EC-SOD gene transfer into dextran sulfate sodium (DSS)-induced colitis mice.

MATERIALS AND METHODS

Experimental colitis was induced by providing Balb/c mice with DSS in sterile distilled water provided as desired. The syngenic fibroblasts were obtained from Balb/c mice embryos and retrovirally transduced with the hEC-SOD gene. These engineered cells were confirmed to secrete EC-SOD in culture medium by enzyme-linked immunosorbent assay and were inoculated subcutaneously in the backs of DSS-treated mice. Mucosal injury of the colon was evaluated by the disease activity index (DAI: body weight, rectal bleeding, and stool consistency), grading of histologic disease severity, and levels of cytokine (tumor necrosis factor-alpha, interleukin-1beta) production. 8-Hydroxydeoxyguanosine (8-OHdG) levels in the mucosal tissue were assessed by immunohistochemical staining. Malondialdehyde (MDA) was measured using a colorimetric assay.

RESULTS

A significant improvement was observed in DAI score and histologic severity as well as in mucosal tissue levels of inflammatory cytokines, 8-OHdG, and MDA of mice treated with the EC-SOD gene as compared with those without gene therapy, not only in a mild colitis model but also in a severe colitis model. Survival of treated mice in these models was significantly prolonged.

CONCLUSIONS

Ex vivo transfer of the EC-SOD gene was feasible for treatment of DSS-induced colitis.

Prevention of inflammation-mediated acquisition of metastatic properties of benign mouse fibrosarcoma cells by administration of an orally available superoxide dismutase

Weakly tumorigenic and nonmetastatic QR-32 cells derived from a fibrosarcoma in C57BL6 mouse are converted to malignant cells once they have grown after being coimplanted with a gelatine sponge which induces inflammation. We administered a newly developed peroral superoxide dismutase (SOD), oxykine, and as control vehicle, gliadin and saline, starting 2 days before the coimplantation and continued daily throughout the experiment. In the oxykine group, tumour incidence was lower (41%) than in the gliadin or saline group (83 and 79%, respectively). The inhibitory effect of oxykine was lost when an individual component of oxykine was administered, that is, SOD alone and gliadin alone. The effect was also abolished when administered by intraperitoneal route. When perfused in situ with nitroblue tetrazolium, an indicator of superoxide formation, the tumour masses from gliadin and saline groups displayed intense formazan deposition, whereas, those from oxykine group had less deposition. Enzymatic activity of SOD was also increased in oxykine group. Arising tumour cells in gliadin and saline groups acquired metastatic phenotype, but those in oxykine group showed reduced metastatic ability. These results suggested that the orally active SOD derivative prevented tumour progression promoted by inflammation, which is thought to be through scavenging inflammatory cell-derived superoxide anion.

Catalase reverses tumorigenicity in a malignant cell line by an epidermal growth factor receptor pathway

We have used a keratinocyte in vivo/in vitro cell model to test the hypothesis that hydrogen peroxide acts as a signaling molecule, contributing to proliferation and tumorigenesis. A cell line, 6M90, that produces squamous cell carcinoma (SCC), has high levels of ROS and low levels of catalase. A new cell line, MTOC2, generated from parental 6M90 cells by introduction of a Tet-responsive catalase transgene, effectively expressed higher peroxisomal catalase. Increased catalase expression diminished constitutive ROS and enhanced viability after treatment with hydrogen peroxide. Protein tyrosine phosphatase activity was higher in the MTOC2 cells with high catalase, consistent with detection of a lower level of phosphorylation at tyrosine 1068 of the epidermal growth factor receptor (EGF-R). Transcription of downstream c-fos, AP-1 transactivation and cell proliferation were higher in the low catalase cells. An EGF-R inhibitor, AG1478, blocks the higher AP-1 transactivation and cell proliferation of the low catalase 6M90 cells. Tumorigenesis in SCID mice was greatly diminished in the high catalase cells. Our data suggest that hydrogen peroxide functions as a signaling molecule that can modulate activity of a protein tyrosine phosphatase/(s) resulting in phosphorylation of tryrosine/(s) on the EGF-R. Therefore, catalase acts as a tumor-suppressor gene in part by decreasing EGF-R signaling.

The radical scavenger edaravone enhances the anti-tumor effects of CPT-11 in murine colon cancer by increasing apoptosis via inhibition of NF-κB

The transcription factor NF-kappaB is reportedly activated by anti-cancer chemotherapeutic compounds in many cancer cell lines and NF-kappaB activation is one mechanism by which tumors become resistant to apoptosis. Antioxidants have been reported to serve as potent NF-kB inhibitors. In this study, we investigated the ability of edaravone to enhance apoptosis induced by CPT-11 through inhibition of NF-kB. In vitro, SN38, the active metabolite of CPT-11, induced activation of NF-kB, the production of intracellular reactive oxygen species, the activation of caspase-3, and apoptosis in colon26 cells. Pretreatment with edaravone scavenged the SN38-produced reactive oxygen species, and inhibited the SN38-induced activation of NF-kB. Moreover, edaravone enhanced the activation of caspase-3, and the level of apoptosis induced by SN38. In vivo, the combination of edaravone with CPT-11 reduced subcutaneous tumor growth and number of pulmonary metastases more effectively than CPT-11 alone. These results demonstrate that the combination of edaravone with CPT-11 may constitute a new strategy for treating primary and metastatic colon cancer.

Superoxide dismutases in malignant cells and human tumors

Reactive oxygen metabolites have multifactorial effects on the regulation of cell growth and the capacity of malignant cells to invade. Overexpression of the superoxide dismutases (SODs) in vitro increases cell differentiation, decreases cell growth and proliferation, and can reverse a malignant phenotype to a nonmalignant one. The situation in vivo is more complex due to multiple interactions of tumor cells with their environment. Numerous in vivo studies show that the superoxide dismutases can be highly expressed in aggressive human solid tumors. Furthermore, high SOD has occasionally been associated with a poor prognosis and with resistance to cytotoxic drugs and radiation. Most of the apparent conflicts between the above in vitro and in vivo observations can be reconciled by considering the net redox status of tumor cells in different environments. Administering high concentrations of SOD to cells in vitro is usually associated with a non- or less malignant phenotype, whereas secondary induction of SOD in tumors in vivo can be associated with an aggressive malignant transformation probably due to the altered (oxidative) redox state in the malignant cells. This concept suggests that for many types of tumors antioxidants could be used to diminish the invasive capability of malignant cells.

Decrease of Smad4 gene expression in patients with essential thrombocythaemia may cause an escape from suppression of megakaryopoiesis by transforming growth factor-beta1

Essential thrombocythaemia (ET) is characterized by the abnormal and sustained proliferation of megakaryocytes. The mechanism for this lineage-specific expansion in ET, remains unclear. We have previously reported that transforming growth factor-beta1 (TGF-beta1) is involved in negative feedback regulation of megakaryopoiesis in both healthy volunteers (HV) and patients with idiopathic thrombocytopenic purpura (ITP). The present study found that megakaryocyte colony-forming units (CFU-MK) of ET patients were less sensitive to TGF-beta1 than those of HV. The expression of Smad4 (Sma- and Mad-related protein-4) in CFU-MK of ET patients was reduced in comparison with that of HV. Finally, to confirm that the impaired TGF-beta1 sensitivity was caused by reduced expression of Smad4, we examined Smad4-transfected CFU-MK from ET patients in the presence of TGF-beta1, and verified that the transfectants were indeed as susceptible as CFU-MK from HV to TGF-beta1. Thus it was surmised that one of the mechanisms for impaired sensitivity of CFU-MK to TGF-beta1 is the reduced expression of Smad4.

Inhibition of lung metastasis of osteosarcoma cell line POS-1 transplanted into mice by thigh ligation

Using a model with external ligation of the thigh, the effect of ischemia-reperfusion injury on tumor growth and the activity of lung metastasis was investigated in mice inoculated a spontaneous murine osteosarcoma cell line (POS-1) in vivo. POS-1 cell suspension was inoculated into the right hind footpad of 70 mice. Four weeks after inoculation, the ipsilateral thigh was ligated for 3 h in 15 mice and the contralateral thigh in 15 mice. Another ten mice were inoculated with POS-1 without ligating the thigh. The number of metastatic foci on the lung surface 6 weeks after inoculation was 2.29+/-0.98 (mean+/-SE) foci/lungs in mice with ipsilateral ligation and 6.25+/-2.41 in mice with contralateral ligation, which were significantly lower than control (13.40+/-1.42 in mice no ligation) (P<0.01). The number of metastatic foci on the lung surface in mice with intraperitoneal injection of superoxide dismutase (SOD) and catalase was 3.25+/-0.65 (mean+/-SE) foci/lungs in mice with ligation which was significantly greater than that in mice without SOD and catalase injection 1.29+/-0.97 (P=0.04). Cell viability was 9.12+/-4.07% with 100 microM H(2)O(2) in 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay. It revealed that at concentrations of 100 microM H(2)O(2) or higher was cytotoxic to POS-1. In cell invasion assay, the number of invading cells with 10 microM H(2)O(2) was 2.80+/-0.53 cells/field, which was significantly lower than control (5.93+/-0.18) (mean+/-SE), indicating that low-dose H(2)O(2) suppressed invasion of POS-1. These results suggested that reperfusion injury had selective cytotoxicity to POS-1 through producing reactive oxygen species. Activated oxygen was considered to inhibit the regional growth and the ability of lung metastasis of POS-1 cells.

Molecular evolution and structure--function relationships of the superoxide dismutase gene families in angiosperms and their relationship to other eukaryotic and prokaryotic superoxide dismutases

This study assesses whether the phylogenetic relationships between SODs from different organisms could assist in elucidating the functional relationships among these enzymes from evolutionarily distinct species. Phylogenetic trees and intron positions were compared to determine the relationships among these enzymes. Alignment of Cu/ZnSOD amino acid sequences indicates high homology among plant sequences, with some features that distinguish chloroplastic from cytosolic Cu/ZnSODs. Among eukaryotes, the plant SODs group together. Alignment of the Mn and FeSOD amino acid sequences indicates a higher degree of homology within the group of MnSODs (>70%) than within FeSODs (approximately 60%). Tree topologies are similar and reflect the taxonomic classification of the corresponding species. Intron number and position in the Cu/Zn Sod genes are highly conserved in plants. Genes encoding cytosolic SODs have seven introns and genes encoding chloroplastic SODs have eight introns, except the chloroplastic maize Sod1, which has seven. In Mn Sod genes the number and position of introns are highly conserved among plant species, but not among nonplant species. The link between the phylogenetic relationships and SOD functions remains unclear. Our findings suggest that the 5' region of these genes played a pivotal role in the evolution of function of these enzymes. Nevertheless, the system of SODs is highly structured and it is critical to understand the physiological differences between the SODs in response to different stresses in order to compare their functions and evolutionary history.

Treatment of murine collagen-induced arthritis by ex vivo extracellular superoxide dismutase gene transfer

OBJECTIVE; Superoxide dismutase (SOD) is a potent antiinflammatory enzyme that has received growing attention for its therapeutic potential. This study was undertaken to examine the efficacy of extracellular SOD (EC-SOD) gene therapy in murine collagen-induced arthritis.

METHODS

Embryonic DBA/1 mouse fibroblasts were infected with a recombinant retrovirus expressing human EC-SOD. DBA/1 mice that had been treated with type II collagen were administered subcutaneous injections of 2 x 10(7) EC-SOD-expressing fibroblasts on day 29, when symptoms of arthritis were already present. The severity of arthritis in individual mice was evaluated in a double-blind manner; each paw was assigned a separate clinical score, and hind paw thickness was measured with a caliper. Mice were killed on day 50 for histologic examination of the joints.

RESULTS

High serum concentrations of EC-SOD were maintained for at least 7 days. Mice treated with the transgene exhibited significant suppression of clinical symptoms such as disabling joint swelling, deformity, and hind paw thickness, compared with the untreated group (mean +/- SD maximum clinical score in the untreated and the transgene-treated groups 2.71 +/- 1.08 and 1.35 +/- 1.22, respectively; P < 0.01, and hind paw thickness 3.04 +/- 0.18 mm and 2.56 +/- 0.12 mm, respectively; P < 0.05). Histologic abnormalities, including destruction of cartilage and bone, infiltration of mononuclear cells, and proliferation of synovial cells, were also markedly improved in the EC-SOD-treated mice compared with the control group (histopathologic score 7.50 +/- 1.13 and 4.13 +/- 1.88 in the untreated and transgene-treated groups, respectively; P < 0.05).

CONCLUSION

These results indicate that EC-SOD gene transfer may be an effective form of therapy for rheumatoid arthritis.