Yun Choi

Suppression of adenine nucleotide translocase-2 by vector-based siRNA in human breast cancer cells induces apoptosis and inhibits tumor growth in vitro and in vivo

IntroductionAdenine nucleotide translocator (ANT) 2 is highly expressed in proliferative cells, and ANT2 induction in cancer cells is known to be directly associated with glycolytic metabolisms and carcinogenesis. In addition, ANT2 repression results in the growth arrest of human cells, implying that ANT2 is a candidate for cancer therapy based on molecular targeting.MethodsWe utilized an ANT2-specific RNA interference approach to inhibit ANT2 expression for evaluating its antitumor effect in vitro and in vivo. Specifically, to investigate the therapeutic potential of ANT2 repression, we used a DNA vector-based RNA interference approach by expressing shRNA to knockdown ANT2 in breast cancer cell lines overexpressing ANT2.ResultsANT2 shRNA treatment in breast cancer cell line MDA-MB-231 repressed cell growth as well as proliferation. In addition, cell cycle arrest, ATP depletion and apoptotic cell death characterized by the potential disruption of mitochondrial membrane were observed from the ANT2 shRNA-treated breast cancer cells. Apoptotic breast cancer cells transfected with ANT2 shRNA also induced a cytotoxic bystander effect that generates necrotic cell death to the neighboring cells. The intracellular levels of TNFα and TNF-receptor I were increased in ANT2 shRNA transfected cells and the bystander effect was partly blocked by anti-TNFα antibody. Ultimately, ANT2 shRNA effectively inhibited tumor growth in vivo.ConclusionThese results suggest that vector-based ANT2 RNA interference could be an efficient molecular therapeutic method for breast cancer with high expression of ANT2.

Over-expression of adenine nucleotide translocase 1 (ANT1) induces apoptosis and tumor regression in vivo.

BackgroundAdenine nucleotide translocase (ANT) is located in the inner mitochondrial membrane and catalyzes the exchange of mitochondrial ATP for cytosolic ADP. ANT has been known to be a major component of the permeability transition pore complex of mitochondria and contributes to mitochondria-mediated apoptosis. Human ANT has four isoforms (ANT1, ANT2, ANT3, and ANT4), and the expression of the ANT isoforms is variable depending on the tissue and cell type, developmental stage, and proliferation status. Among the isoforms, ANT1 is highly expressed in terminally-differentiated tissues, but expressed in low levels in proliferating cells, such as cancer cells. In particular, over-expression of ANT1 induces apoptosis in cultured tumor cells.MethodsWe applied an ANT1 gene transfer approach to induce apoptosis and to evaluate the anti-tumor effect of ANT1 in a nude mouse model.ResultsWe demonstrated that ANT1 transfection induced apoptosis of MDA-MB-231 cells, inactivated NF-κB activity, and increased Bax expression. ANT1-inducing apoptosis was accompanied by the disruption of mitochondrial membrane potential, cytochrome c release and the activation of caspases-9 and -3. Moreover, ANT1 transfection significantly suppressed tumor growth in vivo.ConclusionOur results suggest that ANT1 transfection may be a useful therapeutic modality for the treatment of cancer.

Immune response to firefly luciferase as a naked DNA

Firefly luciferase (Fluc) has been widely used as a reporter gene. The aim of this study was to investigate immune response to luciferase protein after an intradermal injection of pcDNA3.1-Fluc in immunocompetent BALB/c mice. We observed bioluminescence at injection sites from 1 day to 7 days post-injection when pcDNA3.1-Fluc was intradermally injected into ear-pinnae. To observe induced immune response, the percentages of CD8+IFN-γ+ cells in the draining lymphoid cells of immunocompetent BALB/c mice immunized by pcDNA3.1-Fluc were measured. And the tumor growths of CT26/Fluc in pcDNA3.1-Fluc group were monitored by observing bioluminescent signals and measuring tumor mass, and these were compared with those of the pcDNA3.1 group in immunocompetent BALB/c mice and immunodeficient Nu/Nu mice. In the immunocompetent BALB/c mice, percentages of CD8+IFN-γ+ cells in the pcDNA3.1-Fluc group were higher than those in the pcDNA3.1 group. Ten days after tumor inoculation, tumor growth inhibition was found in the pcDNA3.1-Fluc group, but not in the pcDNA3.1 group in the immunocompetent BALB/c mice. No significant difference in tumor growth inhibition was observed when CT26/Fluc was injected into immunodeficient Nu/Nu mice. In terms of cytokine profiles of draining lymphoid cells of immunized mice, IFN-γ protein levels in the pcDNA3.1-Fluc group were higher than 3 in pcDNA3.1 group animals among the immunocompetent BALB/c mice. In conclusion, Fluc induced a Th1 immune response to Fluc protein delivered by injecting pcDNA3.1-Fluc into immunocompetent BALB/c mice. We suggest that immune response to the Fluc gene is cautionary in pre-clinical or clinical trials involving the Fluc gene, and that the immunologic potential of firefly luciferase as a naked DNA may be useful in cancer immunotherapy.

Short-hairpin RNA-induced suppression of adenine nucleotide translocase-2 in breast cancer cells restores their susceptibility to TRAIL-induced apoptosis by activating JNK and modulating TRAIL receptor expression

BackgroundTumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL; apo2 ligand) induces apoptosis in cancer cells but has little effect on normal cells. However, many cancer cell types are resistant to TRAIL-induced apoptosis, limiting the clinical utility of TRAIL as an anti-cancer agent. We previously reported that the suppression of adenine nucleotide translocase-2 (ANT2) by short-hairpin RNA (shRNA) induces apoptosis of breast cancer cells, which frequently express high levels of ANT2. In the present study, we examined the effect of RNA shRNA-induced suppression of ANT2 on the resistance of breast cancer cells to TRAIL-induced apoptosis in vitro and in vivo.ResultsANT2 shRNA treatment sensitized MCF7, T47 D, and BT474 cells to TRAIL-induced apoptosis by up-regulating the expression of TRAIL death receptors 4 and 5 (DR4 and DR5) and down-regulating the TRAIL decoy receptor 2 (DcR2). In MCF7 cells, ANT2 knockdown activated the stress kinase c-Jun N-terminal kinase (JNK), subsequently stabilizing and increasing the transcriptional activity of p53 by phosphorylating it at Thr81; it also enhanced the expression and activity of DNA methyltransferase 1 (DNMT1). ANT2 shRNA-induced overexpression of DR4/DR5 and TRAIL sensitization were blocked by a p53 inhibitor, suggesting that p53 activation plays an important role in the transcriptional up-regulation of DR4/DR5. However, ANT2 knockdown also up-regulated DR4/DR5 in the p53-mutant cell lines BT474 and T47 D. In MCF7 cells, ANT2 shRNA treatment led to DcR2 promoter methylation and concomitant down-regulation of DcR2 expression, consistent with the observed activation of DNMT1. Treatment of the cells with a demethylating agent or JNK inhibitor prevented the ANT2 shRNA-induced down-regulation of DcR2 and activation of both p53 and DNMT1. In in vivo experiments using nude mice, ANT2 shRNA caused TRAIL-resistant MCF7 xenografts to undergo TRAIL-induced cell death, up-regulated DR4/DR5, and down-regulated DcR2. Co-treatment with ANT2 shRNA and TRAIL efficiently suppressed tumor growth in these mice.ConclusionsANT2 suppression by shRNA might be exploited to overcome TRAIL-resistance in cancer.

Human sodium iodide symporter gene adjunctive radiotherapy to enhance the preventive effect of hMUC1 DNA vaccine

We demonstrate the use of combination therapy to overcome the limitations of cancer DNA vaccines by adding radioiodine gene therapy in an animal cancer model. We established a stable cell line (CT26/hMUC1‐hNIS‐Fluc: CMNF) expressing the hMUC1, hNIS and Fluc genes using a retro‐ and lentivirus system. The survival rates (%) of CMNF cells were determined using clonogenic assays after 131I treatment. After i.m. immunization to 4 groups of Balb/c mice (pcDNA3.1, pcDNA3.1+131I, pcDNA3‐hMUC1+PBS and pcDNA3‐hMUC1+131I groups) with pcDNA3‐hMUC1 or pcDNA3.1 once a week for 2 weeks, 1 × 105 CMNF cells were injected s.c. into the right thighs of mice in each group. Twenty‐one days after tumor transplantation, 131I was administered i.p. to the pcDNA3.1+131I and pcDNA3‐hMUC1+ 131I groups. Tumor progression was monitored in the 4 groups by bioluminescent and scintigraphic imaging and by taking caliper measurements. Tumor masses were extracted and weighted at 39 days post‐tumor challenge. We confirmed that CMNF cells highly express hMUC1, hNIS and Fluc by FACS, 125I uptake, and luciferase assay. The survival rates of CMNF were markedly reduced to (14.6 ± 1.5)% after 131I treatment compared with the survival rates of parental cells (p < 0.001). Tumor growth inhibition was significant only in the pcDNA3‐hMUC1+ 131I group at 39 days post challenge. Tumor masses in pcDNA3‐hMUC1+ 131I group were smaller than those of the other groups. This study shows that the weak preventive effects of cancer DNA vaccine can be overcome by radioiodine gene therapy utilizing sodium iodide symporter.

MIDGE/hNIS vaccination generates antigen-associated CD8+IFN-γ+ T cells and enhances protective antitumor immunity

Human sodium iodide symporter (hNIS) is a transmembrane protein that actively transports iodide ions into thyroid cells. hNIS is over‐expressed in some cases of the thyroid cancers compared with the surrounding normal tissues and has been considered to be an attractive target for immunotherapy. The aim of this study is to determine the feasibility of utilizing the hNIS antigenic protein in enhanced‐antigen‐associated immunotherapy using image analysis with a gamma counter. To accomplish this, minimalistic immunogenically defined gene expression (MIDGE), either plain or coupled to a nuclear localization signal (NLS) peptide, was used as a vector system. Vaccination with MIDGE/hNIS, MIDGE/hNIS‐NLS and pcDNA3.1/hNIS produced a significant increase in the number of hNIS‐associated IFN‐γ‐secreting CD8+ T cells, with MIDGE/hNIS having the strongest effect. In addition, immunization with the hNIS encoding vectors induced antigen‐mediated antitumor activity against NIS‐expressing CT26 tumors in vivo, with the highest tumor free rate (100%) and lowest tumor growth being observed up to 40 days after the CT26/NIS tumor challenge with MIDGE/hNIS than those resulting from other immunization groups. Tumor progression could be followed noninvasively and repetitively by monitoring levels of hNIS gene expression in the tumors using scintigraphic image analysis. Overall, hNIS has a potential use as an antigen for immunization approaches, and vaccination with MIDGE/hNIS vectors is an effective means of generating hNIS‐associated immune responses in mice.

A novel chimeric DNA vaccine: Enhancement of preventive and therapeutic efficacy of DNA vaccine by fusion of Mucin 1 to a heat shock protein 70 gene

Intensive efforts to improve vaccines against cancer are currently outgoing. Mucin 1 (Muc1) is a tumor-specific antigen that is overexpressed and heavily glycosylated in a variety of adenocarcinomas. In the present study, the efficacy of an anticancer DNA vaccination strategy was demonstrated using Muc1 fusion vaccines. To enhance antigen presentation and tumor-suppressive efficacy, a chimeric Muc1 vaccine was designed, encoding the transmembrane- and C-terminal domain-deleted Muc1 gene (∆TM) fused to the human HSP70 gene. To confirm the expression and secretion of fusion protein, cell culture supernatants were subjected to Western blotting. We found secreted Muc1 ΔTM-HSP0 fusion protein in the supernatants. These results demonstrate that the Muc1 ΔTM-HSP0 construct can be efficiently expressed and secreted from transfected cells. When the chimeric Muc1 vaccine was administered to mice, antigen-specific cellular immune responses were observed. Notably, we observed that antigen-specific lymphocyte proliferation and cytotoxic responses were effectively induced only in the group of mice that had been vaccinated with the chimeric Muc1 vaccine. Concurrent with the Muc1-specific tumor-suppressive effect, the growth of established Muc1-expressing B16 mouse melanoma cells was also significantly inhibited by vaccination with the chimeric Muc1 vaccine. The growth of B16 mouse melanoma cells expressing human Muc1 in C57BL/6 mice was effectively suppressed by the Muc1-HSP70 chimeric DNA vaccine. Our results reveal that the antitumor efficacy of the chimeric DNA vaccine was improved by the presence of HSP/70.

The C-terminal region of Bfl-1 sensitizes non-small cell lung cancer to gemcitabine-induced apoptosis by suppressing NF-κB activity and down-regulating Bfl-1

Gemcitabine is used to treat several cancers including lung cancer. However, tumor cells often escape gemcitabine-induced cell death via various mechanisms, which include modulating bcl-2 family members and NF-κB activation. We previously reported that the C-terminal region of Bfl-1 fused with GFP (BC) is sufficient to induce apoptosis in 293T cells. In the present study, we investigated the anti-tumor effect of combined BC gene therapy and gemcitabine chemotherapy in vitro and in vivo using non-small cell lung cancer cell lines and a xenograft model. Cell lines were resistant to low dose gemcitabine (4-40 ng/ml), which induced NF-κB activation and concomitant up-regulation of Bfl-1 (an NF-κB-regulated anti-apoptotic protein). BC induced the apoptosis of A549 and H157 cells with caspase-3 activation. Furthermore, co-treatment with BC and low dose gemcitabine synergistically and efficiently induced mitochondria-mediated apoptosis in these cells. When administered alone or with low dose gemcitabine, BC suppressed NF-κB activity, inhibited the nuclear translocation of p65/relA, and down-regulated Bfl-1 expression. Furthermore, direct suppression of Bfl-1 by RNA interference sensitized cells to gemcitabine-induced cell death, suggesting that Bfl-1 importantly regulates lung cancer cell sensitivity to gemcitabine. BC and gemcitabine co-treatment also showed a strong anti-tumor effect in a nude mouse/A549 xenograft model. These results suggest that lung cancer cells become resistant to gemcitabine via NF-κB activation and the subsequent overexpression of Bfl-1, and that BC, which has both pro-apoptotic and NF-κB inhibitory effects, could be harnessed as a gene therapy to complement gemcitabine chemotherapy in non-small cell lung cancer.

Synergistic tumoricidal effect of combined hMUC1 vaccination and hNIS radioiodine gene therapy

We examined the merits of combinatorial hMUC1 vaccination and hNIS radioiodine gene therapy and evaluated its tumoricidal effects in an animal tumor model. CMNF (CT26 expressing hMUC1, hNIS, and firefly luciferase) cells were transplanted into 28 mice, and 4 and 11 days after tumor challenge, tumor-bearing mice were immunized i.m. with pcDNA3.1 or pcDNA-hMUC1 vaccine and subsequently administered PBS or 131I i.p. [four groups (7 mice per group): pcDNA3.1 + PBS, phMUC1 + PBS, pcDNA3.1 + 131I, and phMUC1 + 131I groups]. Thirty-two days after tumor challenge, we rechallenged mice in the pcDNA3.1 + 131I and phMUC1 + 131I groups with CMNF cells. Tumor progression and tumor-free mice (%) were monitored by bioluminescence. We investigated hMUC1-associated immune response generated by combination therapy. Marked tumor growth inhibition was observed in the phMUC1 + 131I group by bioluminescence at 32 days after tumor challenge. Mice in phMUC1 + 131I group showed complete hMUC1-expressing tumor suppression after tumor rechallenge, whereas mice in the pcDNA3.1 + 131I group did not. The tumor-free mice (%) were much higher in the phMUC1 + 131I group than in the other three groups. Levels of hMUC1-associated CD8+IFN-γ+ T cells were higher in the phMUC1 + 131I group than in the other three groups. hMUC1-loaded CD11+ cells in the phMUC1 + 131I group were found to be most effective at generating hMUC1-associated CD8+IFN-γ+ T cells. The activities of hMUC1-associated cytotoxic T cells in the phMUC1 + 131I group were higher than in the other three groups. Our data suggest that phMUC1 + 131I combination therapy synergistically generates marked tumoricidal effects against established hMUC1-expressing cancers. [Mol Cancer Ther 2008;7(7):2252–60]

Treatment With mANT2 shRNA Enhances Antitumor Therapeutic Effects Induced by MUC1 DNA Vaccination

In this study, we developed a combination therapy (pcDNA3/hMUC1+mANT2 shRNA) to enhance the efficiency of MUC1 DNA vaccination by combining it with mANT2 short hairpin RNA (shRNA) treatment in immunocompetent mice. mANT2 shRNA treatment alone increased the apoptosis of BMF cells (B16F1 murine melanoma cell line coexpressing an MUC1 and Fluc gene) and rendered BMF tumor cells more susceptible to lysis by MUC1-associated CD8(+) T cells. Furthermore, combined therapy enhanced MUC1 associated T-cell immune response and antitumor effects, and resulted in a higher cure rate than either treatment alone (pcDNA3/hMUC1 or mANT2 shRNA therapy alone). Human MUC1 (hMUC1)-loaded CD11c(+) cells in the draining lymph nodes of BMF-bearing mice treated with the combined treatment were found to be most effective at generating hMUC1-associated CD8(+)IFNγ(+) T cells. Furthermore, the in vitro killing activities of hMUC1-associated cytotoxic T cells (CTLs) in the combined therapy were greater than in the respective monotherapies. Cured animals treated with the combined treatment rejected a rechallenge by BMF cells, but not a rechallenge by B16F1-Fluc cells at 14 days after treatment, and showed MUC1 antigen-associated immune responses. These results suggest that combined therapy enhances antitumor activity, and that it offers an effective antitumor strategy for treating melanoma.