Adenovirus-mediated transfer of caspase-3 with Fas ligand induces drastic apoptosis in U-373MG glioma cells

The use of adenoviral vectors in gene therapy and vaccine approaches

Adenovirus was first identified in the 1950s and since then this pathogenic group of viruses has been explored and transformed into a genetic transfer vehicle. Modification or deletion of few genes are necessary to transform it into a conditionally or non-replicative vector, creating a versatile tool capable of transducing different tissues and inducing high levels of transgene expression. In the early years of vector development, the application in monogenic diseases faced several hurdles, including short-term gene expression and even a fatality. On the other hand, an adenoviral delivery strategy for treatment of cancer was the first approved gene therapy product. There is an increasing interest in expressing transgenes with therapeutic potential targeting the cancer hallmarks, inhibiting metastasis, inducing cancer cell death or modulating the immune system to attack the tumor cells. Replicative adenovirus as vaccines may be even older and date to a few years of its discovery, application of non-replicative adenovirus for vaccination against different microorganisms has been investigated, but only recently, it demonstrated its full potential being one of the leading vaccination tools for COVID-19. This is not a new vector nor a new technology, but the result of decades of careful and intense work in this field.

Inhibition of PTTG1 expression by microRNA suppresses proliferation and induces apoptosis of malignant glioma cells

The present study aimed to investigate the role of pituitary tumor-transforming gene 1 (PTTG1) in the proliferation, invasion and apoptosis of human malignant glioma U251 cells. Firstly, 2 microRNAs (miRNAs) targeting PTTG1 messenger (m)RNA were ligated into a pcDNA6.2-GW/EmGFP-miR expression vector. The recombinant plasmids, miRNA-1 and miRNA-2 (miR-2), were transfected into U251 cells using the liposome method. PTTG1 mRNA and protein levels were evaluated using quantitative polymerase chain reaction and western blot analysis. The proliferation and invasion abilities of U251 cells were determined using methylthiazol tetrazolium and Matrigel assays. Flow cytometry analysis with Annexin V/propidium iodide double staining was used to determine the percentage of apoptotic cells. PTTG1 expression was effectively suppressed by miR-2. U251 cell growth was inhibited between 10.7 and 34.7% in the miR-2 group compared with the blank group. The Matrigel assay demonstrated that the percentage of infiltrating U251 cells was significantly lower in the miR-2 group (12.3±1.0%) compared to the blank group (24.7±1.4%; P<0.001) and the negative control group (24.0±2.0%; P<0.05). A higher percentage of apoptotic U251 cells were observed in the miR-2 group compared with the blank group (53.6 vs. 32.4%) using flow cytometry due to cycle arrests at the G2/M phase. The miR-2-transfected U251 cells were subcutaneously injected into nude mice, and these mice possessed a decreased tumor tissue growth rate and higher percentage of apoptotic cells compared with the blank and negative control groups. In conclusion, PTTG1 gene expression in human malignant glioma U251 cells was effectively suppressed by exogenous miR-2. The downregulation of PTTG1 induced glioma cell apoptosis and cell cycle arrest at the G2/M phase, which inhibited cell proliferation, reverse invasion and infiltration of glioma cells.

Sequential combination therapy with flavopiridol and autocatalytic caspase-3 driven by amplified hTERT promoter synergistically suppresses human ovarian carcinoma growth in vitro and in mice

Background

Induction of cell apoptosis and regulation of cell cycle are very attractive for treatments of tumors including ovarian carcinoma. Flavopiridol is a potent small molecular cyclin-dependent kinase(cdk) inhibitor, but its antitumor efficacy is not satisfied yet. Caspase-3 play a major role in the transduction of apoptotic signals and the execution of apoptosis in mammalian cells. We have successfully constructed the recombinant adenovirues AdHTVP2G5-rev-casp3 containing autocatalytic caspase-3 (rev-caspase-3) driven by amplified hTERT promoter system (TSTA-hTERTp). In this study, we applied it with flavopiridol to investigate their antitumor effect on ovarian cancer in vitro and in vivo.

Methods

Cell viabilities were determined using Cell Counting Kit 8 and flow cytometry. RT-PCR and immunoblotting assays were used to detect cellular apoptotic activities. Tumor growth and survival of mice bearing tumors were studied.

Results

Flavopiridol or AdHTVP2G5-rev-casp3 at low dosage alone was mildly cytotoxic in vitro with a viability rate of 86.5 ± 4.7% for 300 nM flavopiridol and 88.9 ± 5.4% for AdHTVP2G5-rev-casp3 (MOI 20). By contrast, significant synergism of their sequential combination was observed, and the treatment of AdHTVP2G5-rev-casp3 (MOI 20) infection for 72 h, followed by flavopiridol (300 nM) for 48 h, can result in the most synergistic cell death, with cell survival rate and apoptotic rate of 11.6% and 69.7%, respectively. The sequential combination showed synergistic tumor suppression rate of 77.8%, which was significantly higher than that of AdHTVP2G5-rev-casp3 (33.6%) or flavopiridol (40.1%) alone. The mean survival of mice treated with the combination was 286 ± 8 d, which was synergistically longer than that of mice treated with AdHTVP2G5-rev-casp3 (141 ± 14d), flavopiridol (134 ± 10 d) or controls (106 ± 11 d) (P < 0.01).

Conclusions

The sequential combination of rev-caspase-3 and flavopiridol result in significant synergistic cell killing effects, significant tumor growth suppression and extended survival of mice bearing OVCAR3 cells. The combination should be further explored as a potential clinically useful regimen against ovarian cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s13048-014-0121-3) contains supplementary material, which is available to authorized users.

Between death and survival: retinoic acid in regulation of apoptosis

The vitamin A metabolite all-trans-retinoic acid (RA) regulates multiple biological processes by virtue of its ability to regulate gene expression. It thus plays critical roles in embryonic development and is involved in regulating growth, remodeling, and metabolic responses in adult tissues. RA can also suppress carcinoma cell growth and is currently used in treatment of some cancers. Growth inhibition by RA may be exerted by induction of differentiation, cell cycle arrest, or apoptosis, or by a combination of these activities. Paradoxically, in the context of some cells, RA not only fails to inhibit growth but, instead, enhances proliferation and survival. This review focuses on the involvement of RA in regulating apoptotic responses. It includes brief overviews of transcriptional signaling by RA and of apoptotic pathways, and then addresses available information on the mechanisms by which RA induces apoptosis or, conversely, inhibits cell death and enhances survival.

Treatment of hepatitis C virus core-positive hepatocytes with the transfer of recombinant caspase-3 using the 2',5'-oligoadenylate synthetase gene promoter

Hepatitis C virus (HCV) infection is a leading cause of liver-related morbidity and mortality throughout the world. There is no vaccine available and current therapy is only partially effective. Since HCV infects only a minority of hepatocytes, we hypothesized that induction of apoptosis might be a promising approach for the treatment of hepatitis C. In the present study, recombinant caspase-3 gene (re-caspase-3) was used because it has the ability to induce apoptosis that is independent of the initiator caspases. An HCV-specific promoter is required to regulate the cytotoxic caspase-3 expression in HCV-infected cells. It has been reported that HCV core protein can specifically activate the 2',5'-oligoadenylate synthetase (OAS) gene promoter in human hepatocytes. Therefore, we constructed an expression vector consisting of the re-caspase-3 under the OAS gene promoter (pGL3-OAS-re-caspase-3) and then investigated its effect on HCV core-positive liver cells. It was found that the pGL3-OAS-re-caspase-3 construct induced apoptosis in HCV core-positive liver cells, but not in normal liver cells. These results strongly suggested that the transfer of the re-caspase-3 gene under the OAS promoter was a novel targeting approach for the treatment of HCV infection.

Radio-responsive gene therapy for malignant glioma cells without the radiosensitive promoter: Caspase-3 gene therapy combined with radiation

Caspase-3 plays a critical role as an executioner of apoptosis. The aim of this study is to evaluate the potential of the combination of caspase-3 gene therapy and radiation treatment. We prepared a plasmid (pCI-CSP3) that contained the human caspase-3 gene and the cytomegalovirus promoter. We introduced this plasmid into U251 and U87 human glioma cells and subjected the cells to radiation treatment. The degree of cell death and apoptosis were evaluated. None of the cell lines underwent apoptosis by the overexpression of caspase-3 alone, but the degree of cell death and apoptosis were markedly enhanced by the addition of radiation treatment. Next, we prepared another plasmid (EGR-CSP3) that contained the caspase-3 gene and a radiation-sensitive promoter. Each treatment system using either pCI-CSP3 or EGR-CSP3 showed radio response. The treatment system using pCI-CSP3 more effectively induced apoptosis than that using EGR-CSP3. Caspase-3 gene therapy in combination with radiation treatment has the potential to serve as a radio-responsive gene therapy without any radiation-sensitive promoter.

Procaspase-3 enhances the in vitro effect of cytosine deaminase-thymidine kinase disuicide gene therapy on human ovarian cancer

Because the efficacy of genetic prodrug activation therapy (GPAT) using herpes simplex virus thymidine kinase (tk)/ganciclovir (GCV) or Escherichia coli cytosine deaminase (cd)/5-fluorocytosine (5-FC) is not satisfied in early clinical trials and the mechanism of both the GPATs have been shown to lead to the activation of cell apoptotic pathway, we hypothesized that coexpression of procaspase-3, a central downstream executioner of apoptotic pathways, with cd-tk gene leads to enhanced cell death in ovarian cancer cells in vitro. Following transfection with the vectors encoding cd and tk, 5-FC and GCV treatments lead to greater cell death in procaspase-3-expressing clones of 3AO (3AO-caspase-3) than control cells (3AO-pcDNA3), as well as more rapid activation of caspase-3 and more rapid cleavage of poly (adenosine diphosphate-ribose) polymerase (PARP). There is a greater degree of cell apoptotic rate in the procaspase-3-expressing clones than in control cells following the treatment with cd-tk/5-FC + GCV, and apoptosis is the main cell death form. None of these effects is seen following transfection with a control vector that does not encode tk and cd (pBTdel-279). The results strongly suggest that coexpression of procaspase-3 may lead to a significant enhancement of the efficacy of cd-tk/5-FC + GCV, and this strategy would be a novel and promising approach for the treatment of ovarian cancer.

Anti-gastric cancer active immunity induced by FasL/B7-1 gene-modified tumor cells

AIM: To study the activation of cytotoxic T lymphocytes (CTLs) against gastric cancer cells induced by FasL/B7-1 (FB-11) gene-modified tumor cells, and to explore whether co-expression of FasL and B7-1 in SGC-7901 tumor cells could initiate synergistic antitumor effect.

METHODS: FasL and B7-1 genes were transfected into human SGC-7901 gastric cancer cells with adenovirus vectors. The positive clones were selected by G418. FasL and B7-1 genes were detected by flow cytometry and RT-PCR. Abdominal infiltrating lymphocytes and sensitized spleen cells were obtained from mice that were immunized with SGC-7901/FB-11 or wild type SGC-7901 cells intraperitoneally, and cytotoxicity of these CTLs against tumor cells was determined by MTT assay.

RESULTS: Flow cytometry and RT-PCR showed that FasL and B7-1 genes were highly expressed. FasL and B7-1 transfected cancer cells had a high apoptosis index. DNA laddering suggested that FasL and B7-1 genes induced gastric cancer cell apoptosis. FasL⁺/B7-1⁺SGC-7901 cells (SGC-7901/FB-11) were inoculated subcutaneously in the dorsal skin of C57BL/6 mice and then decreased their tumorigenicity greatly (z = 2.15-46.10, P<0.01). SGC-7901/FB-11 cell-sensitized mice obtained protective immune activity against the rechallenge of wild type SGC-7901 cells (z = 2.06-44.30, P<0.05). The cytotoxicity of CTLs induced by SGC-7901/FB-11 cells against SGC-7901 was significantly higher than that of CTLs activated by wild-type SGC-7901 cells (84.1±2.4% vs 30.5±2.3%, P<0.05).

CONCLUSION: FasL and B7-1 genes can effectively promote the activity of CTLs against gastric cancer cells. FasL/B7-1 molecules play an important role in CTL cytotoxicity.

Gene transfer of constitutively active caspase-3 induces apoptosis in a human hepatoma cell line

BACKGROUND

The caspase-3 gene is expressed at significantly lower levels in human hepatocellular carcinomas than in normal hepatocytes. Gene transfer technologies offer the possibility to restore caspase-3 gene expression. We explored the interest for cancer gene therapy of a constitutively active recombinant caspase-3 (RevCasp3) obtained by rearranging its subunits.

METHODS

An amphotropic retroviral vector was used to express the RevCasp3 gene. HuH7 cells were infected 1 and 2 days after plating. Caspase-3 activity was measured every 24 h for the following 6 days. The level of poly (ADP-ribose) polymerase cleavage induced by caspase-3 was measured by Western blot. The percentage of apoptotic cells was estimated after Hoechst-acridine orange and TUNEL stainings.

RESULTS

Caspase-3 activity significantly increased from days 4 to 7 after infection. Caspase-3 activity peaked on day 7, and was 5.4-fold higher in RevCasp3-transduced HuH7 cells than in control cells. Poly (ADP-ribose) polymerase cleavage was first detected 6 days after the first infection. Hoechst-acridine orange and TUNEL stainings showed that most infected HuH7 cells were apoptotic.

CONCLUSIONS

Apoptosis was selectively induced following infection of HuH7 cells with RevCasp3, demonstrating that retroviruses expressing RevCasp3 are of potential interest for the treatment of hepatocellular carcinomas and other tumour types.

Increased expression of Apaf-1 and procaspase-3 and the functionality of intrinsic apoptosis apparatus in non-small cell lung carcinoma

The intrinsic apoptosis apparatus plays a significant role in generating and amplifying cell death signals. In this study we examined whether there are differences in the expression of its components and in its functioning in non-small cell lung carcinoma (NSCLC) and the lung. We show that NSCLC cell lines express Apaf-1 and procaspase-9 and -3 proteins and that the expression of Apaf-1 and procaspase-3, but not of procaspase-9 and -7, is frequently up-regulated in NSCLC tissues as compared to the lung. NSCLC tissues and lungs and some NSCLC cell lines expressed also caspase-9S(b) and displayed a high caspase-9S(b)/procaspase-9 expression ratio. Procaspase-3 from NSCLCs and lungs was readily processed to caspase-3 by granzyme B or caspase-8, and the granzyme B-generated caspase-3-like activity was significantly higher in tumor tissues and cells than in lungs. By contrast, cytochrome c plus dATP could induce a significant increase of caspase-3-like activity in cytosol only in some NSCLC cell lines and in subsets of studied NSCLC tissues and lungs, while procaspase-3 and -7 were detectably processed only in NSCLC tissues which showed a high (cytochrome c+dATP)-induced caspase-3-like activity. Taken together, the present study provides evidence that the expression of Apaf-1 and procaspase-3 is up-regulated in NSCLCs and indicates that the tumors have a capability to suppress the apoptosome-driven caspase activation in their cytosol.

Chromosome 17p13.2 transfer reverts transformation phenotypes and fas-mediated apoptosis in breast epithelial cells

Transformation of the human breast epithelial cells (HBEC) MCF-10F with the carcinogen benz(a)pyrene (BP) into BP1-E cells resulted in the loss of the chromosome 17 p13.2 locus (D17S796 marker) and formation of colonies in agar-methocel (colony efficiency (CE)), loss of ductulogenic capacity in collagen matrix, and resistance to anti-Fas monoclonal antibody (Mab)-induced apoptosis. For testing the role of that specific region of chromosome 17 in the expression of transformation phenotypes, we transferred chromosome 17 from mouse fibroblast donors to BP1-E cells. Chromosome 11 was used as negative control. After G418 selection, nine clones each were randomly selected from BP1-E-11neo and BP1-E-17neo hybrids, respectively, and tested for the presence of the donor chromosomes by fluorescent in situ hybridization and polymerase chain reaction-based restriction fragment length polymorphism (PCR-RFLP) analyses. Sensitivity to Fas Mab-induced apoptosis and evaluation of transformation phenotype expression were tested in MCF-10F, BP1-E, and nine BP1-E-11neo and BP1-E-17neo clones each. Six BP1-E-17neo clones exhibited a reversion of transformation phenotypes and a dose dependent sensitivity to Fas Mab-induced apoptosis, behaving similarly to MCF-10F cells. All BP1-E-11neo, and three BP1-E-17neo cell clones, like BP1-E cells, retained a high CE, loss of ductulogenic capacity, and were resistant to all Fas Mab doses tested. Genomic analysis revealed that those six BP1-E-17neo clones that were Fas-sensitive and reverted their transformed phenotypes had retained the 17p13.2 (D17S796 marker) region, whereas it was absent in all resistant clones, indicating that the expression of transformation phenotypes and the sensitivity of the cells to Fas-mediated apoptosis were under the control of genes located in this region.

Procaspase 3 expression in ovarian carcinoma cells increases survivin transcription which can be countered with a dominant-negative mutant, survivin T34A; a combination gene therapy strategy

Increased survivin expression is a negative prognostic marker in many tumours, including ovarian cancer. We show here that ovarian carcinoma cells upregulate survivin transcription in response to increased expression of the proapoptotic protein procaspase 3. We have utilized this observation in a combination gene therapy strategy using adenoviral constructs expressing the dominant-negative mutant survivin T34A (Ad Survivin T34A) and procaspase 3 (Ad Caspase 3) in ovarian carcinoma cell lines. Transfection of ovarian carcinoma cells with Ad Survivin T34A induces apoptosis via a caspase 9-mediated pathway that is not affected by cell cycle block prior to G2/M. Ad Survivin T34A-induced apoptosis can be significantly enhanced by cotransfection with Ad Caspase 3, and the combination of Ad Survivin T34A and Ad Caspase 3 leads to a significant increase in survival in a murine intraperitoneal ovarian carcinoma model with some long-term survivors. This suggests that inhibiting endogenous survivin activity while also delivering high levels of procaspase 3 allow proteolytic cleavage and activation of the terminal caspase cascade leading to tumour cell death.

5-Fluorouracil efficiently enhanced apoptosis induced by adenovirus-mediated transfer of caspase-8 in DLD-1 colon cancer cells

BACKGROUND

In order to develop a safe and effective gene therapy for cancer, more powerful therapeutic genes must be selected and a gene transduction methodology needs to be devised that minimizes the total dose of vector required. We investigated the combination effect of 5-fluorouracil (5-FU), a first-choice drug for the treatment of colorectal cancer and adenovirus-mediated transfer of caspase-8 in DLD-1 colon cancer cells.

METHODS

The degree of cell death was assessed by determining the percentage of cells which had died, and the degree of DNA fragmentation. The protein expression levels and degree of activation of caspase-8 were analyzed by Western blot analysis. The degree of transgene expression was assessed using adenoviral vectors expressing lacZ and GFP.

RESULTS

Combination treatment led to a significant induction of apoptosis, whereas treatment with either approach alone resulted in only minimal cytotoxicity. Caspase-8 was only activated in cells that received the combined treatment. Exposure to 5-FU increased the quantity of transgene expression per cell, 48 h post-infection. A potentiating effect of adenoviral treatment was also seen when 5-FU treatment was substituted by the overexpression of cyclin-dependent kinase inhibitors, p21(WAF1/CIP1) and p27(KIP1), suggesting that the cytostatic effect of 5-FU augmented apoptosis induced by caspase-8 gene transduction by inhibiting the dilution of gene products associated with cell division.

CONCLUSIONS

This combination strategy may be very useful in the treatment of 5-FU-resistant colorectal cancers and may also be more generally helpful in minimizing the dose of therapeutic vectors used in cancer gene therapy.

Palgin sensitizes the adriamycin-induced apoptosis via the enhancement of Fas/Fas ligand expression

This study was designed to evaluate the synergistic cytotoxicity of herb prescription, Palgin, in adriamycin-treated cancer cells. The combination of Palgin and adriamycin synergistically augmented the cytotoxicity of Chang and HL-60 cells, but not in Hep3B and Alexander cells. The cytotoxicity of two drugs was revealed as apoptosis characterized by nuclear fragmentation. The apoptotic cell death was accompanied by the activation of caspase-3 as well as cleavage of poly(ADP) ribose polymerase (PARP) in Chang cells. Interestingly, a synergistic increase in apoptosis by the combination of two drugs was accompanied by the enhancement of Fas and Fas ligand (FasL) expression in Chang cells. Taken together, the combination of Palgin and adriamycin significantly augmented the apoptotic cytotoxicity of Fas-positive cells, such as Chang and HL-60 cells, via activation of caspase signaling pathway. This notion will provide a new trial to treat cancer patients in clinical fields as a complementary treatment of Western and Oriental medicine.

Adenovirus-mediated gene transfer of P16INK4/CDKN2 into bax-negative colon cancer cells induces apoptosis and tumor regression in vivo

The tumor-suppressor gene p16INK4/CDKN2 (p16) is a cyclin-dependent kinase (cdk) inhibitor and important cell cycle regulator. Here, we show that adenovirus-mediated gene transfer of p16 (AdCMV.p16) into colon cancer cells induces uncoupling of S phase and mitosis and subsequently apoptosis. Flow cytometric analysis revealed that cells infected with AdCMV.p16 showed an initial G2-like arrest followed by S phase without intervening mitosis (DNA >4N). Using microscopic analysis, deformed polyploid cells were detectable only in cells infected with AdCMV.p16 but not in control-infected cells. Subsequently, AdCMV.p16-infected polyploid cells underwent apoptosis, as assessed by AnnexinV staining and DNA fragmentation, suggesting that cell cycle dysregulation is upstream of the onset of apoptosis. Treatment of mice with subcutaneously transplanted tumors of colorectal cancer cells with AdCMV.p16 but not AdCMV.p53 resulted in significantly reduced tumor volume and prolonged survival. Using an orthotopic model of liver metastasis, we observed both reduced local tumor growth and secondary intrahepatic metastasis after AdCMV.p16 treatment. Importantly, induction of apoptosis in vitro and reduction of tumor growth in vivo by p16 was p53- as well as bax-independent because identical results were obtained using cancer cells, either wild type or mutant for p53 or bax. The studies suggest that an AdCMV.p16-based treatment may be especially effective in patients with bax-negative colon cancer where overexpression of p53 appears not to be of therapeutic value.

Apoptosis during ectromelia orthopoxvirus infection is DEVDase dependent: in vitro and in vivo studies

Ectromelia virus (EV), which causes mousepox, is a member of the orthopoxviruses that are defined as being able to suppress apoptosis. Caspase-3 is one of the key effector proteases which regulates the apoptotic cascade and which is responsible for DNA fragmentation observed during apoptosis. It is well known that viruses, especially poxviruses, can inhibit caspase activity. Here, we report that EV can regulate apoptosis in vitro, suppressing the activity of caspases recognizing the DEVD (Asp-Glu-Val-Asp) motif (caspase-3 and -7) before successful virus replication is completed. Caspase-3 activity measurement showed that an increase in caspase-3 activity preceded the peak of DNA fragmentation demonstrated by TUNEL staining of L929 and RK-13 cells. By using specific caspase inhibitors (Ac-DEVD-CHO, Ac-IETD-CHO and zVAD-fmk), we showed that caspase-3 and -7 (DEVDases) are major effector caspases during EV-induced apoptosis in permissive L929 and RK-13 cell cultures. Apoptosis in vivo seems to play an important role during viraemia as well as during the clearance of EV from genetically susceptible BALB/c (H-2(d)) mice. However, as shown by measurement of caspase-3 activity, caspase-3 protein detection and M30-antibody staining, both DEVDases seem to play an important role during EV clearance from draining lymph nodes and conjunctivae at 15 days p.i. up to 20 days p.i., whereas in the liver and spleen DNA fragmentation coexisted with viral multiplication and secondary viraemia. Apoptosis was DEVDase dependent only in the liver, while spleen DNA fragmentation observed between 5 and 10 days p.i. was caspase independent. Therefore, we conclude that DEVDase- (caspase-3- and caspase-7-) dependent apoptosis is an important mechanism regulating the resolution of EV infection.

Induction of apoptosis in glioma cells by molecules released from activated macrophages

Macrophages play an important role in the regulation of malignant tumors. Although glioma contains abundance of macrophages, their role in apoptosis of glioma is not known. We stimulated macrophages with lipopolysaccharide and culture supernatants of activated macrophages were collected to treat glioma cells. The results showed that molecules released from activated macrophages significantly increased apoptosis of glioma via Fas/FasL and caspase-3 pathways. The level of soluble Fas did not appear to be involved in the mechanism responsible for apoptosis seen in this study, as its level was barely detected in both experimental and control groups. Two cytokines, TNFalpha and IFNgamma, were significantly elevated in the supernatant obtained from the activated macrophages. Considering an important role of these two molecules in the induction of apoptosis mediated by the Fas/FasL system, the present data suggested that TNFalpha and IFNgamma were the main molecules to trigger the cascade of apoptotic reactions in glioma cells. In conclusion, the present study indicates that molecules released from the activated macrophages provide significant signals to stimulate the expression of Fas/FasL and caspase-3, which function to induce apoptosis in glioma cells.

Caspase-8 gene transduction augments radiation-induced apoptosis in DLD-1 cells

Caspase-8 is a member of the cysteine protease family that plays a critical role in death receptor-mediated apoptosis. We previously demonstrated that adenovirally transduced caspase-8 efficiently induced apoptosis in tumor cells (Shinoura et al. (2000) Hum. Gene Ther. 11, 1123-1137). However, to ensure safety in clinical applications some devise for minimization of the dose of adenoviral vector required for sufficient antitumor effect is needed. In this study, we evaluated the proapoptotic effect in DLD-1 colon cancer cells of a combination of low-dose infection with an adenoviral vector expressing caspase-8 and X-ray irradiation. Under these conditions, X-ray irradiation strongly induced apoptosis whereas irradiation without transduction only had a trace proapoptotic effect. Overexpression of bcl-xL strongly blocked the activation of caspase-8 and induction of apoptosis, suggesting that adenovirally transduced caspase-8 was activated at a point downstream of mitochondria. This combination strategy may be a useful modality for gene therapy of colorectal cancer.

Redox control of caspases

Caspases are critical mediators of apoptotic cell death. All members of the caspase family contain the sequence QACXG which contains the active site cysteine. The putative active site of caspase 3 contains a cysteine residue that is subject to redox control. Both thioredoxin and glutathione have been shown to be required for caspase-3 activity to induce apoptosis. The regulation of inducible caspase 3 activity by oxidation-reduction (redox) dependent mechanisms is reviewed. Up until a few years ago, reactive oxygen species (ROS) research mostly focussed on oxidative damage and ROS were thought to be a key trigger for cell death. This view has been refined, leading to the understanding that the biological function of ROS is determined by numerous variables such as concentration, chemical type and cellular localization. For example, ROS and reactive nitrogen species may intercept inducible cell death under certain circumstances via the redox regulation of inducible caspase activity and/or by depleting cellular energy stores. Likewise, death of unwanted diseased or degenerative cells may be facilitated by pharmacologically enhancing the thiol status of such cells using redox-active α-lipoic acid.

Distinct experimental efficacy of anti-Fas/APO-1/CD95 receptor antibody in human tumors

Ligation of the Fas receptor (FasR) is a key step in apoptosis induction. Using a series of human tumor cells (SNB19, SNB79, 143N2, and SHEP), we observed a distinct efficacy of human anti-FasR antibody with an apparent correlation with Fas cell surface antigen expression. In contrast, all cells studied expressed detectable FasR mRNA transcripts. For all anti-FasR antibody-sensitive tumor cells, we showed a similar efficacy of Mab according to dose fractionation and injection site. We showed that, when injected into nude mice bearing human osteosarcoma 143N2, neuroblastoma SHEP, prostatic cancer PAC120, and the two glioblastomas SNB19 and SNB79, anti-FasR Mab induces significant inhibition of the growth rate of 143N2, SHEP, and PAC120 tumors, but has no efficacy on SNB19 and SNB79 tumors, with a relationship between in vitro and in vivo sensitivity to anti-FasR antibody. Altogether, these results suggest the antitumor potential of anti-FasR antibody in human neoplasms.

Evaluation of a new dual-specificity promoter for selective induction of apoptosis in breast cancer cells

The conditional expression of lethal genes in tumor cells is a promising gene therapy approach for the treatment of cancer. The identification of promoters that are preferentially active in cancer cells is the starting point for this strategy. The combination of tissue-specific and tumor-specific elements offers the possibility to artificially develop such promoters. We describe the construction and characterization of a hybrid promoter for transcriptional targeting of breast cancer. In many cases, breast cancer cells retain the expression of estrogen receptors, and most solid tumors suffer from hypoxia as a consequence of their aberrant vascularization. Estrogen response elements and hypoxia-responsive elements were combined to activate transcription in cells that present at least one of these characteristics. When a promoter containing these elements is used to control the expression of the pro-apoptotic gene harakiri, the induction of cell death can be activated by estrogens and hypoxia, and inhibited by antiestrogens such as tamoxifen. Finally, we show evidence that these properties are maintained in the context of an adenoviral vector (AdEHhrk). Therefore, infection with this virus preferentially kills estrogen receptor-positive breast cancer cells, or cells growing under hypoxic conditions. We propose the use of this promoter for transcriptional targeting of breast cancer.

Herpes simplex virus thymidine kinase/ganciclovir-induced cell death is enhanced by co-expression of caspase-3 in ovarian carcinoma cells

There is a need to enhance the efficacy of genetic prodrug activation therapy using herpes simplex virus thymidine kinase (tk) and ganciclovir (GCV) following disappointing results in early clinical trials. tk/GCV has been shown to lead to the activation of caspase-3, a potent executor of apoptosis. We demonstrate that co-expression of pro-caspase-3 with tk/GCV leads to enhanced cell death in ovarian carcinoma cells in vitro. Following transfection with recombinant adenoviral vectors encoding tk, GCV treatment leads to greater cell death in pro-caspase-3-expressing clones of SKOV3 and IGROV1 than control cells, as well as more rapid activation of caspase-3 and more rapid cleavage of PARP. Flow cytometry suggests that there is a greater degree of S-phase block in the pro-caspase-3-expressing clones than in control cells following treatment with tk/GCV. None of these effects is seen following transfection with a control adenovirus that does not encode tk. The increased cell death, early caspase-3 activation and PARP cleavage, and flow cytometric changes seen in pro-caspase-3-expressing cells can be partially inhibited by treatment with benzyloxycarbonyl-val-ala-asp fluoromethylketone, a synthetic caspase inhibitor. Our data suggest that co-expression of pro-caspase-3 may lead to a significant enhancement of the efficacy of tk/GCV therapy.

Pro-caspase-3 overexpression sensitises ovarian cancer cells to proteasome inhibitors

The ubiquitin-proteasome pathway plays a critical role in the degradation of several proteins involved in the cell cycle. Dysregulation of this pathway leads to inhibition of cellular proliferation and the induction of apoptosis. Ubiquitination and its downstream consequences have been investigated intensively as targets for the development of drugs for tumour therapy. Here we have investigated the mechanism of apoptosis induced by the proteasome inhibitors MG-132, lactacystin and calpain inhibitor I (ALLN), in the HEK 293 cell line and the ovarian cancer cell lines SKOV3 and OVCAR3. We have found strong caspase-3-like and caspase-6-like activation upon treatment of HEK 293 cells with MG-132. Using a tricistronic expression vector based on a tetracycline-responsive system we generated stable SKOV3 nd OVCAR3 cell lines with inducible expression of pro-caspase-3. Induction of pro-caspase-3 expression in normally growing cells does not induce apoptosis. However, in the presence of the proteasome inhibitors MG-132, lactacystin or ALLN we found that cells overexpressing pro-caspase-3 are rapidly targeted for apoptosis. Our results demonstrate that pro-caspase-3 can sensitise ovarian cancer cells to proteasome inhibitor-induced apoptosis, and a combination of these approaches might be exploited for therapy of ovarian and other cancers.