Suicide genes have recently emerged as an attractive alternative therapy for the treatment of various types of intractable cancers. The efficacy of suicide gene therapy relies on efficient gene delivery to target tissues and the localized concentration of final gene products. Here, we showed a potential ex vivo therapy that used mesenchymal stem cells (MSCs) as cellular vehicles to deliver a bacterial suicide gene, cytosine deaminase (CD) to brain tumors. MSCs were engineered to produce CD enzymes at various levels using different promoters. When co-cultured, CD-expressing MSCs had a bystander, anti-cancer effect on neighboring C6 glioma cells in proportion to the levels of CD enzymes that could convert a nontoxic prodrug, 5-fluorocytosine (5-FC) into cytotoxic 5-fluorouracil (5-FU) in vitro. Consistent with the in vitro results, for early stage brain tumors induced by intracranial inoculation of C6 cells, transplantation of CD-expressing MSCs reduced tumor mass in proportion to 5-FC dosages. However, for later stage, established tumors, a single treatment was insufficient, but only multiple transplantations were able to successfully repress tumor growth. Our findings indicate that the level of total CD enzyme activity is a critical parameter that is likely to affect the clinical efficacy for CD gene therapy. Our results also highlight the potential advantages of autograftable MSCs compared with other types of allogeneic stem cells for the treatment of recurrent glioblastomas through repetitive treatments.Gliomas are the most common primary tumors of the central nervous system and easily metastasize to other brain regions. Despite recent technical advances in surgery, radiotherapy and chemotherapy, only palliative therapy is available; there is no authentic cure for gliomas. 1,2 Suicide genes from non-human sources have emerged as an attractive alternative therapy for the treatment of brain tumors. Cytosine deaminase (CD) has attracted considerable attention by virtue of its stronger bystander effects than other suicide genes. 3 CD converts a nontoxic prodrug, 5-fluorocytosine (5-FC), into a potent anticancer drug, 5-fluorouracil (5-FU). 5-FU enters neighboring cells through simple diffusion, exerting a cytotoxic effect by interfering with DNA and RNA synthesis. By combining CD and 5-FC in a single therapeutic modality, it may be possible to bypass the systemic toxicity of 5-FU while efficiently increasing the 5-FU concentration in a localized area. 4,5 Neural stem cells (NSCs) and mesenchymal stem cells (MSCs) exhibit strong tropism toward brain tumors that are attributed to receptors for chemokines and growth factors including SDF-1, 6,7 MCP-1, 8 HGF, 9 IL-8, NT3, TGF-b 10 and VEGF. 11 The migratory properties make NSCs and MSCs efficient tools for delivering therapeutic genes to brain tumors. For example, when combined with 5-FC administration,

X-linked chronic granulomatous disease (CGD) is an inherited immunodeficiency caused by a defect in the gp91(phox) gene. In an effort to treat X-CGD, we investigated the safety and efficacy of gene therapy using a retroviral vector, MT-gp91. Two X-CGD patients received autologous CD34(+) cells transduced with MT-gp91 after a conditioning regimen consisting of fludarabine and busulfan. The level of gene-marked cells was highest at day 21 (8.3 and 11.7% in peripheral blood cells) but decreased to 0.08 and 0.5%, respectively, 3 years after gene transfer. The level of functionally corrected cells, as determined by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase assay, reached a peak at day 17 (6.5% patient 1 (P1) and 14.3% patient 2 (P2) of total granulocytes) and declined to 0.05% (P1) and 0.21% (P2), 3 years later. Some retroviral vectors were found to have integrated within or close to the proto-oncogenes MDS1-EVI1, PRDM16, and CCND2; however, no abnormal cell expansion or related hematological malignancy was observed. Overall, the gene transfer procedure did not produce any serious adverse effects and was able to convert a significant fraction of blood cells to biologically functional cells, albeit for a short period of time.

Unfolded protein response (UPR) is crucial for both survival and death of mammalian cells, which is regulated by reactive oxygen species (ROS) and nutrient depletion. In this study, we demonstrated the effect of ROS-accumulation, induced by β-phenethyl isothiocyanate (PEITC), on UPR-mediated apoptosis in ovarian cancer cells. We used ovarian cancer cell lines, PA-1 and SKOV-3, with different p53 status (wild- and null-type, respectively). PEITC caused increased ROS-accumulation and inhibited proliferation selectively in ovarian cancer cells, and glutathione (GSH) depletion in SKOV-3. However, PEITC did not cause any effect in normal ovarian epithelial cells and peripheral blood mononuclear cells. After 48 h of PEITC treatment (5 μM), apoptotic cell death was shown to increase significantly in the ovarian cancer cells and not in the normal cells. The key regulator of UPR-mediated apoptosis, CHOP/GADD153 and endoplasmic reticulum resident chaperone BiP/GRP78 were parallely up-regulated with activation of two major sensors of the UPR [PERK and ATF-6 in PA-1; PERK, and IRE1α in SKOV-3) in response to ROS accumulation induced by PEITC (5 μM). ROS scavenger, N-acetyl-L-cysteine (NAC), attenuated the effect of PEITC on UPR signatures (P-PERK, IRE1α, CHOP/GADD153, and BiP/GRP78), suggesting the involvement of ROS in UPR-mediated apoptosis. Altogether, PEITC induces UPR-mediated apoptosis in ovarian cancer cells via accumulation of ROS in a cancer-specific manner.

A recombination between the short homologous regions of nucleotide sequences in the retroviral vector and packaging cell line has been thought to be a major cause of the production of replication-competent retrovirus (RCR). Therefore, the removal of overlapping sequences between the vector and the packaging constructs is crucial for minimizing the possibility of homologous recombination, and therefore, the production of RCR. We have recently constructed a series of retroviral vectors that contain no viral coding sequences, but still produce high viral titer and high-level gene expression. However, many previously constructed murine leukemia viurs (MLV)-based packaging constructs contained significantly long 5 0 and/or 3 0 untranslated regions of MLV, which are also present in the retroviral vector, and as such could possibly lead to homologous recombination. To make a retroviral production system that is free from homologous recombination, we constructed expression plasmids for gag-pol and env, precisely starting from the start codon and ending at the stop codon of respective open reading frames. When the packaging function was provided from one plasmid, a vector containing bits of all three viral coding sequences produced RCR at a significant frequency, while our vector remained free of any RCR. Our retrovirus production system is anticipated to have the minimum possible frequency of RCR production due to the elimination of potential sites for homologous recombination. Based on these results, a highly efficient new packaging line Vamp that contains no overlapping sequences with our retroviral vector was also developed. Gene Therapy (2003) 10, 706-711. doi:10.1038/sj.gt.3301892Keywords: retroviral vector; packaging line; homologous recombination; RCR Murine leukemia virus (MLV)-based vectors are the most frequently used gene delivery system, employed in almost 40% of approved protocols and 50% of patients who have been subjected to or are undergoing clinical trials. However, there are many problems that need to be improved in order for MLV-based vectors to become a viable form of gene delivery vehicle in actual clinical settings. In particular, the issue of safety has often been raised because of the possibility of the production of replication-competent retrovirus (RCR). The mechanism of RCR generation still remains poorly understood, but it has been thought to result from homologous recombination between the same nucleotide sequences present in the vector and in the packaging constructs. Indeed, it has been reported that homologous recombination could occur between as very short regions of homology as 7 or 11 bp. 1-3We have recently constructed a series of retroviral vectors that are absent of any viral coding sequences without compromising viral titer or the level of gene expression. 4 These vectors are thought to be safer than other existing vectors harboring viral coding sequences because the probability of homologous recombination between the vector and the packaging genome is much lower with these newly d...