Tumor biology influences the prognosis of nephroblastoma patients with primary pulmonary metastases: results from SIOP 93-01/GPOH and SIOP 2001/GPOH.

OBJECTIVE: To analyze the outcome of Wilms' tumor patients with primary lung metastases. SUMMARY BACKGROUND DATA: Radiotherapy and/or surgery are used for local control of primary pulmonary Wilms' tumor metastases. A widely accepted treatment standardization is still lacking. METHODS: Data for 210 patients with Wilms' tumor and primary lung metastases from the collaborative multicenter trials SIOP 93-01/GPOH and SIOP 2001/GPOH of the German Society of Pediatric Oncology and Hematology were reviewed. Analyses included patient data, tumor characteristics, local treatment, outcome and possible prognostic factors. RESULTS: Five-year overall survival (OS) was 83.3% and 5-year event free survival (EFS) was 72.3% for all children. Survival was significantly poorer in children with high risk primary tumor histology (OS 44.4%) compared to low risk (OS 100.0%) and intermediate risk histology (OS 89.2%, P < 0.001). Within the high risk group, tumors of the blastemal subtype (OS 56.5%) were associated with a significantly better outcome than those presenting with diffuse anaplasia (OS 22.2%, P = 0.02). Further, prognostic markers were lacking response to chemotherapy (P = 0.011), persistence of metastases after local treatment (P = 0.007), and vitality of metastases (P = 0.01). CONCLUSIONS: The prognosis of children with primary Wilms' tumor lung metastases mainly depends on the biology of primary tumors and metastases and is excellent with adequate treatment. Pulmonary metastasectomy is indicated if complete remission can be achieved to avoid lung irradiation. In the future a standardized local approach to nonresponding lung metastases (metastasectomy, irradiation, or both) will have to be prospectively evaluated regarding outcome, acute toxicity, and late effects.

Liver cancer protease activity profiles support therapeutic options with matrix metalloproteinase-activatable oncolytic measles virus.

Primary and secondary cancers of the liver are a significant health problem with limited treatment options. We sought here to develop an oncolytic measles virus (MV) preferentially activated in liver tumor tissue, thus reducing infection and destruction of healthy tissue. We documented that in primary tumor tissue, urokinase-type plasminogen activator and especially matrix metalloproteinase-2 (MMP-2) are significantly more active than in adjacent nontumorous tissue. We then generated variants of the MV fusion protein by inserting different MMP substrate motifs at the protease cleavage site and identified the motif PQGLYA as the most efficient cleavage site as determined by syncytia formation on protease-positive tumor cells. The corresponding MMP-activatable oncolytic MV-MMPA1 virus was rescued and shown to be strongly restricted on primary human hepatocytes and healthy human liver tissue, while remaining as effective as the parental MV in the tumor tissue sections. Our findings underline the clinical potency of the MMP activation concept as a strategy to generate safer oncolytic viruses for the treatment of primary and secondary cancers of the liver.

Human precision-cut liver tumor slices as a tumor patient-individual predictive test system for oncolytic measles vaccine viruses.

Availability of an individualized preselection of oncolytic viruses to be used for virotherapy of tumor patients would be of great help. Using primary liver tumor resection specimens we evaluated the precision-cut liver slice (PCLS) technology as a novel in vitro test system for characterization of paramount tumor infection parameters of individual patients. PCLS slices from resection specimens of 20 liver tumor patients were cultivated in vitro for up to 5 days and infected with 5 different oncolytic measles vaccine virus (MeV) strains. Effectiveness of tumor infection was monitored by viral nucleocapsid (N) protein detection in immunofluorescence staining or Western blot analysis or by detection of GFP marker gene expression. MeV spreading in PCLS cultures was visualized by confocal microscopy. Oncolytic MeV vaccine particles were demonstrated to efficiently infect PCLS slices originating from different primary and secondary tumors of the liver with MeV strains Moraten/Edmonston Zagreb and AIK-C showing highest infection rates (75% of all tested tumor specimens). Employing mixed liver tissue slices (exhibiting both tumorous and non-tumorous tissue areas on one and the same sample) a distinct tumor area favouring pattern of MeV infections was observed being in accordance with our finding that primary human hepatocytes are also permissive to MeV particles, albeit at a much lower rate and with a much less pronounced cytopathic effect. Furthermore, confocal microscopy demonstrated virus penetration throughout tumor tissues into deep cell layers. In conclusion, the PCLS technology is suitable to perform a tumor-patient individualized preselection of oncolytic agents prior to clinical virotherapeutic applications.

Adenovirus-mediated cytosine deaminase/5-fluorocytosine suicide gene therapy of human hepatoblastoma in vitro.

BACKGROUND: Multidrug resistance is a key factor for the sobering outcome of relapsed and metastatic human hepatoblastoma (HB). Gene directed treatment approaches were recently identified as possible treatment options against advanced HB, in which standard chemotherapy regimens are partially insufficient. The aim of this study was to systematically analyze the effects of suicide gene therapy in three HB cell lines using a yeast-derived cytosine deaminase (YCD)-combined yeast uracil phosphoribosyltransferase (YUPRT)-based adenovirus-mediated gene transfer. PROCEDURE: YCD and YUPRT were fused to form the bifunctional suicide gene SuperCD. Adeonoviral vectors were used for transduction. Tumor cells transduced at MOI 50 were incubated with 5-fluorocytosine (5-FC) in ascending concentrations. RESULTS: Transduction rates were 87.8% (+6.7) in the mixed HB cell line HUH6, 98.6% (+1.4) in the epithelial HB cell line HepT1 and 93.6% (+0.6) in the multifocal HB embryonal cell line HepT3, respectively. In HepT3 and HepT1 cells suicide gene therapy with SuperCD/5-FC was highly effective leading to HB cell damage far above those of application of the prodrug 5-FC only. In HUH6 cells the approach had no effect due to a lack in activity of the CMV promoter being employed for transcription of the SuperCD transgene. CONCLUSION: Assuming employment of fully active promoters, the SuperCD/5-FC approach may serve as a potentially useful anti-tumor strategy against advanced HB.

In vitro photodynamic therapy in pediatric epithelial liver tumors promoted by hypericin.

Limited treatment results in advanced pediatric liver tumors have emphasised the need for alternative treatment approaches in these malignancies. Photodynamic therapy (PDT) has been proposed as promising treatment approach in various malignancies. Hypericin, a naturally occurring substance found in the St. John's Wort, has regularly and successfully been used for visualisation and as photosensitizer in various tumor models. However, there exist no data on the effects of hypericin as photodynamic agent in pediatric malignant epithelial liver tumors. In this study, we investigated the potential role of hypericin for visualization and treatment in hepatoblastoma (HB) and pediatric hepatocellular carcinoma (HCC) cells. Two HB cell lines (HUH6, HepT1) and one HCC cell line (HepG2) were incubated with ascending concentrations of hypericin. Uptake and fluorescending capability were assessed using fluorescence microscopy and FACS. PDT with white light was performed for varying time intervals. Cell viability, cell proliferation and apoptotic rates were assessed using MTT assay, Ki-67 immunocytochemisty and TUNEL test, respectively. The changes within tumor cells under therapy were monitored using standard cytology. Relevant hypericin uptake was observed in all cell lines according to the applied concentrations. Histological analysis revealed no alterations of cell structure in HB and HCC cells after solely hypericin uptake, but severe alterations were found after PDT. Enhancement of the hypericin concentration (up to 12.5 microM) and illumination time of up to 40 min resulted in a decrease of tumor cell viability (HUH6 99.8+/-2.4%, HepT1 99+/-2%, HepG2 98.4+/-1.6%, p<0.05), proliferative activity and complete apoptosis of all cells in all investigated cell lines. These data show that hypericin might be a useful tool for visualisation and as alternative treatment option in HB and HCC.

Direct and natural killer cell-mediated antitumor effects of low-dose bortezomib in hepatocellular carcinoma.

PURPOSE: Hepatocellular carcinoma (HCC) displays particular resistance to conventional cytostatic agents. Alternative treatment strategies focus on novel substances exhibiting antineoplastic and/or immunomodulatory activity enhancing for example natural killer (NK) cell antitumor reactivity. However, tumor-associated ligands engaging activating NK cell receptors are largely unknown. Exceptions are NKG2D ligands (NKG2DL) of the MHC class I-related chain and UL16-binding protein families, which potently stimulate NK cell responses. We studied the consequences of proteasome inhibition with regard to direct and NK cell-mediated effects against HCC. EXPERIMENTAL DESIGN: Primary human hepatocytes (PHH) from different donors, hepatoma cell lines, and NK cells were exposed to Bortezomib. Growth and viability of the different cells, and immunomodulatory effects including alterations of NKG2DL expression on hepatoma cells, specific induction of NK cell cytotoxicity and IFN-gamma production were investigated. RESULTS: Bortezomib treatment inhibited hepatoma cell growth with IC(50) values between 2.4 and 7.7 nmol/L. These low doses increased MICA/B mRNA levels, resulting in an increase of total and cell surface protein expression in hepatoma cells, thus stimulating cytotoxicity and IFN-gamma production of cocultured NK cells. Importantly, although NK cell IFN-gamma production was concentration-dependently reduced, low-dose Bortezomib neither induced NKG2DL expression or cell death in PHH nor altered NK cell cytotoxicity. CONCLUSIONS: Low-dose Bortezomib mediates a specific dual antitumor effect in HCC by inhibiting tumor cell proliferation and priming hepatoma cells for NK cell antitumor reactivity. Our data suggest that patients with HCC may benefit from Bortezomib treatment combined with immunotherapeutic approaches such as adoptive NK cell transfer taking advantage of enhanced NKG2D-mediated antitumor immunity.

Establishing a novel single-copy primer-internal intron-spanning PCR (spiPCR) procedure for the direct detection of gene doping.

So far, the abuse of gene transfer technology in sport, so-called gene doping, is undetectable. However, recent studies in somatic gene therapy indicate that long-term presence of transgenic DNA (tDNA) following various gene transfer protocols can be found in DNA isolated from whole blood using conventional PCR protocols. Application of these protocols for the direct detection of gene doping would require almost complete knowledge about the sequence of the genetic information that has been transferred. Here, we develop and describe the novel single-copy primer-internal intron-spanning PCR (spiPCR) procedure that overcomes this difficulty. Apart from the interesting perspectives that this spiPCR procedure offers in the fight against gene doping, this technology could also be of interest in biodistribution and biosafety studies for gene therapeutic applications.

Epigenetic combination therapy as a tumor-selective treatment approach for hepatocellular carcinoma.

BACKGROUND: Innovative epigenetic therapeutics comprise histone deacetylase inhibitors (HDAC-I) and demethylating agents (DA). It was recently found that HDAC-I compounds exhibit profound therapeutic activities against hepatocellular carcinoma (HCC). A comprehensive preclinical investigation was performed on the potential of a combined HDAC-I/DA epigenetic regimen for the highly chemotherapy-resistant HCC entity. METHODS: Human HCC-derived cell lines or primary human hepatocytes (PHH) were treated with HDAC-I compound suberoylanilide hydroxamic acid (SAHA) or DA compound 5-aza-2'-deoxycytidine (5-aza-dC) or both and examined for cellular damage, proliferation, histone acetylation pattern, and DNA methylation. In vivo activities were investigated in a xenograft hepatoma model. RESULTS: Monotherapeutic application of SAHA or 5-aza-dC was found to induce substantial antiproliferative effects in HCC-derived cells, strongly enhanced by combined SAHA and 5-aza-dC treatment. PHH from different human donors did not exhibit any relevant cellular damage even when applying high doses of the combination regimen, whereas HCC-derived cell lines showed a dose-dependent damage. In vivo testing demonstrated a statistical significant inhibition of hepatoma cell growth for the combined treatment regime. CONCLUSIONS: Because the combined HDAC-I/DA epigenetic approach was found to produce significant antitumor effects in HCC model systems and did not impair cellular integrity of untransformed hepatocytes, this combination therapy is now considered for further investigation in clinical trials.

In vitro photodynamic therapy of childhood rhabdomyosarcoma.

Treatment of childhood rhabdomyosarcoma is limited by recurrent disease and the development of multidrug resistance. Therefore, novel treatment options are desirable. Photodynamic therapy (PDT) using the photodynamic agent hypericin is proposed as an alternative approach for intraoperative visualization and treatment of this disease. The aim of this study was to investigate in vitro effects of hypericin on childhood rhabdomyosarcoma and to evaluate photodynamic therapy as a possible basis for treatment. Rhabdomyosarcoma cells and fibroblasts (control) were incubated with increasing concentrations of hypericin. in vitro uptake and visualization of hypericin was evaluated by fluorescence microscopy and FACS. For photodynamic therapy, cells were exposed to white light for different time periods. Cytopathologic effects were assessed using standard histology. Cancer cells were investigated for cell viability (MTT assay), proliferative activity (Ki-67 assay), and apoptosis (TUNEL test). A 100% uptake of hypericin was found within the population of rhabdomyosarcoma cells. Uptake of hypericin in the fibroblasts was much less than in rhabdomyosarcoma cells. Hypericin without exposure to white light had no effect on tumor cell viability. After irradiation, PDT resulted in a nearly complete inhibition of cell proliferation of rhabdomyosarcoma cells with a corresponding increase in the frequency of apoptosis. In fibroblasts, PDT was less effective compared to tumor cells. Our data suggest hypericin as a novel tool for visualization and photodynamic therapy of childhood rhabdomyosarcoma.

Optimizing vector application for gene transfer into human hepatoblastoma cells.

Gene targeting is currently of distinct interest as an innovative additive treatment option in various malignancies. Its role in pediatric liver tumors has not yet been evaluated thoroughly. For the first time the authors systematically analyzed both lipid-based transfection as well as transduction with adenovirus vectors (Ad) and Sendai virus vectors (SeVV) in order to optimize gene transfer into hepatoblastoma (HB) cells. Two HB cell lines were infected with Ad or SeVV coding for green fluorescent protein (Ad-GFP, SeVV-GFP); transduction efficiencies and apoptosis were assessed using flow cytometry. Furthermore, lipofection of HB cell lines with plasmid-constructs comprising liver-specific promoters was performed using Lipofectamine 2000 and FuGENE 6; lipofection efficiency was monitored by flow cytometry, microscopy, and luciferase activity. The Ad-GFP showed higher transduction rates (61-86%) than the SeVV-GFP (4-24%) depending on the HB cell line used. Infections with first generation SeVV vectors (SeVV-GFP) led to increased target cell apoptosis (7-43%) compared to Ad-GFP (4-16%). The Lipofectamine 2000 revealed a higher transfection efficiency than the FuGENE 6 for both HB cell lines tested. The liver-specific promoters were found to be differently active in the HB cell lines. This study delineates recombinant adenovirus vectors as a promising tool for gene transduction in the HB cells. Furthermore, enhanced activity of the liver-specific promoters in HUH6 cells compared to HepT1 cells supports the observation of varying biological behavior in histologically differing HB tissues.

HDAC inhibitor treatment of hepatoma cells induces both TRAIL-independent apoptosis and restoration of sensitivity to TRAIL.

Hepatocellular carcinoma (HCC) displays a striking resistance to chemotherapeutic drugs or innovative tumor cell apoptosis-inducing agents such as tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Recently, we found 2 histone deacetylase inhibitors (HDAC-I), valproic acid and ITF2357, exhibiting inherent therapeutic activity against HCC. In TRAIL-sensitive cancer cells, the mechanism of HDAC-I-induced cell death has been identified to be TRAIL-dependent by inducing apoptosis in an autocrine fashion. In contrast, in HCC-derived cells, a prototype of TRAIL-resistant tumor cells, we found a HDAC-I-mediated apoptosis that works independently of TRAIL and upregulation of death receptors or their cognate ligands. Interestingly, TRAIL resistance could be overcome by a combinatorial application of HDAC-I and TRAIL, increasing the fraction of apoptotic cells two- to threefold compared with HDAC-I treatment alone, whereas any premature HDAC-I withdrawal rapidly restored TRAIL resistance. Furthermore, a tumor cell-specific downregulation of the FLICE inhibitory protein (FLIP) was observed, constituting a new mechanism of TRAIL sensitivity restoration by HDAC-I. In contrast, FLIP levels in primary human hepatocytes (PHH) from different donors were upregulated by HDAC-I. Importantly, combination HDAC-I/TRAIL treatment did not induce any cytotoxicity in nonmalignant PHH. In conclusion, HDAC-I compounds, exhibiting a favorable in vivo profile and inherent activity against HCC cells, are able to selectively overcome the resistance of HCC cells toward TRAIL. Specific upregulation of intracellular FLIP protein levels in nonmalignant hepatocytes could enhance the therapeutic window for clinical applications of TRAIL, opening up a highly specific new treatment option for advanced HCC.

In vitro gene targeting in human hepatoblastoma.

Poor treatment results in advanced hepatoblastoma (HB) made alternative treatment approaches desirable. Gene-directed tumor therapy is increasingly investigated in different malignancies. The aim of this study was to analyze possible alternatives of gene transfer into HB cells and to study therapeutic applications based on different strategies. Liposomal transfection of HB cells was assessed using liver-specific promoters, and adenovirus and Sendai virus transductions were performed in vitro. Transfer efficiencies were measured via flow cytometry determining expression of vector-encoded marker gene green fluorescent protein. Gene silencing of the anti-apoptotic bcl-2 gene in HUH6 cells was performed using lipofection of small interfering RNA (siRNA). Additionally, suicide gene therapy was carried out through a yeast-derived cytosine deaminase (YCD)-combined yeast uracil phosphoribosyltransferase (YUPRT)-based adenovirus-mediated gene transfer, leading to a potent intracellular prodrug transformation of 5-fluorocytosine into 5-fluorouracil. Treatment efficiencies were monitored via MTT viability assay. Highest gene transfer rates (86%) were observed using adenovirus transduction. We furthermore observed a significant therapeutic effect of adenovirus-mediated YCD::YUPRT suicide gene transfer. Liposomal-mediated anti-bcl-2 siRNA transfer led to a significant improvement of cisplatin treatment in HUH6 cells. Liver-specific promoters were found to be strongly active in HUH6 cells (mixed HB-derived), but less active in HepT1 cells (embryonal HB-derived). Liposomal transfection and viral transduction are effective approaches to genetically manipulate HB cells in vitro. For the first time, we demonstrate a positive effect of siRNA gene silencing in this malignancy. Additionally, we successfully investigated a model of adenovirus-based suicide gene therapy in HB cell cultures. Our data strongly encourage further studies assessing these alternative treatment approaches.

Severe impairment of dendritic cell allostimulatory activity by Sendai virus vectors is overcome by matrix protein gene deletion.

Delivery of Ags to dendritic cells (DCs) plays a pivotal role in the induction of efficient immune responses ranging from immunity to tolerance. The observation that certain viral pathogens are able to infect DCs has led to a concept in which applications of recombinant viruses are used for Ag delivery with the potential benefit of inducing potent Ag-specific T cell responses directed against multiple epitopes. As a prerequisite for such an application, the infection of DCs by recombinant viruses should not interfere with their stimulatory capacity. In this context, we could show that an emerging negative-strand RNA viral vector system based on the Sendai virus (SeV) is able to efficiently infect monocyte-derived human DCs (moDCs). However, after infection with SeV wild type, both the response of DCs to bacterial LPS as a powerful mediator of DC maturation and the allostimulatory activity were severely impaired. Interestingly, using various recombinant SeV vectors that were devoid of single viral genes, we were able to identify the SeV matrix (M) protein as a key component in moDC functional impairment after viral infection. Consequently, use of M-deficient SeV vectors preserved the allostimulatory activity in infected moDCs despite an efficient expression of all other virally encoded genes, thereby identifying M-deficient vectors as a highly potent tool for the genetic manipulation of DCs.

Expression liver-directed genes by employing synthetic transcriptional control units.

AIM: To generate and characterize the synthetic transcriptional control units for transcriptional targeting of the liver, thereby compensating for the lack of specificity of currently available gene therapeutic vector systems. METHODS: Synthetic transcriptional control unit constructs were generated and analyzed for transcriptional activities in different cell types by FACS quantification, semi-quantitative RT-PCR, and Western blotting. RESULTS: A new bifunctionally-enhanced green fluorescent protein (EGFP)/neo(r) fusion gene cassette was generated, and could flexibly be used both for transcript quantification and for selection of stable cell clones. Then, numerous synthetic transcriptional control units consisting of a minimal promoter linked to "naturally" derived composite enhancer elements from liver-specific expressed genes or binding sites of liver-specific transcription factors were inserted upstream of this reporter cassette. Following liposome-mediated transfection, EGFP reporter protein quantification by FACS analysis identified constructs encoding multimerized composite elements of the apolipoprotein B100 (ApoB) promoter or the ornithin transcarbamoylase (OTC) enhancer to exhibit maximum transcriptional activities in liver originating cell lines, but only background levels in non-liver originating cell lines. In contrast, constructs encoding only singular binding sites of liver-specific transcription factors, namely hepatocyte nuclear factor (HNF)1, HNF3, HNF4, HNF5, or CAAT/enhancer binding protein (C/EBP) only achieved background levels of EGFP expression. Finally, both semi-quantitative RT-PCR and Western blotting analysis of Hep3B cells demonstrated maximum transcriptional activities for a multimeric 4xApoB cassette construct, which fully complied with the data obtained by initial FACS analysis. CONCLUSION: Synthetic transcriptional control unit constructs not only exhibit a superb degree of structural compactness, but also provide new means for liver-directed expression of therapeutic genes.

Natural killer cell-mediated lysis of hepatoma cells via specific induction of NKG2D ligands by the histone deacetylase inhibitor sodium valproate.

Natural killer (NK) cells as components of the innate immunity substantially contribute to antitumor immune responses. However, the tumor-associated ligands engaging activating NK cell receptors are largely unknown. An exception are the MHC class I chain-related molecules MICA and MICB and the UL16-binding proteins (ULBP) which bind to the activating immunoreceptor NKG2D expressed on cytotoxic lymphocytes. A therapeutic induction of NKG2D ligands that primes cancer cells for NK cell lysis has not yet been achieved. By microarray studies, we found evidence that treatment of human hepatocellular carcinoma cells with the histone deacetylase inhibitor (HDAC-I) sodium valproate (VPA) mediates recognition of cancer cells by cytotoxic lymphocytes via NKG2D. VPA induced transcription of MICA and MICB in hepatocellular carcinoma cells, leading to increased cell surface, soluble and total MIC protein expression. No significant changes in the expression of the NKG2D ligands ULBP1-3 were observed. The induction of MIC molecules increased lysis of hepatocellular carcinoma cells by NK cells which was abolished by addition of a blocking NKG2D antibody. Importantly, in primary human hepatocytes, VPA treatment did not induce MIC protein expression. Taken together, our data show that the HDAC-I VPA mediates specific priming of malignant cells for innate immune effector mechanisms. These results suggest the clinical evaluation of HDAC-I in solid tumors such as hepatocellular carcinoma, especially in combination with immunotherapy approaches employing adoptive NK cell transfer.

Apoptosis on hepatoma cells but not on primary hepatocytes by histone deacetylase inhibitors valproate and ITF2357.

BACKGROUND/AIMS: Due to a particular resistance against conventional chemotherapeutics, palliative treatment of hepatocellular carcinomas (HCC) is highly ineffective. Recent demonstration of both proliferation-inhibition and apoptosis of hepatoma cells by a histone deacetylase inhibitor (HDAC-I) treatment opens up a promising new approach. However, little is known about tumor cell death mechanisms and HDAC-I influences on healthy hepatocytes. METHODS: HDAC-I substances with favourable in vivo profiles, valproate (VPA) and ITF2357, were investigated on HCC cell lines and primary human hepatocytes (PHH). Histone acetylation and apoptosis-modulating proteins were investigated by western-blotting, proliferation by sulforhodamin B binding, toxicity by enzyme release, apoptosis by FACS analysis. RESULTS: VPA and ITF2357 inhibited proliferation in HCC cell lines. Both substances induced considerable cellular damage in HCC-derived cells, but PHH tolerated these substances well. A downregulation of anti- and upregulation of proapoptotic factors was found. Moreover, Bcl-X(L) transfection into HCC cells abrogated apoptosis induced by both substances, indicating that modulation of intracellular pro- and anti-apoptotic proteins is a key event in VPA or ITF2357 induced tumor-cell death. CONCLUSIONS: Preferential induction of cell death in HCC-derived cell lines, without toxicity in PHH, demonstrates the potential of VPA and ITF2357 to become promising new tools in the fight against HCC.

Bifunctional chimeric SuperCD suicide gene -YCD: YUPRT fusion is highly effective in a rat hepatoma model.

AIM: To investigate the effects of catalytically superior gene-directed enzyme prodrug therapy systems on a rat hepatoma model. METHODS: To increase hepatoma cell chemosensitivity for the prodrug 5-fluorocytosine (5-FC), we generated a chimeric bifunctional SuperCD suicide gene, a fusion of the yeast cytosine deaminase (YCD) and the yeast uracil phosphoribosyltransferase (YUPRT) gene. RESULTS: In vitro stably transduced Morris rat hepatoma cells (MH) expressing the bifunctional SuperCD suicide gene (MH SuperCD) showed a clearly marked enhancement in cell killing when incubated with 5-FC as compared with MH cells stably expressing YCD solely (MH YCD) or the cytosine deaminase gene of bacterial origin (MH BCD), respectively. In vivo, MH SuperCD tumors implanted both subcutaneously as well as orthotopically into the livers of syngeneic ACI rats demonstrated significant tumor regressions (P<0.01) under both high dose as well as low dose systemic 5-FC application, whereas MH tumors without transgene expression (MH naive) showed rapid progression. For the first time, an order of in vivo suicide gene effectiveness (SuperCD>> YCD>>BCD>>>negative control) was defined as a result of a direct in vivo comparison of all three suicide genes. CONCLUSION: Bifunctional SuperCD suicide gene expression is highly effective in a rat hepatoma model, thereby significantly improving both the therapeutic index and the efficacy of hepatocellular carcinoma killing by fluorocytosine.

Efficient propagation of single gene deleted recombinant Sendai virus vectors.

Recombinant Sendai virus vectors (SeVV) have become an attractive tool for basic virological as well as for gene transfer studies. However, to (i) reduce the cellular injury induced by basic recombinant SeV vectors (encoding all six SeV genes as being present in SeV wild-type (wt) genomes) and to (ii) improve SeV vector safety, deletions of viral genes are necessary for the construction of superior SeVV generations. As a strong expression system recombinant replication-incompetent adenoviruses, coding for SeV proteins hemagglutinin-neuraminidase (HN), fusion (F), or matrix (M), were generated and successfully employed for the propagation of single gene deleted (DeltaHN, DeltaF, DeltaM) recombinant SeVV. Further investigations of the propagation procedures required for single gene deleted recombinant SeVV demonstrated (i) modifications of the cell culture medium composition as well as (ii) incubation with vitamin E as crucial steps for the enhancement of SeVV-DeltaHN, -DeltaF, or -DeltaM viral particle yield. Such optimized propagation procedures even led to a successful propagation of HN-deleted viral particles (SeVV-DeltaHN), which has not been reported before.