Gene therapy for prostate cancer using the cytosine deaminase/uracil phosphoribosyltransferase suicide system

A survivin-driven, tumor-activatable minicircle system for prostate cancer theranostics

Gene vectors regulated by tumor-specific promoters to express transgenes specifically in cancer cells are an emerging approach for cancer diagnosis and treatment. Minicircles are shortened plasmids stripped of prokaryotic sequences that have potency and safety characteristics beneficial for clinical translation. Previously, we developed minicircles driven by the tumor-specific survivin promoter, which exhibits elevated transcriptional activity in aggressive cancers, to express a secreted reporter for blood-based cancer detection. Here we present the first activatable, cancer theranostic minicircle system featuring a pair of diagnostic and therapeutic minicircles expressing Gaussia luciferase for urine-based cancer detection or cytosine deaminase:uracil phosphoribosyltransferase for gene-directed enzyme prodrug therapy. Diagnostic minicircles revealed urinary reporter output related to cellular survivin levels. Notably, mice with aggressive prostate tumors exhibited significantly higher urine reporter activity than mice with non-aggressive tumors and healthy mice after intratumoral minicircle administration. Therapeutic minicircles displayed specific cytotoxicity in survivin-rich cancer cells and significantly attenuated growth of aggressive orthotopic prostate tumors in mice. Use of these minicircles together creates a theranostic system that can first identify individuals carrying aggressive prostate cancer via a urinary test, followed by stringent control of tumor progression in stratified individuals who carry high-risk prostate lesions.

A facile and scalable in production non-viral gene engineered mesenchymal stem cells for effective suppression of temozolomide-resistant (TMZR) glioblastoma growth

BACKGROUND

Mesenchymal stem cells (MSCs) serve as an attractive vehicle for cell-directed enzyme prodrug therapy (CDEPT) due to their unique tumour-nesting ability. Such approach holds high therapeutic potential for treating solid tumours including glioblastoma multiforme (GBM), a devastating disease with limited effective treatment options. Currently, it is a common practice in research and clinical manufacturing to use viruses to deliver therapeutic genes into MSCs. However, this is limited by the inherent issues of safety, high cost and demanding manufacturing processes. The aim of this study is to identify a facile, scalable in production and highly efficient non-viral method to transiently engineer MSCs for prolonged and exceptionally high expression of a fused transgene: yeast cytosine deaminase::uracil phosphoribosyl-transferase::green fluorescent protein (CD::UPRT::GFP).

METHODS

MSCs were transfected with linear polyethylenimine using a cpg-free plasmid encoding the transgene in the presence of a combination of fusogenic lipids and β tubulin deacetylase inhibitor (Enhancer). Process scalability was evaluated in various planar vessels and microcarrier-based bioreactor. The transfection efficiency was determined with flow cytometry, and the therapeutic efficacy of CD::UPRT::GFP expressing MSCs was evaluated in cocultures with temozolomide (TMZ)-sensitive or TMZ-resistant human glioblastoma cell lines. In the presence of 5-fluorocytosine (5FC), the 5-fluorouracil-mediated cytotoxicity was determined by performing colometric MTS assay. In vivo antitumor effects were examined by local injection into subcutaneous TMZ-resistant tumors implanted in the athymic nude mice.

RESULTS

At > 90% transfection efficiency, the phenotype, differentiation potential and tumour tropism of MSCs were unaltered. High reproducibility was observed in all scales of transfection. The therapeutically modified MSCs displayed strong cytotoxicity towards both TMZ-sensitive and TMZ-resistant U251-MG and U87-MG cell lines only in the presence of 5FC. The effectiveness of this approach was further validated with other well-characterized and clinically annotated patient-derived GBM cells. Additionally, a long-term suppression (> 30 days) of the growth of a subcutaneous TMZ-resistant U-251MG tumour was demonstrated.

CONCLUSIONS

Collectively, this highly efficient non-viral workflow could potentially enable the scalable translation of therapeutically engineered MSC for the treatment of TMZ-resistant GBM and other applications beyond the scope of this study.

Engineering Circulating Tumor Cells as Novel Cancer Theranostics

New ways to target and treat metastatic disease are urgently needed. Tumor “self-homing” describes the recruitment of circulating tumor cells (CTCs) back to a previously excised primary tumor location, contributing to tumor recurrence, as well as their migration to established metastatic lesions. Recently, self-homing CTCs have been exploited as delivery vehicles for anti-cancer therapeutics in preclinical primary tumor models. However, the ability of CTCs to self-home and treat metastatic disease is largely unknown.

Methods: Here, we used bioluminescence imaging (BLI) to explore whether systemically administered CTCs home to metastatic lesions and if CTCs armed with both a reporter gene and a cytotoxic prodrug gene therapy can be used to visualize and treat metastatic disease.

Results: BLI performed over time revealed a remarkable ability of CTCs to home to and treat tumors throughout the body. Excitingly, metastatic tumor burden in mice that received therapeutic CTCs was lower compared to mice receiving control CTCs.

Conclusion: This study demonstrates the noteworthy ability of experimental CTCs to home to disseminated breast cancer lesions. Moreover, by incorporating a prodrug gene therapy system into our self-homing CTCs, we show exciting progress towards effective and targeted delivery of gene-based therapeutics to treat both primary and metastatic lesions.

EC-tagging allows cell type-specific RNA analysis

Purification of cell type-specific RNAs remains a significant challenge. One solution involves biosynthetic tagging of target RNAs. RNA tagging via incorporation of 4-thiouracil (TU) in cells expressing transgenic uracil phosphoribosyltransferase (UPRT), a method known as TU-tagging, has been used in multiple systems but can have limited specificity due to endogenous pathways of TU incorporation. Here, we describe an alternative method that requires the activity of two enzymes: cytosine deaminase (CD) and UPRT. We found that the sequential activity of these enzymes converts 5-ethynylcytosine (EC) to 5-ethynyluridine monophosphate that is subsequently incorporated into nascent RNAs. The ethynyl group allows efficient detection and purification of tagged RNAs. We show that ‘EC-tagging’ occurs in tissue culture cells and Drosophila engineered to express CD and UPRT. Additional control can be achieved through a split-CD approach in which functional CD is reconstituted from independently expressed fragments. We demonstrate the sensitivity and specificity of EC-tagging by obtaining cell type-specific gene expression data from intact Drosophila larvae, including transcriptome measurements from a small population of central brain neurons. EC-tagging provides several advantages over existing techniques and should be broadly useful for investigating the role of differential RNA expression in cell identity, physiology and pathology.

Enzyme/Prodrug Systems for Cancer Gene Therapy

The use of enzyme/prodrug system has gained attention because it could help improve the efficacy and safety of conventional cancer chemotherapies. In this approach, cancer cells are first transfected with a gene that can express an enzyme with ability to convert a non-toxic prodrug into its active cytotoxic form. As a result, the activated prodrug could kill the transfected cancer cells. Despite the significant progress of different suicide gene therapy protocols in preclinical studies and early clinical trials, none has reached the clinic due to several shortcomings. These include slow prodrug-drug conversion rate, low transfection/transduction efficiency of the vectors and nonspecific toxicity/immunogenicity related to the delivery systems, plasmid DNA, enzymes and/or prodrugs. This mini review aims at providing an overview of the most widely used enzyme/prodrug systems with emphasis on reporting the results of the recent preclinical and clinical studies.

Effective combination gene therapy using CEACAM6-shRNA and the fusion suicide gene yCDglyTK for pancreatic carcinoma in vitro

The incidence of pancreatic carcinoma, a gastrointestinal malignancy, is on the increase and effective therapeutic strategies are therefore required. This study aimed to construct a recombinant plasmid pcDNA3.1(-) shCEACAM6-yCDglyTK from CEACAM6 targeting shRNA and the fusion suicide gene yCDglyTK for inhibition of SW1990 human pancreatic carcinoma cell growth and invasion. A plasmid containing hU6 promoter and CEACAM6 targeting short hairpin RNA (CEACAM6-shRNA) frame was constructed. It was subcloned to a CEA promoter-driven fusion suicide gene pcDNA3.1(-)yCDglyTK. The recombinant plasmid pcDNA3.1(-) shCEACAM6-yCDglyTK was identified by restriction endonuclease analysis and DNA sequencing. The recombinant plasmid was delivered into SW1990 human pancreatic carcinoma cells, the mRNA and protein expression of yCDglyTK and CEACAM6 was examined by RT-PCR, western blot analysis and immunofluorescence. SW1990 cells were treated with the prodrug 5-fluorocytosine (5-FC), and the cell viability was evaluated using the 3-[4,5-dimethylthiazol-2yl]-2,5-diphenyl tetrazolium bromide (MTT) assay. The invasiveness and migration of SW1990 cells were evaluated by transwell migration assays. The restriction endonuclease analysis and DNA sequencing confirmed the construction of the recombinant plasmid pcDNA3.1(-) shCEACAM6-yCDglyTK. Reverse transcription polymerase chain reaction (RT-PCR) and western blot analysis outcomes showed that yCDglyTK was expressed in SW1990 cells and expression of CEACAM6 in SW1990 cells was significantly knocked down. MTT assay showed that the mean viability of SW1990 cells was significantly reduced after administration of the prodrug 5-FC in vitro. Transwell migration assays showed that invasion and migration action of SW1990 cells was significantly inhibited. In conclusion, recombinant plasmid pcDNA3.1(-) shCEACAM6-yCDglyTK was successfully constructed. The recombinant plasmid may therefore serve as a novel gene therapy approach for pancreatic carcinoma.

Emerging implications of nonmammalian cytosine deaminases on cancer therapeutics

Nonmammalian cytosine deaminases (CDs) have been investigated for last 30 years in the context of cancer therapy. The therapeutic effect of CD is based on its ability to catalyze the conversion of nontoxic prodrug 5-fluorocytosine (5FC) into the anticancer drug 5-fluorouracil (5FU) by deamination of the number 4 carbon of 5FC. This deamination property of CD has been explored to develop innovative therapeutic approach for treatment of cancer. A general overview is needed for the identification of efficient cytosine deaminases for potential use in cancer therapy. In this review, we have discussed about nonmammalian CDs for a variety of prodrug gene/enzyme therapy applications with several recent examples. Finally, we have provided a prospective on the future aspects of CDs and their applications in cancer therapy.

Development and validation of a rapid and sensitive HPLC method for the quantification of 5-fluorocytosine and its metabolites

To study the intracellular metabolism of the prodrug 5-fluorocytosine (5FC), we developed a novel reverse-phase high-performance liquid chromatography method to simultaneously detect 5FC and its four major anabolic metabolites: 5-fluorouracil, 5-fluorouridine, 5-fluorouridine-monophosphate and 5-fluoro-2'deoxyuridine-5'-monophosphate. Separation of each compound was accomplished under isocratic conditions using a C(18) column and mobile phase of formic acid-water (1 : 99 v/v). The method was validated for both accuracy and reproducibility in cell culture media. Additionally, metabolites were assessed for stability at ambient temperatures and following freeze-thaw cycles. Calibration curves were linear over a range of 1-200 microg/mL. Limit of quantification for four of the five compounds was 1 microg/mL in cell culture media (RSD < 11%). This method was successfully used to monitor intracellular conversion of 5FC to its metabolic products over a 24h period.

Validation of an isocratic HPLC method to detect 2-fluoro-beta-alanine for the analysis of dihydropyrimidine dehydrogenase activity

The efficacy of the chemotherapeutic drug 5'-fluorouracil is reduced by catabolism to 2'-fluoro-beta-alanine (FBAL), a three-step reaction in which dihydropyrimidine dehydrogenase (DPD) catalyzes the rate-limiting step. To study in vitro DPD activity, we developed and validated an isocratic, reverse-phase HPLC method to detect and quantify FBAL without using multiple columns or radiolabeled substrates. Pre-column derivatization of FBAL was performed using o-phthalaldehyde in the presence of two sulfur donors, ethanthiol or beta-mercaptoethanol, and the resulting products assayed. Calibration curves were linear over a range of 10-200 microg/ml and the method was successfully applied to the examination of DPD activity in cultured cells.

Molecular and traditional chemotherapy: a united front against prostate cancer

Castrate resistant prostate cancer (CRPC) is essentially incurable. Recently though, chemotherapy demonstrated a survival benefit ( approximately 2months) in the treatment of CRPC. While this was a landmark finding, suboptimal efficacy and systemic toxicities at the therapeutic doses warranted further development. Smart combination therapies, acting through multiple mechanisms to target the heterogeneous cell populations of PC and with potential for reduction in individual dosing, need to be developed. In that, targeted molecular chemotherapy has generated significant interest with the potential for localized treatment to generate systemic efficacy. This can be further enhanced through the use of oncolytic conditionally replicative adenoviruses (CRAds) to deliver molecular chemotherapy. The prospects of chemotherapy and molecular-chemotherapy as single and as components of combination therapies are discussed.

Adipose tissue-derived mesenchymal stem cells expressing prodrug-converting enzyme inhibit human prostate tumor growth

The ability of human adipose tissue-derived mesenchymal stem cells (AT-MSCs), engineered to express the suicide gene cytosine deaminase::uracil phosphoribosyltransferase (CD::UPRT), to convert the relatively nontoxic 5-fluorocytosine (5-FC) into the highly toxic antitumor 5-fluorouracil (5-FU) together with their ability to track and engraft into tumors and micrometastases makes these cells an attractive tool to activate prodrugs directly within the tumor mass. In this study, we tested the feasibility and efficacy of these therapeutic cells to function as cellular vehicles of prodrug-activating enzymes in prostate cancer (PC) therapy. In in vitro migration experiments we have shown that therapeutic AT-MSCs migrated to all the prostate cell lines tested. In a pilot preclinical study, we observed that coinjections of human bone metastatic PC cells along with the transduced AT-MSCs into nude mice treated with 5-FC induced a complete tumor regression in a dose dependent manner or did not even allow the establishment of the tumor. More importantly, we also demonstrated that the therapeutic cells were effective in significantly inhibiting PC tumor growth after intravenous administration that is a key requisite for any clinical application of gene-directed enzyme prodrug therapies.

Tissue specific cytotoxicity of colon cancer cells mediated by nanoparticle-delivered suicide gene in vitro and in vivo

PURPOSE

This study aimed to develop an efficient and safe strategy to introduce suicide genes into colon cancer cells.

EXPERIMENTAL DESIGN

In this study, we fused an enhanced carcinoembryonic antigen promoter (CEA) to a suicide gene, cytosine deaminase (CD). This construct was delivered into colon cancer cells using calcium phosphate nanoparticles (CPNP). The cells were then treated with the prodrug 5-FC. The therapeutic effect was evaluated in vitro and in vivo.

RESULTS

Our study showed that the CEA promoter-driven, CPNP-delivered suicide gene was only expressed in CEA-positive colon cancer cells, and resulted in significant cytotoxicity after administration of the prodrug 5-FC in vitro. Moreover, our in vivo study showed that CPNP-mediated CEA-CD delivery, together with 5-FC treatment, resulted in significant tumor growth delay in xenograft human colon carcinoma.

CONCLUSIONS

Our study indicates that the combination of CPNP and CEA-CD gene expression represents a novel approach for CEA-positive tumor gene therapy.

Specific targeting of prostate cancer cells in vitro by the suicide gene/prodrug system, uracil phosphoribosyltransferase/5-fluorouracil, under the control of prostate-specific membrane antigen promoter/enhancer

This study was designed to investigate the prostate cancer-specific tumoricidal effect of the suicide gene, Escherichia coli uracil phosphoribosyltransferase (UPRT), driven by the human prostate-specific membrane antigen promoter/enhancer (PSMA(E/P)) in vitro. When transfected with PSMA(E/P)-EGFP (enhanced green fluorescence protein) (a plasmid construct with the green fluorescence protein gene driven by the PSMA(E/P)), only the androgen-responsive and PSMA-positive prostate cancer cell line, LNCaP, expressed GFP, indicating the specificity of the PSMA(E/P) activity in androgen-sensitive and PSMA-positive prostate cancer cells. Taking advantage of this prostate cancer-specific property of PSMA(E/P), we successfully introduced bacterial UPRT into LNCaP cells where the tumoricidal effect of 5-fluorouracil (5-FU) was significantly increased when compared with the cells without the exogenous UPRT. We conclude that the efficacy of 5-FU-based chemotherapy in prostate cancers can be significantly improved by targeted expression of the suicide gene UPRT under the control of PSMA(E/P).

Implication of functional activity for determining therapeutic efficacy of suicide genes in vitro

Gene-Directed Enzyme Prodrug Therapy (GDEPT), commonly known as suicide gene therapy, provides a selective approach to eradicate tumor cells that is currently considered as an alternate approach to conventional therapy for cancers due to its high efficacy. Herein, we have demonstrated functional activity of the cytosine deaminase (CD) and the hybrid cytosine deaminase-uracil phosphoribosyltransferase (CD-UPRT) suicide genes in transfected cell lines. We have monitored retention profiles of various metabolites that were formed during enzymatic conversion of the prodrug 5-flurocytosine (5-FC) using reverse phase HPLC method. Therapeutic effect of suicide genes was established by cell viability and toxicity assay, whereas apoptotic induction was confirmed by DNA fragmentation ELISA. Our results demonstrated that 5-FC/CD-UPRT-mediated apoptotic cell death was more than 5-FC/CD, which could be further potentiated with anticancer compound curcumin. Such results corroborated 5-FC/CD-UPRT in combination with curcumin as a better chemosensitization method.

Apoptotic induction with bifunctional E.coli cytosine deaminase-uracil phosphoribosyltransferase mediated suicide gene therapy is synergized by curcumin treatment in vitro

Development of novel suicide gene therapy vector with potential application in cancer treatment has a great impact on human health. Investigation to understand molecular mechanism of cell death is necessary to evaluate the therapeutic application of suicide vectors. For example, the bifunctional E.coli cytosine deaminase & uracil phosphoribosyltransferase fusion (CD-UPRT) gene expression is known to sensitize a wide range of cells toward nontoxic prodrug 5-flurocytosine (5-FC) by converting it to toxic compounds, but the exact pathway of cell death is yet to be defined. Herein, we investigated the mechanism of cell death by 5-FC/CD-UPRT suicide system in both cancer and non-cancer cells and found that the optimum 5-FC concentration led to programmed cell death in vitro. The CD-UPRT expression of transfected cells was measured by the RT-PCR analysis. Biochemical assays, such as mitochondrial activity (MTS) and lactate dehydrogenase (LDH) measurements exhibited cell death. Microscopic experiments showed characteristic onset of apoptosis which was further supported by internucleosomal DNA cleavage of BrdU labeled cellular DNA, appearance of characteristic laddering of chromosomal DNA and involvement of caspase pathway. Furthermore, the 5-FC/CD-UPRT-mediated apoptosis was potentiated with addition of a known anticancer agent curcumin. Our in vitro studies confirmed synergistic induction of apoptotic pathway in the combination treatment. Therefore, combination of 5-FC/CD-UPRT with curcumin could be a potential chemosensitization strategy for cancer treatment.

Functional characterization of a gene encoding a dual domain for uridine kinase and uracil phosphoribosyltransferase in Arabidopsis thaliana

Uridine kinase (UK) and uracil phosphoribosyltransferase (UPRT) are enzymes catalyzing the formation of uridine 5'-monophosphate (UMP) from uridine and adenine 5'-triphosphate (ATP) and from uracil and phosphoribosyl-alpha-l-pyrophosphate (PRPP), respectively, in the pyrimidine salvage pathway. Here, we report the characterization and functional analysis of a gene AtUK/UPRT1 from Arabidopsis thaliana. Sequencing of an expressed sequence tag clone of this gene revealed that it contains a full-length open reading frame of 1461 nucleotides and encodes a protein with a molecular mass of approximately 53 kDa. The sequence analysis revealed that the N-terminal region of AtUK/UPRT1 contains a UK domain and the C-terminal region consists of a UPRT domain. Expression of AtUK/UPRT1 in upp and upp-udk mutants of Escherichia coli supplied with 5-fluorouracil (5-FU) and 5-fluorouridine (5-FD) led to growth inhibition. Identical results were obtained with 5-FD and 5-FU treatments when the UK and UPRT domains were separated by the introduction of translation initiation and stop codons prior to complementation into the upp-udk and upp mutants. These results suggest that the AtUK/UPRT1 product can use uracil and uridine as substrates for the production of UMP. We also investigated the function of AtUK/UPRT1 in an Arabidopsis mutant. The wild-type Arabidopsis plants showed drastic growth retardation when they were treated with 5-FU and 5-FD while the growth of atuk/uprtl mutant plants was not significantly affected. These findings confirm that AtUK/UPRT1 has a dual role in coding for both uridine kinase and uracil phosphoribosyltransferase that form UMP through the pyrimidine salvage pathway in Arabidopsis.

Inhibitory effect of pulmonary carcinoma by adenovirus-mediated CD/UPRT gene

The cell killing effects and bystander effects of double suicide gene on pulmonary carcinoma cells were explored. Lung adenocarcinoma cells (A549) were transfected with different titers of adenovirus vector and followed with different concentrations of 5-FC after a recombinant adenovirus vector carrying CD/UPRT gene (Ad-CD/UPRT) was constructed. The cell viability was measured by MTT assay 4 days later. The cell viability was dropped to 30.57 %-8.62 % after 10 MOI of Ad-CD/UPRT transfected and 5-FC (10-1000 microg/mL) administration. Furthermore, Ad-CD/UPRT-infected A549 cells showed a profound neighbor cell killing effect in the same methods. These results suggested that Ad-CD/UPRT/5-FC system can effectively suppress growth of lung adenocarcinoma cells, which may provide a novel and powerful candidate for lung cancer gene therapy strategies.

Extending HIV care in resource-limited settings

Despite the clear benefits of antiretroviral therapy (ART), only three countries in sub-Saharan Africa have achieved the "3 by 5" goal of treating at least half of the persons living with HIV/AIDS who need it. A major obstacle faced by many lower income countries is the establishment of treatment programs in rural areas where there is a scarcity of trained health care providers and infrastructure. This paper reviews published data on rural ART programs in lower income countries to identify necessary components of such a program. No clearly superior model for rural ART delivery has emerged. All programs document the need for expanded physical infrastructure, laboratory development, recruitment/training of additional health care providers, and/or the introduction of new technologies in order to effectively support the needs of ART roll-out.

Combination of cytosine deaminase with uracil phosphoribosyl transferase leads to local and distant bystander effects against RM1 prostate cancer in mice

BACKGROUND

We aimed to evaluate the efficacy of gene-directed enzyme-prodrug therapy (GDEPT) using cytosine deaminase in combination with uracil phosphoribosyl transferase (CDUPRT) against intraprostatic mouse androgen-refractory prostate (RM1) tumors in immunocompetent mice. The product of the fusion gene, CDUPRT, converts the prodrug, 5-fluorocytosine (5FC), into 5-fluorouracil (5FU) and other cytotoxic metabolites that kill both CDUPRT-expressing and surrounding cells, via a 'bystander effect'.

METHODS

Stably transformed andogen-independent mouse prostate cancer (PC) cells, RM1-CDUPRT, -GFP or GFP/LacZ cells were used. To assess the local bystander effects of CDUPRT-GDEPT, immunocompetent C57BL/6 mice implanted with cell mixtures of RM1-GFP/CDUPRT and RM1-GFP cells in different proportions intraprostatically were treated with 5FC. Pseudo-metastases in the lungs were established by a tail vein injection of untransfected RM1 cells. At necropsy, prostate weight/volume and lung colony counts were assessed. Tumors, lymph nodes, spleens and lungs were frozen or fixed for immunohistochemistry.

RESULTS

CDUPRT expression in RM1-GFP/CDUPRT cells or tumors was confirmed by enzymic conversion of 5FC into 5FU, using HPLC. Treatment of mice bearing intraprostatic RM1-GFP/CDUPRT tumors with 5FC resulted in complete regression of the tumors. A 'local bystander effect' was seen, even though only 20% of the cells expressed CDUPRT. More importantly a significant reduction in pseudo-metastases of RM1 cells in lungs indicated a 'distant bystander effect'. Immunohistochemical evaluation of the treated tumors showed increased necrosis and apoptosis, with decreased tumor vascularity. There was also a significant increase in tumour-infiltration by macrophages, CD4+ T and natural killer cells.

CONCLUSIONS

We conclude that CDUPRT-GDEPT significantly suppressed the aggressive growth of RM1 prostate tumors and lung pseudo-metastases via immune mechanisms involving necrosis and apoptosis.

Combination of cytosine deaminase suicide gene expression with DR5 antibody treatment increases cancer cell cytotoxicity

Combined treatment using adenoviral-directed enzyme/prodrug therapy and immunotherapy has the potential to become a powerful alternative method of cancer therapy. We have developed adenoviral vectors encoding the cytosine deaminase gene (Ad-CD) and cytosine deaminase:uracil phosphoribosyltransferase fusion gene (Ad-CD:UPRT). A monoclonal antibody, TRA-8, specifically binds to death receptor 5, one of two death receptors bound by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). The purpose of this study was to evaluate cytotoxicity in vitro and therapeutic efficacy in vivo of the combination of Ad-CD:UPRT and TRA-8 against human pancreatic cancer and glioma cell lines. The present study demonstrates that Ad-CD:UPRT infection resulted in increased 5-FC-mediated cell killing, compared with Ad-CD. Furthermore, a significant increase of cytotoxicity following Ad-CD:UPRT/5-FC and TRA-8 treatment of cancer cells in vitro was demonstrated. Animal studies showed significant inhibition of tumor growth of MIA PaCa-2 pancreatic and D54MG glioma xenografts by the combination of Ad-CD:UPRT/5-FC plus TRA-8 as compared with either agent alone or no treatment. The results suggest that the combination of Ad-CD:UPRT/5-FC with TRA-8 produces an additive cytotoxic effect in cancer cells in vitro and in vivo. These data indicate that combined treatment with enzyme/prodrug therapy and TRAIL immunotherapy provides a promising approach for cancer therapy.

Kinase domain insert containing receptor promoter controlled suicide gene system selectively kills human umbilical vein endothelial cells

AIM: To study the selective killing of human umbilical vein endothelial cells (HUVECs) by a double suicide gene under the regulation of a kinase domain insert containing receptor (KDR) promoter and mediated by an adenoviral gene vector.

METHODS: Human KDR promoter was cloned by polymerase chain reaction (PCR), and two recombinant adenoviral plasmids pAdKDR-CdglyTK, pAdCMV-CDglyTK were constructed according to a two-step transformation protocol. These two newly constructed plasmids were then transfected into 293 packaging cells to grow adenovirus, which were further multiplied and purified. HUVECs and LoVo cells were infected with either of the two resultant recombinant adenoviruses (AdKDR-CDglyTK and AdCMV-CDglyTK) respectively, and the infection rates were estimated by detection of green fluorescent protein (GFP) expression. Infected cells were cultured in culture media containing different concentrations of 5-fluorocytosine (5-FC) and ganciclovir (GCV), and the killing effects were measured.

RESULTS: The two recombinant adenoviral plasmids pAdKDR-CdglyTK, pAdCMV-CDglyTK were successfully constructed and transfected into 293 cells. The resultant recombinant adenoviruses infected cells caused similar infection rates; and the infected cells exhibited different sensitivity to the prodrugs: HUVECs infected with AdCMV-CDglyTK and LoVo cells infected with AdCMV-CDglyTK were highly sensitive to the prodrugs, and HUVECs infected with AdKDR-CDglyTK were similarly sensitive but significantly more sensitive than the LoVo cells infected with AdKDR-CdglyTK (P < 0.001).

CONCLUSION: Selective killing of HUVECs may be achieved by gene transfer of double suicide gene under the regulation of the KDR promoter. This finding may provide an optional way to target gene therapy of malignant tumors by abrogation of tumor blood vessels.

Sensitivity of 5-fluorouracil-resistant cancer cells to adenovirus suicide gene therapy

A promising approach for cancer gene therapy is the combination of adenovirus vectors (AdV) with the suicide gene cytosine deaminase and uracil phosphoribosyl transferase (CDColon, two colonsUPRT). While such vectors have been tested in tumor cell lines and xenograft models, it is not clear how these therapeutic vectors would perform in primary human tumors. We, thus, examined the effect of the combination of a recombinant adenovirus expressing the CDColon, two colonsUPRT (AdCU) with 5-fluorocytosine (5-FC) on primary cancer cells isolated from the ascites or pleural fluids of patients with metastatic cancers. In such models, we have found a direct correlation between the patients' response to 5-FU and the response shown by the cancer cells in vitro, confirming the clinical relevance of this methodology. Our findings demonstrated that this combination was able to kill primary tumor cells, including those that had developed resistance to 5-FU. Furthermore, while proliferating cells were more susceptible to 5-FU, the combination was effective in both rapid and slow proliferating samples. Our study demonstrated that this gene therapy approach could provide an effective therapeutic option for cancers and is not affected by acquired 5-FU resistance. Also of importance is the effectiveness of this gene therapy approach on slower proliferating cells that is typical of the majority of cancers in vivo. This suggests a greater likelihood that it will be effective in a clinical setting.

Fusion of the HSV-1 tegument protein vp22 to cytosine deaminase confers enhanced bystander effect and increased therapeutic benefit

A major limitation in cancer gene therapy, specifically gene-dependent enzyme prodrug therapy (GDEPT), is inefficient gene delivery and expression. The suicide gene cytosine deaminase (CD) and its substrate, 5-fluorocytosine (5-FC), have been extensively explored due to the inherent 'bystander' effect achieved through diffusion of the toxic metabolite 5-fluorouracil (5-FU). In this study, we aimed to enhance this 'bystander' effect by fusing the Saccharomyces cerevisiae CD to the HSV-1 tegument protein vp22, a novel translocating protein. Two constructs were created: one with vp22 fused to CD (vp22CD) and a second wherein a truncated vp22, lacking the necessary residues for trafficking, fused to CD (delvp22CD). The generated 9L stable lines exhibited similar growth rates, enzyme expression, CD activity, and sensitivity to 5-FC and 5-FU. However, mixed population colony formation assays demonstrated greater bystander effect with the vp22CD fusion as compared to delvp22CD. This enhancement was maintained in vivo where 9L tumors expressing 20 or 50% vp22CD exhibited increased growth delay compared to the respective delvp22CD tumors. Moreover, adenoviral transduction of established wild-type 9L tumors showed increased growth delay with vp22CD (Ad-EF_vp22CD) as compared to equivalent CD (Ad-EF_CD) transduced tumors. Finally, confirming the increased efficacy, (19)F magnetic resonance spectroscopy (MRS) of vp22CD-expressing tumors demonstrated increased 5-FU levels as compared to tumors expressing the nontranslocating CD. These results together demonstrated that fusion of vp22 to CD resulted in CD translocation, which in turn amplified conversion of 5-FC to 5-FU in vivo and enhanced the therapeutic benefit of this GDEPT strategy.

Gene delivery and gene therapy of prostate cancer

Surgery, radiation or hormonal therapy are not adequate to control prostate cancer. Clearly, other novel treatment approaches, such as gene therapy, for advanced/recurrent disease are desperately needed to achieve long-term local control and particularly to develop effective systemic therapy for metastatic prostate cancer. In the last decade, significant progress in gene therapy for the treatment of localised prostate cancer has been demonstrated. A broad range of different gene therapy approaches, including cytolytic, immunological and corrective gene therapy, have been successfully applied for prostate cancer treatment in animal models, with translation into early clinical trials. In addition, a wide variety of viral and nonbiological gene delivery systems are available for basic and clinical research. Gene therapy approaches that have been developed for the treatment of prostate cancer are summarised.

Kinase domain insert containing receptor promotor controlled suicide gene system kills human umbilical vein endothelial cells

AIM: To evaluate the killing effect of double suicide gene mediated by adenovirus and regulated under kinase domain insert containing receptor (KDR) promoter on human umbilical vein endothelial cells.

METHODS: By PCR technology, human KDR promoter gene, Escherichia coli (E. coli) cytosine deaminase (CD) gene and the herpes simple virus-thymidine kinase (TK) gene were cloned. Plasmid pKDR-CDglyTK was constructed with them. Then, a recombinant adenoviral plasmid pAdKDR-CDglyTK was constructed in a “two-step transformation protocol”. The newly constructed plasmids were transfected to 293 packaging cells to grow adenoviruses, which were further propagated and purified. Human umbilical vein endothelial cells (HUVEC) were infected with a different multiplicity of infection (MOI) of resultant recombinant adenovirus, the infection rate was measured with the aid of (GFP) expression. Infected cells were cultured in culture media containing different concentrations of (GCV) and/or 5-(FC), and the killing effects were measured.

RESULTS: Recombinant adenoviruses AdKDR-CDglyTK were successfully constructed, and they infected HUVEC cells efficiently. Our data indicated that the infection rate was relevant to MOI of recombinant adenoviruses. HUVEC cells infected with AdKDR-CDglyTK were highly sensitive to the prodrugs, their survival rate correlated to both the concentration of the prodrugs and the MOI of recombinant adenoviruses. Our data also indicated that the two prodrugs used in combination were much more effective on killing transgeneic cells than GCV or 5-FC used alone.

CONCLUSION: Prodrug/KDR-CDglyTK system is effective on killing HUVEC cells, its killing effect correlates to the concentration of prodrugs and recombinant adenovirus’ MOI. Combined use of the two prodrugs confers better killing effects on transgeneic cells.

Suicide gene therapy with an adenovirus expressing the fusion gene CD::UPRT in human glioblastomas: different sensitivities correlate with p53 status

BACKGROUND

Several gene therapy strategies have been designed for cancer treatment. Intra-tumoral injection of adenoviruses expressing pro-drug-converting enzymes is one such strategy. Although the efficacy of these therapies was tested in animal models, little work has been devoted to the determination of critical variables for success. In this work, we aimed at better understanding variables that affect the cytosine deaminase::uracil phosphoribosyl transferase (CD::UPRT)-based strategy in two human glioblastomas.

METHODS

We have constructed two adenoviruses expressing either CD or the fusion protein CD::UPRT. We have tested their anti-tumor activity in combination with 5-fluorocytosine (5-FC) in the glioblastoma cell lines U87 and U251, which are p53-wt and p53-deficient, respectively. Anti-tumor activity has also been investigated in spheroid structures.

RESULTS

The superiority of CD::UPRT over CD was confirmed in both glioblastoma cells. We found that the pro-drug concentration required for anti-tumor activity was 9-fold higher in U251 than in U87, while multiplicity of infection (MOI) as low as 6 was sufficient to achieve 50% killing. Bystander activity was observed with as few as 2 and 6% transduced cells for U87 and U251, respectively. Differences in sensitivity between U87 and U251 were not due to differences in transduction, transgene expression, or intercellular transport, but were related to 5-FU sensitivity and p53 status. Also, it is noteworthy that, in contrast to U87, U251 spheroids barely responded to the treatment, whereas their monolayer counterparts were very sensitive.

CONCLUSIONS

Our study has shown that p53 status is important for CD::UPRT/5-FC treatment. Moreover, this study demonstrated that the three-dimensional spheroid model is a more stringent in vitro model for suicide gene therapy evaluation than are monolayer cultures.

Antitumor effect of cytosine deaminase/5-fluorocytosine suicide gene therapy system mediated by Bifidobacterium infantis on melanoma

AIM

To construct a Bifidobacterium infantis/CD targeting gene therapy system and observe the antitumor effect of cytosine deaminase/5-fluorocytosine (CD/5-FC) suicide gene therapy system mediated by Bifidobacterium infantis on melanoma in vitro and in vivo.

METHODS

A recombinant CD/pGEX-1LamdaT plasmid was transfected into Bifidobacterium infantis by electroporation. Bifidobacterium infantis transfected by recombinant CD/pGEX-1LamdaT plasmid was incubated with 5-FC anaerobically. Then the supernatant fluid was collected and added to melanoma B16-F10 cells to observe the killing effect for B16-F10 cells. Mice were inoculated with melanoma B16-F10 cells to establish animal models. The mice were then injected with 5-FC and Bifidobacterium infantis transfected by recombinant CD/pGEX-1LamdaT plasmid.

RESULTS

Two segments of approximate 4.9 kb and 1.3 kb were extracted from the 6.2 kb recombinant plasmid, which were equal to the size of the pGEX-1LamdaT plasmid and CD gene, respectively. Sequencing results showed that the full length and sequence of nucleotide acid of the inserted gene in extracted recombinant plasmid was completely identical to the CD gene. In vitro, B16-F10 cells treated by supernatant fluid were remarkably damaged morphologically, and the cell growth was significantly inhibited. Experiments on the mice melanoma model showed that after treatment with a combination of transfected Bifidobacterium infantis and 5-FC, the tumor volume was significantly inhibited compared with controls.

CONCLUSION

The foreign gene, CD gene, was correctly inserted into pGEX-1LambdaT plasmid and transferred into Bifidobacterium infantis. CD/5-FC suicide gene therapy system mediated by Bifidobacterium infantis demonstrated a good antitumor effect on melanoma in vitro and in vivo.

A novel fusion suicide gene yeast CDglyTK plays a role in radio-gene therapy of nasopharyngeal carcinoma

To investigate a novel suicide gene for nasopharyngeal carcinoma (NPC) therapy, the yCDglyTK gene was constructed by fusing yeast cytosine deaminase (CD) and herpes simplex type 1 thymidine kinase. The expression of the yCDglyTK gene was detected by RT-PCR and Western blotting, and its bioactivity was demonstrated by an MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay. An animal study was carried out in which BALB/C nude mice bearing yCDglyTK gene-modified tumors were treated with prodrugs and radiation. Our results revealed that the yCDglyTK gene could be expressed in CNE-2 cells in vitro. In MTT analysis, at the transfection rate of 10%, 66% cells were killed. The synergistic effect of CD and TK showed 91% of yCDglyTK-transfected cells were killed with the treatment of 5-fluorocytosine (5-FC) alone, 60% killed with ganciclovir (GCV) alone, and 75% killed with 5-FC and GCV together. In vivo, the tumor volume in all of the four prodrugs and/or radiation-treated groups were significantly different from that in the PBS-controlled group (P<.01); also yCDglyTK+prodrug+radiation group was different from the other three groups (P<.05). Our findings suggested there was a synergistic antitumor effect when combining suicide gene therapy and radiation, and yCDglyTK has potent antitumor efficacy and may be a candidate suicide gene for cancer therapy.

Viral and non-viral vectors in gene therapy: technology development and clinical trials

Gene therapy as part of modern molecular medicine holds great promise for the treatment of both acute and chronic diseases and has the potential to bring a revolutionary era to cancer treatment. Gene therapy has been named the medicine of the future. For the past 10 years various viral and non-viral vectors have been engineered for improved gene and drug delivery. Although various diseases have been targeted, cancer therapy has been addressed to a large extent because of the straight forward approach. Delivery of toxic or immunostimulatory genes by viral and non-viral vectors has been investigated and encouraging results have been obtained in animal models. A large number of clinical trials have been conducted with some highly promising outcome. We propose that combinations of viruses with liposomes or polymers will solve the problem of systemic viral delivery and tumor targeting, bringing a revolution in molecular medicine and in applications of gene therapy in humans.

Turning tumor cells in situ into T-helper cell-stimulating, MHC class II tumor epitope-presenters: immuno-curing and immuno-consolidation

Immunological control or cure of tumors depends on initiating a robust T helper cell response to MHC class II epitopes of tumor-associated antigens. T helper cells regulate the potency of cytotoxic T lymphocyte and antibody responses. We have developed a novel approach to stimulate T helper cells by converting tumor cells into MHC class II molecule-positive, antigen presenting cells. Furthermore, using antisense methods, we suppress expression of the Ii protein, that normally blocks the antigenic peptide binding site of MHC class II molecules during synthesis in the endoplasmic reticulum. In such gene-engineered tumor cells, the MHC class II molecules pick up antigenic peptides, which have been transported into the endoplasmic reticulum for binding to MHC class I molecules. All nucleated cells create such "surveys of self" to detect viral or malignant transformation. Our method extends that survey of self to MHC class II endogenous tumor-associated antigens. Simultaneous presentation of tumor antigens by both MHC class I and II generates a robust and long-lasting antitumor immune response. Injecting murine tumors with genes, which induce MHC class II molecules and suppress Ii protein, cures a significant number of animals with renal and prostate tumors. We have developed analogous human gene vectors that are suitable for most patients and cancers, because they are monomorphic and active in all HLA-DR alleles. We review our findings, and analyze remaining issues for preclinical study and the design of clinical trials.

Crystal Structure to 1.7 Å of the Escherichia coli Pyrimidine Nucleoside Hydrolase YeiK, a Novel Candidate for Cancer Gene Therapy

Enzymes with nucleoside hydrolase (NH) activity are crucial for salvaging nucleic acid components in purine auxotrophic protozoan parasites, but are also present in prokaryotes and higher eukaryotes. Here we analyze the distribution of genes encoding for putative NH proteins and characterize the yeiK gene product from Escherichia coli as a pyrimidine-specific NH. The crystal structure of YeiK to 1.7 A defines the structural basis for its substrate specificity and identifies residues involved in the catalytic mechanism that differ from both nonspecific and purine-specific NHs. Large differences in the tetrameric quaternary structure compared to nonspecific protozoan NHs are brought forth by minor differences in the interacting surfaces. The first structural and functional characterization of a nonparasitic, pyrimidine nucleoside-specific NH suggests a possible role for these enzymes in the metabolism of tRNA nucleosides. The high catalytic efficiency of YeiK toward 5-fluorouridine could be exploited for suicide gene therapy in cancer treatment.

RNA Editing and Short Variant of Serotonin 2C Receptor mRNA in Neuronally Differentiated NG108-15 Cells

Two types of serotonin 2C subtype receptor mRNA, receptor-type and short variant, has been reported. The expression of the receptor-type mRNA could be detected as well as the short variant in NG108-15 cells by using a high temperature stable reverse transcriptase and the expression of the receptor-type mRNA was enhanced in drug-induced neuronal differentiated cells. The deleted sequence of the short variant include the RNA editing site by adenosine deaminase. Analysis of the sequence at the editing site revealed that the mRNA of undifferentiated cells was highly edited at sites A and B and that cytosine deaminase activity may also be involved in neuronal differentiation.

Prospects and RISC score of viral gene therapy for sarcoma

Soft tissue sarcomas are a challenge for medical oncology and gene therapy. Protective and sensitising approaches that target normal and malignant tissue, respectively, both have their role for opening the therapeutic window. Recent data show that an intensive maintenance chemotherapy significantly reduces metastatic spread and improves disease-free survival in selected patient groups. However, delays of treatment due to cytopenia are frequent. Cytostatic drug resistance gene transfer to haematopoietic progenitor cells using retroviral vectors may allow further improvement of therapy results. In recent years, retroviral vector design, transduction techniques and engraftment capability of transduced cells have been optimised. Safety considerations of retroviral gene transfer have attracted public attention and can be addressed by analysis of genomic vector integration sites. A data bank project, 'retroviral insertion estimate of chromosomal integration' (RISC), containing > 200 integration sequences, has been set up by the authors' group to recognise critical genomic regions and genes involved with possible transforming capacity. Monitoring these parameters will allow the selection of the most suitable vectors for clinical application. Sarcoma cells seem to be highly susceptible to a variety of vectors, such as recombinant adeno-associated virus-2 (rAAV-2) vectors, adenoviral vectors or oncolytic herpes simplex viruses. Results from the first clinical trials with adenoviral vectors encoding for cytokines are promising. The other systems await further development towards clinical applications. Perspectives for further research are discussed in this review.

Management of Antiretroviral Therapy in Neonates, Children, and Adolescents

There have been tremendous advances in the prevention of mother-to-child transmission of HIV and treatment of HIV-infected children and adolescents. Although multiple classes of anti-HIV drugs are available that can control viral replication and stabilize immune function when used in combination, patients and their providers also must manage complex and frequently toxic regimens. This article summarizes official National Institutes of Health guidelines for the prevention of perinatal HIV infection and the management of pediatric and adolescent HIV infection, and provides the most current updates on indications for therapy, recommended first-line therapy, criteria for changing therapy, salvage therapy, and novel management strategies.