Expression of Escherichia coli uracil phosphoribosyltransferase gene in murine colon carcinoma cells augments the antitumoral effect of 5-fluorouracil and induces protective immunity

Uracil phosphoribosyltransferase (UPRT) of Escherichia coli origin can convert 5-fluorouracil (5-FU), a chemotherapeutic agent widely used for solid tumors, to an active intermediate, 5-fluorouridine-5'-monophosphate, as mammalian orotate phosphoribosyltransferase does. To examine whether the E. coli UPRT gene expressed in tumor cells can confer increased sensitivity to 5-FU, we retrovirally transduced Colon 26 cells, a murine colon carcinoma cell line, with the UPRT gene (Colon 26/UPRT cells) and tested the in vivo antitumoral effect of 5-FU in syngeneic immunocompetent mice. After 5-FU administration, tumors of Colon 26/UPRT cells regressed, whereas those of wild-type cells were unaffected. The mice that once eliminated Colon 26/UPRT tumors after 5-FU treatment rejected wild-type cells that were subsequently inoculated but not irrelevant syngeneic tumor cells. This suicide gene/prodrug system was less efficient in nude mice, suggesting that mature alphabeta T cells play a role in the antitumoral effect. The cytotoxicity mediated by the bystander effect was marginal in this system, contrary to the herpes simplex virus-thymidine kinase gene/ganciclovir system. Therefore, expression of the UPRT gene in tumor cells followed by 5-FU administration is a possible strategy for cancer gene therapy, but potentiation of the bystander effect is required for its therapeutic application.     

The oncolytic effect of recombinant vesicular stomatitis virus is enhanced by expression of the fusion cytosine deaminase/uracil phosphoribosyltransferase suicide gene

Vesicular stomatitis virus (VSV) has recently been demonstrated to exhibit significant oncolytic capabilities against a wide variety of tumor models in vitro and in vivo. To potentially enhance the oncolytic effect, we generated a novel recombinant VSV (rVSV) that expressed the fusion suicide gene Escherichia coli cytosine deaminase (CD)/uracil phosphoribosyltransferase (UPRT). rVSV encoding the CD/UPRT fusion gene (VSV-C:U) exhibited normal growth properties and generated high levels of biologically active CD/UPRT that could catalyze the modification of 5-fluorocytosine into chemotherapeutic 5-fluorouracil (5-FU), which exhibited considerable bystander effect. Intratumoral inoculation of VSV-C:U in the presence of the systemically administered prodrug 5-fluorocytosine produced statistically significant reductions in the malignant growth of syngeneic lymphoma (A20) or mammary carcinoma (TSA) in BALB/c mice compared with rVSV treatments or with control 5-FU alone. Aside from detecting prolonged therapeutic levels of 5-FU in VSV-C:U-treated animals harboring TSA tumors and enhancing bystander killing of tumor cells, we demonstrated marked activation of IFN-gamma-secreting cytotoxic T cells by enzyme-linked immunospot analysis that may have also facilitated tumor killing. In conclusion, the insertion of the fusion CD/UPRT suicide gene potentiates the oncolytic efficiency of VSV by generating a strong bystander effect and by contributing to the activation of the immune system against the tumor without detrimentally altering the kinetics of virus-mediated oncolysis and may be useful in the treatment of malignant disease.     

The role of cellular- and prodrug-associated factors in the bystander effect induced by the Varicella zoster and Herpes simplex viral thymidine kinases in suicide gene therapy

To investigate the factors influencing the bystander effect--a key element in the efficacy of suicide gene therapy against cancer--we compared the effect triggered by four extremely efficient gene/prodrug combinations, i.e., VZVtk/BVDU, the thymidine kinase of Varicella zoster virus associated with (E)-5-(2-bromovinyl)-2'-deoxyuridine; VZVtk/BVaraU, the same enzyme associated with (E)-5-(2-bromovinyl)-1-beta-D-arabinofuranosyluracil; HSVtk/BVDU, the association of the Herpes simplex virus thymidine kinase with BVDU; and the classical HSVtk/GCV (ganciclovir) paradigm. The cells used, the human MDA-MB-435 breast cancer, and the rat 9L glioblastoma lines were equally sensitive in vitro to these four associations. In both cell types, the combinations involving pyrimidine analogues (BVDU, BVaraU) displayed a smaller bystander killing than the combination involving the purine analogue (GCV). In addition, the bystander effect induced by all the tk/prodrug systems was reduced in MDA-MB-435 cells in comparison to 9L cells; albeit, the viral kinases were produced at a higher level in the breast cancer cells. All systems induced apoptotic death in the two cell types, but the MDA-MB-435 cells, deprived of connexin 43, were noncommunicating in striking contrast with the 9L cells. That functional gap junctions have to be increased in order to improve the breast cancer cell response to suicide gene therapy was demonstrated by transducing the Cx43 gene: this modification enhanced the bystander effect associated in vitro with GCV treatment and, by itself, decreased the tumorigenicity of the untreated cells. However, the noncommunicating MDA-MB-435 cells triggered a significant bystander effect both in vitro and in vivo with the HSVtk/GCV system, showing that communication through gap junctions is not the only mechanism involved.     

Combined suicide gene therapy for human colon cancer cells using adenovirus-mediated transfer of escherichia coli cytosine deaminase gene and Escherichia coli uracil phosphoribosyltransferase gene with 5-fluorocytosine

The virus-directed enzyme/prodrug system using the Escherichia coli cytosine deaminase (CD) gene and 5-fluorocytosine (5-FC) suffers from a sensitivity limitation in many tumor cells. The E. coil uracil phosphoribosyltransferase (UPRT), which is a pyrimidine salvage enzyme, directly converts 5-fluorouracil (5-FU) to 5-fluorouridine monophosphate at the first step of its activating pathway. To improve the antitumoral effect of the CD/5-FC system, we investigated a combined suicide gene transduction therapy for human colon cancer cells using two separate adenovirus vectors expressing the E. coli CD and E. coli UPRT genes and systemic 5-FC administration (the CD, UPRT/5-FC system). The present study demonstrates that the CD, UPRT/5-FC system generates a co-operative effect of CD and UPRT, resulting in dramatic increases in both RNA- and DNA-directed active forms, including 5-fluorouridine triphosphate incorporated into RNA, 5-fluorodeoxyuridine monophosphate, and the thymidylate synthase inhibition rate, compared with the CD/5-FC system. Furthermore a significant increase in the 5-FC sensitivity of colon cancer cells was demonstrated in the CD, UPRT/5-FC system compared with the CD/5-FC system in vitro and in vivo. These results suggest that the CD, UPRT/5-FC system is a powerful approach in gene therapy for colorectal cancer.     

UPRT/5-FU前药转换酶系统对小鼠胃癌治疗的实验研究

目的　探讨UPRT/ 5 FU前药转换酶系统对小鼠胃癌细胞MFC的杀伤效应。方法　采用PCR技术从大肠杆菌K12基因组中扩增UPRT基因 ,并构建pLXSN逆转录病毒表达载体 ,进一步转染MFC细胞。采用MTT法检测转导UPRT基因前后 ,MFC对 5 FU的敏感性的变化。建立 6 15小鼠胃癌皮下移植瘤模型 ,腹腔内给于 5 FU ,观察治疗效果。结果　体外MTT法检测结果显示 ,转导UPRT基因后可使MFC对 5 FU的敏感性提高约 17.2 6倍。动物实验的结果表明 ,转导UPRT基因不影响MFC的致瘤性 ;经 5 FU治疗后 ,转UPRT基因的肿瘤 ,生长明显受抑 (P <0 .0 0 0 5 ) ,抑瘤率为 89.6 2 %。结论　UPRT基因修饰小鼠胃癌细胞株MFC ,能明显提高MFC对 5 FU杀伤的敏感性 ,增强 5 FU的抗瘤效应。     

瘤内原位转导UPRT基因治疗小鼠胃癌的实验研究

背景与目的:5-FU是临床上重要的化疗药物,但总体疗效有限,如何提高其抗癌疗效一直是临床上亟待解决的难题。本研究采用基因治疗的原理与方法,探讨UPRT(uracilphosphoribosyltransferase)基因对5-FU杀伤效应的增敏作用。方法:采用PCR技术从大肠杆菌K12基因组中扩增UPRT基因,并构建pLXSN逆转录病毒表达载体,进一步转染小鼠胃癌细胞株MFC。采用MTT法检测转导UPRT基因前后MFC对5-FU敏感性的变化。建立615小鼠胃癌皮下移植瘤模型,瘤内反复多次注射携带UPRT基因的浓缩、纯化的逆转录病毒,同时腹腔内给予5-FU,观察抑瘤效果。结果:体外MTT法检测结果显示,转导UPRT基因后可使MFC对5-FU的敏感性提高约17.26倍。以逆转录病毒介导UPRT基因瘤内原位转导,同时联合应用5-FU进行治疗,结果肿瘤生长明显受抑(P<0.005),抑瘤率为87.18%。结论:UPRT基因修饰小鼠胃癌细胞株MFC,能明显提高MFC对5-FU杀伤的敏感性,以逆转录病毒载体介导UPRT基因肿瘤原位基因转导,同时联合应用5-FU,能获得良好的抑瘤效应。     

肿瘤双自杀基因治疗系统pTRKH2-PsT/CD,pTRKH2-PsT/UPRT在厌氧婴儿双歧杆菌中的构建

Objective: We recombine the suicide gene CD, UPRT into plasmid pTRKH2 and clone the recombinant dual suicide gene therapy system into tumor-hypoxia-targeting vector Bifidobacterium infantis and characterize its function. Methods: CD gene, UPRT gene and lactic acid bacteria expression plasmid pTRKH2 were digested by restriction endonuclease BamH I and Sal I, and constructed recombinant plasmids pTRKH2/CD and pTRKH2/UPRT in E. coll. The recombinant plasmids were then transfected into Bifidobacterium Infantis by electroporation. Identification of pTRKH2/CD and pTRKH2/UPRT was processed by dual restriction endonuclease digesting and sequencing. RT-PCR and SDS-PAGE were used to examine the expression of CD and UPRT genes at RNA and protein levels. The killing effects on Melanoma B16-F10 cells by pTRKH2/CD and pTRKH2/UPRT suicide gene therapy system with 5-FC were examined by MTT assay. Results: The CD gene and UPRT gene was successfully recombined into lactic acid bacteria expression plasmid pTRKH2. After dual endonuclease digestion of plasmid purified from the positively transfected E. co/i, two fragments of 6.9 Kb and 1.3 Kb were found for CD gene and two fragments of 6.9 Kb and 620 bp were found for UPRT gene. The sequencing of CD gene and UPRT gene proved consistent sequences with Genebank published data. A fragment of 1.3 Kb for CD gene and fragment of 620 bp for UPRT gene was found in recombinant Bifidobac- terium by RT-PCR. A 52 KDa protein for CD gene was identified in whole-cell protein of recombinant Bifidobacterium and a 26 KDa protein for UPRT gene was identified in supernatant fluid of recombinant Bifidobacterium. The survival rate of tumor cells treated by extracts from culture of recombinant Bifidobacterium with 5-FC showed a strong killing effects of pTRKH2/CD and pTRKH2/UPRT dual suicide gene therapy system on Melanoma B16-F10 cells. Conclusion: CD gene and UPRT gene are suc- cessfully inserted into pTRKH2 and transfected into tumor-hypoxia-targeting vector Bifldobacterium Infantis. This dual suicide gene therapy system shows a high efficiency for tumor cells killing.     

Circumvention of 5-Fluorouracil Resistance in Human Stomach Cancer Cells by Uracil Phosphoribosyltransferase Gene Transduction

A human stomach cancer cell line with acquired resistance to 5-fluorouracil (5-FU), NUGC-3/5FU/L, has been found to possess reduced ability to convert 5-FU into active metabolites. We attempted in vitro gene therapy for this 5-FU-resistant cell line. NUGC-3 and NUGC-3/5FU/L cells were infected with recombinant adenovirus (Ad) containing Escherichia coli uracil phosphoribosyltransferase ( UPRT ) gene driven by CAG promoter (CA), AdCA-UPRT, and changes in their 5-FU metabolism and sensitivity were investigated. Activities of orotate phosphoribosyltransferase increased from 10.2 and 1.56 (nmol/mg protein/30 min) in the uninfected cells of NUGC-3 and NUGC-3/5FU/L to 216 and 237, respectively, after the transfection of UPRT gene. The 5-FU nucleotide level in the acid-insoluble fraction increased from 7.32 to 15.9 (pmol/mg protein) in NUGC-3 cells on infection with AdCA-UPRT, and in NUGC-3/5FU/L cells it increased from 1.91 to 21.4. The 50% growth-inhibition concentration (IC50) was 12.7 μmol/liter for NUGC-3 and much higher than 100 μmol/liter for NUGC-3/5FU/L, indicating over 8-fold resistance. NUGC-3/5FU/L transfected with the UPRT gene showed very high sensitivity to 5-FU with an IC₅₀ of 3.2 μmol/liter. The high resistance in this metabolic activation-deficient cell line was thus completely reversed by transduction of an exogenous gene coding for a 5-FU-anabolizing enzyme.     

Circumvention of 5-fluorouracil resistance in human stomach cancer cells by uracil phosphoribosyltransferase gene transduction.

A human stomach cancer cell line with acquired resistance to 5-fluorouracil (5-FU), NUGC-3/5FU/ L, has been found to possess reduced ability to convert 5-FU into active metabolites. We attempted in vitro gene therapy for this 5-FU-resistant cell line. NUGC-3 and NUGC-3/5FU/L cells were infected with recombinant adenovirus (Ad) containing Escherichia coli uracil phosphoribosyltransferase (UPRT) gene driven by CAG promoter (CA), AdCA-UPRT, and changes in their 5-FU metabolism and sensitivity were investigated. Activities of orotate phosphoribosyltransferase increased from 10.2 and 1.56 (nmol/mg protein/30 min) in the uninfected cells of NUGC-3 and NUGC-3/5FU/L to 216 and 237, respectively, after the transfection of UPRT gene. The 5-FU nucleotide level in the acid-insoluble fraction increased from 7.32 to 15.9 (pmol/mg protein) in NUGC-3 cells on infection with AdCA-UPRT, and in NUGC-3/5FU/L cells it increased from 1.91 to 21.4. The 50% growth-inhibition concentration (IC50) was 12.7 micromol/liter for NUGC-3 and much higher than 100 micromol/liter for NUGC-3/5FU/L, indicating over 8-fold resistance. NUGC-3/ SFU/L transfected with the UPRT gene showed very high sensitivity to 5-FU with an IC50 of 3.2 micromol/liter. The high resistance in this metabolic activation-deficient cell line was thus completely reversed by transduction of an exogenous gene coding for a 5-FU-anabolizing enzyme.     

Intracellular prodrug gene therapy for cancer mediated by tumor cell suicide gene exosomes

Recently, we reported about exosomes possessing messenger RNA (mRNA) of suicide gene secreted from mesenchymal stem/stromal cells (MSCs) engineered to express the suicide gene—fused yeast cytosine deaminase::uracil phosphoribosyltransferase (yCD::UPRT). The yCD::UPRT‐MSC exosomes are internalized by tumor cells and intracellularly convert prodrug 5‐fluorocytosine (5‐FC) to cytotoxic drug 5‐fluorouracil (5‐FU). Human tumor cells with the potential to metastasize release exosomes involved in the creation of a premetastatic niche at the predicted organs. We found that cancer cells stably transduced with yCD::UPRT gene by retrovirus infection released exosomes acting similarly like yCD::UPRT‐MSC exosomes. Different types of tumor cells were transduced with the yCD::UPRT gene. The homogenous cell population of yCD::UPRT‐transduced tumor cells expressed the yCD::UPRT suicide gene and secreted continuously exosomes with suicide gene mRNA in their cargo. All tumor cell suicide gene exosomes upon internalization into the recipient tumor cells induced the cell death by intracellular conversion of 5‐FC to 5‐FU and to 5‐FUMP in a dose‐dependent manner. Most of tumor cell‐derived suicide gene exosomes were tumor tropic, in 5‐FC presence they killed tumor cells but did not inhibit the growth of human skin fibroblast as well as DP‐MSCs. Tumor cell‐derived suicide gene exosomes home to their cells of origin and hold an exciting potential to become innovative specific therapy for tumors and potentially for metastases.     

肿瘤厌氧靶向双自杀基因治疗系统pTRKH2-PsT/CD、pTRKH2-PsT/UPRT的构建

目的 利用婴儿双歧杆菌对实体瘤低氧区的靶向效应,构建肿瘤厌氧靶向双自杀基因治疗系统pTRKH2-PsT /CD和pTRKH2-PsT /UPRT。方法 用PCR的方法从质粒pGEX/CD和pGEX/UPRT中扩增出CD基因和UPRT基因,双酶切CD基因、UPRT基因和质粒pTRKH2-PsT,分别连接后重组于大肠杆菌中。之后用电转化的方法将重组质粒转入婴儿双歧杆菌中。用RT-PCR检测该系统mRNA水平的表达,SDS-PAGE检测该系统在蛋白质水平的表达。在黑色素瘤B16-F10细胞上检测该系统的体外肿瘤细胞杀伤效果。结果 成功地将CD基因和UPRT基因转入了质粒pTRKH2-PsT,CD基因和UPRT基因的测序结果表明序列与Genebank公布的序列一致。RT-PCR检测到CD和UPRT mRNA水平的明显表达。在含有CD基因的婴儿双歧杆菌细胞全蛋白中发现了CD蛋白质的表达,在含有UPRT基因的婴儿双歧杆菌上清液中发现了UPRT蛋白质的表达。黑色素瘤细胞的低存活率证明了pTRKH2-PsT/CD、pTRKH2-PsT/UPRT自杀基因治疗系统对黑色素瘤的显著杀伤作用。结论 肿瘤厌氧靶向双自杀基因治疗系统pTRKH2-PsT/CD、pTRKH2-PsT/UPRT构建成功并显示出杀伤肿瘤细胞的作用。     

Synergistic effect of resveratrol and HSV-TK/GCV therapy on murine hepatoma cells

Despite its low transfer efficiency, suicide gene therapy with HSV-TK is known for its bystander killing effect. The connexin-based gap junction is believed to mediate the bystander effect. Recently, we found that resveratrol, a polyphenol compound, increased the expression of Cx26 and Cx43, which are connexins and important constituents of gap junctions, in murine hepatoma cells. Hypothetically, the resveratrol-induced upregulation of gap junctions may improve the bystander effect that HSV-TK/GCV has on hepatoma cells. Our present investigation revealed that resveratrol could enhance intercellular communication at the gap junctions in CBRH7919 hepatoma cells and thereby enhance the bystander killing effect of GCV on CBRH7919^TK cells. However, inhibition of gap junction using its long-term inhibitor alpha-glycyrrhetinic acid had a negative influence on the bystander effect of gene therapy with HSV-TK/GCV. In addition, combined resveratrol and GCV treatment in tumor-bearing mice with CBRH7919^TK and CBRH7919^WT cells at a ratio of 2:3 resulted in a significant decrease in the volume and weight of the tumor in comparison to GCV or only resveratrol. The present results demonstrate that resveratrol can enhance the bystander effect exerted by the HSV-TK/GCV system by enhancing connexin-mediated gap junctional communication.     

Bystander effect in suicide gene therapy is directly proportional to the degree of gap junctional intercellular communication in esophageal cancer

Gap junctional intercellular communication (GJIC) has been shown to be involved in the bystander effect through herpes simplex virus thymidine kinase/ganciclovir (HSV-tk/GCV) gene therapy. In this study, we examined the expression of connexins, the components of gap junction, and the degree of GJIC in esophageal cancer cell lines and compared the bystander effect in cells with different capacities of GJIC. We found loss in connexin 26 expression and reduced connexin 43 in esophageal cancer. GJIC capacity varied among cell lines and was dependent on the connexin 43 expression in the cell-cell contact areas. In mixing assay, the extent of the bystander effect was tightly correlated with the degree of GJIC capacity. The effects of retinoic acid and cAMP on the bystander effect were also investigated. Treatment with retinoic acid, but not with cAMP, was associated with augmented bystander killing by increase in GJIC in some esophageal cancer cell lines. Our results indicated that the degree of GJIC was predictive to identify a tumor as suitable for gene therapy with the HSV-tk/GCV system. Also GJIC chemically-enhanced with retinoic acid might be useful to improve response in suicide gene therapy.     

Cytosine deaminase suicide gene therapy for peritoneal carcinomatosis

Gene therapy is a novel therapeutic approach that might soon improve the prognosis of some cancers. We investigated the feasibility of cytosine deaminase (CD) suicide gene therapy in a model of peritoneal carcinomatosis. DHD/K12 colorectal adenocarcinoma cells transfected in vitro with the CD gene were highly sensitive to 5-fluorocytosine (5-FC), and a bystander effect could also be observed. Treating CD+ cells with 5-FC resulted in apoptosis as detected by terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate nick-end labeling. In vitro, several human cell lines derived from ovarian or colorectal carcinomas, as well as the rat glioblastoma 9 L cell line, responded to CD/5-FC and showed a very strong bystander effect. 5-FC treatment of peritoneal carcinomatosis generated in syngeneic BDIX rats by CD-expressing DHD/K12 cells led to a complete and prolonged response and to prolonged survival. Our study thus demonstrated the efficacy of CD suicide gene therapy for the treatment of peritoneal carcinomatosis.     

Effective gene therapy of biliary tract cancers by a conditionally replicative adenovirus expressing uracil phosphoribosyltransferase: significance of timing of 5-fluorouracil administration

In order to enhance the efficacy of conditionally replicating adenoviruses (CRAd) in the treatment of cancers of the biliary tract, we studied the efficacy in vitro and in vivo of AxE1CAUP, a CRAd vector that carries a gene for uracil phosphoribosyltransferase (UPRT), which converts 5-fluorouracil (5-FU) directly to 5-fluorouridine monophosphate and greatly enhances the cytotoxicity of 5-FU. AxE1CAUP replicated and induced an increased UPRT expression in biliary cancer cells more efficiently than AxCAUP, a nonreplicative adenovirus carrying the UPRT gene. Whereas AxCAUP and AxE1AdB, a CRAd without the UPRT gene, modestly increased the sensitivity of BC cells to 5-FU, AxE1CAUP markedly increased the sensitivity, especially when the timing of 5-FU administration was appropriately chosen. AxE1CAUP replicated much less efficiently in normal WI-38 fibroblasts without any change in the sensitivity to 5-FU. In nude mice with s.c. biliary cancer xenografts, i.t. AxE1CAUP/5-FU therapy inhibited tumor growth significantly more strongly than AxCAUP/5-FU or AxE1AdB/5-FU therapy. Furthermore, in mice with peritoneally disseminated biliary cancer, i.p. AxE1CAUP efficiently proliferated in the tumors, decreased the tumor burden, and prolonged the survival of the mice when 5-FU was started 10 or 15 days after the vector inoculation, whereas earlier initiation of 5-FU resulted in early eradication of the vector and no survival benefit. The present study shows that the CRAd expressing UPRT was a more potent sensitizer of biliary cancer to 5-FU, than was a nonreplicative UPRT-encoding vector or a CRAd without UPRT gene, even at a lower dose of the vector, and that timing of 5-FU administration was a key factor to maximize the efficacy. This gene therapy with appropriately timed administration of 5-FU should be useful in overcoming the resistance of biliary cancers to 5-FU.     

Increased sensitivity of glioma cells to 5-fluorocytosine following photo-chemical internalization enhanced nonviral transfection of the cytosine deaminase suicide gene

Despite advances in surgery, chemotherapy and radiotherapy, the outcomes of patients with GBM have not significantly improved. Tumor recurrence in the resection margins occurs in more than 80 % of cases indicating aggressive treatment modalities, such as gene therapy are warranted. We have examined photochemical internalization (PCI) as a method for the non-viral transfection of the cytosine deaminase (CD) suicide gene into glioma cells. The CD gene encodes an enzyme that can convert the nontoxic antifungal agent, 5-fluorocytosine, into the chemotherapeutic drug, 5-fluorouracil. Multicell tumor spheroids derived from established rat and human glioma cell lines were used as in vitro tumor models. Plasmids containing either the CD gene alone or together with the uracil phosphoribosyl transferase (UPRT) gene combined with the gene carrier protamine sulfate were employed in all experiments.PCI was performed with the photosensitizer AlPcS_2a and 670 nm laser irradiance. Protamine sulfate/CD DNA polyplexes proved nontoxic but inefficient transfection agents due to endosomal entrapment. In contrast, PCI mediated CD gene transfection resulted in a significant inhibition of spheroid growth in the presence of, but not in the absence of, 5-FC. Repetitive PCI induced transfection was more efficient at low CD plasmid concentration than single treatment. The results clearly indicate that AlPcS_2a-mediated PCI can be used to enhance transfection of a tumor suicide gene such as CD, in malignant glioma cells and cells transfected with both the CD and UPRT genes had a pronounced bystander effect.     

Retrovirus-mediated transfer of the herpes simplex virus thymidine kinase and connexin26 genes in pancreatic cells results in variable efficiency on the bystander killing: implications for gene therapy.

Currently, there is no effective treatment for pancreatic cancer and prodrug-activating gene therapy with the herpes simplex virus thymidine kinase gene (HSV-tk) in combination with ganciclovir (GCV) has been suggested as a candidate approach against this disease. In the present study, we have evaluated the efficacy of the HSV-tk/GCV treatment in a panel of pancreatic tumor cells (NP-9, NP-18, NP-31) and the potentiation of the cytotoxic effect in combination with the overexpression of the connexin 26 gene (Cx26). Pancreatic cells transduced with a retrovirus containing the HSV-tk gene showed different sensitivities to GCV that seemed to be independent of HSV-tk expression levels. The extent of the bystander effect also varied among the pancreatic tumor cells and correlated with the level of gap junction intercellular communication (GJIC). Transduction of the pancreatic tumor cells with a retrovirus carrying the connexin 26 gene resulted in high levels of connexin 26 expression and in an increase in the GJIC that correlated to an extent in the bystander effect in both NP-9Cx26 and NP-18Cx26 cells. Neither an increment in GJIC nor an increase in the bystander killing was detected in NP-31Cx26. The bystander effect in NP-18 Cx26 cells was also prevented by the long term inhibitor of GJIC, 18-alpha-glycyrrhetinic acid (AGA). Together, these results demonstrate that pancreatic tumor cells are highly different as regards the susceptibility to HSV-tk/GCV treatment. Moreover, they indicate that overexpression of the Cx26 gene does not always correspond to an increase in GJIC although they clearly suggest the role of GJIC in mediating the bystander effect.     

Enhancing VSV oncolytic activity with an improved cytosine deaminase suicide gene strategy

Oncolytic viruses (OVs) are promising therapeutic agents for cancer treatment, with recent studies emphasizing the combined use of chemotherapeutic compounds and prodrug suicide gene strategies to improve OV efficacy. In the present study, the synergistic activity of recombinant vesicular stomatitis virus (VSV)-MΔ51 virus expressing the cytosine deaminase/uracil phosphoribosyltransferase (CD::UPRT) suicide gene and 5-fluorocytosine (5FC) prodrug was investigated in triggering tumor cell oncolysis. In a panel of VSV-sensitive and -resistant cells-prostate PC3, breast MCF7 and TSA, B-lymphoma Karpas and melanoma B16-F10-the combination treatment increased killing of non-infected bystander cells in vitro via the release of 5FC toxic derivatives. In addition, we showed a synergistic effect on cancer cell killing with VSV-MΔ51 and the active form of the drug 5-fluorouracil. Furthermore, by monitoring VSV replication at the tumor site and maximizing 5FC bioavailability, we optimized the treatment regimen and improved survival of animals bearing TSA mammary adenocarcinoma. Altogether, this study emphasizes the potency of the VSV-CD::UPRT and 5FC combination, and demonstrates the necessity of optimizing each step of a multicomponent therapy to design efficient treatment.     

Quantitative evaluation and comparison of two prodrug-activating suicide gene therapies on oral squamous cell carcinoma

Prodrug-activating suicide gene therapy (PA suicide gene therapy for short) for cancer is to introduce cancer cells with suicide genes. The enzyme encoded by suicide gene is not toxic but is able to kill cancer cells by converting a non-toxic prodrug into a toxic compound. This approach is a promising cancer gene therapy that could reduce non-specific toxicity to normal tissue. However, there is no quantitative method to evaluate efficacy of suicide gene therapy in preclinical study. The aim of this study is to develop a new method to quantitatively evaluate and compare prodrug-activating suicide gene therapies. This study was carried out on an oral squamous cell carcinoma (OSCC) cell line CAL-27. Suicide genes were integrated into ROSA26 locus of CAL-27 by CRISPR-Cas9. CAL-27 cell lines stably expressing herpes simplex virus-thymidine kinase (TK) or yeast cytosine deaminase (CD) were used to evaluate and compare PA suicide gene therapies. The efficacies of PA suicide gene therapies were quantitatively evaluated from three aspects: effective prodrug concentration, prodrug treatment time, and bystander effect. This method also could be used for different types of suicide gene therapies and different types of cancer. When the prodrug concentration, treatment time, and rate of suicide gene-positive cells (related to bystander effect) are fixed, anti-cancer effects could be quantitatively measured. This information is important for suicide gene therapy preclinical development.     

Gene therapy for intraperitoneally disseminated pancreatic cancers by Escherichia coli uracil phosphoribosiltransferase (UPRT) gene mediated by restricted replication-competent adenoviral vectors

Although patients with unresectable pancreatic tumors have been treated with 5-fluorouracil (5FU)-based combination chemotherapy, the drug resistance of cancer cells presents a crucial therapeutic problem. It was reported that UPRT overcomes 5FU resistance. UPRT catalyzes the synthesis of 5-fluorouridine monophosphate (FUMP) from Uracil and phosphoribosylpyrophosphate (PRPP). The antitumor effect of 5FU is enhanced by augmenting 5-fluorodeoxyuridine monophosphate (FdUMP) converted from FUMP, which inhibits thymidylate synthetase (TS). We first demonstrated that injecting an E1-deficient adenoviral vector (Adv) expressing UPRT (AxCAUPRT) followed by 5-FU treatment resulted in a volume reduction of xenotransplanted human tumors. In examining the therapeutic effect of AxCAUPRT/5-FU against peritoneal dissemination, we found that non-selective gene transduction of AxCAUPRT caused severe adverse effects arising from the increase of F-dUMP in normal intestine. Because the therapeutic gene delivered by a restricted replication-competent Adv lacking 55 kDa E1B protein (AxE1AdB) is speculated to be expressed selectively in tumors, mice with established tumors were injected with AxE1AdB and E1-deleted Adv expressing the lacZ reporter gene (AxCAlacZ). The expression of the reporter gene (lacZ) was selectively enhanced in disseminated tumors. The therapeutic advantage of restricted replication competent Adv that expresses UPRT (AxE1AdB-UPRT) was evaluated in an intraperitoneal disseminated tumor model. To study the anti-tumor effect of AxE1AdB-UPRT/5FU, mice with disseminated AsPC-1 tumors were administered the Adv, followed by the 5FU treatment. It was shown that the treatment with AxE1AdB-UPRT/5FU caused a dramatic reduction of the disseminated tumor burden without toxicity in normal tissues. Our results showed that the AxE1AdB-UPRT/5FU system is a promising tool for intraperitoneal disseminated pancreatic cancer.