Transcriptional regulatory sequences of carcinoembryonic antigen: identification and use with cytosine deaminase for tumor-specific gene therapy

CEA-Regulated Oncolytic Virus Anticancer Therapy: A Promising Strategy for Rare Solid Tumors

BACKGROUND

Rare solid tumors have attracted much more attention due to the great unmet clinical need, limited treatment options, and poor prognosis. As the most thoroughly studied tumor marker, carcinoembryonic antigen (CEA) can not only overexpress in various common solid tumors, but also in several rare solid tumors. Oncolytic virus therapy has achieved excellent anticancer effects in the past decades. Due to the specific high expression of CEA in certain tumor tissues, but not in normal tissues, CEA has been applied to improve the tumor specificity of gene expression.

METHODS

The studies of CEA expression in rare solid tumors and CEA-regulated oncolytic virus therapy were reviewed.

RESULTS

We showed the types of rare solid tumors with overexpression of CEA. Elevated serum CEA levels can indicate the diagnosis, response of surgery or system therapy, distal metastasis, recurrence, and survival. Due to high tumor specificity, CEA-regulated OA therapy has demonstrated a surprising antitumor effect for common CEA-positive tumors in preclinical trials Conclusion: These data suggested that CEA could be a diagnostic and prognostic biomarker for several rare solid tumors. We proposed the hypothesis that CEA-regulated oncolytic virus therapy could be a promising therapeutic strategy for CEA-positive rare solid tumors.

Selective suicide gene therapy of colon cancer cell lines exploiting fibroblast growth factor 18 promoter

Fibroblast growth factor 18 (FGF18) is one of the genes downstream of Wnt, one of the most important signaling pathways activated in colon cancer. An FGF18 promoter containing a single T-cell factor/lymphocyte enhancing factor 1 (TCF/LEF1) binding site was inserted upstream of a thymidine kinase (TK) suicide gene module, while a bacterial beta-Gal (LacZ) element served as the reporter gene. Following transient transfection with pUCFGF18LacZ, beta-Gal staining showed that 5% of SW480, 10% of HCT116, 0% of human umbilical vein endothelial cells (HUVECs) and 0% of normal colon cells (NCCs) had expressed LacZ. beta-Gal enzyme-linked immunosorbent assay revealed that the ratio of pUCFGF18LacZ activity to that of positive control was 0.09 and 0.25 in SW480 and HCT116, respectively (significantly higher than mock plasmid), while there were no significant changes in the beta-Gal expression in HUVEC and NCC cells transfected with pUCFGF18LacZ or mock plasmid. Following transfection with pUCFGF18TK and pUCCMVTK (positive control), cytotoxicity analysis of transfected cells showed that treatment with ganciclovir (GCV) significantly decreased SW480 and HCT116 cell survival at GCV concentrations above 20 microg/mL. An inverse correlation between GCV concentration and cell viability was evident in both colon cancer cell lines following transfection with these suicide plasmids. pUCFGF18TK and pUCCMVTK induced apoptosis after the administration of GCV in HCT116, but not in SW480, as demonstrated by M30 cytodeath antibody. This discrepancy may stem from differences in the mechanisms of TK/GCV-induced apoptosis in p53-proficient (HCT116) and -deficient (SW480) cells. The specific activity of the FGF18 promoter in HCT116 and SW480 may reflect the advantage of this promoter over artificial promoters containing artificial TCF/LEF binding sites.

Selective suicide gene therapy of colon cancer exploiting the urokinase plasminogen activator receptor promoter

Colon cancer is the third and fourth most prevalent cancer among Iranian men and women, respectively. Suicide gene therapy is one of the alternative therapeutic modalities for cancer. The application of specific promoters for therapeutic genes should decrease the adverse effects of this modality. The combined aims of this study were to design a specific suicide gene therapy construct for colon cancer and study its effect in distinct representatives of transformed and nontransformed cells. The KRAS oncogene signaling pathway is one of the most important signaling pathways activated in colon cancer; therefore, we inserted the urokinase plasminogen activator receptor (uPAR; PLAUR gene) promoter as one of the upregulated promoters by this pathway upstream of a suicide gene (thymidine kinase [TK]) and a reporter gene (beta-galactosidase, beta-gal [LacZ]). This promoter is a natural combination of different motifs responsive to the RAS signaling pathway, such as the transcription factors AP1 (FOS/JUN), SP1, SP3, and AP2alpha, and nuclear factor kappa B (NFkappaB). The reporter plasmid under the control of the uPAR promoter (PUCUPARLacZ) had the ability to express beta-gal in colon cancer cells (human colon adenocarcinoma [SW480] and human colorectal carcinoma [HCT116] cell lines), while it could not express beta-gal in nontransformed human umbilical vein endothelial cells (HUVEC) and normal colon cells. After confirming the ability of pUCUPARTK (suicide plasmid) to express TK in SW480 and HCT116 cells by real-time PCR, cytotoxicity assays showed that pUCUPARTK decreased the viability of these cells in the presence of ganciclovir 20 and 40 microg/mL (and higher), respectively. Although M30 CytoDEATH antibody could not detect a significant rate of apoptosis induced by ganciclovir in pUCUPARTK-transfected HCT116 cells, the percentage of stained cells was marked in comparison with untreated cells. While this antibody could detect apoptosis in HCT116 cell line transfected with positive control plasmid, it could not detect apoptosis in SW480 cells transfected with the same positive control. This discrepancy could be attributed to the different mechanisms of TK/ganciclovir-induced apoptosis in tumor protein p53 (TP53)-expressing (HCT116) and -deficient (SW480) cells. Annexin-propidium iodide staining could detect apoptosis in treated, pUCUPARTK-transfected SW480 and HCT116 cells. This study showed that the uPAR promoter can be considered as a suitable candidate for specific suicide gene therapy of colon cancer and probably other cancers in which the RAS signaling pathway is involved in their carcinogenesis process.

Modular Cre/lox system and genetic therapeutics for colorectal cancer

The Cre/lox system is a powerful tool for targeting therapeutic effectors in a wide variety of human disorders. I review a Cre/lox Wnt-targeted system that has shown promise against Wnt-positive colorectal cancer cell lines. In addition to Wnt-specific targeting of cell death inducers, the modular nature of this gene therapy model system can be exploited by designing positive and negative feedback loops to either amplify or inhibit Wnt activity for experimental or therapeutic benefit. I discuss the structural components and performance parameters of the system, the implication of these findings with respect to cancer stem cells, as well as the general applicability of this system to any disorder characterized by differential gene expression. I also consider the issue of gene delivery as well as in vivo testing requirements necessary for the further characterization and development of this system.

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.

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.

Reverse-engineering a transcriptional enhancer: a case study in Drosophila

Enhancers, or cis-regulatory elements, are the principal determinants of spatiotemporal patterning of gene expression. For reasons of clinical and research utility, it is desirable to build customized enhancers that drive novel gene expression patterns, but currently, we largely rely on "found" genomic elements. Synthetic enhancers, assembled from transcription factor binding sites taken from natural signal-regulated enhancers, generally fail to behave like their wild-type counterparts when placed in transgenic animals, suggesting that important aspects of enhancer function are still unexplored. As a step toward the creation of a truly synthetic regulatory element, we have undertaken an extensive structure-function study of an enhancer of the Drosophila decapentaplegic (dpp) gene that drives expression in the developing visceral mesoderm (VM). Although considerable past efforts have been made to dissect the dppVM enhancer, transgenic experiments presented here indicate that its activity cannot be explained by the known regulators alone. dppVM contains multiple, previously uncharacterized, regulatory sites, some of which exhibit functional redundancy. The results presented here suggest that even the best-studied enhancers must be further dissected before they can be fully understood, and before faithful synthetic elements based on them can be created. Implications for developmental genetics, mathematical modeling, and therapeutic applications are discussed.

Midkine promoter-based conditionally replicative adenovirus therapy for midkine-expressing human pancreatic cancer

Background

To develop a novel therapeutic strategy for human pancreatic cancer using a midkine promoter-based conditionally replicating adenovirus.

Methods

We examined midkine mRNA expression and midkine protein expression by seven human pancreatic cancer cell lines (AsPC-1, BxPC-3, CFPAC-1, HPAC, MIAPaCa-2, PANC-1, and Suit-2), as well as by non-cancerous pancreatic tissue and pancreatic cancers. Midkine promoter activity was measured in cancer cell lines by the dual luciferase reporter assay. Adenoviral transduction efficiency was assessed by fluorescent staining of cancer cell lines using adenovirus type 5 containing the green fluorescent protein gene (Ad5GFP). Replication of adenovirus type 5 containing the 0.6 kb midkne promoter (Ad5MK) was assessed by the detection of E1 protein in cancer cell lines. The cytotoxicity of Ad5MK for cancer cells was evaluated from the extent of growth inhibition after viral infection. Infection and replication were also assessed in nude mice with subcutaneous Suit-2 tumors by intratumoral injection of Ad5MK, Ad5GFP, or vehicle. E1a mRNA expression in the treated tumors and expression of the replication-specific adenoviral hexon protein were evaluated. Finally, the anti-tumor activity of Ad5MK against intraperitoneal xenografts of Suit-2 pancreatic cancer cells was examined after intraperitoneal injection of the virus.

Results

Both midkine mRNA expression and midkine protein expression were strong in AsPC-1 and CFPAC-1 cell liens, moderate in BxPC-3, HPAC, and Suit-2 cell lines, and weak in PANC-1 and MIAPaCa-2 cell lines. Expression of midkine mRNA was significantly stronger in pancreatic cancers than in non-cancerous pancreatic tissues. The relative luciferase activity mediated by the 0.6 kb midkne fragment in AsPC-1, PANC-1, and Suit-2 cell lines was approximately 6 to 20 times greater than that in midkne-negative MIAPaCa-2 cell lines. Pancreatic cancer cell lines exhibited a heterogeneous adenoviral transduction profile. E1A expression was higher in cell lines with strong midkine expression than in cell lines with weak midkine expression. Ad5MK showed much greater cytotoxicity for midkine-expressing Suit-2 and PANC-1 cell lines than for midkine-negative MIAPaCa-2 cell lines. In the Suit-2 subcutaneous xenograft model, expression of E1A was detected in Ad5MK-treated tumors, but not in untreated and Ad5GFP-treated tumors. In the Suit-2 intraperitoneal xenograft model, the Ad5MK group survived for significantly longer than the Ad5GFP, PBS, and untreated groups.

Conclusion

Ad5MK has an anti-tumor effect against human pancreatic cancer cell lines that express midkine mRNA. Midkine promoter-based conditionally replicative adenovirus might be a promising new gene therapy for pancreatic cancer.

Adenoviral gene therapy in gastric cancer: A review

Gastric cancer is one of the most common malignancies worldwide. With current therapeutic approaches the prognosis of gastric cancer is very poor, as gastric cancer accounts for the second most common cause of death in cancer related deaths. Gastric cancer like almost all other cancers has a molecular genetic basis which relies on disruption in normal cellular regulatory mechanisms regarding cell growth, apoptosis and cell division. Thus novel therapeutic approaches such as gene therapy promise to become the alternative choice of treatment in gastric cancer. In gene therapy, suicide genes, tumor suppressor genes and anti-angiogenesis genes among many others are introduced to cancer cells via vectors. Some of the vectors widely used in gene therapy are Adenoviral vectors. This review provides an update of the new developments in adenoviral cancer gene therapy including strategies for inducing apoptosis, inhibiting metastasis and targeting the cancer cells.

In vitro evaluation of cancer-specific NF-kappaB-CEA enhancer-promoter system for 5-fluorouracil prodrug gene therapy in colon cancer cell lines

Nuclear factor-kappa B (NF-κB) is a transcription factor with high transcriptional activity in cancer cells. In this study, we developed a novel enhancer–promoter system, κB4-CEA205, in which the basal carcinoembryonic antigen (CEA) promoter sequence (CEA205) was placed downstream of the four tandem-linked NF-κB DNA-binding sites (κB4). In combination with a κB4 enhancer, the transcriptional activity of the CEA promoter was significantly enhanced (three- to eight-fold) in cancer cell lines but not in normal cells. In cancer cell lines, the transcriptional activity of κB4-CEA205 was comparable with that of the SV40 promoter. We also constructed vectors in which the thymidine phosphorylase (TP) cDNA was under the control of CEA205, κB4, κB4-CEA205 and CMV promoters, respectively. TP protein and enzyme activity were detected at comparable levels in κB4-CEA205- and CMV-driven TP cDNA-transfected cancer cell lines (H630 and RKO). The κB4-TP and CEA205-TP-transfected cell lines, respectively, only demonstrated negligible and low levels of TP protein and enzyme activity. Both CMV- and κB4-CEA205-driven TP cDNA transiently transfected cells were 8- to 10-fold sensitised to 5-fluorouracil (5-FU) prodrug, 5′-deoxy-5-fluorouradine (5′-DFUR), in contrast to only 1.5- to 2-fold sensitised by the κB4- and CEA205-driven TP cDNA-transfected cells. The bystander killing effect of CMV- and κB4-CEA205-driven TP cDNA-transfected cells was comparable. This is the first report that indicates that the NF-κB DNA-binding site could be used as a novel cancer-specific enhancer to improve cancer-specific promoter activity in gene-directed enzyme prodrug therapy.

Technology insight: gene therapy and its potential role in the treatment of medullary thyroid carcinoma

Metastatic medullary thyroid cancer (MTC) responds poorly to conventional treatments with chemotherapy and radiotherapy. Gene therapy--the transfer of genetic material for therapeutic purposes--might have therapeutic potential for patients with progressive metastatic MTC that is incurable by conventional treatments. To date, a number of gene-therapy strategies have been explored, primarily those that use replication-deficient adenovirus vectors to transfer therapeutic genes to tumor cells. Tissue-specific expression of the promoter for calcitonin and calcitonin-related polypeptide alpha has allowed therapeutic genes to be specifically expressed in calcitonin-secreting cells and in the MTC tumors derived from them; such tissue-specific expression contributes to improved safety of gene therapies and has the potential to increase their therapeutic index. In addition, the identification of an MTC-specific peptide ligand raises the possibility of developing an MTC-selective vector. In this article, we have described the exciting area of gene therapy in the management of MTC with a focus on preclinical in vitro and in vivo MTC models.

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.

Development and characterization of a synthetic promoter for selective expression in proliferating endothelial cells

BACKGROUND

Systemic administration of non-viral gene therapy provides better access to tumors than local administration. Development of a promoter that restricts expression of cytotoxic proteins to the tumor vasculature will increase the safety of the system by minimizing expression in the non-dividing endothelial cells of the vasculature of non-target tissues.

METHODS

Cell cycle promoters were tested for selective expression in dividing cells vs. non-dividing cells in vitro and promoter strength was compared to the cytomegalovirus (CMV) promoter. Successful promoter candidates were tested in vivo using two proliferating endothelium mouse models. Ovarectomized mice were injected with estradiol prior to lipoplex administration and expression levels were measured in the lungs and uterus 4 days after administration. The second model was a subcutaneous tumor model and expression levels were measured in the lungs and tumors. For both animal models, expression levels from the proliferating endothelium promoter were compared to that obtained from a CMV promoter.

RESULTS

The results showed that the Cdc6 promoter yielded higher expression in proliferating vs. non-proliferating cells. Secondly, promoter strength could be selectively increased in endothelial cells by the addition of a multimerized endothelin enhancer (ET) to the Cdc6 promoter. Thirdly, comparison of expression levels in the lungs vs. uterus in the ovarectomized mouse model and lungs vs. tumor in the mouse tumor model showed expression was much higher in the uterus and the tumor than in the lungs for the ET/Cdc6 promoter, and expression levels were comparable to that of the CMV promoter in the hypervascularized tissues.

CONCLUSIONS

These results demonstrate that the combination of the endothelin enhancer with the Cdc6 promoter yields selective expression in proliferating endothelium and can be used to express cytotoxic proteins to treat vascularized tumors.

Viral and nonviral factors causing nonspecific replication of tumor- and tissue-specific promoter-dependent oncolytic adenoviruses

Restricted replication-competent adenoviruses (RRCAs) using tumor- and tissue-specific promoters (ttsP's) are new tools for cancer gene therapy. In this study we investigated viral and nonviral factors affecting "leakiness" of several ttsP's and their relevance for nonspecific ttsP-dependent RRCA (ttsP-RRCA) replication. The leakiness of the ttsP's in nontarget cells was per se highly variable and correlated with levels of nonspecific ttsP-RRCA replication. Transcriptional regulator elements fused to ttsP's showed variable effects: a hypoxic response element reduced leakiness of an alpha-fetoprotein promoter. In contrast, a mouse tyrosinase enhancer increased leakiness of a tyrosinase promoter, although it was not affected by a human tyrosinase enhancer. Furthermore, leakiness of ttsP's was enhanced by 5'-terminal adenoviral E1A enhancers, and adenoviral E1A-13S was found to be a strong transactivator of ttsP's, leading to "autoactivation" of leaky ttsP-RRCAs. In a proof-of-principle study, ttsP-RRCA replication was shown to be inhibited by a tetracycline-controlled transcriptional silencer via direct ttsP silencing. This opens up the prospect of pharmacological regulation of ttsP-RRCAs. Together, these data indicate that leakiness of ttsP's induced by several factors is a major cause of nonspecific ttsP-RRCA replication. Consideration of these factors may help optimize ttsP-dependent RRCA vectors and may thereby improve their safety.

The insulinoma-associated 1: a novel promoter for targeted cancer gene therapy for small-cell lung cancer

The insulinoma-associated 1 (INSM1) gene is expressed exclusively during early embryonal development, but has been found re-expressed at high levels in neuroendocrine tumors. The regulatory region of the INSM1 gene is therefore a potential candidate for regulating expression of a therapeutic gene in transcriptionally targeted cancer gene therapy against neuroendocrine tumors. We analyzed expression of a reporter gene from a 1.7 kb region of the INSM1 promoter in a large number of small-cell lung cancer (SCLC) cell lines. This INSM1 promoter region showed very high levels of expression in most of the SCLC cell lines and expression was absent in cell lines of non-neuroendocrine origin. Inclusion of the general transcriptional enhancer from SV40 compromised the specificity of the promoter and did not enhance transcription in most of the SCLC cell lines. For comparison, the region of the gastrin releasing peptide (GRP) previously suggested for SCLC gene therapy was analyzed in a similar manner. High expression was observed for a number of cell lines, but unlike for the INSM1 promoter, reporter gene expression from the GRP promoter did not correlate to the relative GRP mRNA levels, demonstrating that this region may not contain all necessary regulatory elements. Expression of the suicide gene herpes simplex virus thymidine kinase (HSV-TK) from the INSM1 promoter in combination with treatment with the prodrug ganciclovir (GCV) caused a significant increase in GCV sensitivity specifically in INSM1-expressing cell lines. The INSM1 promoter is therefore a potential novel tool for transcriptionally targeted gene therapy for neuroendocrine tumors.

Prolonged survival of mice with multiple liver metastases of human colon cancer by intravenous administration of replicable E1B-55K-deleted adenovirus with E1A expressed by CEA promoter

Liver is the most preferential site for metastasis of colon cancer. We, in the present study, constructed a self-replicable adenovirus in which E1A is driven by a CEA promoter and E1B-55K is deleted from the E1B region (AdCEAp/Rep) and examined its effects on multiple metastases of a human colon cancer cell in a mouse xenograft model. We first showed effective replication of the virus in various CEA-producing human colon cancer cells (M7609, HT-29) and subsequent lysis of the infected cells in vitro. We then demonstrated that a single intratumoral injection of the virus (1 x 10(8) PFU/100 microl) induced a complete regression of subcutaneous tumors (M7609) inoculated into nude mice. Further, we demonstrated that systemic administration of the virus (1 x 10(8) PFU/100 microl) through the tail vein to nude mice, which 1 week prior had been inoculated with tumor cells (colon carcinoma cell line HT-29) via the spleen and showed apparent multiple metastases in the liver, effectively suppressed the metastasis formation. The mean survival time of the treated mice was significantly longer than that of the controls. Thus, the systemic administration of AdCEAp/Rep was considered to be effective on multiple liver metastases of CEA-positive colon cancer in a xenograft model.

Adenoviral vectors: development and application

One of the prerequisites for the successful application of gene vaccination and therapy is the development of efficient gene delivery vectors. The rate-limiting nature of vectors was clearly manifested during the first wave of gene therapy testing, resulting in the demand for more effective and suitable vector systems. Adenoviral (Ad) vectors have recently played a central role in the development of gene-vector technology due to their practical advantages and potential applications. A large number of preclinical and clinical studies both have generated an overwhelming amount of data and literature on this vector system. It is the intention of this article to provide a systematic and broad spectrum review of this system, outlining the principle, potential, and limitations, and evaluating the rational development of this delivery approach. Recombinant adenoviruses (Ad), helper cell lines, and related technologies have been developed and applied to many indications owing to progress in virological research, molecular and cellular biology, eukaryotic protein expression, recombinant vaccines, and gene therapy. The technical depth this article covers should be useful to both the experienced researcher and to beginners in this field.

Gene therapy for head and neck cancer

The prognosis of patients with advanced head and neck cancer has not changed significantly in the last twenty years, despite concerted efforts to optimize treatment using conventional modalities such as surgery, radiotherapy and chemotherapy. Novel therapeutic approaches based on our increasing understanding of the molecular changes that underlie the development of cancer have the potential to alter this situation. Gene therapy involves the delivery of genetic sequences in to tumour or normal cells for a therapeutic purpose. A number of viral and non-viral vectors have been developed that have the ability to deliver therapeutic genes specifically to tumours. These therapeutic genes can exert their effects by correcting existing genetic abnormalities, by killing cells directly or indirectly through recruitment of the immune system. In this review, the various gene therapy strategies that are under development are presented with particular reference to the treatment of head and neck cancer.

The use of 19F spectroscopy and diffusion-weighted MRI to evaluate differences in gene-dependent enzyme prodrug therapies

To evaluate noninvasive measures of gene expression and tumor response in a gene-dependent enzyme prodrug therapy (GDEPT), a bifunctional fusion gene between Saccharomyces cerevisiae cytosine deaminase (CD) and Haemophilus influenzae uracil phosphoribosyltransferase (UPRT) was constructed. CD deaminates 5-fluorocytosine (5FC) to 5-fluorouracil (5FU), and UPRT subsequently converts 5FU to fluorouridine monophosphate, and both of these reactions can be monitored noninvasively in vitro and in vivo using 19F magnetic resonance spectroscopy (MRS). Following transient transfection the CD-UPRT fusion protein exhibited both UPRT and CD enzymatic activities as documented by 19F MRS. In addition, an increase in CD activity and thermal stability was witnessed for the fusion protein compared to native CD. Stable expression of CD-UPRT in 9L glioma cells increased both 5FC and 5FU sensitivity in vitro compared to CD-expressing and wild-type 9L cells. Noninvasive 19F MRS of both CD and UPRT gene function in vivo demonstrated that in animals bearing CD-expressing tumors there was limited conversion of 5FC to 5FU with no measurable accumulation of cytotoxic fluorinated nucleotides (F-nucs). In contrast, CD-UPRT-expressing tumors had increased CD gene activity with a threefold higher intratumoral accumulation of 5FU and significant generation of F-nucs. Finally, CD-UPRT yielded increased efficacy in an orthotopic animal model of high-grade glioma. More importantly, early changes in cellular water mobility, which are felt to reflect cellular death, as measured by diffusion-weighted MRI, were predictive of both durable response and increased animal survival. These results demonstrate the increased efficacy of the CD-UPRT GDEPT compared to CD alone both biochemically and in a preclinical model and validate both 19F MRS and diffusion-weighted MRI as tools to assess gene function and therapeutic efficacy.

Carcinoembryonic antigen directed herpes viral oncolysis improves selectivity and activity in colorectal cancer

BACKGROUND

G207 is an oncolytic herpes virus whose replicative cycle requires cellular ribonucleotide reductase (RR) for viral DNA synthesis. We attempt to enhance viral cytotoxicity in carcinoembryonic antigen (CEA)-producing colorectal cancer (CRC) cells through CEA-driven RR production.

METHODS

CEA enzyme-linked immunosorbent assay was performed on LS174T and HCT-8 human CRC cells. The CEA enhancer-promoter (CEA E-P) was functionally assessed by luciferase assay. CEA E-P was cloned upstream of UL39, the gene encoding the large subunit of RR. Cells were transfected with CEA E-P/UL39 and infected with G207 for cytotoxicity assays. LS174T, with or without CEA E-P/UL39, were implanted into athymic mouse flanks (n = 28) and treated with G207.

RESULTS

CEA levels were 7-fold higher in LS174T versus HCT-8 ( P <.00001). CEA E-P increased luciferase expression 7.5-fold in LS174T ( P <.01), with no increase in HCT-8. G207 cytotoxicity of'CEA E-P/UL39-transfected LS174T cells increased 69% by day 10 versus nontransfected cells ( P <.001), with no significant increase in HCT-8. Combining CEA E-P/UL39 with G207 in LS174T flank tumors resulted in a 65% decrease in tumor volume versus G207, phosphate-buffered saline, or'CEA E-P/UL39 alone ( P <.0001).

CONCLUSIONS

CEA-driven RR production by CEA-secreting CRC cells significantly improves oncolytic viral cytotoxicity and specificity in vitro, and reduces tumor burden in vivo.

Pharmacological and genetic modulation of Wnt-targeted Cre-Lox-mediated gene expression in colorectal cancer cells

Wnt-targeted gene therapy has been proposed as a treatment for human colorectal cancer (CRC). The Cre-Lox system consists of methodology for enhancing targeted expression from tissue-specific or cancer-specific promoters. We analyzed the efficiency of Wnt-specific promoters as drivers of the Cre-mediated activity of a luciferase reporter gene or cell death effector gene in CRC cell lines in the presence and absence of two modulators of Wnt activity, sodium butyrate and lithium chloride. Butyrate is present in the colonic lumen after digestion of fiber-rich foods, whereas the colonic lumen is readily accessible to lithium chloride. In both SW620 and HCT-116 CRC cells, a physiologically relevant concentration of butyrate upregulated reporter and effector activity and altered the Wnt-specific expression pattern. Lithium chloride markedly enhanced Cre-Lox-mediated Wnt-specific reporter expression only in APC wild-type CRC cells. Possibilities for genetic modulation of the proposed CRC therapy included Wnt-specific expression of a floxed Lef1-VP16 fusion that enhanced Wnt-specific cell death and of a floxed dominant-negative Tcf4 that specifically downregulated endogenous Wnt activity. These findings demonstrated that the Cre-Lox system, in combination with pharmacological and genetic modulators, represents effective methodology for enhancing Wnt-targeted gene therapy.

Transcriptionally targeted gene therapy to detect and treat cancer

The greatest challenge in cancer treatment is to achieve the highest levels of specificity and efficacy. Cancer gene therapy could be designed specifically to express therapeutic genes to induce cancer cell destruction. Cancer-specific promoters are useful tools to accomplish targeted expression; however, high levels of gene expression are needed to achieve therapeutic efficacy. Incorporating an imaging reporter gene in tandem with the therapeutic gene will allow tangible proof of principle that gene expression occurs at the correct location and at a sufficient level. Gene-based imaging can advance cancer detection and diagnosis. By combining the cancer-targeted imaging and therapeutic strategies, the exciting prospect of a 'one-two punch' to find hidden, disseminated cancer cells and destroy them simultaneously can potentially be realized.

Clinical development of gene therapy for colorectal cancer

Colorectal cancer (CRC) is the second most common type of malignancy in Western nations. Improvements in surgical and radiotherapeutic techniques and the increased availability of new cytotoxic drugs have improved outcome, but 50% of patients still die from recurrent or metastatic disease. Several features of its natural history render CRC a good candidate for gene therapy. Techniques include gene replacement, virus-directed enzyme-prodrug therapy, immune manipulation and virotherapy, all of which have entered clinical trials.

Gene therapy for colorectal cancer

Colorectal cancer is an important public health problem worldwide. Gene therapy has therapeutic potential for patients with advanced or recurrent colorectal cancer, incurable by conventional treatments. To date, many strategies of gene therapy have been explored, including mutant gene correction, prodrug activation, immune stimulation and genetically-modified oncolytic viruses. Although the preclinical results of gene therapy for colorectal cancer have shown promise, gene therapy is still at an early stage of clinical development and has not yet shown a significant therapeutic benefit for patients. The main obstacles for introduction of gene therapy to patients are poor targeting selectivity of the vectors and inefficient gene transfer. As the science supporting tumour-selective vectors evolves, gene therapy may expand rapidly in the clinical practice of colorectal cancer treatment.

Transcriptional Targeting in Cancer Gene Therapy

Cancer gene therapy has been one of the most exciting areas of therapeutic research in the past decade. In this review, we discuss strategies to restrict transcription of transgenes to tumour cells. A range of promoters which are tissue-specific, tumour-specific, or inducible by exogenous agents are presented. Transcriptional targeting should prevent normal tissue toxicities associated with other cancer treatments, such as radiation and chemotherapy. In addition, the specificity of these strategies should provide improved targeting of metastatic tumours following systemic gene delivery. Rapid progress in the ability to specifically control transgenes will allow systemic gene delivery for cancer therapy to become a real possibility in the near future.

Improvement of carcinoembryonic antigen-specific prodrug gene therapy for experimental colon cancer

BACKGROUND

Improvement of tumor-specific gene expression is very important for achieving successful effects in prodrug gene therapy for advanced cancer with metastatic lesions. We used the Cre/loxP system for enhancing carcinoembryonic antigen (CEA)-specific prodrug gene therapy of cytosine (CD)/5-fluorocytosine (5-FC) for the treatment of a colon cancer model accompanied with liver metastases.

METHODS

Orthotopic colon cancer models were developed. Seven days later, adenovirus vector (3 x 10(9) pfu)was injected into the abdominal cavity, and 5-FC was administered for the next 10 days.

RESULTS

In these models, the double administration of AxCEANCre expressing Cre recombinase under the control of the CEA promoter, and AxCALNLCD expressing the CD gene under the control of the CAG promoter by the Cre-mediated switching system, completely inhibited liver metastases, and significantly reduced primary tumor volume compared to the administration of Mock or AxCEACD (P <.001). The survival periods of the mice treated with AxCEANCre and AxCALNLCD were longer than mice treated with Mock or AxCEACD, and longer than the mice treated with AxCACD (P <.05).

CONCLUSIONS

The enhanced CEA-specific prodrug gene therapy using the Cre/loxP system was useful for the treatment of advanced colon cancer with liver metastases, implicating clinical application.

Purification of a functional gene therapy vector derived from Moloney murine leukaemia virus using membrane filtration and ceramic hydroxyapatite chromatography

The ability of membrane ultra- and diafiltration and two chromatography media, Matrex Cellufine Sulfate (Millipore) and Macro-Prep ceramic hydroxyapatite (Bio-Rad), to adsorb, elute, and purify gene therapy vectors based on Moloney murine leukaemia virus (MoMuLV) carrying the 4070A amphotropic envelope protein was studied. Membrane ultra- and diafiltration provided virus concentration up to 160-fold with an average recovery of infectious viruses of 77 +/- 14%. In batch experiments, Macro-Prep ceramic hydroxyapatite (type 2, particle size 40 microm) proved superior to Matrex Cellufine Sulfate for MoMuLV vector particle adsorption. Furthermore, functional vector particles could be eluted using phosphate buffer pH 6.8 (highest titres from >or=300 mM phosphate) from the Macro-Prep adsorbent, with higher specific titres (cfu/mg protein) than the starting material. Similar results were obtained when this ceramic hydroxyapatite was packed into a column and used in a liquid chromatography system. Recovery of transduction-competent virus was between 18 and 31% for column experiments and 32 and 46% for batch experiments.

Regulation of herpes simplex virus 1 replication using tumor-associated promoters

OBJECTIVE

To investigate use of transcriptional regulatory elements (promoters) for tumor-associated antigens to achieve HSV-1 replication preferentially in cells that overexpress the tumor-associated antigens.

SUMMARY BACKGROUND DATA

An important advantage of replicating viruses for cancer therapy is their ability to simultaneously destroy tumor cells by replication and release progeny virion to infect and destroy adjacent cancer cells. This strategy requires regulation of the viral life cycle to obtain robust replication in neoplastic cells and minimize replication in nonneoplastic cells.

METHODS

Promoters for the human carcinoembryonic antigen (CEA) and MUC1/DF3 tumor-associated antigens were characterized and cloned into HSV-1 mutants as heterologous promoters regulating expression of two different HSV-1 genes. Viral replication in tumor cells and cytotoxicity was quantified with in vitro assays. Antineoplastic efficacy was characterized in a flank tumor xenograft model.

RESULTS

Several CEA promoters were cloned and characterized using luciferase reporter assays. The most specific promoter was used to construct and isolate two different HSV-1 mutants in which critical genes are regulated by this promoter (ICP4 and gamma(1) 34.5). Similarly, the promoter for the DF3/MUC1 tumor-associated antigen was cloned into a third HSV-1 mutant such that it regulates expression of gamma(1) 34.5. Regulation of ICP4 expression by the CEA promoter during HSV-1 infection overly attenuates viral replication. Regulation of gamma(1) 34.5 expression by either the CEA promoter or the MUC1/DF3 promoter during HSV-1 infection modulates viral replication, with preferential replication in cells that overexpress the corresponding tumor-associated antigen. A single intratumoral inoculation of an HSV-1 mutant with the MUC1/DF3 promoter regulating gamma(1) 34.5 expression results in significant antineoplastic activity in MUC1-positive pancreatic carcinoma xenografts as compared to mock inoculation.

CONCLUSIONS

Promoters for tumor-associated antigens may be incorporated into the HSV-1 genome to regulate HSV-1 replication. The choices of HSV-1 gene and tumor-associated promoter are important determinants of success of this strategy. Because of its preferential replication in MUC1-positive tumors, an HSV-1 mutant with the MUC1/DF3 promoter regulating gamma(1) 34.5 expression will undergo further examination as a novel cancer therapy agent.

Introduction to cancer gene therapy

Over the past decade, the unprecedented growth in science and technology has fueled the development of novel treatment strategies to combat disease. The creative and innovative efforts of scientists and clinicians to overcome the multitude of unforeseen obstacles to success is no better exemplified than in the field of cancer gene therapy. Since its inception, developers of cancer gene therapy have been charged with the challenge of altering basic tumor biology or, alternatively, the host responses for the purpose of tumor eradication and prevention. Several major therapeutic strategies have emerged from preclinical studies, and results from these early studies hold promise for altering the clinical outcome in a variety of malignancies. These strategies may be broadly subcategorized and range in intent from alteration of the tumor cell phenotype by replacement of defective cellular response genes (e.g., mutated or deleted tumor suppressor genes) to the enhancement of the immunological response to cancer (e.g., amplification of the cell surface antigen signature or modulation of the host response). Not surprisingly, the increasingly intricate nature of tumor biology revealed over the past several years has effectively raised the bar of success for those involved in the development of effective molecular and cancer gene therapy strategies. This, in turn, has led to the development of more complex therapies that frequently draw upon multiple disciplines in an effort to optimize treatment response.

Adenoviral gene therapy

As of May 2001, 532 gene therapy protocols had been approved for evaluation in clinical trials; however, only five of those had been evaluated in phase III clinical trials. Among the most commonly used vectors for the delivery of genetic material into human cells are the adenoviruses. Remarkable progress has been made with these vectors in the last decade, but some shortcomings continue to challenge investigators. The newly acquired knowledge of the adenoviral life cycle and the positive outcomes from phase II clinical trials have led to the application of vectors engineered to selectively target tumor tissue under controlled promoters.

Tumor antigen-specific induction of transcriptionally targeted retroviral vectors from chimeric immune receptor-modified T cells

High-level systemic delivery of viral vectors to tumors has proved problematic as a result of immune neutralization, nonspecific adhesion, and clearance of circulating viral particles. Some cell types localize to tumors in response to particular biological properties associated with tumor growth. Their use to deliver viral vectors to tumors would allow precious viral stocks to be protected until they can be released at high local concentrations. Here, we describe a mechanism by which retroviral vector production by T cells can be regulated by a tumor-specific trigger through engagement of a chimeric immune receptor (CIR) with its target antigen. The virus that is released from the T cells can also be transcriptionally targeted. Finally, we show that it is possible to use vector-loaded, antigen-triggered human T cells as therapeutic, tumor-specific vector delivery cells in models of both local intratumoral and systemic delivery to both lung and liver metastases. This strategy incorporates multiple levels of targeting into the delivery system at the stages of surface targeting, viral production, and gene expression.

Imaging Expression of Cytosine Deaminase-Herpes Virus Thymidine Kinase Fusion Gene (CD/TK) Expression with [124I]FIAU and PET

Double prodrug activation gene therapy using the Escherichia coli cytosine deaminase (CD)herpes simplex virus type 1 thymidine kinase ( HSV1-tk) fusion gene ( CD/TK) with 5-fluorocytosine (5FC), ganciclovir (GCV), and radiotherapy is currently under evaluation for treatment of different tumors. We assessed the efficacy of noninvasive imaging with [124I]FIAU (2′-fluoro-2′-deoxy-1-β-d-arabinofuranosyl-5-iodo-uracil) and positron emission tomography (PET) for monitoring expression of the CD/TK fusion gene. Walker-256 tumor cells were transduced with a retroviral vector bearing the CD/TK gene (W256CD/TK cells). The activity of HSV1-TK and CD subunits of the CD/TK gene product was assessed in different single cell-derived clones of W256CD/TK cells using the FIAU radiotracer accumulation assay in cells and a CD enzyme assay in cell homogenates, respectively. A linear relationship was observed between the levels of CD and HSV1-tk subunit expression in corresponding clones in vitro over a wide range of CD/TK expression levels. Several clones of W256CD/TK cells with significantly different levels of CD/TK expression were selected and used to produce multiple subcutaneous tumors in rats. PET imaging of HSV1-TK subunit activity with [124I]FIAU was performed on these animals and demonstrated that different levels of CD/TK expression in subcutaneous W256CD/TK tumors can be imaged quantitatively. CD expression in subcutaneous tumor sample homogenates was measured using a CD enzyme assay. A comparison of CD and HSV1-TK subunit enzymatic activity of the CD/TK fusion protein in vivo showed a significant correlation. Knowing this relationship, the parametric images of CD subunit activity were generated. Imaging with [124I]FIAU and PET could provide pre- and posttreatment assessments of CD/TK-based double prodrug activation in clinical gene therapy trials.

Conditional gene targeting for cancer gene therapy

Current treatment of solid tumors is limited by severe adverse effects, resulting in a narrow therapeutic index. Therefore, cancer gene therapy has emerged as a targeted approach that would significantly reduce undesired side effects in normal tissues. This approach requires a clear understanding of the molecular biology of both the malignant clone and the biological vectors that serve as vehicles to target cancer cells. In this review we discuss novel approaches for conditional gene expression in cancer cells. Targeting transgene expression to malignant tissues requires the use of specific regulatory elements including promoters based on tumor biology, tissue-specific promoters and inducible regulatory elements. We also discuss the regulation of both replication and transgene expression by conditionally-replicative viruses. These approaches have the potential to restrict the expression of transgenes exclusively to tissues of interest and thereby to increase the therapeutic index of future vectors for cancer gene therapy.

Tissue-specific expression of a suicide gene for selective killing of neuroblastoma cells using a promoter region of the NCX gene

The human NCX gene, a homologue of the murine neural crest homeobox (Ncx/Hox11L.1) gene whose expression is restricted to a subset of neural crest-derived tissues, was expressed in human neuroblastoma cells but not in other tumors or fibroblasts. A 4.5-kb genomic fragment in the 5'-flanking region of the NCX gene efficiently transcribed the fused luciferase reporter gene in human neuroblastoma cells but not in non-neuroblastoma cells. Sequential deletion of this regulatory region from the 5' side demonstrated that a 1.7-kb fragment upstream from the start codon retained the preferential promoter activity in neuroblastoma cells. The transcriptional activation by the NCX promoter was stronger than that by the SV40 T antigen promoter in human neuroblastoma cells. Transfection of neuroblastoma cells with the NCX promoter-linked herpes simplex virus-thymidine kinase (HSV-TK) gene increased their sensitivity to ganciclovir. The regulatory region of the NCX gene is thus useful for neuroblastoma-specific suicide gene therapy.

A minimum c-erbB-2 promoter-mediated expression of herpes simplex virus thymidine kinase gene confers selective cytotoxicity of human breast cancer cells to ganciclovir

The c-erbB-2 gene is frequently overexpressed in human breast cancers as a result of gene amplification and/or elevated transcription. We therefore examined a possible usage of promoter regions of the c-erbB-2 gene to express a suicide gene preferentially in breast cancer cells. Previous studies did not reveal the minimal promoter region that enabled transcriptional activation specific to breast cancer cells. The present reporter gene assays using deletion mutants of the c-erbB-2 promoter region demonstrated that the 251-bp (-213/+38 from the transcriptional start site), but not the 125-bp, fragment (-87/+38) could direct transcription of the linked luciferase gene better than the SV40 immediate early promoter in breast cancer cells. In contrast, the 251-bp fragment-mediated promoter activity in nonbreast cancer cells and in normal fibroblasts was lower than the activity by the SV40 promoter. The 126-bp fragment (-213/-87) thereby contains a cis-acting element(s), which is responsible for the preferential transcriptional activity in breast cancer cells. An electrophoretic mobility shift assay suggested that a possible modification of a transcriptional factor was involved in the tumor specificity. Transfection with the plasmid DNA containing the herpes simplex virus thymidine kinase gene linked with the 251-bp promoter (p256-TK) resulted in increased sensitivity to ganciclovir in breast cancer, but not in nonbreast cancer cells. Administration of ganciclovir into nude mice bearing human breast tumors that were transfected with the p256-TK DNA suppressed subsequent growth of the transplanted tumors. These results suggest that delivery of a suicide gene linked with the 251-bp c-erbB-2 promoter can be a feasible therapeutic strategy specific to breast cancer.

Enhanced suicide gene effect by adenoviral transduction of a VP22-cytosine deaminase (CD) fusion gene

The low transduction efficiency of viral and nonviral vectors is a major limitation in tumour gene therapy. The HSV-1 tegument protein VP22 has been shown to exhibit a novel intercellular transport property. VP22 wild-type as well as VP22 fusion proteins efficiently spread from the original expressing cell to numerous neighbouring cells, so that protein transport by VP22 chimaeric polypeptides into the surrounding cells offers a possible compensation for the inadequate gene transfer efficiencies. To improve the therapeutic efficacy of the E. coli cytosine deaminase (CD) suicide gene we made use of the VP22 transport property in CD transducing adenoviral (Ad) vectors. C- and N-terminal fusions of CD linked in-frame with VP22 were generated and cloned into recombinant adenoviral vectors. Following in vitro transduction immunofluorescence analysis of Ad-transduced producer cells coplated with naive cells confirmed that the characteristic foci pattern of central producer and adjoining neighbour cells displaying nuclear staining was retained. After transduction of rat hepatoma cells with adenoviral vectors and subsequent incubation with the prodrug 5-FC, we observed enhanced cell cytotoxicity when comparing the CD-VP22 fusion (Ad-CD-VP22) with Ad-vectors expressing the CD gene only (Ad-CD). Thereby employment of Ad-vectors encoding VP22 fusion proteins opens up new possibilities to potentiate the efficiency of suicide gene therapy for the treatment of solid tumours.

Hepatic intra-arterial delivery of a retroviral vector expressing the cytosine deaminase gene, controlled by the CEA promoter and intraperitoneal treatment with 5-fluorocytosine suppresses growth of colorectal liver metastases

Targeting of colorectal liver metastases by regional gene therapy was tested in a clinically relevant syngeneic model. First, the CEA-CD-113 retroviral vector containing the cytosine deaminase gene controlled by the CEA specific tumour cell promoter, was shown in vitro to convert 5-fluorocytosine to 5-fluorouracil, resulting in cancer cell killing with a large bystander effect. Second, 10 days after the establishment of liver metastases, retroviral vectors were delivered to the liver by hepatic artery injection. After 5-fluorocytosine administration for 7 days, most surface metastases disappeared and tumour volumes were suppressed up to 8.2-fold. The results support the development of this approach for patient treatment.

Gene delivery from the E3 region of replicating human adenovirus: evaluation of the 6.7 K/gp19 K region

The use of genetically engineered, replication-selective viruses to treat cancer is being realized with viruses such as ONYX-015, a human adenovirus that selectively destroys p53 mutant cancer cells. To enhance further the clinical efficacy of ONYX-015 and viruses like it, we have developed a novel gene delivery system for replicating adenoviruses. This system has two unique features. First, it uses the endogenous adenoviral gene expression machinery (promoter, splicing, polyadenylation) to drive transgene expression. Second, a single region or gene in the multi-gene E3 transcription unit is selectively substituted for by the therapeutic transgene(s). Analyzing various transgene substitutions for the 6.7 K/gp19 K region of E3, we demonstrate the following: (1) transgene expression in this system is predictable and mimics the substituted endogenous gene expression pattern, (2) expression of surrounding E3 genes can be retained, (3) the insertion site choice can effect both the transgene expression level and the viral life cycle, and, (4) expression levels from this system are superior to those generated from a replication-defective virus using the HCMV enhancer-promoter and this is dependent on viral DNA replication. This unique methodology has broad application to the rapidly evolving field of replicating virus-based therapies.

Biological considerations in lung cancer

Our understanding of lung cancer biology has rapidly expanded in recent years. Lung cancer, unlike most human cancers, can be traced to an environmental risk factor in the majority of cases, and this fact is reflected in the vast number of genetic alterations discovered in lung tumors whose pathogenesis is believed to be mediated by carcinogen exposure. The discovery of these alterations has led to a greater understanding of tumor development. The dramatic progress in the understanding of the genetic and molecular basis of oncogenesis and the induction of immunity has led to a rejuvenation of efforts to apply this new knowledge to this common and refractory disease. Further, the resurgent interest in cancer immunology and tumor-host interactions holds promise for the development of new approaches to treatment based on harvesting the immune systems ability to recognize these alterations. Hopefully, this understanding will lead to novel approaches with real and convincing clinical efficacy once some of these strategies are tested in carefully performed randomized clinical trials with appropriate power to detect meaningful differences.

Expression of herpes simplex virus-thymidine kinase gene controlled by a promoter region of the midkine gene confers selective cytotoxicity to ganciclovir in human carcinoma cells

A selective expression of suicide gene(s) in tumor cells should produce a preferential cytotoxic effect on tumors. Promoter region(s) of a gene that is expressed in tumors but not in normal tissues can be useful for tumor-specific transcription of a suicide gene. Midkine (MK), a growth/differentiation factor, is expressed predominantly in various types of human tumors, whereas its expression in adult normal tissues is highly restricted. In our study, we showed that a 2.3-kb fragment of genomic DNA in the 5' upstream region of the MK gene could activate transcription of a fused reporter gene in MK-positive cells but not in MK-negative cells. Efficiency of the cis-acting sequence to permit expression of an exogenous gene in tumor cells was comparable with that of the SV40 promoter. Regulated expression of the herpes simplex virus-thymidine kinase (HSV-TK) gene under the control of the MK promoter conferred increased sensitivity to ganciclovir (GCV) on MK-positive tumor cells. Administration of GCV into nude mice that were implanted with MK-positive tumor cells that expressed the HSV-TK gene under the control of the MK promoter could suppress the subsequent tumor growth. Expression of therapeutic genes restricted to tumors can be achieved by the use of the putative cis-acting MK promoter.

Augmenting transgene expression from carcinoembryonic antigen (CEA) promoter via a GAL4 gene regulatory system

Though extensively studied, the use of tissue- or cell-type-specific promoters to target transgene expression is hampered by their weak activity. We hypothesized that this problem could be addressed by using a GAL4 gene regulatory system, wherein a weak, tissue-specific promoter would drive expression of the GAL4/VP16 fusion protein (GV16), which in turn would transactivate a minimal synthetic promoter, GAL4/TATA (GT), upstream of a transgene. To test this hypothesis, we constructed adenoviral vectors expressing a lacZ or GV16 gene driven by a carcinoembryonic antigen (CEA) promoter (Ad/CEA-LacZ or Ad/CEA-GV16) and evaluated levels of transgene expression they produced in cultured cells and in subcutaneous tumors after intratumoral administration. In CEA-positive cells, treatment with Ad/CEA-GV16 + Ad/GT-LacZ versus Ad/CEA-LacZ increased transgene expression 20- to 100-fold. In CEA-negative cells, treatment with Ad/CEA-GV16 + Ad/GT-LacZ increased transgene expression to a much lower degree (6- to 8-fold). In addition, analysis of Bax gene-mediated cell death revealed that this system can be used to avoid Bax's toxic effects on CEA-negative cells without compromising its ability to kill CEA-positive cells in vitro and in vivo. Thus, the combination of a tissue-specific promoter with the GAL4 gene regulatory system could be useful for targeting transgene expression.

Enhancement of radiotherapy by hyperthermia-regulated gene therapy

PURPOSE

Interleukin 12 (IL-12) has shown strong antitumoral effects in numerous pre-clinical studies and appears to act synergistically with radiation in murine tumors. The major impediment to its clinical use has been its systemic toxicity. While using intratumorally injected viral gene therapy vectors encoding IL-12 reduces systemic side effects substantially, elevated systemic transgene levels are still observed because adenovirus can reach the circulation. Further restricting IL-12 expression in the tumor is therefore desirable in a combined radiation and adenovirus mediated cancer gene therapy regimen. METHODS AND MATERILAS: Hyperthermia-regulated gene therapy was tested in a nonimmunogenic B16.F10 melanoma line that is syngeneic with C57BL/6 mice. For hyperthermic gene therapy, an adenoviral vector coding for IL-12 under the control of the promoter of the human heat shock protein 70B (hsp70B) was used. One week after transplantation (at a 5-7 mm diameter), tumors were irradiated with 3 x 11 Gy (mo-we-fri). Adenovirus was injected at 3 x 10(8) pfu/tumor 24 h before the last radiation fraction or 3 days afterwards. Hyperthermia was performed 24 h later at 42.5 degrees C. Growth delay to reaching 3 times initial tumor volume was chosen as the biologic endpoint. IL-12 levels in tumor and serum were determined by using the enzyme-linked immunosorbant assay (ELISA).

RESULTS

Adenovirus mediated intratumoral expression of IL-12 under the control of a heat inducible promoter in combination with hyperthermia is almost as effective as that under the control of a constitutive cytomegaly virus (CMV) promoter while systemic transgene levels are substantially reduced with the heat inducible promoter. The response to radiotherapy is improved considerably when combined with heat inducible gene therapy without apparent systemic toxicity. When used as a single dose, applying IL-12 gene therapy after completion of radiotherapy appears to be beneficial.

CONCLUSIONS

Hyperthermia-regulated gene therapy in combination with radiation is feasible and therapeutically effective in murine tumors with no apparent systemic toxicity.

Transcriptional control: an essential component of cancer gene therapy strategies?

The therapeutic index of cancer gene therapy approaches will, at least in part, be dictated by the spatial and temporal control of expression of the therapeutic transgenes. Strategies which allow precise control of gene transcription are likely to play a crucial role in the future pre-clinical and clinical development of gene therapy. In this review, we discuss these issues as they relate to tissue and tumor specific promoters. In addition, the exciting opportunities offered by the development of regulated gene expression systems using small molecules, radiation and heat are reviewed. It is realistic to expect that the future offers the prospect of amalgamating elements of a number of these different systems in a co-ordinated gene delivery approach with the potential to increase the efficacy and reduce the toxicity of treatment.