The dominant negative H-ras mutant, N116Y, suppresses growth of metastatic human pancreatic cancer cells in the liver of nude mice

Applications of tissue-specific and cancer-selective gene promoters for cancer diagnosis and therapy

Current treatment of solid tumors with standard of care chemotherapies, radiation therapy and/or immunotherapies are often limited by severe adverse toxic effects, resulting in a narrow therapeutic index. Cancer gene therapy represents a targeted approach that in principle could significantly reduce undesirable side effects in normal tissues while significantly inhibiting tumor growth and progression. To be effective, this strategy requires a clear understanding of the molecular biology of cancer development and evolution and developing biological vectors that can serve as vehicles to target cancer cells. The advent and fine tuning of omics technologies that permit the collective and spatial recognition of genes (genomics), mRNAs (transcriptomics), proteins (proteomics), metabolites (metabolomics), epiomics (epigenomics, epitranscriptomics, and epiproteomics), and their interactomics in defined complex biological samples provide a roadmap for identifying crucial targets of relevance to the cancer paradigm. Combining these strategies with identified genetic elements that control target gene expression uncovers significant opportunities for developing guided gene-based therapeutics for cancer. The purpose of this review is to overview the current state and potential limitations in developing gene promoter-directed targeted expression of key genes and highlights their potential applications in cancer gene therapy.

An Automated High-throughput Array Microscope for Cancer Cell Mechanics

Changes in cellular mechanical properties correlate with the progression of metastatic cancer along the epithelial-to-mesenchymal transition (EMT). Few high-throughput methodologies exist that measure cell compliance, which can be used to understand the impact of genetic alterations or to screen the efficacy of chemotherapeutic agents. We have developed a novel array high-throughput microscope (AHTM) system that combines the convenience of the standard 96-well plate with the ability to image cultured cells and membrane-bound microbeads in twelve independently-focusing channels simultaneously, visiting all wells in eight steps. We use the AHTM and passive bead rheology techniques to determine the relative compliance of human pancreatic ductal epithelial (HPDE) cells, h-TERT transformed HPDE cells (HPNE), and four gain-of-function constructs related to EMT. The AHTM found HPNE, H-ras, Myr-AKT, and Bcl2 transfected cells more compliant relative to controls, consistent with parallel tests using atomic force microscopy and invasion assays, proving the AHTM capable of screening for changes in mechanical phenotype.

Hepatocyte growth factor inhibits anoikis of pancreatic carcinoma cells through phosphatidylinositol 3-kinase pathway

OBJECTIVES

Escape from anoikis, apoptosis induced by loss of cell-cell or cell-extracellular matrix interactions, is important in tumor invasion and metastasis. Hepatocyte growth factor (HGF) is known to play a pivotal role in pancreatic carcinomas. This study aimed to determine the antianoikis effect of HGF in pancreatic carcinoma cells.

METHODS

Antianoikis effect of HGF was evaluated in human pancreatic carcinoma cells in nonadherent culture with or without anti-E-cadherin antibody. Signal pathways were investigated by Western blot analysis and inhibition assay using inhibitors for phosphatidylinositol 3-kinase and p38.

RESULTS

Pancreatic carcinoma cells underwent anoikis in nonadherent culture. However, some of the carcinoma cells survived by forming aggregations in suspension. Anti-E-cadherin antibody dissociated the aggregations, and the separated cells underwent additional anoikis. Hepatocyte growth factor inhibited anoikis irrespective of E-cadherin-mediated cell-cell contact. Inhibition of the phosphatidylinositol 3-kinase/Akt pathway abolished the antianoikis effect of HGF. Phosphorylation of Akt was induced by HGF, and the phosphorylated Akt persisted even when E-cadherin was inhibited.

CONCLUSIONS

Hepatocyte growth factor inhibits anoikis of pancreatic carcinoma cells through phosphatidylinositol 3-kinase pathway in which activation of Akt may be involved. It is thus supposed that HGF may have a potent role in invasion and metastasis of pancreatic carcinoma cells by exerting its antianoikis effect.

Pancreatic cancer: gene therapy approaches and gene delivery systems

IMPORTANCE OF THE FIELD

Due to the absence of early diagnosis, the highly invasive and metastatic features and the lack of effective therapeutic modalities, the prognosis of patients with pancreatic cancer is poor. Gene therapy is currently regarded as a potential and promising therapeutic modality for pancreatic cancer.

AREAS COVERED IN THIS REVIEW

This article summarizes an update of gene therapy approaches and reviews the latest progress in gene delivery systems that have been tested on pancreatic cancer.

WHAT THE READER WILL GAIN

The treatment effectiveness of gene combination therapy is better than that of the regulation of single-gene or single gene therapy approaches. Naked DNA is limited because of degradation by intracellular and extracellular nucleases. Virus vectors show high transfection efficiency but are limited due to immunogenicity, inflammatory response and potential carcinogenicity. Non-viral vectors, such as cationic polymers or inorganic nanoparticles, show an important feature that they can be easily modified, and the progress of materials science will provide more and better non-viral vectors, accordingly improving the efficiency and safety of gene therapy, which will make them the most promising vectors for pancreatic cancer.

RNAi targeting EZH2 inhibits tumor growth and liver metastasis of pancreatic cancer in vivo

The function of EZH2 in tumorigenesis and liver metastasis of pancreatic cancer has never been elucidated in vivo. EZH2 was overexpressed in pancreatic carcinomas and its overexpression was associated with tumor differentiation and pT status. Suppression of EZH2 caused a significant growth inhibition of pancreatic cancer cells in vitro and markedly diminished their tumorigenicity in vivo. Knock-down of EZH2 inhibited liver metastasis of pancreatic cancer in vivo. EZH2 has a crucial role in tumor growth and liver metastasis of pancreatic cancer.

Structure of the dominant negative S17N mutant of Ras

The use of the dominant negative mutant of Ras has been crucial in elucidating the cellular signaling of Ras in response to the activation of various membrane-bound receptors. Although several point mutants of Ras exhibit a dominant negative effect, the asparagine to serine mutation at position 17 (S17N) remains the most popular and the most effective at inhibiting the activation of endogenous Ras. It is now widely accepted that the dominant negative effect is due to the ability of the mutant to sequester upstream activators and its inability to activate downstream effectors. Here, we present the crystal structure of RasS17N in the GDP-bound form. In the three molecules that populate the asymmetric unit, the Mg(2+) ion that normally coordinates the beta-phosphate is absent because of steric hindrance from the Asn17 side chain. Instead, a Ca(2+) ion is coordinating the alpha-phosphate. Also absent from one molecule is electron density for Phe28, a conserved residue that normally stabilizes the nucleotide's guanine base. Except for Phe28, the nucleotide makes conserved interactions with Ras. Combined, the inability of Phe28 to stabilize the guanine base and the absence of a Mg(2+) ion to neutralize the negative charges on the phosphates explain the weaker affinity of GDP for Ras. Our data suggest that the absence of the Mg(2+) should also dramatically affect GTP binding to Ras and the proper positioning of Thr35 necessary for the activation of switch 1 and the binding to downstream effectors, a prerequisite for the triggering of signaling pathways.

Biological approaches to therapy of pancreatic cancer

Pancreatic cancer is a lethal disease and notoriously difficult to treat. Only a small proportion is curative by surgical resection, whilst standard chemotherapy for patients with advanced disease has only modest effect with substantial toxicity. Clearly there is a need for the continual development of novel therapeutic agents to improve the current situation. Improvement of our understanding of the disease has generated a large number of studies on biological approaches targeting the molecular abnormalities of pancreatic cancer, including gene therapy and signal transduction inhibition, antiangiogenic and matrix metalloproteinase inhibition, oncolytic viral therapy and immunotherapy. This article provides a review of these approaches, both investigated in the laboratories and in subsequent clinical trials.

Transcriptional targeting of adenovirus vectors with the squamous cell carcinoma-specific antigen-2 promoter for selective apoptosis induction in lung cancer

Squamous cell carcinoma antigens SCCA1 and SCCA2 are highly homologous serine proteinase inhibitors which have been widely utilized as serological markers for squamous cell cancers, but it has recently been demonstrated that only SCCA2 is truly specific for certain forms of lung cancer. Using a construct containing the 5'-flanking region of the SCCA2 gene between -460 and +0 bp and the luciferase reporter gene, SCCA2 promoter activity was detected in SCCA2-producing SCC cell lines (LK-2, LC-1), but not in SCCA2-nonproducing lung adenocarcinoma cell lines (A549, ABC-1, and RERF-LC-MS) or normal cells (WI-38, SAEC, and NHEK-Adult). Infection with a recombinant adenovirus vector, Ad-SCCA2-DsRed, resulted in cell-specific expression of the SCCA2 promoter-driven DsRed marker gene only in LK-2 and LC-1 cells. The same strategy was used for SCCA2-driven expression of a proapoptotic gene, (KLAKLAK)2, which can cause mitochondrial disruption by triggering mitochondrial permeabilization and swelling, resulting in the release of cytochrome c and induction of apoptosis. Infection with Ad-SCCA2-KLAKLAK2 specifically reduced the growth of the two human lung SCC cell lines compared to the SCCA2 nonproducing cell lines both in vitro and in vivo, suggesting that the SCCA2 promoter had a tumor-specific effect. These results suggest that transduction of SCCA2 promoter-controlled suicide genes by adenoviral vectors can confer transcriptionally targeted cytotoxicity in SCCA2-producing lung SCC cells, and represents a novel strategy for gene transfer specifically targeted to SCC in the lung.

Molecular target-based therapy of pancreatic cancer

Pancreatic cancer is genetically complex, and without effective therapy. Mutations in the Kirsten-ras (K-ras) oncogene occur early and frequently (approximately 90%) during pancreatic cancer development and progression. In this context, K-ras represents a potential molecular target for the therapy of this highly aggressive cancer. We now show that a bipartite adenovirus expressing a novel cancer-specific apoptosis-inducing cytokine gene, mda-7/interleukin-24 (IL-24), and a K-ras AS gene, but not either gene alone, promotes growth suppression, induction of apoptosis, and suppression of tumor development mediated by K-ras mutant pancreatic cancer cells. Equally, the combination of an adenovirus expressing mda-7/IL-24 and pharmacologic and genetic agents simultaneously blocking K-ras or downstream extracellular regulated kinase 1/2 signaling also promotes similar inhibitory effects on the growth and survival of K-ras mutant pancreatic carcinoma cells. This activity correlates with the reversal of a translational block in mda-7/IL-24 mRNA in pancreatic cancer cells that limits message association with polysomes, thereby impeding translation into protein. Our study provides support for a "dual molecular targeted therapy" involving oncogene inhibition and selective cancer apoptosis-inducing gene expression with potential for effectively treating an invariably fatal cancer.

Ras-dependent carbon metabolism and transformation in mouse fibroblasts

Mutational activation of ras genes is required for the onset and maintenance of different malignancies. Here we show, using a combination of molecular physiology, nutritional perturbations and transcriptional profiling, that full penetrance of phenotypes related to oncogenic Ras activation, including the shift of carbon metabolism towards fermentation and upregulation of key cell cycle regulators, is dependent upon glucose availability. These responses are induced by Ras activation, being specifically reverted by downregulation of the Ras pathway obtained through the expression of a dominant-negative Ras-specific guanine nucleotide exchange protein. Our data allow to link directly to ras activation the alteration in energy metabolism of cancer cells, their fragility towards glucose shortage and ensuing apoptotic death.

Gene therapy developments for pancreatic cancer

Treatment options for pancreatic cancer have limited success and it is therefore an appropriate target for the development of new strategies, including gene therapy. Gene therapy approaches include inhibition of activated oncogenes (KRAS, LSM1) with antisense and RNA interference strategies, replacement of inactivated tumour suppressor genes (TP53, CDKN2A, CDKN1A), targeting of cell signalling pathways, gene-directed prodrug-activation therapies and the use of replication-competent oncolytic viruses. Angiogenesis and apoptosis have also been targeted for gene therapy. Clinical trials of gene therapy have shown only moderate anti-tumour effects. As there are many genetic abnormalities in pancreatic cancer, strategies combining different targets or indeed different modalities of treatment, may be more successful. Identification of new targets and improvements in delivery and targeting may further improve the efficacy of gene therapy in pancreatic cancer.

Histone deacetylase inhibitors induced caspase-independent apoptosis in human pancreatic adenocarcinoma cell lines

The antitumor activity of the histone deacetylase inhibitors was tested in three well-characterized pancreatic adenocarcinoma cell lines, IMIM-PC-1, IMIM-PC-2, and RWP-1. These cell lines have been previously characterized in terms of their origin, the status of relevant molecular markers for this kind of tumor, resistance to other antineoplastic drugs, and expression of differentiation markers. In this study, we report that histone deacetylase inhibitors induce apoptosis in pancreatic cancer cell lines, independently of their intrinsic resistance to conventional antineoplastic agents. The histone deacetylase inhibitor-induced apoptosis is due to a serine protease-dependent and caspase-independent mechanism. Initially, histone deacetylase inhibitors increase Bax protein levels without affecting Bcl-2 levels. Consequently, the apoptosis-inducing factor (AIF) and Omi/HtrA2 are released from the mitochondria, with the subsequent induction of the apoptotic program. These phenomena require AIF relocalization into the nuclei to induce DNA fragmentation and a serine protease activity of Omi/HtrA2. These data, together with previous results from other cellular models bearing the multidrug resistance phenotype, suggest a possible role of the histone deacetylase inhibitors as antineoplastic agents for the treatment of human pancreatic adenocarcinoma.

Bystander effect contributes to the antitumor efficacy of CaSm antisense gene therapy in a preclinical model of advanced pancreatic cancer

Pancreatic adenocarcinoma (PC) is an aggressive malignancy resistant to standard treatment modalities. Previously, we have reported that cancer-associated Sm-like protein (CaSm) contributes to the neoplastic transformation of PC. In this study, we utilized a recently established preclinical model of PC to determine if molecular targeting of CaSm can serve as the basis for a novel PC therapy. In a subcutaneous tumor model, intratumoral administration of an adenoviral vector encoding CaSm antisense RNA (Ad-alphaCaSm) significantly inhibited Panc02 tumor growth. Furthermore, in a metastatic tumor model, systemic administration of Ad-alphaCaSm resulted in a significant decrease in the number of hepatic metastases and increased survival time. We assessed the efficiency of in vivo delivery and observed significant levels of vector transduction in tissues containing PC, as well as a bystander effect that was amplifying the efficacy of CaSm gene therapy. This bystander effect was also active in vitro and was shown to be at least partially independent of host-related mechanisms. We conclude that CaSm antisense gene therapy is an effective novel therapy for PC and that the antitumor efficacy is dependent on both direct and bystander mechanisms.

Cancer gene therapy

The prognosis of patients with some kinds of cancers whose patients are often found unresectable upon diagnosis is still dismal. In these fields, development of a new therapeutic modality is needed and gene therapy represents one promising strategy. So far, numerous cancer gene therapy clinical trials based on these principles have been carried out and have shown the safety of such modalities, but have fallen short of the initial expectations to cure cancers. In this review, we would like to make a problem-oriented discussion of current status of cancer gene therapy research by using mainly gastrointestinal cancers as an example. In order to overcome obstacles for full realization of cancer gene therapy, numerous researches have been conducted by many researchers. Various cancer-selective and non-selective genes, as well as lytic viruses themselves have been employed for gene therapy. In the context of gene delivery method, different kinds of viral and non-viral strategies have been utilized. In addition, surrogate assays, such as soluble markers and imaging, have been developed for safer and more informative clinical trials. Many experiments and clinical trials to date have figured out current obstacles for the realization of an effective cancer gene therapy modality. Tireless efforts to overcome such hurdles and continuous infusion of novel concepts into this field should lead to break through technologies and the cure of the patients.

K-ras as a target for cancer therapy

The central role K-, H- and N-Ras play in regulating diverse cellular pathways important for cell growth, differentiation and survival is well established. Dysregulation of Ras proteins by activating mutations, overexpression or upstream activation is common in human tumors. Of the Ras proteins, K-ras is the most frequently mutated and is therefore an attractive target for cancer therapy. The complexity of K-ras signaling presents many opportunities for therapeutic targeting. A number of different approaches aimed at abrogating K-ras activity have been explored in clinical trials. Several of the therapeutic agents tested have demonstrated clinical activity, supporting ongoing development of K-ras targeted therapies. However, many of the agents currently being evaluated have multiple targets and their antitumor effects may not be due to K-Ras inhibition. To date, no selective, specific inhibitor of K-ras is available for routine clinical use. In this review, we will summarize the structure and function of K-ras with attention to its role in tumorigenesis and discuss the successes and failures of the various strategies designed to therapeutically target this important oncogene.

Molecular targeting of pancreatic disorders

During the last decade significant advances in gene therapy have made it possible to treat various pancreatic disorders in both animal models and in humans. For example, insulin gene delivery to non-beta-cell tissues has been shown to reverse hyperglycemia in diabetic mice, and islet transplantation, based on in vitro differentiation of beta cells and concomitant gene targeting to prevent host autoimmune responses, has become more feasible. Additionally, introduction of the glucokinase regulatory protein and protein kinase C-zeta have been shown to improve glucose tolerance in non-insulin-dependent diabetes mellitus animal models. Pancreatic cancer studies utilize several DNA-based strategies for tumor treatment including introduction of tumor suppressor genes, suppression of oncogenes, suicide gene/prodrug therapy, and restricted replication-competent virus therapy. Tumor-specific targeting is an important part of suicide gene therapy, and tumor-specific promoters are used for cell-specific targeting. Tumor-specific suicide gene therapy directed by the rat insulin promoter has been used to eliminate insulinoma tumors in a mouse model. This review compiles a compendium of information related to the treatment of pancreatic disorders using gene therapy.

Establishing a Murine Pancreatic Cancer CaSm Model: Up-regulation of CaSm Is Required for the Transformed Phenotype of Murine Pancreatic Adenocarcinoma

We have recently shown that the cancer-associated Sm-like protein (CaSm) is overexpressed in human pancreatic adenocarcinoma (PC). However, the role of CaSm in the process of neoplastic transformation remains unclear. To define further the role of CaSm in PC transformation, we have established a murine model based on the murine pancreatic cancer cell lines Panc02 and Panc03. CaSm is overexpressed in the aggressive Panc02 cells and expressed at much lower levels in the more indolent Panc03 cells. Up-regulation of CaSm in Panc03 cells increased in vitro proliferation and anchorage-independent growth and promoted subcutaneous tumor establishment and growth in syngeneic mice. Conversely, adenoviral down-regulation of CaSm in Panc02 led to significant inhibition of cellular proliferation and anchorage-independent growth in vitro and complete abolition of tumor growth and metastasis in vivo. Up-regulation of CaSm in NIH3T3 resulted in loss of contact inhibition and increased soft agar colony formation in vitro. The requirement for CaSm overexpression for neoplastic transformation confirms the concept that CaSm is a critical oncogene and potential target for molecular intervention. Furthermore, establishment of the murine clinically relevant model of pancreatic metastases provides a framework for the generation of preclinical data to support the development of novel molecular therapies targeting CaSm.

Tissue MicroArray Analyses of Pancreatic Duodenal Homeobox-1 in Human Cancers

In previous studies, we demonstrated that rat insulin promoter (RIP)-driven gene therapy successfully targeted human pancreatic tumor PANC-1 cells and mouse insulinoma NIT-1 cells, which are both pancreatic duodenal homeobox-1 (PDX-1)-positive. The purpose of this study was to perform a human tissue array analysis to determine potential targets for RIP-driven gene therapy. A custom-designed tissue MicroArray analysis of various human cancer specimens was performed using a PDX-1 polyclonal antibody generated in our laboratory. The custom-designed Tissue MicroArray of human tumor specimens consists of human cancer specimens from different origins, such as the pancreas, breast, colon, prostate, kidney, liver, lung, and ovary. A panel of normal human specimens from 20 organs or tissues was used as a control. All tissues were fixed in formalin and embedded in paraffin. The immunohistochemistry studies of the cytoplasm and the nuclear expression levels were compared using the Loda method and blind reviews. Data are presented as the mean +/- SEM (p < 0.05 was considered significant by the unpaired student t-test). PDX-1 expression intensity was elevated in both benign and malignant tissues from the same patient with pancreas, breast, colon, prostate, and kidney cancers, whereas normal human tissues from control subjects without cancer did not express PDX-1. These results suggest that PDX-1 is an early marker for these cancers and could be potentially used as a diagnostic parameter and perhaps could be targeted by PDX-1-activated gene therapies, such as RIP-TK.

Therapy of human pancreatic carcinoma based on suppression of HMGA1 protein synthesis in preclinical models

Pancreatic carcinoma is one of the most aggressive tumors, and, being refractory to conventional therapies, is an excellent target for new therapeutic approaches. Based on our previous finding of high HMGA1 expression in pancreatic cancer cells compared to normal pancreatic tissue, we evaluated whether suppression of HMGA1 protein expression could be a treatment option for patients affected by pancreatic cancer. Here we report that HMGA1 proteins are overexpressed in pancreatic carcinoma cell lines, and their downregulation through an adenovirus carrying the HMGA1 gene in an antisense orientation (Ad Yas-GFP) results in the death of three human pancreatic carcinoma cell lines (PANC1, Hs766T and PSN1). Pretreatment of PANC1 and PSN1 cells with Ad Yas-GFP suppressed and reduced, respectively, their ability to form xenograft tumors in nude mice. To further verify the role of HMGA1 in pancreatic tumorigenesis, we used a HMGA1 antisense phosphorothioate oligodeoxynucleotide (ODN); its addition induced a decrease in HMGA1 protein levels and a significant reduction of the proliferation rate of PANC1-, Hs766T- and PSN1-treated cells. Therefore, suppression of HMGA1 protein synthesis by an HMGA1 antisense approach seems to be a feasible treatment strategy in pancreatic carcinomas.

Antitumor capacity of a dominant-negative RET proto-oncogene mutant in a medullary thyroid carcinoma model

Gain-of-function mutations in the RET proto-oncogene resulting in a constitutively active receptor tyrosine kinase have been identified as responsible for three subtypes of multiple endocrine neoplasia type 2 (MEN-2) and the development of sporadic medullary and papillary thyroid carcinoma. An important strategy in cancer gene therapy is the inhibition of oncogenic signal transduction by interfering with the molecular mechanisms of activation. In the present study, we tested the therapeutic capacity of an adenovirus expressing a dominant-negative (dn) RET mutant, RET(51).flag, under the control of a synthetic C cell-selective calcitonin promoter (TSE2.CP1) against human medullary thyroid cancer (MTC). Infection of human MTC-derived TT cells with Ad-TSE2.CP1-dn-RET(51).flag resulted in the accumulation of immature RET protein in the endoplasmic reticulum and a strong reduction of oncogenic RET receptor on the cell surface, indicating that RET(51).flag exhibits a dominant-negative effect over endogenous oncogenic protein. Analysis of potential downstream mechanisms associated with the inhibition of oncogenic RET signaling by overexpression of mutant RET(51).flag revealed a significant loss of cell viability in TT cells due to the induction of apoptosis. Finally, we examined the antitumor activity of the dominant-negative RET approach in vivo. Inoculation of Ad-TSE2.CP1- dn-RET(51).flag-expressing MTC cells into nude mice led to complete suppression of tumor growth. Moreover, a single intratumoral injection of Ad-TSE2.CP1-dn-RET(51).flag into established thyroid tumors resulted in prolonged survival of treated mice compared with the controls. Our data suggest that adenoviral delivery of dn-RET(51).flag may be a reliable strategy of effective molecular intervention for RET oncogene-related MTC.

The ras-binding domain of ral GDS-like protein-2 as a ras inhibitor in smooth muscle cells

This study was undertaken to determine whether the response of smooth muscle cells to mitogens can be inhibited by inactivating ras with the ral GDS like protein-2 ras-binding domain (RGL2-RBD). RGL2 is a member of the ral GDS family of proteins that contains a carboxy terminal ras-binding domain which binds the GTP ligated form of ras and rap and a CDC25 homology domain with the structural features of a guanine nucleotide exchange factor. The effect of ras signaling on the smooth muscle cell growth factor response was studied using rat aortic A10 smooth muscle cells transfected with a plasmid that encoded the RGL2-RBD. RGL2-RBD transfection resulted in a 12-fold reduction in the number of clonal colonies that were obtained after selection, and dramatically slowed cell cycle progression. RGBL2-RBD reduced DNA synthesis and inhibited platelet derived growth factor (PDGF)-mediated activation of the MAPK pathway. These findings indicated that interfering with ras signaling inhibits smooth muscle cell proliferation and raise the possibility that ras signaling inhibition might be used therapeutically to control smooth muscle proliferation after vascular injury.

Induction of apoptosis in K562 cells by dominant negative c-myb

OBJECTIVE

The aberrant expression of c-myb in leukemic cells suggests that c-myb may play an important role in leukemogenesis. Therefore, disrupting c-myb function might provide a strategy for controlling leukemic cell growth. Use of dominant negative mutants as a strategy for inhibiting oncogene function has attracted considerable attention. The aim of this study was to induce apoptosis in K562 cells by dominant negative c-myb (DN-myb).

MATERIALS AND METHODS

We constructed a DN-myb plasmid containing the DNA-binding domain of c-myb and transfected the dominant negative mutant, like its wild-type (WT) counterpart, into K562 cells. Consequently, cell viability and induction of apoptosis were measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, nuclear condensation, DNA fragmentation, and Western hybridization analysis for expression of poly(ADP-ribose) polymerase. In addition, the effect of DN-myb on bcl-2 promoter activity and expression of bcl-2 and bcr-abl was studied.

RESULTS

We observed that DN-myb, cotransfected with WT c-myb and a chloramphenicol acetyltransferase reporter construct containing the bcl-2 promoter, bound competitively to the bcl-2 promoter and significantly decreased the activation of chloramphenicol acetyltransferase induced by WT c-myb. Moreover, the inactivation of transcription induced by DN-myb reduced not only the expression of bcl-2 but also the expression of bcr-abl. Further functional studies focused on the effect of DN-myb on the induction of apoptosis in K562 cells. Transfection of DN-myb into K562 cells caused a significant reduction in cell proliferation when cells were exposed to low concentrations of DNA-damaging agents (approximately 30% of control) and remarkably increased apoptosis.

CONCLUSIONS

Our data demonstrate that disruption of c-myb function by dominant negative c-myb is an effective strategy to induce apoptosis of leukemic cells. The results of these studies support the thesis that dominant negative c-myb gene therapy may be useful for treatment of leukemia patients.

Gene therapy for pancreatic cancer

Gene transfer technology has the potential to revolutionize cancer treatment. Developments in molecular biology, genetics, genomics, stem cell technology, virology, bioengineering, and immunology are accelerating the pace of innovation and movement from the laboratory bench to the clinical arena. Pancreatic adenocarcinoma, with its particularly poor prognosis and lack of effective traditional therapy for most patients, is an area where gene transfer and immunotherapy have a maximal opportunity to demonstrate efficacy. In this review, we have discussed current preclinical and clinical investigation of gene transfer technology for pancreatic cancer. We have emphasized that the many strategies under investigation for cancer gene therapy can be classified into two major categories. The first category of therapies rely on the transduction of cells other than tumor cells, or the limited transduction of tumor tissue. These therapies, which do not require efficient gene transfer, generally lead to systemic biological effects (e.g., systemic antitumor immunity, inhibition of tumor angiogenesis, etc) and therefore the effects of limited gene transfer are biologically "amplified." The second category of gene transfer strategies requires the delivery of therapeutic genetic material to all or most tumor cells. While these elegant approaches are based on state-of-the-art advances in our understanding of the molecular biology of cancer, they suffer from the current inadequacies of gene transfer technology. At least in the short term, it is very likely that success in pancreatic cancer gene therapy will involve therapies that require only the limited transduction of cells. The time-worn surgical maxim, "Do what's easy first," certainly applies here.

Novel treatments and therapies in development for pancreatic cancer

Until recently, 5-fluorouracil was the most widely used treatment for non-resectable pancreatic cancer. This treatment, however, only resulted in a median survival time of approximately 4 months. In the last few years, gemcitabine has rapidly become the new treatment benchmark, due more to its superior clinical benefit rather than to it conferring an increased median survival (approximately 5-6 months). Thus, the outlook for patients with pancreatic cancer is still relatively bleak. A number of new treatment options are presently being investigated. Some of these are combination therapies involving gemcitabine and other chemotherapeutic agents or radiation. Other novel treatment strategies are also already being evaluated in clinical studies. Some of the more promising treatments in development are discussed and evaluated in this article.

High expression of tumor-associated antigen RCAS1 in pancreatic ductal adenocarcinoma is an unfavorable prognostic marker

RCAS1 (receptor-binding cancer antigen expressed on SiSo cells) is a recently identified human tumor-associated antigen expressed on various cancer cells. It is thought that tumor cells evade immune surveillance by expression of RCAS1, which induces apoptotic cell death in receptor-positive immune cells. The purpose of our study was to investigate the relation between RCAS1 expression and the clinicopathological variables and clinical outcome in patients with pancreatic adenocarcinoma. Immunohistochemical analysis for RCAS1 was performed on paraffin-embedded specimens of 80 patients (mean age, 62 years) who underwent surgical resection for pancreatic adenocarcinoma. Of the 80 specimens, 77 (96%) were positive for RCAS1. No significant correlation was found between RCAS1 expression and age, gender, depth of invasion, tumor diameter, surgical margin, lymphatic invasion, venous invasion or histopathological grading. Borderline correlations between RCAS1 expression were noted for lymph node metastasis and stage (p = 0.0608 and 0.0934, respectively). RCAS1 expression was very frequently observed and the survival of patients with high RCAS1 expression was significantly shorter than that of those with low expression (p = 0.0012). Multivariate analysis using the Cox regression model indicated that high RCAS1 expression was an independent prognostic factor (risk ratio, 3.090; p = 0.0090). These results suggested that RCAS1 might be a significant tumor marker for pancreatic adenocarcinoma and an unfavorable predictor for prognosis of patients who have undergone surgical resection.

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.

A combinatorial approach for selectively inducing programmed cell death in human pancreatic cancer cells

Pancreatic cancer is an extremely aggressive neoplasm whose incidence equals its death rate. Despite intensive analysis, the genetic changes that mediate pancreatic cancer development and effective therapies for diminishing the morbidity associated with this disease remain unresolved. Through subtraction hybridization, we have identified a gene associated with induction of irreversible growth arrest, cancer reversion, and terminal differentiation in human melanoma cells, melanoma differentiation associated gene-7 (mda-7). Ectopic expression of mda-7 when using a recombinant adenovirus, Ad.mda-7, results in growth suppression and apoptosis in a broad spectrum of human cancers with diverse genetic defects, without exerting deleterious effects in normal human epithelial or fibroblast cells. Despite the apparently ubiquitous antitumor effects of mda-7, pancreatic carcinoma cells are remarkably refractory to Ad.mda-7 induced growth suppression and apoptosis. In contrast, the combination of Ad.mda-7 with antisense phosphorothioate oligonucleotides, which target the K-ras oncogene (a gene that is mutated in 85 to 95% of pancreatic carcinomas), induces a dramatic suppression in growth and a decrease in cell viability by induction of apoptosis. In mutant K-ras pancreatic carcinoma cells, programmed cell death correlates with expression and an increase, respectively, in MDA-7 and BAX proteins and increases in the ratio of BAX to BCL-2 proteins. Moreover, transfection of mutant K-ras pancreatic carcinoma cells with an antisense K-ras expression vector and infection with Ad.mda-7 inhibits colony formation in vitro and tumorigenesis in vivo in nude mice. These intriguing observations demonstrate that a combinatorial approach, consisting of a cancer-specific apoptosis-inducing gene and an oncogene inactivation strategy, may provide the foundation for developing an effective therapy for pancreatic cancer.

CaSm/gemcitabine chemo-gene therapy leads to prolonged survival in a murine model of pancreatic cancer

BACKGROUND

CaSm, the cancer-associated Sm-like oncogene, is overexpressed in greater than 80% of pancreatic tumors. We previously reported that an adenovirus expressing antisense RNA to CaSm (Ad-alpha CaSm) can decrease pancreatic tumor growth in vivo but is not curative. In the current study we investigated the mechanism of Ad-alpha CaSm's antitumor effect to rationally approach combinatorial therapy for improved efficacy.

METHODS

AsPC-1 and Panc-1 human pancreatic cancer cells were treated with Ad-alpha CaSm and examined by MTT assay for in vitro proliferation changes. Flow cytometry determined the effect of CaSm down-regulation on the cell cycle, and then cells treated with Ad-alpha CaSm in combination with cisplatin, etoposide, or gemcitabine chemotherapies were reexamined by MTT assay. SCID-Bg mice bearing subcutaneous AsPC-1 tumors were treated with Ad-alpha CaSm, gemcitabine, or the combination and monitored for tumor growth and survival.

RESULTS

Treatment with Ad-alpha CaSm reduced the proliferation of AsPC-1 and Panc-1 cells (59% and 44%, respectively; P <.05). The cell cycle revealed a cytostatic block with decreased G(1) phase and increased DNA content in treated cells. The combination of Ad-alpha CaSm with gemcitabine significantly reduced in vitro proliferation (66% vs 39% and 48% for controls), decreased in vivo AsPC-1 tumor growth by 71% (n = 10), and extended survival time from 57 to 100 days.

CONCLUSIONS

Down-regulation of CaSm reduces the growth of pancreatic cancer cells by altering the cell cycle in a cytostatic manner. The combination of Ad-alpha CaSm with gemcitabine is more effective than either agent used separately.

Innovative treatments for pancreatic cancer

Pancreatic cancer is the fifth leading cause of cancer deaths in the United States with little or no impact from conventional treatment options. Significant advances in understanding basic immunology have renewed interest in using immunotherapy to treat pancreatic cancer. Cancer immunotherapy, including humanized MAbs, cytokines, and potent vaccine strategies, has been successful in animal models and is being evaluated in clinical trials. Gene therapy is also being explored using methods to inactivate oncogenes, replace defective tumor suppressor genes, confer enhanced chemosensitivity to tumor cells, and increase immunogenicity of tumor cells. Angiogenesis, an essential step in the growth and metastasis of pancreatic cancer, has been targeted by many antiangiogenic agents. Several clinical trials have been initiated to evaluate the role of these innovative strategies in patients with pancreatic cancer with increasingly sophisticated correlative studies to learn more about the mechanisms of tumor rejection with these agents. The rapid translation of basic science discoveries to clinical trials should result in the development of new effective treatments for patients with pancreatic cancer.

Gene therapy for pancreatic cancer--current and prospective strategies

Pancreatic ductal adenocarcinoma is one of the most common causes of cancer death in the developed world. Long-term survival is currently only achieved through surgical resection. Most patients have locally advanced or metastatic disease at the time of diagnosis and are therefore not amenable to resection, whilst chemotherapy and radiotherapy are by and large ineffective. Gene therapy offers an alternative to current adjuvant strategies. With approximately two-thirds of all gene therapy trials worldwide directed at cancer, the gene therapy approaches that are currently being explored for pancreatic cancer are specifically examined. Gene delivery systems, genetic targets, and combined gene delivery with chemotherapy are discussed in the context of pancreatic cancer treatment.