Suicide gene therapy with the yeast fusion gene cytosine deaminase/uracil phosphoribosyltransferase is not enough for pancreatic cancer

Room for improvement in the treatment of pancreatic cancer: Novel opportunities from gene targeted therapy

Pancreatic cancer is one of the highest and in fact, unchanged mortality-associated tumor, with an exceptionally low survival rate due to its challenging diagnostic approach. So far, its treatment is based on a combination of approaches (such as surgical resection with or rarely without chemotherapeutic agents), but with finite limits. Thus, looking for additional space to improve pancreatic tumorigenesis therapeutic approach, research has focused on gene therapy with unexpectedly growing horizons not only for the treatment of inoperable pancreatic disease, but also for its early stages. In vivo gene delivery viral vectors, despite few disadvantages (possible immunogenicity, toxicity, mutagenicity, or high cost), could be one of the most efficient cancer gene therapeutic strategies for clinical application due to their superiority compared with other systems (ex vivo delivery strategies). Their dominance consists of simple preparation, easy operation and a wide range of functions. Adenoviruses are one of the most common used vectors, inducing strong immune as well as inflammatory reactions. Oncolytic virotherapy, using the above mentioned in vivo viral vectors, is one of the most promising non-pathogenic, highly-selective cytotoxic anti-cancer therapy using anti-cancer agents with high anti-tumor potency and strong oncolytic effect. There have been a variety of targeted therapeutic and pre-clinical strategies tested for gene therapy in pancreatic cancer such as gene-editing systems (e.g., clustered regularly interspaced palindromic repeats-Cas9), RNA interference technology (e.g., microRNAs, short hairpin RNA or small interfering RNA), adoptive immunotherapy and vaccination (e.g., chimeric antigen receptor T-cell therapy) with encouraging results.

Gene Therapy for Pancreatic Cancer: Specificity, Issues and Hopes

A recent death projection has placed pancreatic ductal adenocarcinoma as the second cause of death by cancer in 2030. The prognosis for pancreatic cancer is very poor and there is a great need for new treatments that can change this poor outcome. Developments of therapeutic innovations in combination with conventional chemotherapy are needed urgently. Among innovative treatments the gene therapy offers a promising avenue. The present review gives an overview of the general strategy of gene therapy as well as the limitations and stakes of the different experimental in vivo models, expression vectors (synthetic and viral), molecular tools (interference RNA, genome editing) and therapeutic genes (tumor suppressor genes, antiangiogenic and pro-apoptotic genes, suicide genes). The latest developments in pancreatic carcinoma gene therapy are described including gene-based tumor cell sensitization to chemotherapy, vaccination and adoptive immunotherapy (chimeric antigen receptor T-cells strategy). Nowadays, there is a specific development of oncolytic virus therapies including oncolytic adenoviruses, herpes virus, parvovirus or reovirus. A summary of all published and on-going phase-1 trials is given. Most of them associate gene therapy and chemotherapy or radiochemotherapy. The first results are encouraging for most of the trials but remain to be confirmed in phase 2 trials.

Gene therapy in pancreatic cancer

Pancreatic cancer (PC) is a highly lethal disease and notoriously difficult to treat. Only a small proportion of PC patients are eligible for surgical resection, whilst conventional chemoradiotherapy only has a modest effect with substantial toxicity. Gene therapy has become a new widely investigated therapeutic approach for PC. This article reviews the basic rationale, gene delivery methods, therapeutic targets and developments of laboratory research and clinical trials in gene therapy of PC by searching the literature published in English using the PubMed database and analyzing clinical trials registered on the Gene Therapy Clinical Trials Worldwide website (http://www. wiley.co.uk/genmed/ clinical). Viral vectors are main gene delivery tools in gene therapy of cancer, and especially, oncolytic virus shows brighter prospect due to its tumor-targeting property. Efficient therapeutic targets for gene therapy include tumor suppressor gene p53, mutant oncogene K-ras, anti-angiogenesis gene VEGFR, suicide gene HSK-TK, cytosine deaminase and cytochrome p450, multiple cytokine genes and so on. Combining different targets or combination strategies with traditional chemoradiotherapy may be a more effective approach to improve the efficacy of cancer gene therapy. Cancer gene therapy is not yet applied in clinical practice, but basic and clinical studies have demonstrated its safety and clinical benefits. Gene therapy will be a new and promising field for the treatment of PC.

Analogs of vitamin E epitomized by alpha-tocopheryl succinate for pancreatic cancer treatment: in vitro results induce caution for in vivo applications

OBJECTIVES

alpha-Tocopheryl succinate (alpha-TOS) is thought to be toxic only for cancer cells. We ascertained in vitro alpha-TOS effects on pancreatic cancer (PC) and normal cell growth and verified whether the combination of nontoxic alpha-TOS and 5-fluorouracil (5-FU) doses causes cancer cell death and whether alpha-TOS effects are mediated by the proapoptotic proteins Bax/Bak and/or SMAD4/DPC4 status.

METHODS

Five PC cell lines, myoblasts, normal monocytes, wild-type (WT) and Bax/Bak double knockout mouse embryonic fibroblast (MEF) cells, and permanently SMAD4/DPC4-transfected PSN1 cells were cultured in 1% and 10% fetal calf serums (FCSs), without or with alpha-TOS (5-500 micromol/L). Nontoxic 5-FU (0.0001 mmol/L) and alpha-TOS alone or in combination were also evaluated.

RESULTS

Only PSN1 PC cell line, which had SMAD4/DPC4 homozygous deletion, was sensitive to nontoxic alpha-TOS doses (5 micromol/L in 1% FCS and 50 micromol/L in 10% FCS). A 20-micromol/L alpha-TOS inhibited MEF-WT, not MEF-double knockout growth. Only PSN1 cells were sensitive to nontoxic 5-FU and alpha-TOS combination. SMAD4/DPC4 transfection restored PSN1 resistance to the effects of combined 5-FU and alpha-TOS effects.

CONCLUSIONS

Only a minority of PC cells are sensitive to the antiproliferative effects of alpha-TOS, any sensitivity appearing to be correlated with SMAD4/DPC4 homozygous deletion and Bax/Bak expression.

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.

Radiosensitization and Anti-tumour Effects of Cytosine Deaminase and Thymidine Kinase Fusion Suicide Gene in Human Adenoid Cystic Carcinoma Cells

Herpes simplex virus thymidine kinase (HSV-TK) and Escherichia coli cytosine deaminase (CD) can convert innocuous prodrugs into cytotoxic metabolites and are being investigated for use in gene therapy for cancer. Human adenoid cystic carcinoma (ACC-2) cells transduced with a CD/HSV-TK fusion gene (ACC-2/CD-TK cells) were found to be more sensitive to radiation than ACC-2 cells when exposed to 5-fluorocytosine (5-FC; 40 μg/ml) plus ganciclovir (0.1 μg/ml) for 48 h before irradiation. Analysis of radiation survival curves for cells exposed to 5-FC plus ganciclovir before irradiation showed that ACC-2 cells had a higher capacity for sublethal damage repair (Dq value) and greater cellular radiosensitivity (D0 value) than ACC-2/CD-TK cells. Colony formation rate after 2 Gy of irradiation was significantly greater for ACC-2 than for ACC-2/CD-TK cells when cells were treated with 5-FC plus ganciclovir before irradiation. This study, therefore, indicates that addition of radiation might substantially improve the therapeutic potential of CD-TK fusion gene therapy of human adenoid cystic carcinomas.

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.