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

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.

Promoter-Operating Targeted Expression of Gene Therapy in Cancer: Current Stage and Prospect

The technique of targeted expression of interesting genes, including distinct delivery systems and specific gene promoter-operating expression, is an important strategy for gene therapy against cancers. Up to now, extensive literature documented the efficacy of distinct delivery systems, such as the liposome system, nano-particle system, polyetherimide (PEI) system, and so on, in cancer gene therapy. However, a related document on the potential value of using a specific gene promoter, such as a tumor suppressor, in cancer gene therapy was still scary. The main obstacle might be that the selection of an ideal gene promoter to operate interesting gene expression in cancer gene therapy is still not fully understood. Therefore, many efforts need to be done in order to make it a real power tool for the human clinical treatment of cancer patients. The purpose of this review is to clarify the current state and some problematics in development of promoter-operating targeted expression of interesting genes and highlight its potential in cancer gene therapy.

Targeted gene therapy of the HSV-TK/hIL-12 fusion gene controlled by the hSLPI gene promoter of human non-small cell lung cancer in vitro

The incidence of lung cancer and lung cancer-associated mortality have markedly increased worldwide, and gene-targeted therapy has emerged as a promising treatment strategy. The present study aimed to explore the targeted antitumor effect of the herpes simplex virus-thymidine kinase/human interleukin-12 (HSV-TK/hIL-12) fusion gene regulated by the human secretory leukocyte protease inhibitor (hSLPI) promoter of human non-small cell lung cancer (hNSCLC). There were four recombinant eukaryotic expression vectors: pcDNA3.1-CMV-TK, pcDNA3.1-CMV-TK/hIL-12, pcDNA3.1-phSLP-TK and pcDNA3.1-phSLP-TK/hIL-12. These were constructed and transfected into the A549, SPC-A1 and HepG2 cell lines in vitro. The expression of the HSV-TK/hIL-12 fusion gene was detected with reverse transcription-polymerase chain reaction (RT-PCR), and the content of hIL-12 was measured using an ELISA. The antitumor effect of the fusion gene on the A549, SPC-A1 and HepG2 cell lines was determined using an MTT assay. Analysis of the experimental data demonstrated that genes regulated by the cytomegalovirus promoter were expressed at the same level in three different tumor cell lines. Genes regulated by the hSLPI promoter were expressed in the A549 and SPC-A1 cell lines, but not in the HepG2 cell line. Coincidentally, the hIL-12 expression levels were similar to those observed in previous RT-PCR findings. In the Pcmv-TK/Pcmv-TK-hIL-12 group for all three cell lines, as well as in the PSLPI-TK/PSLPI-TK-hIL-12 group for the A549 and SPC-A1 cell lines, the cell survival rate declined significantly and the fusion gene transfection group indicated a lower cell survival rate, when compared with single gene transfection group. The present study indicated that the fusion gene regulated by the hSLPI promoter had a targeted antitumor effect on hNSCLC, and that the combined suicide gene and immune gene therapy had a stronger antitumor effect, compared with single gene therapy.

Tissue Specific Promoters in Colorectal Cancer

Colorectal carcinoma is the third most prevalent cancer in the world. In the most advanced stages, the use of chemotherapy induces a poor response and is usually accompanied by other tissue damage. Significant progress based on suicide gene therapy has demonstrated that it may potentiate the classical cytotoxic effects in colorectal cancer. The inconvenience still rests with the targeting and the specificity efficiency. The main target of gene therapy is to achieve an effective vehicle to hand over therapeutic genes safely into specific cells. One possibility is the use of tumor-specific promoters overexpressed in cancers. They could induce a specific expression of therapeutic genes in a given tumor, increasing their localized activity. Several promoters have been assayed into direct suicide genes to cancer cells. This review discusses the current status of specific tumor-promoters and their great potential in colorectal carcinoma treatment.

An Enterovirus-Like RNA Construct for Colon Cancer Suicide Gene Therapy

Background:

In gene therapy, the use of RNA molecules as therapeutic agents has shown advantages over plasmid DNA, including higher levels of safety. However, transient nature of RNA has been a major obstacle in application of RNA in gene therapy.

Methods:

Here, we used the internal ribosomal entry site of encephalomyocarditis virus and the 3’ non-translated region of Poliovirus to design an enterovirus-like RNA for the expression of a reporter gene (enhanced green fluorescent protein) and a suicide gene (thymidine kinase of herpes simplex virus). The expression of these genes was evaluated by flow cytometry and cytotoxicity assay in human colorectal adenocarcinoma cell line (SW480). We then armed RNA molecules with a target sequence for hsa-miR-143 to regulate their expression by microRNA (miRNA) mimics.

Results:

The results showed effective expression of both genes by Entrovirus-like RNA constructs. The data also showed that the restoration of hsa-miR-143 expression in SW480 leads to a significant translation repression of the introduced reporter and suicide genes.

Conclusion:

Collectively, our data suggest the potential use of Entrovirus-like RNA molecules in suicide gene therapy. Additionally, as a consequence of the possible downregulated miRNA expression in cancerous tissues, a decreased expression of gene therapy constructs armed with target sequences for such miRNA in cancer tissue is expected.

Targeted gene delivery with noncovalent electrostatic conjugates of sgc-8c aptamer and polyethylenimine

BACKGROUND

Several strategies have been shown to improve the transfection efficiency of polyethylenimine (PEI) as a nonviral gene delivery vector. In the present study, a nucleic acid aptamer specific for protein tyrosine kinase 7 (PTK7) surface marker, sgc-8c, was conjugated electrostatically to pre-formed 10-kDa PEI/plasmid DNA polyplexes, and the ability of the conjugate to transfer genetic material was evaluated in MOLT-4 human acute lymphoblastic leukemia T-cells, which express PTK7 on their surface.

METHODS

Polyplexes (plasmid DNA-vector conjugates), prepared using PEI-sgc-8c conjugate and pCMVLuc as a reporter gene, were characterized in terms of particle size, surface charge and the extent of DNA condensation. Polyplexes were also evaluated for cytotoxicity using the MTS colorimetric assay, as well as for transfection efficiency in MOLT-4 cells, and compared with the results obtained in U266 cells, which lack cell surface PTK7.

RESULTS

Relative to pDNA/PEI, the size of pDNA/PEI/sgc-8c aptamer polyplexes increased with decreasing zeta potential. In MOLT-4 cells, pDNA/PEI/sgc-8c aptamer polyplexes exhibited an almost six- to eight-fold increase in transfection efficiency compared to that of pDNA/PEI polyplex, indicating that conjugation of sgc-8c aptamer to pre-formed 10-kDa PEI/plasmid DNA polyplexes achieved effective targeting without covalent attachment, whereas receptor-mediated conducted transfection was confirmed by performing a competitive transfection experiment and a cellular uptake study.

CONCLUSIONS

The results of the present study provide an example of the usefulness of a nucleic acid aptamer in the form of noncovalent, electrostatic conjugates as an approach for enhancing the transfection efficiency of a polycation vector such as PEI without significant induced cytotoxicity.

5-Fluorouracil-loaded poly(ε-caprolactone) nanoparticles combined with phage E gene therapy as a new strategy against colon cancer

This work aimed to develop a new therapeutic approach to increase the efficacy of 5-fluorouracil (5-FU) in the treatment of advanced or recurrent colon cancer. 5-FU-loaded biodegradable poly(ε-caprolactone) nanoparticles (PCL NPs) were combined with the cytotoxic suicide gene E (combined therapy). The SW480 human cancer cell line was used to assay the combined therapeutic strategy. This cell line was established from a primary adenocarcinoma of the colon and is characterized by an intrinsically high resistance to apoptosis that correlates with its resistance to 5-FU. 5-FU was absorbed into the matrix of the PCL NPs during synthesis using the interfacial polymer disposition method. The antitumor activity of gene E from the phage ϕX174 was tested by generating a stable clone (SW480/12/E). In addition, the localization of E protein and its activity in mitochondria were analyzed. We found that the incorporation of 5-FU into PCL NPs (which show no cytotoxicity alone), significantly improved the drug's anticancer activity, reducing the proliferation rate of colon cancer cells by up to 40-fold when compared with the nonincorporated drug alone. Furthermore, E gene expression sensitized colon cancer cells to the cytotoxic action of the 5-FU-based nanomedicine. Our findings demonstrate that despite the inherent resistance of SW480 to apoptosis, E gene activity is mediated by an apoptotic phenomenon that includes modulation of caspase-9 and caspase-3 expression and intense mitochondrial damage. Finally, a strongly synergistic antiproliferative effect was observed in colon cancer cells when E gene expression was combined with the activity of the 5-FU-loaded PCL NPs, thereby indicating the potential therapeutic value of the combined therapy.

The indolic diet-derivative, 3,3'-diindolylmethane, induced apoptosis in human colon cancer cells through upregulation of NDRG1

N-myc downstream regulated gene-1 participates in carcinogenesis, angiogenesis, metastases, and anticancer drug resistance. In the present study, we analyzed the expression pattern of N-myc downstream regulated gene-1 following treatment of human colonic cancer cell lines; HCT-116 (well differentiated with wild-type p53 gene) and Colo-320 (poorly differentiated with mutant p53 gene), with 3,3'-diindolylmethane, a well-established proapoptotic agent product derived from indole-3-carbinol. Treatment of Colo-320 and HCT-116 with 3,3'-diindolylmethane disclosed inhibition of cell viability in a dose-dependent manner, mediated through apoptosis induction. The increased expression of N-myc downstream regulated gene-1 was detected only in poorly differentiated colon cancer cells, Colo-320 cell line. Our results suggest that N-myc downstream regulated gene-1 expression is enhanced by 3,3'-diindolylmethane in poorly differentiated cells and followed by induction of apoptosis. 3,3'-diindolylmethane induced apoptosis may represent a new regulator of N-myc downstream regulated gene-1 in poorly differentiated colonic cancer cells.

Targeted killing effects of double CD and TK suicide genes controlled by survivin promoter on gastric cancer cell

Suicide genes such as cytosine deaminase (CD) and herpes simplex virus thymidine kinase (TK) encode products that convert nontoxic substances (prodrugs) into toxic metabolites. Studies in recent years indicated that survivin(sur) expression was associated with the biological behaviors of gastric carcinoma. In the present study, targeted killing effects of double CD and TK suicide genes controlled by survivin promoter on gastric cancer cell were investigated, the recombinant pSCT vector containing CD and TK genes driven by sur promoter was constructed and transfected into SGC-7901 cells. After adding the CCV and 5-FC, the effects of double suicide genes on cell growth, cell cycle and proliferation were determined by MTT assay and flow cytometry (FCM). The results showed that sur promoter could specifically drive the expression of double CD/TK gene in SGC-7901 cells, whereas not in the normal GES-1 cell. After using CCV and 5-FC, the growth of SGC-7901 cells was inhibited. G1 phase proportion was significantly higher in SGC-7901 cells transfected with double suicide genes than the untransfected cells. These results suggest that CD and TK double suicide genes driven by sur promoter could provide a new approach for enhancing selective suicide gene therapy of CD/5-FC for the treatment of advanced gastric carcinoma.