Adenoviral vectors for prodrug activation-based gene therapy for cancer

Antitumor effect of a dual cancer-specific oncolytic adenovirus on prostate cancer PC-3 cells

PURPOSE

Apoptin can specifically kill cancer cells but has no toxicity to normal cells. Human telomerase reverse transcriptase (hTERT) acts as a tumor-specific promoter, triggering certain genes to replicate or express only in tumor cells, conferring specific replication and killing abilities. This study aimed to investigate the anticancer potential of the recombinant adenovirus Ad-apoptin-hTERTp-E1a (Ad-VT) in prostate cancer.

METHODS

The pGL4.51 plasmid was used to transfect PC-3 cells to construct tumor cells stably expressing luciferase (PC-3-luc). Crystal violet staining and MTS assays determined the ability of Ad-VT to inhibit cell proliferation. Ad-VT-induced apoptosis of PC-3-luc cells was detected using Hoechst, Annexin V, JC-1 staining, and caspases activity analysis. PC-3-luc cells invasion and migration were detected using cell-scratch and Transwell assays. In vivo tumor inhibition was detected using imaging techniques.

RESULTS

Crystal violet staining and MTS results showed that the proliferation ability of PC-3-luc cells decreased significantly. Hoechst, JC-1, and Annexin V experiments demonstrated that Ad-VT mainly induced apoptosis to inhibit PC-3-luc cell proliferation. Ad-VT could significantly inhibit the migration and invasion of PC-3-luc cells over a short period of time. In vivo, Ad-VT could effectively inhibit tumor growth and prolong survival of the mice.

CONCLUSIONS

The recombinant adenovirus, comprising the apoptin protein and the hTERTp promoter, was able to inhibit the growth of prostate cancer PC-3 cells and promote their apoptosis.

Development of a computational promoter with highly efficient expression in tumors

Background

Gene therapy is a potent method to increase the therapeutic efficacy against cancer. However, a gene that is specifically expressed in the tumor area has not been identified. In addition, nonspecific expression of therapeutic genes in normal tissues may cause side effects that can harm the patients’ health. Certain promoters have been reported to drive therapeutic gene expression specifically in cancer cells; however, low expression levels of the target gene are a problem for providing good therapeutic efficacy. Therefore, a specific and highly expressive promoter is needed for cancer gene therapy.

Methods

Bioinformatics approaches were utilized to analyze transcription factors (TFs) from high-throughput data. Reverse transcription polymerase chain reaction, western blotting and cell transfection were applied for the measurement of mRNA, protein expression and activity. C57BL/6JNarl mice were injected with pD5-hrGFP to evaluate the expression of TFs.

Results

We analyzed bioinformatics data and identified three TFs, nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), cyclic AMP response element binding protein (CREB), and hypoxia-inducible factor-1α (HIF-1α), that are highly active in tumor cells. Here, we constructed a novel mini-promoter, D5, that is composed of the binding sites of the three TFs. The results show that the D5 promoter specifically drives therapeutic gene expression in tumor tissues and that the strength of the D5 promoter is directly proportional to tumor size.

Conclusions

Our results show that bioinformatics may be a good tool for the selection of appropriate TFs and for the design of specific mini-promoters to improve cancer gene therapy.

Electronic supplementary material

The online version of this article (10.1186/s12885-018-4421-7) contains supplementary material, which is available to authorized users.

Targeted breast cancer therapy by harnessing the inherent blood group antigen immune system

Cancer gene therapy has attracted increasing attention for its advantages over conventional therapy in specific killing of tumor cells. Here, we attempt to prove a novel therapeutic approach that targets tumors by harnessing the blood antigen immune response system, which is inherently present in patients with breast cancers. Breast cancer MDA-MB-231 cells expressed blood group H antigen precursor. After ectopic expression of blood group A glycosyltransferase, we found that the H precursor was converted into the group A antigen, appearing on the surface of tumor cells. Incubation with group B plasma from breast cancer patients activated the antigen-antibody-complement cascade and triggered tumor cell killing. Interestingly, expression of blood A antigen also reduced tumorigenesis in breast cancer cells by inhibiting cell proliferation, migration, and tumor sphere formation. Cell cycle analysis revealed that cancer cells were paused at S phase due to the activation of cell cycle regulatory genes. Furthermore, pro-apoptotic genes were unregulated by the A antigen, including BAX, P21, and P53, while the anti-apoptotic BCL2 was down regulated. Importantly, we showed that extracellular HMGB1 and ATP, two critical components of the immunogenic cell death pathway, were significantly increased in the blood A antigen-expressing tumor cells. Collectively, these data suggest that blood antigen therapy induces specific cancer cell killing by activating the apoptosis and immunogenic cell death pathways. Further translational studies are thereby warranted to apply this approach in cancer immuno-gene therapy.

Discovery of tumor-specific irreversible inhibitors of stearoyl CoA desaturase

A hallmark of targeted cancer therapies is selective toxicity among cancer cell lines. We evaluated results from a viability screen of over 200,000 small molecules to identify two chemical series, oxalamides and benzothiazoles, that were selectively toxic to the same four of 12 human lung cancer cell lines at low nanomolar concentrations. Sensitive cell lines expressed cytochrome P450 (CYP) 4F11, which metabolized the compounds into irreversible stearoyl CoA desaturase (SCD) inhibitors. SCD is recognized as a promising biological target in cancer and metabolic disease. However, SCD is essential to sebocytes, and accordingly SCD inhibitors cause skin toxicity. Mouse sebocytes were unable to activate the benzothiazoles or oxalamides into SCD inhibitors, providing a therapeutic window for inhibiting SCD in vivo. We thus offer a strategy to target SCD in cancer by taking advantage of high CYP expression in a subset of tumors.

The antitumor effects of oncolytic adenovirus H101 against lung cancer

Lung cancer is the leading cause of cancer mortality in both men and women, with dismal survival rates due to late-stage diagnoses and a lack of efficacious therapies. The new treatment options with completely novel mechanism of therapeutic activity are needed for lung cancer to improve patient outcome. The present study was aimed at testing the efficacy of recombinant adenovirus H101 as an oncolytic agent for killing human lung cancer cell lines in vitro and in vivo. We assessed the coxsackievirus adenovirus receptor (CAR) expression on human lung cancer cell lines by RT-PCR and immunocytochemistry staining. Viral infectivity and viral replication in lung cancer cells was assayed by flow cytometry and real-time fluorescent quantitative PCR. After H101 treatment, cytotoxic effect, cell cycle progression and apoptosis were further examined by lactate dehydrogenase release assay and flow cytometry in vitro, respectively. In vivo, antitumor effects of H101 were assessed on SCID Beige mice xenografted with human lung cancer cells. Receptor characterization confirmed that human lung cancer cell lines expressed CAR receptor for adenovirus type 5. Lung cancer cells were sensitive to infection by the H101 virus. H101 infection and replication resulted in very potent cytotoxicity, G2/M phase arrest and cell lysis. In vivo, we also showed that H101 significantly inhibited tumor growth following intratumoral injection, with virus replication, cell degeneration and necrosis in the tumor tissue. These results have important implications for the treatment of human lung cancer.

Adenoviral-mediated imaging of gene transfer using a somatostatin receptor-cytosine deaminase fusion protein

Suicide gene therapy is a process by which cells are administered a gene that encodes a protein capable of converting a nontoxic prodrug into an active toxin. Cytosine deaminase (CD) has been widely investigated as a means of suicide gene therapy due to the enzyme’s ability to convert the prodrug 5-fluorocytosine (5-FC) into the toxic compound 5-fluorouracil (5-FU). However, the extent of gene transfer is a limiting factor in predicting therapeutic outcome. The ability to monitor gene transfer, non-invasively, would strengthen the efficiency of therapy. In this regard, we have constructed and evaluated a replication-deficient adenovirus (Ad) containing the human somatostatin receptor subtype 2 (SSTR2) fused with a C-terminal yeast CD gene for the non-invasive monitoring of gene transfer and therapy. The resulting Ad (AdSSTR2-yCD) was evaluated in vitro in breast cancer cells to determine the function of the fusion protein. These studies demonstrated that the both the SSTR2 and yCD were functional in binding assays, conversion assays, and cytotoxicity assays. In vivo studies similarly demonstrated the functionality using conversion assays, biodistribution studies, and small animal positron-emission tomography (PET) imaging studies. In conclusion, the fusion protein has been validated as useful for the non-invasive imaging of yCD expression and will be evaluated in the future for monitoring yCD-based therapy.

A fiber-modified adenovirus co-expressing HSV-TK and Coli.NTR enhances antitumor activities in breast cancer cells

Breast cancers especially in late and metastatic stages remain refractory to treatment despite advances in surgical techniques and chemotherapy. Suicide gene therapy based on adenoviral technology will be promising strategies for such advanced diseases. We previously showed that co-expression of herpes simplex virus thymidine kinase (HSV-TK) and Escherichia coli nitroreductase (Coli.NTR) by an hTERT-driven adenovirus vector resulted in additive anti-tumor effects in breast cancer cells in vitro and in vivo. As many tumor tissue and cancer cells express low level of coxsackie-adenovirus receptor (CAR), which is the functional receptor for the fiber protein of human adenovirus serotype 5 (Ad5), novel Ad5 vectors containing genetically modifi ed fiber are attractive vehicles for achieving targeted gene transfer and improving suicide gene expression in these cancer cells. In the present study, we first built a simplified Ad5 vector platform for fiber modification and quick detection for gene transfer. Then a fiber-modified adenovirus vector containing an RGD motif in the HI loop of the fiber knob was constructed. After recombined with HSV-TK and Coli.NTR gene, this fiber-modified Ad5 vector (Ad-RGD-hT-TK/NTR) was compared with that of our previously constructed Ad5 vector (Ad-hT-TK/NTR) for its therapeutic effects in human breast cancer cell lines. The anti-tumor activity of Ad-RGD-hT-TK/NTR was significantly enhanced compared with Ad-hT-TK/NTR both in vitro and in vivo. This new vector platform provided a robust and simplified approach for capsid modification, and the fiber-modified Ad5 with double suicide genes under the control of hTERT promoter would be a useful gene therapy strategy for breast cancer.