A tumor-specific conditionally replicative adenovirus vector expressing TRAIL for gene therapy of hepatocellular carcinoma

Recent advances in oncolytic virus therapy for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a highly refractory cancer and the fourth leading cause of cancer-related mortality worldwide. Despite the development of a detailed treatment strategy for HCC, the survival rate remains unsatisfactory. Oncolytic virus has been extensively researched as a new cancer therapeutic agent in the treatment of HCC. Researchers have designed a variety of recombinant viruses based on natural oncolytic diseases, which can increase the targeting of oncolytic viruses to HCC and their survival in tumors, as well as kill tumor cells and inhibit the growth of HCC through a variety of mechanisms. The overall efficacy of oncolytic virus therapy is known to be influenced by anti-tumor immunity, toxic killing effect and inhibition of tumor angiogenesis, etc. Therefore, a comprehensive review of the multiple oncolytic mechanisms of oncolytic viruses in HCC has been conducted. So far, a large number of relevant clinical trials are under way or have been completed, and some encouraging results have been obtained. Studies have shown that oncolytic virus combined with other HCC therapies may be a feasible method, including local therapy, chemotherapy, molecular targeted therapy and immunotherapy. In addition, different delivery routes for oncolytic viruses have been studied so far. These studies make oncolytic virus a new and attractive drug for the treatment of HCC.

PSMA-specific theranostic nanoplex for combination of TRAIL gene and 5-FC prodrug therapy of prostate cancer

Metastatic prostate cancer causes significant morbidity and mortality and there is a critical unmet need for effective treatments. We have developed a theranostic nanoplex platform for combined imaging and therapy of prostate cancer. Our prostate-specific membrane antigen (PSMA) targeted nanoplex is designed to deliver plasmid DNA encoding tumor necrosis factor related apoptosis-inducing ligand (TRAIL), together with bacterial cytosine deaminase (bCD) as a prodrug enzyme. Nanoplex specificity was tested using two variants of human PC3 prostate cancer cells in culture and in tumor xenografts, one with high PSMA expression and the other with negligible expression levels. The expression of EGFP-TRAIL was demonstrated by fluorescence optical imaging and real-time PCR. Noninvasive (19)F MR spectroscopy detected the conversion of the nontoxic prodrug 5-fluorocytosine (5-FC) to cytotoxic 5-fluorouracil (5-FU) by bCD. The combination strategy of TRAIL gene and 5-FC/bCD therapy showed significant inhibition of the growth of prostate cancer cells and tumors. These data demonstrate that the PSMA-specific theranostic nanoplex can deliver gene therapy and prodrug enzyme therapy concurrently for precision medicine in metastatic prostate cancer.

Tuberin and PRAS40 are anti-apoptotic gatekeepers during early human amniotic fluid stem-cell differentiation

Embryoid bodies (EBs) are three-dimensional multicellular aggregates allowing the in vitro investigation of stem-cell differentiation processes mimicking early embryogenesis. Human amniotic fluid stem (AFS) cells harbor high proliferation potential, do not raise the ethical issues of embryonic stem cells, have a lower risk for tumor development, do not need exogenic induction of pluripotency and are chromosomal stable. Starting from a single human AFS cell, EBs can be formed accompanied by the differentiation into cells of all three embryonic germ layers. Here, we report that siRNA-mediated knockdown of the endogenous tuberous sclerosis complex-2 (TSC2) gene product tuberin or of proline-rich Akt substrate of 40 kDa (PRAS40), the two major negative regulators of mammalian target of rapamycin (mTOR), leads to massive apoptotic cell death during EB development of human AFS cells without affecting the endodermal, mesodermal and ectodermal cell differentiation spectrum. Co-knockdown of endogenous mTOR demonstrated these effects to be mTOR-dependent. Our findings prove this enzyme cascade to be an essential anti-apoptotic gatekeeper of stem-cell differentiation during EB formation. These data allow new insights into the regulation of early stem-cell maintenance and differentiation and identify a new role of the tumor suppressor tuberin and the oncogenic protein PRAS40 with the relevance for a more detailed understanding of the pathogenesis of diseases associated with altered activities of these gene products.

Viral delivery for gene therapy against cell movement in cancer

Viral delivery for cancer gene therapy is a promising approach, where traditional radiotherapy or chemotherapy to limit proliferation and movement of cancer cells has met resistance. Based on the new understanding of the biology of the viral vectors, therapeutic viral vectors for cancer gene therapy have been improved for greater safety and efficacy as well as transitioned from being non-replicating to replication-competent. Traditional oncolytic vectors have focused on eliminating tumor growth, while novel vectors simultaneously target epithelial-to-mesenchymal transition (EMT) in cancer cells, which could further prevent and reverse the aggressive tumor progression. In this review, we highlight the illustrative examples of cancer gene therapy in clinical trials as well as preclinical data and include proposals on methods to further enhance the safety and efficacy of oncolytic viral vectors in cancer gene therapy.

Conditionally replicating adenovirus improves gene replication efficiency and anticancer effect of E1-deleted adenovirus carrying TRAIL in head and neck squamous cell carcinoma

To overcome the low efficiency of gene therapy, we combined a conditionally replicating adenovirus (CRAd) and an adenoviral vector with a therapeutic gene. CRAd has an oncolytic activity in cancer cells with abnormal Rb activity and helps the replication of therapeutic genes incorporated in the E1-deleted adenovirus. We investigated the anticancer effect of a combination of CRAd and adenovirus carrying tumor necrosis factor-related apoptosis inducing ligand (ad-TRAIL). We expected to see increased gene expression in cancer cells as well as an antitumor effect. With the combined application of CRAd and ad-luciferase in head and neck cancer cell lines, we observed considerably increased luciferase activity that was 10- to 50-fold greater than with ad-luciferase alone. The combination of CRAd and ad-TRAIL showed significant suppression of growth in cell lines and increased the sub-G(1) portion of cells 30-fold compared to any single treatment. The expression of TRAIL was highly amplified by the combined treatment and was accompanied by expression of molecules related to apoptosis. In a xenograft animal model, mice treated with CRAd and ad-TRAIL showed complete regression of established tumors, whereas mice treated with CRAd or ad-TRAIL alone did not. In conclusion, this combined strategy using CRAd and adenovirus carrying a therapeutic gene increased the gene transfer rate and enhanced antitumor effects. We expect that this combination strategy could be extended to a multitarget cancer gene therapy by combining multiple adenoviruses and CRAd.

Boundaries in vertebrate genomes: different solutions to adequately insulate gene expression domains

Gene expression domains are normally not arranged in vertebrate genomes according to their expression patterns. Instead, it is not unusual to find genes expressed in different cell types, or in different developmental stages, sharing a particular region of a chromosome. Therefore, the existence of boundaries, or insulators, as non-coding gene regulatory elements, is instrumental for the adequate organization and function of vertebrate genomes. Through the evolution and natural selection at the molecular level, and according to available DNA sequences surrounding a locus, previously existing or recently mobilized, different elements have been recruited to serve as boundaries, depending on their suitability to properly insulate gene expression domains. In this regard, several gene regulatory elements, including scaffold/matrix-attachment regions, members of families of DNA repetitive elements (such as LINEs or SINEs), target sites for the zinc-finger multipurpose nuclear factor CTCF, enhancers and locus control regions, have been reported to show functional activities as insulators. In this review, we will address how such a variety of apparently different genomic sequences converge in a similar function, namely, to adequately insulate a gene expression domain, thereby allowing the locus to be expressed according to their own gene regulatory elements without interfering itself and being interfered by surrounding loci. The identification and characterization of genomic boundaries is not only interesting as a theoretical exercise for better understanding how vertebrate genomes are organized, but also allows devising new and improved gene transfer strategies to ensure the expression of heterologous DNA constructs in ectopic genomic locations.

Antitumor activity of Ad-IU2, a prostate-specific replication-competent adenovirus encoding the apoptosis inducer, TRAIL

In this study, we investigated the preclinical utility and antitumor efficacy of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) delivered by Ad-IU2, a prostate-specific replication-competent adenovirus (PSRCA), against androgen-independent prostate cancer. Through transcriptional control of adenoviral early genes E1a, E1b and E4, as well as TRAIL by two bidirectional prostate-specific enhancing sequences (PSES), expression of TRAIL as well adenoviral replication was limited to prostate-specific antigen (PSA) and prostate-specific membrane antigen (PSMA)-positive cells. Ad-IU2 induced 5-fold greater apoptosis selectively in PSA/PSMA-positive CWR22rv and C4-2 cells than an oncolytic adenoviral control. Furthermore, prolonged infection with Ad-IU2 reversed TRAIL resistance in LNCaP cells. Ad-IU2 exhibited superior killing efficiency in PSA/PSMA-positive prostate cancer cells at doses 5- to 8-fold lower than required by a PSRCA to produce a similar effect. This cytotoxic effect was not observed in non-prostatic cells, however. As an enhancement of its therapeutic efficacy, Ad-IU2 exerted a TRAIL-mediated bystander effect through direct cell-to-cell contact and soluble factors such as apoptotic bodies. In vivo, Ad-IU2 markedly suppressed the growth of subcutaneous androgen-independent CWR22rv xenografts compared to a PSRCA at six weeks post-treatment (3.1- vs. 17.1-fold growth of tumor). This study demonstrates the potential clinical utility of a PSRCA armed with an apoptosis-inducing ligand.

Treatment of hepatocellular carcinoma by AdAFPep/rep, AdAFPep/p53, and 5-fluorouracil in mice

Although conditionally replicable adenovirus (CRAd) has been used in the clinical treatment of hepatocellular carcinoma (HCC), it suffers from the inherent drawback of having relatively low antitumor activity. Here, we have sought to overcome this drawback. First, we combined CRAd (AdAFPep/Rep) driven by alpha-fetoprotein enhancer/promoter (AFPep) with a replication-incompetent adenovirus carrying a p53 transgene that is also driven by AFPep. The synergism of this combination produced a significantly improved tumoricidal effect on the human HCC cell line Hep3B, which has a relatively short doubling time in comparison with other human HCC cell lines, through the transactivation of p53 by early region 1A transcribed by AdAFPep/Rep. This synergistic interaction was augmented by the addition of a subtumoricidal dose (0.5 microg/mL) of 5-fluorouracil (5-FU), which enhanced p53 expression and facilitated the release of virions from tumor cells. When relatively large (10-mm-diameter) Hep3B tumors grown in nude mice were injected with the two viruses in combination, they showed significantly impaired growth in comparison with those treated with each virus separately. The growth suppression effect of the virus combination was enhanced by a low dose (600 microg) of 5-FU. Survival of the tumor-bearing mice treated with these three agents was significantly longer than that of control mice. Moreover, the tumor completely disappeared with the repeated injection of these agents.

CONCLUSION

This combination strategy holds promise for the treatment of relatively large and rapidly growing HCCs that may be encountered clinically.

Reprogrammed viruses as cancer therapeutics: targeted, armed and shielded

Virotherapy is currently undergoing a renaissance, based on our improved understanding of virus biology and genetics and our better knowledge of many different types of cancer. Viruses can be reprogrammed into oncolytic vectors by combining three types of modification: targeting, arming and shielding. Targeting introduces multiple layers of cancer specificity and improves safety and efficacy; arming occurs through the expression of prodrug convertases and cytokines; and coating with polymers and the sequential usage of different envelopes or capsids provides shielding from the host immune response. Virus-based therapeutics are beginning to find their place in cancer clinical practice, in combination with chemotherapy and radiation.

Telomerase-specific oncolytic virotherapy for human hepatocellular carcinoma

AIM: To evaluate the therapeutic efficiency of replicative adenovirus CNHK300 targeted in telomerase-positive hepatocellular carcinoma.

METHODS: CNHK300, ONYX-015 (55 kDa protein deleted adenovirus) and wtAd5 (wild type adenovirus 5) were compared, and virus proliferation assay, cell viability assay, Western blot and fluorescence microscopy were used to evaluate the proliferation and cytolysis selectivity of CNHK300.

RESULTS: The replicative multiples in Hep3B and HepGII after 48 h of CNHK300 proliferation were 40 625 and 65 326 fold, respectively, similar to that of wtAd5.. However, CNHK300 exhibited attenuated replicative ability in normal fibroblast cell line BJ. CNHK300 could lyse hepatocellular carcinoma cells at a low multiplicity of infection (MOI), but could not affect growth of normal cells even at a high MOI.

CONCLUSION: CNHK300 is a cancer-selective replication-competent adenovirus which can cause oncolysis of liver cancer cells as well as wtAd5 (wild type adenovirus 5), but had severely attenuated replicative and cytolytic ability in normal cells. This novel strategy of cancer treatment offers a promising treatment platform.

Anticancer activity of oncolytic adenovirus vector armed with IFN-alpha and ADP is enhanced by pharmacologically controlled expression of TRAIL

We have previously described oncolytic adenovirus (Ad) vectors KD3 and KD3-interferon (IFN) that were rendered cancer-specific by mutations in the E1A region of Ad; these mutations abolish binding of E1A proteins to p300/CBP and pRB. The antitumor activity of the vectors was enhanced by overexpression of the Adenovirus Death Protein (ADP, E3-11.6K) and by replication-linked expression of IFN-alpha. We hypothesized that the anticancer efficacy of the KD3-IFN vector could be further improved by expression of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). E1-deleted Ad vectors were constructed carrying reporter genes for enhanced green fluorescent protein or secreted placental alkaline phosphatase (SEAP) and a therapeutic gene for TRAIL under control of the TetON system. Expression of the genes was increased in the presence of a helper virus and the inducer doxycycline such that up to 231-fold activation of expression for the TetON-SEAP vector was obtained. Coinfection with TetON-TRAIL augmented oncolytic activity of KD3 and KD3-IFN in vitro. Induction of TRAIL expression did not reduce the yield of progeny virus. Combination of TetON-TRAIL and KD3-IFN produced superior antitumor activity in vivo as compared with either vector alone demonstrating the efficacy of a four-pronged cancer gene therapy approach, which includes Ad oncolysis, ADP overexpression, IFN-alpha-mediated immunotherapy, and pharmacologically controlled TRAIL activity.

Oncolytic adenovirus-mediated E1A gene therapy induces tumor-cell apoptosis and reduces tumor angiogenesis leading to inhibition of hepatocellular carcinoma growth in animal model

Oncolytic adenovirus (rAd)-mediated E1A gene therapy of cancer has become a novel therapeutic modality. In this study, we constructed a recombinant oncolytic adenovirus (rAd-E1A) expressing the tumor suppressor E1A gene. We demonstrated that the rAd-E1A replicated in HepG2 and SMMC-7721 human hepatocellular carcinoma (HCC) cells but attenuated in the normal liver cell line HL-7702. It induced HCC cell apoptosis through upregulation of apoptosis-associated Bax, caspase-3, and Fas and downregulation of survivin and Bcl-2 in a p53-dependent pathway. It also downregulated the expression of angiogenesis- associated vascular endothelial growth factor (VEGF) and CD34 genes and reduced tumor vessel formation and angiogenesis. In mice bearing SMMC-7721 tumors, intratumoral injections of rAd- E1A significantly inhibited HCC growth. Therefore, the oncolytic adenovirus-mediated E1A gene therapy may be a useful therapeutic approach for HCC treatment.

Selective replication of E1B55K-deleted adenoviruses depends on enhanced E1A expression in cancer cells

E1B55K-deleted dl1520 could selectively replicate in cancer cells and has been used in clinical trials as an antitumor agent. The mechanism of virus selective replication in cancer cells, including a possible role of p53, is unclear. Studies with established cancer cell lines have demonstrated that some cancer cells are resistant to dl1520 replication, regardless of the p53 status. Hep3B cells supported the E1b-deleted adenoviruses to replicate, whereas Saos2 cells were resistant to viral replication. We applied p53-null Hep3B and Saos2 cells as models to clarify the replication ability of E1B55K-deleted adenoviruses with different expression levels of E1a. We show that lower E1A expression in Saos2 may be the reason for the poor replication in some cancer cells due to the fact that E1a promoter was less activated in Saos2 than in Hep3B. We also demonstrate that the E1B55K protein can increase E1A expression in Saos2 cells for efficient virus replication. In addition, the upstream regions of the E1a promoter have transcriptional activity in Hep3B cells but not in Saos2 cells. The viral E1B55K protein may activate cancer cellular factor(s) that targets the upstream regions of the E1a gene to increase its expression. This is the first study demonstrating that E1B55K protein affects the E1A production levels that is related to cancer selective replication. Our studies have suggested that increase of E1A expression from E1b-deleted adenoviruses may enhance killing cancer cells that otherwise are resistant to viral replication.