Viral genes as oncolytic agents for cancer therapy

Emerging Nano-/Biotechnology Drives Oncolytic Virus-Activated and Combined Cancer Immunotherapy

Oncolytic viruses (OVs) as one promising antitumor methods have made important contributions to tumor immunotherapy, which arouse increasing attention. They provide the dual mechanisms including direct killing effect toward tumor cells and immune activation for elevating antitumor responses, which have been proved in many preclinical studies. Especially, natural or genetically modified viruses as clinical immune preparations have emerged as a new promising approach objective to oncology treatment. The approval of talimogene laherparepvec (T-VEC) by the U.S. Food and Drug Administration (FDA) for the therapy of advanced melanoma could be considered as a milestone achievement in the clinical translation of OV. In this review, we first discussed the antitumor mechanisms of OVs with an emphasis on targeting, replication, and propagation. We further outlined the state of the art of current OVs in tumor and underlined the activated biological effects especially including immunity. More significantly, the enhanced immune responses based on OVs were systematically discussed from different perspectives such as combination with immunotherapy, genetic engineering of OVs, integration with nanobiotechnology or nanoparticles, and antiviral response counteraction, where their principles were shed light on. The development of OVs in the clinics was also highlighted to analyze the actuality and concerns of different OV applications in clinical trials. At last, the future perspectives and challenges of OVs as an already widely accepted treatment means were discussed. This review will provide a systematic review and deep insight into OV development and also offer new opportunities and guidance pathways to drive the further clinical translation.

Canine Parvovirus and Its Non-Structural Gene 1 as Oncolytic Agents: Mechanism of Action and Induction of Anti-Tumor Immune Response

The exploration into the strategies for the prevention and treatment of cancer is far from complete. Apart from humans, cancer has gained considerable importance in animals because of increased awareness towards animal health and welfare. Current cancer treatment regimens are less specific towards tumor cells and end up harming normal healthy cells. Thus, a highly specific therapeutic strategy with minimal side effects is the need of the hour. Oncolytic viral gene therapy is one such specific approach to target cancer cells without affecting the normal cells of the body. Canine parvovirus (CPV) is an oncolytic virus that specifically targets and kills cancer cells by causing DNA damage, caspase activation, and mitochondrial damage. Non-structural gene 1 (NS1) of CPV, involved in viral DNA replication is a key mediator of cytotoxicity of CPV and can selectively cause tumor cell lysis. In this review, we discuss the oncolytic properties of Canine Parvovirus (CPV or CPV2), the structure of the NS1 protein, the mechanism of oncolytic action as well as role in inducing an antitumor immune response in different tumor models.

Identification of a novel cell-penetrating peptide derived from the capsid protein of chicken anemia virus and its application in gene delivery

Cell membranes are a great obstacle for entrance of gene therapeutic agents. Cell-penetrating peptides (CPPs) have been proven as a promising gene delivery tool. However, the early TAT peptide derived from the HIV transcription activator protein has been proven that the sequence contains Furin protease cleaved motifs which limited the TAT application in delivery of exogenous active molecules. In the present study, through the bioinformatics and experimental approach, we have identified a novel CPP derived from the N terminus of VP1 protein of chicken anemia virus (CAV), designated as CVP1-N2, which is rich in arginine residues and contains α-helical structure. Then, the ability of CVP1-N2 cell penetrating was detected using confocal imaging and flow cytometry. FITC-labeled CVP1-N2 peptide could rapidly internalize into different types of live cells with dose dependence and without cytotoxic effects by MTT assay. Surprisingly, CVP1-N2 with a pattern of nuclear sub-location has shown the higher uptake efficiency than TAT. At 10, 1, and 0.1 μM, the mean relative internalization of CVP1-N2 was respectively 1.08-, 12-, and 75-fold higher than that of CVP1, as well as 1.6-, 56-, and 75-fold higher than that of TAT. Moreover, using endocytic inhibitors along with low-temperature stress validated that the CVP1-N2 internalization route is direct translocation pathway. Finally, the capacity of CVP1-N2 for delivery of gene into cells was determined, where it was able to carry red fluorescent protein (RFP) and apoptin genes into cells respectively and induce the apoptosis. All these data indicate that CVP1-N2 could be used as a novel gene delivery vehicle for gene therapy in the future. KEY POINTS: • 1CVP1-N2 was identified as a novel more efficient cell-penetrating peptide. • 2. CVP1-N2 localized to the nucleus through the direct transduction pathway. • 3. CVP1-N2 was able to deliver the apoptin gene into HCT116 cells and induce apoptosis.

Apoptin as a Tumor-Specific Therapeutic Agent: Current Perspective on Mechanism of Action and Delivery Systems

Cancer remains one of the leading causes of death worldwide in humans and animals. Conventional treatment regimens often fail to produce the desired outcome due to disturbances in cell physiology that arise during the process of transformation. Additionally, development of treatment regimens with no or minimum side-effects is one of the thrust areas of modern cancer research. Oncolytic viral gene therapy employs certain viral genes which on ectopic expression find and selectively destroy malignant cells, thereby achieving tumor cell death without harming the normal cells in the neighborhood. Apoptin, encoded by Chicken Infectious Anemia Virus' VP3 gene, is a proline-rich protein capable of inducing apoptosis in cancer cells in a selective manner. In normal cells, the filamentous Apoptin becomes aggregated toward the cell margins, but is eventually degraded by proteasomes without harming the cells. In malignant cells, after activation by phosphorylation by a cancer cell-specific kinase whose identity is disputed, Apoptin accumulates in the nucleus, undergoes aggregation to form multimers, and prevents the dividing cancer cells from repairing their DNA lesions, thereby forcing them to undergo apoptosis. In this review, we discuss the present knowledge about the structure of Apoptin protein, elaborate on its mechanism of action, and summarize various strategies that have been used to deliver it as an anticancer drug in various cancer models.

A combinational therapy of EGFR-CAR NK cells and oncolytic herpes simplex virus 1 for breast cancer brain metastases

Breast cancer brain metastases (BCBMs) are common in patients with metastatic breast cancer and indicate a poor prognosis. These tumors are especially resistant to currently available treatments due to multiple factors. However, the combination of chimeric antigen receptor (CAR)-modified immune cells and oncolytic herpes simplex virus (oHSV) has not yet been explored in this context. In this study, NK-92 cells and primary NK cells were engineered to express the second generation of EGFR-CAR. The efficacies of anti-BCBMs of EGFR-CAR NK cells, oHSV-1, and their combination were tested in vitro and in a breast cancer intracranial mouse model. In vitro, compared with mock-transduced NK-92 cells or primary NK cells, EGFR-CAR-engineered NK-92 cells and primary NK cells displayed enhanced cytotoxicity and IFN-γ production when co-cultured with breast cancer cell lines MDA-MB-231, MDA-MB-468, and MCF-7. oHSV-1 alone was also capable of lysing and destroying these cells. However, a higher cytolytic effect of EGFR-CAR NK-92 cells was observed when combined with oHSV-1 compared to the monotherapies. In the mice intracranially pre-inoculated with EGFR-expressing MDA-MB-231 cells, intratumoral administration of either EGFR-CAR-transduced NK-92 cells or oHSV-1 mitigated tumor growth. Notably, the combination of EGFR-CAR NK-92 cells with oHSV-1 resulted in more efficient killing of MDA-MB-231 tumor cells and significantly longer survival of tumor-bearing mice when compared to monotherapies. These results demonstrate that regional administration of EGFR-CAR NK-92 cells combined with oHSV-1 therapy is a potentially promising strategy to treat BCBMs.

HN protein of Newcastle disease virus sensitizes HeLa cells to TNF-α-induced apoptosis by downregulating NF-κB expression

Hemagglutinin neuraminidase (HN) is a membrane protein of Newcastle disease virus (NDV) with the ability to induce apoptosis in many transformed cell lines. TNF-α is a multi-factorial protein that regulates cell survival, differentiation and apoptosis. In a previous study, we reported that HN protein induces apoptosis by downregulating NF-κB expression. Further, we speculated that downregulation of NF-κB expression might sensitize HeLa cells to TNF-α-mediated apoptosis. Therefore, the present study was undertaken to investigate if HN protein could sensitize HeLa cells to TNF-α and to examine the apoptotic potential of the HN protein and TNF-α in combination. The results revealed that the pro-apoptotic effects were more pronounced with the combination of HN and TNF-α than with HN or TNF-α alone, which indicates that the HN protein indeed sensitized the HeLa cells to TNF-α-induced cell death. The results of the study provide a mechanistic insight into the apoptotic action of HN protein along with TNF-α, which could be valuable in treating tumor types that are naturally resistant to TNF-α.

Poly (I:C) enhances the anti-tumor activity of canine parvovirus NS1 protein by inducing a potent anti-tumor immune response

The canine parvovirus NS1 (CPV2.NS1) protein selectively induces apoptosis in the malignant cells. However, for an effective in vivo tumor treatment strategy, an oncolytic agent also needs to induce a potent anti-tumor immune response. In the present study, we used poly (I:C), a TLR3 ligand, as an adjuvant along with CPV2.NS1 to find out if the combination can enhance the oncolytic activity by inducing a potent anti-tumor immune response. The 4T1 mammary carcinoma cells were used to induce mammary tumor in Balb/c mice. The results suggested that poly (I:C), when given along with CPV2.NS1, not only significantly reduced the tumor growth but also augmented the immune response against tumor antigen(s) as indicated by the increase in blood CD4+ and CD8+ counts and infiltration of immune cells in the tumor tissue. Further, blood serum analysis of the cytokines revealed that Th1 cytokines (IFN-γ and IL-2) were significantly upregulated in the treatment group indicating activation of cell-mediated immune response. The present study reports the efficacy of CPV2.NS1 along with poly (I:C) not only in inhibiting the mammary tumor growth but also in generating an active anti-tumor immune response without any visible toxicity. The results of our study may help in developing CPV2.NS1 and poly (I: C) combination as a cancer therapeutic regime to treat various malignancies.

Combined administration of the apoptin gene and poly (I:C) induces potent anti-tumor immune response and inhibits growth of mouse mammary tumors

BACKGROUND

Many viral proteins exhibit selective cytotoxicity for tumor cells without affecting the normal diploid cells. The apoptin protein of chicken infectious anemia virus is one of such proteins, which has been shown to kill tumor cells specifically. However, an effective cancer treatment strategy also requires assistance from the immune system. Recently, poly (I:C) has been shown to be an effective cancer vaccine adjuvant.

AIM

In this study, we assessed the anti-tumor potential of apoptin gene transfer alone and in combination with poly (I:C) in a 4T1 mouse mammary tumor model.

METHODS

4T1 cells were used to induce mammary tumor in Balb/c mice. Mice bearing tumors were divided into 6 groups, and each group received six intratumoral injections during a period of one month. After the last immunization, the animals were sacrificed, and peripheral blood, spleen, lungs, liver, heart, kidney and tumor tissues were collected for immunological, molecular and pathological analysis.

RESULTS

We report that intratumoral administration of apoptin plasmid along with poly (I:C) not only significantly inhibited the growth of mammary tumor, but also induced a potent anti-tumor immune response as indicated by the increase in blood CD4+, CD8+ cells and infiltration of immune cells in the tumor tissue. Further, blood serum analysis of the cytokines revealed increased secretion of Th1 cytokines (IFN-γ and IL-2).

CONCLUSIONS

The results of our study demonstrate that the inclusion of poly (I:C) significantly enhanced the anti-tumor activity of apoptin mainly by inducing a potent anti-tumor immune response. Therefore, we report the use of apoptin and poly (I:C) combination as a novel and powerful strategy for cancer immunotherapy.