Induction of an effective anti-tumor immune response and tumor regression by combined administration of IL-18 and Apoptin

Microbial cancer therapeutics: A promising approach

The success of conventional cancer therapeutics is hindered by associated dreadful side-effects of antibiotic resistance and the dearth of antitumor drugs' selectivity and specificity. Hence, the conceptual evolution of anti-cancerous therapeutic agents that selectively target cancer cells without impacting the healthy cells or tissues, has led to a new wave of scientific interest in microbial-derived bioactive molecules. Such strategic solutions may pave the way to surmount the shortcomings of conventional therapies and raise the potential and hope for the cure of wide range of cancer in a selective manner. This review aims to provide a comprehensive summary of anti-carcinogenic properties and underlying mechanisms of bioactive molecules of microbial origin, and discuss the current challenges and effective therapeutic application of combinatorial strategies to attain minimal systemic side-effects.

Effects of chicken anaemia virus on experimental leukosis, induced by avian myelocytomatosis virus Mc29

The effects of concomitant infection with chicken anaemia virus (CAV) on the incidence, clinical manifestation and mortality from leukosis, induced by the avian myelocytomatosis virus strain Mc29 were studied. Experimental one-day-old 15 I line White Leghorn chickens were inoculated simultaneously with Mc29 and CAV or with Mc29 alone and observed daily for clinical signs and mortality. Both groups of chickens inoculated with Mc29 virus strain alone or in combination with CAV deve­loped tumours and died within 57 days. Necropsy has been performed on all dead birds following the standard protocol. Organ samples from thymuses, spleens, bone marrow, and livers were collected and histopathologically investigated. Neoplasms detected included myelocytomas, nephroblastomas and hepatocellular carcinomas. In addition, 50% of the CAV/Mc29-inoculated chickens developed epithelial type thymomas. However, no such lesions were found in chickens infected with Mc29 alone. No significant differences in the clinical course of leukosis between the two experimental groups of chickens were observed. The results indicated that CAV infection did not affect substantially the incidence and mortality from avian leukosis, induced by myelocytomatosis virus strain Mc29, but contributed to greater variety of the induced tumours.

Six Birds with One Stone: Versatile Nanoporphyrin for Single-Laser-Triggered Synergistic Phototheranostics and Robust Immune Activation

Simultaneous photodynamic therapy (PDT) and photothermal therapy (PTT) can reduce the risks of drug leakage, body burden, and preparation complexity in traditional combination PDT/PTT. Here, a versatile nanoporphyrin (Pp18-lipos) self-assembled from lipid-purpurin 18 conjugates (Pp18-lipids) and pure lipids is presented. The as-prepared Pp18-lipos with 2 mol% Pp18-lipids can perform effective PDT and fluorescence imaging. The Pp18-lipos with 65 mol% Pp18 can perform potent PTT and photoacoustic imaging. The chelation of Mn²⁺ endows the Pp18-lipids-Mn²⁺ a high T₁ -weighted magnetic resonance imaging contrast. Notably, pretreatment of low-dose PDT facilitates the endocytosis and tumor accumulation of Pp18-lipos, thus achieving synergistic PDT/PTT. Upon exposure to a single 705 nm-laser, the combination of PDT/PTT achieves a significantly higher tumor growth inhibition rate than PDT or PTT alone. In addition, it is found that the synergistic PDT/PTT triggers more potent anti-tumor immune response including tumor infiltration of immune cells and release of related cytokines.

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.

Cancer Treatment Goes Viral: Using Viral Proteins to Induce Tumour-Specific Cell Death

Cell death is a tightly regulated process which can be exploited in cancer treatment to drive the killing of the tumour. Several conventional cancer therapies including chemotherapeutic agents target pathways involved in cell death, yet they often fail due to the lack of selectivity they have for tumour cells over healthy cells. Over the past decade, research has demonstrated the existence of numerous proteins which have an intrinsic tumour-specific toxicity, several of which originate from viruses. These tumour-selective viral proteins, although from distinct backgrounds, have several similar and interesting properties. Though the mechanism(s) of action of these proteins are not fully understood, it is possible that they can manipulate several cell death modes in cancer exemplifying the intricate interplay between these pathways. This review will discuss our current knowledge on the topic and outstanding questions, as well as deliberate the potential for viral proteins to progress into the clinic as successful cancer therapeutics.

Potential CD34 signaling through phosphorylated-BAD in chemotherapy-resistant acute myeloid leukemia

Acute myeloid leukemia (AML) constitutively express growth factors and cytokines for survival. Chemotherapy alters these signals to induce cell death. However, drug resistance in AML remains a major hindrance to successful treatment and early warning is unavailable. Modulation of signaling pathways during chemotherapy may provide a window to detect response and predict treatment outcome. Blood samples collected from AML patients before and at day-3 of induction therapy were compared for changes in expression of CD117, CD34, pro-inflammatory cytokines and mediators of Akt and MAPK pathways, using multi-color flow cytometry. Nine patients were diagnosed as drug-resistant and seven sensitive to chemotherapy. Twelve were paired. Average percentages of CD34 (66.8 ± 11.7% vs. 26.2 ± 5.8%, p = 0.033) and pBAD (66.9 ± 8.2% vs. 28.9 ± 8.2%, p = 0.016) were significantly increased in chemo-resistant (N = 9) compared to chemo-sensitive (N = 5) samples. Percentages of CD34 were strongly correlated with pBAD (R = 0.785; p = 0.001; N = 14) and pFKHR (R = 0.755; p = 0.002; N = 14) at day-3 induction. Chemo-sensitive cases expressed significantly higher percentages of IL-18Rα (71.9 ± 9.6% vs. 29.8 ± 5.8%, p = 0.016). Though not significantly different in the outcome, IL-1β was strongly associated with activated Akt-S473, IL-6 with phosphorylated JNK and FKHR while TNF-α appeared to trigger Bim, in treated samples. These preliminary results suggested AML cells resistant to chemotherapy increased expression of CD34 and may signal through pBAD while cells sensitive to chemotherapy-induced IL18Rα expression. These were observed early during induction therapy. Identifying CD34 is interesting as it is a convenient marker to monitor drug-resistance in AML patients. Inhibition of CD34 and pBAD signaling may be important in treating drug-resistant AML.

Contribution of Inflammatory Cytokine Interleukin-18 Genotypes to Renal Cell Carcinoma

Interleukin-18 (IL-18) is a multi-functional immuno-mediator in the development and progression of many types of infectious and inflammatory diseases. In this study, we evaluated the contribution of IL-18 genotypes to renal cell carcinoma (RCC) in Taiwan via the genotyping of IL-18 -656 (A/C), -607 (A/C), and -137 (G/C). Moreover, we analyzed their interactions with smoking, alcohol drinking, hypertension, and diabetes status. The results showed an association of the AC and CC genotypes of IL-18 -607 with a significant decrease in the risk of RCC compared with the AA genotype (odds ratio (OR) = 0.44 and 0.35, 95% confidence interval (CI) = 0.27⁻0.72 and 0.18⁻0.66, p = 0.0008 and 0.0010, respectively). Furthermore, a significantly lower frequency of the C allele at -607 was observed in the RCC group (35.3% vs. 49.8%; OR = 0.53; 95% CI = 0.35⁻0.71, p = 0.0003). However, IL-18 -656 and -137 did not exhibit a likewise differential distribution of these genotypes between the control and case groups. Stratifying the population according to smoking, alcohol drinking, hypertension, and diabetes status revealed a different distribution of IL-18 -607 genotypes among non-smokers, non-drinkers, and patients without diabetes, but not among smokers, drinkers, or patients with diabetes. These findings suggest that IL-18 -607 genotypes may play a role in the etiology and progression of RCC in Taiwan and may serve as a useful biomarker for early detection.

Interleukin-18 promoter genotype is associated with the risk of nasopharyngeal carcinoma in Taiwan

Background

The incidence rate of nasopharyngeal carcinoma (NPC) has been documented to be high in Southeast Asia. Interleukin-18 (IL-18) is a multifunctional cytokine that augments interferon-γ production and acts as an important immunomediator in the development of several types of cancer.

Patients and methods

This case-control study evaluated the role of IL-18 in NPC at the DNA level by genotyping its promoter polymorphisms at positions -656, -607, and -137 in a Taiwanese population. A total of 176 patients with NPC and age- and gender-matched 352 noncancer controls were included in this study.

Results

The CC genotype of the IL-18-607 polymorphism was found to be associated with significantly decreased risks of NPC compared to the AA genotype (crude OR =0.50, 95% CI =0.29-0.84, P=0.0093). This significant difference persisted even in the dominant and recessive models. A significantly lower C allele frequency at position -607 was detected in the NPC group(41.8% vs 50.3%; OR =0.77; 95% CI =0.63-1.04, P=0.0089). Regarding IL-18-656 and -137 polymorphisms, there were no differential distributions of their genotypes between the NPC and control groups. After substratification of the subjects according to their smoking, alcohol consumption, and areca chewing status, the genotype distribution of the IL-18-607 polymorphism was found to be different only among nonsmokers between the NPC and control subgroups.

Conclusion

This study suggests that IL-18 plays an important role in the carcinogenesis of NPC in Taiwan and that the genotype-phenotype correlation of IL-18-607 polymorphism and its contribution to NPC need to be investigated further.

Evaluation of Lactic Acid Bacteria on the Inhibition of Vibrio parahaemolyticus Infection and Its Application to Food Systems

This study tested the effect of lactic acid bacteria (LAB) inhibition on Vibrio parahaemolyticus BCRC (Bioresource Collection and Research Center) 10806 and BCRC 12865 in a food model. MTT [3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assays indicated that Caco-2 cells were not damaged after a two-hour treatment with lactic acid bacteria (LAB) and V. parahaemolyticus. The LAB cell culture and supernatant effectively inhibited the growth of V. parahaemolyticus in a food model. ELISA (Enzyme-linked immunosorbent assay) results indicated the significant inhibition of TNF-α; IL-1β; and IL-6; but Lactobacillus plantarum PM 222 and L. plantarum LP 735 did not significantly affect IL-8 levels. Real-time polymerase chain reaction (PCR) results indicated that LAB could inhibit the mRNA expression of proinflammatory cytokines IL-8; IL-6; and TNF-α; which were induced by V. parahaemolyticus. After rat-received LAB; the expression levels of TNF-α; IL-6; and IL-8 in the serum decreased significantly. In intestinal histology; the rat that received L. plantarum PM 222 and L. plantarum LP 010 was able to alleviate the intestinal villi damage caused by V. parahaemolyticus; which also helped reduce cell apoptosis. In conclusion; our results indicate that LAB can inhibit inflammatory responses caused by V. parahaemolyticus and can effectively inhibit the growth of V. parahaemolyticus in food products.

Antitumor effect of the Newcastle disease viral hemagglutinin-neuraminidase gene is expressed through an oncolytic adenovirus effect in osteosarcoma cells

Newcastle disease virus (NDV) can specifically kill cancer cells and has less toxicity to normal cells. The hemagglutinin-neuraminidase (HN) protein is an important structural protein in NDV pathogenesis and has been postulated as a promising candidate for antitumor therapy. The aim of this study was to investigate the anticancer potential of recombinant adenovirus Ad-HN-PEG3p-E1a. An MTS assay was performed to determine viral proliferation after viral infection, the data showed that the proliferation ability of osteosarcoma cells decreased, whereas there was no significant change in normal hepatic cells. DAPI and Annexin V experiments showed that osteosarcoma cells were killed because of apoptosis, active oxygen content, and augmented mitochondrial membrane potential loss. Caspase Activity Assay Kits were used to detect the caspase-3 activities of the treated OS-732 for increased expression. Western blot analysis showed that cytochrome C increased significantly and apoptosis of the virus was confirmed in tumor cells. In-vivo experiments show that NDV has an inhibitory effect on tumor growth. The recombinant adenovirus, which is composed of a HN protein and progressive increment promoter PEG3p, could inhibit the growth of OS-732 and promote the apoptosis of tumor cells. However, there was no clear relationship with normal cell (L02) apoptosis.

A novel anti-CD22 scFv-apoptin fusion protein induces apoptosis in malignant B-cells

CD22 marker is a highly internalizing antigen which is located on the surface of B-cells and is being used as a promising target for treatment of B cell malignancies. Monoclonal antibodies targeting CD22 have been introduced and some are currently under investigation in clinical trials. Building on the success of antibody drug conjugates, we developed a fusion protein consisting of a novel anti-CD22 scFv and apoptin and tested binding and therapeutic effects in lymphoma cells. The recombinant protein was expressed in E. coli and successfully purified and refolded. In vitro binding analysis by immunofluorescence and flow cytometry demonstrated that the recombinant protein specifically binds to CD22 positive Raji cells but not to CD22 negative Jurkat cells. The cytotoxic properties of scFv–apoptin were assessed by an MTT assay and Annexin V/PI flow cytometry analysis and showed that the recombinant protein induced apoptosis preferentially in Raji cells with no detectable effects in Jurkat cells. Our findings indicated that the recombinant anti-CD22 scFv–apoptin fusion protein could successfully cross the cell membrane and induce apoptosis with high specificity, make it as a promising molecule for immunotherapy of B-cell malignancies.

Combination of VP3 and CD147-knockdown enhance apoptosis and tumor growth delay index in colorectal tumor allograft

BACKGROUND

Cancer therapies that kill cancer cells without affecting normal cells is the ultimate mode of treating cancers. The VP3, an avian virus-derived protein, can specifically initiate cell death through several signal transduction pathways leading to apoptosis. In cancer, chemoresistance and cell survivability implicate the cell surface protein, CD147.

METHODS

In this study, transfection of VP3 and silencing of CD147 genes was achieved through the treatment of tumors with pVIVO1-GFP/VP3 (VP3), psiRNA-CD147/2 (shCD147/2), and their combination of CT26 colon cancer cell-induced in mice. The effectiveness of tumor-treatment was ascertained by electrophoresis, TUNEL assay, and flow cytometry analysis. While histopathological and biochemical analysis were used as toxic side effect identification.

RESULTS

The tumor growth delay index (TGDI) after treatment with VP3, shCD147/2, and their combination treatments increased by 1.3-, 1.2-, 2.0- and 2.3-fold respectively, over untreated control. The VP3-shCD147/2 combination treatment was more efficacious then either VP3 or shCD147/2 alone in the retardation of mouse CT26 colorectal cell tumor allograft.

CONCLUSION

The antitumor effect of the combination treatment is the result of synergistic effects of VP3 and shCD147/2 on the tumor cells resulting in apoptosis. Thus, the study shows that combination of VP3 and shCD147/2 treatment can be developed into a potential approach for anticolorectal cancer treatment regimen.

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.

Viral genes as oncolytic agents for cancer therapy

Many viruses have the ability to modulate the apoptosis, and to accomplish it; viruses encode proteins which specifically interact with the cellular signaling pathways. While some viruses encode proteins, which inhibit the apoptosis or death of the infected cells, there are viruses whose encoded proteins can kill the infected cells by multiple mechanisms, including apoptosis. A particular class of these viruses has specific gene(s) in their genomes which, upon ectopic expression, can kill the tumor cells selectively without affecting the normal cells. These genes and their encoded products have demonstrated great potential to be developed as novel anticancer therapeutic agents which can specifically target and kill the cancer cells leaving the normal cells unharmed. In this review, we will discuss about the viral genes having specific cancer cell killing properties, what is known about their functioning, signaling pathways and their therapeutic applications as anticancer agents.

Apoptins: selective anticancer agents

Therapies that selectively target cancer cells for death have been the center of intense research recently. One potential therapy may involve apoptin proteins, which are able to induce apoptosis in cancer cells leaving normal cells unharmed. Apoptin was originally discovered in the Chicken anemia virus (CAV); however, human gyroviruses (HGyV) have recently been found that also harbor apoptin-like proteins. Although the cancer cell specific activity of these apoptins appears to be well conserved, the precise functions and mechanisms of action are yet to be fully elucidated. Strategies for both delivering apoptin to treat tumors and disseminating the protein inside the tumor body are now being developed, and have shown promise in preclinical animal studies.

Therapeutic efficacy of an hTERT promoter-driven oncolytic adenovirus that expresses apoptin in gastric carcinoma

The efficacy and specificity of treatment are the major challenges for cancer gene therapy. Oncolytic virotherapy is an attractive drug delivery platform of cancer gene therapy. Previous studies have determined that apoptin is a p53-independent, Bcl-2-insensitive apoptotic protein that has the ability to induce apoptosis specifically in tumor cells. In this study, we show that the administration of a dual cancer-specific oncolytic adenovirus construct, Ad-hTERT-E1a-apoptin [in which the adenovirus early region 1a (E1a) gene is driven by the cancer-specific promoter of human telomerase reverse transcriptase (hTERT) and that expresses apoptin simultaneously], suppresses tumor growth in gastric carcinoma cells in vitro and reduces the tumor burden in vivo in xenografted nude mice. The observation that infection with the Ad-hTERT-E1a-apoptin construct significantly inhibited the growth of gastric cancer cells and protected normal human gastric epithelium from growth inhibition confirmed the induction of cancer cell-selective adenovirus replication, growth inhibition and apoptosis by this therapeutic approach. In vivo assays were performed using BALB/c nude mice that had established primary tumors. Subcutaneous primary tumor volume was reduced not only in the intratumoral injection group but also in the systemic delivery mice following treatment with Ad-hTERT-E1a-apoptin. Furthermore, treatment of primary models with Ad-hTERT-E1a-apoptin increased the mouse survival time. These data reinforce previous research and highlight the potential therapeutic application of Ad-hTERT-E1a-apoptin for the treatment of neoplastic diseases in clinical trials.

Interleukin-18 promoter polymorphism is associated with lung cancer: a case-control study

BACKGROUND

Interleukin-18 (IL-18) is a multifunctional cytokine that augments IFN-gamma production and affects tumor immune response. In the present case-control study, we tested whether IL-18 promoter polymorphism contributes to lung cancer susceptibility in Iranian patients.

MATERIAL AND METHODS

The study groups were 73 patients with lung cancer, including 53 with squamous carcinoma (SC) and 20 with small cell lung carcinoma (SCLC), and 97 healthy regional aged-matched individuals. The frequency of IL-18 promoter single nucleotide polymorphisms (SNPs) at positions -656 (G/T), -607 (C/A), and -137 (G/C) was determined by polymerase chain reaction analyses.

RESULTS

There were significant differences in the IL-18 -607 allele and genotype distributions between the 73 lung cancer patients and controls. A significantly higher A allele frequency at position -607, which is associated with lower IL-18 production, was observed in lung cancer patients (48.6% vs. 35%; OR = 1.75; 95% CI 1.13-2.72). Also, patients with the -607 CA and the AA genotypes had a 2.60-fold (95% CI 1.26-5.36) and 3.15-fold (95% CI 1.16-8.55) increase in risk of lung cancer. Subdivision of the patients according to histological type revealed that SC was significantly associated with IL-18 -607 SNPs. Although the percentages of -607 alleles and genotypes in SCLC patients were similar to the results in SC patients, the differences compared to control individuals did not reach statistical significance. Analysis with Arlequin software identified eight haplotypes from three SNPs analyzed here. The distributions of IL-18 gene haplotypes were not significantly different between patients and controls after Bonferroni correction.

DISCUSSION

This is the first report to investigate the association between IL-18 polymorphism and lung cancer. Our results suggest that IL-18 polymorphism contributes to the lung cancer risk, particularly among SC patients. Further studies with larger numbers of patients are required to determine the possible association between IL-18 polymorphisms and different histological types of lung cancer.

PTD4-apoptin protein therapy inhibits tumor growth in vivo

Apoptin protein harbors tumor-selective cell death activity, which makes it a potential anticancer therapy candidate. This study reports an apoptin therapy approach based on protein transduction domain 4 (PTD4)-mediated transduction of recombinant apoptin protein. In vitro, the PTD4-apoptin fusion protein is located in the nucleus and induces cell death in, e.g., human hepatocarcinoma HepG2 cells. In normal human L-02 hepatocytes, PTD4-apoptin protein retained mainly cytoplasmic and did not induce detectable levels of cell death, illustrating that the PTD4 domain does not affect apoptin's tumor-selective characteristics. In vivo, liver, cervix and gastric carcinoma xenografts treated with PTD4-apoptin protein for 6 days via the tumor epidermis exhibited a significant tumor growth inhibition because of apoptin-mediated cell death. In addition, treatment of human hepatocarcinoma xenografts during 3 weeks showed that PTD4-apoptin protein has significant anticancer activity, whereas control treatment with PTD4-enhanced green fluorescence protein or saline did not. Cell death and disruption of the tumor integrity were apparent in the PTD4-apoptin transduced xenografted tumors. As important, although PTD4-apoptin protein could be detected in the epidermal tissue covering the subcutaneous tumor tissue and in several organs, such as liver and brain, of the treated mice, no tissue disruption or signs of cell death could be detected. Our in vivo data reveal that apoptin protein delivery constitutes a novel powerful and safe anticancer therapy.

Apoptin, a tumor-selective killer

Apoptin, a small protein from chicken anemia virus, has attracted great attention, because it specifically kills tumor cells while leaving normal cells unharmed. The subcellular localization of apoptin appears to be crucial for this tumor-selective activity. In normal cells, apoptin resides in the cytoplasm, whereas in cancerous cells it translocates into the nucleus. The nuclear translocation of apoptin is largely controlled by its phosphorylation. In tumor cells, apoptin causes the nuclear accumulation of survival kinases including Akt and is phosphorylated by CDK2. Thereby, apoptin redirects survival signals into cell death responses. Apoptin also binds as a multimeric complex to DNA and interacts with several nuclear targets, such as the anaphase-promoting complex, resulting in a G2/M phase arrest. The proapoptotic signal of apoptin is then transduced from the nucleus to cytoplasm by Nur77, which triggers a p53-independent mitochondrial death pathway. In this review, we summarize recent discoveries of apoptin's mechanism of action that might provide intriguing insights for the development of novel tumor-selective anticancer drugs.

Apoptosis-inducing proteins in chicken anemia virus and TT virus

Torque teno viruses (TTVs) share several genomic similarities with the chicken anemia virus (CAV). CAV encodes the protein apoptin that specifically induces apoptosis in (human) tumor cells. Functional studies reveal that apoptin induces apoptosis in a very broad range of (human) tumor cells. A putative TTV open reading frame (ORF) in TTV genotype 1, named TTV apoptosis inducing protein (TAIP), it induces, like apoptin, p53-independent apoptosis in various human hepatocarcinoma cell lines to a similar level as apoptin. In comparison to apoptin, TAIP action is less pronounced in several analyzed human non-hepatocarcinoma-derived cell lines. Detailed sequence analysis has revealed that the TAIP ORF is conserved within a limited group of the heterogeneous TTV population. However, its N-terminal half, N-TAIP, is rather well conserved in a much broader set of TTV isolates. The similarities between apoptin and TAIP, and their relevance for the development and treatment of diseases is discussed.

Gene gun delivery systems for cancer vaccine approaches

Gene-based immunization with transgenic DNA vectors expressing tumor-associated antigens (TAA), cytokines, or chemokines, alone or in combination, provides an attractive approach to increase the cytotoxic T cell immunity against various cancer diseases. With this consideration, particle-mediated or gene gun technology has been developed as a nonviral method for gene transfer into various mammalian tissues. It has been shown to induce both humoral and cell-mediated immune responses in both small and large experimental animals. A broad range of somatic cell types, including primary cultures and established cell lines, has been successfully transfected ex vivo or in vitro by gene gun technology, either as suspension or adherent cultures. Here, we show that protocols and techniques for use in gene gun-mediated transgene delivery system for skin vaccination against melanoma using tumor-associated antigen (TAA) human gpl00 and reporter gene assays as experimental systems.

Apoptin: therapeutic potential of an early sensor of carcinogenic transformation

The avian virus-derived protein apoptin induces p53-independent apoptosis in a tumor-specific way. Apoptin acts as a multimeric complex and forms superstructures upon binding to DNA. In tumor cells, apoptin is phosphorylated and mainly nuclear, whereas in normal cells it is unphosphorylated, cytoplasmic, and becomes readily neutralized. Interestingly, apoptin phosphorylation, nuclear translocation, and apoptosis can transiently be induced in normal cells by cotransfecting SV40 large T oncogene, indicating that apoptin recognizes early stages of oncogenic transformation. In cancer cells, apoptin appears to recognize survival signals, which it is able to redirect into cell death impulses. Apoptin targets include DEDAF, Nur77, Nmi, Hippi, and the potential drug target APC1. Apoptin-transgenic mice and animal tumor models have revealed apoptin as a safe and efficient antitumor agent, resulting in significant tumor regression. Future antitumor therapies could use apoptin either as a therapeutic bullet or as an early sensor of druggable tumor-specific processes.

Viral protein apoptin as a molecular tool and therapeutic bullet: implications for cancer control

The chicken anemia virus-derived protein apoptin induces apoptosis in human tumor cells via a p53-independent pathway, while leaving normal cells intact. Moreover, apoptin treatment in preclinical animal studies leads to reduced tumor growth or remission without a detectable effect on healthy tissues. Apoptin is activated by a still unknown tumor-specific kinase activity. The mode of action of apoptin is under intense investigation, as certain features make it a promising tool for discovering early events in tumorigenesis, identifying druggable targets for antitumor treatment and possibly serving as an antitumor therapy in itself.

Additive cytotoxic effect of apoptin and chemotherapeutic agents paclitaxel and etoposide on human tumour cells

Gene therapy experiments in animal models have shown that apoptin expression results in tumour regression without any significant side effects. Therefore, apoptin is regarded as a potential anticancer drug for clinical applications. In this study, we analysed whether chemotherapeutic agents combined with apoptin treatment could result in enhanced cytotoxicity in human tumour cell cultures. Combined treatment with recombinant adenovirus AdAptVP3 expressing apoptin and etoposide clearly showed an additive cytotoxic effect on human osteosarcoma U2OS cells. Paclitaxel treatment combined with apoptin expression significantly inhibited the survival of p53-positive human osteosarcoma U2OS and non-small lung carcinoma A549 cells, p53-negative human osteosarcoma Saos-2 cells and p53-mutant human prostate cancer Du145 cells, already at low doses of the chemotherapeutic agent. Our results indicate that the cytotoxicity-enhancing action by the tumour-specific apoptin in combination with chemotherapeutic agents might offer an effective and safe antitumour therapeutics.

Cytokine gene transfer for cancer therapy

The possibility of inducing a strong immune response to impair tumor growth by ectopically expressing cytokines, followed by the generation of an antitumor memory raised great hopes and enthusiasm as a therapeutic approach. However, the efficacy of this strategy on established tumor models appeared low and the initial results in the clinics were disappointing. Recently, new evidence indicates that cytokine gene combination or the combined use of cytokine genes with additional gene therapy approaches induces a synergistic effect supporting the use of cytokine gene therapy to improve the clinical outcome for cancer patients.