A strategy for specific targeting of therapeutic agents to tumour cells of virus-associated cancers

Non-integrating lentiviral vectors for specific killing of Epstein-Barr virus nuclear antigen 1-positive B cell lymphoma cells

BACKGROUND

Epstein-Barr virus (EBV) causes a range of life-threatening B-lymphocyte malignancies but, despite the use of various strategies, treatment remains problematic.

METHODS

In the present study, we developed a non-integrating lentiviral vector (NILV) that mediates specific killing of EBV nuclear antigen 1 (EBNA1)-expressing cells with minimal toxicity to EBNA1-negative cells. The EBV family of repeats (FR) was cloned intok the NILV genome upstream of various transgenes.

RESULTS

The presence of the FR in the NILV genome induced transcriptional up-regulation and prolonged the expression of a transgene specifically in EBNA1-positive B cells. Transgene expression from an FR-containing NILV was also prolonged in EBV-transformed cells compared to an FR-negative NILV. We found that the delivery of an FR-containing NILV encoding herpes simplex virus 1 thymidine kinase (TK) lead to the killing of more than 99% of EBNA1-positive B cells with minimal toxicity to EBNA1-negative cells in the presence of gancyclovir. EBNA1-positive cells were not killed by an FR-negative vector containing the TK gene. An FR-TK-containing NILV also specifically killed EBNA1-containing cells in a mixed population of EBNA1-positive and EBNA1-negative cells, thus confirming that NILV-FR-TK-mediated killing is specific for EBNA1-expressing cells.

CONCLUSIONS

Transgene expression from our NILVs is both EBNA1-specific and dependent upon the presence of the FR. The results obtained in the present study indicate that NILVs have potential use in the treatment of EBV-associated B cell malignancies.

[Clinical study of undifferentiated carcinoma of the nasopharynx (UNCT) in patients with cervical node type of disease]

Indifferentiated carcinoma of the nasopharyngs is clinicaly-histological-imunologic entity which is often diagnosed in our country. There are three clinical types, but nodal cervical type of disease is the most interesting type for surgeons while the combined type is more interesting for otolaiyngologist. Among seventy-seven patients diagnosed with undifferentiated carcinoma of the nasopharyngs with nodal cervical type of disease, on the Institute of Otolaryngology and Maxillofacial Surgery Clinical Centre of Serbia during the period between 1993-1997 there were N0-21%, N1-49%, N2-18% i N3-12%, no mater of the T category. The disease more often occurs between male population (2:1), mostly between age 41-60. The rate for five year period of surviving for two different chemioterapeutical protocols is as follows: for categories N0 and N1-20% for mono Zorubicin and 61% for the same category for Z-CDDP. The same rate for categories N2 and N3 is 11% for mono Zorubicin and 33% for the same category for Z-CDDP. Much better rate of survival in comparison with previous decades is achieved due to better diagnosing on time in which are sistematicaly ineluded epypharyngoscopy in general anestesia with biopsy, CT and NMR and EBV serology.

Possibility of the use of serological method for the determination of immunoglobuline a antibody against early antigene of Epstein-Barr virus as a marker in the diagnosis of nasopharyngeal tumors

Background/Aim. According to the data from immunological, biological and molecular researches, there is a close association between the undifferentiated carcinoma of nasopharyngeal type (UCNT) and Epstein-Barr virus (EBV). To use IgA EA antibody as a serological marker in our patients with nasopharyngeal carcinoma from a clinical viewpoint. Methods. 91 patients were followed in the period from 1989?1998. In 11 of the patients the antibody titre serum for the early antigen of EBV virus were determinated before the treatment, and in 24 of the patients 3 years after the treatment. There were three control groups of patients: 20 voluntary blood donors, 26 patients with squamocellular laryngeal carcinoma, and 10 patients with squamocellular nasopharyngeal carcinoma. Results. In the group of 11 patients with UCNT before the treatment, the value of anti-EA IgA titre was 31.09, and in the patients after the treatment anti-EA IgA antiody titre was 14.56. In the control groups of patients the results were: in the blood donors 5.00; in the group with the diagnosis of squamocellular laryngeal carcinoma, the titre was 5.00; in the patients with squamocellular nosopharyngeal carcinoma, the titre anti-EA IgA was 5.36. Conclusion. These results were statistically highly significant (p < 0.01). Our research clearly showed that anti-EA IgA EBV marker could be useful in diagnosing, differential diagnosing and prognosing as well.

Novel gene therapy approach for nasopharyngeal carcinoma

This article will provide an overview on the status of cancer gene therapy, focussed specifically on its potential application in nasopharyngeal carcinoma (NPC). The concepts and strategies behind the design of therapeutic targets such as p53, p16, and death genes will be described. One of the major challenges in cancer gene therapy is tumor-specific expression of therapeutic genes, and a transcriptional targeting approach will be reviewed, in reference to NPC. Specifically, the ability to exploit the presence of Epstein-Barr virus (EBV) will be emphasized. The currently available preclinical data on genetic therapeutic approaches for NPC will be reviewed, and an outline for its future role in management of NPC, in conjunction with existing cytotoxic modalities of ionizing radiation and chemotherapy will be provided.

Episomal vectors for gene expression in mammalian cells

An important reason for preferring mammalian cells for heterologous gene expression is their ability to make authentic proteins containing post-translational modifications similar to those of the native protein. The development of expression systems for mammalian cells has been ongoing for several years, resulting in a wide variety of effective expression vectors. The aim of this review is to highlight episomal expression vectors. Such episomal plasmids are usually based on sequences from DNA viruses, such as BK virus, bovine papilloma virus 1 and Epstein-Barr virus. In this review we will mainly focus on the improvements made towards the usefulness of these systems for gene expression studies and gene therapy.

EBNA-1: a protein pivotal to latent infection by Epstein-Barr virus

Epstein-Barr nuclear antigen 1, or EBNA-1, is required for the replication of the EBV genome as an extra-chromosomal element and is a key transcriptional regulator of this virus's latent gene expression. In this review we will describe the salient features of EBNA-1 and oriP, the latent origin of EBV to which EBNA-1 binds site-specifically. EBNA-1's association with host cellular factors, its association with metaphase chromosomes, and its ability to link DNAs to which it binds will be discussed in relation to its roles in replication and transcriptional activation. Although the mechanisms by which EBNA-1 facilitates replication and transcription largely remain enigmatic, EBV's viral replicon has been exploited successfully for applications in gene therapy and in the design of eukaryotic vectors for use in cell culture.

Effective suicide gene therapy in vivo by EBV-based plasmid vector coupled with polyamidoamine dendrimer

This study demonstrates in vivo effectiveness of a nonviral vector system, Epstein-Barr virus (EBV)-based plasmid vector coupled with polyamidoamine (PAMAM) dendrimer (EBV/polyplex), in suicide gene therapy of cancer. The EBV-based vector is a plasmid vector containing EBV nuclear antigen 1 (EBNA1) gene and oriP from EBV genome. HSV-1 tk gene was transferred into Ewing's sarcoma cell lines, A4573 and KP-EWS-YI, by using an EBV-based plasmid vector, pSES.Tk, or a conventional plasmid vector, pS.Tk. Cells transfected with pSES.Tk/dendrimer showed approximately 100 times lower ID50 to ganciclovir (GCV) compared with those transfected with pS. Tk/dendrimer. Intratumoral injection of pSES.Tk/dendrimer but not pS. Tk/dendrimer drastically suppressed the growth of tumors which had generated from A4573 or Huh7 hepatocellular carcinoma (HCC) cells inoculated into severe combined immunodeficiency (SCID) mice. The treatment with pSES.Tk/dendrimer also resulted in significant prolongation of survival of the mice implanted with A4573. These results suggest that the EBV/polyplex system could be useful for in vivo suicide gene therapy of cancer. Gene Therapy (2000) 7, 53-60.

A Long-Term Memory Obtained by Genetic Immunization Results in Full Protection from a Mammary Adenocarcinoma Expressing an EBV Gene

We have tested the capability of a plasmid DNA (pDNA) expressing the EBV nuclear Ag-4 (EBNA-4) to evoke a T cell response-associated protective immune response against a tumor expressing this gene. We have found that ACA mice immunized with EBNA-4-expressing plasmid were partially protected against syngeneic mammary carcinoma line (S6C) expressing EBNA-4 (S6C-E4). This protection was enhanced by coimmunizing mice with EBNA-4- and GM-CSF-expressing plasmids, and a full protection was achieved by coimmunizing mice with EBNA-4- and IFN-γ-expressing plasmids. Furthermore, mice that have rejected the EBNA-4-positive tumor were also resistant against a subsequent challenge with the original nontransfected tumor line. We then checked for the ability of pDNA immunization to provide a protective long-term memory response. We indeed found that even after 3 mo from the last immunization, full protection was obtained by this method, as compared with full tumor outgrowth in the control-immunized group. These findings support the concept that a nonviral, pDNA-based vaccination strategy is useful to fully protect from the outgrowth of tumors expressing this EBV gene.

Epstein-Barr virus vectors for gene expression and transfer

Vectors based on components of Epstein-Barr virus (EBV) have found increasingly wide applications in biotechnology. Three areas of recent advancement comprise the use of EBV vectors to improve the convenience of gene expression systems, the development of EBV vectors for gene transfer in gene therapy, and the use of EBV components to generate large vectors carrying sizable regions of genomic DNA.

Up to 100-fold increase of apparent gene expression in the presence of Epstein-Barr virus oriP sequences and EBNA1: implications of the nuclear import of plasmids

A 100-fold increase in luciferase activity was observed in 293 cells, stably expressing Epstein-Barr nuclear antigen 1 (EBNA1; 293-EBNA1 cells), that had been transiently transfected with plasmids carrying Epstein-Barr virus (EBV) oriP sequences. This increase was observed in comparison to reporter gene activity obtained after transfection with a plasmid carrying no oriP sequences. The luciferase gene on these plasmids was under the control of either the cytomegalovirus immediate-early 1 gene enhancer-promoter (CMV IE1) or the Rous sarcoma virus promoter. The increase of reporter gene activity was not due to plasmid replication, since a similar enhancement was observed in the presence of aphidicolin, an inhibitor of replicative DNA synthesis, or after deletion of the dyad symmetry (DS) element within oriP. Luciferase production was not increased in the presence of only the DS element. Microinjection of plasmids carrying the CMV IE1 promoter-driven luciferase gene with or without oriP sequences into the nuclei of 293-EBNA1 cells resulted in a 17-fold increase in luciferase activity. Cytoplasmic injection of these plasmids led to an enhancement of luciferase activity of up to 100-fold. This difference in the factor of activation after nuclear or cytoplasmic injection could be ascribed to increased transport of plasmids carrying oriP from the cytoplasm to the nucleus in the presence of EBNA1. These data suggest the possibility of substantially increasing the apparent expression of a gene under the control of a strong constitutive promoter in the presence of oriP sequences and EBNA1. This improvement in expression is due to intranuclear enhancement of gene expression. oriP-specific transport of plasmid DNA from the cytoplasm of 293-EBNA1 cells to the nucleus seems to contribute to the observed effect.

Epstein-Barr virus genes and cancer cells

Human B lymphocytes infected with Epstein-Barr virus (EBV) express 11 viral genes, of which six are essential for efficient transformation. The protein products of these genes appear to cause cell growth by modifying cell signal transduction pathways. For example, EBNA-2 mimics the Notch 1 pathway and LMP-1 interacts with the signalling from CD40/CD40-L, which promotes growth in normal B cells. In the human cancers linked to EBV, most of the viral transforming genes are not expressed. It is likely that growth of these cells is controlled by a combination of the EBV genes whose expression continues with altered cell proto-oncogenes and tumour suppressor genes, but other explanations of the role of EBV in cancer cells are also possible. The presence of the virus in the tumour cells of EBV-associated cancers constitutes a potentially useful tumour specific marker that might be used to direct therapy to the tumour cells.