Antitumor effects of a recombinant pseudotype baculovirus expressing Apoptin in vitro and in vivo

Evaluation of Malarial Var2CSA-Displaying Baculovirus Vector in Transduction Efficiency in Human Cancer Cells

Baculovirus vectors (BVs) are able to use for gene transduction in mammalian cells and are recognized as growing viral vectors for cancer gene therapy applications. The transduction efficiency of BVs varies among cancer cell types. To improve the transduction efficiency of BVs in human cancer cells, BV displaying malarial variant surface antigen 2-chondroitin sulfate A (var2CSA) molecules was developed in this study. Var2CSA plays a critical role in the sequestration of Plasmodium falciparum-infected erythrocytes in the placenta. Moreover, var2CSA binds to cancer cells via placenta-like chondroitin sulfate A (CSA), but not to non-cancer cells. Var2CSA BV showed significantly higher gene transduction than control BV in HepG2 and Huh7 cells, human hepatic cancer cells as well as AsPC-1 cells, human pancreatic cancer cells. The transduction efficiency of var2CSA BV was significantly inhibited by the anti-gp64 antibody, free heparin, and CSA. The results of this study suggest that var2CSA BV would be an improved vector for cancer gene therapies, especially in the treatment of hepatic and pancreatic cancers.

Solutions against emerging infectious and noninfectious human diseases through the application of baculovirus technologies

Abstract

Baculoviruses are insect pathogens widely used as biotechnological tools in different fields of life sciences and technologies. The particular biology of these entities (biosafety viruses 1; large circular double-stranded DNA genomes, infective per se; generally of narrow host range on insect larvae; many of the latter being pests in agriculture) and the availability of molecular-biology procedures (e.g., genetic engineering to edit their genomes) and cellular resources (availability of cell lines that grow under in vitro culture conditions) have enabled the application of baculoviruses as active ingredients in pest control, as systems for the expression of recombinant proteins (Baculovirus Expression Vector Systems—BEVS) and as viral vectors for gene delivery in mammals or to display antigenic proteins (Baculoviruses applied on mammals—BacMam). Accordingly, BEVS and BacMam technologies have been introduced in academia because of their availability as commercial systems and ease of use and have also reached the human pharmaceutical industry, as incomparable tools in the development of biological products such as diagnostic kits, vaccines, protein therapies, and—though still in the conceptual stage involving animal models—gene therapies. Among all the baculovirus species, the Autographa californica multiple nucleopolyhedrovirus has been the most highly exploited in the above utilities for the human-biotechnology field. This review highlights the main achievements (in their different stages of development) of the use of BEVS and BacMam technologies for the generation of products for infectious and noninfectious human diseases.

Key points

• Baculoviruses can assist as biotechnological tools in human health problems.

• Vaccines and diagnosis reagents produced in the baculovirus platform are described.

• The use of recombinant baculovirus for gene therapy–based treatment is reviewed.

Protective and Therapeutic Effects of an IL-15:IL-15Rα-Secreting Cell-Based Cancer Vaccine Using a Baculovirus System

This study reports the use of the BacMam system to deliver and express self-assembling IL-15 and IL-15Rα genes to murine B16F10 melanoma and CT26 colon cancer cells. BacMam-based IL-15 and IL-15Rα were well-expressed and assembled to form the biologically functional IL-15:IL-15Rα complex. Immunization with this IL-15:IL-15Rα cancer vaccine delayed tumor growth in mice by inducing effector memory CD4⁺ and CD8⁺ cells and effector NK cells which are tumor-infiltrating. It caused strong antitumor immune responses of CD8⁺ effector cells in a tumor-antigen specific manner both in vitro and in vivo and significantly attenuated Treg cells which a control virus-infected cancer vaccine could induce. Post-treatment with this cancer vaccine after a live cancer cell injection also prominently delayed the growth of the tumor. Collectively, we demonstrate a vaccine platform consisting of BacMam virus-infected B16F10 or CT26 cancer cells that secrete IL-15:IL-15Rα. This study is the first demonstration of a functionally competent soluble IL-15:IL-15Rα complex-related cancer vaccine using a baculovirus system and advocates that the BacMam system can be used as a secure and rapid method of producing a protective and therapeutic cancer vaccine.

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.

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.

Human serum albumin-mediated apoptin delivery suppresses breast cancer cell growth in vitro and in vivo

Gene therapy is one of the most promising potential therapeutic strategies for many types of cancer. Cell apoptosis is an active, programmed physiological process of the body, and its disruption has been closely associated with the occurrence of tumor development. Apoptin is known to induce tumor cell apoptosis. In the present study, the MCF-7 breast cancer cell line was transfected with a human serum albumin (HSA) and apoptin expressing plasmid [HSA-polyethylenimine (PEI)-pcDNA-Apoptin]. Reverse transcription-quantitative polymerase chain reaction and western blotting were performed to detect the expression of apoptin in the transfected MCF-7 cells, while MTT assays and flow cytometry were conducted to detect cell viability and apoptosis. Furthermore, hematoxylin and eosin staining was used to observe the morphology of xenografts from mice injected with MCF-7 cells. It was demonstrated that the HSA-PEI-pcDNA-Apoptin expression plasmid resulted in the upregulation of apoptin in MCF-7 cells, and efficiently suppressed breast tumor growth in vivo. These findings indicated that the use of HSA as an apoptin expression vector has potential therapeutic benefits for cancer and confirms the requirement for the further evaluation of apoptin in clinical trials.

Baculovirus-mediated gene delivery and RNAi applications

Baculoviruses are widely encountered in nature and a great deal of data is available about their safety and biology. Recently, these versatile, insect-specific viruses have demonstrated their usefulness in various biotechnological applications including protein production and gene transfer. Multiple in vitro and in vivo studies exist and support their use as gene delivery vehicles in vertebrate cells. Recently, baculoviruses have also demonstrated high potential in RNAi applications in which several advantages of the virus make it a promising tool for RNA gene transfer with high safety and wide tropism.

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.

AdHu5-apoptin induces G2/M arrest and apoptosis in p53-mutated human gastric cancer SGC-7901 cells

The use of anticancer therapeutic agents is limited largely by their severe toxicity to normal tissues. The development of novel agents with tumor-specific cell-killing and effective gene delivery properties is thus very desirable. We used human adenovirus serotype 5 (AdHu5) as a vehicle to deliver the apoptin gene to specifically target gastric cancer in a recombinant gene delivery approach. AdHu5-apoptin is a safe and efficacious agent for the treatment of gastric cancer (GC). Our results show that apoptin protein encoded by the apoptin gene delivered via AdHu5 significantly inhibited the proliferation of SGC-7901 GC cells. Apoptin reduced the clone number by more than 75% and resulted in cell cycle arrest in the G2/M phase for 48% of the GC cells. It also induced cleavage of caspase-3, caspase-7, and caspase-9 in the GC cells. Intratumoral and peritumoral in vivo injection of AdHu5-apoptin significantly suppressed tumor growth and induced apoptosis in xenogeneic tumors in mice. The apoptosis induced by AdHu5-apoptin was independent of anti-apoptotic Bcl-2 and Bcl-xL proteins and the p53 pathway. Taken together, our results show that AdHu5-apoptin has great potential as a therapeutic agent for effective treatment of gastric tumors.

Therapeutic anti-tumor effect of exogenous apoptin driven by human survivin gene promoter in a lentiviral construct

INTRODUCTION

The aim of this study was to construct a lentivirus vector with survivin promoter (pSur)-driven apoptin and test its efficiency in suppressing the growth of tumor cells.

MATERIAL AND METHODS

Expression cassettes with different fragments of survivin gene promoter (pSur, 161 bp, 272 bp, 990 bp) driving 6XHis-tagged apoptin were constructed to generate recombinant lentivirus, of which the inhibitory effect on tumor cells was compared. The activity of different pSur in 293FT, and 272 bp pSur in primary bone marrow mesenchymal stem cells (BMSCs), SW480, Hela and MCF-7 was examined by Western blot. Their ability to induce apoptosis in SW480 cells was determined by annexin-V staining. The inhibitory effect of letivirus containing different pSur-driven apoptin on nude mice-xenografted SW480 cells was assessed by tumor size and pathological observation.

RESULTS

The 272 bp and 990 bp pSur displayed comparable effects in terms of promoter activity, cell apoptosis/necrosis and G1 phase arrest in vitro, and growth of xenograft tumor in vivo. When lentivirus containing 272 bp pSur was tested, it drove high apoptin expression in tumor cells (SW480, Hela and MCF-7) and weak expression in primary bone marrow mesenchymal stem cells. Xenograft to nude mice using infected Sw480 cells showed that lentiviruses possessing 272 bp and 990 bp pSur were able to significantly induce tumor cell death, focal necrosis, and tumor growth lag.

CONCLUSIONS

The data indicated that pSur-apoptin expression cassette in lentivirus vector ensures specific suppression of tumor cells, and may be applicable to monitor malignant transformation of transplanted cells.

Baculovirus as a gene delivery vector: recent understandings of molecular alterations in transduced cells and latest applications

Baculovirus infects insects in nature and is non-pathogenic to humans, but can transduce a broad range of mammalian and avian cells. Thanks to the biosafety, large cloning capacity, low cytotoxicity and non-replication nature in the transduced cells as well as the ease of manipulation and production, baculovirus has gained explosive popularity as a gene delivery vector for a wide variety of applications. This article extensively reviews the recent understandings of the molecular mechanisms pertinent to baculovirus entry and cellular responses, and covers the latest advances in the vector improvements and applications, with special emphasis on antiviral therapy, cancer therapy, regenerative medicine and vaccine.