In vitro-packaged SV40 pseudovirions as highly efficient vectors for gene transfer

The ABCB1, ABCC2 and RALBP1 polymorphisms are associated with carbamazepine response in epileptic patient: a systematic review

Despite a dramatic increase in treatment options over the past 30 years, Carbamazepine (CBZ) is still considered the standard of care and the most prescribed initial treatment for focal epilepsy. Hence, the identification of genetic biomarkers that influence the response, resistance and toxicity to CBZ remains a challenge. Several research studies have looked into this to highlight the polymorphisms responsible for the variability in the response to CBZ in patients with epilepsy. The aim of this review is to compare the different results published in the literature The systematic review included thirty-nine studies (2005-2021), Meta-analyses were performed on more than twelve polymorphisms in three genes (ABCB1, ABCC2, RALBP1) involved in CBZ cell transport. The current challenges are to identify other new biomarkers of antiepileptic drugs that can only materialize with large-scale collaborative research efforts.

In Vitro Assembly of Virus-Like Particles and Their Applications

Virus-like particles (VLPs) are increasingly used for vaccine development and drug delivery. Assembly of VLPs from purified monomers in a chemically defined reaction is advantageous compared to in vivo assembly, because it avoids encapsidation of host-derived components and enables loading with added cargoes. This review provides an overview of ex cella VLP production methods focusing on capsid protein production, factors that impact the in vitro assembly, and approaches to characterize in vitro VLPs. The uses of in vitro produced VLPs as vaccines and for therapeutic delivery are also reported.

Potentiating activities of chrysin in the therapeutic efficacy of 5-fluorouracil in gastric cancer cells

The incidence and mortality rates of gastric cancer rank among the highest five of all cancer types worldwide. The chemotherapeutic agent 5-fluorouracil (5-FU) is the gold standard for treating gastric cancer, but its efficacy is limited due to high rates of resistance. To improve the therapeutic efficacy of 5-FU and overcome its resistance, the synergistic effect of chrysin with 5-FU was investigated and its mechanism was elucidated. Chrysin was co-administered with 5-FU in AGS cells and 5-FU-resistant AGS cells (AGS/FR). Cytotoxicity was investigated using MTT assay, followed by calculating the combination index (CI). Several biomarkers were detected using western blotting analysis. Apoptosis and cell cycle distribution were measured by flow cytometry. The combination of chrysin and 5-FU significantly increased cytotoxicity more than chrysin or 5-FU alone. 5-FU induced apoptosis through p53-p21 activity, while chrysin arrested the cell cycle in the G2/M phase. The combination of chrysin and 5-FU showed an anticancer effect via S phase arrest. The results indicated that chrysin and 5-FU exhibited anticancer properties via different pathways. Furthermore, the present study found that chrysin enhanced the chemotherapeutic effect of 5-FU in AGS/FR cells. In the resistant cells, the combination of chrysin and 5-FU improved the anticancer effect via G2/M phase arrest. These findings indicated that chrysin potentiated the chemotherapeutic effect of 5-FU in gastric cancer AGS and AGS/FR cells via cell cycle arrest. Therefore, chrysin may be used to treat gastric cancers that have become resistant to 5-FU.

Therapeutic siRNA: state of the art

RNA interference (RNAi) is an ancient biological mechanism used to defend against external invasion. It theoretically can silence any disease-related genes in a sequence-specific manner, making small interfering RNA (siRNA) a promising therapeutic modality. After a two-decade journey from its discovery, two approvals of siRNA therapeutics, ONPATTRO® (patisiran) and GIVLAARI™ (givosiran), have been achieved by Alnylam Pharmaceuticals. Reviewing the long-term pharmaceutical history of human beings, siRNA therapy currently has set up an extraordinary milestone, as it has already changed and will continue to change the treatment and management of human diseases. It can be administered quarterly, even twice-yearly, to achieve therapeutic effects, which is not the case for small molecules and antibodies. The drug development process was extremely hard, aiming to surmount complex obstacles, such as how to efficiently and safely deliver siRNAs to desired tissues and cells and how to enhance the performance of siRNAs with respect to their activity, stability, specificity and potential off-target effects. In this review, the evolution of siRNA chemical modifications and their biomedical performance are comprehensively reviewed. All clinically explored and commercialized siRNA delivery platforms, including the GalNAc (N-acetylgalactosamine)-siRNA conjugate, and their fundamental design principles are thoroughly discussed. The latest progress in siRNA therapeutic development is also summarized. This review provides a comprehensive view and roadmap for general readers working in the field.

Design and biosynthesis of functional protein nanostructures

Proteins are one of the major classes of biomolecules that execute biological functions for maintenance of life. Various kinds of nanostructures self-assembled from proteins have been created in nature over millions of years of evolution, including protein nanowires, layers and nanocages. These protein nanostructures can be reconstructed and equipped with desired new functions. Learning from and manipulating the self-assembly of protein nanostructures not only help to deepen our understanding of the nature of life but also offer new routes to fabricate novel nanomaterials for diverse applications. This review summarizes the recent research progress in this field, focusing on the characteristics, functionalization strategies, and applications of protein nanostructures.

RNAi therapeutic and its innovative biotechnological evolution

Recently, United States Food and Drug Administration (FDA) and European Commission (EC) approved Alnylam Pharmaceuticals' RNA interference (RNAi) therapeutic, ONPATTRO™ (Patisiran), for the treatment of the polyneuropathy of hereditary transthyretin-mediated (hATTR) amyloidosis in adults. This is the first RNAi therapeutic all over the world, as well as the first FDA-approved treatment for this indication. As a milestone event in RNAi pharmaceutical industry, it means, for the first time, people have broken through all development processes for RNAi drugs from research to clinic. With this achievement, RNAi approval may soar in the coming years. In this paper, we introduce the basic information of ONPATTRO and the properties of RNAi and nucleic acid therapeutics, update the clinical and preclinical development activities, review its complicated development history, summarize the key technologies of RNAi at early stage, and discuss the latest advances in delivery and modification technologies. It provides a comprehensive view and biotechnological insights of RNAi therapy for the broader audiences.

Effect of dsDNA on the Assembly Pathway and Mechanical Strength of SV40 VP1 Virus-like Particles

Simian virus 40 (SV40) is a possible vehicle for targeted drug delivery systems because of its low immunogenicity, high infectivity, and high transfection efficiency. To use SV40 for biotechnology applications, more information is needed on its assembly process to efficiently incorporate foreign materials and to tune the mechanical properties of the structure. We use atomic force microscopy to determine the effect of double-stranded DNA packaging, buffer conditions, and incubation time on the morphology and strength of virus-like particles (VLPs) composed of SV40 VP1 pentamers. DNA-induced assembly results in a homogeneous population of native-like, ∼45 nm VLPs. In contrast, under high-ionic-strength conditions, the VP1 pentamers do not seem to interact consistently, resulting in a heterogeneous population of empty VLPs. The stiffness of both in-vitro-assembled empty and DNA-filled VLPs is comparable. Yet, the DNA increases the VLPs' resistance to large deformation forces by acting as a scaffold, holding the VP1 pentamers together. Both disulfide bridges and Ca²⁺, important in-vitro-assembly factors, affect the mechanical stability of the VLPs: the reducing agent DTT makes the VLPs less resistant to mechanical stress and prone to damage, whereas Ca²⁺-chelating EDTA induces a marked softening of the VLP. These results show that negatively charged polymers such as DNA can be used to generate homogeneous particles, thereby optimizing VLPs as vessels for drug delivery. Moreover, the storage buffer should be chosen such that VP1 interpentamer interactions are preserved.

Cre Recombinase Mediates the Removal of Bacterial Backbone to Efficiently Generate rSV40

Gene therapy has been shown to be a feasible approach to treat inherited disorders in vivo. Among the currently used viral vector systems, adeno-associated virus (AAV) vectors are the most advanced and have been applied in patients successfully. An important drawback of non-integrating AAV vectors is their loss of expression upon cell division, while repeating systemic administration lacks efficacy due to the induction of neutralizing antibodies. In addition, a significant percentage of the general population is not eligible for AAV-mediated gene therapy due to pre-existing immunity. Development of additional viral vectors may overcome this hurdle. Simian virus 40 (SV40)-derived vectors have been reported to transduce different tissues, including the liver, and prevalence of neutralizing antibodies in the general population is very low. This renders recombinant SV40 (rSV40) vector an interesting candidate for effective (re-)administration. Clinical use of SV40 vectors is in part hampered by less advanced production methods compared to AAVs. To optimize the production of rSV40 and make it better suitable for clinical practice, we developed a production system that relies on Cre recombinase-mediated removal of the bacterial plasmid backbone.

Generation of a Vero-Based Packaging Cell Line to Produce SV40 Gene Delivery Vectors for Use in Clinical Gene Therapy Studies

Replication-defective (RD) recombinant simian virus 40 (SV40)-based gene delivery vectors hold a great potential for clinical applications because of their presumed non-immunogenicity and capacity to induce immune tolerance to the transgene products in humans. However, the clinical use of SV40 vectors has been hampered by the lack of a packaging cell line that produces replication-competent (RC) free SV40 particles in the vector production process. To solve this problem, we have adapted the current SV40 vector genome used for the production of vector particles and generated a novel Vero-based packaging cell line named SuperVero that exclusively expresses the SV40 large T antigen. SuperVero cells produce similar numbers of SV40 vector particles compared to the currently used packaging cell lines, albeit in the absence of contaminating RC SV40 particles. Our unique SV40 vector platform named SVac paves the way to clinically test a whole new generation of SV40-based therapeutics for a broad range of important diseases.

Production and biomedical applications of virus-like particles derived from polyomaviruses

Virus-like particles (VLPs), aggregates of capsid proteins devoid of viral genetic material, show great promise in the fields of vaccine development and gene therapy. These particles spontaneously self-assemble after heterologous expression of viral structural proteins. This review will focus on the use of virus-like particles derived from polyomavirus capsid proteins. Since their first recombinant production 27 years ago these particles have been investigated for a myriad of biomedical applications. These virus-like particles are safe, easy to produce, can be loaded with a broad range of diverse cargoes and can be tailored for specific delivery or epitope presentation. We will highlight the structural characteristics of polyomavirus-derived VLPs and give an overview of their applications in diagnostics, vaccine development and gene delivery.

RNA encapsidation by SV40-derived nanoparticles follows a rapid two-state mechanism

Remarkably, uniform virus-like particles self-assemble in a process that appears to follow a rapid kinetic mechanism. The mechanisms by which spherical viruses assemble from hundreds of capsid proteins around nucleic acid, however, are yet unresolved. Using time-resolved small-angle X-ray scattering (TR-SAXS), we have been able to directly visualize SV40 VP1 pentamers encapsidating short RNA molecules (500mers). This assembly process yields T = 1 icosahedral particles comprised of 12 pentamers and one RNA molecule. The reaction is nearly one-third complete within 35 ms, following a two-state kinetic process with no detectable intermediates. Theoretical analysis of kinetics, using a master equation, shows that the assembly process nucleates at the RNA and continues by a cascade of elongation reactions in which one VP1 pentamer is added at a time, with a rate of approximately 10(9) M(-1) s(-1). The reaction is highly robust and faster than the predicted diffusion limit. The emerging molecular mechanism, which appears to be general to viruses that assemble around nucleic acids, implicates long-ranged electrostatic interactions. The model proposes that the growing nucleo-protein complex acts as an electrostatic antenna that attracts other capsid subunits for the encapsidation process.

Differential assembly of Hepatitis B Virus core protein on single- and double-stranded nucleic acid suggest the dsDNA-filled core is spring-loaded

Hepatitis B Virus (HBV) cores assemble on viral RNA, which is reverse transcribed within the core to the partially dsDNA genome of mature HBV. However, constraining dsDNA, a stiff polymer, within a core necessarily requires far greater capsid stability than constraining ssRNA. We hypothesized that, unlike ssRNA, dsDNA would be a poor substrate for assembly. We examined titrations of ssDNA and dsDNA with purified HBV core protein, Cp183, by EMSA, EM, DLS, and etheno-DNA fluorescence. Cp183 bound ssDNA with high affinity to form virus-like capsids. However, Cp183 bound dsDNA poorly, forming a mixture of irregular complexes. Nonetheless, we observed some normal cores in dsDNA assembly reactions, indicating that the energy required to bend DNA could be similar to the protein-protein association energy. This similarity of energies suggests that dsDNA stresses mature HBV cores, in agreement with calculation, which may be the basis for the virus maturation signal and DNA release.

Inhibition of multidrug resistance by SV40 pseudovirion delivery of an antigene peptide nucleic acid (PNA) in cultured cells

Peptide nucleic acid (PNA) is known to bind with extraordinarily high affinity and sequence-specificity to complementary nucleic acid sequences and can be used to suppress gene expression. However, effective delivery into cells is a major obstacle to the development of PNA for gene therapy applications. Here, we present a novel method for the in vitro delivery of antigene PNA to cells. By using a nucleocapsid protein derived from Simian virus 40, we have been able to package PNA into pseudovirions, facilitating the delivery of the packaged PNA into cells. We demonstrate that this system can be used effectively to suppress gene expression associated with multidrug resistance in cancer cells, as shown by RT-PCR, flow cytometry, Western blotting, and cell viability under chemotherapy. The combination of PNA with the SV40-based delivery system is a method for suppressing a gene of interest that could be broadly applied to numerous targets.

SV40 vectors carrying minimal sequence of viral origin with exchangeable capsids

Polyomaviral vectors are generated by transfecting 293T cells with three sets of DNAs: DNA for the expression of simian virus 40 (SV40) T antigen; DNA for the expression of SV40 capsid proteins, and vector DNA harboring a reporter gene expression cassette carrying a SV40 origin. The vector DNA harbors a minimal sequence originating from SV40, and thus can carry a longer transgene. Moreover, the viable recombinants are not detectable in the vector preparation, and the vectors can transduce the DNA with efficiency similar to that of virions. Vector particles bearing capsid proteins of BK virus, JC virus, and B-lymphotropic papovavirus instead of SV40 were prepared, and they exhibited differential efficiency of gene transduction to the target cells. This method can be used to develop a surrogate system to study the functions of capsid proteins of polyomaviruses and to generate a set of polyomaviral vectors targeted at specific cell types.

Simian virus 40 vectors for pulmonary gene therapy

Background

Sepsis remains the leading cause of death in critically ill patients. One of the primary organs affected by sepsis is the lung, presenting as the Acute Respiratory Distress Syndrome (ARDS). Organ damage in sepsis involves an alteration in gene expression, making gene transfer a potential therapeutic modality. This work examines the feasibility of applying simian virus 40 (SV40) vectors for pulmonary gene therapy.

Methods

Sepsis-induced ARDS was established by cecal ligation double puncture (2CLP). SV40 vectors carrying the luciferase reporter gene (SV/luc) were administered intratracheally immediately after sepsis induction. Sham operated (SO) as well as 2CLP rats given intratracheal PBS or adenovirus expressing luciferase served as controls. Luc transduction was evaluated by in vivo light detection, immunoassay and luciferase mRNA detection by RT-PCR in tissue harvested from septic rats. Vector abundance and distribution into alveolar cells was evaluated using immunostaining for the SV40 VP1 capsid protein as well as by double staining for VP1 and for the surfactant protein C (proSP-C). Immunostaining for T-lymphocytes was used to evaluate the cellular immune response induced by the vector.

Results

Luc expression measured by in vivo light detection correlated with immunoassay from lung tissue harvested from the same rats. Moreover, our results showed vector presence in type II alveolar cells. The vector did not induce significant cellular immune response.

Conclusion

In the present study we have demonstrated efficient uptake and expression of an SV40 vector in the lungs of animals with sepsis-induced ARDS. These vectors appear to be capable of in vivo transduction of alveolar type II cells and may thus become a future therapeutic tool.

SV40 Pseudovirion gene delivery of a toxin to treat human adenocarcinomas in mice

SV40 vectors packaged in vitro (pseudovirions) are an efficient delivery system for plasmids up to 17.7 kb, with or without SV40 sequences. A truncated Pseudomonas exotoxin gene (PE38) was delivered into various human cells (HeLa, KB-3-1, human lymphoblastoids, and erythroleukemia cells), in vitro using pseudovirions. The number of viable cells was reduced significantly in the PE38-transduced cells. Human KB adenocarcinomas growing in mice were treated with intratumoral injection of PE38 packaged in vitro, and tumor size decreased significantly. Intraperitoneal treatments were as effective in reducing tumor size as intratumoral treatments. To check the viability of mock- or PE38-treated mice, every 4 days they were weighed, their blood was tested, and various tissues were screened for pathology. All parameters showed that the in vitro-packaged vectors, injected into tumors or intraperitoneally, caused no abnormalities in mice. The combined treatment of doxorubicin with in vitro-packaged PE38 reduced tumor size slightly more than each of the treatments separately. However, the combined treatment did not cause the weight loss seen with doxorubicin alone. These results indicate that SV40 in vitro packaging is an effective system for cancer gene delivery using two different routes of injection and in combination with chemotherapy.

Intratumoral injection of dendritic cells transduced by an SV40-based vector expressing interleukin-15 induces curative immunity mediated by CD8+ T lymphocytes and NK cells

Cancer immunotherapy has been extensively attempted by gene transfer of cytokines with viral vectors. In this work, we compared the therapeutic effects of interleukin 12 and 15 (IL-12 and IL-15) genes transferred to tumor cells or to dendritic cells (DCs), which were subsequently injected into established tumors. For this purpose, we used viral vectors based on simian virus 40 (rSV40). Importantly, we observed that nonmatured DCs infected with rSV40 vectors remained phenotypically immature. Infection of CT-26 tumor cells with rSV40 expressing IL-12 (rSVIL-12) or IL-15 (rSVIL-15) failed to inhibit tumor development. In contrast, the intratumoral administration of syngeneic DCs transduced with rSVIL-12 or rSVIL-15 was associated with a strong antitumor response; up to 40% tumor remissions were achieved with DCs transduced by rSVIL-12 and 73% with DCs expressing IL-15. This antitumor effect correlated with the in vivo priming of tumor-specific CD8+ T lymphocytes. Depletion studies showed that rSVIL-15-mediated antitumor efficacy was mediated mainly by CD8+ T lymphocytes and NK cells. We conclude that (i) SV40-derived vectors are an advantageous alternative to transduce genes into DCs and (ii) DCs transferred with IL-15 have an enhanced capability to induce curative antitumor immunity when injected into malignant lesions.

Efficient delivery of RNA interference effectors via in vitro-packaged SV40 pseudovirions

Previously we have shown that in vitro-packaged simian virus 40 (SV40) pseudovirions (IVPs) are an efficient delivery system for supercoiled DNA plasmids of up to 17.7 kb, with or without SV40 sequences. RNA interference (RNAi) is a naturally occurring gene-silencing mechanism mediated by small double-stranded RNA molecules (small interfering RNAs, siRNAs). This study demonstrates the first use of SV40 pseudovirions to deliver into human cells both principal types of RNAi effector molecules: plasmid-expressed short hairpin RNAs (shRNAs) and synthetic siRNAs. We first established the ability of human lymphoblastoid cells to support RNAi, using sequential transduction of .45 cells with packaged plasmid DNA expressing the green fluorescent protein (IVP-GFP), and an shRNA corresponding to the GFP (IVP-shGFP). SV40 mediates DNA transfer of nucleic acid to the cytoplasm, where RNAi-associated cleavage of mRNA principally occurs. Using SV40 pseudovirions, siRNA-mediated RNAi was observed in both .45 cells, after sequential transduction of IVP-GFP and IVP-packaged siRNAs corresponding to GFP (IVP-siGFP), and in HeLa cells stably expressing a GFP transduced with IVP-siGFP. Our findings indicate that SV40 pseudovirions may be a useful addition to the delivery systems currently being used for the transfer of RNAi effector molecules.

Liver-targeted gene therapy by SV40-based vectors using the hydrodynamic injection method

Efficient reconstitution of defective genes in hepatocytes could be used to treat various liver and systemic diseases through gene therapy. To explore the potential of SV40-based vectors in liver gene therapy, we constructed SV/luc, an SV40 T-antigen replacement transduction vector, that was propagated on COS and COT cells, which supply the SV40 T-antigen in trans. For liver targeting, BALB/C mice were injected via the tail vein with SV/luc stocks containing 3 x 10(6) to 10(8) transducing units in a volume of 1-2 ml. Luciferase activity was monitored with a light-detection cooled charged-coupled device (CCCD) camera, which enables continuous in vivo measurement of luc expression. The SV40 vector proved to be efficient in gene delivery to the liver, leading to long-term (> or =107 days) transgene expression in hepatocytes. Optimal results were obtained with 3 x 10(6) to 3 x 10(7) transducing units. The hydrodynamic vector delivery method caused transient liver inflammatory changes, with full recovery within days. Low levels of SV40-neutralizing antibodies were detected in the sera of treated mice; however, there was no indication of vector or transgene-specific cellular immune responses. Vectors packaged in vitro, using recombinant capsid proteins and plasmid DNA, were also effective in liver transduction. These results suggest that SV40 vectors may be useful for liver gene therapy.

Factors Influencing the Production of Recombinant SV40 Vectors

Most gene therapy approaches employ viral vectors for gene delivery. Ideally, these vectors should be produced at high titer and purity with well-established protocols. Standardized methods to measure the quality of the vectors produced are imperative, as are techniques that allow reproducible quantitation of viral titer. We devised a series of protocols that achieve high-titer production and reproducible purification and provide for quality control and titering of recombinant simian virus 40 vectors (rSV40s). rSV40s are good candidate vehicles for gene transfer: they are easily modified to be nonreplicative and they are nonimmunogenic. Further, they infect a wide variety of cells and allow long-term transgene expression. We report here these protocols to produce rSV40 vectors in high yields, describe their purification, and characterize viral stocks using quality control techniques that monitor the presence of wild-type SV40 revertants and defective interfering particles. Several methods for reproducible titration of rSV40 viruses have been compared. We believe that these techniques can be widely applied to obtain high concentrations of high-quality rSV40 viruses reproducibly.

Transduction of multiple cell types using improved conditions for gene delivery and expression of SV40 pseudovirions packaged in vitro

This comprehensive study demonstrates highly efficient transduction of a wide variety of human, murine, and monkey cell lines, using a procedure for in vitro packaging of plasmid DNA in recombinant simian virus 40 (SV40) capsid proteins to form pseudovirions. The pseudovirions are encapsidated by the VP1 major capsid protein, with no SV40 sequence requirement, and are able to carry up to 17.7 kb of supercoiled plasmid DNA. We developed a procedure to scale-up production of SV40 pseudovirions, as well as an efficient protocol to concentrate the virions with no loss of activity. We also developed a method that allows transduction of 10 times more cells than the original protocol. This protocol was tested using supercoiled in vitro-packaged plasmid carrying the human multidrug-resistance gene (MDR1 encoding P-glycoprotein; P-gp), or the enhanced green fluorescent protein reporter gene (EGFP) in .45 human lymphoblastoid cells and in K562 human erythroleukemia cells. Multiple transductions at 24-h intervals were shown to increase expression using the EGFP reporter gene. The protocols developed in this study establish in vitro-packaged SV40 pseudovirions as one of the most efficient gene delivery systems.

Simian Virus-40 as a Gene Therapy Vector

Simian virus-40 (SV40), an icosahedral papovavirus, has recently been modified to serve as a gene delivery vector. Recombinant SV40 vectors (rSV40) are good candidates for gene transfer, as they display some unique features: SV40 is a well-known virus, nonreplicative vectors are easy-to-make, and can be produced in titers of 10(12) IU/ml. They also efficiently transduce both resting and dividing cells, deliver persistent transgene expression to a wide range of cell types, and are nonimmunogenic. Present disadvantages of rSV40 vectors for gene therapy are a small cloning capacity and the possible risks related to random integration of the viral genome into the host genome. Considerable efforts have been devoted to modifing this virus and setting up protocols for viral production. Preliminary therapeutic results obtained both in tissue culture cells and in animal models for heritable and acquired diseases indicate that rSV40 vectors are promising gene transfer vehicles. This article reviews the work performed with SV40 viruses as recombinant vectors for gene transfer. A summary of the structure, genomic organization, and life cycle of wild-type SV40 viruses is presented. Furthermore, the strategies utilized for the development, production, and titering of rSV40 vectors are discussed. Last, the therapeutic applications developed to date are highlighted.

Cancer gene therapy: an awkward adolescence

At the Eleventh International Conference on Gene Therapy of Cancer (December 12-14, 2002, San Diego, CA) progress on using gene transfer technology to treat cancer was presented. Although there is as yet no cancer gene therapy being marketed, considerable progress has been made in defining likely strategies and likely targets for gene therapy of cancer. These strategies, including viral and non-viral delivery systems, and potential targets in cancer cells linked to our developing knowledge of cancer cell biology, are reviewed in this paper. Use of gene therapy to sensitize tumors to radiation and chemotherapy is one promising area of investigation. Some of the ancillary benefits of research on cancer gene therapy, including the development of public-private partnerships, recruitment of laboratory scientists into clinical research, and credentialing of potential cancer cell targets for therapies other than gene therapy, are noted.

High cloning capacity of in vitro packaged SV40 vectors with no SV40 virus sequences

In vitro packaging of plasmid DNA using recombinant SV40 capsid proteins is a potentially useful procedure that overcomes some restrictions of the other SV40 systems such as the requirement for SV40 sequences and the limitation in size of DNA that can be packaged. The in vitro packaging system uses the four SV40 proteins (VP1, VP2, VP3, and agno) or VP1 only. The ability to confer drug resistance by three ABC transporter genes (MDR 1, MRP 1, or MXR) was determined using the surrogate fluorescent substrates rhodamine-123 or calcein AM and their specific inhibitors, or by using specific antibodies to the transporters to detect cell surface expression by fluorescence-activated cell sorter analysis (FACS). A green fluorescent protein plasmid (EGFP-C1) was also used to monitor gene transfer. The packaged plasmids ranged in size from 4.2 to 17.6 kb, and only slightly affected particle size as determined by electron microscopy. When 9.5 kb and larger plasmids were packaged using all SV40 proteins, MDR1 expression was decreased compared to VP1 alone. The size of the 15.2 kb DNA after packaging was the same as the original DNA. Packaging with SV40 capsid proteins in vitro does not require any SV40 sequences. Using either the MDR1 or the GFP gene we could demonstrate enhanced expression when cells were pretreated with phorbol 12-myristate 13-acetate (PMA) at low concentrations. Interferon-gamma did not alter expression. We conclude that in vitro packaging is more flexible then previously realized, permitting packaging of at least 17 kb plasmid DNA without the requirement for any viral sequences. This system combines efficient gene delivery of the SV40 viral vector with the presumed safety of nonviral vectors.