Strategies for cancer gene therapy using adenoviral vectors

Regression of Human Breast Carcinoma in Nude Mice after Adsflt Gene Therapy Is Mediated by Tumor Vascular Endothelial Cell Apoptosis

Two vascular endothelial growth factor (VEGF) receptors, FLT-1 and KDR, are expressed preferentially in proliferating endothelium. There is increasing evidence that recombinant, soluble VEGF receptor domains interfering with VEGF signaling may inhibit in vivo neoangiogenesis, tumor growth and metastatic spread. We hypothesized that a soluble form of FLT-1 receptor (sFLT-1) could inhibit the growth of pre-established tumors via an anti-angiogenic mechanism. A replication-deficient adenovirus (Ad) vector carrying the sflt-1 cDNA (Adsflt) was used to overexpress the sFLT-1 receptor in a breast cancer animal model. MCF-7 cells, which produce VEGF, were used to establish solid tumors in the mammary fat pads of female nude mice. After six weeks, tumors were injected either with Adsflt or a negative control virus (AdCMV.βgal). After six months, average tumor volume in the Adsflt-infected group (33 ± 22 mm3) decreased by 91% relative to that of the negative control group (388 ± 94 mm3; p < 0.05). Moreover, 10 of 15 Adsflt-infected tumors exhibited complete regression. The vascular density of Adsflt-infected tumors was reduced by 50% relative to that of negative controls (p < 0.05), which is consistent with sFLT-1-mediated tumor regression through an anti-angiogenic mechanism. Moreover, cell necrosis and fibrosis associated with long-term regression of Adsflt−infected tumors were preceded by apoptosis of tumor vascular endothelial cells. Mice treated with Adsflt intratumorally showed no delay in the healing of cutaneous wounds, providing preliminary evidence that Ad-mediated sFLT-1 overexpression may be an effective anti-angiogenic therapy for cancer without the risk of systemic anti-angiogenic effects.

Cancer gene therapy update

Objective. To provide an update about gene marking and gene therapy trials in cancer patients.

Data Sources. A MEDLINE search using the term “gene therapy” was conducted for the period 1985 to 1998. The reference lists from retrieved articles were reviewed. Meeting abstracts from the American Society of Clinical Oncology annual meeting (published in their proceedings) and the Annual Cancer Gene Therapy Symposium (published in Cancer Gene Therapy) that concerned gene therapy in cancer patients were also included.

Data Extraction. Both authors reviewed the retrieved material and included preclinical data, case reports, and clinical trials related to gene transfer or gene therapy in cancer patients.

Data Synthesis. There are several possible approaches to using gene therapy for the diagnosis and treatment of cancer and for the monitoring of cancer therapy. Exogenous genes may be used to mark cells to help better understand cancer biology or may be used directly for cancer treatment. Gene-marking trials have already provided new information about cancer biology and have demonstrated that reinfused progenitor cells may be a source of relapse in patients with acute or chronic myelogenous leukemia and neuroblastoma.

Approaches using gene therapy for cancer treatment include: using lymphocytes as gene carriers, using foreign genes to increase tumor immunogenicity, introducing tumor regression antigen genes into viruses, introducing “sensitivity” genes to produce new cytotoxic agent(s) within tumors, producing new protein product(s) to protect normal cells, replacing missing or mutant tumor suppressor genes, and inactivating oncogenes. Clinical trials using these strategies have demonstrated that gene transfer is feasible (albeit with low transduction efficiency) and that gene expression occurs; in addition, clinical responses have been noted.

Adenoviral vectors: development and application

One of the prerequisites for the successful application of gene vaccination and therapy is the development of efficient gene delivery vectors. The rate-limiting nature of vectors was clearly manifested during the first wave of gene therapy testing, resulting in the demand for more effective and suitable vector systems. Adenoviral (Ad) vectors have recently played a central role in the development of gene-vector technology due to their practical advantages and potential applications. A large number of preclinical and clinical studies both have generated an overwhelming amount of data and literature on this vector system. It is the intention of this article to provide a systematic and broad spectrum review of this system, outlining the principle, potential, and limitations, and evaluating the rational development of this delivery approach. Recombinant adenoviruses (Ad), helper cell lines, and related technologies have been developed and applied to many indications owing to progress in virological research, molecular and cellular biology, eukaryotic protein expression, recombinant vaccines, and gene therapy. The technical depth this article covers should be useful to both the experienced researcher and to beginners in this field.

Optimization of folate-conjugated liposomal vectors for folate receptor-mediated gene therapy

A folate-targeted transfection complex that is internalized by certain cancer cells and displays several properties reminiscent of enveloped viruses has been developed. These liposomal vectors are comprised of a polycation-condensed DNA plasmid associated with a mixture of neutral and anionic lipids supplemented with folate-poly(ethylene glycol)-dioleylphosphatidylethanolamine for tumor cell-specific targeting. N-Citraconyl-dioleylphosphatidylethanolamine is also included for pH-dependent release of endosome-entrapped DNA into the cytoplasm, and a novel plasmid containing a 366-bp segment from SV40 DNA has been employed to facilitate transport of the plasmid into the nucleus. Because formation of the DNA core is an important step in the assembly of liposomal vectors, considerable effort was devoted to comparing the transfection efficiencies of various DNA condensing agents. It was found that complexation of plasmid DNA with high molecular weight polymers such as acylated-polylysine and cationic dendrimers leads to higher folate-mediated transfection efficiency than DNA complexed with unmodified polylysine. In contrast, compaction of plasmid DNA with small cationic molecules such as spermine, spermidine, or gramicidin S yields only weakly active folate-targeted liposomal vectors. Compared to analogous liposomal vector preparations lacking an optimally compacted DNA core, a cell-specific targeting ligand, a caged fusogenic lipid, and a nucleotide sequence that facilitates nuclear uptake, these modified liposomal vectors display greatly improved transfection efficiencies and target cell specificity.

Transduction of dendritic cells by DNA viral vectors directs the immune response to transgene products in muscle fibers

Immune responses to vector-corrected cells have limited the application of gene therapy for treatment of chronic disorders such as inherited deficiency states. We have found that recombinant adeno-associated virus (AAV) efficiently transduces muscle fibers in vivo without activation of cellular and humoral immunity to neoantigenic transgene products such as beta-galactosidase, which differs from the experience with recombinant adenovirus, where vibrant T-cell responses to the transgene product destroy the targeted muscle fibers. T cells activated following intramuscular administration of adenovirus expressing lacZ (AdlacZ) can destroy AAVlacZ-transduced muscle fibers, indicating a prior state of immunologic nonresponsiveness in the context of AAV gene therapy. Adoptive transfer of dendritic cells infected with AdlacZ leads to immune mediated elimination of AAVlacZ-transduced muscle fibers. AAVlacZ-transduced antigen-presenting cells fail to demonstrate beta-galactosidase activity and are unable to elicit transgene immunity in adoptive transfer experiments. These studies indicate that vector-mediated transduction of dendritic cells is necessary for cellular immune responses to muscle gene therapy, a step which AAV avoids, providing a useful biological niche for its use in gene therapy.

In vivo therapy of hepatocellular carcinoma with a tumor-specific adenoviral vector expressing interleukin-2

A recombinant adenovirus (AdVAFP1-IL2) containing the murine alpha-fetoprotein (AFP) promoter was constructed to direct hepatocellular carcinoma (HCC)-specific expression of the human interleukin-2 (IL-2) gene. In vitro testing of AdVAFP1-IL2 showed HCC-specific IL-2 gene expression three to four orders of magnitude higher in AFP-producing HCC lines compared to non-AFP producing non-HCC lines. The in vivo efficacy and tumor specificity of AdVAFP1-IL2 was evaluated compared to AdVCMV-IL2 (in which the IL-2 gene is driven by the strong constitutive cytomegalovirus promoter) in the treatment of established human HCC (Hep 3B/Hep G2) xenografts growing in CB-17/SCID mice. Intratumoral injection of AdV resulted in growth retardation and regression in a majority of established hepatomas, but with a much wider therapeutic index and less systemic toxicity using the AFP vector. This study illustrates the superiority of using transcriptionally targeted recombinant AdV vectors in cytokine-based gene therapy.