Improvement of Antitumor Activity by Gene Amplification with a Replicating but Nondisseminating Adenovirus

Abstract

Gene therapy is a promising approach for cancer treatment; however, efficacy of current vectors remains insufficient. To improve the success of suicide gene therapy, we constructed a replication-competent adenoviral vector that has its protease gene deleted and expresses bacterial cytosine deaminase fused with bacterial uracil phosphoribosyltransferase (CU). The prodrug, 5-fluorocytosine, is transformed into the highly toxic and tissue-diffusible 5-fluorouracil by CU in infected cells. This vector is incapable of producing infectious particles but is able to undergo a single round of replication, thereby increasing transgene copy number and expression. In the presence of 5-FC, compared with the first-generation vector (AdCU), the replication-competent vector, Ad(dPS)CU-IRES-E1A, was significantly more efficacious for in vitro tumor cell killing and in bystander assays, whereas 25-fold fewer viral particles were required in a three-dimensional spheroid model. For in vivo experiments, in which virus was injected into preestablished intracranial glioma xenografts, followed by 5-FC treatment, mice receiving Ad(dPS)CU-IRES-E1A had significantly smaller tumors at 35 days postinjection as well as significantly longer median survival than mice treated with the replication-deficient, protease-deleted vector [Ad(dPS)CU]. In an immunocompetent syngeneic model, Ad(dPS)CU + 5-FC-treated mice had a median survival of only 23 days, whereas Ad(dPS)CU-IRES-E1A + 5-FCtreated animals had a survival of 57.1% at 365 days. In conclusion, Ad(dPS)CU-IRES-E1A in the presence of 5-FC produces more potent tumoricidal effects than its replicationdeficient counterparts. [Cancer Res 2007;67(7):3387-95]

Immunogenic and protective properties of GP5 and M structural proteins of porcine reproductive and respiratory syndrome virus expressed from replicating but nondisseminating adenovectors

“…The M-GP5- and M-GP5m-encoding sequences were inserted into the Bgl II site of the adenovirus transfer vector pAdenoVator-CMV5(CuO)-IRES-E1A [45]. The recombinant plasmids were rescued into the genome of the pAdeasyΔPS by homologous recombination in E .…”

“…These adenovectors are devoid of functional protease (PS) gene, preventing the maturation process of capsid proteins and assembly of viral particles [44]. For this reason these vectors are considered safe because of their inability to spread among the population [45]. In addition, these vectors are functional in the E1A gene, allowing replication of the viral genome, and, thereof, expression of the proteins of interest to high levels within the inoculated host [45].…”

“…For this reason these vectors are considered safe because of their inability to spread among the population [45]. In addition, these vectors are functional in the E1A gene, allowing replication of the viral genome, and, thereof, expression of the proteins of interest to high levels within the inoculated host [45]. Finally, these adenovectors are of the human type rendering them very attractive for use in the pig which is fully permissive to the vector and does not have vector-specific pre-existing immunity [46].…”

Gene Therapy of Glioblastoma Multiforme - Clinical Experience on the Use of Adenoviral Vectors

“…One of the limitations of direct intratumoural administration is that it is possible to do only with solid tumours. In case of (20) www.intechopen.com systemic administration of the gene transfer vector, targeting of the vector specifically to the tumour cells or restricting the expression of the transgene to tumour cells is essential (Bourbeau et al, 2007). (Figure 2).…”

Perspectives in Engineered Mesenchymal Stem/Stromal Cells Based Anti- Cancer Drug Delivery Systems

“…5-FU itself is cytotoxic when it is directly administrated. But, when a combination of a suicidal gene and prodrug of 5-FU, namely 5-FC is administered, 5-FU is produced selectively at tumor cells [96,97]. This possibility presented in the work of Chang et al, 2010 [98] is explained as being applicable on humans, ex vivo therapeutic modality, wherein by using bacterial CD-expressing MSCs, the recurrence of malignant brain tumors can be effectively suppressed.…”