Transient suppression of transgene expression by means of antisense oligonucleotides: a method for the production of toxin-transducing recombinant viruses

Generation of an adenovirus-parvovirus chimera with enhanced oncolytic potential

In this study, our goal was to generate a chimeric adenovirus-parvovirus (Ad-PV) vector that combines the high-titer and efficient gene transfer of adenovirus with the anticancer potential of rodent parvovirus. To this end, the entire oncolytic PV genome was inserted into a replication-defective E1- and E3-deleted Ad5 vector genome. As we found that parvoviral NS expression inhibited Ad-PV chimera production, we engineered the parvoviral P4 early promoter, which governs NS expression, by inserting into its sequence tetracycline operator elements. As a result of these modifications, P4-driven expression was blocked in the packaging T-REx-293 cells, which constitutively express the tetracycline repressor, allowing high-yield chimera production. The chimera effectively delivered the PV genome into cancer cells, from which fully infectious replication-competent parvovirus particles were generated. Remarkably, the Ad-PV chimera exerted stronger cytotoxic activities against various cancer cell lines, compared with the PV and Ad parental viruses, while being still innocuous to a panel of tested healthy primary human cells. This Ad-PV chimera represents a novel versatile anticancer agent which can be subjected to further genetic manipulations in order to reinforce its enhanced oncolytic capacity through arming with transgenes or retargeting into tumor cells.

Improving the titer of recombinant adenovirus by suppressing problematic transgene transcription during packaging

A new strategy to package "problematic" transgenes in adenovirus was developed that was based on modifications of the tetracycline-inducible system. This strategy used two components: the adenoviral genome containing the transgene under control of a hybrid TRE promoter/SV40 enhancer and a trans-encoded tTS suppressor Using luciferase reporters, expression of tTS in 293A cells reduced transcription from the promoter/enhancer 25-fold. Procaspase 8 adenovirus was then tested, since it is known to package poorly with standard adenoviral systems. Expression of tTS in 293A cells increased the titer of procaspase 8 adenovirus by 22-fold in initial viral packaging (using transiently transfected tTS) and 9-fold in subsequent viral reamplification (using 293A cells stably expressing tTS). The Tac antigen gene (i.e., CD25), which packages in adenovirus without difficulty, was also tested as a control. In contrast to that observed with procaspase 8, tTS expression did not alter the titer obtained when packaging the CD25 gene, thus excluding nonspecific effects of tTS expression on adenoviral titer Since tTS was provided in trans and did not package in the resulting adenoviruses, strong transcription of the transgenes occurred in transducted cells without the need of additional reagents.

Oncolytic viruses in cancer therapy

Oncolytic virotherapy is a promising form of gene therapy for cancer, employing nature’s own agents to find and destroy malignant cells. The purpose of this review is to provide an introduction to this very topical field of research and to point out some of the current observations, insights and ideas circulating in the literature. We have strived to acknowledge as many different oncolytic viruses as possible to give a broader picture of targeting cancer using viruses. Some of the newest additions to the panel of oncolytic viruses include the avian adenovirus, foamy virus, myxoma virus, yaba-like disease virus, echovirus type 1, bovine herpesvirus 4, Saimiri virus, feline panleukopenia virus, Sendai virus and the non-human coronaviruses. Although promising, virotherapy still faces many obstacles that need to be addressed, including the emergence of virus-resistant tumor cells.