The construction of recombinant adenoviruses expressing apoptin

The use of oncolytic viruses is one of the promising areas of malignant diseases modern treatment methods. In numerous studies of the adenoviruses strains oncolytic properties, their efficacy and safety in the treatment of various cancers were shown. The vast majority of the studies were carried out with the use of adenovirus serotype 5. To improve these anticancer agents means to increase their specificity for cancer cells and their lytic activity. To this end, adenovirus serotype 5 recombinant variants were constructed expressing apoptin (VP3 protein of chicken anemia virus) and causing p53 and bcl-2 independent apoptosis, increasing the lytic properties of viruses. Furthermore, to increase the specificity of adenovirus replication towards tumor cells, telomerase reverse transcriptase promoter (hTERT) was used. According to the data indicating that the apoptin expression in the cells is accompanied by induction of apoptosis in tumor cells only, the adenoviruses variants were constructed in which apoptin expression is regulated by cytomegalovirus promoter (CMV), which is stronger than hTERT. As a result, the design of apoptin gene sequences, CMV and hTERT promoters and the construction of recombinant plasmids bearing them, which are necessary for constructing recombinant adenoviruses, was created. Using the methodology of homologous recombination and co-transfection of cells, two replications of defective recombinant adenovirus AdΔE1a-hT-Apo and AdΔE1a-CM-Apo with insertions of apoptin gene under the control of the hTERT-and CMV-promoter, respectively, were obtained. In these recombinants, E1A and E1B genes, necessary for viral replication, are deleted, which makes such agents safer. The third constructed recombinant represents replication competent adenovirus AdhTE1a-CM-Apo with deletion of E1B-55K protein gene and insertion of apoptin gene and E1A gene under the control of the hTERT-promoter. The use of the tumor-specific promoter in this recombinant strain allows the virus to replicate only in the cells with an active telomerase. Furthermore, the specificity of this adenoviral variant to tumor cells is enhanced by deletion of the gene coding E1B-55Kprotein, limiting its replication in normal cells, which are not able to complement the function of this protein. The sequencing of recombinant adenoviruses genomic DNA demonstrated the presence of engineered gene cassettes in their genomes, the validity of the introduced transgenes and regulatory sequences and their compliance with the chosen design scheme. The obtained adenovirus vectors can serve as a basis for creating perspective oncolytic agents with high specificity due to the control of viral replication by hTERT promoter and high lytic activity due to the presence of the apoptin gene as a transgene causing p53 and bcl-2-independent apoptosis in tumor cells.

Keywords

Authors

References