Deletion analysis of Ad5 E1a transcriptional control region: impact on tumor-selective expression of E1a and E1b

Abstract

The regulatory sequences upstream of E1a, the first viral protein expressed upon infection of cells with adenovirus, have binding sites for multiple transcription factors including two binding sites for E2f and five binding sites for Pea3. We evaluated the impact of deletions, which remove one or more of these transcription factor-binding sites on the expression of E1a in a panel of tumor cells and non-transformed cells. We demonstrated that specific deletions in the E1a enhancer markedly reduced the expression of E1a in growth-arrested cells while having a minimal impact on the expression of E1a in a panel of tumor cells. In particular, deletion of a 50-bp region located from À305 to À255 upstream of the E1a initiation site resulted in marked reduction of E1a and E1b expression and cytolytic activity in growth-arrested cells, while retaining near wild-type of expression of E1a and E1b and cytolytic activity in tumor cells. This deletion removed two Pea3 sites and one E2f site. The characteristics of this vector, TAV-255, was compared with dl1520 (Onyx-015) and demonstrated restricted cytolytic activity in growth-arrested cells similar to dl1520 and superior cytolytic activity in a panel of tumor cell lines. In this current study, we demonstrate that TAV-255, an E1a enhancer deletion vector, possesses tumor selective expression of both E1a and E1b along with potent tumor-selective oncolytic activity.

Histone Deacetylase Inhibitor Suberoylanilide Hydroxamic Acid Suppresses Human Adenovirus Gene Expression and Replication

“…HDAC inhibitors have been shown to alter the expression level and function of cellular proteins p21, E2F1, and SP1 (71)(72)(73)(74), all of which can impact upon optimal viral gene expression and growth. The transcription factors E2F1 and SP1 both play a role in transcriptional control of E1A (75,76). E2F1 and SP1 also bind to the E2 promoter and the MLP, respectively, and binding is required for the maximum expression of proteins from those regions (17,58,(77)(78)(79).…”

A novel immunocompetent murine model for replicating oncolytic adenoviral therapy

“…Adenovirus TAV-255 (AdTAV-255) carries a 50 nucleotide deletion in the promoter of E1A, possesses tumor selective expression of both E1a and E1b along with potent tumor-selective oncolytic activity. 9 AdTAV-255 was produced in HEK-293A cells. Cells were infected with multiplicity of infection (MOI) of 1 and after 3 days post infection, cells were collected and resuspended in complete medium and lysed by three freeze-thaw cycles.…”

Homologous recombination-based adenovirus vector system for tumor cell-specific gene delivery

“…22,23 Second, the specific tumor cell killing does not rely on E1 mutations that can compromise the production yield, viral replication and spread. 24,25 Third, in contrast to the tumorspecific promoters, the systems utilize a more universal strong CMV promoter to achieve high transgene expression. Moreover, the transgene expression occurs in the late of Ad life cycle.…”