Infectivity and expression of the early adenovirus proteins are important regulators of wild-type and ΔE1B adenovirus replication in human cells

Abstract

An adenovirus mutant lacking the expression of the large E1B protein (DE1B) has been reported to replicate selectively in cells lacking the expression of functionally wild-type (wt) p53. Based on these results the DE1B or ONYX-015 virus has been proposed to be an oncolytic virus which might be useful to treat p53-de®cient tumors. Recently however, contradictory results have been published indicating that p53-dependent cell death is required for productive adenovirus infection. Since there is an urgent need for new methods to treat aggressive, mutant p53-expressing primary tumors and their metastases we carefully examined adenovirus replication in human cells to determine whether or not the DE1B virus can be used for tumor therapy. The results we present here show that not all human tumor cell lines take up adenovirus e ciently. In addition, we observed inhibition of the expression of adenovirus early proteins in tumor cells. We present evidence that these two factors rather than the p53 status of the cell determine whether adenovirus infection results in lytic cell death. Furthermore, the results we obtained by infecting a panel of di erent tumor cell lines show that viral spread of the DE1B is strongly inhibited in almost all p53-pro®cient and -de®cient cell lines compared to the wt virus. We conclude that the e ciency of the DE1B virus to replicate e ciently in tumor cells is determined by the ability to infect cells and to express the early adenovirus proteins rather than the status of p53.

Selective replication of E1B55K-deleted adenoviruses depends on enhanced E1A expression in cancer cells

“…The results clearly indicate that the endogenous E1a promoter in the E1B55K-deleted virus is more activated in Hep3B cells than that in Saos2 cells. Unlike the data reported by Steegenga, 34 we showed that Hep3B and Saos2 cells could be equally infected by adenoviruses (Figure 1c). This conclusion was further verified by comparing the viral DNA uptake between the two cell lines after dl1520/ÀE2a infection.…”

“…At 2 days after infection, cells were observed for CPE that were characterized by unattached and rounded-up cells. Similar to the data reported by Steegenga et al, 34 CPE were observed in Hep3B cancer cells infected with dl1520 but not in the Saos2 cells (Figure 2). In fact, all the viruses can destroy Hep3B cells.…”

“…Adenovirus dl1520 could efficiently replicate in Hep3B cells, but not in Saso2 cells. 30,31,34,35 We showed that dl1520 produced much higher levels of E1A proteins in Hep3B cells than that in Saos2 cells (Figure 3). The repression of E1A production from dl1520 in Saos2 cells may lead to limited viral DNA replication.…”

“…This seems to be in agreement with the concept that E1B55K is required for virus replication in Saos2 cells but not in Hep3B cells. 34 On the other hand, application of the strong CMV promoter to control E1A expression could lead to replication (Figure 3a) and CPE induction (Figure 2) of the E1B55K-deleted Adhz69 in Saos2 cells. These results of viral replications and CPE together suggest that the E1B55K-deleted viruses (dl1520 and Adhz51) can efficiently replicate in Hep3B cells but not in Saos2, and that viruses (Adhz69) with the E1a ORF controlled by the strong CMV promoter can overcome the restriction of viral replication of the E1B55K-deleted viruses in some cancer cells, such as Saos2 cells.…”

“…Hep3B cells efficiently support dl1520 replication, but Saos2 cells strongly inhibit the virus replication. 30,31,34,35 Both Hep3B 36,37 and Saos2 38,39 are p53 null. We applied Hep3B and Saos2 cells as cancer cell models to investigate virus-cancer selective replication with the goal of improving the efficacy of virotherapy by overcoming tumor resistance to virus replication.…”