The Oncolytic Adenovirus Adp53-sensor Replicates Selectively in p53-altered Tumor Cells and Potential Tumor Spectrum is not Limited by the p73 Status

Oncolytic virotherapy provides a promising and novel mean for the treatment of solid tumors. Major challenges in virotherapy are tight restriction of viral replication to malignant cells and a broad range of potential target tumors. The aim of the study was the establishment of a conditionally replicating adenovirus able to recognize the transcriptional p53-status of target cell and able to consequently respond by the selective onset of viral replication in cells lacking functional p53. We constructed Adp53-sensor harboring E1A controlled by a GAL4-binding CMV-promoter and the GAL4KRAB-repressor controlled by the p53-sensitive promoter prMinRGC. Vector selectivity, and therapeutic efficacy were characterized by luciferase assays, western blots, oncolysis assays, adenoviral replication kinetics, and tumor size measurements in vivo. First, the artificial promoter prMinRGC applied in Adp53-sensor showed enormous induction by endogenous or overexpressed p53, but was completely silent in p53-negative cells. Though the promoter was sensitive to overexpressed p73-b, but not other members of the p53 family, prMinRGC was completely silent in p53-altered cells including p73-positive cells. As endogenous p73 seems to be insufficient to activate prMinRGC, the p73-status should not limit the potential tumor spectrum of therapeutic Adp53sensor application. We could further show selectivity and oncolytic efficacy of Adp53sensor by comparing a large panel of cell lines with different p53/p73 status including HCC-cells. Furthermore, p53-selectivity was confirmed in human hepatocytes where Adp53-sensor replication was inhibited. Western Blots demonstrated correct function of the p53-dependent, GAL4-KRAB regulated E1A expression in cells harboring or lacking intact p53. Doxorubicin pretreatment significantly enhanced selectivity of Adp53-sensor. In oncolysis assays Adp53-sensor showed slightly reduced oncolytic properties compared to Ad-wt but was both more p53-selective and efficient compared to ONYX–015. The vector was also more efficient in the treatment of s.c. grown Hep3B-xenografts and treatment resulted in partial remissions. Our data suggest that Adp53-sensor represents an effective tool for p53-selective virotherapy of cancer. p53-selectivity and oncolytic properties of Adp53-sensor are improved compared to ONYX–015. The vector can be applied to a broad tumor spectrum as the selective function is not limited by the p73 status of the target tumors.