1012. Survivin-Responsive Conditionally Replicating Adenovirus Exhibits Strictly Cancer-Specific and Efficient Viral Replication

Abstract

Top of pageAbstract Background, aims and methods: Although conditionally replicating adenovirus (CRA), which shows cancer-selective viral replication and death, is potentially an innovative anti-cancer agent, a current limitation results from the incompleteness of cancer-specific and efficient viral replication. Most importantly, previously reported tissue-specific promoters have the disadvantage of targeting only limited types of cancer, as well as showing less cancer specificity and weak activity even in cancer cells. Here we constructed survivin-responsive CRAs (Surv.CRAs), in which the expression of wild or mutant adenoviral early region 1A gene is regulated by the promoter of survivin, a new member of the inhibitor of apoptosis gene family (Surv.CRAwt and Surv.CRAmt, respectively). Both types of Surv.CRAs have the deletion of E1B55kD, which are driven by the CMV promoter, and contain EGFP marker genes. We carefully explored the cancer-specificity and the effectiveness of viral replication of Surv.CRAs and their therapeutic potential against cancer. Results: Survivin mRNA was expressed in all of the 11 human cancer cells that were derived from various tissue origins, whereas survivin mRNA was very low in normal cells. The survivin promoter was revealed to be strongly active in all these cancer cells studied at levels similar to or even higher than those of representative strong promoters (the RSV and the CMV promoters); in contrast, no detectable activity was observed in normal cells. In careful in vitro experiments (e.g., the speed of the viral replication assessed by the spread of EGFP-positive cells on flowcytometric analysis and by the spread of the cells showing the features of cytopathic effects), both types of Surv.CRAs (i.e., Surv.CRAwt and Surv.CRAmt) efficiently replicated and potently induced death in most types of cancer, in contrast to minimal viral replication resulting in no detectable cytotoxicity in normal cells. A single injection of either of Surv.CRAs into a pre-established tumor expressing survivin, even at a relatively low level, significantly induced tumor death and inhibited tumor growth. There are no different phenotypes in any cells between Sruv.CRAwt and Surv.CRAmt. Furthermore, Surv.CRAs were superior to telomerase (TERT)-dependent CRAs (Tert.CRAs), currently among the best CRAs, both in terms of cancer-specificity and efficiency. Namely, the activity of the survivin promoter was higher than that of the TERT promoter in cancer cells, however, the former is lower than the latter in normal cells. Moreover, Surv.CRAwt is more efficient in replicating in cancer cells than Tert.CRAwt, although the former is more quiescent in normal cells than the latter. Conclusion: Surv.CRAs may be an attractive anti-cancer agent that effectively and specifically treats a variety of cancers.