While its replication could proceed regularly in 
cells lacking the expression of this miRNA. Since miR-199 is highly expressed in normal liver, but not in HCC, this virus seems to be well suited for the treatment of liver cancer. By testing various experimental in vivo models, we confirmed this potential opportunity. First, in 3 days old mice, which have a limited or absent Torin 1 immune response, Ad-199T was not able to replicate in the liver while an identical control virus, lacking the miR-199 target sites, could efficiently undergo several rounds of replication. In this model, control adenovirus, but not Ad-199T, induced an evident hepatoxicity, as evidenced by histological and immunohistochemical analyses. This foreseeable finding was a consequence of the inhibitory effect imposed by miR-199 on Ad-199T replication, thereby preventing its lytic activity in healthy cells. This property is shared with other recently developed miRNA dependent oncolytic adenoviruses, like miR-122-based adenovirus detargeting vectors, which exhibited a reduced virus-related liver toxicity. However, miR-122 is a liver-specific miRNA and is not expressed in any other tissue, leaving open the possibility that toxicities due to viral replication could eventually affect other tissues. Since miR-199 is instead expressed at variable but significant level in any normal tissues, Ad-199T could lack toxicity in tissues other than liver as well. To support the anti-tumor oncolytic activity of Ad-199T, we proved that the virus could slow-down the growth of xenografts made of liver cancer cells subcutaneously implanted into nude mice. Also in this model, the reduced viral toxicity was supported by the fact that all treated immune deficient mice could survive following 6 consecutive administrations of large amounts of replication-competent viruses. As found with other oncolytic adenoviruses, Ad-199T did not cause tumor regression, but the anti-tumor effect was significant. As previously mentioned, it is possible that this virus, like other CRAds, could find its best use to boost efficacy of chemo or radiotherapy. We also investigated the anti-tumor effect in an immunecompetent host mouse model, highly susceptible to the development of liver primary tumors. Administration of Ad-199T induced a significant reduction of the number and size of tumor nodules, most likely because Ad-199T could replicate more efficiently in neoplastic than in normal liver cells. A conceptually similar but different oncolytic virus was developed by Jin et al. It was engineered as a let-7 dependent oncolytic adenovirus, able to replicate only in cells lacking the let-7 miRNA. The authors specify that let-7 is down-regulated in about 36% of HCC, thereby suggesting that this virus could Rapamycin produce a potential therapeutic effect in this subset of HCCs. Together with the studies on miR-122 and let-7, the present study indicates that the knowledge of miRNA expression levels in normal and cancer cells may be applied to the design of oncolytic viruses that combine selective efficacy against cancer cells with minimal adverse toxic effects. In nonmuscle-invasive tumors progression to muscle-invasive disease is rare and occurs in 3 to 5% of all cases. While patients with genetically stable nonmuscle invasive low grade tumors show an excellent 5 year survival rate of 96%, patients with deep muscle infiltrating high grade tumors have the worst prognosis with a 5 year survival rate of about 20%. In exophytic, nonmuscle invasive low grade tumors transurethral resection is the local, bladder preserving, therapy of choice. In muscle infiltrating tumors radical cystectomy with extended pelvic lymph node dissection is the generally accepted treatment with curative intent. In patients with severe comorbidities alternative treatment option is the combined chemo- and radiation therapy.