Purpose: Oncolytic adenoviruses (Ad) have been actively pursued as potential agents for cancer treatment. Among the various types of oncolytic Ads, the telomerase-specific replication-competent Ad (TRAD), which possesses an E1 gene expression cassette driven by the human telomerase reverse transcriptase promoter, has shown promising results in human clinical trials; however, the E1 gene is also slightly expressed in normal cells, leading to replication of TRAD and cellular toxicity in normal cells.Experimental Design: To overcome this problem, we utilized a microRNA (miRNA)-regulated gene expression system. Four copies of complementary sequences for miR-143, -145, -199a, or let-7a, which have been reported to be exclusively downregulated in tumor cells, were incorporated into the 3 0 -untranslated region of the E1 gene expression cassette.Results: Among the TRAD variants (herein called TRADs) constructed, TRADs containing the sequences complementary to miR-143, -145, or -199a showed efficient oncolytic activity comparable to the parental TRAD in the tumor cells. On the other hand, replication of the TRADs containing the miRNA complementary sequences was at most 1,000-fold suppressed in the normal cells, including primary normal cells. In addition, to suppress the replication of the TRADs in hepatocytes as well as other normal cells, we constructed a TRAD containing 2 distinct complementary sequences for miR-199a and liver-specific miR122a (TRAD-122a/199aT). TRAD-122a/199aT exhibited more than 10-fold reduction in viral replication in all the normal cells examined, including primary hepatocytes.Conclusions: This study showed that oncolytic Ads containing the sequences complementary to normal cell-specific miRNAs showed significantly improved safety profiles without altering tumor cell lysis activity.
Fiber-substituted adenovirus (Ad) vectors containing fibers of Ad serotype 35 (AdF35) efficiently transduce a variety of human cells because their receptor, human CD46, is ubiquitously expressed on almost all nucleated cells. However, the ubiquitous expression of CD46 might lead to unexpected transduction in untargeted organs. In this study, we developed fiber-modified AdF35 vectors with an integrinbinding Arg-Gly-Asn (RGD) peptide incorporated into the FG, HI or IJ loop, which have been identified as important regions for binding to CD46. Incorporation of foreign peptides into these loops does not inhibit trimerization of the fibers. In CD46-negative cells, fiber-mutant AdF35 vectors containing an RGD peptide in the FG or HI loop showed 6-to 30-fold higher transduction efficiencies in an RGD-peptide-dependent manner than the unmodified AdF35 vectors. In contrast, in CD46-positive cells, insertion of foreign peptides markedly reduced the transduction efficiencies of the AdF35 vectors, indicating that insertion of foreign peptides significantly inhibits binding to CD46. In particular, CD46-mediated transduction was completely diminished by insertion of foreign peptides into the HI loop. Our findings indicate that HI loop is the most suitable domain to mediate a foreign peptide-dependent and CD46-independent transduction by incorporation of foreign peptides into the Ad35 fiber knob.
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