Enhanced Safety Profiles of the Telomerase-Specific Replication-Competent Adenovirus by Incorporation of Normal Cell-Specific microRNA-Targeted Sequences

Abstract

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.

MicroRNA Regulation of Oncolytic Adenovirus 6 for Selective Treatment of Castration-Resistant Prostate Cancer

“…Silencing E1A gene in Ad6miR substantially enhanced liver safety due to the stringent posttranscriptional hepatocyte-detargeting capacity of Ad6miR (Fig. 2D), which is consistent to the published findings in Ad5 (23). In good agreement with the miR122 expression profile of the prostate cancer cell lines, Ad6miR exhibited similar anticancer activity in the CRPC model as compared with Ad6 in vitro (Fig.…”

“…3B, P > 0.05), which explained the similar oncolytic capacity. Notably, Ad6miR exhibited similar burst size as compared with Ad6, consistent with the data recently reported on microRNA-regulated Ad5 (23). We also tested the killing efficacy of Ad6miR in primary prostate cancer cells isolated from patients with advanced prostate cancer bone metastasis.…”

“…Incorporation of the tissue-specific microRNA target sequences into E1A expression cassette selectively suppressed the Ad5 replication in normal tissues and decreased the virus-related systemic toxicity, although maintained the comparable antitumor efficacy after i.v. injection (22)(23)(24)(25). MicroRNA miR122 is one of the candidates, which is abundantly expressed only in hepatocytes (26,27).…”

MicroRNA-mediated multi-tissue detargeting of oncolytic measles virus

“…29,38,39 Combinations of multiple miRTS as well as combinations with other targeting strategies can be implemented to tailor the natural tropism of oncolytic viruses to a specific cancer entity. Sugio et al 40 generated a cancer-specific promoterdependent oncolytic adenovirus containing miRTS for miR-122 and miR-199a. Fu et al 25 combined a liver-specific promoter and miRTS for miR-122, miR-124 and let-7 in an oncolytic herpes simplex virus.…”

Switching a Replication-Defective Adenoviral Vector into a Replication-Competent, Oncolytic Adenovirus

“…However, difficulties in restricting Flp expression to when it was desired as well as in undesirable recombination events led us to separate the Flp function into a second vector. It is possible that a more desirable single-vector construct could be engineered not only by trying to transcriptionally restrict Flp expression but also by adding appropriate microRNA target sequences to the 3=-untranslated region (UTR) of Flp (24)(25)(26). For instance, the CAG promoter in HnR-CF could be replaced by other promoters that are regulated by the microenvironment and/or pharmacologic agents for temporal regulation of Flp gene transcription (27)(28)(29).…”