Virotherapy targeting cyclin E overexpression in tumors with adenovirus-enhanced cancer-selective promoter

Abstract

Oncolytic virotherapy can selectively destroy cancer cells and is a potential approach in cancer treatment. A strategy to increase tumor-specific selectivity is to control the expression of a key regulatory viral gene with a tumor-specific promoter. We have previously found that cyclin E expression is augmented in cancer cells after adenovirus (Ad) infection. Thus, the cyclin E promoter that is further activated by Ad in cancer cells may have unique properties for enhancing oncolytic viral replication. We have shown that high levels of viral E1a gene expression are achieved in cancer cells infected with Ad-cycE, in which the endogenous Ad E1a promoter was replaced with the cyclin E promoter. Ad-cycE shows markedly selective oncolytic efficacy in vitro and destroys various types of cancer cells, including those resistant to ONYX-015/dl1520. Furthermore, Ad-cycE shows a strong capacity to repress A549 xenograft tumor growth in nude mice and significantly prolongs survival. This study suggests the potential of Ad-cycE in cancer therapy and indicates the advantages of using promoters that can be upregulated by virus infection in cancer cells in development of oncolytic viruses.

Adenovirus with DNA Packaging Gene Mutations Increased Virus Release

“…AdGFP is E1 ( E1a and E1b ) deleted, with green fluorescent protein (GFP) expression driven by the cytomegalovirus (CMV) promoter [35]. AdGFP, as a negative control, does not replicate nor induce cytopathic effects (CPE) [9,23]. All Ads used in this study express E1 and E4 unless otherwise specified, and are based upon Ad5 backbone sequences (GENEID# AC_000008.1).…”

“…Both E1B55K and E1B19K proteins have been shown to protect infected cells from E1A-induced stabilization of p53 and apoptosis [17]. E1B55K also enhances viral E1a expression and is involved in the induction of cyclin E required for Ads to efficiently replicate [9,18,19,20,21,22,23]. The Ad E1B19K protein is a putative B-cell lymphoma 2 (Bcl-2) functional homolog [24,25,26] which prevents E1A-induced apoptosis by inhibiting the pro-apoptotic proteins Bak and Bax [27].…”

“…These viruses were shown to be safe, but without producing clinically relevant therapeutic responses. We recently developed Ad-cycE, in which E1a is regulated by the human cyclin E promoter [23,35]. Cyclin E overexpression has been observed in lung, liver, gastrointestinal, glioma/blastoma, bone, and breast cancers [36].…”

“…Cyclin E overexpression has been observed in lung, liver, gastrointestinal, glioma/blastoma, bone, and breast cancers [36]. We have previously shown that Ad infection stimulated the activity of the cyclin E promoter [19,20], therefore, the inclusion of the cyclin E promoter to control E1a augmented the oncolytic efficacy of Ads [35,37]. …”

Strategic Combinations: The Future of Oncolytic Virotherapy with Reovirus

“…Unlike viruses with a ds DNA genome, like adenoviruses and herpes simplex viruses, the decreased genomic stability provided by an RNA backbone makes genetic engineering more difficult and more prone to hazardous mutation. In DNA viruses, genetic manipulation provides a way to suppress pathogenicity and increase tumor-targeting specificity and oncolytic potency (10). However, even without engineered capabilities, reovirus is pathologically benign and tumor cytotoxic, making it an appealing OV for therapeutic development.…”