Dual promoter-controlled oncolytic adenovirus CG5757 has strong tumor selectivity and significant antitumor efficacy in preclinical models.

PURPOSE: Transcriptionally controlled oncolytic adenovirus CG5757 is engineered with two tumor-specific promoters from E2F-1 and human telomerase reverse transcriptase genes. This virus has broad anticancer spectrum and higher specificity. The objective of the current study is to show its antitumor selectivity and therapeutic potential. EXPERIMENTAL DESIGN: The antitumor specificity of E2F-1 and human telomerase reverse transcriptase promoters was evaluated in a panel of tumor and normal cells. Under the control of these promoters, the tumor-selective expression of E1a and E1b genes was evaluated. Further in vitro antitumor specificity and potency of this virus were characterized by viral replication and cytotoxicity assays followed by a newly developed ex vivo tumor culture assay. Subsequently, in vivo antitumor efficacy and toxicology studies were carried out to assess the therapeutic potential of this oncolytic agent. RESULTS: In a broad panel of cells, E2F-1 and human telomerase reverse transcriptase promoters were activated in a tumor-selective manner. Under the control of these promoters, expression of E1a and E1b genes appears only in tumor cells. This specificity is extended to viral replication and hence the cytotoxicity in a broad range of cancer cells. Furthermore, CG5757 only replicates in cancer tissues but not in normal tissues that are derived from clinical biopsies. The safety profile was further confirmed in in vivo toxicology studies, and strong efficacy was documented in several tumor xenograft models after CG5757 was given via different routes and regimens. CONCLUSIONS: CG5757 has strong antitumor selectivity and potency. It has low toxicity and has great potential as a therapeutic agent for different types of cancers.

Carcinoembryonic antigen-producing cell-specific oncolytic adenovirus, OV798, for colorectal cancer therapy.

Human carcinoembryonic antigen (CEA) is overexpressed in most colorectal cancers and has been widely used as a clinical marker for the management of colon cancer patients. The transcriptional regulatory elements (TREs) of CEA include two enhancer elements and a promoter in the 5'-flanking region of the CEA gene. By using these elements in different combinations to control reporter gene expression and the replication of adenovirus variants in various tumor cells, we have identified an optimal CEA regulatory cassette that tightly controls gene expression and viral replication in CEA-producing colon cancer cells. One of these variants, OV798, in which this regulatory cassette controls E1A expression, was further characterized. OV798 preferentially replicates in and kills CEA-producing colorectal cancer cell lines such as LoVo and SW1463, but its replication is attenuated by 1000-fold in the CEA-negative cell lines Colo-320DM (colon cancer), PA-1 (ovarian cancer), G361 (melanoma), U118 MG (glioma), and HBL-100 (human breast epithelial cell). The antitumor activity of OV798 was further examined in BALB/c nu/nu mice carrying s.c. human colon tumor xenografts. A single intratumoral administration of OV798 resulted in growth inhibition of human LoVo colon cancer xenografts. Six weeks after treatment, relative tumor volume decreased to 90% of baseline for the OV798 treatment group, compared to an increase to 1200% of baseline at 4 weeks for the vehicle-treated group. In vitro and in vivo characterization indicate that OV798 could be used as a therapy for human colon cancer.