Directed Evolution Generates a Novel Oncolytic Virus for the Treatment of Colon Cancer

Abstract

BackgroundViral-mediated oncolysis is a novel cancer therapeutic approach with the potential to be more effective and less toxic than current therapies due to the agents selective growth and amplification in tumor cells. To date, these agents have been highly safe in patients but have generally fallen short of their expected therapeutic value as monotherapies. Consequently, new approaches to generating highly potent oncolytic viruses are needed. To address this need, we developed a new method that we term “Directed Evolution” for creating highly potent oncolytic viruses.Methodology/Principal FindingsTaking the “Directed Evolution” approach, viral diversity was increased by pooling an array of serotypes, then passaging the pools under conditions that invite recombination between serotypes. These highly diverse viral pools were then placed under stringent directed selection to generate and identify highly potent agents. ColoAd1, a complex Ad3/Ad11p chimeric virus, was the initial oncolytic virus derived by this novel methodology. ColoAd1, the first described non-Ad5-based oncolytic Ad, is 2–3 logs more potent and selective than the parent serotypes or the most clinically advanced oncolytic Ad, ONYX-015, in vitro. ColoAd1's efficacy was further tested in vivo in a colon cancer liver metastasis xenograft model following intravenous injection and its ex vivo selectivity was demonstrated on surgically-derived human colorectal tumor tissues. Lastly, we demonstrated the ability to arm ColoAd1 with an exogenous gene establishing the potential to impact the treatment of cancer on multiple levels from a single agent.Conclusions/SignificanceUsing the “Directed Evolution” methodology, we have generated ColoAd1, a novel chimeric oncolytic virus. In vitro, this virus demonstrated a >2 log increase in both potency and selectivity when compared to ONYX-015 on colon cancer cells. These results were further supported by in vivo and ex vivo studies. Furthermore, these results have validated this methodology as a new general approach for deriving clinically-relevant, highly potent anti-cancer virotherapies.

Oncolytic viruses: From bench to bedside with a focus on safety

“…[43][44][45] Using 'directed evolution' or 'accelerated evolution' strategies, ColoAd1 and other crHAdVs have been generated which appear to be more potent than their parental HAdV-5 based vectors. 46,47 A total of 458 clinical trials employing HAdV-mediated gene therapy have been reported to date. ONYX-015, H101 (Oncorine) and other first-generation oncolytic crHAdVs have gone through several phase I/II trials without relevant signs of high grade toxicity but also without significant therapeutic effects, resulting in discontinuation of further trails.…”

Transduction of Liver Metastases After Intravenous Injection of Ad5/35 or Ad35 Vectors With and Without Factor X-Binding Protein Pretreatment

“…We therefore decided to use an immunodeficient mouse model with liver metastases derived from human colon cancer HT-29 cells. HT-29 cells secrete carcinoembryonic antigen (CEA), and serum CEA levels in mice directly correlate with the tumor burden, as we have shown in one study (Kuhn et al, 2008). As a model oncolytic adenovirus, we used Ad5= 35.IR.E1A=TRAIL (Sova et al, 2004).…”

“…Importantly, pretreatment of mice with X-bp greatly increased the therapeutic effect of Ad5=35.IR-E1A=TRAIL as reflected in CEA levels and tumor burden ( p < 0.001). Because, previously, an Ad5-based oncolytic vector (ONYX-015) did not exert a significant antitumor effect in the HT-29 liver metastasis model (Kuhn et al, 2008), we did not include an Ad5-based vector in this study.…”

In vitro analysis of cidofovir and genetically engineered TK expression as potential approaches for the intervention of ColoAd1-based treatment of cancer

“…1 In addition, they have the ability to circulate within the body, making the treatment of both primary and metastatic lesions possible. However, to date, oncolytic viruses have yet to reach their full potential as an effective new class of anticancer agents.…”

“…1 This virus has been shown to have superior potency over its parental viruses in vitro (on a panel of tumor cell lines), ex vivo (on patient tumor explants) and in vivo (in a liver metastasis colon cancer model). Although ColoAd1 has shown a high degree of selectivity and safety in all studies that have been carried out to date, these are artificial systems that may not fully mimic the conditions in a cancer patient.…”