A Novel Imaging Approach for Single-Cell Real-Time Analysis of Oncolytic Virus Replication and Efficacy in Cancer Cells.

Oncolytic viruses (OVs) are novel cancer gene therapies that are moving toward the forefront of modern medicines. However, their full therapeutic potential is hindered by the lack of convenient and reliable strategies to visualize and quantify OV growth kinetics and therapeutic efficacy in live cells. In this study, we present an innovative imaging approach for single-cell real-time analysis of OV replication and efficacy in cancer cells. We selected SG33 as a prototypic new OV that derives from wild-type Myxoma virus (MYXV). Lausanne Toulouse 1 (T1) was used as control. We equipped SG33 and T1 genomes with the ANCHOR system and infected a panel of cell lines. The ANCHOR system is composed of a fusion protein (OR-GFP) that specifically binds to a short nonrepetitive DNA target sequence (ANCH) and spreads onto neighboring sequences by protein oligomerization. Its accumulation on the tagged viral DNA results in the creation of fluorescent foci. We found that (1) SG33 and T1-ANCHOR DNA can be readily detected and quantified by live imaging, (2) both OVs generate perinuclear replication foci after infection clustering into horse-shoe shape replication centers, and (3) SG33 replicates to higher levels as compared with T1. Lastly, as a translational proof of concept, we benchmarked SG33 replication and oncolytic efficacy in primary cancer cells derived from pancreatic adenocarcinoma (PDAC) both at the population and at the single-cell levels. , SG33 significantly replicates in experimental tumors to inhibit tumor growth. Collectively, we provide herein for the first time a novel strategy to quantify each step of OV infection in live cells and in real time by tracking viral DNA and provide first evidence of theranostic strategies for PDAC patients. Thus, this approach has the potential to rationalize the use of OVs for the benefit of patients with incurable diseases.