# Improved Safety of New MicroRNA-Regulated Oncolytic Coxsackievirus B3 Observed After Intravenous Administration in Colorectal-Tumor-Bearing Mice

## TL;DR

Scientists improved the safety of a virus used to treat colorectal cancer in mice by adding microRNA targets to prevent it from infecting healthy organs.

## Contribution

New microRNA-regulated oncolytic coxsackievirus B3 variants with enhanced safety after intravenous administration in mice.

## Key findings

- PD-H caused multi-organ damage when administered intravenously, but microRNA-regulated variants PD-622TS and PD-145TS reduced organ infection and tissue damage.
- The modified viruses showed comparable cytotoxicity in cancer cells but failed to induce therapeutic effects in peritoneal carcinomatosis.
- MicroRNA-regulated PD-H variants demonstrate improved safety profiles but limited therapeutic efficacy after intravenous injection.

## Abstract

Oncolytic coxsackievirus B3 (oCVB3) strain PD-H has shown potent oncolytic efficacy and a remarkable safety profile in the treatment of colorectal cancer in vivo after intratumoral (i.t.) injection. In this study, we investigated the safety and efficiency of PD-H following intravenous (i.v.) virus administration. When injected i.v. into Balb/C mice bearing subcutaneous Colon-26 tumors, PD-H led to slightly reduced tumor progression and a significant increase in animal survival, but it also caused multi-organ infection and tissue damage. To improve the safety profile of PD-H, we inserted microRNA target sites (miR-TS) of the heart-specific miR-1, pancreas-specific miR-375, liver-specific miR-122, and brain-specific miR-124 or the tumor-suppressor miR-145 into the genome of PD-H and generated the viruses PD-622TS and PD-145TS. Both viruses replicated similarly and induced cytotoxicity comparable to that of PD-H in the colorectal carcinoma cell lines Colon-26 and CT-26Luc. Their replication was inhibited in HEK293T cells transiently transfected with the cognate microRNAs. In vivo, i.v. administration of PD-145TS and PD-622TS to healthy Balb/C mouse resulted in significantly lower viral titers in the organs of mice and led to significantly less-intense pathological alterations compared to PD-H. PD-622TS injected i.v. into Balb/C mice with CT-26Luc-induced peritoneal carcinomatosis did not induce off-target alterations in normal organs, but it failed to induce a therapeutic effect. These data indicate that PD-H or microRNA-regulated PD derivatives exhibit only limited therapeutic efficacy following i.v. injection in colorectal tumor-bearing mice. However, the newly engineered microRNA-regulated PD-H variants demonstrate improved safety profiles.