Expression of Oncolytic Adenovirus-Encoded RNAi Molecules Is Most Effective in a pri-miRNA Precursor Format

Area of Science:

• Oncolytic virotherapy
• Molecular biology
• Gene therapy

Background:

• Oncolytic adenoviruses are emerging anti-cancer agents.
• Enhancing their efficacy involves incorporating RNA interference (RNAi) molecules.
• RNAi molecules can be expressed in various precursor formats, influencing their effectiveness.

Purpose of the Study:

• To determine the most effective precursor format for expressing RNAi molecules within oncolytic adenoviruses.
• To compare the expression levels and functional impact of different RNAi precursor formats.

Main Methods:

• Construction of three Δ24-type oncolytic adenoviruses expressing human microRNA-1 (miR-1) in short hairpin RNA (shRNA), precursor microRNA (pre-miRNA), and primary miRNA (pri-miRNA) formats.
• Assessment of virus replication, mature miR-1 expression, and target gene silencing in cancer cells.
• Validation of pri-miR-1 processing dependence on host cell miRNA machinery (Drosha knockout).

Main Results:

• Incorporation of RNAi cassettes had minimal impact on virus replication.
• The pri-miRNA format yielded approximately 100-fold higher mature miR-1 expression compared to shRNA and pre-miRNA formats.
• Stable mature miR-1 expression was observed upon long-term virus propagation.
• The pri-miR-1 expressing virus effectively silenced validated miR-1 targets (FOXP1, MET).
• A similar virus expressing miR-26b demonstrated silencing of its target (PTGS2).

Conclusions:

• The primary miRNA (pri-miRNA) format is superior for high-level expression of RNAi molecules in oncolytic adenoviruses.
• Adenovirus-encoded pri-miRNA processing relies on the host cell's miRNA machinery.
• This study establishes a versatile platform for developing oncolytic adenoviruses with enhanced RNAi delivery capabilities for cancer therapy.