Inhibition of coxsackievirus B3 in cell cultures and in mice by peptide-conjugated morpholino oligomers targeting the internal ribosome entry site.

Coxsackievirus B3 (CVB3) is a primary cause of viral myocarditis, yet no effective therapeutic against CVB3 is available. Nucleic acid-based interventional strategies against various viruses, including CVB3, have shown promise experimentally, but limited stability and inefficient delivery in vivo remain as obstacles to their potential as therapeutics. We employed phosphorodiamidate morpholino oligomers (PMO) conjugated to a cell-penetrating arginine-rich peptide (to form 'PPMO') to address these issues. Eight CVB3-specific PPMO were evaluated in HeLa cells and HL-1 cardiomyocytes in culture, and in a murine infection model. One of the PPMO (PPMO-6), designed to target sequence in the 3' portion of the CVB-3 internal ribosomal entry site, was found to be especially potent against CVB3. Treatment of cells with PPMO-6 prior to CVB3 infection produced an approximately 3 log10 decrease in viral titer, and largely protected cells from viral-induced cytopathic effect. A similar antiviral effect was observed when PPMO-6 treatment began shortly after the virus infection period. A/J mice receiving intravenous administration of PPMO-6 once prior to and once after CVB3 infection showed approximately 2 log10 less viral titer in myocardium at seven days post-infection, and a significantly decreased level of cardiac tissue damage, compared to controls. Thus, PPMO-6 provided potent inhibition of CVB3 amplification both in cell culture and in vivo, and appears worthy of further evaluation as a candidate for clinical development.