Methods: We designed four PNAs that target domains I, J (base and head of domain J structure), and K of an internal ribosomal entry site (IRES) region within the 5’ untranslated region of HPeV3. The IRES region is needed for the cap-independent translation. The PNAs were conjugated to cell-penetrating peptide (RXR)4XB (R = L-arginine, X = 6-aminohexanoic acid, B = β-alanine). LLC-MK2 cells were treated with 0.1-10µM of each PNA or water-containing growth medium for 4h. The cells were then infected with HPeV3 at the multiplicity of infection (MOI) of 10 for 1h. The infected cells were incubated for 7 days at 37ºC in 5% CO2. Extracellular levels of HPeV3 RNA were measured by real-time PCR on days 0 and 7.
Results: Without any treatment, an extracellular level of HPeV3 RNA increased to 8.2 x 106 copies/µL on day 7. When the cells were treated with 10µM of PNA targeting the domain I of IRES, an extracellular level of HPeV3 RNA was suppressed to 4.7 x 104 copies/µL (-99%) on day 7. Using the same PNA with lower concentrations, 1µM and 0.1µM of the PNA suppressed 24% and 0% of extracellular levels of HPeV3 RNA, respectively, which demonstrated the effect is dose-dependent. In contrast, 10µM of PNAs targeting domain J (base), J (head), and K suppressed 94%, 92%, and 20% of extracellular levels of HPeV3 RNA, respectively, compared to control.
Conclusion: The PNA-(RXR)4XB targeting the domain I of IRES suppressed extracellular levels of HPeV3 RNA in an in vitro model in a dose-dependent manner. Thus, PNA treatment may be a therapeutic candidate for HPeV3 infected patients. This novel therapy could target other HPeV genotypes given that the target sequence used in this study is identical to those of other clinically significant HPeVs.
K. Watanabe, None
A. Saitoh, None