Silencing Herpes Simplex Virus Type 1 Capsid Protein Encoding Genes by siRNA: A Promising Antiviral Therapeutic Approach

<div><p>Herpes simplex virus type 1 (HSV-1), a member of the <i>herpesviridae</i>, causes a variety of human viral diseases globally. Although a series of antiviral drugs are available for the treatment of infection and suppression of dissemination, HSV-1 remains highly prevalent worldwide. Therefore, the development of novel antiviral agents with different mechanisms of action is a matter of extreme urgency. During the proliferation of HSV-1, capsid assembly is essential for viral growth, and it is highly conserved in all HSV-1 strains. In this study, small interfering RNAs (siRNAs) against the HSV-1 capsid protein were screened to explore the influence of silencing capsid expression on the replication of HSV-1. We designed and chemically synthesized siRNAs for the capsid gene and assessed their inhibitory effects on the expression of target mRNA and the total intracellular viral genome loads by quantitative real-time PCR, as well as on the replication of HSV-1 via plaque reduction assays and electron microscopy. Our results showed that siRNA was an effective approach to inhibit the expression of capsid protein encoding genes including <i>UL18</i>, <i>UL19</i>, <i>UL26</i>, <i>UL26.5</i>, <i>UL35</i> and <i>UL38 in vitro</i>. Interference of capsid proteins VP23 (<i>UL18</i>) and VP5 (<i>UL19</i>) individually or jointly greatly affected the replication of clinically isolated acyclovir-resistant HSV-1 as well as HSV-1/F and HSV-2/333. Plaque numbers and intracellular virions were significantly reduced by simultaneous knockdown of <i>UL18</i> and <i>UL19</i>. The total intracellular viral genome loads were also significantly decreased in the <i>UL18</i> and <i>UL19</i> knockdown groups compared with the viral control. In conclusion, interfering with <i>UL18</i> and <i>UL19</i> gene expression could inhibit HSV-1 replication efficiently in vitro. Our research offers new targets for an RNA interference-based therapeutic strategy against HSV-1.</p>