Herpes Simplex Virus Type 1 Clinical Isolates Respond to UL29-Targeted siRNA Swarm Treatment Independent of Their Acyclovir Sensitivity

Abstract

Acyclovir is the drug of choice for the treatment of herpes simplex virus (HSV) infections. Acyclovir-resistant HSV strains may emerge, especially during long-term drug use, and subsequently cause difficult-to-treat exacerbations. Previously, we set up a novel treatment approach, based on enzymatically synthesized pools of siRNAs, or siRNA swarms. These swarms can cover kilobases-long target sequences, reducing the likelihood of resistance to treatment. Swarms targeting the UL29 essential gene of HSV-1 have demonstrated high efficacy against HSV-1 in vitro and in vivo. Here, we assessed the antiviral potential of a UL29 siRNA swarm against circulating strains of HSV-1, in comparison with acyclovir. All circulating strains were sensitive to both antivirals, with the half-maximal inhibitory concentrations (IC50) in the range of 350–1911 nM for acyclovir and 0.5–3 nM for the UL29 siRNA swarm. Additionally, we showed that an acyclovir-resistant HSV-1, devoid of thymidine kinase, is highly sensitive to UL29 siRNA treatment (IC50 1.0 nM; Imax 97%). Moreover, the detected minor variations in the RNAi target of the HSV strains had no effect on the potency or efficacy of UL29 siRNA swarm treatment. Our findings support the development of siRNA swarms for the treatment of HSV-1 infections, in order to circumvent any potential acyclovir resistance.

The In Vitro Replication, Spread, and Oncolytic Potential of Finnish Circulating Strains of Herpes Simplex Virus Type 1

“…ACV sensitivity was studied with a plaque reduction assay on Vero cells, as before [3,7]. The assay was conducted in a 96-well plate format with infections of 50 pfu/well and an acyclovir concentration ranging from 128 µg/mL to 0.03 µg/mL.…”

“…Based on their genotypes, HSV-1 isolates may be divided into three geographic clusters, the Eastern, Western, and Southern clades [2][3][4]. The clinical isolates vary from each other also by phenotype, such as by viral fitness and response to antivirals [3,[5][6][7]. In most cases, the observed phenotype cannot be predicted by genotype, as viral phenotype has not been yet connected to any genomic groups nor any pattern of geographic diversity [3,8].…”

Liposomal siRNA Formulations for the Treatment of Herpes Simplex Virus-1: In Vitro Characterization of Physicochemical Properties and Activity, and In Vivo Biodistribution and Toxicity Studies

“…siRNA therapeutics have been applied most notably in different types of cancer [19][20][21] and genetic disorders [22], and in viral infections [23]. Several studies demonstrate the therapeutic potential of siRNA for inhibiting HSV-1 and HSV-2 infection in vitro [23][24][25][26][27][28][29].…”

“…siRNA therapeutics have been applied most notably in different types of cancer [ 19 , 20 , 21 ] and genetic disorders [ 22 ], and in viral infections [ 23 ]. Several studies demonstrate the therapeutic potential of siRNA for inhibiting HSV-1 and HSV-2 infection in vitro [ 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. A therapeutic effect has been demonstrated in rodents following local intravaginal application of siRNAs complexed with a transfection agent [ 30 , 31 ], and by a topical administration of siRNA solution in a corneal infection model [ 32 ].…”

Antiviral CD19+CD27+ Memory B Cells Are Associated with Protection from Recurrent Asymptomatic Ocular Herpes Infection

“…Despite the availability of many intervention strategies, the global picture for ocular herpes continues to deteriorate (4). Current anti-viral drug therapies (e.g., Acyclovir and derivatives) do not eliminate the virus and reduce recurrent herpetic disease by only ~45% (5,6). The challenge in developing an effective herpes treatment or vaccine is to determine the immune correlates of protection (7)(8)(9)(10)(11)(12)(13).…”