Targeted Drug Delivery – RNA-mediated treatment of HSV-1 infections

Herpes simplex virus infections are among the most common skin diseases. More than 90 percent of the world’s population is infected with Type 1 Herpes simplex (HSV-1). Aside from the characteristic skin lesions, HS viruses can also cause serious conditions involving other organs (ocular herpes), as well as the central nervous system (herpes encephalitis, herpes meningitis), which may prove fatal. Until now, there is still no effective treatment for herpes infections available. HSV infections have been exclusively treated with antivirals so far, mainly nucleoside analogues. These are merely able to alleviate the symptoms and to shorten the duration of the infection but cannot prevent reactivation of the virus. One aim is therefore to develop an alternative therapy approach for the treatment of HSV-1 infection.

RNA-based drugs represent a possible alternative to the antiviral drugs used to date. The use of RNA interference (RNAi) enables the targeted knockdown of individual genes, for example, those involved in the proliferation of HSV-1. For this purpose, small ribonucleic acid (RNA) molecules (siRNA or miRNA) are introduced into the cells, allowing the targeted inhibition of the key proteins decisive for viral reactivation, proliferation or replication, thereby achieving long-term inhibition of the outbreak of a latent herpes infection.

One of the main problems in the application of the RNAi method is the targeted transport of the RNA molecules into the cells and the form of administration. RNA is a naturally unstable molecule, which is rapidly degraded by the body’s enzymes. Furthermore, the negative charge of RNA molecules results in an extremely limited membrane permeability. In order to overcome these problems and enable the use of RNA molecules as active agents in herpes treatment, we, in cooperation with the Hebrew University of Jerusalem, are developing a formulation of specific RNAs and a biodegradable polymer with nanometer-scale dimensions – also referred to as RNA nano-carrier system. Such a formulation can protect the non-membrane permeable, unstable RNA molecules against degradation from the immune system and enable their absorption through the skin. This targeted drug delivery is to be achieved by coupling the nanoparticles to viral envelope protein fragments or specific antibody fragments, which are targeted to a specific epitope of neural cells. Thus, the nanoparticles are specifically targeted to neural cells, which are potentially infected with HSV-1. Whereas, the coupling of viral envelope protein fragments to nanoparticles enables targeted delivery for all cell types.

Complex, cell-based test systems have been developed at the Fraunhofer IGB for many years. This expertise will be employed to prove the effectiveness and compatibility of the oligonucleotide-based drug and its formulation. The Activity-Selectivity (AS) assay allows the effectiveness and simultaneously the compatibility of the RNA nano-carrier formulation to be examined [1]. Accompanying examinations of the immunomodulatory effects of the carrier are performed with the cell-based pyrogen assay developed and patented at the IGB [2]. Cell or membrane permeability, as well as continuing efficacy studies of the nano-carriers loaded with specific miRNA are carried out in an established co-culture system. The equally patented in-vitro HSV-1 infection model can subsequently be used to examine the skin permeability, targeted transport and specific inhibition of viral reactivation by the RNA nano-carriers in a complex test system [3, 4].

The use of RNAi technology is intended to achieve a targeted preferably long-term prevention of HSV-1 outbreaks and thereby significantly reduce the suffering of many affected patients. It is likely that this new technology can also be adapted for other virus infections and therefore present great potential in antiviral therapy.

[1] Burger-Kentischer, A.; Finkelmeier, D.; Keller, P.; Bauer, J.; Eickhoff, H., Kleymann, G. et al. (2011) A screening assay based on host-pathogen interaction models identifies a set of novel antifungal benzimidazole derivatives. Antimicrob Agents Chemother. 55(10): 4789-801

[2] Zellbasiertes Testsystem zur Identifizierung und Differenzierung von Keimspektren (2009) DE 10 2006 031 483

[3] In vitro-Testsystem für virale Infektionen (2012) DE 10 2010 023 156

[4] Hogk, I.; Rupp, S.; Burger-Kentischer, A. (2013) 3D-Tissue model for herpes simplex virus-1 infections. Methods in Molecular Biology, in press.

We would like to thank the Fraunhofer-Gesellschaft for funding the project “Novel Drug/Gene Delivery Systems for Herpes Simplex Virus (HSV) Therapy”, within the ICON program.

• Hebrew University of Jerusalem, Institute for Drug Research (IDR), Jerusalem, Israel