1. ¹Gene Regulations, Sangamo BioSciences, Richmond, CA
2. ²Department of Molecular Genetics and Biochemistry, University of Pittsburgh, School of Medicine, Pittsburgh, PA

Abstract

Neuropathic pain is a complex disorder resulting from injury to the nerve, spinal cord or brain. Current therapies for neuropathic pain using small-molecule drugs are limited by a range of drug-related side effects, primarily due to their lack of specificity in targeting the receptor/channel of choice. Gene therapy approaches to the treatment of neuropathic pain address this problem in two ways. Firstly, the difficulty in selectively targeting key biologically validated pain receptors at the protein level is circumvented by treatments that can derive specificity at the DNA level and drive the regulation of the target gene. Secondly, the effector molecule can be coupled to a delivery vector that specifically targets the organ of interest |[ndash]| in this case the dorsal root ganglia (DRG) |[ndash]| thus creating a more |[ldquo]|local|[rdquo]| treatment.

We have developed zinc-finger protein transcription factors (ZFP TFs) for the repression of target gene expression. Such ZFP TFs hold therapeutic promise as they have been shown to be highly efficacious and yet function with singular specificity within the mammalian genome. We have chosen to focus our efforts on the development of ZFP TF repressors against two well-validated targets: Tyrosine kinase A receptor or high-affinity NGF receptor (TrkA), and the sodium channel Nav1.8 (or PN3, SCN10A). Here we report that we have successfully obtained TrkA-specific ZFP TFs capable of potent target gene repression in cell line models in vitro. Consequently, we have initiated experiments aimed at evaluating the efficiency and efficacy of viral delivery into the DRG neurons using non-replicating herpes simplex virus (HSV) vectors. HSV vectors are naturally neurotropic and have been demonstrated to transduce the DRG in vivo with high efficiency following a single subcutaneous injection. We are currently evaluating our ZFP TF reagents when delivered by HSV vectors in both primary cell DRG cultures and subsequently in animal models of neuropathic pain. Our preliminary data has indicated that i) DRG neurons could be transduced to high efficiency by viral HSV vectors; ii) HSV vectors drive good expression of the gene specific ZFP TFs and; (iii) HSV driven ZFP TF expression results in target gene repression in DRG neurons. These data support the pre-clinical evaluation of ZFP TF in additional animal models of neuropathic pain.