Epigenetic Regulation of the Kcc2/KCC2 Promoter for Gene Expression Enhancement in Pathologic Pain and Itch

Excitatory-inhibitory balance is vital for physiologic functioning of the central nervous system. For incoming sensory information, various forms of injury to neural structures can cause pain. Pain establishing itself in the central nervous system in terms of chronic, pathologic pain is associated with less effective action of the neurotransmitters GABA and glycine. These transmitters are critical for normal relay in the sensory gate of the spinal cord, the spinal cord dorsal horn. Here, sensory relay neurons are affected by elevated intra-neuronal chloride levels which in turn corrupts inhibitory neurotransmission by GABA and glycine. The cause for elevated intra-neuronal chloride is lack of gene expression of the Kcc2/KCC2 gene (mouse/human gene), caused by the neural injury. Because of relative absence of the Kcc2/KCC2 gene product, the neuronal chloride extruding transporter, KCC2, chloride ions are not extruded sufficiently out of these sensory relay neurons, thus increasing the excitability of this primary afferent neural circuit. In order to remedy this particular aspect of the etio-pathogenesis of chronic pathologic pain, we have focused on epigenetic regulation of the Kcc2/KCC2 promoter activity and conducted a molecular screening campaign with the goal of finding Kcc2/KCC2 gene expression-enhancing compounds. Out of 2 NCI chemical libraries of shelved cancer drugs (n=1057), we found 137 first-round hit compounds. These 137 winners were interrogated more in-depth with a yield of 4 top-winner compounds, of which we selected kinase inhibitor Kenpaullone. We demonstrated Kenpaullone to inhibit GSK3-beta as a neuro-cellular mechanism to potently and lastingly attenuate pain of nerve constriction, inflammation and bone cancer, as well as chronic itch of contact allergy, in preclinical mouse models. GSK3-beta inhibition by Kenpaullone facilitated nuclear transfer of delta-catenin, which bound to KAISO transcription factors and DNA binding sites in the Kcc2 promoter, switching Kcc2 gene repression to enhancement via this specific epigenetic mechanism.