1097. Retroviral Delivery of the RheoSwitch® Therapeutic System for Precisely Regulated Expression of BMP-2 for Bone Regeneration

Gene therapy approaches to a variety of diseases will require the therapeutic gene to be expressed in a regulated fashion so that the precise amount of the gene product can be delivered in the appropriate tissues at the desired time and for the desired duration. This may be particularly important when the therapeutic gene is used for controlled regeneration of tissues. We have developed the RheoSwitch® Therapeutic System (RTS) that can be precisely controlled by an orally active synthetic small molecule ligand (Activator Drug) for regulated expression of therapeutic genes. The RTS consists of two component proteins that heterodimerize to create a functional inducible transcription factor complex. The ligand- binding component is the DEF domain of a mutant ecdysone receptor that is fused to a Gal4 DNA binding domain. The second component is the EF domain of a chimeric RXR that is fused to the VP16 activation domain. These proteins can be constitutively expressed under a ubiquitous or tissue-specific promoter, and, in the presence of a potent ligand, can induce in vivo gene expression from a responsive promoter. The RTS components have been assembled into single vector systems that are adapted for delivery by retroviral as well as other viral vector systems.The RTS has been tested for the expression of many therapeutic proteins including cytokines and growth factors. We now demonstrate the adaptation of the RTS in retroviral vectors and the potential for the repair of damaged skeletal tissue in a variety of degenerative diseases by controlled delivery of BMP2 from fibroblast cells that are transduced by retroviral vectors carrying the BMP-2 gene under the RTS. As safety is becoming paramount in the development of cell and gene therapies, having the ability to control the gene expression in-vivo adds a new level of control to product development. Moreover, regenerative processes such as osteogenesis often require differential expression of genes for varying times.This poster will present the preliminary data of the integration of BMP-2 and the RTS system, and discuss some of our future plans in the development of a regulated system for expression of growth factors in bone healing applications.