616. Disc Gene Therapy: Development of a Novel Inducible System To Regulate Expression of the Therapeutic Transgene TIMP1

Abstract

Introduction: Gene therapy using the anti-catabolic factor Tissue Inhibitor of Metalloproteinase-1 (hTIMP1) has shown promising efficacy in treating disc degeneration. However, a major limitation of the current gene therapy technique is the use of a constitutive promoter to drive transgene expression that results in uncontrolled and excessive expression of therapeutic gene product which could result in undesirable side effects. To overcome this important limitation, we successfully developed a new gene therapy recombinant adeno-associated viral (rAAV)vector, rAAV-NFkB-hTIMP1, in which the therapeutic recombinant human TIMP1 gene is placed under the control of a promoter containing the NF-kB element. The rAAV-NFkB-hTIMP1 construct is designed to produce the therapeutic gene product TIMP1 only when the cells experience stress which activates the NF-kB pathway. Hence we expect using this strategy that hTIMP1 will be selectively expressed in cells under inflammatory conditions typically found in active degenerating discs and not under normal conditions, in which the therapeutic gene was not needed. In this study we tested our hypothesis that rabbit annulus fibrosus cells transfected with aserotype 2 of rAAV vector carrying a hTIMP1 gene will not express high level of hTIMP1 unless stimulated with the IL-1b.Methods: Cultured rabbit annulus fibrosus (rAF) cells were divided into six groups; “Control” (cell only); “rAAV-CMV-hTIMP1(cells transfected with AAV-CMV-hTIMP1 plasmid DNA)” and “rAAV-NFkB-hTIMP1(cells transfected with AAV-NFkB-hTIMP1 plasmid DNA)” treated with and without IL-1b (n=4 for each group). Production of hTIMP1 was determined by RT-PCR. To determine if MMP activity was inhibited by the produced TIMP1, MMP activity assay was measured by following cleavage of a fluorogenic substrate.Results: RT-PCR analysis demonstrated that the level of hTIMP1 transcription from cells and culture media transfected with rAAV-NFkB-hTIMP1 construct was greater than in the IL-1b stimulated condition compared to unstimulated control. The result shows that the level of MMP activity was decreased compared to baseline levels or cells exposed to IL-1.Discussion: The RT-PCR result showed cells transfected with AAV-NFkB-hTIMP1 plasmid DNA had significant increase in the hTIMP-1 mRNA expression after stimulation with IL-1b. These results demonstrate the novelty of this strategy in which the NF-kB element containing promoter ensures that the transgene hTIMP1 is expressed highly only under conditions of inflammation typically found in injured and degenerating discs which would act to block MMP-mediated matrix proteolytic destruction. Low levels of hTIMP1 were also observed under unstimulated conditions and the bioenergetic consequences of the cell are unclear.