Insulinlike growth factor-I gene therapy applications for cartilage repair

Cartilage function after resurfacing with cell-based transplantation proced ures or during the early stages of arthritic disease may be bolstered by th e addition of growth factor genes to the transplanted tissue. Insulinlike g rowth factor-I maintains chondrocyte metabolism in normal cartilage homeost asis and has been shown to improve cartilage healing in vivo. Given the rel atively short half-life of insulinlike growth factor-I in biologic systems, however, maintenance of effective concentrations of this peptide has neces sitated either very high initial doses or repeated treatment. Delivery of t he insulinlike growth factor-I gene, using a deleted adenovirus vector, spe cifically targeting graftable articular chondrocytes, bone marrow-derived c hondroprogenitor cells, or synovial lining cells, may provide more durable insulinlike growth factor-I fluxes to articular tissues. Cultured equine ar ticular chondrocytes, mesenchymal stem cells, synovial explants, and synovi al intimal cells were readily transfected with an E1-deleted adenoviral vec tor containing equine insulinlike growth factor-I coding sequence. Optimal viral concentrations for effective transduction were 100 multiplicities of infection in synoviocytes, 500 multiplicities of infection in chondrocytes, and 1000 multiplicities of infection in mesenchymal stem cells. Production of insulinlike growth factor-I ligand varied from 65 ng/mL to 246 ng/mL in medium from chondrocytes and synovial explants, respectively. For chondroc ytes, these concentrations were sufficient to produce significant stimulati on of cartilage matrix gene expression and subsequent proteoglycan producti on. Moreover, cells in infected cultures maintained a chondrocytic phenotyp e and continued to express elevated insulinlike growth factor-I levels duri ng 28 days of monolayer culture. Minimal synthetic activity, other than ins ulinlike growth factor-I ligand synthesis, was evident in synovial cultures . These experiments suggest several avenues for insulinlike growth factor-I supplementation of articular cartilage, including preimplantation adenovir al-insulinlike growth factor gene transfer to chondrocytes or chondroprogen itor cells, and direct injection of adenoviral-insulinlike growth factor to transfect the synovial structures in situ.