Nikhil O. Dhoot

Grafting of Encapsulated BDNF-Producing Fibroblasts into the Injured Spinal Cord Without Immune Suppression in Adult Rats

Grafting of genetically modified cells that express therapeutic products is a promising strategy in spinal cord repair. We have previously grafted BDNF-producing fibroblasts (FB/BDNF) into injured spinal cord of adult rats, but survival of these cells requires a strict protocol of immune suppression with cyclosporin A (CsA). To develop a transplantation strategy without the detrimental effects of CsA, we studied the properties of FB/BDNF that were encapsulated in alginate-poly-L-ornithine, which possesses a semipermeable membrane that allows production and diffusion of a therapeutic product while protecting the cells from the host immune system. Our results show that encapsulated FB/BDNF, placed in culture, can survive, secrete bioactive BDNF and continue to grow for at least one month. Furthermore, encapsulated cells that have been stored in liquid nitrogen retain the ability to grow and express the transgene. Encapsulated FB/BDNF survive for at least one month after grafting into an adult rat cervical spinal cord injury site in the absence of immune suppression. Transgene expression decreased within two weeks after grafting but resumed when the cells were harvested and re-cultured, suggesting that soluble factors originating from the host immune response may contribute to the downregulation. In the presence of capsules that contained FB/BDNF, but not cell-free control capsules, there were many axons and dendrites at the grafting site. We conclude that alginate encapsulation of genetically modified cells may be an effective strategy for delivery of therapeutic products to the injured spinal cord and may provide a permissive environment for host axon growth in the absence of immune suppression.

Surface modification of PLGA microspheres for targeting

RGD peptide was conjugated to hollow microspheres to develop PLGA ultrasound contrast agents that enhance ultrasound imaging. The microcapsules were coated with an RGD peptide that targets integrins specific to angiogenesis, /spl alpha/v/spl beta/3 and /spl alpha/v/spl beta/5. The microcapsules were then bound to rat neuroblastoma cells in vitro within 6 hours. The RGD peptide modified microcapsules makes them ideal candidates for targeted therapeutic imaging and drug delivery vehicles.

Modification of surfactant contrast agent for targeted ultrasound imaging

Fibronectin peptide fragments were conjugated to a surfactant stabilized ultrasound contrast agent to develop a targeted contrast agent that enhances ultrasound imaging. The agent was modified with PEG and conjugated with a generic GRGDS peptide sequences that targets integrins specific to angiogenesis. The microbubbles bound to human breast cancer cells in vitro within 3 minutes under flow conditions. The GRGDS peptide modified-microbubbles show promise as candidates for targeted therapeutic imaging and eventually drug delivery vehicles.