Restenosis, currently estimated to occur in 30-50% of dilated lesions, continues to be a major limitation to the success of current interventional cardiovascular procedures. Presently, no established therapy prevents or ameliorates this complication. We propose an alternate method for reducing the rate of restenosis that utilizes localized delivery of inhibitors of smooth muscle cell (SMC) growth to injured arteries. SMCs were targeted because they are recognized as the major proliferative component of the stenotic lesion. The work in this thesis was specifically aimed at creating a biodegradable implantable microparticle delivery system, which when loaded with inhibitors of SMC growth, could be used to reduce the lesion. The effect of controlled delivery of two novel therapeutic compounds from this microparticle system on SMC growth was included in this investigation.
A method was developed to fabricate poly(DL-lactic-co-glycolic acid)/poly(ethylene glycol) (PLGA/PEG) blend microparticles that involves a double-emulsion-solvent-extraction technique to investigate the effect of polymer blend ratio on release kinetics. Two model drugs (FITC-IgG and FITC-dextran) were entrapped using this technique with high efficiency. In vitro release studies showed that the initial burst effect was dependent on the PLGA/PEG blend ratio. Moreover, the release rate increased in direct relation to PEG content. A linear release profile was obtained for microparticles loaded with FITC-IgG for initial PEG weight fractions up to 5 wt%, and a biphasic release profile was obtained for FITC-dextran loaded microparticles with rates dependent on the PEG content. These results demonstrate the feasibility of modulating the release profile of entrapped drug compounds from biodegradable microparticles by adjusting the PLGA/PEG blend ratio.
Tenascin, a large extracellular matrix glycoprotein, is thought to play an important role in SMC growth. Hence, we proceeded to investigate the inhibition of SMC proliferation and migration in vitro by an antisense (AS) oligodeoxynucleotide (ODN) targeted to the tenascin mRNA and released from PLGA/PEG blend microparticles. Release of AS-ODN was characterized by a small initial burst effect followed by a period of controlled release. SMC proliferation studies exhibited dose dependent growth inhibition with AS-ODN loaded microparticles. Microparticles loaded with scrambled (SC) ODN showed less growth inhibition than AS-ODN. Moreover, only the AS-ODN loaded microparticles inhibited migration. These results demonstrate the feasibility of entrapping an AS-ODN to rat tenascin into PLGA/PEG microparticles for controlled delivery to inhibit SMC proliferation and migration.
Basic fibroblast growth factor (bFGF) is a potent mitogen for SMCs and is believed to play a key role in neointimal formation. Consequently, we fabricated PLGA/PEG blend microparticles loaded with an antibody (Ab) against bFGF, and determined the effect of the Ab-bFGF released on smooth muscle cell proliferation in vitro. This work demonstrated the feasibility of entrapping an Ab-bFGF into PLGA/PEG microparticles for controlled delivery to inhibit bFGF stimulated SMC proliferation.
Lastly, preliminary in vivo studies demonstrated that PLGA/PEG microparticles can be implanted and immobilized adventitially in the rat carotid artery. (Abstract shortened by UMI.)