Efficient in vivo catheter-based pericardial gene transfer mediated by adenoviral vectors

Adenoviral vectors are promising agents for a number of in vivo gene therap y applications including diseases of the heart and coronary vessels. Effici ent intravascular gene transfer to specific sites has been achieved in occl uded vessels, but otherwise is hampered by the effect of blood flow on loca lized vector uptake in the vessel wall. An alternative delivery approach to coronary arteries is the expression of diffusible gene products into the p ericardial space surrounding the heart and coronary arteries. However, in v ivo pericardial access is comparatively difficult and has been limited to s urgical approaches. We hypothesized that efficient adenovirus-mediated gene expression in pericardial lining mesothelium could be achieved by transmyo cardial vector delivery to the pericardium. To evaluate this concept, a hol low, helical-tipped penetrating catheter was used to deliver vector-contain ing fluid directly into the intrapericardial space. The catheter was introd uced percutaneously in anesthetized mongrel dogs, advanced into the right v entricle, and the tip passed through the apical right ventricular myocardiu m under direct radiographic visualization until the open end of the cathete r tip resided in the intrapericardial space. Adenoviral vectors expressing either nuclear-localizing beta-galactosidase, cytoplasmic luciferase, or se creted human alpha 1AT reporters (Av1nBg, Av1Lu, or Av1Aa, respectively) we re instilled through the catheter into the intrapericardial space. Three da ys later the animals were sacrificed and reporter gene expression was evalu ated in pericardium, epicardium, and multiple other tissues. In animals rec eiving AvlnBg, beta-galactosidase activity was evident in most of the peric ardial lining endothelium, up to 100% in many areas. In animals receiving A v1Lu, luciferase reporter activity was abundant in pericardial tissues, but near-background levels were observed in other organs. In animals receiving Av1Aa, human alpha 1AT was abundant (16-29 mg/ml) in pericardial fluid, bu t was undetectable in serum. All animals tolerated the procedure well with no electrocardiographic changes and no clinical sequelae. These observation s demonstrate highly efficient adenovirus vector delivery and gene transfer and expression in the pericardium and support the feasibility of localized gene therapy via catheter-based pericardial approaches. We suggest that th e pericardial sac may serve as a sustained-release protein delivery system for the generation of desired gene products or their metabolites for diffus ion into the epicardial region.