A Pharmacokinetic Analysis of Molecular Cardiac Surgery With Recirculation Mediated Delivery of βARKct Gene Therapy: Developing a Quantitative Definition of the Therapeutic Window

Background: Two major problems for translating gene therapy for heart failure therapy are: safe and efficient delivery and the inability to establish a relationship between vector exposure and in vivo effects. We present a pharmacokinetics (PK) analysis of molecular cardiac surgery with recirculating delivery (MCARD) of scAAV6-beta ARKct. MCARD's stable cardiac specific delivery profile was exploited to determine vector exposure, half-life, and systemic clearance. Methods and Results: Five naive sheep underwent MCARD with 10(14) genome copies of scAAV6-beta ARKct. Blood samples were collected over the recirculation interval time of 20 minutes and evaluated with quantitative polymerase chain reaction (qPCR). C(t) curves were generated and expressed on a log scale. The exposure, half-life, and clearance curves were generated for analysis. qPCR and Western blots were used to determine biodistribution. Finally, all in vivo transduction data was plotted against MCARD's PK to determine if a relationship existed. Vector concentrations at each time point were (cardiac and systemic, respectively): 5 minutes: 9.16 +/- 0.15 and 3.21 +/- 0.38; 10 minutes: 8.81 +/- 0.19 and 3.62 +/- 0.37; 15 minutes: 8.75 +/- 0.12 and 3.69 +/- 0.31; and 20 minutes: 8.66 +/- 0.22 and 3.95 +/- 0.26; P < .00001. The half life of the vector was 2.66 +/- 0.24 minutes. PK model data revealed that only 0.61 +/- 0.43% of the original dose remained in the blood after delivery, and complete clearance from the system was achieved at 1 week. A PK transfer function revealed a positive correlation between exposure and in vivo transduction. Robust beta ARKct expression was found in all cardiac regions with none in the liver. Conclusion: MCARD may offer a viable method to establish a relationship between vector exposure and in vivo transduction. Using this methodology, it may be possible to address a critical need for establishing an effective therapeutic window. (J Cardiac Fail 2011;17:691-699)