Pharmacokinetics and Biodistribution of a pGT2-VEGF Plasmid DNA After Administration in Rats

Abstract

Intramyocardial administration of gene therapy vectors expressing angiogenic factors have been attempted as an alternative to conventional surgical methods for the management of myocardial ischemia. In this study, we have developed the pGT2-VEGF, a plasmid DNA vector expressing human VEGF165, for the management of ischemic cardiovascular disease and investigated in vivo pharmacokinetics and tissue distribution of pGT2-VEGF after intramyocardial and intravenous administration in rats. A high concentration of pGT2-VEGF was observed in the heart after intramyocardial injection of 300 microg, which is in line with the assumption that direct intramyocardial delivery enables extended localization at the administration site. Leakage of the pGT2-VEGF to the blood circulation was observed after intramyocardial injection, with an area under the curve (AUC) of 3.8 microg min/mL, as compared with 37.3 microg min/mL after intravenous injection of the same dose. The pGT2-VEGF concentration in blood peaked at 5 minutes after intramyocardial administration and declined rapidly to undetectable levels by 2 hours post-administration. In tissue distribution studies, pGT2-VEGF peaked at 5 minutes post-administration in various organs but was undetectable at 2 hours in all organs except heart, lung, and liver. Taken together, the results suggest that intramyocardial-delivered pGT2-VEGF was degraded rapidly in vivo and mainly persisted in target tissues, the heart. In addition, intramyocardial-administered pGT2-VEGF was expressed for longer periods than the persistence of the pGT2-VEGF plasmid DNA in a target tissue. Therefore, a direct myocardial injection of pGT2-VEGF might be useful for local therapeutic angiogenesis.

Indirect imaging of cardiac-specific transgene expression using a bidirectional two-step transcriptional amplification strategy

“…The in vivo assessment of cardiac specificity was limited by the use of HTV injection for highly efficient hepatic transfection, which would be otherwise difficult to achieve with intramyocardial administration alone because of the limited half-life of plasmid DNA in blood (<5 min) 31. Biodistribution studies that are typically performed for viral vector-mediated gene delivery are not applicable here because of inadequate uptake and expression of plasmids in most non-cardiac tissues 32. Therefore, the in vivo results presented here do not comprise a complete assessment of tissue specificity, but do support the notion that the bidirectional TSTA strategy can effectively minimize extra-cardiac expression.…”

Noninvasive Imaging of Hypoxia-Inducible Factor-1α Gene Therapy for Myocardial Ischemia

“…This was supported by the fact that we were not able to detect significantly more myocardial VEGF expression after pcTnT-HIF-1a-VP2-TSTA-fluc delivery using enzymelinked immunosorbent assay (data not shown), even though we were able to detect significant FLuc expression or activation of the HIF-1a/HRE pathway (via the RLuc reporter) using the more sensitive reporter enzyme assays or BLI. Furthermore, because of the limited half-life of plasmid DNA in blood ( < 5 min) (Lew et al, 1995), biodistribution studies that are typically done for viral vector-mediated gene delivery were not useful here for assessing the transcriptional targeting capability of our bidirectional TSTA vector because of inefficient plasmid transfection in most noncardiac tissues (e.g., liver, lungs, spleens, kidneys) after intramyocardial vector delivery (e.g., < 1% of myocardial transfection in our preliminary studies; data not shown) (Son et al, 2005). Therefore, to both improve the therapeutic efficacy of our vector and allow for a better assessment of transcriptional targeting, we will need to incorporate our vector design into a high-capacity adenoviral vector for more efficient gene delivery.…”

A Titratable Two-Step Transcriptional Amplification Strategy for Targeted Gene Therapy Based on Ligand-Induced Intramolecular Folding of a Mutant Human Estrogen Receptor

“…Furthermore, a viral vector will undoubtedly lead to more efficient myocardial transduction, thus making up for any loss of transgene expression due to the limited production of the GAL4-mER(LBD)-VP2 transactivator fusion protein secondary to cTnT’s known weak promoter activity. Second, the caveat of using a plasmid vector is that it does not lead to appreciable retention and expression in non-cardiac tissues (e.g., liver) following intramyocardial delivery despite fair amount of leakage from the myocardium [19]. The rapid clearance of plasmid in blood has been attributed to the working of plasma endonucleases, tissue surface enzymes, and non-parenchymal liver cells that act to scavenge and degrade plasmid DNA.…”