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

Hypoxia-inducible factor-1 alpha (HIF-1 alpha) gene therapy holds great promise for the treatment of myocardial ischemia. Both preclinical and clinical evaluations of this therapy are underway and can benefit from a vector strategy that allows noninvasive assessment of HIF-1 alpha expression as an objective measure of gene delivery. We have developed a novel bidirectional plasmid vector (pcTnT-HIF-1 alpha-VP2-TSTA-fluc), which employs the cardiac troponin T (cTnT) promoter in conjunction with a two-step transcriptional amplification (TSTA) system to drive the linked expression of a recombinant HIF-1 alpha gene (HIF-1 alpha-VP2) and the firefly luciferase gene (fluc). The firefly luciferase (FLuc) activity serves as a surrogate for HIF-1 alpha-VP2 expression, and can be noninvasively assessed in mice using bioluminescence imaging after vector delivery. Transfection of cultured HL-1 cardiomyocytes with pcTnT-HIF-1 alpha-VP2-TSTA-fluc led to a strong correlation between FLuc and HIF-1 alpha-dependent vascular endothelial growth factor expression (r(2) = 0.88). Intramyocardial delivery of pcTnT-HIF-1 alpha-VP2-TSTA-fluc into infarcted mouse myocardium led to persistent HIF-1 alpha-VP2 expression for 4 weeks, even though it improved neither CD31 + microvessel density nor echocardiographically determined left ventricular systolic function. These results lend support to recent findings of suboptimal efficacy associated with plasmid-mediated HIF-1 alpha therapy. The imaging techniques developed herein should be useful for further optimizing HIF-1 alpha-VP2 therapy in preclinical models of myocardial ischemia.