The kinetics and tissue distribution of protein transduction in mice

Protein transduction domains (PTDs) offer an exciting therapeutic opportunity for the treatment of many diseases. An 11-amino acid fragment of human immunodeficiency type 1 (HIV-1) TAT-protein can transduce large, biologically active proteins into mammalian cells; recent evidence has shown an in vivo PTD for the 116 kDa β-galactosidase protein. However, there is little information on the in vivo distribution of the TAT fusion protein to define the viability of PTDs for human studies. In this study we examined the tissue kinetics and tissue distribution of the PTD-transduced TAT fusion protein in mice. Low (100 μg) or high (500 μg) doses of TAT-β-galactosidase fusion protein were administrated to mice through four routes (portal vein, i.v., i.p., and oral). Tissues were harvested 15 min, 1 h, 6 h, 10 h, and 24 h after treatment. Distribution of β-galactosidase in various tissues was analysed by in situ staining, enzymatic activity assay, and Western blot analysis. β-Galactosidase enzyme activity was observed in all tissues (liver, kidney, spleen, lung, bowel, and brain). β-Galactosidase activity peaked at 15 min in most tissues after portal vein, i.v., and i.p. administration and at 1 h after oral dosing in all tissues. β-Galactosidase activity in the liver at 15 min after portal vein injection (67 milliunits [mU]/mg) was higher than after i.v. (9.8 mU/mg), i.p. (4.4 mU/mg), and oral (0.3 mU/mg) dosing. In situ staining and Western blot results correlated closely with β-galactosidase enzyme activity assay. The median initial half-life for activity was 2.2 h, ranging from 1.2 h to 3.4 h (coefficient of variation = 28.9%). The bioavailability of β-galactosidase activity after an orally administered PTD was 24%. This study details the kinetics and tissue distribution of delivering of a model TAT fusion protein into the mouse via PTD. These data allow rational selection of delivery route and schedules for therapeutic PTD and will aid the use of TAT fusion protein transduction in the development of protein therapies.