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However, a unique class of peptides known as cell penetrating peptides (CPPs) has the ability to traverse this barrier and convey cargo molecules attached to it across the cell membrane [1]. CPPs are short peptides (generally less than 30 residues) with net positive charge and acting in a receptor- and energy-independent manner.
Amongst a variety of natural and chimeric CPPs, HIV-1 tat protein derived Tat peptide (Tat ) has received much attention mainly because of its high efficiency to deliver a 49-57 large variety of cargo molecules across the membrane.
Noninvasive imaging techniques like MRI possess the prospective to observe molecular-genetic and cellular processes. The combination of these exogenously
administered molecular imaging agents with CPPs may enhance their intracellular delivery, thus solving several queries at sub-cellular level.
Improved cellular uptake of the unnatural retro-inverso isomer of Tat, d-Tat57-49 (rrrqrrkkr), has been reported in comparison to l-Tat (RKKRRQRRR) [2]. 49-57 Considering the potential of Tat as a molecular transporter, we coupled l-Tat and d- 49-57 Tat with fluorescence imaging agent FITC as well as with MR agent Gd-DTPA, 57-49 thus obtaining l-Tat-Lys(FITC)-(Gd)DTPA (l-Tat CA) and d-Tat-ys(FITC)-(Gd)DTPA (d-Tat CA), respectively. Based on optical imaging and relaxation time measurements we compared cellular internalization and contrast enhancement
efficiencies of these two bimodal cell internalizing contrast agents.
