Modification of Short Non‐Permeable Peptides to Increase Cellular Uptake and Cytostatic Activity of Their Conjugates

Cell‐penetrating peptides (CPPs) are well‐known delivery vectors, oligoarginines are an important class of CPPs, which was modified to increase the cellular uptake and change the internalization mechanism. A minimum number of four Arg residues was used and tetrarginine sequence was modified by 4‐((4‐(dimethylamino)phenyl)azo)benzoic acid (Dabcyl) and Trp(s). The Dabcyl group was attached to the N‐terminus, while peptides were different in the number and position of Trp in their sequence. Their internalization was studied on breast cancer cells (MCF‐7 and MDA‐MB‐231), and Chinese hamster ovary cells (CHO) using different fluorescence techniques. Our most active CPPs, Dabcyl‐RRWRRK and Dabcyl‐WRRRRK were conjugated to antitumor drugs, resulting in considerable cytostatic activity, especially on MDA‐MB‐231 cell lines. These newly developed cell‐penetrating tetrarginine derivatives may enter cells very efficiently, mainly by direct translocation and caveolae‐mediated endocytosis, thus they may be promising delivery vehicle. Tetragrinines are considered inefficient CPPs, but with our modifications, we rendered them effective. In this work, we describe the synthesis and investigation of a variety of Dabcyl containing cell penetrating peptides. A variety of Dabcyl‐containing analogues were prepared, to improve the cellular uptake of tetrarginines. We studied the number and location of Trp within the sequence, and we noticed that the presence of Trp in our sequences can enhance the uptake of the peptides, especially if it is placed at the N‐terminus, adjacent to Dabcyl.