The Pancreatic Ductal Adenocarcinoma (PDAC) is one of the most aggressive and dangerous cancerous diseases, leading to a high rate of mortality. Therefore, the development of new, more efficient treatment approaches is necessary to cure this illness. Peptide-based drug targeting provides a new tool for this purpose. Previously, a hexapeptide Cys-Lys-Ala-Ala-Lys-Asn (CKAAKN) was applied efficiently as the homing device for drug-loaded nanostructures in PDAC cells. In this research, Cys was replaced by Ser in the sequence and this new SKAAKN targeting moiety was used in conjugates containing daunomycin (Dau). Five different structures were developed and tested. The results indicated that linear versions with one Dau were not effective on PANC-1 cells in vitro; however, branched conjugates with two Dau molecules showed significant antitumor activity. Differences in the antitumor effect of the conjugates could be explained with the different cellular uptake and lysosomal degradation. The most efficient conjugate was Dau=Aoa-GFLG-K(Dau=Aoa)SKAAKN-OH (conjugate 4) that also showed significant tumor growth inhibition on s.c. implanted PANC-1 tumor-bearing mice with negligible side effects. Our novel results suggest that peptide-based drug delivery systems could be a promising tool for the treatment of pancreatic cancers.

Cell-penetrating peptides (CPPs) are promising delivery vehicles. These short peptides can transport wide range of cargos into cells, although their usage has often limitations. One of them is the endosomatic internalisation and thus the vesicular entrapment. Modifications which increases the direct delivery into the cytosol is highly researched area. Among the oligoarginines the longer ones (n > 6) show efficient internalisation and they are well-known members of CPPs. Herein, we describe the modification of tetra- and hexaarginine with (4–((4–(dimethylamino)phenyl)azo)benzoyl) (Dabcyl) group. This chromophore, which is often used in FRET system increased the internalisation of both peptides, and its effect was more outstanding in case of hexaarginine. The modified hexaarginine may enter into cells more effectively than octaarginine, and showed diffuse distribution besides vesicular transport already at low concentration. The attachment of Dabcyl group not only increases the cellular uptake of the cell-penetrating peptides but it may affect the mechanism of their internalisation. Their conjugates with antitumor drugs were studied on different cells and showed antitumor activity.

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Calpains are intracellular cysteine proteases with several important physiological functions. Calpain inhibitors may be promising tools in the analysis of the function of the enzyme in diseases caused by overexpression/activation. Here, we report on the synthesis, solution conformation, and characterization of novel group of azapeptides whose sequences originate from an efficient m-calpain substrate, TPLKSPPPSPR, described by us earlier and possess varying levels of calpain inhibition. The Lys residue at P1 position was replaced with azaglycine (NH2 -NH-COOH) and further changes were made as follows: the N-terminal or/and C-terminal were truncated, amino acids were also changed at P3, P2, P'1, or P'2 positions. Our results indicate that the identity of amino acid moieties between P4 and P'5 positions is essential for the inhibitory activity. Only changes at position P3 (Pro) are tolerated. Azapeptide analogs, described in this communication could be considered as useful set of compounds for elucidation of the enzyme interaction at P and P' sites.