Many biologically active compounds, including macromolecules that are used as various kinds of drugs, must be delivered to the interior of cell or organelles such as mitochondria or nuclei to achieve a therapeutic effect. However, very often, lipophilic cell membrane is impermeable for these molecules. A new method in the transport of macromolecules through the cell membrane is the one based on utilizing cell-penetrating peptides (CPPs). Invented 25 years ago, CPPs are currently the subject of intensive research in many laboratories all over the world. CPPs are short compounds comprising up to 30 amino acid residues, which penetrate the cell membrane but do not cause cell damage. Additionally, CPPs can transfer hydrophilic molecules (peptides, proteins, nucleic acids) which exceed their mass, and for which the cell membrane is generally impermeable. In this review, we concentrate on the cellular uptake mechanism of CPPs and a method of conjunction of CPPs to the transported molecules. We also highlight the potential of CPPs in delivering various kinds of macromolecules into cells, including compounds of therapeutic interest.

Introduction. Cell penetrating peptides (CPPs) have the ability to translocate through cell membranes with high efficiency and therefore can introduce biological agents with pharmaceutical properties into the cell. Transportan (TP) and its shorter analog transportan 10 (TP10) are among the best studied CPPs, however, their effects on viability of and cargo introduction into colorectal cancer (CRC) cells have yet not been investigated. The aim of our study was to evaluate the cytotoxic effects of TP and TP10 on representative CRC lines and the efficiency of protein (streptavidin) and siRNA cargo delivery by TP-biotinylated derivatives (TP-biot). Material and methods. HT29 (early stage CRC model) and HCT116 (metastatic CRC model) cell lines were incubated with TP, TP10, TP-biot1, TP-biot13 and TP10-biot1. The effects of studied CPPs on cell viability and cell cycle were assessed by MTT and annexin V assays. The uptake of streptavidin-FITC complex into cells was determined by flow cytometry and fluorescence microscopy, with the inhibition of cellular vesicle trafficking by brefeldin A. The efficiency of siRNA for SASH1 gene delivery was measured by quantitative PCR (qPCR). Results. Since up to 10 µM concentrations of each CPP showed no significant cytotoxic effect, the concentrations of 0.5-5 µM were used for further analyses. Within this concentration range none of the studied CPPs affected cell viability and cell cycle. The efficient and endocytosis-independent introduction of streptavidin-FITC complex into cells was observed for TP10-biot1 and TP-biot1 with the cytoplasmic location of the fluorescent cargo; decreased SASH1 mRNA level was noticed with the use of siRNA and analyzed CPPs. Conclusions. We conclude that TP, TP10 and their biotinylated derivatives can be used as efficient delivery vehicles of small and large cargoes into CRC cells.