Tez özetleri Astronomi ve Uzay Bilimleri Anabilim Dalı

The effects of some antimicrobial peptides on breast cancer cell lines
Antimicrobial peptides are present in many organisms ranging from insects to mammals and they are different in amino acid sequences and secondary structures. Recent studies have shown that these peptides are effective on both microorganisms and tumor cells. Tumor cell membranes, which have anionic character like bacterial membranes, are attacked by cationic antimicrobial peptides bind by an electrostatic manner and after they interact with membranes, they locate at the membrane and impair its integrity. In addition to this direct effect of cationic antimicrobial peptides, some peptides are known to penetrate into the cells and impair the integrity of mitochondrial membrane and to induce apoptosis in the cancer cells.
In this study, it was aimed to investigate the effects of four different antimicrobial peptides, whose anticancer activities were not studied before, on MCF-7 and MDA-MB 231 cells, which are breast cancer cell lines. The possible anticancer peptides of our interest were cyclic dodecapeptide, present in bovine (Bos taurus) neutrophiles, esculentin-2PLa, which was detected in the skin secretion of frogs (Rana palustris), cryptonin, which was detected in the hemolymph of cicada (Cryptotympana dubia), and last but not least, apiadecin, which is present in the hemolymph of bumblebee (Bombus pascuorum). It was considered that these peptides, present in different organisms, were selected because they are cationic and amphipathic in character and they might interact with tumor cell membranes. For the investigation of effects to normal cells, mouse 3T3 fibroblast cell line was used.
The peptides, which were investigated in terms of anticancer activity, were studied for cancer cell viability with thiazolyl blue tetrazolium bromide (MTT) test, possible lytic effects on the cells were studied by measuring the lactate dehydrogenase (LDH) release, apoptose-inducing effects were detected by spectrophotometric measurement of caspase-3 activity and also by agarose gel electrophoresis of DNA fragmentation, morphologic means of determination of cell death was performed with acridine orange/ethidium bromide dual fluorescence dying technique on fluorescent microscope. Scanning electron microscope was used to investigate the possible damages of cationic antimicrobial peptides to cell membranes. The possible affinities of these peptides against anionic heparin sulphate and chondroitine sulphate, which were suggested to support the negativity of cancer cell membranes, were investigated with solid phase heparin sulphate and chondroitine sulphate binding measurements. In order to investigate the electrostatic interactions between antimicrobial peptides which were studied in terms of anticancer activity and negatively charged tumor cell membranes, the affinity of antimicrobial peptides against normal cells and tumor cells was investigated with peptide binding measurements.
According to the results we obtained, it was determined that cyclic dodecapeptide, esculentin-2PLa, and cryptonin decrease cell viability in breast cancer cells; however, apidaecin was found to have no such effect. This effect of cyclic dodecapeptide was observed against MCF-7 and MDA-MB 231 cells, but no reduction was obtained in the fibroblast cell viability. Esculentin-2PLa and cryptonin not only decreased tumor cells' viability, but also fibroblast cells' viability. These three cationic antimicrobial peptides, the anticancer activity of which were presented for the first time, were shown to kill breast cancer cells by impairing the membrane integrity and causing necrotic cell death by forming pores in the membranes. These three different cationic antimicrobial peptides were observed to bind to the negatively charged glycosaminoglycanes and show more affinity against breast cancer cells than fibroblast cells.
When the results were evaluated, cyclic dodecapeptide, esculentin-2PLa and cryptonin was determined to have therapeutic importance due to their toxicity against breast cancer cells, but cyclic dodecapeptide has more therapeutic value to its selective toxicity when compared to the other two peptides. In addition, although the activity of these peptides are unknown in in vivo cancer models, after they are selectively delivered to tumor cells which are resistant to chemotherapy, they might induce tumor cell death by necrosis and help overcome the problems seen in chemotherapy.