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    Autoinhibitory feedback control over photodynamic action
    (AMER CHEMICAL SOC, 2019) Yurt, Mediha Nur Zafer.; Cakmak, Yusuf.; Tekin, Gulsum.; Karakurt, Serdar.; Erbas-Cakmak, Sundus.
    In biology, the activity of enzymes is usually regulated by feedback loops, which enables direct communication between enzymes and the state of the cell. In a similar manner, with the intention to have automated activity regulation, the therapeutic effect of a photosensitizer (BOD1) is shown to be reduced through a negative feedback loop initiated by the photosensitizer. Photodynamic action produces cytotoxic O-1(2) and this reactive oxygen species reacts with ascorbate, generating H2O2. Peroxide-mediated oxidation of the photosensitizer auxiliary group leads to the formation of inactive BOD2 from the parent photosensitizer. BOD1 is shown to accumulate in mitochondria, and cell viability is shown to decrease significantly with BOD1 compared to the loop end product, BOD2. Photoinduced enhancement of fluorescence indicates the formation of inactive BOD2 under cellular conditions, and enhanced fluorescence acts as a reporter for the activity of the photosensitizer. We present the first example of PDT autoinactivation, and such a feedback control mechanism would enable a decrease in post-therapy side effects.
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    Red and blue emitting fluorescent probe for cyanide and hypochlorite ions: Biological sensing and environmental analysis
    (ELSEVIER SCI LTD, 2020) Malkondu, Sait.; Erdemir, Serkan.; Karakurt, Serdar.
    Excessive levels of hypochlorite and cyanide ions are considered as the major threats towards human health and environment. Therefore, many researchers make considerable effort to develop small molecules for the quick, accurate and easy detection of biologically and environmentally important anions. Moreover, design of multiple analyte sensing sensors is still challenging issue due to broad application area. In the present study, we introduce a novel chemosensor (P) based on benzothiazole and diaminomaleonitrile units for the detection hypochlorite and cyanide ions in biological and environmental samples. The detection ability of P was examined towards a pool of analyte containing anions, cations and reactive oxygen species. P undergoes sharp turn-on fluorescence enhancement induced by hypochlorite or cyanide over other anions. The fluorescence response is attributed to oxidation of imine bond by hypochlorite or deprotonation of -NH2 and -OH functions by cyanide. The selectivity and sensitivity data demonstrated by P over other anions renders it an excellent candidate for hypochlorite and cyanide detection in biological and aqueous environments. Moreover, this is the first study that single probe has an ability of detecting both hypochlorite and cyanide anions through two distinct sensing modes.
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    Synthesis and evaluation of the antitumor activity of Calix[4]arene L-proline derivatives
    (ACADEMIC PRESS INC ELSEVIER SCIENCE, 2020) Oguz, Mehmet.; Gul, Alev.; Karakurt, Serdar.; Yilmaz, Mustafa.
    The unique conformational properties, functionality, low toxicity, and low cost make calixarene-based compounds a valuable candidate against cancer. The aim of the present study is the synthesis of the upper rim and lower rim-functionalized L-proline-based calix[4]arene derivatives and evaluation of their cytotoxic potential for human cancerous cells as well as to determine the death mechanism. Synthesized calix[4]arene (3, 8a, 8b 13a, and 13b) derivatives were characterized by different spectroscopic techniques such as (HNMR)-H-1, (CNMR)-C-13, and FTIR. In vitro effects of compounds 3, 8a, 8b, 13a and 13b were tested on human cancerous cells (HEPG2, PC-3, A-549, and DLD-1) as well as human healthy epithelium cell (PNT1A). Results show that compounds 3, 8a, 8b and 13b have cytotoxic potential on human colorectal carcinoma cells (DLD-1) with IC50, values of 43 mu M, 45.2 mu M, 64.57 mu M, and 29.35 mu M respectively. Apoptosis ratios of cell death were investigated with flow cytometer using 7-AAD and Annexin-V as markers. Cytotoxic potential of 8a was found to be higher due to increased apoptosis, when compared with healthy cells the apoptotic cell death was significantly (p < 0.0001) increased up to 1.7-fold and 2.4-fold in DLD-1 and A549 cells, respectively. In conclusion, these L-proline derived calix[4]arenes with their selective cytotoxic potential on human cancerous cells may be a potential candidate for the treatment of human CRC and lung cancer.