6th Global Summit on Toxicology and Applied Pharmacology
University of Arkansas for Medical Sciences, USA
Title: Enzymatic DNA fragmentation: the mechanism and marker of drug toxicity
Biography: Alexei G Basnakian
DNA is the longest polymer and the only cellular molecule that cannot be resynthesized if destroyed. The destruction of DNA beyond DNA repair capacity is provided by DNA endonucleases and causes the termination of DNA and mRNA syntheses. Since DNA destruction occurs immediately prior and after cell death, the endonucleases do not need to be induced to provide DNA fragmentation. Independently of cell death cause and mechanism, the endonuclease-mediated DNA fragmentation is the universal marker of irreversible cell death. Most active cellular DNA-fragmenting endonucleases are DNase I and Endonuclease G (EndoG). We studied whether overexpression of these two endonucleases would cause DNA fragmentation (TUNEL) and cell death (LDH release) without and in the presence of anticancer drugs (cyclophosphamide, cisplatin, docetaxel, etoposide, or camptothecin). Our experiments showed that expression levels of the two endonucleases strongly correlated with drug sensitivity of breast cancer and prostate cancer cells. Invasive cancer cell lines usually did not express DNase I, and the level of EndoG expression correlated with the degree of dedifferentiation. Overexpression of the endonucleases was not very cytotoxic by itself but made the cancer cell lines more sensitive to the drugs, while silencing of the endonucleases partially protected them from the drug toxicities. Orthotopic EndoG-deficient prostate cancer xenografts were not sensitive to docetaxel, but became sensitive after overexpression of EndoG. Normal kidney cells and mouse kidneys in vivo were highly sensitive to cisplatin toxicity, which was mediated by the same endonucleases. Newly developed chemical inhibitors of DNase I and EndoG protected cancer and kidney cells from anticancer drugs. These observations indicate the importance of the endonucleases in cancer drug toxicities, and suggest potential benefits of using them as helper drugs for anticancer therapy and as targets for protecting normal tissues against drug toxicities.