Enzyme-specific Inhibition of human Glutathione transferases by Dinitronaphthalene derivatives by Hilary Groom A Thesis presented to The University of Guelph In partial fulfilment of requirements for the degree of Master of Science in Molecular and Cellular Biology Guelph, Ontario, Canada © Hilary Groom, August, 2014 Abstract Enzyme-Specific Inhibition of Human Glutathione Transferases by Dinitronaphthalene Derivatives M. Hilary Groom Advisor: University of Guelph, 2014 Dr. P. David Josephy The enzyme glutathione transferase (GST) superfamily catalyzes the detoxication of many xenobiotics and byproducts of aerobic metabolism. GSTs catalyze the conjugation of glutathione with reactive functional groups of xenobiotics. Overexpression of GSTs can contribute to drug and apoptosis resistance in cancer cells and this has motivated research to develop GST inhibitors as adjuvants to chemotherapies. 1-Chloro-2,4-dinitrobenzene (CDNB) is one of the most commonly used substrates for GST activity assays. This project focuses on the interactions of naphthalene congeners of CDNB with recombinant human GST enzymes (Alpha, Mu, and Pi classes). Several dinitronaphthalene derivatives were found to be GST inhibitors. 1-Chloro-2,4-dinitronaphthalene was not a GST substrate, but inhibited the CDNB conjugation activity of GST enzymes. The mechanism of inhibition occurs by formation of a dead-end intermediate Meisenheimer complex in the enzyme active site. Significant mutagenic and toxic effects of these dinitronaphthalene derivatives were observedby conducting Salmonella Ames assays. iii Acknowledgements I would like to thank the many supporters who have assisted me with my project and offered me personal support while at the University of Guelph. First of all, I would like to thank my advisor, Dr. Josephy. He has provided excellent knowledge and guidance during my research project, and has greatly enriched my experience as a graduate student by his participation with the lab group. I am grateful for all the experiences and conferences I had the fortune to attend during my MSc. I would like to thank my fellow lab mates. Leah McGurn, who was invaluable for helping me adapt to an unfamiliar school and Minah Hwang, who mentored me on unfamiliar lab equipment. As well as current lab mates, Kaja and Reema, I thank for their moral support. I appreciate my parents, for their moral support and for being proud of my work and my sister and pet dogs, I would like to thank for reminding me to have fun. Lastly I would like to acknowledge the great mentors I encountered during my undergrad at UOIT. These professors and T.A. include Dr. Strap, Dr. Desaulniers, Dr. Bardin, and PhD- graduate, Tim. They have provided a great foundation of knowledge that has assisted me during my graduate work and they have helped me build my confidence to pursue graduate studies. iv Table of contents Acknowledgements ........................................................................................................................ iii i. List of Tables ...................................................................................................................... vi ii. List of Figures .................................................................................................................... vii A. Introduction ............................................................................................................................. 1 i. Glutathione transferases ....................................................................................................... 1 a. Glutathione ....................................................................................................................... 3 b. GST conjugation and the mercapturic acid pathway ....................................................... 4 c. Human glutathione transferase ......................................................................................... 5 d. Catalytic mechanism of cytosolic GSTs .......................................................................... 6 e. Human cytosolic glutathione transferases ........................................................................... 7 f. Model substrates of human glutathione transferases ..................................................... 10 g. Substrate specificity of human glutathione transferases ................................................ 13 ii. Inhibitors of glutathione transferase .................................................................................. 14 a. Applications of glutathione transferase inhibitors ......................................................... 16 iii. Nitronaphthalenes .............................................................................................................. 20 a. Genotoxicity of nitroarenes ............................................................................................ 21 b. Salmonella Ames test ..................................................................................................... 23 c. Genotoxicityof nitronaphthalenes .................................................................................. 25 d. Metabolism of 1-nitronaphthalene in mammals ............................................................ 25 B. Study Summary ..................................................................................................................... 26 C. Materials and Methods .......................................................................................................... 27 i. Chemicals ........................................................................................................................... 27 ii.Media and Agar ......................................................................................................................... 27 iii. Synthesis of dinitronaphthalene derivatives and GSH-CDNN conjugate ......................... 28 a. Analytical analysis of DNNSG conjugate ...................................................................... 30 iv. Recombinant human GST expressing strains .................................................................... 30 a. Recombinant GST purification ...................................................................................... 30 v. Enzyme kinetics instrumentation ....................................................................................... 33 vi. Inhibitor IC50 measurement ................................................................................................ 33 vii.Characterization of inhibition mechanism (kinetics) ........................................................... 34 v viii. Characterization of Meisenheimer complexes ............................................................... 34 a. Reversibility of Meisenheimer complex formation ....................................................... 35 ix. Mutagenicity and Genotoxicity: Salmonella Ames Assay ................................................ 35 b. Salmonella YG1024 ....................................................................................................... 36 c. Salmonella mutagenicity assay protocol ........................................................................ 36 d. NICE automated colony counting .................................................................................. 36 D. Results and Discussion .......................................................................................................... 37 i. Synthesis of CDNN-GSH adduct....................................................................................... 37 ii. Protein purification ............................................................................................................ 38 iii. Identification of GST inhibitors ..................................................................................... 39 iv. Potency of GST inhibition by dinitronaphthalene derivatives ....................................... 41 a. Inhibition of GSTMu class enzymes by dinitronaphthalene derivatives ....................... 44 b. Inhibition of GST Alpha class enzymes by dinitronaphthalene derivatives .................. 46 c. Inhibition of GST Pi class enzyme by dinitronaphthalene derivatives .......................... 48 d. Other GST enzyme specific inhibitors ........................................................................... 49 v. Inhibition mechanism of DNN inhibitors .......................................................................... 52 vi. Meisenheimer complex formation in the GSTM2 active site ........................................ 53 a. Meisenheimer complex stability in the GST active site ................................................. 55 b. Meisenheimer complex formation by other GST inhibitors .......................................... 57 c. Possible intramolecular Meisenheimer complex formation of DNNSG ........................... 59 vii. Salmonella Mutagenicity Assay ..................................................................................... 60 viii. Biological functions of GSTM2-2.................................................................................. 63 E. Conclusions ........................................................................................................................... 66 F. References ............................................................................................................................. 69 G. Appendices ...........................................................................................................................