Design, Synthesis An Biological Application Of Selectively Selenocysteine-targeted Fluorescent Probes And Antitumor Drugs

Thioredoxin reductase (TrxR) is an important component of the thioredoxin (Trx) system, and plays vital roles in maintaining cellular redox balance. Mammalian TrxRs are essential selenocysteine (Sec)-containing flavoenzymes with a uniform-Gly-Cys-Sec-Gly active site at the C-terminus. As the 21st amini acid in ribosome-mediated protein synthesis, the Sec residue is indispensible for the function of TrxR. In this thesis, we prepared selective Sec probes and small molecule inhibitors of TrxR by targeting the Sec residue in the enzyme. The contents are summarized in following five chapters:Chapter 1:A general introduction of flurescence probes was presented, and the recent development of probes for thiols were reviewed. We then introduced the biological importance of Sec and selenoproteins, and the recent development of probes for Sec. In addition, the structure and function of selenoprotein TrxR were breifly reviewed, and the potential role of TrxR as anticancer drug target was discussed.Chapter 2:We reported herein the design, synthesis, and biological evaluations of a series of potential Sec probes. After the initial screening, the structural determinants for selective recognition of Sec were recapitulated. The follow-up studies identified that probe 19 (Sel-green) responds to Sec. Sel-green was successfully applied to quantify the Sec content in the selenoenzyme thioredoxin reductase and image endogenous Sec in live cells. With the aid of Sel-green, we further demonstrated that the cytotoxicity of different selenocompounds is correlated to their ability metabolizing to selenols in cells. The elucidation of the structure-activity relationship for selective recognition of selenols paves the way for further design of novel probes to better understand the pivotal role of Sec as well as selenoproteins in vivo.Chapter 3:The development of activatable red or near-infrared (NIR) fluorogenic probes with emission wavelength>600 nm is ideal for interrogating biological systems, as the longer wavelengths provide less background autofluorescence and higher tissue penetration. Based on the results from the Chapter 2, we prepared and evalulated the selective Sec probes with red and near infrared emissions.Chapter 4:The results from the Chapter 2 demonstrated that the fluorescent probes which possess 2,4-dinitrobenzene moiety linked to the fluorophores via ether or sulfonamide bond could selectively recognize Sec and the Sec residue in TrxR. So we synthesized a series of compounds bearing such scaffolds, and evalulated them as potential TrxR inhibitors. The biological action of the compounds with better inhibitin of TrxR were further tested in cancer cells.Chapter 5:Natural products and their derivatives are invaluable fountain of therapeutic agents. It is roughly estimated that half of modern marketed drugs are natural products or their derivatives. Xanthohumol (Xn), a naturally occurring polyphenol chalcone from hops, has received increasing attention due to its multiple pharmacological activities. We synthesized a series of Xn and its analogues, and evaluated their cytotoxicity in different types of cancer cells. In the cultured HeLa cells, compound 13n displayed the greatest potency more than 30-fold increase compared to the lead compound Xn. Further mechanistic studies disclose that 13n may selectively inhibit TrxR by primarily targeting the Sec residue in the antioxidant enzyme, leading to the accumulation of ROS. As a consequence,13n elicits oxidative stress, and eventually induces apoptosis in HeLa cells.