title: Environmentally Robust Rhodamine Reporters for Probe-based Cellular Detection of the Cancer-linked Oxidoreductase hNQO1.
abstract: We successfully synthesized a fluorescent probe capable of detecting the cancer-associated
  quinoneoxidoreductase isozyme-1 within human cells, based on results from an investigation of the stability of various rhodamines and seminaphthorhodamines toward the biological reductant NADH, present at ∼100-200 μM within cells. While rhodamines are generally known for their chemical stability, we observe that NADH causes significant and sometimes rapid modification of numerous rhodamine analogues, including those oftentimes used in imaging applications. Results from mechanistic studies lead us to rule out a radical-based reduction pathway, suggesting rhodamine reduction by NADH proceeds by a hydride transfer process to yield the reduced leuco form of the rhodamine and oxidized NAD(+). A relationship between the structural features of the rhodamines and their reactivity with NADH is observed. Rhodamines with increased alkylation on the N3- and N6-nitrogens, as well as the xanthene core, react the least with NADH; whereas, nonalkylated variants or analogues with electron-withdrawing substituents have the fastest rates of reaction. These outcomes allowed us to judiciously construct a seminaphthorhodamine-based, turn-on fluorescent probe that is capable of selectively detecting the cancer-associated, NADH-dependent enzyme
  quinoneoxidoreductase isozyme-1 in human cancer cells, without the issue of NADH-induced deactivation of the seminaphthorhodamine reporter.
authors.affiliation: Department of Chemistry, Louisiana State University , Baton Rouge, Louisiana 70803-1804, United States.
authors.forename: Quinn A
authors.initials: QA
authors.lastname: Best
authors.affiliation: Department of Chemistry, Louisiana State University , Baton Rouge, Louisiana 70803-1804, United States.
authors.forename: Amanda E
authors.initials: AE
authors.lastname: Johnson
authors.affiliation: Department of Chemistry, Louisiana State University , Baton Rouge, Louisiana 70803-1804, United States.
authors.forename: Bijeta
authors.initials: B
authors.lastname: Prasai
authors.affiliation: Department of Chemistry, Louisiana State University , Baton Rouge, Louisiana 70803-1804, United States.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Rouillere
authors.affiliation: Department of Chemistry, Louisiana State University , Baton Rouge, Louisiana 70803-1804, United States.
authors.forename: Robin L
authors.initials: RL
authors.lastname: McCarley
mesh_terms: D045744:Cell Line, Tumor; D005456:Fluorescent Dyes / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D015394:Molecular Structure; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000032:analysis* / Q000737:chemistry / Q000378:metabolism; D009369:Neoplasms / Q000175:diagnosis* / Q000201:enzymology*; D012235:Rhodamines / Q000737:chemistry*
chemical_list: D005456:Fluorescent Dyes; D012235:Rhodamines; D016660:NAD(P)H Dehydrogenase (Quinone); C447479:NQO1 protein, human