title: Structure-based development of anticancer drugs: complexes of NAD(P)H:quinone oxidoreductase 1 with chemotherapeutic quinones.
abstract: BACKGROUND
  NAD(P)H:quinone acceptor oxidoreductase (QR1) protects animal cells from the deleterious and carcinogenic effects of quinones and other electrophiles. Remarkably, the same enzyme activates cancer prodrugs that become cytotoxic only after two-electron reduction. QR1's ability to bioactivate quinones and its elevated expression in many human solid tumors makes this protein an excellent target for enzyme-directed drug development. Until now, structural analysis of the mode of binding of chemotherapeutic compounds to QR1 was based on model building using the structures of complexes with simple substrates; no structure of complexes of QR1 with chemotherapeutic prodrugs had been reported.
  
  
  RESULTS
  Here we report the high-resolution crystal structures of complexes of QR1 with three chemotherapeutic prodrugs: RH1, a water-soluble homolog of dimethylaziridinylbenzoquinone; EO9, an aziridinylindolequinone; and ARH019, another aziridinylindolequinone. The structures, determined to resolutions of 2.0 A, 2.5 A, and 1.86 A, respectively, were refined to R values below 21% with excellent geometry.
  
  
  CONCLUSIONS
  The structures show that compounds can bind to QR1 in more than one orientation. Surprisingly, the two aziridinylindolequinones bind to the enzyme in different orientations. The results presented here reveal two new factors that must be taken into account in the design of prodrugs targeted for activation by QR1: the enzyme binding site is highly plastic and changes to accommodate binding of different substrates, and homologous drugs with different substituents may bind to QR1 in different orientations. These structural insights provide important clues for the optimization of chemotherapeutic compounds that utilize this reductive bioactivation pathway.
authors.affiliation: Department of Biophysics and Biophysical Chemistry, Johns Hopkins Medical School, Baltimore, MD 21205, USA.
authors.forename: M
authors.initials: M
authors.lastname: Faig
authors.forename: M A
authors.initials: MA
authors.lastname: Bianchet
authors.forename: S
authors.initials: S
authors.lastname: Winski
authors.forename: R
authors.initials: R
authors.lastname: Hargreaves
authors.forename: C J
authors.initials: CJ
authors.lastname: Moody
authors.forename: A R
authors.initials: AR
authors.lastname: Hudnott
authors.forename: D
authors.initials: D
authors.lastname: Ross
authors.forename: L M
authors.initials: LM
authors.lastname: Amzel
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry* / Q000494:pharmacology; D016227:Benzoquinones / Q000737:chemistry; D001665:Binding Sites; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D015195:Drug Design; D006801:Humans; D007700:Kinetics; D008956:Models, Chemical; D011485:Protein Binding; D011808:Quinone Reductases / Q000737:chemistry*; D011809:Quinones / Q000737:chemistry / Q000627:therapeutic use*; D011994:Recombinant Proteins / Q000737:chemistry
chemical_list: D000970:Antineoplastic Agents; D016227:Benzoquinones; D011809:Quinones; D011994:Recombinant Proteins; C041831:NADH dehydrogenase (quinone); D011808:Quinone Reductases