title: Substituents on etoposide that interact with human topoisomerase IIalpha in the binary enzyme-drug complex: contributions to etoposide binding and activity.
abstract: Etoposide is a widely prescribed anticancer agent that stabilizes topoisomerase II-mediated DNA strand breaks. The drug contains a polycyclic ring system (rings A-D), a glycosidic moiety at C4, and a pendant ring (E-ring) at C1. A recent study that focused on yeast topoisomerase II demonstrated that the H15 geminal protons of the etoposide A-ring, the H5 and H8 protons of the B-ring, and the H2', H6', 3'-methoxyl, and 5'-methoxyl protons of the E-ring contact topoisomerase II in the binary enzyme-drug complex [ Wilstermann et al. (2007) Biochemistry 46, 8217-8225 ]. No interactions with the C4 sugar were observed. The present study used DNA cleavage assays, saturation transfer difference [ (1)H] NMR spectroscopy, and enzyme-drug binding studies to further define interactions between etoposide and human topoisomerase IIalpha. Etoposide and three derivatives that lacked the C4 sugar were analyzed. Except for the sugar, 4'-demethyl epipodophyllotoxin is identical to etoposide, epipodophyllotoxin contains a 4'-methoxyl group on the E-ring, and 6,7- O, O-demethylenepipodophyllotoxin replaces the A-ring with a diol. Results suggest that etoposide-topoisomerase IIalpha binding is driven by interactions with the A- and B-rings and potentially by stacking interactions with the E-ring. We propose that the E-ring pocket on the enzyme is confined, because the addition of bulk to this ring adversely affects drug function. The A- and E-rings do not appear to contact DNA in the enzyme-drug-DNA complex. Conversely, the sugar moiety subtly alters DNA interactions. The identification of etoposide substituents that contact topoisomerase IIalpha in the binary complex has predictive value for drug behavior in the enzyme-etoposide-DNA complex.
authors: Department of Biochemistry, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-0146, USA.
authors: Ryan P
authors: RP
authors: Bender
authors: Michael J
authors: MJ
authors: Jablonksy
authors: Mohammad
authors: M
authors: Shadid
authors: Ian
authors: I
authors: Romaine
authors: Norma
authors: N
authors: Dunlap
authors: Clemens
authors: C
authors: Anklin
authors: David E
authors: DE
authors: Graves
authors: Neil
authors: N
authors: Osheroff
mesh_terms: D000951:Antigens, Neoplasm / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D000972:Antineoplastic Agents, Phytogenic / Q000737:chemistry* / Q000494:pharmacology; D004247:DNA / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D015195:Drug Design; D005047:Etoposide / Q000031:analogs & derivatives / Q000737:chemistry* / Q000494:pharmacology; D006801:Humans; D011034:Podophyllotoxin / Q000031:analogs & derivatives / Q000737:chemistry; D011485:Protein Binding
chemical_list: D000951:Antigens, Neoplasm; D000972:Antineoplastic Agents, Phytogenic; D004268:DNA-Binding Proteins; D005047:Etoposide; D004247:DNA; D004250:DNA Topoisomerases, Type II; D011034:Podophyllotoxin; C072088:4'-demethylepipodophyllotoxin