title: Tubulin-perturbing naphthoquinone spiroketals.
abstract: Several natural and synthetic naphthoquinone spiroketals are potent inhibitors of the thioredoxin-thioredoxin reductase redox system. Based on the antimitotic and weak antitubulin actions noted for SR-7 ([8-(furan-3-ylmethoxy)-1-oxo-1,4-dihydronaphthalene-4-spiro-2'-naphtho[1'',8''-de][1',3'][dioxin]), a library of related compounds was screened for tubulin-perturbing properties. Two compounds, TH-169 (5'-hydroxy-4'H-spiro[1,3-dioxolane-2,1'-naphthalen]-4'-one) and TH-223 (5'-methoxy-4'H-spiro[1,3-dioxane-2,1'-naphthalen]-4'-one), had substantial effects on tubulin assembly and were antiproliferative at low micromolar concentrations. TH-169 was the most potent at blocking GTP-dependent polymerization of 10 mum tubulin in vitro with a remarkable 50% inhibitory concentration of ca. 400 nm. It had no effect on paclitaxel-induced microtubule assembly and did not cause microtubule hypernucleation. TH-169 failed to compete with colchicine for binding to beta-tubulin. The 50% antiproliferative concentration of TH-169 against human cancer cells was at or slightly below 1 mum. Flow cytometry showed that 1 mum TH-169 caused an increase in G(2)/M and hypodiploid cells. TH-169 eliminated the PC-3 cells' polyploid population and increased their expression of p21(WAF1) and Hsp70 in a concentration-dependent manner. The antiproliferative effect of TH-169 was irreversible and independent of changes in caspases, actin, tubulin, glyceraldehyde phosphate dehydrogenase or Bcl-x(S/L). This structurally simple naphthoquinone spiroketal represents a small molecule, tubulin-interactive agent with a novel apoptotic pathway and attractive biological function.
authors.affiliation: Department of Pharmaceutical Sciences, University of Pittsburgh, Pittsburgh, PA 15213, USA.
authors.forename: Raghavan
authors.initials: R
authors.lastname: Balachandran
authors.forename: Tamara D
authors.initials: TD
authors.lastname: Hopkins
authors.forename: Catherine A
authors.initials: CA
authors.lastname: Thomas
authors.forename: Peter
authors.initials: P
authors.lastname: Wipf
authors.forename: Billy W
authors.initials: BW
authors.lastname: Day
mesh_terms: D000970:Antineoplastic Agents / Q000737:chemistry* / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics; D004354:Drug Screening Assays, Antitumor; D005663:Furans / Q000494:pharmacology*; D006160:Guanosine Triphosphate / Q000494:pharmacology; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics; D006801:Humans; D009285:Naphthoquinones / Q000494:pharmacology*; D017239:Paclitaxel / Q000494:pharmacology; D013141:Spiro Compounds / Q000494:pharmacology*; D014404:Tubulin / Q000187:drug effects*; D015854:Up-Regulation
chemical_list: D000970:Antineoplastic Agents; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D005663:Furans; D018840:HSP70 Heat-Shock Proteins; D009285:Naphthoquinones; D013141:Spiro Compounds; D014404:Tubulin; C520774:spiroketal; D006160:Guanosine Triphosphate; D017239:Paclitaxel