title: Action of SN 28049, a new DNA binding topoisomerase II-directed antitumour drug: comparison with doxorubicin and etoposide.
abstract: OBJECTIVE
  We have examined the cellular action of SN 28049 (N-[2-(dimethylamino)ethyl]-2,6-dimethyl-1-oxo-1,2-dihydrobenzo[b]-1,6-naphthyridine-4-carboxamide), a DNA binding drug with curative activity against the Colon 38 transplantable murine carcinoma, on human tumour cells. Its action has been compared with that of two topoisomerase II-targetted drugs, etoposide and doxorubicin.
  
  
  METHODS
  The NZM3 melanoma and HCT116 colon carcinoma cell lines, each expressing wild-type p53, were cultured and responses were compared by flow cytometry, electrophoresis, microscopy, and growth of tumour xenografts.
  
  
  RESULTS
  Responses of NZM3 cells to all three drugs, as measured by histone H2AX γ-phosphorylation, induction of the p53 pathway and cell cycle arrest, were comparable and typical of those of topoisomerase II poisons. Xenografts of NZM3 cells responded to SN 28049 with a tumour growth delay of 16 days. In contrast, HCT116 cells had an attenuated DNA damage response to the drugs and SN 28049 had no in vivo activity, consistent with low topoisomerase II activity. However, SN 28049 inhibited HCT116 cell growth in vitro and activated the p53 pathway to induce a state with G(2)/M-phase DNA content, low mitotic index and a high proportion of binucleate cells. Treated cells expressed cyclin E and the senescence marker β-galactosidase but showed low expression of cyclin B and survivin. In comparison, etoposide caused little p53 expression or cycle arrest, and doxorubicin had an intermediate effect.
  
  
  CONCLUSIONS
  The action of SN 28049 in NZM3 cells is typical of a topoisomerase II poison, but the low topoisomerase IIα activity of HCT116 cells allowed the detection of a second antiproliferative action of SN 28049 in which cells undergo post-mitotic cycle arrest and induction of p53.
authors.affiliation: Auckland Cancer Society Research Centre, Faculty of Medical and Health Sciences, The University of Auckland, Private Bag 92019, Auckland, New Zealand. cath.drummond@newcastle.ac.uk
authors.forename: Catherine J
authors.initials: CJ
authors.lastname: Drummond
authors.forename: Graeme J
authors.initials: GJ
authors.lastname: Finlay
authors.forename: Laura
authors.initials: L
authors.lastname: Broome
authors.forename: Elaine S
authors.initials: ES
authors.lastname: Marshall
authors.forename: Emma
authors.initials: E
authors.lastname: Richardson
authors.forename: Bruce C
authors.initials: BC
authors.lastname: Baguley
mesh_terms: D000818:Animals; D000951:Antigens, Neoplasm / Q000378:metabolism; D000970:Antineoplastic Agents / Q000737:chemistry / Q000494:pharmacology*; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004247:DNA / Q000378:metabolism*; D004249:DNA Damage; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D004317:Doxorubicin / Q000494:pharmacology*; D005047:Etoposide / Q000494:pharmacology*; D005434:Flow Cytometry; D059585:G1 Phase Cell Cycle Checkpoints / Q000187:drug effects; D045325:HCT116 Cells; D006801:Humans; D020128:Inhibitory Concentration 50; D051379:Mice; D009287:Naphthyridines / Q000737:chemistry / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects; D057891:Tetraploidy; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism; D023041:Xenograft Model Antitumor Assays; D019014:fas Receptor / Q000378:metabolism
chemical_list: D000951:Antigens, Neoplasm; D000970:Antineoplastic Agents; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004268:DNA-Binding Proteins; C491901:FAS protein, human; C533598:N-(2-(dimethylamino)ethyl)-2,6-dimethyl-1-oxo-1,2-dihydroxybenzo(b)-1,6-naphthyridine-4-carboxamide; D009287:Naphthyridines; D016159:Tumor Suppressor Protein p53; D019014:fas Receptor; D005047:Etoposide; D004317:Doxorubicin; D004247:DNA; D004250:DNA Topoisomerases, Type II