title: Proteasomal inhibition potentiates drugs targeting DNA topoisomerase II.
abstract: The reaction mechanism of DNA topoisomerase II (TOP2) involves a covalent double-strand break intermediate in which the enzyme is coupled to DNA via a 5'-phosphotyrosyl bond. This normally transient enzyme-bridged break is stabilised by drugs such as mitoxantrone, mAMSA, etoposide, doxorubicin, epirubicin and idarubicin, which are referred to as TOP2 poisons. Removal of topoisomerase II by the proteasome is involved in the repair of these lesions. In K562 cells, inhibiting the proteasome with MG132 significantly potentiated the growth inhibition by these six drugs that target topoisomerase II, and the highest level of potentiation was observed with mitoxantrone. Mitoxantrone also showed the greatest potentiation by MG132 in three Nalm 6 cell lines with differing levels of TOP2A or TOP2B. Mitoxantrone was also potentiated by the clinically used proteasome inhibitor PS341 (Velcade). We have also shown that proteasome inhibition with MG132 in K562 cells reduces the rate of removal of mitoxantrone or etoposide stabilised topoisomerase complexes from DNA, suggesting a possible mechanism for the potentiation of topoisomerase II drugs by proteasomal inhibition.
authors.affiliation: Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom.
authors.forename: Ka C
authors.initials: KC
authors.lastname: Lee
authors.affiliation: Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom.
authors.forename: Rebecca L
authors.initials: RL
authors.lastname: Bramley
authors.affiliation: Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom.
authors.forename: Ian G
authors.initials: IG
authors.lastname: Cowell
authors.affiliation: Institute for Cellular Medicine, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom.
authors.forename: Graham H
authors.initials: GH
authors.lastname: Jackson
authors.affiliation: Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom. Electronic address: caroline.austin@ncl.ac.uk.
authors.forename: Caroline A
authors.initials: CA
authors.lastname: Austin
mesh_terms: D000951:Antigens, Neoplasm / Q000378:metabolism; D000069286:Bortezomib / Q000494:pharmacology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004247:DNA / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D019008:Drug Resistance, Neoplasm; D004357:Drug Synergism; D005047:Etoposide / Q000494:pharmacology; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology*; D008942:Mitoxantrone / Q000494:pharmacology; D000075223:Poly-ADP-Ribose Binding Proteins; D061988:Proteasome Inhibitors / Q000494:pharmacology*; D059005:Topoisomerase II Inhibitors / Q000494:pharmacology*
chemical_list: D000951:Antigens, Neoplasm; D004268:DNA-Binding Proteins; D007976:Leupeptins; D000075223:Poly-ADP-Ribose Binding Proteins; D061988:Proteasome Inhibitors; D059005:Topoisomerase II Inhibitors; D000069286:Bortezomib; D005047:Etoposide; D004247:DNA; D008942:Mitoxantrone; D004250:DNA Topoisomerases, Type II; C000618811:TOP2A protein, human; C000618814:TOP2B protein, human; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde
keywords: DNA topoisomerase II; MG132; Mitoxantrone; Proteasome; Velcade