title: Mitoxantrone in combination with an inhibitor of DNA-dependent protein kinase: a potential therapy for high risk B-cell chronic lymphocytic leukaemia.
abstract: Defects in the DNA damage response pathway [e.g. del(17p)] are associated with drug-resistant B-cell chronic lymphocytic leukaemia (CLL). We previously demonstrated that over-expression of DNA-dependent protein kinase (DNA-PK) correlates with chemo-resistance and that inhibition of DNA-PK sensitizes CLL cells to chemotherapeutics. Here, we investigated expression of DNA-PK and other proteins that impact on drug resistance, and evaluated the effects of a DNA-PK inhibitor (NU7441) on mitoxantrone-induced cytotoxicity in CLL cells. NU7441 sensitized cells from 42/49 CLL samples to mitoxantrone, with sensitization ranging from 2- to 200-fold Co-culture of CLL cells in conditioned stromal medium increased chemoresistance but did not reduce sensitization by NU7441. Mitoxantrone treatment induced γH2AX foci and NU7441 increased their longevity (24 h). NU7441 prevented mitoxantrone-induced autophosphorylation of the DNA-PK catalytic subunit (DNA-PKcs) at Ser 2056, confirming that DNA-PK participates in repair of mitoxantrone-induced DNA damage. del(17p) cases were more resistant to mitoxantrone than del(13q) cases, but were resensitized (7-16 fold) by co-incubation with NU7441. Expression of DNA-PKcs, Ku80, P-glycoprotein and topoisomerase IIβ were significantly higher in del(17p) cases. PRKDC mRNA levels correlated with DNA-PKcs protein expression, which predicted shorter survival. These data confirm the potential of DNA-PK as a therapeutic target in poor prognosis CLL.
authors.affiliation: Newcastle Cancer Centre at the NorthernInstitute for Cancer Research, Medical School, Newcastle University, Newcastle upon Tyne, UK.
authors.forename: Sarah L
authors.initials: SL
authors.lastname: Elliott
authors.forename: Clark
authors.initials: C
authors.lastname: Crawford
authors.forename: Evan
authors.initials: E
authors.lastname: Mulligan
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Summerfield
authors.forename: Paula
authors.initials: P
authors.lastname: Newton
authors.forename: Jonathan
authors.initials: J
authors.lastname: Wallis
authors.forename: Tryfonia
authors.initials: T
authors.lastname: Mainou-Fowler
authors.forename: Paul
authors.initials: P
authors.lastname: Evans
authors.forename: Clare
authors.initials: C
authors.lastname: Bedwell
authors.forename: Barbara W
authors.initials: BW
authors.lastname: Durkacz
authors.forename: Elaine
authors.initials: E
authors.lastname: Willmore
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D016923:Cell Death / Q000187:drug effects; D002867:Chromones / Q000494:pharmacology; D017077:Culture Media, Conditioned; D004260:DNA Repair / Q000187:drug effects; D051747:DNA-Activated Protein Kinase / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004353:Drug Evaluation, Preclinical; D019008:Drug Resistance, Neoplasm; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000201:enzymology / Q000235:genetics / Q000473:pathology*; D008942:Mitoxantrone / Q000494:pharmacology; D009025:Morpholines / Q000494:pharmacology; D009363:Neoplasm Proteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D014407:Tumor Cells, Cultured
chemical_list: C499693:8-dibenzothiophen-4-yl-2-morpholin-4-yl-chromen-4-one; D002867:Chromones; D017077:Culture Media, Conditioned; D009025:Morpholines; D009363:Neoplasm Proteins; D008942:Mitoxantrone; D051747:DNA-Activated Protein Kinase