title: Killing of chronic lymphocytic leukemia by the combination of fludarabine and oxaliplatin is dependent on the activity of XPF endonuclease.
abstract: OBJECTIVE
  Chronic lymphocytic leukemia (CLL) resistant to fludarabine-containing treatments responds to oxaliplatin-based therapy that contains fludarabine. We postulated that a mechanism for this activity is the incorporation of fludarabine into DNA during nucleotide excision repair (NER) stimulated by oxaliplatin adducts.
  
  
  METHODS
  We analyzed CLL cell viability, DNA damage, and signaling pathways in response to treatment by fludarabine, oxaliplatin, or the combination. The dependency of the combination on oxaliplatin-induced DNA repair was investigated using siRNA in CLL cells or cell line models of NER deficiency.
  
  
  RESULTS
  Synergistic apoptotic killing was observed in CLL cells after exposure to the combination in vitro. Oxaliplatin induced DNA synthesis in CLL cells, which was inhibited by fludarabine and was eliminated by knockdown of XPF, the NER 5'-endonuclease. Wild-type Chinese hamster ovarian cells showed synergistic killing after combination treatment, whereas only additive killing was observed in cells lacking XPF. Inhibition of repair by fludarabine in CLL cells was accompanied by DNA single-strand break formation. CLL cells initiated both intrinsic and extrinsic apoptotic pathways as evidenced by the loss of mitochondrial outer membrane potential and partial inhibition of cell death upon incubation with FasL antibody.
  
  
  CONCLUSIONS
  The synergistic cell killing is caused by a mechanistic interaction that requires the initiation of XPF-dependent excision repair in response to oxaliplatin adducts, and the inhibition of that process by fludarabine incorporation into the repair patch. This combination strategy may be useful against other malignancies.
authors.affiliation: Department of Experimental Therapeutics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA.
authors.forename: Alma
authors.initials: A
authors.lastname: Zecevic
authors.forename: Deepa
authors.initials: D
authors.lastname: Sampath
authors.forename: Brett
authors.initials: B
authors.lastname: Ewald
authors.forename: Rong
authors.initials: R
authors.lastname: Chen
authors.forename: William
authors.initials: W
authors.lastname: Wierda
authors.forename: William
authors.initials: W
authors.lastname: Plunkett
mesh_terms: D000818:Animals; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use* / Q000633:toxicity; D017209:Apoptosis / Q000187:drug effects; D016466:CHO Cells; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D006224:Cricetinae; D003412:Cricetulus; D004249:DNA Damage / Q000187:drug effects; D004260:DNA Repair / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004357:Drug Synergism; D004720:Endonucleases / Q000378:metabolism*; D015973:Gene Expression Regulation, Leukemic; D020868:Gene Silencing; D006801:Humans; D015451:Leukemia, Lymphocytic, Chronic, B-Cell / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism; D009944:Organoplatinum Compounds / Q000627:therapeutic use* / Q000633:toxicity; D000077150:Oxaliplatin; D015398:Signal Transduction / Q000187:drug effects; D014740:Vidarabine / Q000031:analogs & derivatives* / Q000627:therapeutic use / Q000633:toxicity
chemical_list: D004268:DNA-Binding Proteins; D009944:Organoplatinum Compounds; C095888:xeroderma pigmentosum group F protein; D000077150:Oxaliplatin; D004720:Endonucleases; D014740:Vidarabine; C024352:fludarabine