title: 5-aminoimidazole-4-carboxamide riboside enhances effect of ionizing radiation in PC3 prostate cancer cells.
abstract: OBJECTIVE
  The nucleoside 5-aminoimidazole-4-carboxamide riboside (AICAR) is a low-energy mimetic and adenosine monophosphate (AMP)-activated protein kinase (AMPK) agonist that can affect the phenotype of malignant cells by diminishing their anabolism. It does this by being converted to 5-aminoimidazole-4-carboxamide ribotide (ZMP), an AMP analog. We combined this promising antineoplastic agent with ionizing radiation in an attempt to increase its efficacy.
  
  
  METHODS
  The effect of AICAR on cell proliferation, cell viability, apoptosis, reactive oxygen species production, radiosensitivity, and AMPK activation was determined in the human prostate cancer cell line PC3. To elucidate the radiosensitizing mechanism, clonogenic survival assays in the presence of a drug agonist or antagonist or with small interfering RNA targeting AMPK were done, as well as measurements of ZMP production and double strand break repair. Moreover, immunoblot analysis of the radiation response signaling pathways after AICAR treatment was performed.
  
  
  RESULTS
  The incubation of human PC3 prostate cancer cells with AICAR-activated AMPK inhibited cell proliferation, decreased viability, increased apoptosis, and generated reactive oxygen species in a dose- and time-dependent manner. None of these endpoints gave more than additive effects when radiation was added. Radiosensitization was observed but only after 72 hours of treatment with 250 μM AICAR, suggesting that it was independent of AMPK activation. This finding was confirmed by small interfering RNA knockdown of AMPK. The mechanism of radiosensitization was associated with imbalanced deoxynucleotide pools owing to ZMP accumulation after AICAR administration that interfered with DNA repair.
  
  
  CONCLUSIONS
  Our findings on the favorable interaction between low doses of AICAR and ionizing radiation in PC3 cells could open new perspectives for the clinical use of this or similar compounds. However, additional research is still required to establish the ZMP pathway as being of general applicability.
authors.affiliation: Department of Radiation Oncology, University Hospitals Leuven Campus Gasthuisberg, and Department of Experimental Medicine and Endocrinology, Katholieke Universiteit Leuven, Leuven, Belgium. sofie.isebaert@med.kuleuven.be
authors.forename: Sofie F
authors.initials: SF
authors.lastname: Isebaert
authors.forename: Johannes V
authors.initials: JV
authors.lastname: Swinnen
authors.forename: William H
authors.initials: WH
authors.lastname: McBride
authors.forename: Adrian C
authors.initials: AC
authors.lastname: Begg
authors.forename: Karin M
authors.initials: KM
authors.lastname: Haustermans
mesh_terms: D055372:AMP-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004789:Enzyme Activation; D055785:Gene Knockdown Techniques; D006801:Humans; D008297:Male; D008660:Metabolism; D011471:Prostatic Neoplasms / Q000378:metabolism / Q000532:radiotherapy*; D034741:RNA, Small Interfering; D011836:Radiation Tolerance / Q000187:drug effects*; D011839:Radiation, Ionizing; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D017382:Reactive Oxygen Species / Q000378:metabolism; D012263:Ribonucleosides / Q000494:pharmacology*; D012265:Ribonucleotides / Q000378:metabolism; D013997:Time Factors; D014410:Tumor Stem Cell Assay
chemical_list: D034741:RNA, Small Interfering; D011838:Radiation-Sensitizing Agents; D017382:Reactive Oxygen Species; D012263:Ribonucleosides; D012265:Ribonucleotides; D000620:Aminoimidazole Carboxamide; C011651:acadesine; D055372:AMP-Activated Protein Kinases; C031143:AICA ribonucleotide