title: Efficacy of RNA polymerase II inhibitors in targeting dormant leukaemia cells.
abstract: BACKGROUND
  Dormant cells are characterised by low RNA synthesis. In contrast, cancer cells can be addicted to high RNA synthesis, including synthesis of survival molecules. We hypothesised that dormant cancer cells, already low in RNA, might be sensitive to apoptosis induced by RNA Polymerase II (RP2) inhibitors that further reduce RNA synthesis.
  
  
  METHODS
  We cultured leukaemia cells continuously in vitro in the presence of an mTOR inhibitor to model dormancy. Apoptosis, damage, RNA content and reducing capacity were evaluated. We treated dormancy-enriched cells for 48 hours with the nucleoside analogues ara-C, 5-azacytidine and clofarabine, the topoisomerase targeting agents daunorubicin, etoposide and irinotecan and three multikinase inhibitors with activity against RP2 - flavopiridol, roscovitine and TG02, and we measured growth inhibition and apoptosis. We describe use of the parameter 2 × IC50 to measure residual cell targeting. RNA synthesis was measured with 5-ethynyl uridine. Drug-induced apoptosis was measured flow cytometrically in primary cells from patients with acute myeloid leukaemia using a CD34/CD71/annexinV gating strategy to identify dormant apoptotic cells.
  
  
  RESULTS
  Culture of the KG1a cell line continuously in the presence of an mTOR inhibitor induced features of dormancy including low RNA content, low metabolism and low basal ROS formation in the absence of a DNA damage response or apoptosis. All agents were more effective against the unmanipulated than the dormancy-enriched cells, emphasising the chemoresistant nature of dormant cells. However, the percentage of cell reduction by RP2 inhibitors at 2 × IC50 was significantly greater than that of other agents. RP2 inhibitors strongly inhibited RNA synthesis compared with other drugs. We also showed that RP2 inhibitors induce apoptosis in proliferating and dormancy-enriched KG1a cells and in the CD71neg CD34pos subset of primary acute myeloid leukaemia cells.
  
  
  CONCLUSIONS
  We suggest that RP2 inhibitors may be a useful class of agent for targeting dormant leukaemia cells.
authors.forename: Monica
authors.initials: M
authors.lastname: Pallis
authors.forename: Francis
authors.initials: F
authors.lastname: Burrows
authors.forename: Abigail
authors.initials: A
authors.lastname: Whittall
authors.forename: Nicholas
authors.initials: N
authors.lastname: Boddy
authors.forename: Claire
authors.initials: C
authors.lastname: Seedhouse
authors.forename: Nigel
authors.initials: N
authors.lastname: Russell
mesh_terms: D000208:Acute Disease; D000227:Adenine Nucleotides / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D001087:Arabinonucleosides / Q000494:pharmacology; D001374:Azacitidine / Q000494:pharmacology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D000077866:Clofarabine; D003561:Cytarabine / Q000494:pharmacology; D003630:Daunorubicin / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005047:Etoposide / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006576:Heterocyclic Compounds, 4 or More Rings / Q000494:pharmacology; D006801:Humans; D007951:Leukemia, Myeloid / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D010880:Piperidines / Q000494:pharmacology; D011687:Purines / Q000494:pharmacology; D012319:RNA Polymerase II / Q000037:antagonists & inhibitors* / Q000378:metabolism; D012334:RNA, Neoplasm / Q000235:genetics / Q000378:metabolism*; D000077546:Roscovitine; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: C570909:14-methyl-20-oxa-5,7,14,26-tetraazatetracyclo(19.3.1.1(2,6).1(8,12))heptacosa-1(25),2(26),3,5,8(27),9,11,16,21,23-decaene; D000227:Adenine Nucleotides; D000970:Antineoplastic Agents; D001087:Arabinonucleosides; D004791:Enzyme Inhibitors; D005419:Flavonoids; D006576:Heterocyclic Compounds, 4 or More Rings; D010880:Piperidines; D011687:Purines; D012334:RNA, Neoplasm; D003561:Cytarabine; D000077546:Roscovitine; C077990:alvocidib; D005047:Etoposide; D000077866:Clofarabine; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; D012319:RNA Polymerase II; D001374:Azacitidine; D020123:Sirolimus; D003630:Daunorubicin