title: Enhancement of hypoxia-activated prodrug TH-302 anti-tumor activity by Chk1 inhibition.
abstract: BACKGROUND
  The hypoxia-activated prodrug TH-302 is reduced at its nitroimidazole group and selectively under hypoxic conditions releases the DNA cross-linker bromo-isophosphoramide mustard (Br-IPM). Here, we have explored the effect of Chk1 inhibition on TH-302-mediated pharmacological activities.
  
  
  METHODS
  We employed in vitro cell viability, DNA damage, cellular signaling assays and the in vivo HT29 human tumor xenograft model to study the effect of Chk1inhibition on TH-302 antitumor activities.
  
  
  RESULTS
  TH-302 cytotoxicity is greatly enhanced by Chk1 inhibition in p53-deficient but not in p53-proficient human cancer cell lines. Chk1 inhibitors reduced TH-302-induced cell cycle arrest via blocking TH-302-induced decrease of phosphorylation of histone H3 and increasing Cdc2-Y15 phosphorylation. Employing the single-cell gel electrophoresis (comet) assay, we observed a potentiation of the TH-302 dependent tail moment. TH-302 induced γH2AX and apoptosis were also increased upon the addition of Chk1 inhibitor. Potentiation of TH-302 cytotoxicity by Chk1 inhibitor was only observed in cell lines proficient in, but not deficient in homology-directed DNA repair. We also show that combination treatment led to lowering of Rad51 expression levels as compared to either agent alone. In vivo data demonstrate that Chk1 inhibitor enhances TH-302 anti-tumor activity in p53 mutant HT-29 human tumor xenografts, supporting the hypothesis that these in vitro results can translate to enhanced in vivo efficacy of the combination.
  
  
  CONCLUSIONS
  TH-302-mediated in vitro and in vivo anti-tumor activities were greatly enhanced by the addition of Chk1 inhibitors. The preclinical data presented in this study support a new approach for the treatment of p53-deficient hypoxic cancers by combining Chk1 inhibitors with the hypoxia-activated prodrug TH-302.
authors.affiliation: Threshold Pharmaceuticals, 170 Harbor Way, Suite 300, South San Francisco, CA, 94080-6108, USA. fmeng@thresholdpharm.com.
authors.forename: Fanying
authors.initials: F
authors.lastname: Meng
authors.affiliation: Threshold Pharmaceuticals, 170 Harbor Way, Suite 300, South San Francisco, CA, 94080-6108, USA. dbhupathi@thresholdpharm.com.
authors.forename: Deepthi
authors.initials: D
authors.lastname: Bhupathi
authors.affiliation: Threshold Pharmaceuticals, 170 Harbor Way, Suite 300, South San Francisco, CA, 94080-6108, USA. jsun@thresholdpharm.com.
authors.forename: Jessica D
authors.initials: JD
authors.lastname: Sun
authors.affiliation: Threshold Pharmaceuticals, 170 Harbor Way, Suite 300, South San Francisco, CA, 94080-6108, USA. jliu@thresholdpharm.com.
authors.forename: Qian
authors.initials: Q
authors.lastname: Liu
authors.affiliation: Threshold Pharmaceuticals, 170 Harbor Way, Suite 300, South San Francisco, CA, 94080-6108, USA. dahluwalia@thresholdpharm.com.
authors.forename: Dharmendra
authors.initials: D
authors.lastname: Ahluwalia
authors.affiliation: Threshold Pharmaceuticals, 170 Harbor Way, Suite 300, South San Francisco, CA, 94080-6108, USA. wyan@thresholdpharm.com.
authors.forename: Yan
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Threshold Pharmaceuticals, 170 Harbor Way, Suite 300, South San Francisco, CA, 94080-6108, USA. mmatteucci@thresholdpharm.com.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Matteucci
authors.affiliation: Threshold Pharmaceuticals, 170 Harbor Way, Suite 300, South San Francisco, CA, 94080-6108, USA. chart@thresholdpharm.com.
authors.forename: Charles P
authors.initials: CP
authors.lastname: Hart
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects; D016203:CDC2 Protein Kinase / Q000378:metabolism; D059447:Cell Cycle Checkpoints / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D000071877:Checkpoint Kinase 1; D003110:Colonic Neoplasms / Q000188:drug therapy*; D004249:DNA Damage / Q000187:drug effects; D005260:Female; D019073:HT29 Cells; D006657:Histones / Q000378:metabolism; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D009154:Mutation; D009593:Nitroimidazoles / Q000494:pharmacology* / Q000627:therapeutic use; D010750:Phosphoproteins / Q000378:metabolism; D010752:Phosphoramide Mustards / Q000494:pharmacology* / Q000627:therapeutic use; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D011494:Protein Kinases / Q000378:metabolism*; D051135:Rad51 Recombinase / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013876:Thiophenes / Q000494:pharmacology* / Q000627:therapeutic use; D016159:Tumor Suppressor Protein p53 / Q000172:deficiency / Q000235:genetics; D014508:Urea / Q000031:analogs & derivatives* / Q000494:pharmacology / Q000627:therapeutic use
chemical_list: C532363:3-(carbamoylamino)-5-(3-fluorophenyl)-N-(3-piperidyl)thiophene-2-carboxamide; D000970:Antineoplastic Agents; C468783:H2AX protein, human; D006657:Histones; D009593:Nitroimidazoles; D010750:Phosphoproteins; D010752:Phosphoramide Mustards; D047428:Protein Kinase Inhibitors; C552526:TH 302; D013876:Thiophenes; D016159:Tumor Suppressor Protein p53; D014508:Urea; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; C000605869:Chek1 protein, mouse; D016203:CDC2 Protein Kinase; D051135:Rad51 Recombinase