title: Hyperthermia inhibits recombination repair of gemcitabine-stalled replication forks.
abstract: BACKGROUND
  Gemcitabine is a potent nucleoside analogue against solid tumors, but development of drug resistance is a substantial problem. Removal of gemcitabine incorporated into DNA by repair mechanisms may contribute to resistance in chemo-refractory solid tumors. Human hepatocellular carcinoma (HCC) is usually very chemoresistant to gemcitabine.
  
  
  METHODS
  We treated HCC in vitro and in vivo (orthotopic murine model with human Hep3B or HepG2 xenografts, 7-10 CB17SCID mice per group) with gemcitabine. The role of homologous recombination repair proteins in repairing stalled replication forks was evaluated with hyperthermia exposure and cell-cycle analysis. The Student t-test was used for two-sample comparisons. Multiple group data were analyzed using one-way analysis of variance. All statistical tests were two-sided.
  
  
  RESULTS
  We demonstrated that Mre11-mediated homologous recombination repair of gemcitabine-stalled replication forks is crucial to survival of HCC cells. Furthermore, we demonstrated inhibition of Mre11 by an exonuclease inhibitor or concomitant hyperthermia. In orthotopic murine models of chemoresistant HCC, the Hep3B tumor mass with radiofrequency plus gemcitabine treatment (mean ± SD, 180±91mg) was statistically significantly smaller compared with gemcitabine alone (661±419mg, P = .0063).
  
  
  CONCLUSIONS
  This study provides mechanistic understanding of homologous recombination inhibiting-strategies, such as noninvasive radiofrequency field-induced hyperthermia, to overcome resistance to gemcitabine in refractory human solid tumors.
authors.affiliation: Department of Surgery, University of Arizona, Tucson, AZ (MR); Department of Surgical Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX (MR, CZ, BTC, HL, SJC, SAC); Department of Surgery, Baylor College of Medicine, Houston, TX (SAC, SJC); Department of Chemistry, Rice University, Houston, TX (LJW, SJC).
authors.forename: Mustafa
authors.initials: M
authors.lastname: Raoof
authors.affiliation: Department of Surgery, University of Arizona, Tucson, AZ (MR); Department of Surgical Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX (MR, CZ, BTC, HL, SJC, SAC); Department of Surgery, Baylor College of Medicine, Houston, TX (SAC, SJC); Department of Chemistry, Rice University, Houston, TX (LJW, SJC).
authors.forename: Cihui
authors.initials: C
authors.lastname: Zhu
authors.affiliation: Department of Surgery, University of Arizona, Tucson, AZ (MR); Department of Surgical Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX (MR, CZ, BTC, HL, SJC, SAC); Department of Surgery, Baylor College of Medicine, Houston, TX (SAC, SJC); Department of Chemistry, Rice University, Houston, TX (LJW, SJC).
authors.forename: Brandon T
authors.initials: BT
authors.lastname: Cisneros
authors.affiliation: Department of Surgery, University of Arizona, Tucson, AZ (MR); Department of Surgical Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX (MR, CZ, BTC, HL, SJC, SAC); Department of Surgery, Baylor College of Medicine, Houston, TX (SAC, SJC); Department of Chemistry, Rice University, Houston, TX (LJW, SJC).
authors.forename: Heping
authors.initials: H
authors.lastname: Liu
authors.affiliation: Department of Surgery, University of Arizona, Tucson, AZ (MR); Department of Surgical Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX (MR, CZ, BTC, HL, SJC, SAC); Department of Surgery, Baylor College of Medicine, Houston, TX (SAC, SJC); Department of Chemistry, Rice University, Houston, TX (LJW, SJC).
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Corr
authors.affiliation: Department of Surgery, University of Arizona, Tucson, AZ (MR); Department of Surgical Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX (MR, CZ, BTC, HL, SJC, SAC); Department of Surgery, Baylor College of Medicine, Houston, TX (SAC, SJC); Department of Chemistry, Rice University, Houston, TX (LJW, SJC).
authors.forename: Lon J
authors.initials: LJ
authors.lastname: Wilson
authors.affiliation: Department of Surgery, University of Arizona, Tucson, AZ (MR); Department of Surgical Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX (MR, CZ, BTC, HL, SJC, SAC); Department of Surgery, Baylor College of Medicine, Houston, TX (SAC, SJC); Department of Chemistry, Rice University, Houston, TX (LJW, SJC). steven.curley@bcm.edu.
authors.forename: Steven A
authors.initials: SA
authors.lastname: Curley
mesh_terms: D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology*; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy / Q000235:genetics / Q000628:therapy*; D002453:Cell Cycle / Q000187:drug effects / Q000235:genetics; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D004261:DNA Replication / Q000187:drug effects* / Q000235:genetics; D004273:DNA, Neoplasm / Q000187:drug effects* / Q000235:genetics; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors*; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D004195:Disease Models, Animal; D019008:Drug Resistance, Neoplasm; D005092:Exonucleases / Q000037:antagonists & inhibitors; D006801:Humans; D006979:Hyperthermia, Induced / Q000379:methods*; D008113:Liver Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000628:therapy*; D000076228:MRE11 Homologue Protein; D051379:Mice; D016513:Mice, SCID; D009374:Neoplasms, Experimental / Q000628:therapy; D011846:Radio Waves; D000078702:Radiofrequency Therapy; D059767:Recombinational DNA Repair / Q000187:drug effects*; D000093542:Gemcitabine
chemical_list: D000964:Antimetabolites, Antineoplastic; D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; C121766:MRE11 protein, human; D003841:Deoxycytidine; D005092:Exonucleases; D000076228:MRE11 Homologue Protein; D000093542:Gemcitabine