title: Gemcitabine-mediated radiosensitization of human soft tissue sarcoma.
abstract: OBJECTIVE
  Local and systemic control of soft tissue sarcoma (STS) remains a clinical challenge, particularly for retroperitoneal, deep truncal, or advanced extremity disease. 2',2'-Difluoro-2'-deoxycytidine (gemcitabine) is a potent radiosensitizer in many tumor types, but it has not been studied in human STS. The purpose of this study was to determine the radiosensitizing potential of gemcitabine in preclinical models of human STS.
  
  
  METHODS
  The in vitro radiosensitizing activity of gemcitabine was assessed with clonogenic survival assay on three human STS cell lines: SK-LMS-1 (leiomyosarcoma), SW-872 (liposarcoma), and HT-1080 (fibrosarcoma). Cell cycle distribution was determined using dual-channel flow cytometry. The in vivo radiosensitizing activity of gemcitabine was assessed with subcutaneous SK-LMS-1 nude mice xenografts. Tumor-bearing mice were treated with concurrent weekly gemcitabine and fractionated daily radiotherapy (RT) (2 Gy daily) for 3 weeks (a total dose of 30 Gy).
  
  
  RESULTS
  The 50% inhibitory concentration (IC(50)) of gemcitabine for the human STS cell lines ranged from 10 to 1000 nM. Significant in vitro radiosensitization was demonstrated in all three human STS cell lines using gemcitabine concentrations at and below the IC(50). Maximal radiosensitization was associated with accumulation of cells in early S-phase. SK-LMS-1 xenografts displayed significant tumor growth delay with combined gemcitabine and RT compared to either treatment alone. Treatment related toxicity was greatest in the gemcitabine plus RT arm, but remained at an acceptable level.
  
  
  CONCLUSIONS
  Gemcitabine is a potent radiosensitizer in preclinical models of human STS. Clinical trials combining gemcitabine and RT in human STS are warranted.
authors.affiliation: Department of Radiation Oncology, University of Michigan, Ann Arbor, MI, USA.
authors.forename: James D
authors.initials: JD
authors.lastname: Murphy
authors.forename: David R
authors.initials: DR
authors.lastname: Lucas
authors.forename: Yash R
authors.initials: YR
authors.lastname: Somnay
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Hamstra
authors.forename: Michael E
authors.initials: ME
authors.lastname: Ray