title: [Combined radiotherapy and gemcitabine. Evaluation of clinical data based on experimental knowledge].
abstract: BACKGROUND
  In experimental studies the nucleoside analog Gemcitabine (2',2' difluorodesoxycytidine) clearly demonstrates radiation enhancing properties. After describing the pharmacological Gemcitabine-related data and the clinical studies regarding combined radiochemotherapy and taking under consideration the in-vitro data and the results provided by animal models, this overview is aimed to draw clinically relevant conclusions, resulting in the improvement of treatment approaches.
  
  
  METHODS
  The available literature data regarding the metabolism and the mechanism of action, the evaluation of possible schedules of administration, and combined radiochemotherapy including Gemcitabine has been reviewed. Publications reporting experimental data in vitro and in vivo as well as our own experimental results have been incorporated.
  
  
  RESULTS
  In clinical phase I and II studies, the favorable tumor response is accompanied by a high incidence of grade III-IV toxicities whereby the maximum-tolerated dose (MTD) of the various schedules of administration used is always lower compared to the MTD of single-agent treatment. In in-vitro and in-vivo data addressing the description and the evaluation of the radiation enhancing mechanism (especially influence on cell cycle, depletion of the dATP pool, induction of apoptosis, inhibition of DNA synthesis, reduction of DNA repair) this effect is already observed with non and moderately toxic Gemcitabine concentrations and depends on drug concentration and exposure time. Independent of the fractionation effect of radiotherapy, the radiation enhancement is persistent for at most 72 hours after the end of drug exposure. Taking under consideration the single dose per day and the target volume, a prolonged infusion and/or a twice-weekly administration of Gemcitabine at low concentration each and simultaneous radiotherapy are presumably considered to resemble the experimental data.
  
  
  CONCLUSIONS
  It is without doubt that data provided by clinical studies are of highest relevance for the evaluation of an optimized radiochemotherapy with Gemcitabine. However, although it is often difficult to transfer experimental data into the clinical situation, these data offer the possibility to develop an improved schedule of administration in patient treatment based on rational evidence in tumor biology.
authors.affiliation: Klinik für Strahlentherapie, Johann-Wolfgang-Goethe-Universität Frankfurt am Main. S.Mose@vff.uni-frankfurt.de
authors.forename: Stephan
authors.initials: S
authors.lastname: Mose
authors.forename: Reiner
authors.initials: R
authors.lastname: Class
authors.forename: Hans-Walter
authors.initials: HW
authors.lastname: Weber
authors.forename: Agi
authors.initials: A
authors.lastname: Oszvald
authors.forename: Angelika
authors.initials: A
authors.lastname: Rahn
authors.forename: Luther W
authors.initials: LW
authors.lastname: Brady
authors.forename: Heinz-D
authors.initials: HD
authors.lastname: Böttcher
mesh_terms: D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000009:adverse effects / Q000627:therapeutic use*; D002986:Clinical Trials as Topic; D003131:Combined Modality Therapy; D003841:Deoxycytidine / Q000009:adverse effects / Q000031:analogs & derivatives* / Q000627:therapeutic use*; D004305:Dose-Response Relationship, Drug; D006801:Humans; D009369:Neoplasms / Q000000981:diagnostic imaging / Q000188:drug therapy*; D011859:Radiography; D018714:Radiotherapy, Adjuvant; D016896:Treatment Outcome; D000093542:Gemcitabine
chemical_list: D000964:Antimetabolites, Antineoplastic; D003841:Deoxycytidine; D000093542:Gemcitabine
vernacular_title: Kombination von Radiotherapie und Gemcitabine. Bewertung der klinischen Daten auf der Basis experimenteller Erkenntnisse.