Radioprotective effects of amifostine in vitro and in vivo measured with the comet assay.
OBJECTIVE
The authors investigated whether a potential radioprotective effect of amifostine (WR-2721) after in vitro or in vivo administration can be detected with the comet assay. Moreover, it was determined whether radioprotection by WR-2721 is dependent on the concentration of amifostine or alkaline phosphatase (AP, the enzyme which activates the prodrug). Furthermore, the authors tried to detect possible interindividual differences in radioprotection by amifostine.


METHODS
In vitro administration of amifostine: Freshly isolated lymphocytes from two healthy volunteers were incubated with different concentrations of AP (0-210 U/ml) and amifostine (0-5,000 microg/ml). IN VIVO ADMINISTRATION OF AMIFOSTINE: Blood samples were collected from six postoperative rectal cancer patients before and after intravenous administration of amifostine 500 mg (no pretreatment with radio- or chemotherapy). Leukocytes and lymphocytes were irradiated and repaired in vitro and investigated with the alkaline comet assay. The radioprotective effect was evaluated by calculating dose-modifying factors (DMFs) and the paired t-test.


RESULTS
Amifostine alone did not alter the radiation-induced DNA damage in vitro. The addition of at least 0.5-1 U/ml AP was required. A significant radioprotective effect (p < 0.05) was seen after administration of amifostine in vitro for all concentrations investigated (250-5,000 microg/ml, initial DNA damage). A comparable radioprotective effect after in vivo administration of 500 mg amifostine was measured with a mean DMF of 0.87. Interindividual differences were present in vivo and in vitro.


CONCLUSIONS
Amifostine 500 mg intravenously yields an adequate radioprotective concentration. The effect was only marginally improved by extreme concentrations of amifostine in in vitro experiments. The comet assay is capable of detecting small changes in radiosensitivity by amifostine.
Müller
Arndt-Christian
AC
Department of Radiotherapy, Martin Luther University of Halle-Wittenberg, Halle, Germany. arndt.mueller@medizin.uni-halle.de
Pigorsch
Steffi
S
Beyer
Claus
C
Lautenschläger
Christine
C
Dunst
Jürgen
J
D000328:Adult; D000469:Alkaline Phosphatase / Q000378:metabolism; D004999:Amifostine / Q000494:pharmacology*; D020552:Comet Assay; D004249:DNA Damage; D004260:DNA Repair / Q000528:radiation effects; D005260:Female; D006801:Humans; D008214:Lymphocytes / Q000187:drug effects* / Q000528:radiation effects; D008297:Male; D011837:Radiation-Protective Agents / Q000494:pharmacology*; D012016:Reference Values; D014965:X-Rays
D011837:Radiation-Protective Agents; D000469:Alkaline Phosphatase; D004999:Amifostine