Amifostine (WR-2721) selective protection against melphalan genotoxicity

Amifostine (WR-2721) is an aminothiol compound dephosphorylated at the tiss ue site by alkaline phosphatase to the active metabolite, which is able to inactivate electrophilic substances and scavenge free radicals. Amifostine effects against melphalan-induced DNA strand breaks were studied in normal human white blood cells (WBC) and K562 leukemic cells using the single cell gel electrophoresis (SCGE) or Comet assay, a reported method for measuring DNA damage in individual cells. Prior to treatment (1 h, 37 degrees C) wit h increasing doses of melphalan, with or without S9, the cells were treated (15 min, 37 degrees C) with a control medium or amifostine (3 mg/ml). Trea tment of normal and leukemic cells with melphalan induced a dose-dependent 'comet formation'. Melphalan-induced DNA damage follows a normal distributi on in WBC. On the other hand, in K562, a significant proportion of undamage d cells remains even with doses at which mean DNA damage is serious. Pretre atment with WR-2721 protects WBC, but not K562, against the genotoxic effec t of melphalan, Amifostine might even strengthen the action of the antiblas tic drug against K562 cells. S9 addition appears to enhance melphalan effec tiveness. SCGE appears as a suitable primary screening method for in vitro and in vivo studies on drug-DNA interactions and their modulations by endog enous/exogenous factors.