PROTECTION AGAINST RADIATION-INDUCED MUTAGENESIS AT THE HPRT LOCUS BYSPERMINE AND ''-(DITHIODI-2,1-ETHANEDIYL)BIS-1,3-PROPANEDIAMINE (WR-33278)

The polyamine spermine and the disulfide N,N''-(dithiodi-2,1-ethanediy l)bis-1 ,3-propanediamine (WR-33278) are structurally similar agents c apable of binding to DNA. WR-33278 is the disulfide moiety of the clin ically studied radioprotective agent S-2-(3-aminopropylamino)ethylphos phorothioic acid (WR-2721). Because of their reported structural and f unctional similarities, it was of interest to compare their effects on cell survival and mutation induction at the hypoxanthine-guanine phos phoribosyl transferase (hprt) locus in Chinese hamster AA8 cells. WR-3 3278 and spermine (at concentrations of 0.01 and 0.001 mM) were electr oporated into cells. Electroporation, 300 V and 125 mu F, was performe d either 30 min prior to or 3 h following exposure of cells to 750 cGy of ionizing radiation. Electroporation alone reduced cell survival to 75% but had no effect on hprt mutation frequency. The electroporation of either spermine or WR-33278 at concentrations greater than 0.01 mM was extremely toxic. The exposure of cells to both electroporation an d irradiation gave rise to enhanced cell killing and mutation inductio n, with the sequence of irradiation followed 3 h later by electroporat ion being the more toxic protocol. Cell survival was only enhanced fol lowing electroporation of 0.01 mM of spermine and WR-33278 30 min prio r to irradiation. Protection against radiation-induced hprt mutations was observed for both spermine and WR-33278 under all experimental con ditions tested. Spermine at exposure concentrations of 0.01 and 0.001 mM administered 30 min before or 3 h after irradiation reduced mutatio n frequencies by factors of 2.2, 1.2, 1.9 and 2.2, respectively. WR-33 278 at concentrations of 0.01 and 0.001 mM administered 30 min or 3 h after irradiation with 750 cGy lowered mutation frequencies by factors of 1.8, 1.3, 1.4 and 2.0, respectively. These data suggest that the p roperties of radioprotection and chemoprevention exhibited by the phos phorothioate (WR-2721) and associated aminothiol WR-1065 and disulfide (WR-33278) metabolites may be mediated in part via endogenous spermin e-like polyamine processes (i.e. chromatin stabilization). Such a mech anism would have important implications with respect to the design and development of new generation drugs for use in radioprotection and ch emoprevention.