THE RADIOPROTECTOR WR-2721 REDUCES NEUTRON-INDUCED MUTATIONS AT THE HYPOXANTHINE GUANINE PHOSPHORIBOSYL TRANSFERASE LOCUS IN MOUSE SPLENOCYTES WHEN ADMINISTERED PRIOR TO OR FOLLOWING IRRADIATION

An in vitro T-lymphocyte cloning technique has been applied to study the effects of JANUS fission-spectrum neutron irradiation and the radioprotector S-2-(3-aminopropylamino) ethylphosphorothioic acid (WR-2721) on the subsequent development of somatic mutations at the hypoxanthine-guanine phosphoribosyl transferase (hprt) locus in hybrid B6CF1 male mice. In control studies performed to establish an in vitro cloning technique, the mutant frequencies of splenic T-lymphocytes, as a result of exposure to a 100 cGy dose of neutrons, increased with time from a control level of 9 x 10(-7) to a maximum value of 1.7 x 10(-5) at 56 days following irradiation. Between 56 and 150 days after irradiation, mutant frequencies were observed to plateau and remain stable. All subsequent determinations were performed at 56 days following the experimental treatment of animals. WR-2721 at a dose of 400 mg/kg was effective in protecting against the induction of hprt mutants (i.e. a mutant frequency reduction factor, MFRF) following the largest dose of neutrons used (i.e. 150 cGy), whether it was administered i.p. 30 min before, 5 min after, 3 h after, or three times at 3, 24, and 48 h after, as evidenced by MFRFs of 6.0, 6.6, 4.8 and 5.8 respectively. The antimutagenic effectiveness of WR-2721 administered 30 min prior to irradiation was unaffected, even when the dose was reduced to 200 mg/kg, MFRF = 7.0; 100 mg/kg, MFRF = 3.8; and 50 mg/kg, MFRF = 8.9. These findings confirm our earlier report using the radioprotector N-(2-mercaptoethyl)-1,3-diaminopropane (WR-1065) under in vitro conditions, and demonstrate that these agents can be used as effective antimutagens even when they are administered up to 3 h following radiation exposure.