Radioprotection of colony forming units-spleen against heavy charged particle damage by WR 2721

WR2721 is known to protect a wide range of normal tissues against low LET radiation damage. Recently, protection against fission neutron damage to the gastrointestinal tract by thiophosphates was also demonstrated. The present study was undertaken to determine the LET dependence of the radioprotective effect of WR2721 on CFU-S using heavy charged particles. Donor CB/sub 6/Fl mice were given total body doses of /sup 40/Ar (330 MeV/μ) or /sup 28/Si (670 MeV/μ) ions in the plateau region of the Bragg curve 30 minutes after an IP dose of 400 mg/kg of WR2721. Marrow collected 30 to 90 minutes after irradiation was transplanted into supralethally irradiated syngeneic recipients and the CFU-S survival curves were computed. Results from replicate experiments with /sup 40/Ar ions (LET -- 130 keV/μm) show WR 2721 produced a significant increase in the D/sub 0/ and a DMF of 1.2. Preliminary results with /sup 28/Si ions (LET -- 50 keV/μm) indicate a DMF greater than 1.2. Additional experiments are in progress and DMF estimates for /sup 28/Si and /sup 20/Ne ions are presented