ORAL VEHICLE ADMINISTRATION BEFORE RADIATION CAUSES RADIOPROTECTION OF MURINE SCCVII TUMORS

The effect of administering various vehicles on the response to radiat ion of SCCVII tumors in C3H mice was investigated. When saline, 0.5% c arboxymethyl cellulose solution, or 1% hydroxypropylmethyl cellulose ( HPMC) solution was given orally 30 min before single 15 Gy irradiation , the tumor regrowth was significantly faster than that seen after 15 Gy treatment alone. There was no difference in this radioprotective re sponse due to the type of vehicle. On the other hand, the tumor regrow th was similar to that seen after 15 Gy alone when saline was given in travenously 20 min before irradiation or intraperitoneally 30 min befo rehand, or when 1% HPMC was given orally 2 h beforehand. Oral vehicle administration shortly before irradiation can cause radioprotection of murine tumors, probably by increasing the hypoxic fraction.