Effects of Aminoethylisothiouronium Bromide and 5-Hydroxtryptamine on the Response of C3H Mammary Tumour Isografts to irradiationin vivo

Abstract

Both A.E.T. and 5-H.T. were found to inhibit the response of the isogenic mammary carcinoma to doses of radiation which are normally curative in unmedicated controls, reducing the cure-rate to about half of its control level. Total body irradiation (3 × 100 rads to the whole mouse in addition to local treatment of the tumour), also reduced the cure-rate to approximately the same degree. Combination of the two procedures, however, produced no additive effects; with application of the drugs, a trend towards an increasing cure-rate, slightly higher than that obtained in totally irradiated mice without medication, became evident. Direct trans-thoracic irradiation of both tumour and host tissues with the standard test dose of 7,500 rads was uniformly lethal to unprotected controls. It was noted, however, that 5-H.T. appeared to protect mice from the early mortality associated with the visceral phase of the post-irradiation syndrome, thus prolonging survival time, while A.E.T. reduced the overall mortality, presumably by protecting the haemopoietic system. It is concluded that, while A.E.T. is probably too toxic for clinical use, a trial of 5-H.T. may be justified in certain deep-seated cancers where adequate radiation dosage is precluded by the limited tolerance of adjacent viscera.