Evaluation of radio- and chemotoxic effects of 125I-UdR on tumour growth and host survival.

The toxicity of 5-iodo-2'-deoxyuridine (I-UdR) was assayed in male C57 BL/6J mice bearing the syngeneic mammary adenocarcinoma EO 771 by injecting different doses of 'cold' I-UdR or 125-iodine labelled I-UdR. Host survival, tumour growth, DNA-precursor incorporation, whole-body retention and tumour activity loss rates were chosen as biological end points. There was no measurable effect on host survival up to doses of 5 micrograms I-UdR or 50 microCi 125I-UdR per mouse during a mean life-span of 25 days. Adjusted to a constant amount of 0.55 micrograms I-UdR/mouse, radiotoxicity of 125I-UdR on tumour growth (up to 17 days after implantation), tracer incorporation, whole-body and tumour retention (up to 12 days after 125I-UdR injection) could be excluded up to a dosage of 50 microCi 125I-UdR/mouse. It is concluded that in situ evaluation of tumour activity loss rates in carcinoma EO 771 is not disturbed by toxic effects of I-UdR or 125I-UdR within the dose limits mentioned.