Biodistribution and scintigraphy of 11C-toremifene in rats bearing DMBA-induced mammary carcinoma.

A new antioestrogenic antitumour compound toremifene was labeled with 11C or 3H. The tissue distribution and tumour uptake of the compounds in DMBA induced breast tumour bearing rats was investigated. 11C-toremifene was localized by gamma camera scintigraphy and tissue counting. 3H-Toremifene was determined by liquid scintillation counting after oxidizing the tissue samples. Toremifene was distributed to several tissues due to the lipophilicity and was not taken up specifically by the tumours to any great extent. However, the radioactivity of the tumours increased as a function of time although it declined e.g. in the liver. The accumulation to the tumour was a slow process and cannot be followed up reliably by such short half-life radionuclides as 11C. The tumour uptake properties of toremifene resemble those of tamoxifen and several other oestrogen receptor binding compounds. These substances have limited use in diagnosing and imaging oestrogen receptor rich breast tumours in man.