Accumulation of estramustine and estromustine in adipose tissue of rats and humans

The tissue distribution of estramustine and estromustine, two cytotoxic lipophilic metabolites of estramustine phosphate (Estracyt, EMP) was studied in rats and humans. A single dose of [3H]-estramustine was given i.v. to groups of rats. At 24 h after administration, the concentration of radioactivity in fat was about 20, 12, and 2 times that in muscle, plasma, and liver, respectively. Liquid chromatography verified that the radioactivity represented estramustine and estromustine. The clinical relevance of these results was investigated in pancreas cancer patients treated with a single oral dose of Estracyt at 12-16 h before surgery. As judged by gas chromatography, the concentration of estromustine, which is the main metabolite in man, was about 13 times higher in fat than in plasma and was also higher in adipose tissue than in muscle and liver. After 5 days of Estracyt treatment, the adipose uptake of estromustine was even higher, namely, about 40 times that in plasma and 8 times that in muscle and liver. Thus, our results demonstrate that estramustine and estromustine are stored in adipose tissue after the administration of EMP; this is important for the pharmacokinetics and, consequently for the therapeutic effects of Estracyt.