Estramustine (EM), a complex between
estradiol-17 beta and
nornitrogen mustard, is commonly used in the treatment of
prostatic cancer. The exact mechanism of action is unknown but has previously been considered to be mediated through non-
DNA targets, specifically with the mitotic spindle, and to be related to the intact EM complex. In the present study, using different cell-systems (monocyte phagocytosis transformed fibroblasts,
colon cancer cells), the EM cytotoxicity was also found to involve direct interaxtion with
DNA and cell membranes. The interaction with
DNA was shown by
a DNA precipitation assay using 3H- and 14C-
thymidine, and the cell membrane damage by using 86Rb- accumulation as a sensitive marker for active
potassium uptake. EM effects in the fibroblasts were inhibited by various
metal chelators and radical scavengers. Involvement of free
oxygen radicals was further indicated in a cell-free system with an
oxygen electrode. The EM inhibition of monocyte phagocytosis was related to the engulfment, and was not at all influenced by radical scavengers. In contrast to EM, neither of its components alone, or together, affected monocyte engulfment. Finally, it was shown that the
colon cancer cell-line HT-29 was resistant to both of the two suggested and separate mechanisms for EM toxicity: an interaction with the microtubuli system by the intact EM complex and a more unspecific action mediated by free-
oxygen radicals.