Estramustine Phosphate Sodium

Estramustine phosphate sodium is a unique antineoplastic agent that acts as a microtubule inhibitor through its metabolites, estramustine and estromustine. These metabolites accumulate in human prostatic tissue and bind to microtubule-associated proteins and tubulin, disrupting normal microtubule activity, and also bind to the RNA-protein network of the nuclear matrix, interfering with DNA replication. As a single agent, estramustine phosphate has demonstrated cytostatic and anti-invasive activity in vitro. The drug also exerts hormonal effects through estrone and estradiol, which are products of estramustine phosphate metabolism, resulting in reduced testosterone levels.
In combination with vinblastine, paclitaxel, docetaxel, or etoposide, estramustine phosphate demonstrated synergistic cytotoxicity in specific prostate cancer cell lines. In patients with hormone-refractory prostate cancer, estramustine phosphate-based regimens produced PSA response rates of 48 to 67 percent with taxanes, which were significantly greater than comparator regimens.

Fig. 1 Efficacy of estramustine phosphate in combination therapy. (Simpson D, Wagstaff A J. 2003)