The l-alanine ester form of estramustine, a combination of the nitrogen mustard normustine coupled via a carbamate to estradiol, with antineoplastic activity. Upon conversion of alestramustine to estramustine, estramustine binds to microtubule-associated proteins (MAPs) and beta tubulin, thereby interfering with microtubule dynamics and leading to microtubule disassembly and cell cycle arrest. Due to the estrogen moiety, this agent is able to selectively bind to and be taken up by estrogen receptor-positive cells.