The effect of estramustine on microtubuli is different from the direct action via oxygen radicals on DNA and cell membrane
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R Henriksson1, L Bjermer, E Von Schoultz
1Department of Oncology, University Hospital, Umeå, Sweden.
Abstract:
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.
Insights
Estramustine (EM) exhibits cytotoxicity through DNA and cell membrane interactions, involving free oxygen radicals. However, colon cancer cells show resistance to its known mechanisms of action.
Area of Science:
- Oncology
- Molecular Biology
- Pharmacology
Background:
- Estramustine (EM), a conjugate of estradiol-17 beta and nornitrogen mustard, is a chemotherapeutic agent used for prostate cancer.
- Its precise mechanism of action remains incompletely understood, with prior hypotheses focusing on non-DNA targets like the mitotic spindle via the intact EM complex.
Purpose of the Study:
- To investigate the cytotoxic mechanisms of Estramustine (EM) in various cell systems.
- To elucidate the roles of DNA interaction, cell membrane damage, and free oxygen radicals in EM's cytotoxicity.
- To assess the resistance of colon cancer cells to proposed EM toxicity mechanisms.
Main Methods:
- Utilized monocyte phagocytosis, transformed fibroblasts, and colon cancer cells (HT-29) as model systems.
- Assessed DNA interaction using DNA precipitation assays with radiolabeled thymidine (3H and 14C).
- Measured cell membrane damage via 86Rb- accumulation and evaluated free oxygen radical involvement using metal chelators, radical scavengers, and an oxygen electrode.
Main Results:
- Estramustine (EM) demonstrated cytotoxicity through direct interaction with DNA and cell membranes.
- EM's effects on fibroblasts were mitigated by metal chelators and radical scavengers, suggesting free oxygen radical involvement.
- EM inhibited monocyte phagocytosis via engulfment, independent of radical scavengers, and neither EM component alone or combined affected this process.
- Colon cancer cell line HT-29 exhibited resistance to both microtubule-targeting and free-oxygen radical-mediated toxicity mechanisms of EM.
Conclusions:
- Estramustine (EM) exerts cytotoxicity via direct DNA and cell membrane interactions, potentially involving free oxygen radicals.
- Monocyte phagocytosis inhibition by EM is linked to engulfment and is not influenced by radical scavengers.
- Colon cancer cells display resistance to established Estramustine (EM) toxicity pathways, highlighting potential therapeutic limitations.