The antineoplastic agent estramustine and the derivative estramustine-phosphate inhibit secretion of interleukin-3 in leukemic cells. Possible roles of MAPs

The compound 14-keto-stypodiol diacetate from the algae Stypopodium flabelliforme inhibits microtubules and cell proliferation in DU-145 human prostatic cells

We investigated the effects of the drug 14-keto-stypodiol diacetate (SDA) extracted from the seaweed product Stypopodium flabelliforme, in inhibiting the cell growth and tumor invasive behavior of DU-145 human prostate cells. In addition, the molecular action of the drug on microtubule assembly was analyzed. The effects of this diterpenoid drug in cell proliferation of DU-145 tumor cells in culture revealed that SDA at concentrations of 5 microM decreased cell growth by 14%, while at 45 microM a 61% decrease was found, as compared with control cells incubated with the solvent but in the absence of the drug. To study their effects on the cell cycle, DU-145 cells were incubated with increasing concentrations of SDA and the distribution of cell-cycle stages was analyzed by flow cytometry. Interestingly, the data showed that 14-keto-stypodiol diacetate dramatically increased the proportion of cells in the G2/M phases, and decreased the number of cells at the S phase of mitosis, as compared with appropriate controls. Studies on their action on the in vitro assembly of microtubules using purified brain tubulin, showed that SDA delayed the lag period associated to nucleation events during assembly, and decreased significantly the extent of polymerization. The studies suggest that this novel derivative from a marine natural product induces mitotic arrest of tumor cells, an effect that could be associated to alterations in the normal microtubule assembly process. On the other hand, a salient feature of this compound is that it affected protease secretion and the in vitro invasive capacity, both properties of cells from metastases. The secretion of plasminogen activator (u-PA) and the capacity of DU-145 cells to migrate through a Matrigel-coated membrane were significantly inhibited in the presence of micromolar concentrations of SDA. These results provide new keys to analyze the functional relationships between protease secretion, invasive behavior of tumor cells and the microtubule network.

The secretion of urokinase-like plasminogen activator is inhibited by microtubule-interacting drugs

The secretion of proteinases into the extracellular matrix is one of the main features of tumour cells, as related to their invasive behaviour. Considering the role of the microtubule cytoskeleton, and particularly the action of microtubule-associated protein (MAPs) in mediating protein secretion, the effects of the anti-microtubule drugs estramustine and taxol, on the secretion of urokinase-type plasminogen activator (u-PA) and the 72 kDa gelatinase were investigated. Treatment of 5637 bladder carcinoma cells with estramustine and taxol inhibited u-PA secretion into the conditioned medium in a drug concentration-dependent fashion. This inhibition was confirmed by determinations of u-PA enzymatic activities and by measurements of the levels of immunoreactive activator. Studies using gelatin zymograms also showed an inhibition of another tumoural proteinase namely the 72 kDa gelatinase. Time-course uptake experiments showed that estramustine was incorporated into the cells, a process which depended on temperature. On the other hand, immunofluorescence studies indicated that the microtubule network was affected by taxol with the formation of bundles of microtubules at different cell domains. Minor effects were visualized after treatment of the cells with estramustine-phosphate, a drug that blocks primarily the action of microtubule-associated proteins. The studies provide a way to analyse the relationships between u-PA secretion and the integrity of the cytoskeletal network.