Monastrol

Monastrol does not inhibit progression through S and G2 phases of the cell cycle or centrosome duplication. The mitotic arrest due to monastrol is also rapidly reversible. Monastrol also inhibits bipolar spindle formation in Xenopus egg extracts. Monastrol arrests cells in mitosis with monoastral spindles comprised of a radial array of microtubules surrounded by a ring of chromosomes while it does not affect microtubules in interphase cells or microtubule polymerization in vitro^[1]. Exposure of cultured sympathetic neurons to monastrol for a few hours increases both the number and the growth rate of the axons. With additional time, the overall lengths of the axons are indistinguishable from controls. Sensory neurons shows a similar short-term increase in axonal growth rate. However, prolonged exposure results in shorter axons, suggesting that sensory neurons may be more sensitive to toxic effects of the drug. Nevertheless, the overall health of the cultures is still far more robust than cultures treated with taxol, a drug commonly used for anti-cancer therapy^[2]. In HeLa cells, monastrol activates the spindle checkpoint, leading to mitotic arrest and apoptosis^[3].

For the double thymidine arrest, exponentially growing BS-C-1 cells are cultured for 16 h in normal growth medium containing 2 mM thymidine. After this, the cells are released into normal growth medium supplemented with 24 μM deoxycytidine for 9 h. The second thymidine block is imposed for 16 h during which the cells were maintained in serum-free medium containing 2 mM thymidine. Finally, the cells are released into normal growth medium containing 24 μM deoxycytidine to which is added either 100 μM monastrol or 0.1% DMSO. To assess the reversibility of the effect of monastrol and nocodazole treatment, BS-C-1 cells plated on coverslips are treated for 4 h in normal growth medium containing either 2 μM nocodazole or 100 μM monastrol and then released into normal medium. At the different time points, coverslips are processed for immunofluorescence and the cells in interphase or mitosis are counted and categorized.