Epothilone A (Epo A) is a microtubule-stabilizing agent with EC0.01 of 2 μM.

Tubulin:2 μM(EC0.01)

Epothilone A induces microtubule polymerization, causing cell cycle arrest at the G2-M phase, and exhibits cytotoxicity, as well as induces apoptosis. It effectively inhibits the proliferation of HCT116 cells with an IC50 of 4.4 nM. Epothilone A possesses cytotoxicity against KB3-1, KBV-1, Hela, and Hs578T cells with IC50 values ranging from 13 nM to 160 nM. Additionally, Epothilone A competitively binds to microtubules against paclitaxel, with an IC50 of 2.3 μM.

Tubulin polymerization assay: Samples for electron microscopy are placed on carbon-over-Parlodion-coated grids (300 mesh) and negatively stained with 2% uranyl acetate. Microtubule assembly in the presence or absence of Epothilone A is monitored spectrophotometrically by using a spectrophotometer equipped with a thermostatically regulated liquid circulator. The temperature is held at 35 °C and changes in turbidity (representative of polymer mass) are monitored at 350 nm. Effective concentration (EC0.01), defined as the interpolated concentration capable of inducing an initial slope of 0.01 OD/min rate, is calculated using the formula EC0.01 = concentration/slope.

Cell lines: KB3-1,KBV-1,Hela,and Hs578T cells. Concentrations: 0–2 μM. Method: cells are plated either in 48-well plates (for trypan blue and cell counting) or onto coverslips.After 24 hours,cells are treated with Epothilone A and are scored at regular intervals.For the cytotoxicity analysis,cells are counted and scored as trypan blue positive or negative.