Paclitaxel, Molecular model of the chemotherapy drug paclitaxel (Taxol). Paclitaxel was first isolated from the bark of the Pacific yew tree (Taxus brevifolia), but is now made synthetically. The drug acts by stabilising microtubules, part of the cell cytoskeleton involved in cell division. The microtubules become unable to disassemble and so cannot move chromosomes around the cell. Paclitaxel is used to treat ovarian, breast and non-small cell lung cancer. Atoms are represented as spheres and are colour-coded: carbon (black), nitrogen (blue) and oxygen (red).