Taxol Mechanism of action

Taxol (paclitaxel)is anticancer drug which was produced natually .Taxol is a mitotic inhibitor used in cancer chemotherapy. It was discovered in a National Cancer Institute program at the Research Triangle Institute in 1967 when Monroe E. Wall and Mansukh C. Wani isolated it from the bark of the Pacific yew tree, Taxus brevifolia and named it 'taxol'.
Paclitaxel is now used to treat patients with lung, ovarian, breast cancer, head and neck cancer, and advanced forms of Kaposi's sarcoma. Paclitaxel is also used for the prevention of restenosis.

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The anti-cancer drug Taxol works by interfering with processes within cells. The way in which Taxol binds to microtubule and prevents cell division is shown in this animation.

Taxol works by interfering with normal microtubule breakdown during cell division. Together with docetaxel, it forms the drug category of the taxanes. It was the subject of a notable total synthesis by Robert A. Holton.
Mechanism of action
Taxol interferes with the normal function of microtubule breakdown. Whereas drugs like colchicine cause the depolymerization of microtubules, paclitaxel arrests their function by having the opposite effect; it hyper-stabilizes their structure. This destroys the cell's ability to use its cytoskeleton in a flexible manner. Specifically, paclitaxel binds to the β subunit of tubulin. Tubulin is the "building block" of microtubules, and the binding of paclitaxel locks these building blocks in place. The resulting microtubule/paclitaxel complex does not have the ability to disassemble. This adversely affects cell function because the shortening and lengthening of microtubules (termed dynamic instability) is necessary for their function as a mechanism to transport other cellular components. For example, during mitosis, microtubules position the chromosomes during their replication and subsequent separation into the two daughter-cell nuclei.

Further research has indicated that paclitaxel induces programmed cell death (apoptosis) in cancer cells by binding to an apoptosis stopping protein called Bcl-2 (B-cell leukemia 2) and thus arresting its function.
In addition to stabilizing microtubules paclitaxel may act as a molecular mop by sequestering free tubulin effectively depleting the cells supply of tubulin monomers and/or dimers. This activity may trigger the aforementioned apoptosis.
One common characteristic of most cancer cells is their rapid rate of cell division. In order to accommodate this, the cytoskeleton of a cell undergoes extensive restructuring. Paclitaxel is an effective treatment for aggressive cancers because it adversely affects the process of cell division by preventing this restructuring. Cancer cells are also destroyed by the aforementioned anti-Bcl-2 mechanism. Other cells are also affected adversely, but since cancer cells divide much faster than non-cancerous cells, they are far more susceptible to paclitaxel treatment.

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