One of the most widely used chemotherapy agents
Paclitaxel is an anti-cancer drug, also known as Taxol and Onxol. The drug is first-line treatment for ovarian, breast, lung, and colon cancer and second-line treatment for AIDS-related Kaposi’s sarcoma. It is so effective that some oncologists refer to the period before 1994 as the "pre-Taxol" era for treating breast cancer.
Paclitaxel is classified as an antimicrotubule agent; it stops the growth of the cancer by inhibiting multiplication of malignant cells. During mitosis, the cell uses structures called microtubules to move around the chromosomes. This class of chemotherapy drug works by throwing a wrench into the G2-Phase and M-Phase of the cell cycle.
Taxol is typically administered intravenously. (Oral administration has been demonstrated but is rarely used.) It is supplied as a clear, viscous, non-aqueous concentrate, in 30mg/5 ml to 30mg/50ml multi dose vials. The diluted solution is stable at ambient temperatures and room lighting conditions for 24 hours. Normal IV tubing and filters are employed.
The drug goes throughout the body ("systemic") and gets in all tissues and fluids, which can lead to negative side effects. For some cancers, oncologists put the Taxol in a bodily cavity to concentrate its effect in one part of the body.
A common regimen would be 175 mg / m2 delivered over 3 hours every 3 weeks for 4 cycles in combination with another chemotherapy agent. Severe hypersensitivity reactions occur in 2-4% of patients. (Fatal reactions have occurred but are rare.)
Related to paclitaxel is docetaxel. Both are grouped in the taxane chemotherapy drug class. Docetaxel (taxorene) is made from a chemical extracted from the leaves of the European yew tree, Taxus baccata. This source is more plentiful and renewable than the Pacific Yew bark that paclitaxel was originally derived from, and the high cost and scarcity of paclitaxel in the early days was a spur to research that led to docetaxel.
A Bioprospecting Success Story
Paclitaxel is one of the most recognizable, celebrated, and controversial products in the fight against cancer. Some have called paclitaxel a miracle drug. Since doctors started using it for the treatment of breast cancer, the survival rate has doubled. (This increase in survival rate is not all due to the paclitaxel.) Paclitaxel as a commercial product has received the ire of conservationists, holds records for sales volume, and has been the subject of public debate and congressional hearings. Its discovery and development as a drug is a fascinating story of chance, intuition, expensive risk taking, perseverance, and success.
After a study of medicinal herbs and folkloric knowledge, extracts from juniper trees were found to have some anti-cancer properties. This led to a search for more active conifers. In 1962, a botanist working for the US Department of Agriculture in Washington State was sampling trees with “cancer plant” potential. The 1645th plant sample collected was a Pacific Yew tree. This tree is a very slow growing hardwood that grows in the shadows of giant conifers and has long been considered a “trash tree”. The tree has very few pests because almost every part of the tree is poisonous. Historically, the wood from the Yew tree has been good for making bows as well as poison arrows; it is associated with death. The Latin name Taxus brevifolia is related to the word "toxin".
In addition to the brand name Taxol, Paclitaxel is sold in Canada under the names Abraxane® and Apo-Paclitaxel®. In Mexico it goes by the names Aclixel, Asotax, Bristaxol, Cryoxet, and Praxel .