page_title: Chemotherapy
section_title: Anti-microtubule agents
hierarchical_section_title: Chemotherapy / Treatment strategies / Types / Anti-microtubule agents
caption_attribution_description: English: Microtubules are hollow tubular structures found within cells. They are formed from heterodimers alpha- and beta-tubulin. Anti-cancer drugs target these structures by either preventing their assembly or disassembly. This leads to defective mitosis.
context_page_description: Chemotherapy is a type of cancer treatment that uses one or more anti-cancer drugs as part of a standardized chemotherapy regimen. Chemotherapy may be given with a curative intent, or it may aim to prolong life or to reduce symptoms. Chemotherapy is one of the major categories of the medical discipline specifically devoted to pharmacotherapy for cancer, which is called medical oncology.
  The term chemotherapy has come to connote non-specific usage of intracellular poisons to inhibit mitosis or induce DNA damage, which is why inhibition of DNA repair can augment chemotherapy. The connotation of the word chemotherapy excludes more selective agents that block extracellular signals. The development of therapies with specific molecular or genetic targets, which inhibit growth-promoting signals from classic endocrine hormones are now called hormonal therapies. By contrast, other inhibitions of growth-signals like those associated with receptor tyrosine kinases are referred to as targeted therapy.
context_section_description: Anti-microtubule agents are plant-derived chemicals that block cell division by preventing microtubule function. Microtubules are an important cellular structure composed of two proteins; α-tubulin and β-tubulin. They are hollow, rod-shaped structures that are required for cell division, among other cellular functions. Microtubules are dynamic structures, which means that they are permanently in a state of assembly and disassembly. Vinca alkaloids and taxanes are the two main groups of anti-microtubule agents, and although both of these groups of drugs cause microtubule dysfunction, their mechanisms of action are completely opposite. The vinca alkaloids prevent the formation of the microtubules, whereas the taxanes prevent the microtubule disassembly. By doing so, they prevent the cancer cells from completing mitosis. Following this, cell cycle arrest occurs, which induces programmed cell death (apoptosis). Also, these drugs can affect blood vessel growth; an essential process that tumours utilise in order to grow and metastasise.
  Vinca alkaloids are derived from the Madagascar periwinkle, Catharanthus roseus (formerly known as Vinca rosea). They bind to specific sites on tubulin, inhibiting the assembly of tubulin into microtubules. The original vinca alkaloids are natural products that include vincristine and vinblastine. Following the success of these drugs, semi-synthetic vinca alkaloids were produced: vinorelbine (used in the treatment of non-small-cell lung cancer), vindesine, and vinflunine. These drugs are cell cycle-specific. They bind to the tubulin molecules in S-phase and prevent proper microtubule formation required for M-phase.
  Taxanes are natural and semi-synthetic drugs. The first drug of their class, paclitaxel, was originally extracted from the Pacific Yew tree, Taxus brevifolia.  Now this drug and another in this class, docetaxel, are produced semi-synthetically from a chemical found in the bark of another Yew tree; Taxus baccata. These drugs promote microtubule stability, preventing their disassembly. Paclitaxel prevents the cell cycle at the boundary of G2-M, whereas docetaxel exerts its effect during S-phase. Taxanes present difficulties in formulation as medicines because they are poorly soluble in water.
  Podophyllotoxin is an antineoplastic lignan obtained primarily from the American Mayapple (Podophyllum peltatum) and Himalayan Mayapple (Podophyllum hexandrum or Podophyllum emodi). It has anti-microtubule activity, and its mechanism is similar to that of vinca alkaloids in that they bind to tubulin, inhibiting microtubule formation. Podophyllotoxin is used to produce two other drugs with different mechanisms of action: etoposide and teniposide.
caption: Vinca alkaloids prevent the assembly of microtubules, whereas taxanes prevent their disassembly. Both mechanisms cause defective mitosis.
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