Taxanes: Paclitaxel and Docetaxel

Taxanes are antineoplastic agents — paclitaxel was originally isolated from the Pacific yew (Taxus brevifolia) — that bind microtubules and stabilise them. Unlike the destabilising vinca alkaloids, taxanes lock microtubules in place, suppressing the dynamics the mitotic spindle requires and arresting dividing cells.

Definition

Taxanes are microtubule-stabilising antineoplastic drugs that bind the taxane site on beta-tubulin, promote and stabilise microtubule assembly, suppress microtubule dynamics, and thereby block cells in mitosis.

Scope

This topic covers the taxane mechanism of microtubule stabilisation, the two principal agents paclitaxel and docetaxel, and the characteristic toxicities (notably peripheral neuropathy and myelosuppression) and hypersensitivity considerations that arise from the class. It is a mechanism-and-pharmacology reference, not a prescribing guide.

Core questions

• How does taxane binding stabilise microtubules, and why does stabilising them still kill dividing cells?
• How do paclitaxel and docetaxel relate as members of the same class?
• Why do taxanes share neuropathy with the vinca alkaloids despite an opposite effect on microtubule polymer mass?
• What is the basis of taxane hypersensitivity and resistance?

Key concepts

• Taxane binding site on beta-tubulin
• Microtubule stabilisation (suppressed depolymerisation)
• Suppression of microtubule dynamics
• Mitotic arrest via the spindle assembly checkpoint
• Paclitaxel versus docetaxel
• Peripheral neuropathy and myelosuppression
• Hypersensitivity related to formulation vehicle

Mechanisms

Taxanes bind a site on beta-tubulin and promote the assembly of microtubules while inhibiting their disassembly, increasing polymer stability (Schiff, Fant, & Horwitz, 1979). Although this is the opposite of the depolymerising vinca alkaloids in terms of polymer mass, the consequence is the same in principle: the dynamic instability that spindle microtubules need is suppressed, chromosomes cannot segregate, and the spindle assembly checkpoint holds cells in mitosis, leading to cell death (Jordan & Wilson, 2004). Paclitaxel and docetaxel are the two principal taxanes; like the vinca alkaloids, their action on neuronal microtubules contributes to peripheral neuropathy, and the class is also associated with myelosuppression and, for some formulations, hypersensitivity reactions linked to the solubilising vehicle (Rowinsky & Donehower, 1995).

Clinical relevance

Taxanes are widely used cytotoxic agents across several common cancers, and their stabilising mechanism explains both their antitumour activity and their characteristic neuropathy. This entry describes mechanism, class members, and toxicity patterns at a reference level; it does not provide dosing, premedication protocols, or individualised treatment decisions, which belong to specialist oncology care.

Evidence & guidelines

The mechanistic and pharmacological account draws on the original demonstration of taxane action and on authoritative clinical and cell-biology reviews (Schiff et al., 1979; Jordan & Wilson, 2004; Rowinsky & Donehower, 1995). Clinical use, premedication, and monitoring for specific taxanes follow oncology guidelines outside the scope of this topic.

History

Paclitaxel (taxol) was isolated from the bark of the Pacific yew and its structure reported in 1971 (Wani et al., 1971); the discovery that it acts by promoting and stabilising microtubule assembly, reported by Schiff, Fant, and Horwitz in 1979, revealed a novel mechanism distinct from the destabilising alkaloids and established the taxanes as a major drug class (Schiff et al., 1979).

Key figures

• Susan Band Horwitz
• Peter B. Schiff
• Monroe E. Wall
• Mansukh C. Wani
• Eric K. Rowinsky

Seminal works

• schiff-1979
• wani-1971
• jordan-wilson-2004

Frequently asked questions

If taxanes stabilise microtubules and vinca alkaloids destabilise them, why do both arrest cells in mitosis?

Both shift microtubules away from the normal dynamic instability the mitotic spindle needs; whether the polymer is over-stabilised or destabilised, chromosomes cannot segregate properly and the spindle assembly checkpoint blocks the cell in mitosis.

What are paclitaxel and docetaxel?

They are the two principal taxane drugs; paclitaxel was the first, isolated from the Pacific yew, and docetaxel is a related semisynthetic taxane, both acting by stabilising microtubules.