Quotes from Richard A. Harvey

Mechanism of action: Both drugs are active in the G2/M phase of the cell cycle. They bind reversibly to the ?-tubulin subunit, but unlike the vinca alkaloids, they promote polymerization and stabilization of the polymer rather than disassembly (Figure 39.27). Thus, they shift the depolymerization-polymerization process to accumulation of microtubules.