"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.