Plant 87

Catharanthus roseus (L.) G.Don (Apocynaceae)


Rosy periwinkle

The name Lantana is derived from the Latin name of the unrelated wayfaring tree (Viburnum lantana) which has flowers that look similar to those of Lantana. The genus comprises about 150 species from the Americas and Africa, although one of the most familiar is Lantana camara.

Catharanthus roseus is endemic to Madagascar where it is endangered in the wild. It is however widespread across the tropics and sub-tropics, where it has become naturalised and is even considered an invasive weed in some areas. Rosy periwinkle is an evergreen subshrub that is easy to grow from seed or propagate by cuttings. In temperate areas it is valued as a summer bedding plant for its relative drought tolerance and long flowering season.

In the 1950s, Clark Noble sent his brother Robert an envelope containing 25 rosy periwinkle leaves. Clark Noble had received them from a patient of his in Jamaica who said that the local people were using the leaves of this plant to make a tea to treat themselves for diabetes when insulin was unavailable. Robert Noble was the Associate Director of the Collip Medical Research Laboratory at the University of Western Ontario and was researching endocrine-related cancers.

When the rosy periwinkle leaves were tested, no anti-diabetic activity was found but it was observed that the test animals suffered from depleted white blood cell levels. This suggested the plant could have potential as an anti- cancer agent and so the search began for the active constituent(s). In 1954, the British chemist, Charles Beer, who had received his doctorate in organic chemistry from the University of Oxford in 1948, joined Robert Noble's research group and set about isolating the active component. The two main chemicals responsible for biological activity were isolated and identified as vincristine and vinblastine. In collaboration with the pharmaceutical company Eli Lily these two drugs have since been rigorously tested and proven to be very effective. Vincristine was approved by the United States' Federal Drugs Administration in 1963.

Vincristine and vinblastine work by inhibiting the assembly of microtubule structures, which arrests the cell cycle in the metaphase. These drugs are important components of many chemotherapy regimens. Vincristine is especially important for the treatment of childhood leukaemia. The chemical structures are very complicated and, although total synthesis has been achieved in the laboratory, it is not a commercially viable process. Even though the plants only contain very small quantities of the chemicals, they are farmed commercially in places such as Texas, USA in order to extract the chemicals. Vincristine makes up 0.0003% of the dry weight of the plant, whilst vinblastine is more abundant at 0.01%. Fortunately vinblastine can be changed into vincristine by chemical transformation.

Further reading

Swerlow, JL 2000. Nature's medicine: plants that heal. National Geographic, pp. 218-221.

van Bergen M and Snoeijer W 1996. Catharanthus G.Don. The Madagascar periwinkle and related species. Wageningen Agricultural University Papers 96-3: 1-120.

Alison Foster