About 150 alkaloids have now been isolated from C.roseus,some for example,ajmalicine lochnerine,serpentine and tetrahydroalstonine occur in other genera of the family.A gouup of about 20 bisindole alkaloids which contains those having antineoplastic activity,including leurocristine(Vineristine) and vincaleukoblastine (Vinblastine).
Vinblastine is synthesized from two indole alkaloids catharanthine and vindoline both of which are present in free form.
Vincristine is structurally similar to vinblastine,but has a formyl group rather than a methyl on the indole nitrogen in the vindoline derived portion.
The plant produces a much higher amount of vinblastine but there is a more demand for vincristine rather than vinblastine.
Now it is possible to convert vinblastine into vincristine either chemically, or via a microbiological N-demethylation using streptomyces albogriseolus.
Vinblastine and vincristine bind tightly to tubulin and interfere with the functioning of the microtubule system which is a component of the mitotic spindle so arrest the cell division in metaphase vincristine has superior antitumor activity compared to vinblastine but is more neurotoxic.
It is a salt of an analkaloil extracted from catharenthus plant.It is unstable and is available in sealed ampules which stored in refrigerator to ensure the extended stability
It is also used for the treatment of generalized Hodgkin disease and Non-Hodgkin lymphomas. It is also used for breast cancer unresponsive to other therapies.
The usual does is given intravenously is a single dose of 3.7 mg/m2 of body surface for an adult 2.5mg/m2 for a child once weekly.Each succeeding dose is increased by increments of 1.8mg/m2 for adults and 1.5mg/m2 for a child once a week until a maximum dose is a reached as determined by a white-blood cell count.
Prescription product velban vincristine sulphate is also obtained from catharanthus.Despite the structural smilarities there are difference in the antitumor spectra of the to compounds and no cross resistance has been observed.
Vincristine sulphate is unstable, refrigerated storage in sealed ampules to ensure extended stability.
It is used for the treatment of acute lympocyticleukaemia in children.It has other application for lympomas,small cell lung cancer,cervical and breast cancers.
It is given intravenously at weekly intervals in dose of 1.4mg/m2 for adults and 2mg/m2 for children.
Vindesine (Eldisine) a semi synthetic derivatives of vinblastine is used in patients who have become resistant to vincristine and vinblastine.It is also used in the treatment of acute lymphoid leukemia in children.