3. PLANT ALKALOIDS
These are anti-tumor agents derives from plants. The drugs in
this class are identified basing on where they were first identified
a) Vinca alkaloids
These were isolated from periwinkle plant. Examples
of drugs in this class are;
- Vincristin
- vinblastine and
- Vindesine.
They act by binding to tubulin (globular
proteins that polymerize into microtubules during cell division) and inhibiting
microtubule formation. This results in hindered cell division and therefore prevents
progression of cancer. They are mostly used in the treatment of hematologic and
sometimes non-hematologic cancers.
These drugs however are known for their
potential to cause neurotoxicity
See (General
principles of care in oncology)
b) Epipodophyllotoxins
It is a synthetic derivative of podophyllotoxin
an extract of mandrake plant. It works
by binding and forming a ternary complex with DNA and the topoisomerase II
enzyme (which aids in DNA unwinding), preventing re-ligation of the DNA
strands, and by doing so causes DNA strands to break. Cancer cells rely on this
enzyme more than healthy cells, since they divide more rapidly.
The only drug in this class is - Etoposide
c) Texans
Are derived from taxus (yews)
plants. They work by binding to tubulin (globular proteins that polymerize
into microtubules during cell division).
Taxanes cause hypersensitivity
reactions and patients should be premedicated with steroids, H1 and H2
antagonists prior to treatment.
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