July 13, 2010

MRCP 1 Question 18

Currently it is known that antitumor agents can arrest cell division by one or several mechanisms.

What mode of action is implicated in the use of vinblastine as an antitumor agent?
a) Microtubule Interference
b) Topoisomerase Catalytic Inhibition
c) DNA Alkylation
d) DNA Inhibition
e) Protein Synthesis Inhibition

The correct answer is A


Microtubules are dynamic, polymeric structures, which (besides other biological functions) are major constituents of the mitotic spindle, the latter being essential for the separation of chromosomes during mitosis.

Chemically, they are polymers of certain heterodimers of alpha- and beta-tubuline.

A range of secondary metabolites of plants interfere with the process of assembling and disassembling of microtubules, resulting in the arrest of cells in mitosis and apoptosis.

The most significant are the Vinca alkaloids, colchicine, maytansine, and paclitaxel.

Both Vinca alkaloids (vincristine, vinblastine, and especially the second generation vinorelbine) and taxanes (paclitaxel, and especially docetaxel), largely used as antitumor agents in the conventional treatment of lung cancer, are derived by semisynthesis of natural plant compounds.

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