2.3. Mode of action
The mode of action of PPT is to polymerize tubulin, thus destabilize mitotic-spindles microtubules and prevent cell division. Various semi-synthetic products of PPT, such as etoposide and, teniposide act directly on the enzyme topoisomerase II and form an irreversible enzyme-DNA complex resulting n DNA double-strand breaks (Hartmann and Lipp, 2006). Both inhibitory effects of PPT on microtubulin formation and topoisomerase II are depicted in Fig. 3 .