Celllular Cycle

Many efficient frmacos against the cancer exert its action on the cells that if find in the cellular cycle, being called frmacos cycle-cellular specific (CCS). As a group of agents, called frmacos cycle-cellular not specific (CCNS), has the capacity of exterminar the tumorais cells independently to be crossing the cycle or to be in rest in the Go compartment (Graebin and Lima, 2006). Although so far to have postulate that the activity of anti-cancergenos frmacos can only be classified in agents cycle-cellular specific (CCS) or not specific cellular cycle (CCNS), it was observed more recently than, amongst this last, factor most important, for the antitumoral activity and potentiality for its use in the treatment of the different neoplasias, it is that the studied antitumorais most used and are agents who generally act as eletrfilos on nucleoflicas macro-molecules, particularly the DNA (Hahn and Weinberg, 2002). However, although to admit itself that these agents are not cycle-cellular specific, already it was observed that the cells are more sensible to the alquilao in phases G and S of the cellular cycle, presenting blockade in G2. These antitumorais agents comprovadamente form linkings crossed with ribbons or filaments of DNA, being able themselves to observe, the different types of crossed linkings that can occur (Hahn and Weinberg, 2002). All these linkings produce injuries in the DNA, being that provoked for the crossed linkings interfilamentares is most cytotoxic, therefore the alquilao of an only filament of DNA can easily until being repaired, but the linkings cruzades interfilamentares, with the produced ones for bifunctional alquilantes agents, demand more complex mechanisms of repairing, being able until inhibiting its response (Almeida et al., 2005). It has diverse classrooms of antineoplsicos agents who have this type of action mechanism: nitrogenadas mustards, nitrossurias, triazeno, alquilsulfonatos, complexes of platinum coordination and others. It fits to stand out, first, that these alquilantes agents are strong eletroflicos reagents, forming linkings crossed covalentes for reaction of alquilao with nucleoflicos centers of the DNA, mainly the purnicas and pirimidnicas bases (Rajski and Williams, 1998).

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