Classical multidrug resistance

'Classical' drug resistance has been the most studied form of this phenomenon in the laboratory and results from overexpression of 170 KD glycoprotein known as p-glycoprotein. This spans the outer cell membrane and acts as an energy-dependent drug efflux pump. Thus, as the drug enters the tumour cell, by diffusion or transport, the drug in the interior of the cell is picked up and is effluxed into the extracellular environment. This reduces the effective concentration of the drug within the cell and allows the cell to express resistance to the agent in question.

The development of this form of resistance is most commonly associated with exposure to the anti-tumour antibiotics, the anthra-cyclines, taxanes and etoposide. In fact, resistance to one of this group of agents usually confers resistance to the other groups in addition, thereby leading to the phenomenon of'multi-drug resistance'.

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