[Multidrug resistance of malignant tumors].

The development of resistance to chemotherapy is a major problem in the treatment of malignant tumors. Clinically, this is characterized by short periods of remission and failure to respond to subsequent therapy. Multidrug-resistance or pleiotropic resistance describes the simultaneous expression of cellular resistance to a vide range of structurally unrelated drugs (e.g. alkaloids, anthracyclines, antibiotics, etc.). The most frequently reported alteration of multidrug-resistant cells is the overexpression of a 170 kD glycoprotein (P--170 or P-glycoprotein) encoding by the MDR gene family. A great deal of evidence has suggested that the P-glycoprotein is, in fact, an energy-dependent drug efflux pump. Pharmacological overcome of MDR may indicate to circumvent clinically observed drug resistance.