[Hydrophilic regulator hexapeptides as inhibitors of tumor cell multiple drug resistance].

Multiple drug resistance (MDR) of tumor cells to cytostatics is one of the most often and severe complications of chemotherapy in oncological patients. The phenomenon of MDR could be due to a sharp increase of the activity of the ATP-dependent transport proteins of the ABC system, that provides pumping of the drug from the cells to the extracellular space. Up to now, all the attempts to design agents preventing MDR were of no success. One of the prospective trends is the use of hydrophilic regulator hexapeptides. Three regulator hydrophilic hexapeptides of the linear and cyclic structure were used as the MDR modulators. The sensitivity of the tumor cells to various cytostatics in the presence of the peptides was determined by the MTT-test and the direct counting of the survived cells. The effect of the hexapeptides on MCF7, KB8-5 and PC3 cells was investigated. It was concluded that the hydrophilic hexapeptides of the linear and cyclic structure increased the sensitivity to doxorubicin (a cytostatic). The tumor cell MDR inhibition was mediated by the ATP-dependent transport protein MRP. Such a characteristic of the hexapeptides is of interest for their use as agents preventing MDR.