The impact of the induction of multidrug resistance transporters in therapies by used drugs: recent studies

Multidrug resistance (MDR) against groups of therapeutic drugs emerged to a central problem in the treatment of various diseases, i.e. cancer and infectious diseases like HIV or malaria. ABC transporters namely P-glycoprotein (P-gp) and various multidrug resistance associated proteins (MRPs) mainly contribute to the MDR phenomenon in cancer treatment and HIV therapy. Their cellular expression in respective cells like cancer cells lowers the intracellular drug concentrations and thus reasons the cellular resistance. The induction of such efflux pumps occurs during the therapy with drugs which will be affected by the MDR phenomenon as a consequence of the induction. In this review studies which report such drugs-caused inductions will be viewed. The review will cover the literature of recent years and attract attention to this important question in drug resistance. Finally, the discussion will suggest possible strategies to overcome the problem, i. e. by using non-inducing drugs.

Antitumor activity of terpenoids against classical and atypical multidrug resistant cancer cells

Nineteen terpenoids, including macrocyclic diterpenes, diterpenic lactones and other polycyclic diterpenes, steroids and a triterpene isolated from the methanolic extracts of Euphorbia species, were evaluated for their potential antineoplastic activity in various human cancer cell lines that were derived from three tumor entities: gastric (EPG85-257), pancreatic (EPP85-181) and colon (HT-29) carcinomas. Furthermore, different multidrug-resistant variants of these cancer cell lines with over-expression of MDR1/P-gp or no MDR1/P-gp expression were also investigated. In parental drug-sensitive cell lines, the tested compounds showed a moderate/weak antiproliferative effect or were inactive. Most of them were found more effective in drug-resistant cells than in the parental, drug-sensitive ones, and some of them showed high antineoplastic efficacy in classical or atypical drug-resistant cells. The most active compounds were the lathyrane diterpenes latilagascenes C and D, and the diterpenic lactones 3beta-acetoxy-helioscopinolide B and helioscopinolide E which exhibited high antineoplastic activities against the drug-resistant subline EPG85-257RDB derived from gastric carcinoma. In addition, the macrocyclic lathyrane diterpene jolkinol B was found to be highly effective in the multidrug-resistant variant HT-29RNOV.