Inhibitors of ABC transporters and biophysical methods to study their activity.

Multidrug resistance caused by the presence and overproduction of ABC transporters makes serious problems in cancer treating. The drugs administered during therapy are pumped outside the cell using the energy obtained from ATP hydrolysis. The augmented dosage of drugs to overcome the multidrug resistance is not sufficient. Thus knowledge of the structure of ABC proteins is necessary to understand the rules of their action. It could be also helpful to understand how the multidrug resistance could be overcome. One of the strategies involves the treatment of cancer cells with a mixture of anticancer drugs and inhibitors of ABC transporters. The yeast Saccharomyces cerevisiae, whose PDR pumps are analogues of mammalian MDR proteins responsible for multidrug resistance, is a suitable research model. Biophysical methods with different fluorescent dyes seem to be very suitable for the measurement of the efflux pump activity. This review describes some known inhibitors of ABC proteins and biophysical methods which could be used for measuring the ABC transporters activity.

Inhibitory effect of some natural and semisynthetic phenolic lipids upon acetylcholinesterase activity.

The effect of phenolic lipids isolated from rye grains and cashew nut shell liquid (CNSL) from Anacardium occidentale and their semisynthetic derivatives on erythrocyte ghost's acetylcholinesterase activity was studied. It has been shown that all tested compounds decreased the enzymatic activity of acetylcholinesterase. This effect depends on the type of studied compounds. Three of them completely inhibit acetylcholinesterase activity at the micromolar concentration.

A semisynthetic 5-n-alkylresorcinol derivative and its effect upon biomembrane properties.

MSAR (1-sulfate-3-myristoyl-5-pentadecylbenzene) is a semisynthetic derivative of 5-n-pentadecylresorcinol (C15:0). MSAR exhibits hemolytic activity against sheep erythrocytes with a EH50 value of (35 +/- 1.7) microM. At low concentrations MSAR also exhibits the ability to protect cells against their hypoosmotic lysis. This protective effect is significant as, at 0.1 microM of MSAR, the extent of osmotically induced cell lysis is reduced by approx. 20%. It was demonstrated that the 9-anthroyloxystearic acid signal was most intensively quenched by MSAR molecules, suggesting a relatively deep location of these molecules within the lipid bilayer. MSAR causes an increase of the fluorescence of the membrane potential sensitive probe. This indicates an alteration of the surface charge and a decrease of the local pH value at the membrane surface. At low bilayer content (1-4 mol%) this compound causes a significant increase of the phospholipid bilayer fluidity (both under and above the main phase transition temperature) of dipalmitoylphosphatidylcholine (DPPC) liposomes. At this low content MSAR slightly decreases the main phase transition temperature (T(c)) value. The effects induced in the phospholipid bilayer by higher contents of MSAR molecules (5-10 mol%) make it impossible to determine the T(c) value and to evaluate changes of the membrane fluidity by using pyrene-labeled lipid. MSAR also causes a decrease of the activity of membrane-bound enzymes - red blood cell acetylcholinesterase (AChE) and phospholipase A2 (PLA2). MSAR decreases the AChE activity by 40% at 100 microM. The presence of MSAR in the liposomal membrane induces a complete abolishment of the lag time of the PLA2 activity, indicating that these molecules induce the formation of packing defects in the bilayer which may result from imperfect mixing of phospholipids.