REVERSAL OF MULTIDRUG-RESISTANCE IN-VITRO BY FATTY-ACID PEG FATTY-ACID DIESTERS

Fatty acid ester surfactants, e.g., Cremophor EL and Solutol HS 15, th at modulate multi-drug resistance (MDR) have been described; however, the drug potential of these preparations is unclear because of the mol ecular heterogeneity of these and other commercial surfactants. In pre vious experiments, an active but still polydisperse preparation, desig nated CRL 1337, was synthesized by reacting purified oleic acid with a 10-fold molar excess of ethylene oxide. We have subjected this prepar ation to chromatographic separation, and infrared analysis of the acti ve fractions revealed a significant component of diester structures (f atty acid-PEG-fatty acid). A new generation of diester compounds has n ow been synthesized. Preparations comprised of 99% diesters were signi ficantly more potent than monoester preparations for MDR modification activity in vitro. As previously determined for ethylene oxide-derived preparations similar to CRL 1337, the nature of the fatty acid domain s proved to be important for activity, as was the relative length of t he polyethylene glycol domain (which determines the hydrophile-lipophi le balance). The ester linkage appeared unimportant since homologous d iethers and diamides had activity similar to that of diesters. Stearic acid diester was 1.5- to 7-fold more potent than CRL 1337 when tested in cell proliferation inhibition assays. In light of these structural restrictions on drug potentiation, and since these surfactants are ac tive at relatively low concentrations (below 1 mu g/ml), investigation s of their mechanism of action were initiated by exploring specific in teractions with P-glycoprotein. Both active and inactive diesters inhi bited azidopine labeling of P-glycoprotein, suggesting that fatty acid -PEG diesters can interfere with P-glycoprotein substrate binding. Oth er attributes of these preparations must contribute to their ability t o reverse MDR. (C) 1996 Wiley-Liss, Inc.