Synthesis of New Steroidal Inhibitors of P-Glycoprotein-Mediated Multidrug Resistance and Biological Evaluation on K562/R7 Erythroleukemia Cells

A simple route for improving the potency of progesterone as a modulator of P-gp-mediated multidrug resistance was established by esterification or etherification of hydroxylated 5 alpha/beta-pregnane-3,20-dione or 5 beta-cholan-3-one precursors. X-ray crystallography of representative 7 alpha-, 11 alpha-, and 17 alpha-(2'R/S)-O-tetrahydropyranyl ether diastereoisomers revealed different combinations of axial-equatorial configurations of the anomeric oxygen. Substantial stimulation of accumulation and chemosensitization was observed on K562/R7 erythroleukemia cells resistant to doxorubicin, especially using 7 alpha,11 alpha-O-disubstituted derivatives of 5 alpha/beta-pregnane-3,20-dione, among which the 5 beta-H-7 alpha-benzoyloxy-11 alpha-(2'R)-O-tetrahydropyranyl ether 22a revealed promising properties (accumulation index 2.9, IC50 0.5 mu M versus 1.2 and 10.6 mu M for progesterone), slightly overcoming those of verapamil and cyclosporin A. Several 7 alpha,12 alpha-O-disubstituted derivatives of 5 beta-cholan-3-one proved even more active, especially the 7 alpha-O-methoxymethyl-12 alpha-benzoate 56 (accumulation index 3.8, IC50 0.2 mu M). The panel of modulating effects from different O-substitutions at a same position suggests a structural influence of the substituent completing a simple protection against stimulating effects of hydroxyl groups on P-gp-mediated transport.