A newly synthesized
calmodulin antagonist, (S)-
P-(2-aminoethyloxy)-N-[2-(4-benzyloxy-carbonylpiperazinyl++ +)-1-(P-methoxybenzyl)ethyl]-N-methylbenzenesulfonamide dihydrochloride (W-77), acts as a
calcium-independent uncompetitive antagonist which binds to
glutathione-S-transferase (GST). We purified GST from human placenta using
drug affinity chromatography on a column of
W-77 coupled with
Sepharose 6B and demonstrated that
W-77 bound to GST. A spectrophotometric assay also showed that
W-77 inhibited GST activity. We prepared
Adriamycin-resistant and -sensitive cells from human ovarian
serous cystadenocarcinomas. Immunoblot analysis revealed that GST expression was increased in the
Adriamycin-resistant cells. We also purified GST from
Adriamycin-resistant cells and found that
W-77 bound to the GST obtained from these ovarian
carcinoma cells.
Adriamycin resistance was partially overcome by the addition of
W-77 (10 microM) to the cultured cells. In addition, we investigated the effect of
W-77 on
P-glycoprotein. Northern blot analysis revealed MDR1 gene expression in
Adriamycin-resistant cells. Although
W-77 was less potent in increasing the intracellular
Adriamycin content than
verapamil, it was more effective in overcoming
Adriamycin resistance. These results suggest that
W-77 enhances the antitumor activity of
Adriamycin by inhibiting both GST and
P-glycoprotein.