GLUTATHIONE CONJUGATION OF CHLORAMBUCIL - MEASUREMENT AND MODULATION BY PLANT POLYPHENOLS

Chlorambucil (CMB), an anticancer drug, was cytotoxic at concentration s of 5-20 mu M to human colon adenocarcinoma cells. It inhibited [C-14 ]thymidine uptake in a dose-dependent manner. Both effects were potent iated by simultaneous exposure of the cells to 10 mu M plant polypheno ls. In an attempt to explain the possible mechanism of action of the p olyphenols in relation to these observations, an HPLC-radiometric meth od was developed to measure the conjugation of CMB with glutathione in these cells and to monitor the export of monochloromonoglutathionyl C MB (MG-CMB), its main glutathione conjugate. At micromolar concentrati ons, five polyphenols, namely quercetin, butein, tannic acid, 2'-hydro xychalcone and morin, inhibited the efflux of CMB significantly; an in hibition of 40% was observed with 10 mu M quercetin. The glutathione S -transferase (GST) activity of the cancer cells, measured with 1-chlor o-2,4-dinitrobenzene, was also inhibited by the polyphenols. Their com bined action on GST and on the efflux of MG-CMB conjugate could provid e an enhanced positive modulation of sensitivity of the tumour cells t o CMB.